Enhanced Anaerobic Digestion Of Chicken Manure By Bentonite Addition

Anaerobic digestion( AD) of livestock manure provides several benefits by producing renewable energy, improving fertilizer qualities and reducing odors and pathogens, which could achieve goals of both pollution control and energy recovery. Chicken manure(CM) is nitrogen rich substrate with low carbon-nitrogen(C/N) ratio, which could cause inhibition during AD process. Also, CM is easily biodegradable compared to other livestock wastes.Organic acids and ammonia nitrogen accumulation occurs more easily during AD process of CM. Thus, CM is unsuitable for AD.Calcium bentonite(bentonite) was selected as additive for its excellent adsorption and cation exchange properties. Batch experiments based on orthogonal design L8(23) were conducted to investigate the effects of bentonite dosage( wt.%, on a dry weight basis),manure dosage( g VS) and inoculum concentration( %, v/v) on biogas production, organic acids production, ammonia speciation, pH and electrical conductivity(EC) during CM degradation at the mesophilic temperature(35±1) ℃, optiminal dosage of bentonite was obtained as well. How bentonite enhanced AD of CM was also studied by using thermal-modified bentonite as additive. Characterstics of natural and thermal-modified bentonite, such as structures and element contents in micro-area were observed and analysed for further mechanism clarification. The main results were as follows.(1) Methane production was significantly raised with bentonite addition. Cumulative methane production per VS was increased significantly by 22.72% and 27.72% with 3.0% and1.5% betonite addition separately compared to the control group with low CM dosage( P<0.05). Methane production under low CM addition dosage with 3.0% and 1.5% betonite addition had no significant difference( P>0.05). Intrestingly, methane production could be very significantly increased by adding betonite under high CM dosage( P<0.01). Cumulative methane production per VS was increased by 78.68% and 55.41% separately with 3.0% and1.5% betonite addition compared to the control group with high CM dosage. Methane production under high CM dosage with 3.0% and 1.5% betonite addition had significant difference( P<0.01). Highest methane production was observed with 19.91 g VS of CM,3.0% bentonite addition and 20% inoculum concentration, whose cumulative methane per VS was 302 mL, very significantly higher than control group(87.8% more).(2) Bentonite addition could enhance the stability of carbon and nitrogen degration during AD of CM process. Total ammonia nitrogen and EC could be reduced very significantly with both 1.5% and 3.0% dosage of bentonite(P<0.01). The drastic variation of free ammonia concentration was avoided as well. Furthermore, stabilization of organic acids,dissolved organic carbon and dissolved inorganic carbon variation was also enhanced with bentonite addition.(3) Thermal-modify could improve performance of bentonite during AD of CM process.Cumulative methane production per VS from AD of CM with 300 ℃ thermal-modified bentonite addition was 291 mL, which was very significant higher(25.18%) than with natural bentonite(P<0.01). Thermal-modify could significantly improve the sorption capacity of total ammonia nitrogen and stabilization of free ammonia nitrogen. 300 ℃ was the best temperature for thermal-modify to enhance the stability of total ammonia nitrogen and pH variation during AD of CM.