MICROBIAL AND COD REMOVAL IN A MUNICIPAL WASTEWATER TREATMENT PLANT USING COAGULATION FLOCCULATION PROCESS

ABSTRACT

This study was designed to improve the removal efficiency of COD, SS, and microorganism at the S. Giovanni a Teduccio municipal wastewater treatment plant, Naples, Italy. The plant consists of screen, sand grinder, oil removal, coagulation, flocculation and sedimentation units, hypochlorite disinfection, mechanical dewatering, and thermal sludge conditioning. A series of Jar-test was conducted on twelve samples taken after screen using FeSO₄ alone or together with Ca(OH)₂ at 100 rpm rapid mixing for 1 min, 30 rpm for slow mixing for 20 min and 30 min for settling. 150 mg L⁻¹ and 450 mg/L doses of FeSO₄ were used at a pH interval in between 6 and 9. The removals of COD, TSS, Escherichia coli and total coliforms were measured ranging from 40 to 70%, 70 to 90%, 96 to 99% and 97 to 99%, respectively when FeSO₄ was used alone at 150 mg L⁻¹ and 450 mg L⁻¹ doses and at pH 6, 7 and 8. Wastewater discharge standards could be safely obtained at 150 mg L⁻¹ dose of FeSO₄ with the use of 220 mg L⁻¹ Ca(OH)₂ at pH 8 in terms of COD and E. coli removals resulted in 65% and 98%, respectively, with less sludge production to be disposed. Additionally, none of influent and supernatant samples tested in this study was found to be acute toxic on 24 h-born Daphnia magna at 50% dilution.

Keywords:

• Microbial removal
• Municipal wastewater
• Coagulation–flocculation
• Ferrosulphate
• Calcium hydroxide
• Daphnia magna

ACKNOWLEDGMENTS

This work was partly supported by the Italian Ministry of Foreign Affairs (S. Meriç). The authors thank the authority of S. Giovanni a Tedduccio Domestic Wastewater Treatment Plant for their kind hosting and help.