Application of biochar and alkalis for recovery of sour anaerobic digesters

Commercial digesters handling complex waste and organic overloading often encounter unbalanced conditions or failures. With limited studies on the digester recovery from an industry-based waste stream, a complex and high-strength digestate containing up to 79 g COD l⁻¹ from acidified commercial digester was investigated for biochar and alkaline treatments. The addition of biochar and calcium hydroxide successfully decomposed excessive volatile fatty acid up to 18.9 ± 2.5 g l⁻¹ and resumed methane production. The maximum methane yield was obtained from the digester amended with biochar (373.4 ± 6.0 ml g COD⁻¹), followed by calcium hydroxide (350.1 ± 2.5 ml g COD⁻¹). Calcium hydroxide treatment showed a shorter lag phase than the biochar by 44%. Methane production could not be recovered by using sodium hydroxide or untreated digester. This study provides a strategic approach to justify the use of alkalis for restoring sour digesters from industry-based waste streams.