Treatment of Sewage Using Waste Materials as Media in Rock Filter System

This study investigated a natural, sustainable and cost-effective rock filter system for sewage treatment. Two rock filter systems with four compartments were constructed; first a conventional rock filter system containing gravel of different sizes as media in the four compartments while the other a hybrid system comprising of three types of media. First two compartments filled with waste materials (boiler slag and waste concrete), third compartment with gravel and the fourth/last compartment filled with combined three types of media; boiler slag, waste concrete and gravel. This compartment was planted with cattails and functions as a subsurface horizontal flow constructed wetland. Both filters were operated in parallel with same environmental conditions and filtration rate was 0.1 m/h. The overall efficiency as well as efficiencies of individual compartment were assessed. Water samples were collected from outlet of each compartment, and analyzed following standard methods. Overall, hybrid system showed better results; chemical oxygen demand COD (+15%), 5-day biochemical oxygen demand BOD5 (+4%), ammonia nitrogen AN (+4%), E-Coli (+16%). However, conventional system showed slightly better results for total suspended solids TSS (+1%) and turbidity (+8%) removal. Amongst the various media used, boiler slag showed the highest removal of COD (44%), BOD (36%), TSS (44%), AN (48%) and E-Coli (51%) while waste concrete also showed good removal efficiencies; COD (22%), BOD (17%), TSS (27%), AN (48%), E-Coli (51%). Both systems complied with local wastewater discharge standards. Waste materials can be used as media in rock filters providing multiple benefits of sustainable waste and water management.