Effectiveness of biochar filters vegetated with Echinochloa pyramidalis in domestic wastewater treatment

Abstract

The use of biochar in constructed wetlands for domestic wastewater treatment is gradually being acclaimed by environmentalists due to its high specific surface area and porosity. In this study, the effectiveness of corn cob biochar (CCB) and rice husk biochar (RHB) in vertical flow constructed wetlands vegetated with Echinochloa pyramidalis was studied with sand as common reference material. The filters were fed with primarily treated domestic wastewater at a hydraulic loading rate of about 350 L/m2/day for 6 months. Water samples were collected monthly for physicochemical and bacteriological analysis and plant growth assessed every two weeks throughout the study. Biochar filters were highly performant in wastewater improvement with no significant differences between the biochar types. Both biochars were more efficient than sand in the removal of chemical oxygen demand (COD), biochemical oxygen demand (BOD), true colour, total suspended solids (TSS) and total dissolved solids (TDS). However, sand filters performed better in the reduction of nutrients. All wetlands showed positive plant growth though the plants did not significantly affect the performance of the different filters for most parameters. However, a better plant growth was observed in the CCB filters. The study shows that CCB and RHB can effectively replace sand as substrates in constructed wetlands for wastewater treatment. HIGHLIGHTS Valorisation of crop wastes through biochar production.; Biochar filters are less effective in the removal of nutrients compared to sand.; Significant organic matter removal in vegetated constructed wetlands.; Significant reduction of bacteriological parameters regardless of substrate type.; Biochar substrates promote the growth of Echinochloa pyramidalis.;

Keywords

• biochar
• constructed wetlands
• echinochloa pyramidalis
• filtration
• vertical flow
• wastewater treatment