An analysis of the chemical safety of secondary effluent for reuse purposes and the requirement for advanced treatment

This paper presents a study on the chemical safety of the secondary effluent for reuse purposes and the requirement of advanced treatment. Water quality analysis was conducted regarding conventional chemical items, hazardous metals, trace organics and endocrine disrupting chemicals (EDCs). Generally speaking, the turbidity, COD, BOD, TN and TP of the secondary effluent can meet the Chinese standards for urban miscellaneous water reuse but higher colour is a problem. Further removal of BOD and TP may still be required if the water is reused for landscape and environmental purposes especially relating to recreation. In addition, Hazardous metals, trace organics and endocrine disrupting chemicals (EDCs) are not the main problems for water reuse. At the same time, several tertiary treatment processes were evaluated. The coagulation–filtration process is effective process for further improvement of the conventional water quality items and removal of hazardous metals but less effective in dealing with dissolved organic matter. The ultrafiltration (UF) can achieve almost complete removal of turbid matter while its ability to remove dissolved substances is limited. The ozone–biofiltration is the most effective for colour and organic removal but it can hardly remove the residual hazardous metals. Therefore, the selection of suitable process for different water quality is important for water use.