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 2nm 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.