A circular strategy for biogas production from poultry litter, coupled with microalgae cultivation and co-fermentation with corn stover

Poultry manure is produced in huge and increasing amount worldwide generating considerable environmental concerns. We propose a simple scheme to return this material, which is considered as “waste” today, into the global nitrogen (N), phosphorus (P) and carbon cycles and gain renewable energy in the form of biogas. Water extraction of chicken manure (CM) under mild and inexpensive conditions removes a considerable part of soluble components and the residual solid fraction becomes suitable for anaerobic degradation (AD) to yield biogas, the renewable energy carrier, and the fermentation residue, which can replace artificial fertilizers in agricultural applications. The aqueous phase from the water extraction is a dark brown liquid, which can be used as growth medium for algae after suitable dilution. The supernatant of pre-treated CM is excellent growth medium for the alga-bacterial (AB) community, which accumulates the dissolved N, P, and C in their biomass. AB, as well as pure Chlorella vulgaris, can be employed as AD substrate thus closing the circular economy based re-utilization of chicken manure and the agricultural by-product corn stover. The technical feasibility of the individual bioprocessing steps are demonstrated in this study at small scale to establish the route for future development. Responses of the microbial communities to the various conditions and substrate compositions are demonstrated and analyzed at genus level using new generation whole metagenomic sequencing. This knowledge may lead to rationally designed AD community development for more efficient CM utilization and recycling in biorefinery schemes.