REDUCTION OF TRACE POLLUTANTS IN RECLAIMED WASTEWATER THROUGH SOLID AQUIFER TREATMENT

The use of rainwater, groundwater and treated wastewater is a solution for sustainable utilization of water resources, particularly in urban areas. However various contaminants remaining in these new water resources may pose risk on human being and ecology. Groundwater recharge with the above new water resources is a possible way to remedy the risks in addition to saving transportation cost and acquisition of public acceptance although groundwater recharge with reclaimed wastewater is legally prohibited in Japan. The possibility of alternate water resources should be sought for various usage of reclaimed wastewater, particularly through soil-aquifer treatment system. In this study, therefore, we performed a soil column experiment in consideration of soil aquifer treatment of treated wastewater. The column was packed with a surface soil and treated wastewater was fed into the column in a down-flow mode at a constant flow rate for 80 days. Water qualities of the influent and effluent were evaluated by instrumental analysis and three types of bioassay. As a result, heavy metals were sufficiently removed from the column influent. The removal efficiency of nonylphenol, which has low biodegradability, showed a slow decline, whereas, that of estrogens and estrogenic activity was stably high. Total phosphorus and phosphate-phosphorus were effectively removed. Beside this, dramatically reduction of the concentration of ammonium-nitrogen was observed and subsequent increase in the concentration of nitrate-nitrogen was observed, thus suggesting groundwater pollution by nitrite may be concerned. In the results from bioassay, obvious inhibition for algal growth was observed for the effluent, not for marine bacteria. The results of our study suggested the soil aquifer treatment for the treated wastewater was effective for removal of inorganic phosphorus, heavy metals and estrogens. Finally, the influent and the effluent of the soil columns were compared with the states of water quality of Japanese major rivers. The water quality items of BOD and TP in reclaimed wastewater evaluated as poorest were improved as several best river waters in Japan. Estrogenic activity evaluated also as poorest were improved as relatively better river waters. However, TN in the reclaimed wastewater evaluated as poorest was still worst in the river waters.