Assisted Pretreatment Agents Enhancing Yield of Organic Degradation and Biogas Recovery

Anaerobic digestion is a well-known technology that is technologically simple, with low energy
demand and can be used to convert organic materials from many types of wastewater, solid wastes,
and biomass into methane. The effects of ultrasonic and ozonation pretreatments on organic
solubilization, anaerobic biodegradability, and biogas production were elucidated in this study. Two
pretreatment methods for batch anaerobic digestion for biogas recovery with the same material and
experimental conditions were the focus for comparison. Anaerobic digestion experiments were
conducted at ambient temperature with the solid retention time set to 25 days. The obtained results
indicated that the soluble chemical oxygen demand increased from 0.344 without pretreatment to
1.023 and 1.228 g/L with ultrasound and ozone pretreatments, respectively, whereas the yields of
biogas production in the 25 days increased by 32.3 and 52.9% via ultrasonic irradiation and ozonation
relative to the control case, respectively. The biodegradability of the organic compounds of the
samples for the cases of ultrasound, ozone pretreatments, and control achieved 55.9, 64.31, and
39.18%, respectively, in terms of chemical oxygen demand (COD) removal efficiencies. The
physicochemical characteristics of sludge flocs were investigated via scanning with particle sizes,
which were obviously affected by pretreatments of sonication and ozonation, resulting in finer
particles than in the control case. The results of this work showed that the soluble COD and ultimate
yield of biogas using ozone pretreatment were better than those of ultrasonic pretreatment and the
control.