Impact of Organic Loading Rate on Psychrophilic Anaerobic Digestion of Solid Dairy Manure

Optimisation and Modelling of Anaerobic Digestion of Whiskey Distillery/Brewery Wastes after Combined Chemical and Mechanical Pre-Treatment

Whiskey distillery waste streams consisting of pot ale (liquid residue) and spent grain (solid residue) are high strength organic wastes and suitable feedstock for anaerobic digestion (AD) from both economic and environmental stand points. Anaerobic digestion of pot ale and pot ale/spent grain mixtures (with mixing ratios of 1:1, 1:3, and 1:5 by wet weight) was performed after implementation of a novel hybrid pre-treatment (combined chemical and mechanical) in order to modify lignocellulosic structure and ultimately enhance digestion yield. Lignin, hemicellulose, and cellulose fractions were determined before and after chemical pre-treatment. Effects of different inoculum rates (10–30–50% on wet basis) and beating times (0–7.5–15 min) on anaerobic digestion of pot ale alone and of pot ale/spent grain mixtures were investigated in lab scale batch mode with a major focus of optimising biogas yield by using response surface methodology (RSM) in Design Expert Software. The highest biogas yields of 629 ± 8.5 mL/g vs. (51.3% CH4) and 360 ± 10 mL/g vs. (55.0 ± 0.4) with anaerobic digestion of pot ale alone and spent grain mix after 1M NaOH and 7.5 min beating pre-treatments with 50% inoculum ratio respectively. The optimum digestion conditions to maximise the biogas quality and quantity were predicted as 10 and 13 min beating times and 32 and 38 °C digestion temperatures for anaerobic digestion of pot ale alone and spent grain mix respectively.

Improving methane yield and quality via co-digestion of cow dung mixed with food waste

Methane (CH₄) production and quality were enhanced by the co-digestion of cow dung and food waste (FW) mixed with organic fraction of municipal solid waste (OFMSW) under optimized conditions in bench and semi continuous-scale mode for a period of 30 days. A bacterium capable of high yield of CH₄ was enriched and isolated by employing activated sewage sludge as the inoculums. The thirteen bacterial isolates were identified through morphological and biochemical tests. Gas chromatography was used to analyze the chemical compositions of the generated biogas. CH₄ yields were significantly higher during co-digestion of Run II (7.59 L) than Run I (3.7 L). Therefore, the co-digestion of FW with OFMSW and Run II was observed to be a competent method for biogas conversion from organic waste resources.

Effect of organic loading rate during anaerobic digestion of municipal solid waste

The effect of chemical oxygen demand (COD) and volatile solids (VS) on subsequent methane (CH4) production during anaerobic digestion (AD) of organic fraction of municipal solid waste (OFMSW) was studied in a laboratory-scale digester. The experiment was performed in 2L anaerobic digester under different experimental conditions using different input mass co-digested with inoculum and organic loading rate (OLR) for 27days at 38±2°C. Three digesters (digesters 1, 2 and 3) were operated at initial loading of 5.1, 10.4 and 15.2g/L CODS per batch which were reduced to 77.9% and 84.2%, respectively. Cumulative biogas productions were 9.3, 10.7 and 17.7L in which CH4 yields were 84.3, 101.0 and 168.4mL/gVS removal in digesters 1, 2, and 3, respectively. The observed COD removal was found to be influenced on variation in CH4 production. Co-efficient of determination (R(2)) was 0.67 and 0.74 in digesters 1 and 2, respectively.

Biotic and abiotic roles of leachate recirculation in batch mode solid-state anaerobic digestion of cattle manure

Solid state anaerobic digestion, with leachate recirculation, is suitable for exploiting manure with a high solid content. The biotic and abiotic effects of the leachates were studied in lab-scale leach bed reactors (LBRs). LBRs were fed with cow manure and four leachates either biologically active or inert. The biotic impact of leachate was assessed by monitoring the microbial communities in the manure and in the leachates. LBRs with biologically active leachates, regardless to their origin, produced equivalent methane volumes (114.52±19.05 and 99.79±6.4NL/kgVS) while LBRs with inert leachates produced half less methane (60.22±5.71 and 58.87±13.2NL/kgVS) attesting to the biotic role of leachate. Moreover, its beneficial abiotic role is mainly due to its initial nutrient content, pH, and buffering capacity. The microbial community in the manure was strongly involved in methane production, and no transfer of microorganisms from the liquid phase was found (p<0.05).

High rate psychrophilic anaerobic digestion of undiluted dairy cow feces

Novel high rate psychrophilic (20°C) anaerobic digestion (PAD) of undiluted cow feces (11.5-13.5% total solids) was demonstrated using sequence batch reactor in long-term operation with successive cycles of 21days treatment cycle length (TCL). At organic loading rates (OLR) 9.0, 10.0, 11.0 and 12.0g TCOD kg(-1) inoculum d(-1) average specific methane yield (SMY) was 154.0±11.7, 152.1±12.2, 126.0±2.8 and 116.0±6.1NL CH4 per kg of VS fed, respectively. Volatile solids removal averaged around 31.7±3.3%, 32.2±1.0%, 27.9±2.2% and 23.4±0.5%, respectively. Substrate-to-inoculum ratio (SIR; wet-mass basis) ranged between 1.17±0.06 and 1.43±0.05. Concentration of volatile fatty acids in the bioreactors during the TCL indicated that hydrolysis was the rate limiting reaction. High rate PAD of undiluted cow feces is possible at OLR (g TCOD kg(-1) inoculum d(-1)) 9.0 and 10.0 with a TCL of 21days; however, OLR of 11.0 and 12.0 are also possible but require longer TCL to maintain the SMY.