24.2.1 History of distilling co-products

One of the first bio-based feed materials was produced as early as 1790, when the surplus grain from the Kilbagie Distillery, Clackmannanshire, was recorded as being fed to cattle. Indeed in the early days of distilling, it was natural to feed the residues of producing the water of life ‘uisage beatha’ to livestock. The scale of this production, approximately 2.3 million litres alcohol per annum from approximately 8,000 tons of barley, compares with a modern bioethanol plant producing in excess of 400 million litres of ethanol from approximately one million tons of grain. Production of potable ethanol is a mature technology using enzyme liquefaction and saccharification of starch to produce glucose which is then fermented by Saccharomyces cerevisiae yeast to produce ethanol. The leftover mash (whole stillage) is decanted into a fibrous wet grain and a liquid component, thin stillage, which contains the majority of the yeast protein and soluble components. Thin stillage has a very high water content, with only around 60–85 g/kg dry matter (Mustafa et al., 1999), so it is evaporated into a syrup, remixed with the wet grain and dried to form distillers dried grains with solubles (DDGS). The drying of the co-product is an energy-demanding, expensive necessity in order to remove all the ‘waste’ material not required for the production of ethanol from the distillery which, if not removed, would congest the primary process of ethanol production.

24.2.2 Scale of bioethanol production

The European Commission published the Biofuels Directive in 2003 (EU, 2003a) which promotes renewable fuels as a means of reducing carbon emissions. Targets were set for member states and in the UK these were incorporated into the Renewable Transport Fuel Obligation, which specifies that renewable fuels must make up 3.5% of fuel supplied on UK forecourts (RTFO, 2007), increasing up to a 5% inclusion by 2014. In 2010/11, 1,507 million litres (Ml) of biofuel were supplied in the UK, of which 41% was bioethanol (618 Ml/year), the majority of which was imported from Brazil and the USA (Department for Transport, 2012). In 2011 the EU produced 4,400 Ml, an increase of 105% on 2007 making it the third largest producer behind Brazil and the US (European Bioethanol Fuel Association, 2012). The significance of these figures for feed ingredients is based on the one-third rule: in first generation bioethanol production it is generally recognised that from the grain feedstock, one third of the grain goes into ethanol, one third into carbon dioxide and one third into animal feed. Growth in bioethanol production leads to growth in feed production.

Biodiesel production is globally some way behind bioethanol production (Fig. 24.1), but makes up the majority of the biofuel production in the EU. Feedstock accounts for 80 percent of the cost of a gallon of biodiesel, so feedstock availability is the driver for biodiesel production. This accounts for the relatively small production in the US, although this is increasing and 1.1 billion gallons were produced in 2011 (The National Biodiesel Board, 2012). The growth in renewable fuel produced from the fermentation of plant material has resulted in an equal growth in the co-product residue, which as indicated earlier has traditionally been targeted predominantly to one segment of the animal feed market, namely ruminant nutrition.

24.2.3 The demand for feed: attributes and trends

Increases in consumer demand for meat, especially in developing countries, will require increasing protein supplies for animal feed. Beyond the energy component of the diet, protein forms the largest dietary component for pigs, poultry and fish. The usefulness or quality of a plant protein source for animal feeds depends on three main factors: the volume of protein provided, the availability of that protein to the animal and the number of antinutritional factors (ANFs) contained with the material. Antinutritional factors are components within a plant-derived feed material that invoke a detrimental response within the animal, such as reduced growth or tumour induction. Availability of protein depends on how closely the profile of amino acids in the protein source matches the requirements of the growing animal and also how easily each amino acid may be digested.

The major protein sources in use are plant-derived meals (e.g., soya and rape meals), fishmeal and meat and bone meal, with some protein also being sourced from industry co-products and legumes. The majority of protein used in animal feed is from oilseed; Gilbert (2002) quotes an annual figure of 316 million tonnes (Mt) of oilseed protein, 14 Mt from animal by-products and 7 Mt from fishmeal. However, in the EU, legislation constrains the use of animal by-products in animal feed (TSE regulation 999/2001; ABPR 1774/2002). Similarly, although fishmeal is a high quality protein source, overfishing has led to introduction of restrictions to conserve fish stocks and Hardy (2010) stated that further reduction in use of fishmeal will be required in the future. Biorefinery co-products can go some way towards meeting the demand for sustainable animal protein. Globally, around 44 million tonnes of distillery co-products were incorporated into the production of animal feed in 2011, which is an increase of 23.7% on the previous 12-month period (DEFRA, 2011). The majority of these co-products are currently used in ruminant feed.

24.3.1 Distillers dried grains with solubles (DDGS)

Distillers dried grains with solubles (DDGS) are produced from de-alcoholised fermentation residues, after the yeast fermentation of grains to convert starch to alcohol (Weigel et al., 1997) and are a co-product of both bioethanol and potable alcohol production. DDGS is an internationally recognised protein source for cattle. An excellent review of the use of DDGS as a feed source has been written at Iowa State University (Babcock et al., 2008). Figure 24.2 shows the global DDGS production since 2002.

Nutritional value of DDGS as a feed ingredient

Removal of the starch from the cereal source through fermentation approximately triples the concentration of all remaining components including valuable nutrients such as protein in the DDGS product (see Table 24.1; Thacker and Widyaratyne, 2007). Unfortunately, in periods when grain may be of poor quality from moulding, for example, the concentration of the mould in the final product will also be tripled. The nutritional variability found in DDGS can affect feed manufacturing as nutrients contributed by DDGS can vary so widely that the final feed can be out of tolerance for final product specification (Behnke, 2007).

Table 24.1

Comparison of nutritional content of wheat, wheat DDGS and maize DDGS

Variable	Wheat	Wheat DDGS	Maize DDGS
Moisture	11.8	8.1	11.8
Crude protein	19.8	44.5	30.3
Non-protein N	4.6	10.2	5.4
Fat	1.8	2.9	12.8
Ash	2.1	5.3	4.8
ADF	2.7	21.1	14.6
NDF	9.4	30.3	31.2

Source: Thacker and Widyaratyne, 2007.

The digestible amino acid content of DDGS does not necessarily correspond to its increased protein content compared to the native cereal, as some amino acids (such as proline and alanine) concentrate more rapidly than others during fermentation (e.g., histidine and leucine) (Liu, 2011). Also, the high possibility of Maillard reactions during DDGS drying leaves lysine digestibility as a major concern for the use of DDGS as a feed ingredient. Maillard browning reactions result in the formation of indigestible polymers based on the epsilon amino group of lysine and a reducing sugar.

The major feedstock for DDGS in the US is maize, whereas wheat is the major feedstock in Europe. Currently wheat DDGS is successfully used in ruminant nutrition at inclusion levels of between 25 and 35% without affecting nutrient digestibility or growth characteristics (Li et al., 2011; Yang et al., 2012), with maximum performance characteristics found with around 20% inclusion of DDGS (Buckner et al., 2007; Klopfenstein et al., 2008). The high fibre content decreases feed intake and limits nutrient utilisation in both pigs (Nyachoti et al., 2005) and chicks (Thacker and Widyaratyne, 2007), as the fibre increases dietary bulk. Wheat DDGS has been used successfully in pig feed at 30% with no effect on performance traits (McDonnell et al., 2011) and in broiler feeds at 15% inclusion (Thacker and Widyaratyne, 2007; Youssef et al., 2008). Loar et al. (2010) suggested that feeding DDGS levels of 15% or higher may adversely affect young chicks less than 28 days of age, but that feed intake in older chicks is reduced if chicks are not exposed to DDGS in starter diets. Although levels up to 12% have no effect on meat quality or consumer acceptance, above these levels there may be a negative effect on thigh meat as increased fatty acids may increase oxidation (Corzo et al., 2009; Schilling et al., 2010).

For maize DDGS, suggested inclusion rates for broilers are 24% when fully balanced for amino acids (Shim et al., 2011) and 6% when not fully supplemented (Lumpkins et al., 2004). Wang et al. (2007) did suggest that there may be a possible loss of breast meat yield at 20% maize DDGS inclusion. Inclusion rates for layers are suggested at 10% (Lumpkins et al., 2005), and Masa’deh et al. (2011) found that egg weight was reduced when more than 15% DDGS was included in the diet.

DDGS has also been investigated in aquaculture diets; in tilapia, Schaeffer et al. (2010) found that higher levels of DDGS (over 20%) reduced feed conversion ratio and bodyweight gain. These authors also hypothesised that replacing fishmeal with DDGS would require amino acid supplementation at higher inclusion levels. Again in tilapia diets, it has been shown that diets supplemented with lysine can contain up to 40% DDGS without any reduction in performance (Li et al., 2011). Figure 24.3 shows the current usage of DDGS in the different animal feed sectors.

24.3.2 Oilseed meals

Oilseeds not only provide a valuable fuel source, but also a valuable feed material as the high oil content of the seed is usually coupled with high protein content. Post-oil extraction, the resulting meals form the backbone of protein supply to the global animal feed industry. The dominant feed protein product is soya bean meal, due to its widespread availability and balanced amino acid profile, which is generally well suited to the requirements of growing non-ruminant animals.

A number of oilseed meals other than soya also make a significant contribution to global animal feed protein. Table 24.2 shows the global production of oil-bearing seeds in 2011 and the digestible protein content of the subsequent meal.

24.3.3 Corn gluten meal

The majority of global bioethanol production uses the simple dry grind process which produces DDGS as a co-product. However, there is an alternative wet grind process, which is both a more capital requiring and intensive process which separates parts of the corn kernel to make syrups, oil and other products. The final by-product of the wet grind process is corn gluten meal which is a protein product primarily used as cattle feed but which is now gaining acceptance as a protein supplement in a number of different applications including aquanutrition.

24.3.4 Liquid feeds

There are a number of liquid biorefinery co-products that are well suited and economical for use in feed. However, in addition to the challenges over variability in nutritional value discussed earlier for dry biorefinery feed products, transportation costs are increased by the lower nutrient density of liquid feeds.

Whilst the majority (around 70%) of bioethanol production blends fibrous and liquid fractions to create DDGS as the primary feed product, bioethanol production may also yield two feed liquid products which rising cereals costs are likely to promote as attractive feed materials. Condensed distillers solubles (CDS) from the bioethanol dry milling process are suited to liquid feeding systems used for pig production. CDS can positively affect growth performance but low palatability limits inclusions to a maximum of 20% in pig diets (de Lange et al., 2006) and presence of live yeast may lead to additional fermentation and frothing during storage. Corn steepwater (also known as condensed steepwater solubles) from the bioethanol wet milling process is viewed as an excellent source of soluble protein for beef cattle liquid feed supplements. Corn steepwater contains substantially more crude protein, ash, phosphorus and lactic acid than CDS, but the low oil levels leave it with low energy content. The similarity in consistency of CDS to molasses has raised interest in the product as a pellet quality enhancer, but the hygroscopicity of CDS is relatively high, presenting risk of mould contamination of pellets (DeFrain et al., 2003).

A final molasses-type product under consideration as an animal feed is the 5 carbon sugar product from the hemicellulose component of cellulosic bioethanol production, termed 5C molasses, which is 65% dry matter (Persson, 2009). To date, a pilot plant in Kalundborg, Denmark, is producing 11,100 tonnes per annum of 5C molasses which has been successfully trialled in pig diets (data not published) and is currently being marketed both as pig and cattle feed but may ultimately be re-directed into further bioethanol production. Another by-product of cellulosic ethanol production is lignin, which is used to produce pellet binders which increase production and enable the use of hard-to-pellet materials in animal feed, such as DDGS. Their inclusion in diets has also been shown to have a positive effect on poultry performance and caecal fermentation (Kivimäe, 1978; Moran and Conner, 1992) and may improve gastrointestinal health by providing fermentable oligosaccharides (Flickinger et al., 1998).

Biodiesel production from triglycerides yields one liquid product used in animal feed: glycerol. The 2004 boom in biodiesel production more than doubled crude glycerol production and exceeded the capacity of glycerol refineries. Existing markets required refinement of glycerol so the extra one million tonnes of glycerol produced alongside biodiesel was directed into the animal feed sector as crude glycerol. Ruminant feeds appear particularly well suited to incorporation of glycerol, as glycerol is a natural product of rumen fermentation of fat. Inclusion of up to 10% glycerol in the total mixed ration of dairy cows increased milk yield and decreased post-calving weight loss (Bodarski et al., 2005). The plummet in glycerol cost and concurrent hike in cereal costs have heightened interest in the use of glycerol as an energy source for pigs and poultry: it has been successfully incorporated into diets in poultry at levels of up to 9% (Dozier et al., 2008) and up to 10% in pig diets. These inclusion levels also improve pellet quality and production efficiency in the mill (Groesbeck et al., 2008).

24.4.1 Drying technologies

The drying method can affect the nutritional content of the finished product, although product deterioration is usually due to the application of excess heat, rather than the moisture removal (Morris et al., 2004). Drying types can be classified by either the mechanism of heating or mechanism of vapour transport. Air drying requires a high temperature air which supplies the heat and removes the water vapour, whereas vacuum drying uses a reduction in pressure to remove the vapour (Chen and Mujumder, 2009).

24.4.2 Maillard reactions

Maillard browning reactions are a complex series of stages, beginning with a condensation between a reducing sugar and most commonly the ε-amino group of lysine (Purlis, 2010). When pentoses and hexoses are involved, the reaction forms brown polymers (Martins et al., 2001). Maillard reactions impair the nutritional content and the bioavailability of amino acids and proteins (Moralez et al., 2007). Colour has been correlated to amino acid digestibility by a number of researchers (Batal and Dale, 2006; Fastinger et al., 2006), with lysine digestibility reducing from 80% to 60% with darker DDGS (Ergul et al., 2003). Very dark samples have recently been reported to give very low ileal digestibility values in pigs (Cozannet et al., 2010) and in cockerels (Cozannet et al., 2011a). This heat processing damage also negatively affects the digestible energy content of both maize (Fastinger et al., 2006) and wheat DDGS (Cozannet et al., 2011b). In wheat DDGS, amino acid digestibility was found to be lower in pigs when compared to wheat and some amino acids (including lysine) were significantly reduced by the drying process (Pederson and Lindberg, 2010).

24.4.3 Use of enzymes during processing

The viscosity of a co-product stream may influence the recovery efficiency, which is an effect experienced in the brewing industry. The viscosity of the stream is influenced by the composition of the dissolved solids: in particular, the presence of short chain non-starch polysaccharides (NSP) in the liquid stream will contribute to increased viscosity. Exogenous enzymes such as glucanases are available to counteract the effect of viscosity (Bamforth, 2009). Bamforth and Kanauchi (2001) hypothesised that within barley cell walls, the accessibility to β glucan is hindered by arabinoxylan content, reducing its solubility. Scheffler and Bamforth (2005) provided more evidence to support this hypothesis, and also suggested that it is β glucan rather than arabinoxylan which causes viscosity issues in mash. There is also a role for xylanase in separating the β glucan, so a mixture of enzymes is most effective for viscosity reduction in barley mashes, specifically a xylanase/glucanase mix.

24.5.1 Subfractionation

If DDGS could be modified and made more suitable for monogastric nutrition, it would enable the co-product to be more easily utilised in alternative market segments such as the large pig and poultry feed markets as opposed to the current application which is mainly for cattle. Efforts have been made to produce higher protein DDGS. The Elusieve process uses a combination of sieving and air flow to produce a higher protein enhanced DDGS (Srinivasan et al., 2008, 2009). This process has been used with maize DDGS and the high protein fraction was fed to chickens resulting in a partial increase in final bodyweight compared with the non-sieved DDGS (Loar et al., 2009) but no differences in digestible energy or amino acid content were observed (Kim et al., 2010). Using the same process, sieved wheat DDGS improved energy digestibility in rainbow trout (Randall and Drew, 2010). The improvements to DDGS using this process to date have been small and as with DDGS, batch variability and product drying remain key issues. Whilst this product has higher protein than DDGS, its high fibre content renders it fundamentally similar to DDGS and therefore not considered by feed formulators as a yeast protein for use in non-ruminant diets.

24.5.2 Process improvements of bioethanol co-product

The yeast component of bioethanol co-product provides a valuable source of protein if it can be economically separated from DDGS, leaving a high fibre fraction which is nutritionally appropriate for ruminant feeding. A novel, factory scale, continuous-flow process is being developed to separate a yeast-containing, high protein fraction from the distillery stillage called yeast protein concentrate (YPC) (Williams, 2010; Williams et al., 2009). Once separated, the YPC is dried to produce a powder, which may be suitable as either a protein source or a feed additive for monogastric feeds. This technology could be applied in the emerging bioethanol industry, in the existing potable alcohol industry and also in any large-scale grain fermentation facility.

The separation undertaken has three distinct stages: decanting, liquid removal and drying. Decanters are solid walled, horizontal centrifuges used to separate suspensions with a high concentration of solids. In the case of ethanol stillage, the decanter is the first stage of separation after distillation. A decanter houses a rotating horizontal bowl with a cylindrical and a conical section, and a scroll integrated in the bowl. The stillage enters the separation chamber through a centrally arranged feed pipe, and due to centrifugal forces, the solid particles are flung towards the wall of the chamber. The rotating screw in the separating bowl conveys the solids to the cone end of the bowl where they are then discharged. Regulating tubes allow the level of liquid to be altered within the bowl. The liquid phase, containing the yeast flows in the opposite direction to the solid discharge through the cylindrical part of the bowl to discharge under gravity. Further clarification of the liquid fraction is carried out using a centrifugal separator or disk stack.

The disk stack is a continuously operating nozzle centrifuge which is specially designed for liquid separation. Using a centrifuge to remove water is more cost effective than drying (V’ant Land, 1991). The disk stack comprises a rotating bowl equipped with a large number of inserts; conically arranged discs which are stacked into the bowl with small interspaces. The liquid fraction from the decanter enters the bowl through a central feed tube and the product is accelerated and conveyed into the disc portion of the separator. Solids are flung against the underside of the disk above due to their higher density and then they flow down the disc. The separated solids are continuously discharged though nozzles at the bowl periphery. The liquid in the bowl is then picked up by a centripetal pump which discharges the liquid. In the case of the alcohol stillage separation, the solid fraction from the disk stack is a yeast containing high protein cream which is dried to a powder for use as an animal feed ingredient.

However, as with DDGS, batch variability and product drying remain key issues, and any separated product may still contain some of the anti-nutritional factors present in wheat. Initial feeding studies have shown positive performance effects when feeding YPC to both poultry and fish. Digestible amino acid content of this yeast protein concentrate has been shown to be comparable with soya for broiler chicks, and higher than the feedstock alone (Scholey et al., 2011a), although this is heavily influenced by the drying process used. In feeding studies with broiler chicks, dietary inclusion levels of 6% bioethanol YPC gave improved performance characteristics (Scholey et al., 2011b). Bioethanol sourced YPC has been fed to several aquaculture species, with 20% dietary inclusion appearing optimal for performance (Omar et al., 2012; Gause and Trushenski, 2011a, 2011b).

Due to the high ethanol exposure during the process, bioethanol yeast may have a thicker, toughened cell wall, which is more resistant to enzyme proteolysis (Caballero-Cordoba and Sgarbieri, 2000). Rumsey et al. (1991) showed that salmonids fed disrupted yeast had an increased nitrogen absorption compared with whole yeast. This improvement in nutrient utilisation in homogenised yeast has also been shown in poultry (Vananuvat, 1977; Vananuvat and Chiraratananon, 1977) and shrimp (Coutteau et al., 1990). The disk stack process exerts mechanical shear forces on the yeast, which has been shown to disrupt the cell walls, thereby increasing access to the intracellular nutrients. Yeast cell walls can be considered a prebiotic which can improve performance characteristics in poultry (Parks et al., 2001; Hooge et al., 2003) and pigs (Davis et al., 2004) and positively affect gut morphology in broiler chicks (Santin et al., 2001; Zhang et al., 2005; Morales-Lopez et al., 2009).

24.6.1 Registration of materials for marketing as animal feeds or feed additives

The use of materials as animal feed is tightly governed by legislation ultimately aimed at protecting human and animal health. Legislation surrounding animal feed is most stringent in the EU (EU, 2009), with severity reducing in less developed Asia-Pacific markets. A collaboration between the EU regulatory authority, the European Food Standards Agency (EFSA) and the US authority, the US Food and Drug Administration (FDA), to align EU and US standards resulted in the FDA Food Safety Modernization Act (2011). Additionally, western consumer awareness of food safety is placing pressure on countries exporting animal-based human food products to comply with western legislation.

US and EU legislation on the use and marketing of all animal feeds requires feed to fulfil stipulations relating to safety, quality, purity and traceability. Some aspects of these guidelines are of particular relevance when considering the use of biorefinery products for animal feed. The EU includes restriction on the use of medicated feed, i.e. inclusion of antibiotics (EU, 1990), the need for specific consent for the marketing of any GMOderived product within the EU (EU, 2003b), maximum acceptable levels of microbial contamination and specific legislation on the marketing and use of feed additives (EU, 2003c).

24.6.2 Antibiotics

Antibiotics are used commonly in American bioethanol production to reduce microbial overload. It is estimated that over half of plants are routinely using antibiotics (Olmstead, 2009), usually penicillin or virginiamycin (Hynes et al., 1997; Stroppa et al., 2000) and often prophylactically. There are issues relating to the presence of antibiotic residues in co-products leading to possible resistance and public health consequences (Muthaiyan and Ricke, 2010). There are other options to minimise contamination of bioethanol plants such as chlorine dioxide and natural hop-derived enzymes which are becoming more widely used. FEFAC states that antibiotic bactericides are not routinely used in the EU bioethanol industry, and not used at all in the spirit industry (FEFAC, 2008). There have been several instances in the EU where antibiotic residues have been found in DDGS from bioethanol, but these have been exclusively on Brazilian imports (Pol et al., 2009).

24.6.3 Mycotoxins

There are 400 recognised mycotoxins which may contaminate 25% of cereal feedstocks, but only one of these, Alflatoxin B1 has maximum permitted limit status (EU, 2002). This contamination is concentrated up to three times in DDGS, so contamination needs to be considered and treated in the feedstock. Wu and Munkvold (2008) estimated that contamination from a single mycotoxin could cost the pig industry alone up to $147 million annually, depending on level of DDGS usage.

24.6.4 Feed additives

Some biofuel co-products such as mannan-rich fractions of yeast cell walls may have beneficial properties beyond the simple supply of nutrients: they may improve the quality of feed or the quality of food from animal origin, or improve the animals’ performance and health. Materials with such properties obviously claim a higher price than basic feed materials. However, any such claims cause the product to be classified as a feed additive rather than a feed material and therefore bound to comply with EU and US requirements for scientific verification of efficacy, health and safety of both human handlers and animal consumers of the material (EU, 2003c). Compiled evidence is presented in a dossier that may take 3 years to produce, at an approximate cost of 1 million euros, before authorisation to market the additive within the EU is granted for a specific animal species, under specific conditions of use, for ten-year periods. Similarly in the US, a food additive petition (FAP) is required by the FDA to demonstrate that a material is safe for the proposed use in an animal feed. These requirements are likely to heavily influence decisions on whether to present novel feed products from biorefining as feed materials or feed additives.

24.7.1 Water remediation

In a first generation bioethanol refinery, the ratio of ethanol produced to water used in the process is approximately 1:5. Approximately 40% of the energy use of the plant is used in dewatering the co-product and producing a dry product (DDGS) that can be transported off site. It is inconceivable that such a process can maintain profitability in a situation of rising energy cost, when 40% of total energy is used in dewatering to produce a feed product which has mediocre nutritional value. The stillage stream is generally a dilute solution but rich in protein and non-starch polysaccharides, which are a potential nutrient source for downstream processing. The initial challenge posed in utilising this material is the removal and disposal of the water. Developing processes that either enable the wastewater to be recycled or alternatives to heat to remove water from the co-product stream post-fermentation in a bioethanol plant offer significant benefits in terms of energy saving.

24.7.2 Algae

The need to address water remediation is driving bioethanol production towards adoption of technologies which either reduce reliance on high water volume or permit a higher degree of water recirculation. Algae are ubiquitous in the environment and, as such, a wide variety of organisms have developed the capacity to utilise a range of substrates as nutrients for growth under diverse environmental conditions. A characteristic of algae is the very high rate of biomass production and the fact that the organism has the ability to simultaneously produce a range of products. Large-scale algae production is recognised as a potential future energy source. The value of algae from an ethanol biorefinery is that the feedstock is already a recognised registered feedstuff, hence (barring the introduction of any extraneous components) algae produced in the system are suitable for use in feed. Algae are recognised as a valuable source of protein (Becker, 2007). It is a natural, sustainable feedstuff and for fish can be used as a part replacement of fishmeal supplying both protein and EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) omega-3 oils. Algae may also supply a valuable source of carotenoids. Trials have already been completed with algae bioreactors co-located with bioethanol plants in the US and Scotland, demonstrating that geography and climate are not an impediment to the process. In these trials, the algae were fed to poultry and performance was comparable to high protein soya, with the algae also providing increased dietary energy content. These results are significant as they demonstrate that the co-product from a bioethanol plant can be used in the monogastric market segment rather than the traditional use of bioethanol co-products in the ruminant segment. There is the potential that algae from biofuel production could replace a third of soya in pig and poultry diets (Lei, 2012). In poultry rations, algae up to a level of 5–10% can be used safely as partial replacement for conventional proteins (Spolaore et al., 2006).

The drive to discover alternative water remediation processes was also addressed by a group from Iowa State University. The same principles described above were used to grow a fungus (Rhizopus microspores) on stillage. They reported that the fungus removes about 60% of the organic material and most of the solids from thin stillage, allowing the water in the thin stillage to be recycled back into production. The fungus, once harvested and dried, is a protein-rich nutrient which is high in polyunsaturated fatty acids and may be suitable for use in feed for pigs and poultry.

Bioethanol plants are already adopting anaerobic digesters as a means of using the non-starch polysaccharides in the stillage to generate methane. Anaerobic digestion combines energy generation with a degree of water remediation. However, in order to efficiently operate an anaerobic digester, it has been found beneficial to reduce the nitrogen content of the stillage, the major proportion of which is contained in the spent yeast in the stillage. In an anaerobic digester excess nitrogen in the form of protein results in the generation of ammonia which can poison the digestion process. One solution to the recovery of yeast is the production of YPC. The integration of YPC and anaerobic digestion is a prospective breakthrough in novel water remediation.

24.7.3 The potential for genetic modification

There is potential for genetic modification to contribute to the co-product feeds that are produced from biorefining. In the long term, there is the chance that the co-products of biorefining will create more value than the current primary product of ethanol either for fuel or potable alcohol. The principle has been established with soya bean; where the original primary product was oil, now the range of protein materials produced creates more value than the oil in the bean. In biorefining, the primary feedstock is normally plant material with either single cell organisms or products from microorganisms (such as enzymes) used in the conversion process, hence there is the opportunity for genetic modification at both these points in the process.