Equation Chapter 1 Section 1 Techno-Economic Analysis for the Selection of Cost-Effective Treatment for Algae Removal in Drinking Water Treatment Plants

Abstract

In this study, the responses of Dissolved Air Flotation (DAF), sedimentation, and sand filtration treatment processes on feed water with varied algal concentrations were investigated, based on a technical–economic analysis using data collected from a drinking water treatment plant (DWTP) in Guangxi, China. Cost-effective drinking water treatment processes for water sources with varied algae concentrations were proposed. The results showed that DAF was able to achieve almost 95% removal efficiency, while sedimentation was only able to reach 90% under different Polyaluminum Chloride (PACl)/dry cell weight concentrations in the DWTP. When algae concentrations increase, switching from sedimentation to DAF reduces treatment costs as DAF is more efficient for algae removal, which extends the backwashing interval of sand filtration. The threshold of sedimentation/DAF switching also depends on the quality requirement of the treated water. The lower the algae concentration in the treated water, the earlier the switch should be made from sedimentation to DAF. For instance, when the effluent thresholds are 1.2 mg·L−1, 0.8 mg·L−1, or 0.4 mg·L−1, DAF should be adopted instead of sedimentation—at feed algae concentrations of 43.9 mg·L−1, 31.5 mg·L−1, and 17.3 mg·L−1, respectively, in the raw water. The results set a baseline for a cost-effective drinking water treatment strategy based on a techno-economic model, which can precisely control the coagulation dosage and backwash interval of sand filtration coupled with sedimentation/DAF switching in algae-laden raw water.