High-rate activated sludge process as a pre-treatment alternative to direct filtration with microfiltration/ultrafiltration for municipal wastewater reclamation to produce cooling water

Industries use reclaimed water for their makeup water requirements of cooling towers to decrease their water footprints. Makeup water quality depends on the type of cooling tower design; however, total suspended solids (TSS), biological oxygen demand (BOD₅), fecal coliform, pH, total dissolved solids (TDS), some ions (sulphate, chloride, ammonium) and heavy metals (aluminum, silica, manganese, iron) are important parameters to prevent contamination, scaling, and corrosion. In the first part of this study, cooling water production from municipal wastewater was experimentally investigated, in the second part of this study cost of treatment alternatives was estimated. Six different treatment configurations (C1: microfiltration (MF)+nanofiltration (NF); C2: ultrafiltration (UF)+NF; C3: high-rate activated sludge (HRAS)+NF; C4: MF+reverse osmosis (RO); S5: UF+RO; C6: HRAS+RO) were analyzed. Thanks to the high treatment performances of NF and RO membranes, reclaimed water in each scenario met the suggested cooling water quality. The effluent of the HRAS process showed the worst effluent quality in terms of turbidity (42.1 ± 2.6 NTU of turbidity) compared to MF and UF direct filtration (turbidity of DMF permeates were below 5 NTU). However, since HRAS process is less costly than direct membrane filtration (DMF) via MF or UF membranes, the lowest treatment cost was achieved with the C3 (HRAS+NF) treatment configuration (0.52 €/m³ reclaimed water). This study demonstrates that the HRAS+NF configuration can produce water suitable for cooling tower makeup, highlighting its potential as a sustainable solution to reduce water footprints and promote water circularity in industries.