Purpose This study aimed to assess the impact of two biochars applied at the rate of 15 t ha −1 on physico-chemical parameters of an oxisol in Cameroon. Methods The biochars were made from slow pyrolysis (~ 300 °C, 4 h) of eucalyptus tree bark and corncobs and then incorporated into the top 15 cm of the soil with or without straw. The soil tillage mode was either flat plots or furrows and ridges. Soil porosity, bulk density, saturated hydraulic conductivity, available water content, pH, nitrogen, potassium, phosphorus, cation exchange capacity and electrical conductivity were analysed before biochar application, then 6 and 12 months after. Results None of the measured soil physical parameters were affected by the presence or type of biochar. The total porosity was lower during the second production period compared to the first, while available water content and van Genuchten parameters increased during the second production period. No significant difference was observed between soil nitrogen, phosphorus, potassium, cation exchange capacity and electrical conductivity of control and treated plots. Conclusion We recommend that straw be pyrolysed and the resulting biochar incorporated into soil instead of burying straw (as is actually done in furrow and ridges tillage mode).
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.
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