Study of oxidation-reduction potential in activated sludge hydrolysis and acidification process

In order to use biodegradable organics, produced from excess activated sludge (EAS) hydrolysis and acidification, as carbon source for nitrogen and phosphorus removal, chemical pretreatment by adding NaOH was used in this study to enhance the hydrolysis efficiency of the EAS. Batch experiments were conducted at ambient temperature, the effect of sludge characteristics, initial pH, and MLSS on the SCOD and ORP was investigated. It was found that SCOD production was increased with the increasing of the pH, the optimal pH for the SCOD production is 11, SCOD concentration was reached 2322mg/L after 10h reaction when pH at 11. The sludge characteristic have an important effect on the efficiency of activated sludge hydrolysis and acidification, the sludge collected from A²/O process produced the highest SCOD (791mg/L) compared to the SBR, step-feeding (SF) and oxidation ditch (OD) process. SCOD concentration was increased with the MLSS concentration increasing, which was increased from 186mg/L to 935mg/L when the MLSS increased from 4000mg/L to 10000mg/L. Profiles of oxidation-reduction potential (ORP) values were monitored on-line, model covering the relationship between the change of ORP value and increase in SCOD was developed, and high relativity coefficient was achieved (R2>;0.85). This verified that the ORP monitoring technique is not only useful to investigate the solubilization rate but also suitable for the determination of optimal solubilization in EAS treatment.