Progress in the production of biogas from Virginia mallow after alkaline-heat pretreatment

Abstract

This study aimed to analyze the coupled effect of electromagnetic microwave radiation and sodium hydroxide on the structure of a lignocellulosic complex of Virginia mallow and to determine the susceptibility of the pretreated substrate to anaerobic degradation. Effects of substrate digestion with conventional and microwave heating were compared as well. NaOH dose increase from 0.02 g·gt.s−1. to 0.2 g·gt.s−1. caused biogas production to increase in both heating variants. In turn, NaOH dose increase to 0.4 g·gt.s−1. resulted in diminished biogas production in variants with both microwave and conventional heating, i.e. by 15.3% and 20.8%, respectively. The highest biogas production effectiveness was achieved during fermentation of the substrate conditioned using microwave radiation coupled with the addition of NaOH in a dose of 0.2 g·gt.s−1., and the result obtained was by 10% higher compared to the conventionally-heated sample and by 39.4% higher compared to the microwave-heated and chemically-untreated sample. The coupled use of microwave heating and alkaline treatment allowed achieving a higher volume of biogas produced. Methane content in gaseous bacterial metabolites ranged from 58 to 61%, irrespective of NaOH dose and heating method.