Biological activated carbon treatment of a highly saline ro concentrate from municipal wastewater reclamation

Reverse osmosis (RO) concentrate (ROC) streams generated from RO-based municipal wastewater reclamation processes contain high concentrations of organic compounds and nutrients (N & P). The waste streams pose potential environmental and health risks on their disposal to confined water environments such as bays, and hence limit the sustainability of wastewater recycling practice. The present work was to evaluate the effectiveness of potentially low-cost biological activated carbon (BAC) treatment in removing organic and nutrient content from a highly saline municipal wastewater ROC (TDS ~16,000 mg/L, EC ~23 mS/cm) at lab scale. The effect of pretreatment options including oxidation (UV/H2O2) and chemical coagulation (FeCl3) was also examined for improving the treatment efficacy. Over its stable operation for 80 days at the empty bed contact time (EBCT) of 60 min, the BAC treatment gave 36%, 72% and 8% reduction in dissolved organic carbon (DOC), total nitrogen (TN) and total phosphorus (TP), respectively. The oxidation pretreatment resulted in improved treatment efficiency with 58% DOC and 15% TP removed from the ROC, whereas the coagulation led to 60% and 97% reduction in these parameters, respectively. However, the two pretreatments led to some decrease in TN removal (66% for oxidation and 22% for coagulation), although the reduction in ammonia nitrogen by the BAC remained high under all conditions (>90%). The sequential treatment with coagulation, UV/H2O2 and BAC led to a further improvement in organic matter removal efficiency (67% DOC). This study demonstrated that BAC can be utilised as a robust and resilient treatment for reducing the risks associated with the ROC. Better understanding of the impact of process conditions on the halophilic nitrifying/denitrifying bacteria is required for further optimisation of the BAC treatment