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Featured Application: The application of this work is directly related to food processing industries such as slaughterhouses which produce high strength wastewater. An additional featured application is the opportunity for co-digestion where co-located industries, such as nearby beef feedlots, can develop synergistic partnerships in which waste can contribute to anaerobic digestion systems at slaughterhouse facilities to help optimise the process and also result in waste disposal for one industry and energy production and offsets for the other. This work represents and reviews a compilation of investigations into improving anaerobic digestion performance of high-strength wastewater in the Australian Red Meat Processing industry. The industry produces significant quantities of organic-rich wastewater which requires treatment prior to release to the environment. Anaerobic lagoons are a cost-effective method of waste treatment where land availability is not an issue; however, the high fat load in the wastewater can negatively impact the anaerobic lagoon system and result in compromised anaerobic digestion performance. This paper will discuss the importance of upstream primary pre-treatment and review a series of investigations focused on optimising digester performance and improving fat biodegradability. These studies include: 1. the effect of temperature and mixing; 2. the influence of feedstock trace element composition and supplementation, and; 3. the potential benefit from pre-treatments such as chemical, thermobaric, thermochemical and bio-surfactant. This paper discusses the implications of these findings for covered anaerobic lagoon operation and provides recommendations to promote optimum digester performance and future opportunities in adopting alternate anaerobic digestion technology options. Finally, the paper provides recent trends toward the use of other waste streams for co-digestion and discusses this in terms of digester optimization and technology options. [ABSTRACT FROM AUTHOR]

[Display omitted] • First report of biochemical methane potential (B 0) for grazing dairy effluent. • B 0 of grazing dairy effluent is 161 L CH4 ·kg VS -1. • B 0 of intensive dairy (barn) effluent is 202 L CH4 ·kg VS -1. • Manure solids content is affected by cleaning method; and amount by capture extent. • Mechanical manure separation can reduce fugitive methane losses from effluent ponds. This study investigated biochemical methane potential (B 0) of manure residues and solid–liquid separation fractions from Australian dairies. This is important for country-specific sector emissions and biogas potential estimates. A range of samples were collected from 12 farms across 4 Australian states, and B 0 was measured. A first B 0 value for grazing dairy effluent is reported, at 161 L CH4 ·kg VS -1. The B 0 of manure residues from intensive dairies with total mixed ration feeding was not significantly different, at 202 L CH4 ·kg VS -1. Passive solid–liquid separation decreased B 0 with potential fugitive methane losses. Mechanical separation preserved B 0 , allowing organic matter diversion to reduce fugitive methane emissions. Cleaning method at a dairy significantly influenced residue total solids content, important for solid–liquid separation and selection of anaerobic digestion technology. Overall, B 0 for Australian dairy residues was estimated at 76.2 million m3 N methane per annum, with a total energy content of 2.8 petajoules·annum−1. [ABSTRACT FROM AUTHOR]

Thermobaric pre-treatment of a combination of dissolved air flotation (DAF) sludge and slaughterhouse wastewater was evaluated for performance over 50 days of continuous anaerobic digestion. Continuous digestion was conducted over three phases represented by varying fat, oils and grease (FOG) concentrations and organic loading. In comparison with earlier biochemical methane potential (BMP) investigations using thermobaric treated substrate by Harris, Schmidt and McCabe (Harris et al., 2017) which yielded an 8.32% increase in specific methane production, pre-treated DAF sludge produced negative impacts on digestion under continuous conditions. Average pH was consistently lower by 0.04, and loss of volatile organics during pre-treatment reduced methane yield by 12.1%. H 2 S concentration was 56% higher on average with 795 ppm compared with 510 ppm in the controls owing to enhanced protein degradation. Alkalinity was low due to insufficient replacement from the substrate. Fresh substrate containing double the fat content (236 mg/L) and reduced organic loading rate (OLR) caused both control and treatment reactors to fail, highlighting the need for consistent substrate characteristics. Magnesium hydroxide addition effectively recovered both pH and biogas production within digesters rapidly, addressing the underlying complication of insufficient alkalinity contribution by the substrate. [ABSTRACT FROM AUTHOR]

Bovine bile was assessed as a novel bio-surfactant pre-treatment to enhance anaerobic digestion of lipid-rich dissolved air flotation (DAF) sludge using biochemical methane potential (BMP) tests. Bile was dosed at arbitrary concentrations from 0.2–6 g/L. At 0.6 g bile/L, methane yield increased by 7.08%. Doses above 2 g bile/L produced negative impacts on SMP, kinetics and digestion profile. At 6 g/L bile produced a 6% decrease in specific methane production and up to 79% additional inhibitory duration, delayed time of peak methane production by up to 74%, and slowed total digestion time by up to 65%. Reaction kinetics declined linearly with respect to bile addition, reaching half the control value at 6 g/L bile concentration. Subsequent anaerobic toxicity assays between 1 and 6 g bile/L revealed that bile has an inhibitory effect under BMP testing at these higher doses. The economic viability of using bile as a bio-surfactant was assessed. In comparison to the current use of bile as a sale product to pharmaceutical companies, the addition of 0.2 g bile/L to existing slaughterhouse waste streams could increase the value of bile to 220% of its current sale value. The promising results of bile dosed at 0.6 g/L under BMP testing warrant further investigation into long-term impact of bile pre-treatments of high-fat slaughterhouse wastewater in semi-continuous digestion experiments. [ABSTRACT FROM AUTHOR]

This work aimed to enhance the anaerobic digestion of fat-rich dissolved air flotation (DAF) sludge through chemical, thermobaric, and thermochemical pre-treatment methods. Soluble chemical oxygen demand was enhanced from 16.3% in the control to 20.84% (thermobaric), 40.82% (chemical), and 50.7% (thermochemical). Pre-treatment altered volatile fatty acid concentration by −64% (thermobaric), 127% (chemical) and 228% (thermochemical). Early inhibition was reduced by 20% in the thermochemical group, and 100% in the thermobaric group. Specific methane production was enhanced by 3.28% (chemical), 8.32% (thermobaric), and 8.49% (thermochemical) as a result of pre-treatment. Under batch digestion, thermobaric pre-treatment demonstrated the greatest improvement in methane yield with respect to degree of pre-treatment applied. Thermobaric pre-treatment was also the most viable for implementation at slaughterhouses, with potential for heat-exchange to reduce pre-treatment cost. Further investigation into long-term impact of pre-treatments in semi-continuous digestion experiments will provide additional evaluation of appropriate pre-treatment options for high-fat slaughterhouse wastewater. [ABSTRACT FROM AUTHOR]

This paper explores pre-treatment options for the anaerobic digestion (AD) of high-fat cattle slaughterhouse wastewater by assessing and attempting to compare pre-treatment methods used to treat various waste streams. The central focus on cattle slaughterhouse wastewater stems from the problematic nature of high fat, oil and grease (FOG) present in Australian red meat processing (RMP) waste water. Fully integrated abattoirs such as those operating in Australia typically produce wastewaters that carry high FOG loads of 100–4000+ mg/L. While excessive levels of fat can be inhibitory to the AD process, these fats contain a very high theoretical methane potential of 1014 L CH 4 /kg VS when compared with carbohydrates at 370 L CH 4 /kg VS and proteins at 740 L CH 4 /kg VS. However, due to the hydrophobic and inhibitory nature of fat, oil and grease, accessing this methane potential is difficult. This article serves as a review of the literature in the field of pre-treatment of wastewaters and subsequent anaerobic digestion with the goal of increasing biogas yield, with an emphasis on digestion of wastes high in fat, oil and grease. This review covers mechanical pre-treatments including high-pressure homogenisation, ultrasonication and electrokinetic disintegration, and other forms of pre-treatment including thermal, chemical, thermochemical, and enzymatic hydrolysis, and biochemical emulsification. Biological pre-treatments, also known as pre-hydrolysis and two stage digestion are briefly reviewed. The most significant considerations for selecting a pre-treatment technology are the energy balance and costs. Therefore, this review will also provide a commentary on the advantages and disadvantages of the pre-treatment methods reviewed and conclude by evaluating their relative worth in pre-treating FOG. [ABSTRACT FROM AUTHOR]

On-farm, intensive feeding and processing in Australian red meat, dairy and pork industries produce substantial quantities of organic waste (∼79 GL·annum−1 liquid waste plus ∼2 megatonnes·annum−1 solid waste) and waste management is a major cost (∼180 million Australian dollars. annum−1 for red meat plus dairy processing). Anaerobic digestion can instead extract value from organic waste as biogas energy and biofertiliser to reduce operational costs and environmental impacts, and to improve industry profitability. Understanding key information gaps is a fundamental step towards fully realizing profitable opportunities for anaerobic digestion. This is addressed here via a critical evaluation of available information on Australian agro-industries (specifically dairy, pork and red meat), their waste availability, biogas energy potential, and potential anaerobic digestion approaches. The analysis revealed varying extents of information, but good biogas energy potential (∼13.8 PJ·annum−1) to meet a significant energy demand (∼18 PJ·annum−1). Waste management within respective agro-industries influenced waste amounts and characteristics, which affected anaerobic digestion options. Anaerobic co-digestion, involving aggregated digestion of two or more waste types within or across industries, can provide further opportunities by boosting biogas production and harnessing spare digestion capacity. Overall, cross-industry collaboration, policy support and technology development could help harness the significant opportunities for aggregated biogas production in Australian agro-industries. • Extensive cross-industry review on anaerobic digestion (AD) of agro-industry waste. • Considers pork and dairy on-farm, beef feedlots, and milk and meat processing. • Onsite management affects organic waste (e.g. solid vs. liquid) and AD options. • Biogas potential is significant, and anaerobic co-digestion can boost performance. [ABSTRACT FROM AUTHOR]