Treatment of mixed (fresh and salt) wastewater

Hong Kong has the geographical advantage of being situated on the coast and therefore it is possible to use dual water supply systems (fresh + sea water systems in two separate distribution networks) for potable and non-potable uses. From the sea water supply system, about three quarters of the population in Hong Kong is supplied with salt water for toilet flushing. The seawater is extracted from the sea directly and pumped by pumping stations located near the shore and supplied to the households. The used toilet flushing water (saline wastewater) is discharged into the sewerage system which conducts the mixed (fresh + salt) wastewater into the STW (sewage treatment works). The salt concentration of the mixed wastewater is between 5,000 mg/l to 6,000 mg/l, about one-fifth of seawater salt concentration, in Hong Kong.