Boosting low-temperature methane and lipid production from ozone pretreated sludge through integrated anaerobic...

With the escalating demand for renewable energy and the need to manage waste activated sludge (WAS), exploring integrated approaches for converting waste into resources becomes critical. In this work, ozone pretreatment was conducted to promote the methane yield of WAS at 25 °C, and the fermentative effluent was used as a substrate for microalgae, which could reduce the pollutants and produce lipids. It was found that optimal methane yield of 370.08 ± 2.50 mL/L was obtained with WAS after 0.4 g/g total solids (TS) ozone pretreatment, which was 9.5 % higher than the control group. Utilizing the fermentative effluent from this specific condition for cultivating the microalgae led to the maximum biomass concentration of 1.38 ± 0.13 g/L. The utilization rate of soluble chemical oxygen demand, ammonium nitrogen, and total phosphorus in the fermentative effluent reached 92.4 %, 99.3 % and 98.1 %, respectively. The group pretreated with 0.4 g O₃/g TS also achieved the highest lipid productivity of 67.16 ± 5.40 mg/L/d, with a 64.4 % increase compared to the control group. The saturated fatty acids occupied a high proportion, reflecting the excellent prospect of microalgae lipids for biodiesel production. This work underscores the synergy between ozone pretreatment, enhanced methane fermentation, and lipid accumulation in microalgae, providing significant insights for the reuse of WAS in cold regions.