Anaerobic codigestion of livestock manure and agro-industrial waste in a CSTR reactor: Operational aspects, digestate characteristics, and microbial community dynamics

Abstract

Anaerobic codigestion of animal manure and agro-industrial waste offers an efficient alternative to monodigestion, due to the synergy between different substrates. This study investigated the digestion of five types of waste: swine manure, cattle manure, poultry hatchery waste, bone and protein waste, and dissolved air flotation sludge. Biochemical Methane Potential tests and a codigestion trial in a CSTR reactor were conducted, with increases in organic loading rate (OLR). The genera Clostridium_sensu_stricto_1 and DTU014, belonging to the phylum Firmicutes, predominated in the codigestion. The archaeal community was dominated by Methanosaeta and Methanosarcina. Genes encoding enzymes related to acetoclastic methanogenesis were predicted to be more abundant in the initial phases, demonstrating that despite fluctuations in physicochemical parameters an adaptation process occurred. The results showed that in an OLR of 3.67 kg_VSadd m⁻³_reactor d⁻¹ exhibited the best performance, with a methane yield of 521 L_NCH4 kg_VSadd d⁻¹ and a methane productivity of 1.91 L_NCH4 L_reactor⁻¹ d⁻¹. Digestate analysis revealed an increase in nutrient concentration, particularly nitrogen, indicating its potential as a biofertilizer. This study confirms the feasibility of anaerobic codigestion for optimizing biogas production and utilizing waste with different characteristics, promoting a sustainable and circular economy approach for the agro-industrial and livestock waste management.