Keywords: biogas, biomass, pretreatment, microorganism
Summary:The quest for renewable energy generation is fast increasing globally due to environmental degradation by fossil fuels. In this study, biogas generation from the anaerobic co-digestion of pineapple peel and poultry manure was evaluated using the computer controlled anaerobic reactor. Prior to digestion, the pineapple peel was pretreated using a strong acid (sulfuric acid) and low-cost alkali hydrogen peroxide. The physicochemical and structural parameters of the biomass were determined using standard method while the Fourier Transform Infra-red (FTIR) spectra were used to quantify the structural changes that took place after pretreatments. The community structure variation was monitored at the genus and phylum levels using the PowerSoil® DNA Isolation Kit with 16S ribosomal RNA (16S rRNA) while the microbial community structure was investigated using the illumina sequencer (MiSeq). Results showed that the application of alkaline H2O2 pretreatment brought about the removal of the lignin content of pineapple peel by 71.34% (from initial 17.8 to 5.1 % m.m-1), reduced hemicellulose by 61% (22.8 to 8.8 % m.m-1) but increased the cellulose content by 39% (from initial 26.6 to 43.3 % m.m-1). The alkaline pretreated pineapple peel was able to produce about 91% more LNbiogas.kg VSad-1 than the acidic pretreated biomass and 36% more than the two untreated biomass samples that were digested. The results of the microbial analyses showed efficient degradation of organic acids to produce methane. In all, the Archaea methanogen species (aceticlastic methanogens) utilize both acetate and hydrogen to produce methane and the dominance was exhibited by members of the genera Methanosaeta, Methanosarsina and Methanococcus. Prior to this research, alkaline pretreatment using mild alkali H2O2 remained grossly unexplored in the treatment of lignocelluloses for the purpose of enhanced biogas production whereas use of strong alkalis and acids such as NaOH, KOH, and H2SO4 for conventional biomass treatments are well studied. The results of an economic assessment of pretreatment also showed that investment into the use of H2O2 for pretreatment is economically feasible with high net thermal and electrical energy gain while that of acid pretreatment results in loses. Therefore, the use of mild alkaline pretreatment is hereby solicited in the biotechnological conversion of pineapple peels/wastes for biogas. This will be more beneficial for renewable and sustainable energy generation especially in major pineapple producing regions of the world.