Anaerobic co-digestion of swine manure with energy crop residues

Abstract

Anaerobic co-digestion involves the treatment of different substrates with the aim of improving the production of biogas and the stability of the process. In this research, co-digestion of swine manure (SM) and energy crop residues (ECRs) was studied. The mixtures evaluated contained SM combined with maize (Mz), rapeseed (Rs) or sunflower (Sf) residues. Batch and semi-continuous experiments were performed to determine methane (CH 4 ) yields and the behavior of reactors while co-digesting agricultural wastes. Three different proportions of ECRs were tested in batch experiments for co-digestion with SM: 25, 50, and 75% volatile solids (VS). On the basis of the results obtained from batch tests, a mixture with a 50% ECR content was selected for the second stage of the study. Mesophilic reactors with a 3 L working volume were used for semicontinuous experiments. The hydraulic retention time (HRT) was set at 30 days and the reactors were kept under these operational conditions over four HRTs. The addition of ECR to the co-digestion system resulted in a major increase in the amount of biogas produced daily. The highest biogas yield was obtained when co-digesting Rs (3.5 L/day), although no improvement was observed in specific gas production from the addition of the co-substrate.

Comparison of Reactor Configurations for Biogas Production from Rapeseed Straw

“…Kaparaju et al (2009) noted that the methane percentage was 59% when the reactor was fed with only wheat straw hydrolysate, but it increased to 62.3% to 66.6% during co-digestion with cow manure. Cuetos et al (2011) and Søndergaard et al (2015) also reported methane contents of 63% to 66% and 64% to 65%, respectively, in biogas produced by the co-digestion of crop residues and manure. The reason for this may be attributed to the composition of the substrates.…”

“…This could be due to the use of a higher temperature (53 °C) and a much smaller particle size for the substrate (0.1 mm to 0.4 mm) in the BMP assays by Søndergaard et al (2015). Cuetos et al (2011) reported a BMP yield of about 120 mL/gVS for rapeseed straw. The lower BMP yield could be because of a higher lignin content (16.6% TS) in the substrate, compared to the lignin content of 11.7% TS in this study.…”

“…This range of methane content was in agreement with the values reported by Nges and Björnsson (2012) (52% to 58%), Rincón et al (2012) (53%), and Kacprzak et al (2010) (53%), in which the carbohydrate-rich substrates were also used alone, without adding any manure as the co-digestion substrates in the CSTR systems. Some studies (Kaparaju et al 2009;Cuetos et al 2011;Søndergaard et al 2015) conducted in CSTR have shown that codigestion of the carbohydrate-rich biomass with materials such as agricultural residues and manures not only can improve the quantity, but also the quality of the biogas. Kaparaju et al (2009) noted that the methane percentage was 59% when the reactor was fed with only wheat straw hydrolysate, but it increased to 62.3% to 66.6% during co-digestion with cow manure.…”

“…In some literature (Cuetos et al 2011;Li et al 2014), co-digestion of agricultural residues with manure has been reported to greatly improve the anaerobic digestion of agricultural residues due to the various nutrients in manure. However in China, developing large-scale and intensive livestock farms is the main trend at present, resulting in a reduced total number of farms, although household-scale farms or small-scale farms still exist in some places.…”

Anaerobic co-digestion of sugar beet tops silage and dairy cow manure under thermophilic condition

“…Anaerobic co-digestion, which is the simultaneous treatment of two or more wastes in single reactor, offers several benefits which include balancing the nutrient content [2,3], providing buffer capacity [4,5] and producing high methane yields [1,6]. Different studies have indicated that co-digesting animal manure with energy crop residues is a promising way of improving biogas production [1,7].…”