High rate psychrophilic anaerobic digestion of undiluted dairy cow feces

A robust, low-temperature, closed-loop anaerobic system for high-solid mixed farm wastes: advancing agricultural waste management solutions in Canada

This study investigates the effectiveness of low-temperature (20 ± 1 °C) anaerobic digestion (AD) for two organic multiple farm substrate combinations: Set 1 comprising chicken manure (CM), dairy manure (DM), and waste corn silage (CS) and Set 2 comprising CM, DM, pig manure (PM), and CS. Inoculum adaptation steps were carried out using CM and CM+DM for Set 1 and Set 2, respectively. Over three consecutive operating cycles spanning 245 days with increasing organic loads, 4.3 and 2.8 g VS L-1 d-1 for Sets 1 and 2 during Cycles 1 to 5.1 and 4.6 g VS L-1 d-1for Sets 1 and 2 during Cycle 3, a closed-loop two-stage liquid-solid AD system was employed, with performance assessed via stability ratios of short-chain volatile fatty acids and alkalinity. Results demonstrate that mono-digestion of CM with adapted inoculum yielded the highest biogas production of 424 ± 4 L over 77 days, indicating superior performance by Set 1 during Phase I, whereas a similar performance was observed during Phase 2, where Sets 1 and 2 exhibited highest specific methane yields of 0.233 ± 0.028 and 0.262 ± 0.004 L g-1 VSfed, respectively, over 68 days. Analysis of heavy metal concentrations in digestates revealed a significant decrease compared to initial raw substrate concentrations, highlighting their role as nutrients for microbial growth. This study, the first of its kind, highlights the potential of low-temperature AD systems to manage diverse organic residues/byproducts and offers insights into effective performance monitoring without compromising system integrity.

Methane emissions of manure from dairy cows fed red clover- or corn silage-based diets supplemented with linseed oil

The objective of this study was to investigate the effects of forage source (red clover silage: RCS vs. corn silage: CS) and diet supplementation with linseed oil (LO) on CH₄ emissions of manure from dairy cows. For this purpose, 12 lactating cows were used in a 2 × 2 factorial arrangement of treatments. Cows were fed (ad libitum) RCS- or CS-based diets (forage:concentrate ratio 60:40; dry matter basis) without or with LO addition (4% dry matter). Feces and urine were collected from each cow and mixed with residual sludge obtained from a manure storage structure. Manure was incubated for 17 wk at 20°C under anaerobic conditions (O₂-free N₂) in 500-mL glass bottles. Methane emissions and changes in chemical composition of the manure were monitored during the entire incubation period. The total amount of feces and urine excreted by cows was not affected by dietary treatments and averaged 6.6 kg/d of volatile solids (VS). Compared with manure from cows fed RCS-based diets, maximum CH₄ production potential of manure from cows fed CS-based diets was 54% higher (182 vs. 118 L/kg of VS) throughout the incubation period. Maximum CH₄ production potential from manure also increased (by 17%) when cows were fed LO-supplemented diets compared with those fed nonsupplemented diets. Similar to maximum CH₄ production potential, VS degraded during incubation (i.e., VS loss) was higher from manure from cows fed CS-based diets versus cows fed RCS-based diets (30.6 vs. 22.5%), and increased (+3 percentage units, on average) with the addition of LO to the diets. Ammonia concentration in manure was higher when cows were fed CS-based diets compared with RCS-based diets, and declined with LO supplementation to CS and RCS diets. It is concluded that both dietary forage source and fat supplementation affect maximum CH₄ production potential from manure and this should be taken into account when such dietary options are recommended to mitigate enteric CH₄ emissions from dairy cows.

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.

Microbial community composition and electricity generation in cattle manure slurry treatment using microbial fuel cells: effects of inoculum addition

Microbial fuel cell (MFC) is a sustainable technology to treat cattle manure slurry (CMS) for converting chemical energy to bioelectricity. In this work, two types of allochthonous inoculum including activated sludge (AS) and domestic sewage (DS) were added into the MFC systems to enhance anode biofilm formation and electricity generation. Results indicated that MFCs (AS + CMS) obtained the maximum electricity output with voltage approaching 577 ± 7 mV (~ 196 h), followed by MFCs (DS + CMS) (520 ± 21 mV, ~ 236 h) and then MFCs with autochthonous inoculum (429 ± 62 mV, ~ 263.5 h). Though the raw cattle manure slurry (RCMS) could facilitate electricity production in MFCs, the addition of allochthonous inoculum (AS/DS) significantly reduced the startup time and enhanced the output voltage. Moreover, the maximum power (1.259 ± 0.015 W/m²) and the highest COD removal (84.72 ± 0.48%) were obtained in MFCs (AS + CMS). With regard to microbial community, Illumina HiSeq of the 16S rRNA gene was employed in this work and the exoelectrogens (Geobacter and Shewanella) were identified as the dominant members on all anode biofilms in MFCs. For anode microbial diversity, the MFCs (AS + CMS) outperformed MFCs (DS + CMS) and MFCs (RCMS), allowing the occurrence of the fermentative (e.g., Bacteroides) and nitrogen fixation bacteria (e.g., Azoarcus and Sterolibacterium) which enabled the efficient degradation of the slurry. This study provided a feasible strategy to analyze the anode biofilm formation by adding allochthonous inoculum and some implications for quick startup of MFC reactors for CMS treatment.