Performance comparison of sand and fine sawdust vermifilters in treating concentrated grey water for urban poor

摘要

A comparative investigation was conducted for 10 months with sand and fine sawdust vermifilters and a control unit to treat concentrated grey water generated from a poor urban household in Ouagadougou, Burkina Faso. Each of the filters was made up of cylindrical DN200-PVC pipes and filled with 10cm of gravel at the bottom. On top of the gravel layer, filter 1 (fully sand, F1) was completed with 40cm of sand and 10cm of fine sawdust, filter 2 (partially sand, F2) with 20cm of sand and 30cm of fine sawdust, respectively, and filter 3 (fully sawdust, F3) and 4 (control, F4) with 50cm of fine sawdust only. Two hundred Eudrilus eugeniae earthworms were inoculated in each of the vermifilters. The vermifiltration system was supplied with grey water four times per day at a hydraulic loading rate of 64L/m(2)/day on a batch basis. The removal efficiencies of biological oxygen demand, total chemical oxygen demand, and dissolved chemical oxygen demand (dCOD) by the vermifilters were 25-30% higher than the control, but little differences were observed in terms of total suspended solids and coliform removal efficiencies. Though there was no significant difference in the performance of the three vermifilters (p>0.05), except for dCOD removal efficiency, the lifespan of F2 and F3 was longer than that of F1. Therefore, fine sawdust can substitute sand as a filter medium in vermifilters.