Effect of Pretreatment on Physico-Chemical Parameters of Matrix and Pollutant Removals in Subsurface Wastewater Infiltration System

Two pilot subsurface wastewater infiltration systems(SWISs) were filled with the same mixed matrix and operated in the intermittent feeding mode with hydraulic loading of 0.1 m~3/(m~2·d) for 140 d.One of SWISs was fed with wastewater which was previously settled(ST),and the other with the same wastewater but in addition treated with a coagulation process(CT).After 140 d of operation,in the upper layer of ST system the effective porosity decreased by 4.1%and the organic matter(OM) content increased by 246.4%,whereas only decreased by 0.7%and increased by 35.7%of CT system,respectively.During the study,clogging didn’t occur in CT system and occurred in ST system.Effluent chemical oxygen demand(COD),total phosphorus(TP) and ammonia nitrogen(NH~+ —N) concentrations in CT system were less than those in ST system.In ST system,effluent COD,TP,NH~+—N concentrations increased and suspended solid(SS) concentration decreased after clogging.The results indicated that the use of a prior coagulation treatment was a good alternative for improving the effluent quality and avoiding an anticipated clogging.