Biochar-microorganism interactions for organic pollutant remediation: Challenges and perspectives

Numerous harmful chemicals are introduced every year in the environment through anthropogenic and geological activities raising global concerns of their ecotoxicological effects and decontamination strategies. Biochar technology has been recognized as an important pillar for recycling of biomass, contributing to the carbon capture and bioenergy industries, and remediation of contaminated soil, sediments and water. This paper aims to critically review the application potential of biochar with a special focus on the synergistic and antagonistic effects on contaminant-degrading microorganisms in single and mixed-contaminated systems. Owing to the high specific surface area, porous structure, and compatible surface chemistry, biochar can support the proliferation and activity of contaminant-degrading microorganisms. A combination of biochar and microorganisms to remove a variety of contaminants has gained popularity in recent years alongside traditional chemical and physical remediation technologies. The microbial compatibility of biochar can be improved by optimizing the surface parameters so that toxic pollutant release is minimized, biofilm formation is encouraged, and microbial populations are enhanced. Biocompatible biochar thus shows potential in the bioremediation of organic contaminants by harboring microbial populations, releasing contaminant-degrading enzymes, and protecting beneficial microorganisms from immediate toxicity of surrounding contaminants. This review recommends that biochar-microorganism co-deployment holds a great potential for the removal of contaminants thereby reducing the risk of organic contaminants to human and environmental health.

Revamping highly weathered soils in the tropics with biochar application: What we know and what is needed

Fast weathering of parent materials and rapid mineralization of organic matter because of prevalent climatic conditions, and subsequent development of acidity and loss/exhaustion of nutrient elements due to intensive agricultural practices have resulted in the degradation of soil fertility and productivity in the vast tropical areas of the world. There is an urgent need for rejuvenation of weathered tropical soils to improve crop productivity and sustainability. For this purpose, biochar has been found to be more effective than other organic soil amendments due to biochar's stability in soil, and thus can extend the benefits over long duration. This review synthesizes information concerning the present status of biochar application in highly weathered tropical soils highlighting promising application strategies for improving resource use efficiency in terms of economic feasibility. In this respect, biochar has been found to improve crop productivity and soil quality consistently through liming and fertilization effects in low pH and infertile soils under low-input conditions typical of weathered tropical soils. This paper identifies several advance strategies that can maximize the effectiveness of biochar application in weathered tropical soils. However, strategies for the reduction of costs of biochar production and application to increase the material's use efficiency need future development. At the same time, policy decision by linking economic benefits with social and environmental issues is necessary for successful implementation of biochar technology in weathered tropical soils. This review recommends that advanced biochar strategies hold potential for sustaining soil quality and agricultural productivity in tropical soils.

Environmentally safe release of plant available potassium and micronutrients from organically amended rock mineral powder

The staggering production of rock dusts and quarry by-products of mining activities poses an immense environmental burden that warrants research for value-added recycling of these rock mineral powders (RMP). In this study, an incubation experiment was conducted to determine potassium (K) and micronutrients (Zn, Cu, Fe and Mn) release from a quarry RMP to support plant nutrition. Four different size fractions of the RMP were incubated with organic amendments (cow dung and legume straw) under controlled conditions for 90 days. Samples were collected at different intervals (7, 15, 30, 45, 60 and 90 days) for the analysis of available K and micronutrients in the mineral-OM mixtures and leachates. There was a significant (p <0.05) increase in pH of leachates from the mineral-OM mixtures. The K release was significantly higher from the finer size fraction of RMP. About 18.7% Zn added as RMP was released during the incubation period. Zn release increased from 4.7 to 23.2% as the particle size of RMP decreased. Similarly, Cu release from RMP increased from 2.9 to 21.6%, with a decrease in the particle size. Fe and Mn recovery from RMP recorded 11.2 and 6.6%, respectively. Combined application of OM and RMP showed significantly higher nutrient release than other treatments. This study indicates that effective blending of RMP with organic amendments could be a potential source of K and micronutrients in agriculture without posing a risk of toxic element contamination to the soil.

Repurposing distillation waste biomass and low-value mineral resources through biochar-mineral-complex for sustainable production of high-value medicinal plants and soil quality improvement

High cost of synthetic fertilizers and their hazardous effects catapult the exploration of alternative nutrient formulations and soil amendments. This study aimed to synthesize a novel biochar-mineral-complex (BMC), and evaluate its nutrient supplying and soil improvement performances. In a hydrothermal reaction, the BMC was prepared using a biochar derived from distillation waste of Lemongrass (Cymbopogon flexuosus) and farmyard manure, for the first time via fortification with low-grade rock phosphate and waste mica. The BMC showed improved physico-chemical properties and nutrient availability than the pristine biochar. When applied to a deeply weathered acidic soil, the BMC significantly (P < 0.05) improved the herbage and bioactive compound (sennoside) yields of a medicinal plant (senna; Cassia angustifolia Vahl.) compared to the pristine biochar, farmyard manure, vermicompost, and chemical fertilizers. The BMC also improved the soil quality by increasing nutrient and carbon contents, and microbial activities. Soil quality improvement facilitated greater nutrient uptake in senna plants under BMC compared to the pristine biochar, and conventional organic and chemical fertilizer treatments. This study thus encourages the development of BMC formulations not only to overcome the limitation of sole biochar application to soils, but also to phaseout chemical fertilizers in agriculture. Moreover, BMC could bestow resilience and sustainability to crop production via value-added recycling of waste biomass and low-grade mineral resources.

Valorization of Java citronella (Cymbopogon winterianus Jowitt) distillation waste as a potential source of phenolics/antioxidant: influence of extraction solvents

Solid residues obtained after essential oil extraction from Cymbopogon winterianus Jowitt (Java citronella) was explored as a potential source of phenolics/antioxidant. Both the non-distilled plant materials and their solid residues were extracted with Soxhlet extraction method using solvents of various polarity viz. petroleum ether, chloroform, ethyl acetate, acetone, ethanol, methanol, water and various combination of (50% and 75%) of methanol, ethanol, and acetone in water. Different antioxidant assays like 2,2-diphenyl-1- picrylhydrazyl (DPPH), 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS), superoxide anion (SO) radical scavenging assay, ferric-reducing antioxidant power (FRAP) and iron chelating ability along with total phenol (TPC) and flavonoid content (TFC) was measured to evaluate the extract. Compared to distilled materials, the non-distilled plant materials had significantly higher TPC/TFC content and also exhibited higher antioxidant activities. 50% aqueous methanol showed the highest extractive yield, whereas 75% aqueous methanol exhibited the highest TPC and TFC content. The 50% or 75% aqueous methanolic extract also exhibited the highest DPPH, ABTS and SO scavenging activity and ferric-reducing antioxidant power activity. However, ethyl acetate and 75% aqueous acetone extract of non-distilled and distilled plant materials, respectively showed the highest iron chelating activity. The half maximal effective concentration (IC₅₀ = µg/mL) for DPPH, ABTS, SO and metal chelating ability in non-distilled plant extract ranged from 64-387, 92-761, 285-870, and 164-924, respectively, and corresponding value of distilled materials ranged from 144-865, 239-792, 361-833 and 374-867, respectively. The EC₅₀ (µg/mL) for FRAP assay ranged from 118-840 and 151-952 for non-distilled and distilled materials, respectively. The findings of this study indicate the potential of these by-products as a natural antioxidants source.

Validation of a QuEChERS-based gas chromatographic method for analysis of pesticide residues in Cassia angustifolia (senna)

A simple multi-residue method based on modified QuEChERS (Quick, Easy, Cheap, Effective, Rugged and Safe) approach was established for the determination of 17 organochlorine (OC), 15 organophosphorous (OP) and 7 synthetic pyrethroid (SP) pesticides in an economically important medicinal plant of India, Senna (Cassia angustifolia), by gas chromatography coupled to electron capture and flame thermionic detectors (GC/ECD/FTD) and confirmation of residues was done on gas chromatograph coupled with mass spectrometry (GC-MS). The developed method was validated by testing the following parameters: linearity, limit of detection (LOD), limit of quantification (LOQ), matrix effect, accuracy-precision and measurement uncertainty; the validation study clearly demonstrated the suitability of the method for its intended application. All pesticides showed good linearity in the range 0.01-1.0 μg mL(-1) for OCs and OPs and 0.05-2.5 μg mL(-1) for SPs with correlation coefficients higher than 0.98. The method gave good recoveries for most of the pesticides (70-120%) with intra-day and inter-day precision < 20% in most of the cases. The limits of detection varied from 0.003 to 0.03 mg kg(-1), and the LOQs were determined as 0.01-0.049 mg kg(-1). The expanded uncertainties were <30%, which was distinctively less than a maximum default value of ±50%. The proposed method was successfully applied to determine pesticide residues in 12 commercial market samples obtained from different locations in India.