Effects of Different Parameters and Co-digestion Options on Anaerobic Digestion of Parboiled Rice Mill Wastewater: a Review

A growing paddy crop produces large quantities of parboiled rice mill wastewater (PRMWW), which contains several organic and inorganic compounds and nutrients (nitrogen and phosphate). Discharges of the rice industry's wastewater pose a substantial threat to aquatic bodies and the surrounding environment, so an eco-friendly treatment plan is necessary. Parboiling stands out among grain-processing methods due to its numerous nutritional and physical advantages. Fewer literatures have only mentioned about the severity of the organic rich liquid effluents generated after parboiling process. Generating renewable energy from anaerobic digestion (AD) is one of the most environmentally friendly technologies to address the growing energy demands. This study is intended to give a systematic and critical review of the parboiling process, solid and liquid fractions of wastes generated, and various treatment options, with special emphasis on scope of application of AD for treating PRMWW along with energy recovery. The study explains various glitches in the AD processes of PRMWW for biogas generation and also recommends co-digesting PBMWW with other carbonaceous organic substrates for improved digestibility, and to reduce the inhibitions caused by lack of alkalinity, acid accumulation, and pH imbalance. To this end, this literature review seeks to provide a broad overview of knowledge to laypeople, entrepreneurs, and researchers.