The use of biochar in constructed wetlands for domestic wastewater treatment is gradually being acclaimed by environmentalist 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 COD, BOD, true colour, TSS and 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.

Biochar has gained attention in agricultural studies due to its ability to ameliorate soil conditions. However, due to its low nutrient content, positive effects on plant growth are generally only observed if combined with mineral fertilizers or manures. The study aimed to test the hypothesis that biochar used to treat domestic wastewater can become enriched with nutrients and subsequently serve as a better soil amendment. The impact of the application of biochar used as substrate in a filter for domestic wastewater treatment (TB) on the growth of  lettuce (Lactuca sativa var. crispa)  plant was evaluated. Its effect on plant growth was compared to pure biochar (BC) using bare soil as a control. The biochars were applied with and without fertilizer using 3 biochar application rates (10, 20 and 30 t/ha). Results showed that biochar does not become enriched after wastewater purification in the short run. Instead, there was a reduction in the mineral composition, available phosphorus and pH in TB compared to BC. Only the BC treatments were significantly different (p=0.001) from the control. However, higher biomass production at 30 t/ha was observed in BC (+322%) and TB (+142%), compared with the unfertilized control. There were no significant differences in biomass production between the biochar and control treatments for application rates below 30 t/ha. Fertilization significantly (p=0.024) improved biomass production with the BC30+F treatments demonstrating the highest performance (+315%) compared to the fertilized control.