Biogenic stabilization and heavy metal immobilization during vermicomposting of vegetable waste with biochar amendment

Protaetia brevitarsis larvae produce frass that can be used as an additive to immobilize Cd and improve fertility in alkaline soils

Bioconversion of agricultural waste by Protaetia brevitarsis larvae (PBL) holds significant promise for producing high-quality frass organic amendments. However, the effects and mechanisms of PBL frass on Cd immobilization in an alkaline environment remain poorly understood. In this study, three types of frass, namely maize straw frass (MF), rice straw frass (RF), and sawdust frass (SF), were produced by feeding PBL. The Cd immobilization efficiencies of three frass in alkaline solutions and soils were investigated through batch sorption and incubation experiments, and spectroscopic techniques were employed to elucidate the sorption mechanisms of Cd onto different frass at the molecular level. The results showed that MF proved to be an efficient sorbent for Cd in alkaline solutions (176.67-227.27 mg g-1). X-ray absorption near-edge structure (XANES) spectroscopy indicated that Cd immobilization in frass is primarily attributed to the association with organic matter (OM-Cd, 78-90%). And MF had more oxygen-containing functional groups than the other frass. In weakly alkaline soils, MF application (0.5-1.5%) significantly decreased Cd bioavailability (5.65-18.48%) and concurrently improved soil nutrients (2.21-56.79%). Redundancy analysis (RDA) unveiled that pH, CEC, and available P were important factors controlling Cd fractions. Path analysis demonstrated that MF application affected Cd bioavailability directly and indirectly by influencing soil chemical properties and nutrients. In summary, MF, the product of PBL-mediated conversion maize straw, demonstrated promise as an effective organic amendment for Cd immobilization and fertility improvement in alkaline soils.

Bacterial dispersal enhances the elimination of active fecal coliforms during vermicomposting of fruit and vegetable wastes: The overlooked role of earthworm mucus

Earthworms play a pivotal role in the elimination of fecal coliforms during vermicomposting of fruit and vegetable waste (FVWs). However, the specific mechanisms underlying the action of earthworm mucus remain unclear. This study investigated the mechanisms of fecal coliform reduction related to earthworm mucus during FVWs vermicomposting by comparing treatments with and without earthworms. The results show that the secretion of earthworm mucus decreased by 13.93 % during the startup phase, but significantly (P < 0.001) increased by 57.80 % during the degradation phase. Compared to the control without earthworms, vermicomposting led to a significant (P < 0.05) 1.22 -fold increase in the population of active bacteria, with a strong positive correlation between mucus characteristics and dominant bacterial phyla. As the dominant fecal coliforms, Escherichia coli and Klebsiella pneumoniae significantly (P < 0.05) declined by 86.20 % and 93.38 %, respectively, in the vermi-reactor relative to the control. Bacterial dispersal limitation served as a key factor constraining the elimination of E. coli (r = 0.73, P < 0.01) and K. pneumoniae (r = 0.77, P < 0.001) during vermicomposting. This study suggests that earthworm mucus increases the active bacterial abundance and cooperation by weakening the bacterial dispersal limitation, thus intensifying competition and antagonism between fecal coliforms and other bacteria.

Enhanced multi-metals stabilization: Synergistic insights from hydroxyapatite and peroxide dosing strategies

Sediment contamination by heavy metals is a pressing environmental concern. While in situ metal stabilization techniques have shown promise, a great challenge remains in the simultaneous immobilization of multi-metals co-existing in contaminated sediments. This study aims to address this challenge by developing a practical method for stabilizing multi-metals by hydroxyapatite and calcium peroxide (HAP/CaO2) dosing strategies. Results showed that dosing 15.12 g of HAP/CaO2 at a ratio of 3:1 effectively transformed labile metals into stable fractions, reaching reaction kinetic equilibrium within one month with a pseudo-second-order kinetic (R2 > 0.98). The stable fractions of Nickel (Ni), Chromium (Cr), and lead (Pb) increased by approximately 16.9 %, 26.7 %, and 21.9 %, respectively, reducing heavy metal mobility and ensuring leachable concentrations complied with the stringent environmental Class I standard. Mechanistic analysis indicated that HAP played a crucial role in Pb stabilization, exhibiting a high rate of 0.0176 d-1, while Cr and Ni stabilization primarily occurred through the formation of hydroxide precipitates, as well as the slowly elevated pH (>8.5). Importantly, the proposed strategy poses a minimal environmental risk to benthic organisms exhibits almost negligible toxicity towards Vibrio fischeri and the Chironomus riparius, and saves about 71 % of costs compared to kaolinite. These advantages suggest the feasibility of HAP/CaO2 dosing strategies in multi-metal stabilization in contaminated sediments.

Synergistic effect of biochar amendment in milk processing industry sludge and cattle dung during the vermiremediation

The effective and sustainable management of fast growing and large quantities of industrial waste is a serious issue. The purpose of the present study was to assess the synergistic effect of biochar (BC) amended in milk processing industry sludge (MS) mixed with cattle dung (CD) in different ratios through vermiremediation. The MS₂₅ and MS₂₅BC₁₀ (25:75 + 10 % BC) showed the least mortality and greatest earthworm growth and development. The final product from all feed mixtures recorded a decrease in pH, total organic carbon and C/N ratio. Other parameters viz., electrical conductivity, total available phosphorus, total Kjeldahl nitrogen, total sodium, total potassium and ash content was observed to be increased after vermicomposting. Significantly lower heavy metal content was found in all biochar amended feed mixtures than in mixtures without biochar. The germination index of Trigonella foenum-graecum showed a value ranging from 89.14 to 131.46 % for mixtures without BC and 115.18-153.47 % for biochar amended mixtures.

Effect of biochar addition on copper and zinc passivation pathways mediated by humification and microbial community evolution during pig manure composting

The mobility and bioavailability of Cu and Zn are the main threats associated with the land application of pig manure (PM) compost products. This study investigated the impacts of biochar (BC) concentration on passivation of Cu and Zn associated with the compost maturity. The results indicated that 15% and 10% BC favoured the passivation of Cu and Zn, respectively. BC promoted passivation of Cu by accelerating HA production and optimized the abundance of Firmicutes. BC promoted the passivation of Zn by increasing the high temperature peak and the corresponding pH (8-8.5). A higher level (15% and 20%) of BC altered the dominant bacterial phylum from Firmicutes to Proteobacteria. 20% BC inhibited the passivation of Cu and Zn by reducing the highest temperature and lowering the alkalinity of substrate. These results offer new insights into understanding how the addition of BC could reduce the risk of hazardous products during PM composting.

Juxtaposing the quality of compost and vermicompost produced from organic wastes amended with cow dung

Composting is a propitious technology to change bio-degradable solid waste into organic fertilizers. Considering this, five types of organic waste viz., leaf litter (Tectona grandis), water hyacinth (Eichhornia crassipes), cauliflower waste (Brassica oleracea var. botrytis), coir pith, and mushroom spent waste were composted with and without the use of earthworm (Eisenia fetida). The reaction (pH) and electrical conductivity of compost and vermicompost ranged from 6.98 to 7.45 and 6.97 to 7.36, 0.11 to 0.21 dSm^-1, and 0.11 to 0.25 dSm^-1, respectively. The chemical oxygen demand both the compost and vermicompost ranged from 687 to 1170 mg l^-1 and 633-980 mg l^-1 respectively. Cation exchange capacity (CEC) ranged from, 75 to 121 (c mol (p+) kg^-1, and 80 to 127 (c mol (p+) kg^-1, respectively. The C:N of compost and vermicompost varied from 16:1 to 33:1 and 12:1 to 19:1, respectively. The organic carbon content was decreased (18.3-38.7%), while secondary and micronutrient contents increased over the initial concentration. The NH₄⁺ and NO₃^- content of compost and vermicompost ranged from 270 to 510 mg kg^-1 and 230-430 mg kg^-1, 560 to 105 mg kg^-1, and 690-1100 mg kg^-1, respectively. The nitrification index (NH₄⁺/NO₃^-) ranged from 0.3 to 0.9 in composts and 0.3 to 0.6 in vermicomposts. The dehydrogenase and urease activity varied from 685 to 1696 μg g^-1 hr^-1 and 938-2549 μg TPF g^-1 day^-1 respectively. The bacteria, fungi and actinomycetes population were 2-3, 0.3-0.7 and 3-8 times more in vermicompost over the corresponding compost. This study confirmed that compared to compost, vermicompost showed better nutrients and microbial properties.

Vermiremediation of allopathic pharmaceutical industry sludge amended with cattle dung employing Eisenia fetida

The present study aims to vermiremediate allopathic pharmaceutical industry sludge (AS) amended with cattle dung (CD), in different feed mixtures (AS:CD) i.e (AS₀) 0:100 [Positive control], (AS₂₅) 25:75, (AS₅₀) 50:50, (AS₇₅) 75:25 and (AS₁₀₀) 100:0 [Negative Control] for 180 days using earthworm Eisenia fetida. The earthworms could thrive and grow well up to the AS₇₅ feed mixture. In the final vermicompost, there were significant decreases in electrical conductivity (29.18-18.70%), total organic carbon (47.48-22.39%), total organic matter (47.47-22.36%), and C: N ratio (78.15-54.59%). While, significant increases in pH (9.06-16.47%), total Kjeldahl nitrogen (69.57-139.58%), total available phosphorus (30.30-81.56%), total potassium (8.92-22.22%), and total sodium (50.56-62.12%). The heavy metals like Cr (50-18.60%), Cd (100-75%), Pb (57.14-40%), and Ni (100-50%) were decreased, whereas Zn (8.37-53.77%), Fe (199.03-254.27%), and Cu (12.90-100%) increased significantly. The toxicity of the final vermicompost was shown to be lower in the Genotoxicity analysis, with values ranging between (76-42.33%). The germination index (GI) of Mung bean (Vigna radiata) showed a value ranging between 155.02 and 175.90%. Scanning electron microscopy (SEM) analysis showed irregularities with high porosity of texture in the final vermicompost than in initial mixtures. Fourier Transform-Infrared Spectroscopy (FT-IR) spectra of final vermicompost had low peak intensities than the initial samples. The AS₅₀ feed mixture was the most favorable for the growth and fecundity of Eisenia fetida, emphasizing the role of cattle dung in the vermicomposting process. Thus, it can be inferred that a cost-effective and eco-friendly method (vermicomposting) with the proper amendment of cattle dung and employing Eisenia fetida could transform allopathic sludge into a nutrient-rich, detoxified, stable, and mature vermicompost for agricultural purposes and further could serve as a stepping stone in the allopathic pharmaceutical industry sludge management strategies in the future.

Application of Rice Husk Biochar and Earthworm on Concentration and Speciation of Heavy Metals in Industrial Sludge Treatment

The aim of this study was to assess the total concentration and speciation variation of heavy metals (Pb, Cd, Cu and Zn) during composting and vermicomposting of industrial sludge with different addition rations of rice husk biochar. Results indicated that pH, EC, total phosphorus (TP) and total potassium (TK) were increased and total organic carbon (TOC) and total nitrogen (TN) were decreased during the composting of industrial sludge with biochar compared with the control (sludge without biochar). The addition of earthworm to the biochar-amended sludge further decreased pH and TOC but highly enhanced the EC, TN, TP and TK. Comparatively lower concentrations of total and DTPA-extractable heavy metals were observed in biochar-amended sludge treatments mixed with earthworm in comparison with the biochar-amended sludge treatments without earthworm or the control. Sequential extraction methods demonstrated that vermicomposting of sludge with biochar converted more metals bound with exchangeable, carbonate and organic matter into the residual fraction in comparison with those composting treatments of sludge with biochar. As a result, the combination of rice husk biochar and earthworm accelerated the passivation of heavy metals in industrial sludge during vermicomposting. Rice husk biochar and earthworm can play a positive role in sequestering the metals during the treatment of industrial sludge. This research proposed a potential method to dispose the heavy metals in industrial sludge to transform waste into resource utilization.

Impact of wine grape pomace on humification performance and microbial dynamics during pig manure composting

The polyphenol humification pathway is essential for soil-forming and compost maturing processes. This study explored the effects of adding different proportions of polyphenol-rich wine grape pomace (WGP) on humification performance and microbial dynamics during pig manure (PM) composting. The results demonstrated that WGP effectively prolonged the duration of the thermophilic period, and improved humification production and compost maturity by enhancing beneficial interactions among microorganisms. Moreover, adding 40% WGP was optimal for nitrogen conservation, and the corresponding germination index (GI) reached 95%. Excitation-emission matrix (EEM) fluorescence spectroscopy analysis suggested that optimizing the WGP content was conducive to the conversion of protein-like substances, which improved the humification of organic matter. In addition, structural equation modelling (SEM) demonstrated that polyphenol content and temperature were the key parameters affecting the humification products. The results showed that WGP holds great promise to improve composting progress and fertilizer quality for biowaste utilization.

Biochars modify the degradation pathways of dewatered sludge by regulating active microorganisms during gut digestion of earthworms

Biochar can accelerate the degradation and mineralization of organic matter during vermicomposting of sludge and the resulted vermicompost is termed as vermi-char containing active enzymes and microorganisms. However, the mechanisms by which biochars affect vermicomposting of the dewatered sludge during gut digestion of earthworms remain unclear. This study aimed to investigate the effects of biochar on the degradation pathways of organic matter and the involved active microorganisms in dewatered sludge during gut digestion of earthworms. The earthworms Eisenia fetida were fed on three sludge substrates; 1) sludge mixed with 5% corncob biochar, 2) sludge mixed 5% rice husk biochar, and 3) sludge without biochar. The results showed that dissolved organic carbon significantly decreased by 5.65%-21.81% after the 5-day gut digestion of earthworms (P < 0.05) and that biochar addition could accelerate the decomposition of aromatic protein-like substances. Contrarily, the nitrate in earthworms casting with biochars significantly increased by 47.32%-122.64% (P < 0.05) compared with the control. The numbers of active bacteria and eukaryotes in earthworm castings with biochars significantly enhanced by 1.34-1.45 times and 0.45-5.91 times, respectively, than the control (P < 0.05). Active Actinobacteria and Bacteroidetes dominated the castings with biochars significantly enriched by 76.18%-88.83% and 4.02%-18.59% (P < 0.05), respectively, compared to control. As for eukaryotes, the biochars amendment increased Cercozoa abundance by 114.23%-136.31% but decreased Annelida by 55.61%-75.88% in the castings. The partial least squares path model revealed that the biochars could change the content and structure of organic matter in earthworm castings during vermicomposting of sludge by affecting environmental factors, microbial abundance, and microbial community composition.

Performance evaluation of a novel two-stage biodegradation technique through management of toxic lignocellulosic terrestrial weeds

The present study investigates the biodegradation of two potentially toxic terrestrial weeds Parthenium hysterophorus and Lantana camara, implementing a novel two-stage biodegradation technique; Rotary drum composting followed by vermicomposting (RV). The RV approach was refined for a 7-day thermophilic degradation in an in-vessel rotary drum composter, followed by a 20-day mesophilic degradation utilizing Eisenia fetida and Eudrilus eugeniae vermi-monocultures. However, rotary drum composting (RDC) was performed for both the weeds (for 27 days), facilitating only initial thermophilic degradation to compare the efficacy of the RV technique. Lignocelluloses analysis revealed that cellulose degradation doubled during RV technique, indicating efficient biodegradation in reactors administered with E. fetida vermiculture compared to RDC (19.60 to 42.80% and 26.80 to 66.50% in P. hysterophorus and L. camara feedstocks). Further, these results also correlated with the X-Ray diffractograms of all trials showing the degradation of crystalline cellulose at 2θ: 20-50° for RV. Moreover, to ensure product safety, the analyzed total heavy metals content also unveiled the advantage of RV over RDC as validated by the accumulation of higher concentrations of zinc (45% and 33% in P. hysterophorus and L. camara feedstocks) and lead (55% and 45% in P. hysterophorus and L. camara feedstocks) in reactors with E. fetida. The material's seed germination index increased to 80% in the final product of all trials in the RV technique, indicating the diminishing of the phytotoxic nature. Subsequently, pot studies also indicated that the RV technique was coherent in managing noxious weeds.

Biochar can mitigate co-selection and control antibiotic resistant genes (ARGs) in compost and soil

Heavy metals (HMs) contamination raises the expression of antibiotic resistance (AR) in bacteria through co-selection. Biochar application in composting improves the effectiveness of composting and the quality of compost. This improvement includes the elimination and reduction of antibiotic resistant genes (ARGs). The use of biochar in contaminated soils reduces the bioaccessibility and bioavailability of the contaminants hence reducing the biological and environmental toxicity. This decrease in contaminant bioavailability reduces contaminants induced co-selection pressure. Conditions which favour reduction in HMs bioavailable fraction (BF) appear to favour reduction in ARGs in compost and soil. Biochar can prevent horizontal gene transfer (HGT) and can eliminate ARGs carried by mobile genetic elements (MGEs). This effect reduces maintenance and propagation of ARGs. Firmicutes, Proteobacteria, and Actinobacteria are the major bacteria phyla identified to be responsible for dissipation, maintenance, and propagation of ARGs. Biochar application rate at 2-10% is the best for the elimination of ARGs. This review provides insight into the usefulness of biochar in the prevention of co-selection and reduction of AR, including challenges of biochar application and future research prospects.

Dynamics of fungal species related to nitrogen transformation and their network patterns during cattle manure-corn straw with biochar composting

Fungi are reputed to play a significant role in the composting matrix as decomposers of recalcitrant organic materials like cellulose and lignin. However, information on the fungi communities' roles in nitrogen transformation under a compost-biochar mixture is scarce. This study investigated shifts in fungal species mediating N transformation and their network patterns in cattle manure-corn straw (CMCS) and CMCS plus biochar (CMCB) composting using high-throughput sequencing data. The results revealed that the addition of biochar altered fungal richness and diversity and significantly influenced their compositions during composting. Biochar also altered the compost fungal network patterns; CMCS had a more complex network with higher positive links than CMCB, suggesting stable niche overlap. The consistent agreement of multivariate analyses (redundancy, network, regression, Mantel and path analyses) indicated that Ciliophora_sp in CMCS and unclassified_norank_Pleosporales in CMCB were the key fungal species mediating total N transformation, whereas Scedosporium_prolificans in CMCS and unclassified_Microascaceae in CMCB were identified as major predictive indices determining NO₃^--N transformation. Also, Coprinopsis cinerea and Penicillium oxalicum were the predictive factors for NH₄⁺-N transformation in CMCS and CMCB during composting. These results indicated that the effects of biochar on N conversions in composting could be unraveled using multivariate analyses on fungi community evolution, network patterns, and metabolism.

Process optimization by combining in-vessel composting and vermicomposting of vegetable waste

The process parameters of in-vessel rotary drum composting (RDC) with vermicomposting (VC) were investigated for the conversion of vegetable waste into vermicompost. After 7-day initial thermophilic exposure (maximal 51.5 °C in 24 h), the partially degraded RDC waste was divided into R1 (no vermiculture), R2, R3, and R4 (with Eudrilus eugeniae; Eisenia fetida; and Perionyx excavates monocultures, respectively). R3 derived vermicompost displayed maximum optimal process parameters and desirable compost qualities. Against the constant 2.2% nitrogen content of R1, an increase from 1.4 to 4.15% was seen in R3, with a 52.5% reduction in total organic carbon (TOC). A clear testimony to the enhanced nutritional content and fitness of the novel combination of RDC thermophilic biodegradation and E. fetida based vermicomposting. In an environmentally compatible mode, the faster organic deconstruction in 27 days could substantially alter organic waste treatment in the immediate future.

Effect of pyrolysis conditions on environmentally persistent free radicals (EPFRs) in biochar from co-pyrolysis of urea and cellulose

Biochar derived from nitrogen-rich pyrolysis of biomass can be used as a soil conditioner, but it contains a large amount of environmental persistent free radicals (EPFRs). EPFRs are a newly identified environmentally harmful substance, and the detection and research on EPFRs in nitrogen-rich pyrolyzed char is lacking. Biochars prepared from cellulose-urea mixtures at different temperatures, residence times, and urea ratios were analyzed in this study. EPFRs in biochar prepared at 500 °C had the highest spin concentrations. Substituted aromatic compounds were the precursors to the EPFRs. The types of EPFRs in biochars shifted from oxygen-centered at 400 °C to carbon- and oxygen-centered in the 450-600 °C range due to a reduction in oxygen-containing functional groups. Residence time experiments showed that most EPFRs formed in the first 5 min of pyrolysis. C was the main element used for the formation of EPFRs, while N content was negatively correlated with the concentration of EPFRs. Pyrolysis temperature was the key factor determining the types of EPFRs produced, while proportion of urea only affected the concentrations of EPFRs and not type. The results of this study are of great significance for understanding the environmental behavior of common EPFRs in nitrogen-rich biochar.

Improving the efficiency of vermicomposting of polluted organic food wastes by adding biochar and mangrove fungi

Vermicomposting of food waste amended with biochar and cow dung was studied during a 90-day composting period. The improvement of the vermicomposting process by adding three mangrove fungal species as additional amendments were studied. The use of mangrove fungi Acrophialophora jodhpurensis as a bio-catalytic actor during vermicomposting proved to be beneficial in terms of final compost quality (available N, P and K) and the shortening of the composting period. All three fungal species, however, reached the neutral pH at the end of the composting period and appeared to be beneficial. Heavy metal (Cd, Ni, Pb, Zn, Cu and Cr) concentrations decreased throughout the composting process. Food waste can be treated using vermicomposting with biochar, cow dung and the mangrove fungi A. jodhpurensis. The final vermicomposting product is suitable for agricultural use.

Ultra-efficient catalytic degradation of malachite green dye wastewater by KMnO4-modified biochar (Mn/SRBC)

In this work, KMnO₄-modified biochar was prepared from spirulina residue as the research object. Herein, we report the synthesis, characterization, and catalytic degradation performance of KMnO₄-modified biochar, given that heterogeneous catalytic oxidation is an effective way to treat dye wastewater rapidly. The Mn/SRBC catalyst prepared by KMnO₄ modification was characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffractometry, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, nitrogen adsorption–desorption and laser Raman spectroscopy. In addition, we compared the results with that of the unmodified SRBC. The results showed that the Mn/SRBC catalyst prepared by KMnO₄ modification had a rich pore structure, which provided sufficient contact area for the catalytic reaction. In the presence of H₂O₂, the catalyst could be used to catalyze the oxidative degradation of malachite green in aqueous solution with ultra-high efficiency. In the experiment, the initial pH values of the reaction system had a significant influence on the reaction rate. The removal effect of biochar on the malachite green was poor in an alkaline environment. Within a specific range, the removal rate of malachite green was proportional to the concentration of H₂O₂ in the reaction system. The degradation rate of malachite green dye at 8000 mg L⁻¹ was about 99% in the presence of the catalyst over 5 mmol L⁻¹ hydrogen peroxide for 30 min. These results show the potential application of algae residue biochar and carbon-based composite catalysts for degrading and removing dye wastewater.

In this work, KMnO₄-modified biochar was prepared from spirulina residue as the research object.

Interactive effects of biochar and mussel shell activated concoctions on immobilization of nickel and their amelioration on the growth of rapeseed in contaminated aged soil

Mussel shell (MS) and biochar (BC) are commonly used for the remediation of metal contaminated soil. However, less research has been focused to examine the efficacy of their combinations to reduce metal toxicity in crop plants. This study was therefore conducted to investigate the effects of BC, MS and their activated concoctions on the soil properties, enzyme activities and nickel (Ni) immobilization in aged Ni contaminated soil. Moreover, the growth, photosynthetic pigments and anti-oxidative machnery of Brassica napus plants has also been investigated in order to determine amendments efficiency in reducing soil Ni toxicity for plants. The results showed that the application of Ni adversely affected soil health and trigged stress responses by inducing oxidative stress in B. napus. However, the incorporation of amendments reduced the bioavailability of Ni, and the concoctions of BC and MS showed promising results in the immobilization of Ni. Among various combinations of BC and MS, treatment with BC + MS (3:1) significantly reduced Ni uptake, decreased reactive oxygen species (ROS) and enhanced antioxidant defense of B. napus plants. Results showed that amendment's combinations stimulated the transcriptional levels of ROS scavenging enzymes and suppressed the expression level of Ni transporters. The morphological and physical characterization techniques (i.e. SEM, BET, EDS, FTIR and X-ray diffraction analyses) showed that amendment's combinations had relatively higher Ni adsorption capacity, indicating that BC and MS concoctions are efficient immobilizing agents for minimizing Ni availability, preventing oxidative toxicity and promoting growth and biomass production in rapeseed plants under metal stress conditions.

Feasibility of vermicomposting for spent drilling fluid from a nature-gas industry employing earthworms Eisenia fetida

This study investigated the vermicomposting of spent drilling fluid (SDF) from the nature-gas industry mixed with cow dung in 0% (T1), 20% (T2), 30% (T3), 40% (T4), 50% (T5), and 60% (T6) ratio employing Eisenia fetida under a 6 weeks trial. Eisenia. fetida showed better growth and reproduction performances in the first three vermireactors (T1-T3), and the mortality was higher in the vermireactors that contained more spent drilling fluid (≥40%). Vermicomposting results in a decrease in total organic carbon, C/N ratio, and an increase in EC, total nitrogen, total phosphorous, total potassium compared to their initial values. The RadViz and VizRank showed that vermicomposting results in a greater impact on the C/N ratio (15.24-35.48%) and EC (7.29-26.45%) compared to other parameters. Activities of urease and alkaline phosphatase during vermicomposting initially increased and then declined suggesting vermicompost maturity. Also, seed germination, mitotic index and chromosomal abnormality assays using cowpea signified that the vermicomposts T2 is suitable for agricultural use due to the lower phytotoxicity and cytotoxicity. The results indicated that SDF could be converted into good quality manure by vermicomposting if mixed up to 20% with cow dung.

Vermicomposting: A management tool to mitigate solid waste

Solid waste management is a serious ecological problem in Saudi Arabia due to rapid industrialization, population growth and urbanization. Recycling and sorting are in their infancy in Saudi Arabia and huge amounts of mixed household and industrial wastes are still dumped without any pre-treatment. Solid waste management techniques such as incineration, pyrolysis and gasification have high investment costs. Composting and vermicomposting of solid organic waste have been considered as an economically viable and sustainable waste management technologies. However, wastes often contain pollutants, such as heavy metals that are toxic to decomposer micro-organisms. Thus, heavy metals are a challenge for the successful biological treatments. Waste may also contain a mixture of organic pollutants that certain microbes, such as micro-algae are known to degrade. The present review paper focuses on understanding the role of vermicomposting as a management tool in mitigating solid organic wastes. It is noteworthy to mention that the microbes also play a pivotal role in the degradation process, wherein the enzymes secreted during the process aid in decomposition of complex molecules into simpler compounds. Also, the extracellular polymeric substance secreted by the earthworm under metal stress serves a source of nutrient for the bacteria to flourish. Henceforth the goal of discussion in present review shows the way forward in using vermicomposting as a novel approach in dealing with solid organic waste.

Metallothionein dependent-detoxification of heavy metals in the agricultural field soil of industrial area: Earthworm as field experimental model system

Earthworms are known to reclaim soil contamination and maintain soil health. In the present study, the concentration of DTPA extractable heavy metals, Cd, Cu, Cr, Pb, and Zn in vermicasts and tissues of the earthworms (anecic: Lampito mauritii; epigeic: Drawida sulcata) collected from the soils of four different industrial sites, Site-I (Sago industry), Site-II (Chemplast industry), Site-III (Dairy industry) and Site-IV (Dye industry) have been studied. The heavy metals in industrial soils recorded were 0.01-326.42 mg kg^-1 with higher Cu, Cr, and Zn contents while the vermicasts showed lower heavy metal loads with improved physicochemical properties and elevated humic substances. The higher humic substances dramatically decreased the heavy metals in the soil. The bioaccumulation factors of heavy metals (mg kg^-1) are in the order: Zn (54.50) > Cu (17.43) > Cr (4.54) > Pb (2.24) > Cd (2.12). The greatest amount of metallothionein protein (nmol g^-1) was recorded in earthworms from Site-IV (386.76) followed by Site-III (322.14), Site-II (245.82), and Site-I (232.21). Drawida sulcata can produce a considerable amount of metallothionein protein than Lampito mauritii as the metallothionein production is dependent upon the presence of pollutants. The molecular docking analysis indicates a binding score of 980 for Cd, Cr and Cu, and 372 for Zn. Pb may bind with a non-metallothionein protein of earthworms and bio-accumulated in the internal chloragogenous tissues. Metallothionein neutralizes the metal toxicity and controls the ingestion of essential elements.

Biochar industry to circular economy

Biochar, produced as a by-product of pyrolysis/gasification of waste biomass, shows great potential to reduce the environment impact, address the climate change issue, and establish a circular economy model. Despite the promising outlook, the research on the benefits of biochar remains highly debated. This has been attributed to the heterogeneity of biochar itself, with its inherent physical, chemical and biological properties highly influenced by production variables such as feedstock types and treating conditions. Hence, to enable meaningful comparison of results, establishment of an agreed international standard to govern the production of biochar for specific uses is necessary. In this study, we analyzed four key uses of biochar: 1) in agriculture and horticulture, 2) as construction material, 3) as activated carbon, and 4) in anaerobic digestion. Then the guidelines for the properties of biochar, especially for the concentrations of toxic heavy metals, for its environmental friendly application were proposed in the context of Singapore. The international status of the biochar industry code of practice, feedback from Singapore local industry and government agencies, as well as future perspectives for the biochar industry were explained.

Precomposting and green manure amendment for effective vermitransformation of hazardous coir industrial waste into enriched vermicompost

Vermitransformation of coir pith (CP) into enriched vermifertilizer has been achieved by amending a green-manure plant, Sesbania sesban (SS) for the first time, and cow dung (CD) in five different combinations: T1_(1:0:1), T2_(4:3:3), T3_(5:3:2), T4_(5:4:1) and T5_(1:1:0). The substrates were 28 days precomposted with Pleurotus sajor-caju followed by 50 days vermicomposting with Eisenia fetida and Eudrilus eugeniae. Results showed a significant reduction in cellulose, lignin, organic carbon, C/N ratio, C/P ratio and an increase in plant nutrients compared to control. The fertilization index and efficiency of nutrient recovery rate were higher in SS and CD amended CP vermicompost, with a maximum in T2_(4:3:3) for E. fetida and T3_(5:3:2) for E. eugeniae. The activity of dehydrogenase, urease and cellulase, and phytotoxicity assays further revealed vermicompost stability. The study concludes that T2_(4:3:3) and T3_(5:3:2) combinations respectively for E. fetida and E. eugeniae is suitable for vermitransformation of CP into enriched vermicompost.

Elucidating the role of earthworms in N2O emission and production pathway during vermicomposting of sewage sludge and rice straw

Vermicomposting is a sustainable option for the recycling of biodegradable organic waste. However, it also produces nitrous oxide (N₂O), which is a highly potent greenhouse gas. In this study, the N₂O stable isotope and functional genes for nitrogen cycling were determined to investigate the sources of N₂O during vermicomposting. The results showed that vermicomposting promoted the organic degradation and nitrogen nitrification, and the presence of earthworms increased the emission of N₂O during vermicomposting compared to that during the control treatment with no earthworms. The site preference analysis of N₂O stable isotope showed that both nitrification and denitrification were present during the early stages of vermicomposting, while nitrification was the dominant contributor to N₂O production in the later stages. Moreover, earthworms increased the gene copies of amoA, and stimulated the nitrifying bacteria, and hence, increased the N₂O emission via nitrification. In addition, the activity of earthworms reduced the gene number of nosZ during vermicomposting, while the denitrification was the main source of N₂O in the earthworm gut, as the conditions inside the gut inhibited nosZ. Overall, nitrification was the major pathway (55.8-88.7 %) for N₂O production, which was promoted by the introduction of earthworms through nitrification.

Biochar reduces nutrient loss and improves microbial biomass of composted cattle manure and maize straw

In this study, nutrient loss, the direct and indirect relationship between period, compost types, temperature, total nitrogen (TN), nitrate nitrogen (NO3−‐N), ammonium nitrogen (NH4+‐N), microbial biomass carbon (MBC), and microbial biomass nitrogen (MBN) were investigated during composting of cattle manure–maize straw mixture. This study findings revealed that biochar addition lowered NH4+‐N but did not increase NO3−‐N concentrations unlike no biochar piles during composting. The first‐order kinetic models showed that biochar accelerated organic matter (OM) degradation and improved nitrogen mineralization, consequently reducing TN losses by 13.6% and OM losses by 12.66%. Transformation ratio of MBC/MBN, coupled with other chemical components of the entire microbial community, suggested a shift in the microbial succession and diversity during composting from the dominant bacteria and actinomycetes to fungi. The structural equation model and path coefficient revealed temperature to be the main factor mediating the evolution of MBC and MBN in composting. The physicochemical variables, phytotoxicity, and final product quality revealed that biochar incorporation to the composting feedstock is an ideal material for mitigating problems of TN and OM losses in composting and ultimately enhancing the fertility potential of the final compost product.