Ozonation and BDOC removal: effect on water quality

Batch experiments indicate biological treatment improves overall water quality and reduces biological regrowth. Batch experiments were conducted to determine the effect of several ozone dosages and biological treatment on a surface water. Total organic carbon (TOC) concentration, chlorine demand, bacterial regrowth, and disinfection by‐product (DBP) formation were measured after ozonation and after subsequent biodegradation. TOC removal increased with ozone dosage, but the extent of removal from biodegradation alone leveled out after an ozone dose of 1 mg O 3 /mg TOC. Chlorine demand reduction was highly correlated with the TOC removal, and chlorine residuals were maintained significantly longer in ozonated and biologically treated water, compared with water treated with ozone alone. Biological organic carbon removal delayed bacterial regrowth in chlorinated water, and DBP formation was reduced for ozone doses at or below 3 mg O 3 /mg TOC. Although higher chlorine residuals were maintained in the biologically treated water, higher DBP concentrations were not produced, indicating that biological treatment reduced DBP precursor levels.