Direct Membrane Filtration (DMF) of municipal wastewater – A study on the prevention and remediation of fouling

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Direct membrane filtration (DMF) has gained a lot of attention in recent years because of its potential to treat low-strength and low temperature wastewater, where biological based treatments are inefficient. However, fouling is a major concern which keeps this technique from being more widely used. The main aim of this study was to investigate membrane fouling, its mitigation approaches and the organic/nutrient retention during DMF of municipal wastewater by adjusting operational parameters and pretreating the sewage. In a laboratory-scale setup employing crossflow to mitigate fouling, both ultrafiltration and microfiltration membranes were utilized. Physicochemical pre-treatment of sewage with polyaluminum chloride and polyamide significantly inhibited membrane fouling and improved organics/nutrient retention. Subsequent experiments with physiochemically pre-treated sewage, using microfiltration and ultrafiltration separately, revealed that (i) an increase in crossflow velocity from 1 to 2 m s −1 improved filtration performance by reducing irreversible fouling, (ii) elevating transmembrane pressure from 0.18 to 0.4 bar increased both reversible and irreversible fouling, and (iii) periodic relaxation increased the extent of irreversible fouling, contributing to higher overall fouling in ultrafiltration. When employing DMF for sewage concentration, ultrafiltration demonstrated superior filtration performance and organics retention compared to microfiltration. Furthermore, through pre-precipitation and microsieving (100 μm) followed by DMF with ultrafiltration membranes, a remarkable removal efficiency of 92 % for chemical oxygen demand (COD), 98 % for total phosphorus (TP), and 100 % for total suspended solids (TSS) was achieved. By cleaning the fouled membranes using an alkaline cleaning solution (Ultrasil-10) at 50 °C, combined with a crossflow of 1 m s−1, the permeability was completely restored. Overall, this study demonstrates that by optimizing operational settings and cleaning conditions, a sustainable DMF process for wastewater treatment with controlled membrane fouling and improved resource recovery can potentially be developed for upscaling. Short abstractThis study investigated the effectiveness of direct membrane filtration for municipal wastewater treatment. It was found that physicochemical pre-treatment with polyaluminum chloride and polyamide significantly reduced membrane fouling and improved nutrient retention. Ultrafiltration membranes demonstrated superior performance and nutrient retention compared to microfiltration membranes. By optimizing operational parameters and cleaning conditions, a sustainable direct membrane filtration process with controlled fouling and improved resource recovery can be developed for wastewater treatment.