Pretreatment techniques for digestate derived from a single-stage biogas digester

Abstract

Food waste is one of the most common types of organic waste generated across the world, with an estimated amount of 1.05 billion tons, and managing it effectively continues to be a major environmental challenge. Anaerobic digestion (AD) has emerged as the most promising technology to turn waste into energy by converting organic waste into biogas and nutrient-rich digestate. The liquid fraction of the digestate has a high concentration of suspended, dissolved, and organic solids, which may restrict its efficiency and wider application. In the present study, the food waste digestate was obtained from a single-stage 1 m 3 biogas digester located at the Jaypee University of Information Technology, Solan, Himachal Pradesh campus. The efficacy of physical and chemical pretreatment methods with particular focus on coagulation-flocculation to improve the quality of digestate was evaluated. A comparative assessment of alum and ferric chloride for digestate clarification was performed based on treatment performance and cost-effectiveness. The study findings indicate that, at an optimum dose of 5000 mg/L, alum achieved the highest turbidity removal efficiency of approximately 93%, whereas ferric chloride achieved only 44% removal at an optimum dose of 1000 mg/L. Both coagulants achieved moderate volatile solids removal efficiencies of 37-39%. Alum was found to be more cost-effective due to its low cost (₹15/kg), improved clarity performance, and wider effective dosage range, even though ferric chloride required a lower treatment cost (₹55/m³). The implementation of proposed pretreatment techniques can be a sustainable and cost-effective strategy for lowering dependence on chemical-based fertilizers and supporting the circular economy.