Performance and mechanisms of greywater treatment in a bio-enhanced granular-activated carbon dynamic biofilm reactor

The potential of source-diverted graywater reuse mainly relies on the efficiency and cost of graywater treatment technology. Oxygen (O2) supply and utilization rate directly determine the energy consumption and pollutants removal rate in the biological graywater treatment. This study developed a gravity flow self-supplying O2 and easy-to-maintain bio-enhanced granular-activated carbon dynamic biofilm reactor (BhGAC-DBfR) for on-site graywater treatment. Results showed that increasing of saturated/unsaturated ratio led to the continuous growth of biomass on GAC surface. Division of saturated and unsaturated zones favors the formation of aerobic-anoxic-anaerobic biofilm in the reactor. A saturated/unsaturated ratio of 1:1.1 achieved the maximum removal rate of chemical oxygen demand (COD), linear alkylbenzene sulfonates (LAS), ammonia nitrogen, and total nitrogen at 98.3%, 99.4%, 99.8%, and 83.5%, respectively. Key is that adsorption and biodegradation play important and distinct roles in the quick uptake and continuous removal of both organics and N in the system. The related genus and enzymes functional for LAS mineralization, deamination of organic N, ammonium oxidation, and nitrate respiration enabled the efficient and simultaneous removal of organics and N in the BhGAC-DBfR. This study offers a promising engineering alternative technology with great potential to achieve efficient and low-energy-input graywater treatment.