Nutrient contributions and biogas potential of co-digestion of feedstocks and dairy manure

Methane yields during anaerobic co-digestion of animal manure with other feedstocks: A meta-analysis

Anaerobic co-digestion of animal manure with other feedstocks (aka co-digestion) is increasingly being used to enhance methane yield and organic waste management. The benefits accruing from co-digestions compared to mono-digestions, however, vary greatly in the literature. The goal of this research was to use meta-analysis to critically compare methane yields between mono- and co-digestions and identify relevant factors (co-substrate type, substrate dose, carbon to nitrogen (C/N) ratio, volatile solids (VS), substrate pH, organic loading rate (OLR), and hydraulic retention time (HRT)) contributing to methane yield. Published studies (n = 64 representing 384 case-studies) with sufficient detail on methane yield were identified for the meta-analysis. Analysis indicated that co-digestion of animal manure with other feedstocks significantly increased methane yield (249 L kg^-1[VS]), compared with anaerobic mono-digestion of animal manure (171 L kg^-1[VS]). Similar methane yields increases (47-57 L kg^-1[VS]) were obtained from co-digestions in batch reactors of swine (238-287 L kg^-1[VS]), poultry (213-260 L kg^-1[VS]), and cattle manure (147-204 L kg^-1[VS]). In continuous digesters of cattle manure (175-299 L kg^-1[VS]) co-digestion had the greatest methane yield improvement of 124 L kg^-1[VS], swine manure (212-322 L kg^-1[VS]) co-digestion ranked second with 110 L kg^-1[VS], and poultry manure ranked third with 70 L kg^-1[VS]. Improved methane yield were obtained at optimum C/N ratio ranging from 26 to 34. The respective optimum OLR for co-digestion of swine, poultry, and cattle manure were 1.2, 1.4 and 3.4 kg VS m^-3 d^-1, while the recommended HRT was 30-40 d. Taken together, anaerobic co-digestion of animal manure with other feedstock significantly improved anaerobic digestion. Factors contributing to methane yields included: substrate-type and dose, VS, C/N, OLR, and HRT.

Pretreatment of used disposable nappies: Super absorbent polymer deswelling

Typical used disposable nappies usually consist of nonwoven fabrics, Super Absorbent Polymer (SAP), and organic material, namely fluffy pulp, urine and/or excreta. Currently, this waste stream is being disposed to landfills causing many environmental issues. An alternative management method could be the valorisation of the biodegradable material through anaerobic digestion, and the recycling of plastics and SAP. Pretreatment of nappies is mandatory to separate SAP and plastics from the organic material. The aim of this work was the development of a process to minimize SAP's volume, as this component can swell up to 1500 times its own mass by water absorbance, thus hindering any further biological process. CaCl₂, MgCl₂, and a range of CaCl₂/MgCl₂ combinations were tested against their deswelling efficiency on SAP, residual reagent concentration and reagent cost. The mixture of 20% CaCl₂ and 50% MgCl₂ (w/w) of SAP was concluded as the suitable combination of salts achieving a final SAP volume reduction of 92.7% with low residual cation concentrations and minimum cost. The physicochemical characterization of nappies' hydrolysate that took place to estimate its adequacy as substrate for anaerobic digestion resulted to a COD:N ratio within the acceptable range for a subsequent anaerobic digestion processing.

A Review on the Fate of Nutrients and Enhancement of Energy Recovery from Rice Straw through Anaerobic Digestion

Open field burning and tilling the rice straw (RS) back into the fields causes environmental threats by contributing to the increased greenhouse gas emissions. Energy and nutrient recovery from RS through anaerobic digestion (AD) is an effective solution for its utilization. Although RS has good methane potential, its characteristics make it a difficult substrate for AD. This paper reviews the characteristics of RS, mass balance, and distribution of nutrients into liquid and solid digestate in the AD. The present review also discusses the effect of temperature, co-digestion, mixing, inoculum, organic loading rate, recycling liquid digestate, the addition of trace elements, and their bioavailability on the enhancement of biogas/methane yield in the AD of RS. In addition, the digestion of RS at various scales is also covered in the review.

Biogas production from the liquid waste of distilled gin production: Optimization of UASB reactor performance with increasing organic loading rate for co-digestion with swine wastewater

This study is the first test that proves high rate anaerobic digestion as an efficient technological process for the treatment of gin spent wash. The gin spent wash was co-digested in UASB reactors with swine wastewater, which provided nutrients and alkalinity. The process was optimized by increasing the proportion of gin spent wash in the feed, and thus the organic loading rate (OLR) up to reactor failure. Stable high- efficiency operation was reached at an OLR as high as 28.5 kg COD m^-3 d^-1, yielding 8.4 m³ CH₄ m^-3 d^-1 and attaining a COD removal of 97.0%. At an organic loading rate of 32.0 kg COD m^-3 d^-1, the process became unstable and the reactor underwent over-acidification that drastically lowered the pH and suppressed methanogenesis. The failure of the reactor was caused by a combination of an organic overloading and alkalinity deficit that uncoupled acidogenesis and methanogenesis.

The auto fluorescence characteristics, specific activity, and microbial community structure in batch tests of mono-chicken manure digestion

Batch tests inoculated with granular and suspended sludge of mono chicken manure (CM) digestion were conducted. Kinetic analysis showed a maximum bio-CH₄ generation (6 mL/gVS/d) at an optimal TS of 10-12%. At a TS of 25%, serious inhibition was found for granular sludge and even greater inhibition for the suspended sludge caused by free ammonia. The auto fluorescence of Excitation-mission matrix with parallel factor analysis (PARAFAC) showed that the dissolved organic matter (DOM) varied between the form C1, C2, C3 and C4. The split component of the SMP-like C2 and protein-like C4 significantly related to the bio-methane production in time series. The canonical correlation analysis (CCA) indicated that ammonia, pH, and TS influenced the PARAFAC component significantly. The aceticlastic methanogens of the genus Methanosaeta and acetogens of the genus Syntrophobacter predominated in the CM sludge. The methanogens and acetogens formed a metabolic cooperation, making the process a stable methane produced activity.

Cow manure as a lignocellulosic substrate for fungal cellulase expression and bioethanol production

Conversion of various lignocellulosic materials into bioethanol is growing in demand but greatly depends on feedstock availability. Dairy cow manure is an agricultural waste widely distributed worldwide. This study investigated the induction of cellulases by cow manure and the conversion of cow manure materials into lignocellulosic ethanol. Alkaline NaOH pretreatment improved the accessibility of cow manure lignocellulose to enzymes followed by enzymatic hydrolysis using Penicillium oxalicum cellulases. The ethanol yields from pretreated cow manure and anaerobically digested cow manure were 0.19 and 0.13 g/g-raw biomass, respectively, using recombinant Saccharomyces cerevisiae strain LF1 designed for lignocellulosic ethanol production through simultaneous saccharification and fermentation. Fed-batch supplementation with cellulolytic enzymes and substrates after initial enzymatic hydrolysis also contributed to ethanol production up to 25.65 g/L. These results demonstrate that cow manure is a potential feedstock for inducing fungal cellulase expression and converting lignocellulose into bioethanol.