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An assessment of coagulation process efficiency as a pre-treatment for reusing filtration backwash in water treatment plants
DOI:
https://doi.org/10.24425/ace.2025.153331Abstract
The growing water deficit around the world contributes to the need to reduce water losses and implement a circular economy. This is the main reason for searching for additional water sources or limiting water losses. In the case of water supply companies, apart from water losses in the distribution system, the greatest amounts of water are used for filter backwashing. The returning of backwash to the drinking water system can be suitable method for recycling of 3-10% of water treated in water treatment plants (WTPs), but high levels of backwash pollution make pretreatment necessary prior to recirculation. Backwash from surface and infiltration water treatment plants is characterized by different level of pollution and types of contaminants, except for microorganisms, which are present in both backwash types. The aim of this study was to evaluate the effectiveness of coagulation as a method of pre-treating backwash before recirculation to the main water treatment system. Prehydrolized coagulant is characterized by a higher removal efficiency for all pollutants, which allows the use of smaller doses. Optimal doses were 5 mg/L and 7 mg/L for PAX XL3 and ALS coagulants respectively. Independent of doses and type of coagulants, coagulation and sedimentation processes did not provide enough efficiency of microorganism removal. The results of this study have found that it is necessary to include other processes, especially disinfection, for pre-treating backwash prior to recirculating it to the treatment system. On the other hand, the cost of backwash recirculation is higher than the cost of intake water.References
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