Chemically enhanced membrane process–towards a novel sewage treatment concept to potentially replace biological processes

Abstract: This study tested the potential of a chemically enhanced membrane process as a novel treatment system producing reusable effluent from domestic wastewater and potentially replacing biological treatment. The process involved chemical conditioning followed by a sequence of ultrafiltration and nanofiltration. Polyaluminum chloride (PACs) was selected as the optimum chemical reducing chemical oxygen demand (COD) in the supernatant to 80–100 mg/L, below the soluble COD level of 170 mg/L in domestic wastewater. Particle size distribution (PSD) analysis indicated that chemical conditioning removed 40–45% of the soluble COD fraction below 2 nm and modified the size distribution of residual COD below 450 nm, suitable for the following membrane treatment. Performance of the selected coagulant was also compared with FeCl₃. PSD results were also confirmed by batch experiments indicating that the proposed novel process was capable of generating a clear effluent with a COD of around 60 mg/L with micro/ultrafiltration and 35 mg/L with nanofiltration. The process offered the possibility of conserving more than 90% of the available energy in domestic wastewater, through both chemical conditioning/settling and entrapment by the membrane, which may be reused and/or recovered as part of sludge processing and disposal. The use of PACs was also observed to avoid bulky sludge generation associated with conventional chemical treatment.