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

N. Ferdousi
Department of Agriculture, First Capital University of Bangladesh, Chuadanga, Bangladesh.

S. M. Imamul Huq
Bangladesh–Australia Centre for Environmental Research, Department of Soil, Water and Environment, University of Dhaka, Dhaka-1000, Bangladesh.

Abstract/ Executive Summary:

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 cowdung 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.

Keywords: Phytoavailability, Biochar, Feedstock, Pyrolysis, Temperature

Location: Manikgonj Sadar Upazilain Manikganj district

Start Date:

End Date:

Program Area: Risk Management in Agriculture

Commodity: Soil Health

Objectives:

The objective of our study was to find out the differences in various characteristics of biochar (surface area, pore volume, pH, CEC, nutrient content etc.) resulting from the difference in biomass sources (i.e, cowdung, poultry manure, sewage sludge) and their impact on the phytoavailability of As in soil.

Methodology:

The different sources of biomass/feedstock materials (i.e., cowdung, poultry manure and sewage sludge) were collected locally for biochar preparation. The biomass samples were air dried and ground. Biochar was produced at low (+250ºC) temperature pyrolysis process. An earthen pot containing the biomass and covered with an earthen lid was heated on an open fire. During this process, air was not allowed to enter into the pot and the temperature of the pot was maintained. It took about 45 minutes to turn all the biomass into biochar.In this slow pyrolysis process, the total biomass gets converted into about 30% of water, 35% of syngas and 35% of char. Both biomass and biochar samples were screened through 5mm sieve for pot experiment and 0.25 mm sieve for various chemical and physicochemical analysis. Soil sample was collected from a depth of 0-15 cm by composite soil sampling method from Manikgonj Sadar Upazilain Manikganj district (23°51.884’N and 90°06.219’E), Bangladesh. It is a Young Brahmaputra Floodplain soil belonging to the Melandaha series. According to the USDA soil taxonomy, the soil is a typic endoaquepts belonging to the order Inceptisols. According to the FAO-UNESCO legend, it is Gleysol. The Soil was air dried, cleared off the debris and crushed to make the bigger clods smaller. The crushed soil samples were screened through 5mm sieve. The sieved samples were then mixed thoroughly for making a composite sample. Soil sample was used for pot experiment and incubation study. The texture, pH, CEC and N of the soil and biochar samples were determined using Marshall’s triangle by hydrometer method, glass electrode method, ammonium acetate extraction method and Kjeldahl’s method respectively. For the total elemental analysis of P, K and S; the soil and the biochar samples were digested with aqua regia. The total K and S was determined by flame photometer. The total P content was determined using spectrophotometer. The As content of the soil (both initial and after harvest and also of he incubated soil), biochar and plant samples were determined by ‘Hydride Generation Atomic Absorption Spectrophotometry (HGAAS)’. All the statistical analysis was done using Minitab (version 16 package). The surface area, total pore volume, mean pore diameter of biochar were measured by BET plot method by BELSORP mini-II. It is a compact, precision instrument for measuring surface area and pore size distribution by the volumetric gas adsorption technique. Surface morphology of biochar was measured by SEM (Scanning Electron Microscope) and elemental content (C and As) by EDX (Energy Dispersive X-ray Spectroscopy). Different sources of biochars were saturated with As solution (1 ppm) for 15 days. Then SEM-EDX was done for both As treated and As non-treated biochar samples. Kalmi plant (Ipomoea aquatica) was used as a study plant in pot culture experiment using 7 treatments including control arranged in a completely randomized design. Plastic pots without hole at the bottom were filled with 1kg soil per pot. According to the design setup, soil of each pot was mixed with different biochar samples at a rate of 5 t/ha i.e. 2gm/kg. The pots were kept at ambient condition for 15 days for the biochar to be stabilized when the seeds were sown (10 seeds per pot). After the germination, 7 seedlings were kept in each pot and allowed to grow. After three days of germination, Arsenic (80% arsenite + 20% arsenate) at a rate of 1mg per liter was applied every day at a rate of 100ml per day as irrigation water. The plants were irrigated with 100ml of irrigation water every day. But during the rainy days, no irrigation was done. The plants were uprooted after 45 days of growth. The plants were dried and processed. Soil samples from each pot was also collected after harvest and processed as described above. An in vitro incubation study was also conducted to see the sorption and release of As. For incubation, 500g sized plastic pots were filled with 450 g soil sample. Then the soils were incubated at field moisture condition for 0, 15, 30 and 45 days. The field moisture condition was maintained by visual observation. The experimental setup was similar to that of the pot culture experiment. After incubation, the soil from each of the pot was collected for further analysis.

Source of Information: International Journal of Plant & Soil Science; 32(9): 93-108, 2020

Article Link (Online Journal): DOI https://doi.org/10.9734/ijpss/2020/v32i930330

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

It could be concluded that among low temperature biochar materials, S_bc and P_bc showed positive impact in reducing As accumulation in plant. This study also suggested that, low pyrolysis temperature and the different source materials regulate the properties of biochar as well as the effects of biochar in remediating As contamination. However, more research is required in future to fully identify the As-biochar interaction in soil along with the behavior of biochar developed from slow pyrolysis condition and various feedstock materials to develop more reliable and sustainable biochar for application on an industrial scale.

Knowledge Management: Journal