Enhancing anaerobic digestion of poultry litter in field digestors by incorporating in-line pre-digestor assembly

Abstract

Anaerobic fermentation inside the digestor is the continuous process which results in the formation of useful biogas fuel. All feedstocks are not easily decomposable thereby necessitating the design of an “optional in-line pre-digestor assembly”. Initially a 2 m3 modified fixed dome ‘Deenbandhu’ type biogas plant was commissioned with cattle dung, bypassing the pre-digestor assembly. In a phased manner, cattle dung was substituted with poultry litter as feedstock. Gradually increasing the substitution @ of 10% per fortnight, complete substitution of cattle dung could be attained in 18 week time. Poultry droppings assorted with paddy husk from deep litter system of poultry housings were used as feedstock. As paddy husk were indecomposable inside the digestor, an in-line pre-digestor assembly was used to remove the unwanted paddy husk by water dissolution technique. Enzymatic hydrolysis initiated in the pre-digestion tank in the 24 hours residence time improved the digestibility of the feedstock for generating biogas. The process of cattle dung substitution with poultry litter was complete in 18 weeks duration. Daily gas production was recorded with the help of wet type gas flow meter. The gas produced was continuously used for domestic cooking. The total solid (TS) content of the poultry litter based feedstock slurry was maintained at around the same TS (9 - 10%) as that of cattle dung (dung to water at 1:1 ratio) slurry. With 100% use of poultry droppings at 10.3 % TS, average gas production level was 208.5 lit per kg of TS.

Keywords

• Food waste
• septage
• anaerobic
• co-digestion
• energy
• biogas
• methane