Utilization of biochar coupled with coal combustion products for degraded soil amendment

Abstract

Nowadays, bottom ash and flue gas desulfurization (FGD) gypsum are by-products of the coal combustion process from coal-fired power plant. Bottom ash has been applied in many applications such as landfill, cement industry etc., and FGD gypsum is applied in cement and wallboard industry. Also, they can be used in agricultural activities for soil amendment but the amount of bottom ash and FGD used in this function is still low. Furthermore, biochar has long been used to improve soil fertility. The positive impacts of biochar amendment on soils are that it can increase soil capacity to adsorb plant nutrients, decrease soil bulk density, increase plant available water retention and so on.

In Thailand, some areas like Nan province have a problem of soil degradation from deforestation and excess use of chemical fertilizer. Therefore, this study was to evaluate the effects bottom ash and FGD of coal combustion coupled with biochar as a soil amendment on the qualities of soil such as pH, soil texture, soil bulk density, electrical conductivity (EC) and on plant growing. In this study, the concentration of biochar was ranged from 5-30% by weight, and the concentration of bottom ash and FGD were ranged from 5-25% by weight. For the parameters used to measure the properties of soil are pH, soil texture, soil bulk density and electrical conductivity (EC). Also, corn is selected to grow at Nan province, Thailand, in the real field and in the container from September to November 2018 and January to April 2019, respectively. The parameters used to measure for corn grow including corn height, chlorophyll, relative humidity (RH), conductivity (ECp), temperature of soil and corn yields. In addition, heavy metal such as mercury (Hg), arsenic (As), lead (Pb), cadmium (Cd) and chromium (Cr) is measured in the samples before corn growing, and after corn growing in 2 times. Soil, corn seed, combined shell and core of corn and combined root, stem and leaf of corn were sent to analyze heavy metal.

From the results show that the soil quality has been improved in that pH can increases in all ratios. The soil texture has changed in the better quality from clay to silty loam, loam and sandy loam. The bulk density of soil is reduced to have more space for air and water for all mixtures which are conducive to plant growth. Furthermore, biochar coupled with CCPs applied for soil amendment can help plant growth compared to the normal soil. It is better if used the biochar coupled with CCPs and fertilizer for growing a plant. Moreover, the concentrations of all metals in soil, bottom ash, FGD, biochar and fertilizer are below the minimum permissible limit of heavy metal for soil FAO/WHO. After corn growing from both cases, the concentrations of heavy metals in all soil samples are lower than the minimum permissible limit of heavy metal for soil (FAO/WHO), mercury (Hg) and cadmium (Cd) in soil are not detectable (<0.25 mg/kg). The concentration of heavy metals in seed of corn, heavy metals are not detectable (<0.25 mg/kg) as well. On the other hand, the concentration of heavy metals in combined of root + stem +leaf of corn and shell + core of corn, lead (Pb), arsenic (As) and chromium (Cr) are higher than the minimum permissible limit FAO/WHO standard for concentration of heavy metal in plant, but mercury (Hg) and cadmium (Cd) cannot detect (<0.25 mg/kg). From the results of this research, it is expected that biochar coupled with bottom ash and FGD can be applied to increase the quality of soil and products in agriculture for the future.