Improving production characteristics of methane and organic acid during anaerobic batch digestion of poultry manure by adding bentonite

Abstract: There were approximately 20 billion chickens in the world in 2010, with 23% of the chicken population found in China. In 2009, the rapid development of chicken farms in China resulted in the production of 126 million tons of poultry manure. If managed inappropriately, poultry manure can cause serious environmental problems by polluting water, air, and soil. Anaerobic digestion is a complex bioconversion process that can treat organic waste and generate biogas with a high methane content that can be used as renewable energy, hence reducing the consumption of fossil fuel and curtailing greenhouse gas emissions. Ca2+-betonite is an environmental friendly material and is widely used in compost, heavy metal removal, pollutant adsorption, etc. In order to investigate the effect of betonite addition on anaerobic digestion of poultry manure, an orthogonal experiment L8（23）was conducted to determine amount of poultry manure (organic loading rate (OLR)), amount of bentonite and inoculum concentration on characteristics of methane production and organic acid production during anaerobic batch digestion of poultry manure under mesophilic condition (35±1) ℃. The results showed that bentonite addition could significantly increase methane production per VS by 22.72% and 27.72% with 3.0% and 1.5% betonite addition (based on poultry manure total solids), respectively compared to the control group under low OLR condition. Methane production from poultry manure with 3.0% or 1.5% betonite addition had no significant (P>0.05) difference under low OLR condition. Specifically, methane production could be very significantly (P<0.05) increased by adding betonite under high OLR condition. Methane production was increased by 78.68% and 55.41% with 3.0% and 1.5% betonite addition, respectively, compared to the control group under high OLR condition. Methane production from poultry manure with 3.0% or 1.5% betonite addition had significant (P<0.05) difference under high OLR condition. In the treatment with 19.91 g VS (volatile solid) poultry manure, 3.0% bentonite addition and 20% inoculum concentration, the highest methane production was observed with methane production 301.92 mL/g, very significantly higher (P<0.05) than control group (87.8% more) and its variable cost was also the lowest with 2.43 Yuan per m3 methane among all treatments. Variable costs of methane production from anaerobic digestion of poultry manure with betonite were 0.40 to 1.68 Yuan per m3 lower than from anaerobic digestion of poultry manure only. Peak values of dissolved organic carbon (DOC) appeared five days earlier and were lower than the control group under low OLR condition. Variance of DOC, pH value and dissolved inorganic carbon (DIC) in control group was higher than treatment groups with betonite showed stability of poultry manure anaerobic digestion could be improved by bentonite addition through increasing consistent of DOC degradation. Interestingly, formic acid and propionic acid were not found during the whole anaerobic digestion process of poultry manure with betonite. Variance of acetate, lactate and n-butyrate of treatment groups with betonite were lower than the control group showing that betonite addition could enhance the stability of anaerobic digestion process of poultry manure. Organic loading rate was the key factor of anaerobic digestion of poultry manure with bentonite under low OLR condition. Amount of betonite was the key factor of poultry manure anaerobic digestion with bentonite under high OLR condition. Inoculum concentration and OLR had significant interaction on acetate concentration. Organic loading rate had significant effect on lactate concentration. No interactions of these three factors were found on lactate concentration.