Quantification, characterization, and anaerobic digestion of sheep manure: The influence of diet and addition of crude glycerin

Abstract

The objective of this study was to evaluate the influence of roughage-to-concentrate ratio on quantification and characterization of sheep manure, and to verify whether the addition of crude glycerin improves the efficiency of the anaerobic digestion process. The characterization study was carried out with two treatments (diet 1 with 40% roughage and 60% concentrate and diet 2 with 60% roughage and 40% concentrate) and 12 replicates per treatment. Parameters evaluated were as follows: production of manure, total solids (TS), volatile solids (VS), most probable number (MPN) of total (TC) and thermotolerant coliforms (TTC), chemical oxygen demand (COD), and residue coefficient. The digestion test was performed in batch digesters that were loaded with sheep manure with the doses of crude glycerin: 0, 3, 6, 9, 12, and 15% in the substrate. The process efficiency was measured by the reduction of TS, VS, and COD as well as the production of biogas. No differences were observed for the production of TS and manure among the diets. The contents of VS, COD, and MPN of TC and TTC were greater in manure from animals fed with higher concentrate ratio. Multiple linear models were generated according to the reductions of VS, TS, COD and production and potential of biogas and methane production and hence, both the additions of concentrate in the diet and crude glycerin in the codigestion influenced, in a positive way, the removal organic load in digesters.

Anaerobic co-digestion of animal manure at different waste cooking oil concentrations

“…, respectively) ( Table 1 and Figure 2) were obtained by adding 52 and 64g waste cooking oil.kg manure -1 , respectively. These values are similar to the ones reported by ORRICO et al (2015) when studying co-digestion of swine manure and different levels of waste cooking oil inclusions. Those authors reported maximum yield of 263.6L biogas.kg VS added -1 when 6.08% oil were added, which justified recommending co-digestion.…”

“…The inclusion of waste cooking oil provided sources of more readily degradable carbon than dietary fibers present in the diet of those animals, while fibers could be more easily digested after medium acidification since hemicellulose is more soluble in acid conditions (NEVES et al, 2009;OGEDA & PETRI, 2010). It is believed the ideal waste cooking oil inclusion levels (Table 1), which maximized reductions, complemented the characteristics of the substrates by providing sources of more easily degradable carbon, which enabled favorable nutrient concentrations for the process as observed by ORRICO et al (2015) when working with swine manure co-digestion and different levels of oil addition that research reported increases in COD, and; consequently, in carbon similar to those in the present study. Conversely, when the levels of waste cooking oil inclusion were exceeded, the process was hampered with decreased reduction values of these constituents.…”

“…According to HUNTER LONG et al (2012), the use of lipid waste has been identified as a way to expand biogas yield by 30% or more, as this type of substrate improves the concentrations of degradable carbon in the characteristics of the waste. This behavior can be verified in a study carried out by ORRICO JUNIOR & ORRICO (2015) on cattle waste and addition of 15% crude glycerin with high lipid content. Those authors reported yields of up to 422.09L biogas.kg VS added -1 , a 53% increase in relation to not using glycerin.…”

“…The values reported were higher than those reported by researches using animal waste and residues with high lipid contents. SIMM et al (2017) assessed co-digestion of dairy cattle waste with crude glycerin and found mean values of 46.8%, while ORRICO et al (2015) assessed the joint digestion of swine manure and waste cooking oil and obtained mean reduction values of 38.5%.…”

“…These values; however, were lower than the ones observed for swine substrates since biogas yield may have been hampered by the high fiber content in the material, which is difficult for anaerobic microorganisms to break down. Adding a more easily degradable material, i.e., waste cooking oil, may have allowed more available sources of C for microbial metabolization to be added and; consequently, increased biogas yield (ORRICO JUNIOR & ORRICO, 2015).…”