3
Aerated Constructed Wetlands for Treatment of Municipal and Food Industry Wastewater

A. Pascual1,3, D. De la Varga2,3, M. Soto2,3, D. Van Oirschot4, R.M. Kilian5, J.A. Álvarez1, P. Carvalho6, H. Brix6 and C.A. Arias6

1AIMEN, Spain

2Sedaqua (Spin-off from University of A Coruña), Spain

3University of A Coruña, Spain

4Rietland bvba, Van Aertselaerstraat 70, Minderhout, Belgium

5Kilian Water Ltd., Denmark

6Department of Bioscience – Aquatic Biology, Aarhus University, Aarhus, Denmark

3.1 Introduction

Constructed Wetlands (CWs) are engineered wastewater treatment systems that have been designed and constructed to mimic processes that occur in natural wetlands. Vegetation, soils, and their associated microbial assemblages are combined to effectively treat wastewater [1].

CWs are shallow basins, generally from 0.3 to 1.0 m. Wastewater can circulate freely, like natural ponds, and this kind of CW is called a free water surface (FWS) system, with aquatic vegetation rooted in the bottom, or floating plants. Another type of CW are planted beds filled with sand or gravel, and they are called subsurface flow systems (SSF). Depending on the flow direction, they are horizontal flow (HF) or vertical flow (VF) systems.

HF are permanently flooded, water flows horizontally and is not exposed to the atmosphere level as it is maintained under the surface (about 1–5 cm). On the other hand, VF wetlands are intermittently pulse-loaded, on top, and wastewater percolates through the unsaturated substrate. Aeration pipes connecting the atmosphere to a manifold of perforated drainage pipes are installed to provide a pathway for air to be drawn into the substrate from the bottom of the bed. Thus, air enters the bed from either the top or the bottom and maintains aerobic conditions in the bed. This approach provides a significant improvement of subsurface oxygen availability compared to HF designs.

Engineered treatment wetlands are other options of CWs systems that might include “reciprocating”, also known as “tidal flow” or “fill-and-drain” wetlands. As the wetland bed is drained, air is drawn into the bed [2], oxygenating the exposed biofilms on the wetland substratum. This improves the treatment performance compared to systems with a static water lever [3, 4]. Mechanical aeration of SSF wetlands using air distribution pipes installed at the bottom of the wetland bed has also been utilized as a means to increase oxygen transfer in wetland treatment systems. They are called (artificially) aerated wetlands or Forced Bed Aeration Wetlands (FBA®).

CWs have been used for wastewater treatment for more than fifty years to treat different types of polluted waters around the world. CWs became a widely accepted technology to deal with both point and non-point sources of water pollution as they offer a technical, low-energy, and low-operational-requirements alternative to conventional treatment systems, besides being able to meet discharge standards. Used initially to treat municipal wastewaters, the application of CWs has been expanded to the treatment of industrial effluents, agricultural wastewaters, livestock farm effluents, landfill leachate and stormwater runoff, among others [5–7].

The processes involved in pollutant removal include sedimentation, sorption, precipitation, evapotranspiration, volatilization, photodegradation, diffusion, plant uptake, and microbial degradation processes such as nitrification, denitrification, sulphate reduction, carbon metabolization, among others [8].

CW systems treat industrial effluents from petrochemical, dairy, meat processing, abattoir, and pulp and paper factory production. Brewery, winery, tannery and olive mills wastewaters have been recently added to CW applications. CWs can be applied to several and different kinds of industrial wastewaters, including acid mine wastewater with low organic matter content and landfill leachate. Vymazal [9] reported the use of CWs for the treatment of industrial wastewaters with influent concentrations up to 10,000–24,000 mg of chemical oxygen demand (COD)/L and up to 496 mg NH4+/L. However, there are no general rules for selecting the most suitable type of CW for a certain industrial wastewater or even urban wastewater. Every single case must be studied according to several conditions: type of wastewater, land availability, amount of flow and pollutant load, outlet discharge limits, etc. [8].

Industrial wastewaters differ substantially in composition from municipal sewage, as well as among themselves. Industrial wastewaters can present very high concentrations of organics, total suspended solids (TSS), ammonia and other pollutants; therefore the use of CWs almost always requires some kind of pretreatment. The BOD/COD ratio is a parameter which tentatively indicates the biological degradability. If this ratio is greater than 0.5, the wastewater is easily biodegradable, such as wastewaters from dairies, breweries, the food industry, abattoirs or starch and yeast production. The BOD/COD ratio for these wastewaters usually ranges between 0.6 and 0.7 but could be as high as 0.8. On the other hand, wastewaters with a low BOD/COD ratio and, thus, low biodegradability are represented, for example, by pulp and paper wastewaters. Tentative comparison of the industrial wastewater strength with municipal sewage could be done on the basis of population equivalent (PE: 60 g BOD5 per person per day).

3.2 Aerated Constructed Wetlands

Oxygen availability to support aerobic processes is the main limitation in HF CWs, especially when nitrification (and subsequent total nitrogen removal) is a treatment objective [10]. As a result, to increase the oxygen availability, CWs have evolved into more effective treatment systems by installing an aeration system capable of transferring sufficient oxygen to perform aerobic processes. Design variants now span from completely passive systems (HF), to moderately engineered systems (unsaturated VF systems with pulse loading) up to highly engineered or intensified systems, with increased pumping, water level fluctuation, or forced aeration [11].

As a result, most of the treatment wetland design and operational modifications developed in the last decade aim at improving subsurface oxygen availability. The simplest (most passive) modification is the construction of shallow HSF flow beds, highlighted by Garcia et al. [12]. Their findings suggest that by limiting the depth of the HF bed, all of the wastewater is forced through the root zone. Their results show improved treatment performance for COD, BOD5, and NH4-N in shallow beds (27 cm water depth) compared to deeper ones (50 cm water depth). However, recent studies suggest that this positive effect of shallow beds is limited to low surface loading rates [13, 14].

Recirculation of treated effluent has also been shown to improve removal of ammonium nitrogen and organic matter [15–19]. Operational adaptations to improve subsurface oxygen availability include water level fluctuations such as batch loading [20–22], “fill-and-drain”, “reciprocating”, or “tidal flow” [23–28]. A step forward is the use of active aeration (e.g., a network of air distribution pipes installed at the bottom of the bed connected to a blower pump to supply atmospheric air) which has also been applied to HF to constructed wetland beds [29–32] and saturated VF systems [33, 34], often showing a more than ten-fold increase of removal rates compared to passive systems. Most of the reports on intensified treatment wetland designs come from private engineering companies which hold patents. However, the potential use of intensified treatment wetland is widely recognized, and design guidance and parameters have yet to be determined [35].

As indicated, VF CWs have predominant aerobic conditions, while HF CWs mainly presented anaerobic conditions. Combining both types of CW in hybrid systems could achieve complete nitrogen removal, so in more recent years, interest in the study of multi-step and hybrid systems has increased [9, 36, 37]. The most commonly used hybrid system is the two-step VF-HF CW, which has been used for treatment of both sewage and industrial wastewaters [9, 38, 39]. In general, all types of hybrid CWs are comparable with single VF CWs in terms of NH3-N removal rates whilst they are more efficient in TN removal than single HF or VF CWs [9]. However, even in hybrid VF+HF systems, the TN removal remains low [9, 40, 41]. The effectiveness of alternating aerobic and anaerobic conditions in VF-HF hybrid systems was evaluated by Gaboutloeloe et al. [40], who reported that the most limiting factor of these systems was nitrate accumulation, mainly caused by the depletion of carbon during the aerobic phase. Tanner et al. [41] pointed out that the endogenous organic carbon supply from plant biomass decay and root-zone exudation has often been found to be insufficient to achieve full denitrification in VF+HF hybrid systems. In order to solve this handicap and improve TN removal, several authors studied the effect of step-feeding in tidal and saturated VF CWs [42–45]. Tanner et al. [41] proved the use of carbonaceous bioreactors, which incorporate a slow-release source of organic C (e.g., wood chips) aiming to increase denitrification. Recirculation has been employed in various configurations [46–50] in order to increase simultaneous nitrification and denitrification processes in either a single CW unit or in the two-step HF+VF system. Artificial aeration in hydraulic saturated units, attaining to only part of the system or timed, has a high potential as an alternative to enhance TN removal [32, 51–53].

3.2.1 Oxygen Transfer at the Water–Biofilm Interface

Early HF wetland designs were based on the Root Zone Method (RZM) [54]. Plant-mediated oxygen transfer was thought to be a key mechanism in RZM designs, but actual oxygen transfer rates generally did not meet these design expectations [55] and the systems often clogged. This led to the development of VF wetlands in the late 1980s. However, if VF wetlands are hydraulically or organically overloaded, ponding of wastewater occurs. This effectively cuts off air circulation and promotes clogging, which dramatically reduces oxygen transfer [56].

Mechanisms for oxygen transfer in treatment wetlands include atmospheric diffusion, plant-mediated oxygen transfer, and oxygen transfer at the water–biofilm interface [10]. Research in the recent years identified several design and operation factors, which improve oxygen transfer at the water–biofilm interface, such as artificial aeration [51, 52, 57, 58] and fill-and-drain operations [3, 59]. Since the rate of air circulation (and thus oxygen transfer) is related to the frequency of water level fluctuation in filling and draining systems, internal recycling to rapidly fill and drain multiple wetland compartments is often employed.

From a pilot-scale research facility in Langenreichenbach, Germany, Nivala et al. [10] estimated oxygen consumption rates (OCR) for the main CW designs. Measured OCRs (g/m2/d) were in the range of 0.5–13 for HF CW, 8–59 for VF CWs and 11–88 for intensified CW systems. Similar or even higher OCRs were previously reported in literature. However, as pointed out by Nivala et al. [10], those rates may not necessarily be sustainable over the long term operation of the system. Intensifying oxygen input in the CWs through the use of artificial aeration combine the advantage of maintaining low energy consumption and clogging prevention [31]. Artificial aeration strategies can vary extensively from partial to total aeration in relation to time and space, and from low to high intensity. Although some small and large field applications of aerated CW have been reported, properly described experiences of artificial aerated CWs are mainly limited to a few laboratory and pilot scale systems [31, 32, 51, 52, 57].

Aerated HCW varied from 0.3 m to 1 m in depth [32, 51, 52]. Probably, an efficient aeration process requires a higher depth in order to reach a high oxygen transfer rate (OTR) enhanced by sufficient long contact time between the supplied air and WW. Automated aeration devices were used in some cases, setting dissolved oxygen (DO) concentration set point to activate air pumps in the range of 0.2–0.6 mg/L [51]. In other cases, continuous aeration was provided, over the overall wetland bed surface [10, 52] or only near the inlet zone [32]. However, intermittent aeration or a spatial segregation of aerated and non-aerated zones has been considered possible in order to reach simultaneous nitrification and denitrification [32, 43, 53, 60, 61]. In efficient aerated HF CW, nitrification occurs when the aeration system is turned on, while denitrification requires anoxic conditions, which could be obtained by ceasing aeration. Aeration intensities were reported for VF CW by Pan et al. [62] and Maltais-Laundry et al. [32] ranging from 0.12 to 0.76 m3/m2/h. These authors found that oxygen utilization efficiency decreased when the aeration intensity increased.

3.2.2 Benefits of Artificial Aeration in Constructed Wetlands

Important factors affecting the treatment performance include the flow type, substrate characteristics, plant species, hydraulic loading rate (HLR) and temperature. HLR, related to the space available for the water to flow through the CW, is a principal parameter for the design and operation of CW. Sakadevan and Bavor [63] reported that the removal of pollutants in a CW was improved by decreasing HLR when the applied hydraulic retention time (HRT) ranged from 4 to 15 days. A lower HLR implies more contact time and more treatment stability, however, it occupies a larger land area [5].

Physical processes such us sedimentation and decantation, important in particulate organic matter removal, are mostly unaffected by winter conditions. However, biological processes are temperature dependent, and winter removal performances of HF CWs for nitrogen and soluble organic matter, both highly driven by biological activity, may be reduced [59, 64].

Besides lower winter temperature, low oxygen availability, which is already a common limiting factor in HF CWs during the growing season, may be even more so in winter. Oxygen solubility is higher in colder water [65], but gas exchange in HF CWs may be reduced by the additional insulation layer and the fact that plants are dormant. Low oxygen content results in low aerobic organic matter decomposition [28, 66–68]. This leads to fermentation processes [69, 70] that can represent, in certain overload cases, the main way of organic matter decomposition [71]. Moreover, the nitrification step represents the main limiting factor for N removal in HF CWs because of low oxygen availability [72]. In addition, to the TN concentration, the form of N is also often a crucial factor affecting the receiving water body. For instance, besides being toxic to aquatic biota, the associated nitrogenous biochemical oxygen demand of NH4+-N can depress DO levels.

Although in CWs, oxygen availability may be enhanced by the presence of macrophytes through diffusion of oxygen via the aerenchym to the rhizomes [66], the exact contribution of plants remains in debate [52, 73–76]. It was reported that the contribution of plants to pollutant removal was usually less than 10% [77], although it has been found to be important for nutrient removal in low loaded systems [77, 78]. Caldheiros et al. [80] also found that there was no significant difference in pollutant removal between the planted and unplanted wetlands during a 17-month operation period. The primary role of plants is to hold the wetland components in place, preventing erosion and landscape integration. Therefore, artificial aeration appears necessary when the CW is operated under a high HLR.

3.2.3 Dissolved Oxygen Profile along CWs

DO plays an important role in the activity of microbes in wetlands. To achieve the simultaneous removal of organic matter (COD) and nutrients (N, P), the aerobic and anoxic regions in wetlands need optimization depending on wastewater characteristics and operational manipulation.

Dong et al. [58] compared different aeration strategies in three VF CWs: non-aeration (NA), continuous-aeration (CA) and intermittent-aeration (IA), to treat heavily polluted river water. The VF CWs were continuously fed from a feed tank using a metering pump. Although the VF CWs have higher oxygen mass transfer efficiency than the HF ones, the DO concentrations (averaged over three tested HLRs) in the 5–40 cm region above the reactor bottom were below 1 mg/L in NA, which could inhibit the nitrification process.

For the CA, DO concentrations ranged from 1.3 to 2.2 mg/L (in the 5–20 cm profile) and from 3.8 to 4.4 mg/L (in the 40–60 cm profile). However, for the IA, DO concentrations varied from 0.8 to 1.1 mg/L and from 2.5 to 2.8 mg/L in the mentioned DO profiles.

It was reported that no obvious nitrification was observed when the DO concentration was lower than 0.5 mg/L [81]. According to the DO values, artificial aeration significantly improved the oxygen availability in the VF CWs. Although all DO concentrations in IA and CA appeared to exceed that required for anoxic condition (i.e., 0.2–0.5 mg/L), anoxic regions could still exist in the aerated VF CWs due to the spatial stratification of biofilms in both IA and CA operation modes, and particularly in the IA operation mode, which would facilitate denitrification.

3.2.4 TSS Removal

Several authors found that supplemental aeration of CWs had a positive effect on TSS reduction [82, 83]. Ouellet-Plamondon et al. [31] concluded that artificial aeration may have reduced matter accumulation by increasing degradation kinetics and prevented clogging.

3.2.5 COD Removal

COD removal is related to HLR. The increase of HLR makes the removal efficiencies of COD decrease. Increasing HLR would reduce the contact time between wastewater and microbes, enhance the detachment of microbes off substrate surfaces, and decrease the oxygen availability [84]. Although organic matter can be degraded both aerobically and anaerobically by heterotrophic bacteria in the wetlands depending on local DO concentrations, aerobic degradation is usually more important [85]. Dong et al. [58] found that COD removal efficiency was positively correlated with the aeration condition: CA > IA > NA, continuous-aeration, intermittent-aeration and non-aeration conditions, respectively (see Section 3.3.3).

As reported by Ouellet-Plamondon et al. [31], during summer, there was a slight improvement in COD removal in planted mesocosms compared to unplanted (p < 0.01), but no effect of artificial aeration, regardless of the presence of plants. In winter, the expected reduction in COD removal in non-aerated mesocosms was totally compensated with a significant improvement in aerated mesocosms, both for planted and unplanted units. The added oxygen in winter probably counterbalanced the reduction of removal kinetics due to temperature and plants dormancy [31].

When oxidation decreases, the amount of residual inert organic matter accumulated increases and aggregates in filtration matrix changing the hydraulic conditions by reducing HRT [3, 84] and biological properties [87]. Increasing oxygen availability with artificial aeration could enhance mineralization and reduce hydraulic clogging [88]. Sulphate reduction, a typical diagnostic of poor oxygen conditions in CWs [89], could also be inhibited by artificial aeration. Thus, for organic matter removal, their results suggest that artificial aeration in HF CWs could be beneficial in winter, when plants are dormant.

3.2.6 Nitrogen Removal

Nitrogen removal in CWs occurs through adsorption, assimilation into biomass, ammonia volatilization and coupled nitrification/denitrification, of which the nitrification/denitrification process is the most important [90, 91].

Since nitrification and denitrification are two operationally separate processes (either temporally or spatially), which respectively require aerobic and anoxic conditions, the rate of nitrification significantly impacts the removal of TN. The removal efficiency of TN significantly dropped with an increase of HLR. Artificial aeration significantly improved the oxygen availability and thus enhanced the removal of NH4-N in the VF CWs. Intermittent aeration was optimal for TN removal, which facilitated denitrification due to both spatial and temporal formations of anoxic zones in the VF CWs. Although continuous aeration achieved the highest nitrification rate, the denitrification process was notably suppressed due to an excessive oxygen supply that artificial aeration significantly enhanced NH4-N removal in VF CWs [53, 58].

Besides all this, average TKN removal in winter was lower than in summer, most likely because of the lower winter temperature, which was well under optimal temperature for nitrifying activity [92]. In winter, artificial aeration improved TKN removal for all mesocosms (p < 0.01), with a more pronounced improvement for unplanted units [31].

3.3 HIGHWET Project

The HIGHWET project was addressed to improve the capacity and effectiveness of CWs as high-rate and sustainable wastewater treatment system. HIGHWET aimed to perform and validate new approaches based on the combination of the hydrolytic up-flow sludge bed (HUSB) anaerobic digester and CWs with forced aeration for decreasing the required surface of conventional HF CWs and improving the final effluent quality. For this purpose, two demonstration plants were designed and constructed in Spain and Denmark. The first configuration (A Coruña, NW of Spain) consisted of a HUSB and HF CWs for raw municipal wastewater treatment [53], while second configuration (at KT Food, nearby Aarhus, Denmark) consisted of a combination of a HUSB and hybrid (FV-HF) CWs for treatment of high load organic industrial wastewater. The effect of effluent recirculation, aeration regime and different phosphorus adsorbent materials was planned to be checked in both plants. The authors report in this chapter the results obtained in the KT Food HIGHWET plant.

3.3.1 KT Food Pilot Plant

KT Food is a food producing company located at Randersvej 147, in the town of Purhus (56o 33' 38.58” N 9o 51' 26.08” E) in Denmark. Additional to the production of food, the site also generates water from a small dairy farm and domestic activities. To meet the discharge standards demanded by the environmental authorities, a wastewater treatment system was built. The plant was constructed in August 2014 as a research plant funded by the European Union under the FP7 grant agreement N° 605445. After technical, environmental considerations and to meet the discharge demands, it was decided to design and construct the treatment plant using a combination of an anaerobic digester as primary treatment, followed by two parallel treatment trains (aerated line and non-aerated line) of constructed wetlands, several wells to allow controlled recirculation of treated waters and additional wells to host reactive media to remove P before discharge The conceptual design of the system installed is shown in Figure 3.1.

Schematic illustration of the conceptual design of the system installed at KT Food.

Figure 3.1 Conceptual design of the system installed at KT Food. Empty circle and numbers indicate the sampling points along the treatment trains 1) inlet; 2) after the HUSB; 3) after the aerated VF; 4) after the aerated HF bed; 5) after the P removal filtered filled with Tobermorite; 6) after the non-aerated bed; 7) after the aerated bed; 8) after the P removal filter filled with Polonite; 9) final effluent. Treatment trains: aerated line (1–2–3–4–5) and non-aerated line (1–2–6–7–8).

The wastewater is collected from the house and the two industrial plants, homogenized in a well where fat and grease is removed. Thereafter, wastewater is pumped to the treatment plant where flow is measured using an ultrasound digital flow meter. Once the research project is finished, all the wastewater produced at the site is being treated by the plant.

After the first well, water is transported to a second well where pollutant concentration can be increased by adding a prepared feedstock solution in order to reach the desired concentrations for the research project. The primary treatment consisted of a Hydrolytic Upflow Sludge Blanket (HUSB) digester. After the HUSB, water flows to a pumping well that is fitted with two pumps, where direction and flow volume can be selected to any of the two treatment trains. Both treatment trains consist of a VF CW followed by HF beds and phosphorous removal wells. The surface of the VF beds is 16 m2, while both of the HF beds are 3 m2. In the eastern train, the VF bed is fitted with forced aeration. while the bed of the western train is passively aerated. Both of the HF beds are fitted with forced aeration. The aeration systems installed to supply air to the beds use individual compressors that provide atmospheric air to increase the oxygen availability, and improve the aerobic processes of pollutant degradation. Additionally, the aeration time and cycles to each one of the beds can be controlled with automatic timers according to the operation planned.

3.3.2 Research Operational Plan of KT Food Treatment Plant

During the research phase, the WWTP operated with different loading schemes where pollutant loadings, aeration cycles and recirculation were modified to obtain the largest amount of data possible and to determine the treatment capacity. Sampling strategy was to take grab samples from nine different points along the treatment train (Figure 3.1). Five sampling campaigns were performed for different aeration schemes and effluent recirculation (Table 3.1). Analyses were carried out as described in Standard Methods [91].

Table 3.1 Planned exploitation parameters for each of the sampling campaigns.

Campaign
Operation parametera12345
MonthJanuaryMarchMayJulySeptember
AE VF CW – AE HF CW (L/d)b8008008008001440
VF CW – AE HF CW (L/d)c200200200200360
RecirculationNoNoNoNo80%
VF CW aeration time (h on/h off)24/024/04/46/224/0
HF CW aeration (h on/h off)24/024/024/024/024/0

aPlanned influent concentration was 5000 mg COD/L, 500 mg TN/L and 30 mg TP/L along the whole study.

bAE VF CW – AE HF CW = Aerated Vertical Flow Constructed Wetland – Aerated Horizontal Flow Constructed Wetland.

cVF CW = Vertical Flow Constructed Wetland.

Any change of operational parameters implies the need of acclimation time so that the processes can become stable and performance is optimized. Therefore a period of three to four weeks acclimation time was allowed between the measuring campaigns.

After the first samples were collected during plant start-up (data not shown), it was evident that the wastewater produced at the site did not reach the aimed high concentration to achieve the organic or nutrient overloading stated in the exploitation plan. Therefore, it was necessary to install a system that could supply a prepared solution to reach the planned pollutant and hydraulic loadings. The system was built using a 1 m3 tank, and a time controlled dosing pump that fed the solution to the well located before the HUSB. The loading solution was prepared using a blending of fresh pig manure, molasses, starch, urea and fertilizer. The volumes of each component were calculated to reach the planned loading and were monitored regularly to maintain a constant loading. The flow was controlled and always was close to the desired overall flow of 1,000 L/d.

After the initial adaptation period, plant equipment including aeration pumps and a dosing system functioned without any problems, in spite of the low temperatures and the snow that covered the system, which is to be expected for the winter period in Denmark (Figure 3.2e). As it can be seen in Figure 3.2, no plant development was present during Campaigns 1 and 2, but plant development started in April, before Campaign 3 carried out in May.

Photo illustrations of the satellite images showing the locations of the treatment plant.

Figure 3.2 Satellite image showing the location of the treatment plant (a); a general view of the plant once it was established (b); details of HF bed (c); detail of P removal unit (d); state of the system during Campaign 1 at winter 2015 (e); state of the non-aerated VF bed during Campaign 2 (f); the two VF beds during Campaign 3 (aerated VF bed: g; passively aerated VF bed: h).

According to the exploitation plan, the last campaign included increasing the flow by recirculating 80% of the treated water that went through the aerated VF bed. That means that during the campaign, the overall influent flow to the beds was of 1,800 L/d. The flow to the forced aerated bed was 1,440 L/d and to the passively aerated bed 360 L/d, while the hydraulic loading rates were 9 cm/d and 2.25 cm/d, respectively.

3.3.2.1 Campaign 1

Campaign 1 was carried out during winter 2015. Averages and the standard deviation of the evaluated parameters are presented in the following tables (Tables 3.2–3.4). Even though environmental temperature was below or close to 0°C, the wastewater temperature was always above freezing in the beds. Temperature was uniform along the components of the treatment. Electrical Conductivity (EC) decreased along the treatment. pH was in the range of 6.7–10.6 in the different beds, being the highest after the Polonite well. As expected, DO was low at the inlet and after the HUSB. As water went through the system, the DO increased to reach oxygen saturation.

Table 3.2 In-situ monitored parameters during Campaign 1.

Temperature (°C)EC (μS/cm)pHDO (mg/L)
Sampling placeAverStdvAverStdvAverStdvAverStdv
1: Inlet7.92.01,7752856.90.93.43.3
2: After HUSB7.81.01,3254456.71.30.40.2
3: After aerated VF bed7.41.88172088.00.210.21.8
4: After HF bed6.81.76972038.30.312.10.8
5: After Tobermorite6.71.57211829.30.19.01.9
6: After non-aerated VF bed6.81.97332338.10.28.62.5
7: After HF bed6.31.95661808.20.212.41.0
8: After Polonite6.21.950415610.60.510.30.8
9: Effluent6.52.15971889.80.59.02.0

Table 3.3 Average TSS, COD and BOD5 in the system during Campaign 1.

TSS (mg/L)COD (mg/L)BOD5 (mg/L)
Sampling placeAverStdvAverStdvAverStdv
1: Inlet9649.1755383812567603
2: After HUSB4012.0225414591317580
3: After aerated VF Bed127.350364.01,0
4: After HF bed4.81.370215.06.1
5: After Tobermorite5,81.6392118.014.7
6: After non-aerated VF bed82.21193312.79.6
7: After HF bed51.452293.33.2
8: After Polonite83.263353.34,0
9: Effluent3.94.651164.72.5

Table 3.4 Average nutrient concentrations and performance along the system during Campaign 1.

NH4-N (mg/L)NO3-N (mg/L)TN (mg/L)TP-P (mg/L)
Sampling placeAverStdvAverStdvAverStdvAverStdv
1: Inlet116694914489713217.6
2: After HUSB878212152327228.3
3: After aerated VF Bed008.87.554230.7
4: After HF bed008.56.558320.4
5: After Tobermorite128.57.150220.4
6: After non-aerated VF bed116.75.3121210.2
7: After HF bed008.14.98350.80.4
8: After Polonite014.22.36620.40.2
9: Effluent012.82.840010.3

Table 3.3 presents the results of the average concentrations of TSS, COD and BOD5 during the campaign. TSS concentration varied between 96 mg/L at the inlet to 3.9 at the effluent. The overall removal of TSS was 96% while the reduction in the HUSB was around 60%. There is further reduction along the system and the final concentration is sufficient to meet any discharge standard. A high reduction of COD occurred in the HUSB where 50% of the COD was removed. Further COD removal happened in the aerated bed reaching 98% removal. The removal between the HUSB and the non-aerated bed was also high, reaching 95%. After the two VF beds, there were low removal but it can be explained by the low COD concentrations after the VF beds. Average BOD5 concentration during the campaign at the influent was around 2,600 mg/L and around 5 mg/L at the effluent, with an overall removal of 99%. Between the influent and the HUSB, the removal of BOD5 reached 49%. After the HUSB, the removal of BOD5 reached 99%, both in the aerated VF bed and in the non-aerated bed.

Conversion of nitrogen compounds and total phosphorus is given in Table 3.4. Nitrification in the system was effective and the overall nitrification was close to 100%. The nitrification process occurred mainly while the water was in the VF beds. Simultaneous to nitrification, denitrification was also taking place along the treatment and the overall denitrification rate was 94%. Denitrification occurred in the HUSB where 75% of the NO3-N was removed. P removal in the system occurred in all the structures, reaching up to 97%. The two reactive materials tested showed that they can produce effluents with concentrations below 1 mg/L.

3.3.2.2 Campaign 2

The results obtained for Campaign 2 are presented in Tables 3.5–3.7. Table 3.5 shows the average temperature along the structures which are affected by the external temperature, ranging from around 12°C to 9°C. EC was higher at the influent and decreased along the treatment. pH was around 8 but increased above 11 after the Polonite tank. DO concentration was low at the influent but increased along the treatment to reach nearly DO saturation concentrations after the first VF beds in both treatment trains.

Table 3.5 In-situ measured parameters during Campaign 2.

Temperature(°C)EC (μS/cm)pHDO (mg/L)
Sampling placeAverStdvAverStdvAverStdvAverStdv
1: Inlet11.80.91,7735497.80.51.62.1
2: After HUSB10.20.91,5032128.10.50.80.5
3: After aerated VF Bed10.40.21,2142668.60.112.00.2
4: After HF bed9.60.61,2222668.60.19.70.4
5: After Tobermorite9.30.59822039.30.19.70.4
6: After non-aerated VF bed9.80.51,4904138.20.19.30.6
7: After HF bed9.21.09622288.60.212.10.3
8: After Polonite8.80.67098711.20.110.70.4
9: Effluent9.40.58293209.80.510.01.0

Table 3.6 Average TSS, COD and BOD5 in the system during Campaign 2.

TSS (mg/L)COD (mg/L)BOD5 (mg/L)
Sampling placeAverStdvAverStdvAverStdv
1: Inlet235566108154735001061
2: After HUSB1152017481611625530
3: After aerated VF Bed198,05788,53,5
4: After HF bed6,73,14951,50,7
5: After Tobermorite8,40,44551,00,0
6: After non-aerated VF bed117,567203,01,4
7: After HF bed61,83712,50,7
8: After Polonite103,22821,00,0
9: Effluent8,21,03831,00,0

Table 3.7 Average nutrient concentrations (mg/L) and performance along the system during Campaign 2.

NH4-NNO3-NTNTP-P
Sampling placeAverStdvAverStdvAverStdvAverStdv
1: Inlet10146265.3152612612.9
2: After HUSB8941.10.28934163.3
3: After aerated VF Bed349238.9581150.3
4: After HF bed254243.861940.3
5: After Tobermorite9621138320.2
6: After non-aerated VF bed48323313.4891330.9
7: After HF bed76245.430610.1
8: After Polonite00161.61910.40.1
9: Effluent65180.828220.7

In spite of TSS concentration in the influent was higher than the previous campaign, TSS concentration after the HUSB was already 51% lower (Table 3.6). Further removal occurred along the treatment reaching an overall TSS removal of 97%. COD was around 6,000 mg/L with an overall removal of 99% at the effluent. The HUSB removed 71% and the VF beds were able to remove the rest of the COD. Similarly, BOD5 at the influent was on average 3,500 mg/L with a removal of 54% in the HUSB. The VF beds removed on average more than 99% of the remaining BOD5 leaving very little BOD to be removed in the following structures.

Regarding nutrient removal (Table 3.7), different behavior took place compared to the previous campaign. Dynamics of the removal along the beds were different than in previous campaigns, reaching an overall removal of 94%. NH4-N average concentration in the inlet was around 100 mg/L, with only 10% removal in the HUSB. In the aerated VF the removal was close to 60%. The NH4-N removal in the non-aerated bed was less effective and only 46% was removed. The rest of the system continued to remove NH4-N to reach a final concentration of 6 mg/L. Nitrate in the system was removed in all the structures, especially in the HUSB, where all the NO3-N was removed. Along the bed there was an increase of NO3-N as a result of nitrification in the structures. Both of the tested media presented good P removal capacity, reaching 92% through the overall system.

3.3.2.3 Campaign 3

After Campaign 2, aeration time for the aerated VF bed was set to intermittent aeration (4 hours on, 4 hours off). The results obtained Campaign 3 are presented in Tables 3.8–3.10. The third campaign took place in May when temperatures began to increase and weather was milder. The plants in all the beds began to grow due to the noticeable effect of the season being more effective in the aerated beds because of the higher water flow that allowed better nutrient availability. Even though weather was milder, it was not reflected in the water temperature. This can be explained by the low temperatures reached at night. DO concentrations were as expected, with anaerobic conditions in the inlet and at the outlet of the HUSB. Except for the aerated VF bed, DO concentrations were close to saturation. The lower DO in the aerated VF bed effluent can be explained by the fact that during this campaign, aeration was carried out in cycles, with 4 hours of aeration and 4 hours with no aeration. Even though DO was lower, it was still above 60% saturation.

Table 3.8 In-situ monitored parameters during Campaign 3.

Temperature(°C)pHEC (μS/cm)DO (mg/L)
Sampling pointsAverStdvAverStdvAverStdvAverStdv
1: Inlet12.10.67.60.618837460.70.4
2: After HUSB10.30.57.70.315392890.70.4
3: After aerated VF Bed10.50.28.00.113941406.30.9
4: After HF bed9.60.78.70.013526411.90.1
5: After Tobermorite9.60.49.30.01126659.50.2
6: After non-aerated VF bed9.90.68.20.116712449.10.6
7: After HF bed9.11.28.70.0106313012.00.3
8: After Polonite8.40.511.30.07635010.60.3
9: Effluent9.30.69.60.39811249.60.8

Table 3.9 Average TSS, COD and BOD5 concentrations in the system during Campaign 3.

TSS (mg/L)COD (mg/L)BOD5 (mg/L)
Sampling pointAverStdvAverStdvAverStdv
1: Inlet117145,2689174,1674,404
2: After HUSB25.26.42,05515161,383693
3: After aerated VF bed22.626.821137.54425
4: After HF bed33.621.715613.562
5: After Tobermorite33.831.71566.862
6: After non-aerated VF bed86.523.01746032
7: After HF bed101.739.3826.120
8: After Polonite102.736.9612.922
9: Effluent47.231.013024.033

Table 3.10 Average nutrient concentrations and performance along the system during Campaign 3.

NH4-N (mg/L)NO3-N (mg/L)TN (mg/L)TP (mg/L)
Sampling PointAverStdvAverStdvAverStdvAverStdv
1: Inlet250162.2113.516.538240425.118.5
2: After HUSB19767.43.64.620141918.212.2
3: After aerated VF Bed5.22.31.20.111125.20.4
4: After HF bed0.120.0215.00.6944.00.3
5: After Tobermorite0.140.0194.50.611192.20.1
6: After non-aerated VF bed0.100.010347.64262.90.2
7: After HF bedBDLBDL365.740121.20.1
8: After Polonite0.70.0406.545210.50.1
9: Effluent0.30.0266.627111.80.1

TSS in the raw water was within the expected limits of raw wastewater (Table 3.9). At the beginning of this campaign, a problem with the HUSB occurred, due to the presence of grease in the water surface. It was rapidly skimmed and removed from the reactor before the sampling campaign. The final effluent was about 34 mg/L. The aerated VF bed produced effluent COD concentration higher than the passively aerated bed. However, it should be considered that the aerated bed was loaded with four times the loading compared to the passively aerated bed. The targeted COD at the inlet was as planned and removal in the HUSB was effective. After the HUSB and through the two treatment trains, removal of COD was high with similar concentrations in the effluent of both VF beds. During this campaign, BOD concentration was higher than the previous campaign. This can be explained by possible changes in the food processing, as the loading solution was prepared as usual. The HUSB removed more than half of the BOD concentration. Along the system BOD was removed to low concentrations. The highest concentration of 45 mg/L was observed in the aerated VF bed.

Nitrogen species concentrations were below the targeted 500 mg/L TN (Table 3.10). This can be explained due to uncertainty about the actual concentrations of the pig manure used to prepare the solution. It can vary depending on the storage, weather conditions and the washing practices in the farm. Removal of NH4-N was low through the HUSB. After the HUSB, removal of ammonia was effective in both trains. Results presented in Table 3.10 show that NO3-N was denitrified in the HUSB and also in the wetlands during the shut-off of aeration periods. The passively aerated bed did not show the same effective denitrification and the effluent had a NO3-N concentration of 40 mg/L. The same dynamics were followed by the TN.

3.3.2.4 Campaign 4

As indicated in Table 3.1, after Campaign 3, the aeration time for the aerated VF bed was set to 6 hours on, 2 hours off. Working to these conditions, the results obtained for Campaign 4 are presented in Tables 3.11–3.13. During the fourth campaign, ambient temperature increased so water temperature along the system was affected increasing to around 17°C (Table 3.11). pH behaved similarly to the previous campaigns with around 7 along the treatment and changing when water went through the P removal media. DO was low at the inlet and after the HUSB. After the aerated VF bed, DO was low but it increased as water went through the different structures of the treatment plant.

Table 3.11In-situ monitored parameters during Campaign 4.

Temperature(°C)pHEC (μS/cm)DO (mg/L)
Sampling pointsAverStdvAverStdvμS/cmStdvmg/LStdv
1: Inlet17.00.36.80.71,6901,1962.21.9
2: After HUSB17.30.46.20.51,0594161.41.0
3: After aerated VF Bed17.40.38.30.11,043821.50.4
4: After HF bed17.30.49.20.01,039788.00.1
5: After Tobermorite16.80.29.70.01,070685.51.0
6: After non-aerated VF bed16.80.38.50.1641936.60.2
7: After HF bed16.50.49.20.07921228.50.1
8: After Polonite16.80.411.40.69141468.10.4
9: Effluent17.00.810.40.39911087.70.6

Table 3.12 Average TSS, COD and BOD5 in the system during Campaign 4.

TSS (mg/L)COD (mg/L)BOD5 (mg/L)
Sampling pointAverStdvAverStdvAverStdv
1: Inlet117144,7711,6582,2500
2: After HUSB25.26.42,5167431,375106
3: After aerated VF bed22.626.89966.82634
4: After HF bed33.621.75521.411
5: After Tobermorite33.831.7527.822
6: After non-aerated VF bed8.52.3632651
7: After HF bed10.73.34210.066
8: After Polonite10.73.93721.200
9: Effluent4.23.0534.121

Table 3.13 Nitrogen and phosphorus concentrations in the different points during Campaign 4.

NH4-N (mg/L)NO3-N (mg/L)TN (mg/L)TP (mg/L)
Sampling pointAverStdvAverStdvAverStdvAverStdv
1: Inlet25032.411316.538210433.413.2
2: After HUSB23913.53.64.62437921.33.3
3: After aerated VF bed5.22.31.20.1725.71.7
4: After HF bed0.010.0215.00.6645.10.6
5: After Tobermorite0.010.0194.50.6523.90.6
6: After non-aerated VF bed0.010.010347.64562.60.4
7: After HF bed0.0000.000365.748122.30.4
8: After Polonite0.00.0406.546181.10.0
9: Effluent0.00.0266.634212.30.7

Raw water TSS was lower if compared to the previous campaign and the HUSB removed more than half of the influent TSS (Table 3.12). This suggests that skimming the grease and fat had a positive effect. The aerated bed further removed additional TSS so the concentration in the effluent was below the discharge limits. COD was around the targeted concentration and about half was removed by the HUSB. The aerated bed removed around 90%. No considerable further removal was archived in this train. Through the other treatment train, the passively aerated bed performed well and was able to remove COD down to 50 mg/L. BOD followed the same pattern as COD in spite of the fact that the BOD/COD ratio was lower than in previous campaigns. The aerated bed produced an effluent, with 26 mg/L being further removed along the following structures. The treatment train with the passively aerated bed performed well reaching BOD concentrations down to 10 mg/L after the bed.

Nitrogen species in the inlet were close to the targeted concentration of 500 mg TN/L (Table 3.13). Through the HUSB there was considerable denitrification and the NO3-N present was denitrified effectively. The HUSB did not remove NH4-N. Nitrification seemed to be effective in the aerated bed, with inlet NH4-N concentrations around 239 mg/L and outlet concentrations of 5 mg/L. NO3-N was also as low as 1 mg/L suggesting that the intermittent aeration can enhance the N removal. On the other treatment train, wastewater was nitrified effectively, but denitrification did not occur at the same rate with intermittent aeration. No further considerable denitrification was registered in the treatment train.

3.3.2.5 Campaign 5

The fifth campaign included recirculation of the effluent of the aerated bed back to the pumping well to increase the hydraulic loading on the beds (Tables 3.14–3.16). The calculated hydraulic loading increased corresponds to around 80% more water to each one of the beds (Table 3.1). Initially and when the flow was increased, both beds presented an increase in TSS and the release of biofilm from the media was evident. A decrease in TSS concentration along time and no further biofilm was present in the effluent when the campaign started. Temperature was similar to the previous campaign because ambient temperature was mild. pH was close to neutral except when water went through the P removal material, which increased pH and in the case of Polonite up to 11. DO was low for raw wastewater and through the HUSB and relatively low after effluent of the aerated bed when measured concentration was below 4 mg/L. During this campaign 100% saturation was never achieved through the other structures.

Table 3.14 In-situ monitored parameters during Campaign 5.

Temperature (°C)pHEC (μS/cm)DO (mg/L)
Sampling pointAverStdvAverStdvAverStdvAverStdv
1: Inlet16.00.46.61.02,2081,3331.00.6
2: After HUSB15.70.36.50.91,1302281.70.3
3: After aerated VF bed16.20.48.90.21,057943.73.2
4: After HF bed15.80.39.10.11,058687.00.5
5 After Tobermorite15.30.510.00.01,102305.30.4
6 After non-aerated VF bed15.10.48.30.19241186.20.6
7 After HF bed14.90.69.10.41,163678.40.1
8 After Polonite14.70.811.10.31,220447.80.4
9 Effluent15.40.410.10.21,143516.80.3

Table 3.15 Average TSS, COD and BOD5 in the system during Campaign 5.

TSS mg/LCOD mg/LBOD5 mg/L
Sampling pointAverStdvAverStdvAverStdv
1: Inlet2171455,2689174,267404
2: After HUSB96.09.22,0551,5161,167419
3: After aerated VF bed23.37.621137.52212
4: After HF bed7.64.415613.531
5: After Tobermorite9.65.01566.841
6: After non-aerated VF bed12.04.71746094
7: After HF bed6.46.0826.121
8: After Polonite8.96.7612.911
9: Effluent6.95.613024.031

Table 3.16 Average nutrient concentrations and performance along the system during Campaign 5.

NH4-N (mg/L)NO3-N (mg/L)TN (mg/L)TP (mg/L)
Sampling pointAverStdvAverStdvAverStdvAverStdv
1: Inlet367171.412515.04931574025
2: After HUSB316198.03.62.4320196152.2
3: After aerated VF bed5.92.13.21.2916.31.2
4: After HF bed0.000.0012.90.51306.20.5
5: After Tobermorite3.81.226.49.430115.50.2
6: After non-aerated VF bed0.10.1533.05335.71.3
7: After HF bedBDLBDL11921.6119222.60.4
8: After Polonite0.10.11337.013371.00.3
9: Effluent2.92.16017.163161.30.9

TSS influent concentration was around 200 mg/L and the HUSB removed around 2/3 of the TSS. After the aerated VF Bed, the TSS concentration was already down to 20 mg/L. While water went through the other structures, concentration continued to drop and the final effluent was more than enough below the discharge requirements. COD influent reached the targeted concentration and the HUSB removed half of the concentration. Through the aerated bed, an additional 90% was removed and no considerable further removal occurred in the treatment train. The treatment train fitted with the non-aerated bed showed similar performance. BOD influent concentration was relatively high if compared to previous concentration, but the HUSB was able to remove around 60% of the load. The two treatment trains had no difficulty dealing with the BOD and final effluent reached concentrations close to the detection limit.

The inlet TN concentration target was reached. The HUSB did not nitrify but nitrification took place in the aerated bed. Further nitrification happened through the treatment and the wastewater was nitrified at the end of the process. Denitrification occurred in the HUSB and also in the aerated bed. After the aerated bed, no denitrification was evident. The passive aerated bed denitrified a fraction, but no further denitrification happened in this treatment train.

3.3.3 Comparison of Results

Applied SLR (g/m2/d) in the aerated line of KT Food HIGHWET project were 2.5 ± 1.8, 92 ± 14, 58 ± 7, 9.1 ± 3.5, 7.8 ± 4.2 and 0.8 ± 0.1 for TSS, COD, DBO5, TN, NH4+-N and TP, respectively, whilst SLRs were four times lower in the non-aerated line (i.e., 0.6 ± 0.4, 23 ± 4, 15 ± 2, 2.3 ± 0.9 and 2.0 ± 1.0 for TSS, COD, DBO5, TN and NH4+-N, respectively). Thus, the non-aerated line operated at conservative design loading rates and reached satisfactory contaminant removal, usually from 90 to 99% of TSS, COD, BOD5 and ammonia. Similar or even higher percentage removal rates were obtained in the aerated line, operated at four times higher loading rates.

TN removal reached 43 ± 7% in the HUSB digester, due to the denitrification of influent nitrate. Overall, TN removal was 85 ± 7% in the non-aerated line and 91 ± 9% in the aerated line. The aerated VF CW unit reached 80 ± 27% TN removal (91 ± 10% excluding Campaign 2), whilst the non-aerated VF CW unit reached 58 ± 36% TN removal (73 ± 17% excluding Campaign 2). TN removal was not found in the small size aerated HF units.

TP removal reached 39 ± 14% in the HUSB digester, whilst overall TP removal was 98 ± 1% in the non-aerated line and 90 ± 3% in the aerated line. Both the aerated and non-aerated VF CW units noticeable contributed to TP removal, reaching 72 ± 10% and 82 ± 13%, respectively. Additional TP removal took place in the aerated HF units, reaching 18 ± 12% and 42 ± 25% for HF1 and HF2, respectively. According to Vymazal [82], these TP removal rates obtained under average loading rates of 0.8 g TP/m2/d may be considered very satisfactory. Finally, the P removal units with Polonite as phosphorus adsorbant material reached 56 ± 5% TP removal whilst TP removal in the unit with Tobermorite decreased from about 50% at Campaigns 2 and 3 to 11% at Campaign 5.

Therefore, the aerated line was successful in treating a four times higher loading rate and with similar or higher treatment efficiency than the non-aerated VF CW unit for organic matter and nitrogen removal and only slightly lower for phosphorus removal. The HUSB efficiently contributed to TSS, COD, BOD and nitrate removal. These high percentage removal rates were obtained at organic SLR in the range of referred studies for different kind of industrial wastewaters while ammonia and TN loading rates were higher in the aerated line of the KT Food HIGHWET plant.

Studies on industrial wastewater treatment on artificially aerated CWs are scarce. Results for coffee processing wastewater [94], dairy parlor wastewater [83], aquaculture effluent [95] and dye containing wastewater [96, 97] are summarized below.

Rossmann et al. [94] treated coffee processing wastewater (CPW) with aerated and non-aerated influent previously to pilot-scale HF CWs. The applied organic load during the experiment was 89 g COD/m2/d, and the HRT was 12 d. Removal efficiencies of COD, BOD and TSS ranged from 87.9 to 91.5, from 84.4 to 87.7 and from 73.7 to 84.8%, respectively. Aeration of CPW in the storage tank for 2.5 days did not affect the removal efficiencies of organic matter in the CWs, which agrees with previous findings of Zhang et al. [51], due to low redox values and anoxic conditions in spite of the aeration. In this study [94], phosphorus removal (54.3–72.1%) was statistically different among treatments, with better performance for the aerated planted system, and worse for the non-aerated unplanted.

The feedlot runoff and dairy parlor wastewater in Burlington (Vermont, USA) was treated in four HF CWs (non-aerated unplanted CW1, aerated planted CW2, non-aerated planted CW3, and aerated planted CW4) of 225 m2 each in an experiment carried out by Tunçsiper et al. [83]. HRT in CWs ranged from 3 to 16 days. Over the four years of monitoring, the CWs operated with surface loading rate of 210 g BOD5/m2/d and 70 g TSS/m2/d in average. Average BOD5 removals were 83%, 78%, 84% and 86% for CW1, CW2, CW3 and CW4, respectively. The authors of this study concluded that supplemental aeration of CWs had a positive effect on BOD5 reduction.

Aquaculture effluent under high HLR was assessed in Jingzhou city (China) by Zhang et al. [95]. Two parallel, identical hybrid wetland systems (CW 1+2), each with down, up and HF chambers were constructed in the field. The HLR was approximately 8.0 m/day, giving a theoretical HRT of 0.96 h. For the wetland with diffused-air enhancement, there was a significant decrease in COD and NH4+-N concentrations after filtration. Further, the aeration significantly increased the levels of DO, ORP, nitrite, and TN, while significantly decreasing the levels of EC, COD, NH4+-N, and TP concentrations in the outflow compared to the non-aerated treatment. High organic loading rates of 132 and 146 g COD/m2/d were applied for the non-aerated (stage 1) and aerated (stage 2) conditions. Concentration of COD in the effluent of aerated wetland was significantly lower than in the non-aerated wetland. TN removal was higher in the non-aerated wetland in which sedimentation of organic N was determined to be the main process of TN removal. On the other hand, TN removal was dominated by ammonium removal in the aerated stage. In the non-aerated wetland, NH4+-N outlet concentrations were generally higher than in the inlet, observing an opposite trend in the aerated wetland. The authors concluded that denitrification process was contained with short HRT (0.96 h) even though carbon source seemed to be enough for denitrification. Concerning P removal, higher percentage reductions were observed in the aerated wetland.

Ong et al. [97] studied the mineralization of diazo dye (Reactive Black 5, RB5) in wastewater using recirculated up-flow CW reactor in Malaysia. The HRT was 2 days. COD removal in the aerated reactor (92%) was higher than that in the non-aerated reactor (83%) whilst RB5 removal efficiency presented the opposite trend (81 and 89%, respectively).

Ong et al. [96] conducted other experiment to study the removal of azo dye Acid Orange 7 (AO7) in three parallel lab-scale CWs of 0.3 m height and 0.18 m of diameter. The CWs were planted with Phragmites australis, and there were aerated (A), non-aerated (B) and non-aerated unplanted (C). With an HRT of 2 days, COD removal in the aerated and non-aerated CWs was 95% and 62%, respectively (both higher than COD removal in control unplanted CW). The three CWs removed more than 94% of AO7, being slightly higher in the aerated one. The ammonia removal was significantly higher in the aerated CW (86%) than in the non-aerated CW (14%) which, additionally, performed better than the control CW (4%).

3.4 Conclusions

This study reports the effect of effluent recirculation, aeration regime and different phosphorus adsorbent materials in a system that combines a HUSB, hybrid (FV-HF) CWs and two different phosphorus adsorbent materials for treatment of industrial wastewater. Applied SLR (g/m2/d) in the aerated line were 2.5 ± 1.8, 92 ± 14, 58 ± 7, 9.1 ± 3.5, 7.8 ± 4.2 and 0.8 ± 0.1 for TSS, COD, DBO5, TN, NH4+-N and TP, respectively, whilst SLRs were four times lower in the non-aerated line (i.e. 0.6 ± 0.4, 23 ± 4, 15 ± 2, 2.3 ± 0.9 and 2.0 ± 1.0 for TSS, COD, DBO5, TN and NH4+-N, respectively). The non-aerated line reached satisfactory contaminant removal, usually from 90 to 99% of TSS, COD, BOD5 and ammonia. Similar or even higher percentage removal rates were obtained in the aerated line. TN removal reached 43 ± 7% in the HUSB digester, due to the denitrification of influent nitrate. Overall, TN removal was 85 ± 7% in the non-aerated line and 91 ± 9% in the aerated line. The aerated VF CW unit provided 80 ± 27% TN removal, whilst the non-aerated VF CW unit reached 58 ± 36% TN removal. Overall TP removal was 98 ± 1% in the non-aerated line and 90 ± 3% in the aerated line. Both the aerated and non-aerated VF CW units noticeable contributed to TP removal, reaching 72 ± 10% and 82 ± 13%, respectively. Additional TP removal was obtained in Polonite unit (56 ± 5%) at 0.2 g TP/m2/d during the whole study whilst TP removal in Tobermorite unit at 0.87 g TP/m2/d decreased from about 50% to 11% after 6 month of treatment. These results showed that the aerated VF CW was successful in treating a four times higher loading rate and with similar or higher treatment efficiency than the non-aerated VF CW.

Acknowledgements

This work was supported by the EU's seventh framework programme for research, technological development and demonstration under grant agreement n° 605445.

References

  1. 1 Vymazal J. Constructed wetlands for treatment of industrial wastewater: A review. Ecol Eng. 2015; 73:724–751.
  2. 2 Green M, Friedler E, Ruskol Y, Safrai I. Investigation of alternative method for nitrification in constructed wetlands Water Sci Technol. 1997; 35(5):63–70.
  3. 3 Tanner C, Sukias J, Upsdell M. Substratum Phosphorus Accumulation during Maturation of Gravel-bed constructed wetlands. Water Sci. Technol. 1999; 40:147.
  4. 4 Leibowitz SG. Isolated wetlands and their functions: an ecological perspective, Wetlands BioOne 2003; 23(3):517–531.
  5. 5 Kadlec RH, Knight RL, Vymazal J, Brix H, Cooper P, Haberl R. Constructed Wetlands for Pollution Control: Processes, Performance, Design and Operation. IWA Specialist Group on Use of Macrophytes in Water Pollution Control, Scientific and Technical Report 8; 2000.
  6. 6 Vymazal J. The use constructed wetlands with horizontal sub–surface flow for various types of wastewater. Ecol Eng. 2009; 35(1):1–17.
  7. 7 Vymazal J. Constructed wetlands for wastewater treatment: five decades of experience. Environ Sci Technol. 2011; 45(1):61–69.
  8. 8 De la Varga D, Soto M, Arias CA, Oirschot DV, Kilian R, Pascual A, Álvarez JA. Constructed Wetlands for Industrial Wastewater Treatment and Removal of Nutrients. In: Technologies for the Treatment and Recovery of Nutrients from Industrial Wastewater, 2016; pp. 202–230.
  9. 9 Vymazal J. The use of hybrid constructed wetlands for wastewater treatment with special attention to nitrogen removal: A review of a recent development. Water Res. 2013; 47:4795–4811.
  10. 10 Nivala J, Headley T, Wallace S, Bernhard K, Brix H, van Afferden M, Müller R. Comparative analysis of constructed wetlands: The design and construction of the ecotechnology research facility in Langenreichenbach, Germany. Ecol Eng. 2012; 61(B): 527–543.
  11. 11 Fonder N, Headley T. Systematic classification, nomenclature and reporting for constructed treatment wetlands. In: Vymazal J, editor. Water and Nutrient Management in Natural and Constructed Wetlands. Springer Science + Business Media B.V.: Dordrecht; 2010, pp. 191–219.
  12. 12 García J, Aguirre P, Barragán J, Mujeriego R. Effect of key design parameters on the efficiency of horizontal subsurface flow constructed wetlands Ecol Eng. 2003; 25(4):405–418.
  13. 13 De la Varga D, Ruiz I, Soto M. Winery wastewater treatment in subsurface constructed wetlands with different bed depths. Water Air Soil Pollut. 2013; 224:1485–1497.
  14. 14 De la Varga D, Díaz MA, Ruiz I, Soto M. Avoiding clogging in constructed wetlands by using anaerobic digesters as pre-treatment. Ecol Eng. 2013; 52:262–269.
  15. 15 Arias CA, Brix H. Initial experience from a compact vertical flow constructed wetland treating single household wastewater. In: Vymazal J, ed. Natural and Constructed Wetlands: Nutrients, Metals and Management. Backhuys Publishers, Leiden, The Netherlands; 2005, pp. 52–64.
  16. 16 García-Pérez A, Grant B, Harrison M. Water quality effluent from a recirculating, vertical-flow constructed wetland. Small Flows Quart. 2006; 7(4):34–38.
  17. 17 Gross A, Sklarz MY, Yakirevich A, Soares MI. Small scale recirculating vertical flow constructed wetland (RVFCW) for the treatment and reuse of wastewater Water Sci Technol. 2008; 58(2):487–494.
  18. 18 Konnerup D, Trang NTD, Brix H. Treatment of fishpond water by recirculating horizontal and vertical flow constructed wetlands in the tropics. Aquaculture 2011; 313(1–4):57–64.
  19. 19 Torrijos V, Gonzalo OG, Trueba-Santiso A, Ruiz I, Soto M. Effect of bypass and effluent recirculation on nitrogen removal in hybrid constructed wetlands for domestic and industrial wastewater treatment. Water Res. 2016; 103:92–100.
  20. 20 Stein OR, Hook PB, Beiderman JA, Allen WC, Borden DJ. Does batch operation enhance oxidation in subsurface flow constructed wetlands. Water Sci Technol. 2003; 48(5):149–156.
  21. 21 Corzo A, Pedescoll A, Álvarez E, García J. Solids accumulation and drainable porosity in experimental subsurface flow constructed wetlands with different primary treatments and operating strategies. In: Billore SK, Dass P, Vymazal P, editors. Proceedings, 11th International Conference on Wetland Systems for Water Pollution Control, Vikram University and IWA, Indore, India; 1–7 November 2008, pp. 290–295.
  22. 22 Põldvere E, Karabelnik K, Noorvee A, Maddison M, Nurk K, Zaytsev I, Mander Ü. Improving wastewater effluent filtration by changing flow regimes – Investigations in two cold climate pilot scale systems. Ecol Eng. 2009; 35(2):193–203.
  23. 23 Behrends LL. Patent: Reciprocating subsurface flow constructed wetlands for improving wastewater treatment. United States: US 5,863,433; 1999.
  24. 24 McBride GB, Tanner CC. Modelling biofilm nitrogen transformations in constructed wetland mesocosms with fluctuating water levels Ecol Eng. 2000; 14(1–2):93–106.
  25. 25 Austin DC. Patent: Tidal vertical flow wastewater treatment system and method. United States: US 6,896,805 B2; 2005.
  26. 26 Sun G, Gray KR, Biddlestone AJ, Cooper DJ. Treatment of agricultural wastewater in a combined tidal flow: downflow reed bed system. Water Sci Technol. 1999; 40(3):139–146.
  27. 27 Ronen T, Wallace SD. TAYA – Intensive wetland technology facilitates the treatment of high loads of organic pollutants and ammonia. In: Masi F, Nivala J, editors. Proceedings, 12th International Conference on Wetland Systems for Water Pollution Control, IRIDRA S.r.l. and IWA, Venice, Italy; 4–8 October 2010, pp. 872–878.
  28. 28 Wu S, Zhang D, Austin D, Dong R, Pang C. Evaluation of a lab-scale tidal flow constructed wetland performance: oxygen transfer capacity, organic matter and ammonium removal. Ecol Eng. 2011; 37(11):1789–1795.
  29. 29 Wallace SD. Patent: System for removing pollutants from water. United States: US 6,200,469 B1; 2001.
  30. 30 Higgins JP. The use of engineered wetlands to treat recalcitrant wastewaters., Southampton, United Kingdom; WIT Press. 2003: pp. 137–160.
  31. 31 Ouellet-Plamondon C, Chazarenc F, Comeau Y, Brisson J. Artificial aeration to increase pollutant removal efficiency of constructed wetlands in cold climate. Ecol Eng. 2006; 27:258–264.
  32. 32 Maltais-Landry G, Maranger R, Brisson J, Chazarenc F. Nitrogen transformations and retention in planted and artificially aerated constructed wetlands. Water Res. 2009; 43:535–545.
  33. 33 Murphy C, Cooper D. An investigation into contaminant removal in an aerated saturated vertical flow constructed wetland treating septic tank effluent. In: Vymazal J, ed. Joint Meeting of Society of Wetland Scientists, WETPOL, and Wetlands Biogeochemistry, Czech University of Life Sciences, Prague, Czech Republic; 3–8 July 2011: p. 224.
  34. 34 Wallace SD, Liner MO. Design and performance of the wetland treatment system at Buffalo Niagara International Airport. IWA Specialist Group on Use of Macrophytes in Water Pollution Control. No. 38:36–42; 2011.
  35. 35 Kadlec RH, Wallace SD. Treatment Wetlands. 2nd ed. Boca Raton, USA: CRC Press, Taylor & Francis Group; 2009.
  36. 36 Ávila C, Garfí M, García J. Three-stage hybrid constructed wetland system for wastewater treatment and reuse in warm climate regions. Ecol Eng. 2013; 61:43–49.
  37. 37 Vymazal J, Kröpfelová L. Wastewater Treatment in Constructed Wetlands with Horizontal Subsurface Flow. Dordrecht: Springer; 2008.
  38. 38 Stefanakis AI, Akratos CS, Tsihrintzis VA. Vertical flow constructed wetlands: Eco-engineering systems for wastewater and sludge treatment, 1st edn. Amsterdam, The Netherlands: Elsevier; 2014.
  39. 39 Kim SH, Cho JS, Park JH, Heo JS, Ok YS, Delaune RD, Seo DC. Long-term performance of vertical-flow and horizontal-flow constructed wetlands as affected by season, N load, and operating-stage for treating nitrogen from domestic sewage. Environ Sci Pollut. Res. 2016; 23:1108–1119.
  40. 40 Gaboutloeloe G, Chen S, Barber M, Stöckle C. Combinations of horizontal and vertical flow constructed wetlands to improve nitrogen removal. Water Air Soil Pollut. 2009; 9:279–282.
  41. 41 Tanner CC, Sukias JPS, Headley TR, Yates CR, Stott R. Constructed wetlands and denitrifying bioreactors for on-site and decentralised wastewater treatment: Comparison of five alternative configurations. Ecol Eng. 2012; 42:112–123.
  42. 42 Yang Y, Zhao YQ, Wang SP, Guo XC, Ren YX, Wang L, Wang XC. A promising approach of reject water treatment using a tidal flow constructed wetland system employing alum sludge as main substrate. Water Sci Technol. 2011; 63(10):2367–2373.
  43. 43 Hu YS, Zhao YQ, Zhao XH, Kumar JLG. Comprehensive analysis of step–feeding strategy to enhance biological nitrogen removal in alum sludge-based tidal flow constructed wetlands. Bioresour Technol. 2012; 111:27–35.
  44. 44 Fan J, Liang S, Zhang B, Zhang J. Enhanced organics and nitrogen removal in batch-operated vertical flow constructed wetlands by combination of intermittent aeration and step feeding strategy. Environ Sci Pollut Res. 2013; 20:2448–2455.
  45. 45 Wang Z, Liu C, Liao J, Liu L, Liu Y, Huang X. Nitrogen removal and N2O emission in subsurface vertical flow constructed wetland treating swine wastewater: Effect of shunt ratio. Ecol Eng. 2014; 73:446–453.
  46. 46 Brix H, Arias CA, Johansen NH. Experiments in a two–stage constructed wetland system: nitrification capacity and effects of recycling on nitrogen removal. In: Vymazal J, ed. Wetlands – Nutrients, Metals and Mass Cycling. Leiden, The Netherlands: Backhuys Publishers; 2003, pp. 237–258.
  47. 47 Brix H, Arias CA. The use of vertical flow constructed wetlands for on-site treatment of domestic wastewater: New Danish guidelines. Ecol Eng. 2005; 25:491–500.
  48. 48 Ayaz SÇ, Aktaş Ö, Fındık N, Akça L, Kınacı C. Effect of recirculation on nitrogen removal in a hybrid constructed wetland system. Ecol Eng. 2012; 40:1–5.
  49. 49 Foladori P, Ruaben J, Ortigara ARC. Recirculation or artificial aeration in vertical flow constructed wetlands: A comparative study for treating high load wastewater. Bioresour Technol. 2013; 149:398–405.
  50. 50 Vázquez MA, De la Varga D, Plana R, Soto M. Vertical flow constructed wetland treating high strength wastewater from swine slurry composting. Ecol Eng. 2013; 50:37–43.
  51. 51 Zhang L, Zhang L, Liu Y, Shen Y, Liu H, Xiong Y. Effect of limited artificial aeration on constructed wetland treatment of domestic wastewater. Desalination. 2010; 250(3):915–920.
  52. 52 Nivala J, Wallace S, Headley T, Kassa K, Brix H, van Afferden M, Müller R. Oxygen transfer and consumption in subsurface flow treatment wetlands. Ecol Eng. 2013; 61:544–554.
  53. 53 Pascual A, De la Varga D, Arias CA, Van Oirschot D, Kilian R, Álvarez JA, Soto M. Hydrolytic anaerobic reactor and aerated constructed wetland systems for municipal wastewater treatment – HIGHWET project. Environ Technol. 2017; 38(2):209–219.
  54. 54 Kickuth R. Abwasserreinigung in Mosaikmatritzen aus aeroben und anaeroben Teilbezirken. In: Moser, F. (ed.) Grundlagen der Abwasserreinigung. MÚnchen, Wien: Verlag Oldenburg; 1981, pp. 630–665.
  55. 55 Brix H. Gas exchange through the soil–atmosphere interphase and through dead culms of Phragmites australis in a constructed reed bed receiving domestic sewage. Water Res. 1990; 24:259–266.
  56. 56 Platzer C, Mauch K. Soil Clogging in Vertical-flow Reed Beds – Mechanismns, Parameters, Consequences and …Solutions? Water Sci. Technol. 1997; 35(5):175–181.
  57. 57 Chazarenc F, Gagnon V, Comeau Y, Brisson J. Effect of plant and artificial aeration on solids accumulation and biological activities in constructed wetlands. Ecol Eng. 2009; 35(6):1005–1010.
  58. 58 Dong H, Qiang Z, Li T, Jin H, Chen W. Effect of artificial aeration on the performance of vertical-flow constructed wetland treating heavily polluted river water. J Environ Sci. 2012; 24(4):596–601.
  59. 59 Pedescoll A, Corzo A, Álvarez E, Puigagut J, García J. Contaminant removal efficiency depending on primary treatment and operational strategy in horizontal subsurface flow treatment wetlands. Ecol Eng. 2011; 37:372–380.
  60. 60 Tao W, Wang J. Effects of vegetation, limestone and aeration on nitritation, anammox and denitrification in wetland treatment systems. Ecol Eng. 2009; 35:836–842.
  61. 61 Li HB, Li YH, Sun TH, Wang X. The use of a subsurface infiltration system in treating campus sewage under variable loading rates. Ecol Eng. 2012; 38:105–109.
  62. 62 Pan JZ, Li WC, Ke F, Wang L, Li XJ. Oxygen transfer efficiency of four kinds substrates applied in artificial aeration vertical-flow wetland. In Chinese. Env Sci. 2009; 30(2):402–406.
  63. 63 Sakadevan K, Bavor HJ. Nutrient removal mechanisms in constructed wetlands and sustainable water management. Water Sci Technol. 1999; 40:121–128.
  64. 64 Kadlec RH, Reddy KR. Temperature effects in treatment wetlands. Water Environ Res. 2001; 73:543–557.
  65. 65 Stein OR, Hook PB. Temperature, plants and oxygen: how does season affect constructed wetland performance? J. Environ Sci Health A. 2005; 40(6–7):1331–1342.
  66. 66 Brix H. Constructed wetlands for municipal wastewater treatment in Europe. In: Mitsch WJ, ed. Global wetlands: old world and new. Amsterdam: Elsevier Science; 1994: 325–333.
  67. 67 Reed SC, Brown D. Subsurface flow wetlands – a performance evaluation. Water Environ Res. 1995; 67244–67248.
  68. 68 IWA (International Water Association). Constructed Wetlands For Pollution Control: Processes, Performance, Design and Operation. London: Scientific and Technical Report No 8. IWA Publishing; 2000, pp. 156.
  69. 69 Mander Ü, Kuusemets V, Lõhmus K, Mauring T, Teiter S, Augustin J. Nitrous oxide, dinitrogen and methane emission in a subsurface flow constructed wetland. Water Sci Technol. 2003; 48(5):135–142.
  70. 70 Johansson AE, Gustavsson AM, Oquist MG, Svensson BH. Methane emissions from a constructed wetland treating wastewater – seasonal and spatial distribution and dependence on edaphic factors. Water Res. 2004; 38:3960–3970.
  71. 71 Baptista JDC, Donelly T, Rayne D, Davenport RJ. Microbial mechanisms of carbon removal in subsurface flow wetlands. Water Sci Tech. 2003; 48(5):127–134.
  72. 72 Kuschk P, Wiessner A, Kappelmeyer U, Weissbrodt E. Annual cycle of nitrogen removal by a pilot-scale subsurface horizontal flow in a constructed wetland under moderate climate. Water Res. 2003; 37(1):4236–4242.
  73. 73 Bedford BL, Bouldin DR, Beliveau BD. Net oxygen and carbon dioxide balances in solutions bathing roots of wetland plants. J Ecol. 1991; 79:943–959.
  74. 74 Sorrell BK, Armstrong W. On the difficulties of measuring oxygen release by root systems of wetland plants. J Ecol. 1994; 82:177–183.
  75. 75 Armstrong W, Cousins D, Armstrong J, Turner DW, Beckett PM. Oxygen distribution in wetland plant roots and permeability barriers to gas–exchange with the rhizosphere: a microelectrode and modeling study with Phragmites australis. Ann Bot. 2000; 86:687–703.
  76. 76 Wieβner A, Kuschk P, Kaestner M, Stottmeister U. Abilities of halophyte species to release oxygen into rhizospheres with varying redox conditions in laboratory-scale hydroponic systems. Int. J. Phytoremediation 2002; 4:1–15.
  77. 77 Olson RK. Created and Natural Wetlands for Controlling Non-Point Source Pollution. Man-Tech Environmental Technologies, Inc., USEPA, Corvallis, OR, USA; 1993.
  78. 78 Tanner C Plants as ecosystem engineers in subsurface-flow treatment wetlands. Water Sci Technol. 2001; 44(11–12):9–17.
  79. 79 Carballeira T, Ruiz I, Soto M. Effect of plants and surface loading rate on the treatment efficiency of shallow subsurface constructed wetlands. Ecol Eng. 2016; 90:203–214.
  80. 80 Calheiros CSC, Rangel AOSS, Castro PML. Constructed wetland systems vegetated with different plants applied to the treatment of tannery wastewater. Water Res. 2007; 41(8):1790–1798.
  81. 81 Vymazal J. Removal of nutrients in various types of constructed wetlands. Sci Total Environ. 2007; 380:48–65.
  82. 82 Redmond E, Just CL, Parkin GF. Nitrogen removal from wastewater by an aerated subsurface-flow constructed wetland in cold climates. Water Environ Res. 2014; 86(4):305–313.
  83. 83 Tunçsiper B, Drizo A, Twohig E. Constructed wetlands as a potential management practice for cold climate dairy effluent treatment. USA CATENA (135); 2015, pp. 184–192.
  84. 84 Toet S, Van Logtestijn RSP, Kampf R, Schreijer M, Verhoeven JTA. The effect of hydraulic retention time on the removal of pollutants from sewage treatment plant effluent in a surface-flow wetland system. Wetlands. 2005; 25(2):375–391.
  85. 85 Vymazal J. Nitrogen removal in constructed wetlands with horizontal sub-surface flow – can we determine the key process? In: Vymazal J, ed. Nutrient cycling and retention in natural and constructed wetlands. Backhuys: Leiden; 199, pp. 1–17.
  86. 86 He Q, Mankin KR. Seasonal variation in hydraulic performance of rock plant filters. Environ Technol. 2001; 22:991–999.
  87. 87 Machate T, Noll H, Behrens H, Kettrup A. Degradation of phenanthrene and hydraulic characteristics in a constructed wetland. Water Res. 1997; 31(3):554–560.
  88. 88 Carballeira T, Ruiz I, Soto M. Aerobic and anaerobic biodegradability of accumulated solids in horizontal subsurface flow constructed wetlands. Int Biodet Biodeg. 2017; 119:396–404.
  89. 89 Faulkner SP, Richardson CJ. Physical and chemical characteristics of freshwater wetland soils. In: Hammer DA, ed. Constructed Wetlands for Wastewater Treatment: Municipal, Industrial and Agricultural; 1989.
  90. 90 Nurk K, Truu J, Truu M, Mander Ü. Microbial characteristics and nitrogen transformation in planted soil filter for domestic wastewater treatment. J Environ Sci Health 2005; 40:1201–1214.
  91. 91 Saeed T, Sun G. A review on nitrogen and organics removal mechanisms in subsurface flow constructed wetlands: Dependency on environmental parameters, operating conditions and supporting media. J Environ Manage. 2012; 112:429–448.
  92. 92 Spieles DJ, Mitsch WJ. Macroinvertebrate community structure in high–and low–nutrient constructed wetlands. Wetlands BioOne 2000; 20(4):716–729.
  93. 93 APHA. Standard Methods for the Examination of Water and Wastewater. 21st edn, Washington: American Public Health Association/American Water Works Association/Water Environment Federation; 2005.
  94. 94 Rossman M, Teixeira A, Carneiro E, Fonseca F, Carraro A. Effect of influent aeration on removal of organic matter from coffee processing wastewater in constructed wetlands. J Environ Manage 2013; 128:912–919.
  95. 95 Zhang S, Li G, Chang J, Li X, Tao L. Aerated enhanced treatment of aquaculture effluent by three-stage, subsurface flow constructed wetlands under a high loading rate. Pol J Environ Stud 2015; 23(5):1821–1830.
  96. 96 Ong SA, Ho LN, Wong YS, Chen SF, Dugil DL, Samad S. Semi-batch operated constructed wetlands planted with Phragmites australis for treatment of dyeing wastewater. J Eng Sci Technol. 2011; 6:619:627.
  97. 97 Ong SA, Ho LN, Wong YS, Chen SF, Viswanathan M, Bahari R. Mineralization of diazo dye (Reactive Black 5) in wastewater using recirculated up-flow constructed wetland reactor. Desalination Water Treat. 2012; 46:312–320.
..................Content has been hidden....................

You can't read the all page of ebook, please click here login for view all page.
Reset