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In this study, the coagulation process is evaluated in treatment of municipal wastewater on the basis of organic material (e.g. chemical oxygen demand, COD) and suspended solids (TSS) removal efficiency. Alum-coagulation was optimized on the samples (24 sampling campaigns) taken from 4 wastewater treatment plants and a pilot plant at the University laboratory (Naples, Italy) to meet the Italian water quality discharge limits. A series of jar test experiments was run at 100 rpm for 1 min, 30 rpm for 20 min and 30 min for settling. 150 mg/l and 450 mg/l doses of alum were applied at pH ranging from 4 to 10 and room temperature. An anionic polyelectrolyte was used for flocculation. Raw and coagulated wastewater samples were analyzed for their COD, TSS and aluminium (RA) concentrations. The jar test experiments provided evidence that coagulation process could not provide sufficient COD removal efficiency in the Cuma and the University pilot plant wastewater even at an alum dose of 450 mg/l whereas the treatment with coagulation process using 150 mg/l alum in Nola and S. Giovanni plants was sufficient to meet COD (<160 mg/l) and TSS (80 mg/l) limits. The highest COD removal (80%) was obtained at the range of 6.0–8.0 pH values in the Nola plant, whereas COD removal was lesser in the Marcianese wastewater although its initial COD value was in the same order with the Nola plant. COD removal of the university plant improved from 55 to 75–85% in parallel to TSS removal by pH increase (up to 8.0). The statistical analyses showed different correlation values/behaviour between COD and TSS removals in each plant due to wastewater origin, pH and applied alum dose. RA was found significantly related to pH of coagulation process. RA concentration increased at pH value <5.0. These obtained results should contribute to, in particular, further RA studies dealing with the RA *Corresponding author. Presented at the 9th Environmental Science and Technology Symposium, September 1–3, 2005, Rhodes, Greece. Organized by the Global NEST organization and prepared with the editorial help of the University of Aegean, Mytilene, Greece and the University of Salerno, Fisciano (SA), Italy. 0011-9164/07/$– See front matter © 2007 Elsevier B.V. All rights reserved

The jar test experiments were performed on five municipal wastewater (Cuma, C; Nola, N; COD removal (%) A B pH TSS removal (%) A B pH Fig. 3. COD and TSS removal by jar test using 150 (A) and 450 mg/l (B) of alum in the San Giovanni (SG) samples.