Arsenic Mitigation Approach in Soil by Some Indigenous Sources of Biochar Made at Low Pyrolysis Temperature

Abstract

Biochar is being reported now a-days to potentially reduce the bioavailability of arsenic (As). A pot culture and an in vitro incubation study was conducted to evaluate the efficacy of biochar produced from different sources (viz., cow dung, poultry manure and sewage sludge) at low temperature (250ºC) on the phytoavailability of As. An experimental setup containing two sets of treatments (As and no-As) were followed. Biochar was applied at the rate of 5t/ha to the soils that received As treatment at a rate of 1mg/L As (80% arsenite and 20% arsenate). After 45 days of growth of Kalmi (Ipomoea aquatica), plant and soil samples were analyzed. Biochar insignificantly increased plant growth.  Biochar was observed to be more effective in alleviating As accumulation in plant than the biomass. The incubation study was done for 0, 15, 30 and 45 days to diagnose the temporal sorption of water soluble As by biochars. All the biochar materials reduced As availability than their corresponding biomass materials. Measurement of different physical (e.g. surface area, morphology, elemental composition), chemical (CEC, nutrient content, As) and physicochemical (pH) properties of the biochar showed that through pyrolysis process nitrogen(N), sulfur (S), phosphorus (P) content and pH of the biomass decreased and on the other hand potassium (K), As content and CEC increased. Slow pyrolysis process and variation in biomass material influenced the properties and behavior of biochar. Among the biochars, sewage sludge biochar showed the maximum and cowdAsung showed the minimum sorption capacity for As. Due to the threat of As to health and environment, this topic requires more consideration.  Moreover, covering all the above issues, this study identifies research gaps in the use of biochar as an adsorbent for As and proposes potential areas for future application of biochar.