Effect of ozonation on biodegradability enhancement and biomethanation potential of pretreatment process wastewaters from 2G ethanol production

Abstract

BACKGROUND The production of second‐generation (2G) ethanol from lignocellulosic biomass generates large quantities of high‐strength complex wastewaters from various stages of the process. An effective pretreatment is necessary in order to overcome the low biodegradability of these wastewaters for further biomethane recovery. The present study reports the effect of ozonation on the biodegradability enhancement and biomethanation potential of complex 2G ethanol pretreatment process wastewaters, from acid (H2SO4) and alkali (NaOH) pretreatment process. RESULTS Ozonation (9.33 g m−3) was performed for both acid and alkali pretreatment wastewaters at a flow rate of 10 L min−1 for 1 h. Ozonation of both wastewaters increased biodegradability index (BI) up to 36% along with minimal chemical oxygen demand (COD; 7 ± 3%), color (10 ± 4%), and toxicity (22.5 ± 7.5%) reduction. Biomethane potential tests were carried out for the control and ozonated wastewaters having BI > 0.4. The acid‐pretreatment wastewater indicated poor biomethanation potential due to high presence of sulfates (COD/SO4 ~ 3.0). However, ozonation of alkali‐pretreatment wastewater facilitated up to twofold enhancement in the cumulative methane volume, while the enhancement in the rate of methane production was found to be up to 47%. Fourier transform infrared spectroscopic analysis of control and ozonated wastewaters revealed the breakdown of complex organic molecules and aromatics to readily biodegradable intermediates. The kinetics of methane generation could be predicted by the modified Gompertz model. CONCLUSION The study demonstrated the efficacy of ozonation as an effective pretreatment option to facilitate biodegradability enhancement of 2G ethanol pretreatment process wastewaters. The enhancement in biodegradability was observed to enable subsequent biogas recovery via anaerobic digestion along with COD removal. © 2023 Society of Chemical Industry (SCI).