Technical and economical evaluation of hybrid ozonation in an activated carbon bed to reduce algae and organic materials from raw water entering to municipal drinking water treatment plant

Abstract

Introduction: Currently, growth of algae and algal bloom is one of the most important problems in water stored in dams at all climatic zones of the country. Then it resulted execration of metabolites and toxic substances by algae and the possibility of forming secondary by products of chlorination such as trihalomethane in drinking water and causing undesirable taste and odor in water and sometimes the defiance consumers .The aim of this study was to technical and economical evaluation of hybrid ozonation in an activated carbon bed to reduce algae and organic materials from raw water entering to the municipal drinking water treatment plant. Materials and methods: Sampling of raw water from municipal water treatment plant was conducted 4 times and each time the volume was as much as 60 liters. After carring the samples to the laboratory, they were injected to the ozonation columns. In the processes of O3 and activated carbon catalyzed ozonation (ACCO), O3 were injected with dose of 0.1-13.0 mg L−1 at contact times from 0.2 – 30.0 minutes. The experiments were carried out in four periods in a way that six replications per each dose were obtained till less than 5% variation between measurements were obtained. The mean and standard deviation were calculated for parameters obtained from input and output of the processes. Finally, Lack-of-fit test and Pearson correlation were conducted between removal efficiency of chlorophyll a and the other physical indicators for O3 and ACCO columns. Results: Results indicated that in ACCO, average removal efficiency of 90.5% for chlorophyll a was achieved at ozone dosage of 0.2 mg L−1 and increasing ozone dosing has increased the removal rate. The average residual concentration of chlorophyll a in the outlet of the O3 and ACCO columns was 9.7 and 4.7 µg L−1, respectively. O3 process exhibited an approximately 36% increase in DOC concentration at ozone dosage of 0.5 mg L−1, while ACCO resulted in 53.5% and 76.0% DOC removal at ozone dosages of 0.5 and 1.0 mg L−1, respectively (DOC residual <0.2 mg L−1). The color and turbidity elimination via ACCO process was about twice as much as achieved with ozonation. Pearson’s correlation showed good correlations between removal efficiency of chlorophyll a with removal efficiency of UV254 (P-vaLue = 0.006), but, for turbidity (P-vaLue = 0.010) and color (P-vaLue = 0.185) showed low correlation. Univariate analysis of the variance revealed that turbidity and UV254 are better surrogate to predict elimination of chlorophyll a in the both O3 and ACCO processes. Conclusion: The ACCO showed better performance than the O3 process to remove chlorophyll a, turbidity, color and UV254. This can be attributed to the promoter roles of AC in ozone transformation into the OH radicals. Turbidity and UV254 can be used as inexpensive, simple and reliable substitutes to determine eliminated of chlorophyll a through O3 and ACCO processes. Finally, ACCO may be a better alternative to ozonation and a promising and promoting process to remove algae from drinking water. Keywords: water treatment, Advanced oxidation processes (AOPs), Catalytic oxidation, Activated carbon + zone, OH radicals, used as inexpensive, simple and reliable substitutes to determine eliminated of chlorophyll a through O3 and ACCO processes. Finally, ACCO may be a better alternative to ozonation and a promising and promoting process to remove algae from drinking water.