Codigestão de resíduos de apara de grama resíduos de frutas e vegetais e esgoto sanitário: efeito do pré-tratamento e reutilização do digestato

Abstract

Maintenance activities for green areas, food commercialization centers and basic sanitation generate waste grass clippings (RAG), fruit and vegetable waste (RFV) and sanitary sewage (ES), respectively. Anaerobic digestion (AD) is an alternative for the treatment of these organic residues and it results in biogas, a renewable energy source. However, the monodigestion of these residues can result in process limitations due to the physical-chemical composition of each isolated substrate. The objective of this work was to evaluate the anaerobic codigestion of RAG, RFV and ES incorporating the pretreatment of the RAG and the recirculation of the digestate as strategies to improve the process. The RAGs were pretreated (RAGP) with NaOH solution in concentrations of 1%, 3% and 5% for 12 hours and the biochemical potential of methane (PBM) was evaluated from batch tests. The semi-continuous test took place in a reactor with an operating volume of 3 L, mesophilic temperature (37 ° C) and daily feeding. The reactor was operated for 221 days, divided into 4 strategies: (A) start; (B) co-management with fresh waste; (C) co-management with RAGP and (D) co-management with digestate recirculation. The PBM of RAG, RFV and ES was 273, 620 and 313 LNCH4kg SV-1. The PBM of the pre-treated RAG (RAGP) in 1%, 3% and 5% was 314, 309, 316 LNCH4kg SV-1, with an increase of 15%, 13% and 16% in relation to RAG, the best operational condition of the semicontinuous reactor was B (co-digestion with fresh residues) with productivity of 1,25 Lbiogas/Lreactor. Co-digestion with RAGP resulted in a lower productivity of 1,10 Lbiogas/Lreactorand instability (CV> 10%) in terms of biogas volume and pH. The co-digestion with recirculation of the digestate was 19% lower than the previous step, however there was an increase in the total alkalinity (TA) content from 2.700 to 3.267 mg CaCO3L-1, allowing the system to recover its stability. Therefore, the positive effect obtained by pretreatment in batch tests was not replicated in a semi-continuous regime, resulting in system instability, which was recovered with a digestate recirculation strategy.