Optimal design of a hybrid system composed of coagulation process and multi-stage filtration unit for on-site treatment of greywater in rural area

In the present study, a simple, low-cost and user-friendly hybrid system composed of coagulation chamber (chemical treatment) followed by multi-stage filtration unit (physical treatment) was used to treat greywater for reducing organic chemical compounds and turbidity to reach the required quality standards for irrigation water. First, the optimum coagulant concentration for greywater treatment was determined. Then, the hybrid system was used to investigate the removal efficiencies of chemical oxygen demand (COD) and turbidity of greywater in optimum coagulant dose for developing the filtration unit through 49 experiments in different configurations and thicknesses varying from one to four-layer. Multilayer nonlinear machine learning model was utilized to evaluate the performance of this hybrid system and adaptive heuristic search algorithm was used to achieve the optimal configuration of multilayer sand filter using optimization technique. Results show that coagulation followed by three stages filtration unit composed of 15 cm of medium sand, 15 cm of fine sand, and 30 cm of activated carbon had the best performance with the maximum reduction of COD (90.8%) and turbidity (98.9%). Also, electrical conductivity and pH of treated greywater have been in the normal range for irrigation use. Based on the optimization-simulation model and experimental results, coagulation process followed by a filtration unit consisting of 17 cm of fine sand, 9 cm of medium sand and 34 cm of activated carbon results in the maximum efficiency and can reduce the COD and turbidity of greywater by 90.12% and 99.03%, simultaneously.