Substrate removal kinetics and performance assessment of recirculation sand filters for treating restaurant greywater

Treated wastewater reuse for agriculture is an effective solution to cope with water scarcity conditions in arid and semi-arid areas. The aim of this study was the performance evaluation of a bench scale recirculation sand filter (RSF) for organic matter and nutrients removal from restaurant greywater at the University of Kashan. The average percent removal of 96.9 %, 96.3 %, 98.3 %, 92.8 %, and 70 %, corresponding to five-day biological oxygen demand (BOD5), chemical oxygen demand (COD), turbidity, total nitrogen, and total phosphorous indicated satisfactory performance of the system for treatment of restaurant greywater with higher concentrations of pollutants compared to typical households greywater. Substrate removal kinetics of the system were assessed by measuring BOD5 and COD values of septic tank, recirculation tank, and filter bed effluents. First order and second order kinetic models were applied to obtain COD and BOD5 removal kinetic coefficients for the recirculation tank and the filter bed. Kinetic parameters of the recirculation tank were determined using regression analysis and the results showed that both models were appropriate to describe the substrate removal in the recirculation tank. The reaction rate constants of K=1.9 1/d and 0.4 1/d respectively for BOD5 and COD were obtained by the first order model, while the corresponding values for the second order model were K=0.004 L/mg.d and 0.0003 L/mg.d. For the filter bed, the first-order reaction rate constants K=1.3 1/d and 1.73 1/d were found for BOD5 and COD, respectively. The second order model was not well qualified for evaluation of the filter bed performance. The results of kinetic models can be used to predict the behavior or design of the recirculation sand filter in full scale applications.