Ozonation for improved sludge reduction, cytotoxicity and estrogenicity control in anaerobic digestion

Anaerobic digestion (AD) is a common treatment for sludge reduction and stabilization. Simultaneously reductions in sludge chemical oxygen demand (COD), cytotoxicity, and estrogenicity are desired for safer handling and reuse. We investigated the impact, mechanism, and control strategy of ozonation (common sludge biodegradability method) on AD, methane production, and sludge cytotoxicity and estrogenicity modulations. Results revealed that ozone treatment could boost the methane production potential and rate by up to 36.5 and 69.2 %, respectively, but only after partial sludge digestion. Ozone modulated sludge cytotoxicity and estrogenicity, significantly improving this effect (maximum reductions of 28 and 23 %, respectively) by introducing anaerobically digested sludge to the ozonation module due to lowered volatile solids (VS) compared to raw sludge and less competition from the abundant biodegradable organics. Results support introducing ozone during AD for simultaneous COD reduction, and cytotoxicity and estrogenicity control.