Microbial-assisted soil chromium immobilization through zinc and iron-enriched rice husk biochar

Abstract

Soil chromium toxicity usually caused by the tannery effluent compromises the environment and causes serious health hazards. The microbial role in strengthening biochar for its soil chromium immobilization remains largely unknown. Hence, this study evaluated the effectiveness of zinc and iron-enriched rice husk biochar (ZnBC and FeBC) with microbial combinations to facilitate the chromium immobilization in sandy loam soil. We performed morphological and molecular characterization of fungal [Trichoderma harzianum (F1), Trichoderma viride (F2)] and bacterial [Pseudomonas fluorescence (B1), Bacillus subtilis (B2)] species before their application as soil ameliorants. There were twenty-five treatments having ZnBC and FeBC @ 1.5 and 3% inoculated with bacterial and fungal isolates parallel to wastewater in triplicates. The soil analyses were conducted in three intervals each after 20, 30, and 40 days. The combination of FeBC 3%+F2 reduced the soil DTPA-extractable chromium by 96.8% after 40 days of incubation (DAI) relative to wastewater. Similarly, 92.81% reduction in chromium concentration was achieved through ZnBC 3%+B1 after 40 DAI compared to wastewater. Under the respective treatments, soil Cr(VI) retention trend increased with time such as 40 > 30 > 20 DAI. Langmuir adsorption isotherm verified the highest chromium adsorption capacity (41.6 mg g−1) with FeBC 3% at 40 DAI. Likewise, principal component analysis (PCA) and heat map disclosed electrical conductivity-chromium positive, while cation exchange capacity-chromium and pH-organic matter negative correlations. PCA suggested the ZnBC-bacterial while FeBC-fungal combinations as effective Cr(VI) immobilizers with >70% data variance at 40 DAI. Overall, the study showed that microbes + ZnBC/FeBC resulted in low pH, high OM, and CEC, which ultimately played a role in maximum Cr(VI) adsorption from wastewater applied to the soil. The study also revealed the interrelation and alternations in soil dynamics with pollution control treatments. Based on primitive soil characteristics such as soil metal concentration, its acidity, and alkalinity, the selection criteria can be set for treatments application to regulate the soil properties. Additionally, FeBC with Trichoderma viride should be tested on the field scale to remediate the Cr(VI) toxicity.

Trichoderma asperellum L. Coupled the Effects of Biochar to Enhance the Growth and Physiology of Contrasting Maize Cultivars under Copper and Nickel Stresses

“…These enzymes are involved in the Calvin cycle and electron transport chain (ETC), and their degradation leads to damaged thylakoid membranes, chloroplast and stomatal conductance. Likewise, the chlorophyll contents (a and b) were significantly ( p ≤ 0.01) decreased with applied stresses, especially in T2 and T3 when compared with control; however, BC application can enhance plant chlorophyll contents and its growth rate through indirectly improving the soil physiochemical parameters including water availability to the plants and improving soil natural microbial biota [ 19 , 39 ] ( Figure 4 ). A study by Kumar [ 40 ] also supported such findings under Cr stress.…”

“…In our previous experiments, we observed that applied biochar with Trichoderma sp. enhanced the porosity and surface area of soil, which increased the sorption or binding of metals and improved the functioning and synthesis of secondary metabolites such as total protein and phenolics which might be attributed to the enhanced water-holding capacity (WHC) of soil ( Figure 4 and Table S1 ) [ 19 , 20 ]. Soliman [ 41 ] also reported that the application of T. harzianum to Cucurbita pepo plants significantly improved the photosynthetic pigments and metabolites under salinity stress.…”

“…can be enhanced with BC application as the latter not only provides energy to the Trichoderma sp. but also performs similar chelating mechanisms to remove HMs from soil [ 19 ]. Herliana [ 22 ] stated that the application of T. harzianum showed the higher adsorption of Pb in soil by intracellular metal immobilization and biosorption of metal ions to cell wall of fungi.…”

“…Similarly, the utilization of biochar is commonly believed to be an efficient amendment that can reduce the mobility and availability of these metals in polluted soil, hence reducing their accumulation in plants [ 17 , 18 ]. Bioremediation through the value addition processes such as biochar/engineered biochar are recent methods used to mitigate the harmful effects of lead (Pb) and chromium (Cr) toxicity in the soil [ 19 , 20 ]. The T. harzianum sp.…”

“…Recently, we investigated the potential of Trichoderma sp. with iron and zinc (Zn)-enriched biochars against soil Cr and Pb immobilization [ 19 ]; however, a detailed study was required to categorize the different fungal species on their HM removal efficiency and then select the most suitable fungal sp. to evaluate its effects with/or without biochar on different maize cultivars.…”