Improving secondary sludge biodegradability using free nitrous acid treatment

This study presents a novel strategy based on free nitrous acid (FNA) treatment to improve the biodegradability of secondary sludge. Several experiments were conducted to demonstrate the biocidal effect of FNA on activated sludge. The viable fraction as well as the biological activity of the biomass decreased significantly after 8–48 h treatment with FNA. The biodegradability of the FNA treated sludge was compared to that of the same sludge without FNA treatment by aerobically digesting these sludges with a full-scale activated sludge for 14 and 6 days respectively. Ninety percent of the FNA treated biomass was consumed during the 14-day aerobic digestion compared to 41% achieved with the untreated biomass. During the 6-day aerobic digestion, 50% of the FNA-treated sludge was degraded. The results indicate that FNA treatment substantially increases sludge biodegradability.