Bioremediation of petroleum refinery wastewater using Bacillus subtilis IH-1 and assessment of its toxicity.

Environmental contamination from petroleum refinery operations has increased due to the rapid population growth and modernization of society, necessitating urgent repair. Microbial remediation of petroleum wastewater by prominent bacterial cultures holds promise in circumventing the issue of petroleum-related pollution. Herein, the bacterial culture was isolated from petroleum-contaminated sludge samples for the valorization of polyaromatic hydrocarbons and biodegradation of petroleum wastewater samples. The bacterial strain was screened and identified as Bacillus subtilis IH-1. After six days of incubation, the bacteria had degraded 25.9% of phenanthrene and 20.3% of naphthalene. The treatment of wastewater samples was assessed using physico-chemical and Fourier-transform infrared spectroscopy analysis, which revealed that the level of pollutants was elevated and above the allowed limits. Following bacterial degradation, the reduction in pollution parameters viz. EC (82.7%), BOD (87.0%), COD (80.0%), total phenols (96.3%), oil and grease (79.7%), TKN (68.8%), TOC (96.3%) and TPH (52.4%) were observed. The reduction in pH and heavy metals were also observed after bacterial treatment. V. mungo was used in the phytotoxicity test, which revealed at 50% wastewater concentration the reduction in biomass (30.3%), root length (87.7%), shoot length (93.9%), and seed germination (30.0%) was observed in comparison to control. When A. cepa root tips immersed in varying concentrations of wastewater samples, the mitotic index significantly decreased, suggesting the induction of cytotoxicity. However, following the bacterial treatment, there was a noticeable decrease in phytotoxicity and cytotoxicity. The bacterial culture produces lignin peroxidase enzyme and has the potential to degrade the toxic pollutants of petroleum wastewater. Therefore the bacterium may be immobilised or directly used at reactor scale or pilot scale study to benefit the industry and environmental safety.

Effects of pelletization on biomethane production from wheat straw.

The high lignin content and low bulk density of wheat straw pose challenges for biogas production. To overcome these hurdles, pretreatment and biomass pelletization have emerged as viable options. Thus, this research aims to reduce the recalcitrant nature of WS by employing various thermal pretreatment techniques and identifying the optimum parameters (temperature and time). To prepare pellets, a mixture comprising wheat straw (subjected to the best pretreatment) and cow manure pellets (WCP) at varying substrate and binder (Svs/Bvs) ratios ranging from 0.5 to 2.5 were used. Parameters such as density, water absorption, and drop shattering were evaluated to evaluate the physical characteristics of produced WCP. Additionally, the biomethane yield test of WCP (exhibiting the most favourable physical characteristics) was performed with various total solids (TS) concentrations from 4 to 12%. The WS demonstrated the highest sCOD solubilisation of 9066 mg/L when subjected to a hot air oven pretreatment (90 min at 110°C). The physical qualities of WCP were found to be dependent on the Svs/Bvs ratio (with the optimal ratio being 2.0). It was also observed that a TS content of 6% yielded the highest biomethane production (253.85 mL/g-VSconsumed). In summary, this study's conclusion waves the path of management of wheat straw and cow dung while simultaneously generating bioenergy.

Co-densification of rice straw and cow dung in different food-to-microorganism ratios for biogas production.

Agricultural residues such as rice straw (RS) are desirable raw materials for biogas generation. However, the recalcitrant nature of RS hinders biogas production, and its low bulk density increases storage space requirements, transportation needs, and overall costs. These challenges could be resolved by pretreatment and pelletization. In this study, various thermal pretreatments were performed, and the best conditions (temperature and time) were identified. Also, rice straw and cow dung pellets (RCP) at different food-to-microorganism (F/M) ratios (0.5-2.5) were prepared. Parameters such as bulk density, moisture absorption, and drop shatter tests were conducted to evaluate the physical properties. Finally, the biochemical methane potential (BMP) study of the best RCP with varying total solids (TS: 4-12%) content was investigated. The results indicate that hot air oven pretreatment (for 60 min at 120 °C) resulted in maximum solubilization. In physical characteristics, RCP with an F/M ratio of 2.5 pellets was ideal. The bulk density of RCP 2.5 was found to be around 25 times that of the raw. Also, the TS 8% yielded maximum biomethane (279 mL/g-VSconsumed) as compared to other TS contents. Overall, this study will propel the growth of bioenergy while simultaneously tackling the pressing issues related to RS management.

Assessment of pyrolysis potential of Indian municipal solid waste and legacy waste via physicochemical and thermochemical characterization.

This study explores the viability of utilizing municipal solid waste (MSW) and legacy waste as a renewable energy source through pyrolysis, akin to solid fuels. The heating value of MSW and legacy waste were found to be 37737.89 and 40432.84 kJ/kg, respectively. Proximate analysis shows that MSW fits within Tanner diagram parameters, eliminating the need for auxiliary fuel in pyrolysis. With 47.6 % and 44.16 % lignin content in MSW and legacy waste were deemed suitable for char production. Thermal degradation resulted in mass losses of 68 % for MSW and 82 % for legacy waste. The kinetic and thermodynamic assessment indicates lower activation energy (Ea) and Gibbs free energy (ΔG) for MSW (5.72 kJ/mol and 170.37 kJ/mol, respectively) compared to fossil fuels, suggesting faster reactions without additional energy requirement. MSW emerges as a promising alternative to fossil fuels, aligning with the United Nations' 2030 Sustainable Development Goals.

Perspectives and understanding on the occurrence, toxicity and abatement technologies of disinfection by-products in drinking water.

Disinfection by-products (DBPs) are one of the significant emerging contaminants that have caught the attention of researchers worldwide due to their pervasiveness. Their presence in drinking water, even in shallow concentrations (in levels of parts per billion), poses considerable health risks. Therefore, it is crucial to understand their kinetics to understand better their formation and persistence in the water supply systems. This manuscript demonstrates different aspects of research carried out on DBPs in the past. A systematic approach was adopted for the bibliographical research that started with choosing appropriate keywords and identifying the most relevant manuscripts through the screening process. This follows a quantitative assessment of the extracted literature sample, which included the most productive and influential journal sources, the most widely used keywords, the most influential authors active in the research domain, the most cited articles, and the countries most actively engaged in the research field. Critical observations on the literature sample led to the qualitative assessment, wherein the past and current research trends were observed and reported. Finally, we identified the essential gaps in the available literature, which further led to recommending the course ahead in the research domain. This study will prove fruitful for young and established researchers who are or wish to work in this emerging field of research.

Unleashing synergistic potential of microbially enhanced anaerobic co-digestion of petroleum refinery biosludge and yard waste: Impact of nutrient balance and microbial diversity.

Petroleum refinery sludge, an egregious solid residue generated from the wastewater treatment plants poses an environmental hazard owing to its intricate hydrocarbon composition, necessitating competent treatment for secure disposal. The study proposes a green solution through anaerobic co-digestion of nitrogen-rich petroleum refinery sludge (PS) with carbon-rich yard waste (YW), balancing the nutrients and moisture content for efficient microbial proliferation. Using Central Composite Design-Response Surface Methodology, 1 L batch experiments were conducted with varying carbon/nitrogen (C/N) ratios and pH to achieve maximum biogas yield within 50 days of co-digestion. However, the sluggish biogas recovery (40%) indicated a slow rate-limiting hydrolysis, necessitating pretreatment. Feedstock incubation with Bacillus subtilis IH1 strain, isolated from the microbially-enriched PS, at 108 colony forming units (CFU) per mL for 5 days maximized the soluble chemical oxygen demand and volatile fatty acids by 2.2 and 1.4 folds respectively compared to untreated feedstock. Scale-up Bacillus subtilis aided co-digestion studies further augmented biogas by 76% against untreated monodigestion of PS with significant total petroleum hydrocarbons, emulsions, and lignocellulosic degradation. Further identification of major organic pollutants in the batch digestate revealed significant degradation of the toxic organic hydrocarbon pollutants apotheosizing the efficacy of the synergistic sustainable technique for the management of PS. ENVIRONMENTAL IMPLICATION: The effluent treatment plants (ETPs) of petroleum refining industries generate sludge which is a complex mixture of petroleum hydrocarbons, oil-water (O/W) emulsions and heavy metals. These petroleum hydrocarbon constituents can be linear/cyclic alkanes, polyaromatics, resins and asphaltenes, whose intricate composition is reportedly carcinogenic, cytogenic and mutagenic, classifying it as hazardous waste. Biological treatment of these sludge through anaerobic digestion leads to utilization of petroleum hydrocarbons with subsequent energy recovery. Co-digestion of these sludge with competent co-substrates leads to nutrient balance, diverse microbial proliferation and toxicant dilution. Microbially aided co-digestion further augments methane rendering a digestate with utmost pollutant degradation.

Evaluating the potential of biodegradation of swine manure through rotary drum composting utilizing different bulking agents.

The rapid expansion of the pig industry and the concurrent increase in pig units have posed a significant waste management challenge, particularly in the form of piggery waste. In this study, the potential of three different bulking agents (sawdust, dry leaves, and rice straw) for the biodegradation of piggery waste was evaluated through rotary drum composting (RDC). Following the composting time of 20 days, evaluations of macro and micronutrient concentrations and the C/N ratio revealed stable, matured compost that could be used in farming. However, the saw dust amended RDC (RDC1) outperformed among the studied trails; the total nitrogen content of 1.54%, total phosphorus of 7.68 g kg-1, and total potassium of 23.45 g kg-1 demonstrated the bioproduct produced through RDC1 resulted in superior-quality end product achieved in only 20 days in comparison with other bulking agents studied. Further, the outcomes of the study can serve the swine livestock sector through effective bioconversion of the waste.

Ecological and health risk assessment associated with translocation of heavy metals in Lycopersicum esculentum from farmland soil treated with different composts.

To meet the United Nations' Sustainable Development Goals, agricultural soil which is a non-renewable natural resource must be carefully managed. Heavy metals present in agricultural soil may imperil food security and instigate extreme risks to human health. Organic wastes have been long known for valuable amendments to soil thereby, improving overall soil health. In the present study, Echhornia crassipes, Hydrilla verticillata, and vegetable waste, was utilized to prepare compost amendments. Lycopersicum esculentum was used to metal uptake from compost amended soils. 5%, 10%, 15%, 25%, and 35% compost: soil (w/w) were studied to understand metal translocation in plants. Potential Ecological risk indices showed that while the degree of risk was medium for the natural soil, it reduced to slight for the soil amended with WHC and VWC for all compositions. The non-carcinogenic risks associated with the human health reduced on application of the composts, however, they still remained substantial for Fe, As, and Pb for WHC, HVC, and VWC composts at higher application ratios, especially among children. On the other hand, the carcinogenic health index values which were calculated to estimate the risk associated with ingestion of L. esculentum, showed a decrease in risk for all the metals studied, upon soil amendment. Soil amended with HVC compost showed an increase in carcinogenic risk for As, Pb, and Cr. Finally, we conclude that biological soil remediation is economical and a sustainable land management strategy that may lead to green and clean remediation solutions for metal contaminated soil.

Critical review with science mapping on the latest pre-treatment technologies of landfill leachate.

The most frequent strategy for solid waste management, adopted across the globe is landfill. Through microbial decomposition municipal solid waste degrades, producing end products such as carbon dioxide, methane, volatile organic compounds, and leachate. High levels of organic waste and heavy metals content in leachate can cause pervasive damage to the ecosystem and contaminate groundwater. Leachate requires extensive treatment before being released into the environment because of its complex chemical composition and identifying the appropriate technologies for leachate treatment remains a key problem for municipal landfill operations. Given the possible harm caused by substantially contaminated leachate, it should adhere to stricter quality criteria for direct disposal of leachate and one treatment method cannot efficiently tackle all the pollutants. In order to reduce the landfill leachates high fouling power, pre-treatment of landfill leachate is necessary. The study provides a comprehensive review of pre-treatment technologies, as well as a critical assessment of strengths and limitations. Current review-based analysis was undertaken based on the filtered 395 papers published for science mapping and to evaluate the qualitative studies in the area of pre-treatment of Landfill Leachate till 2022. A three-step process was employed to conduct bibliometric analysis, qualitative valuation, and identification of influential and productive journals, countries, researchers and articles, emerging technology, and outlining some of the major research gaps in the research field.

Bioconversion of Eichhornia crassipes into vermicompost on a large scale through improving operational aspects of in-vessel biodegradation process: Microbial dynamics.

Eichhornia crassipes is a common, abundant aquatic weed biomass found globally. The present study examined optimum biodegradation procedures through batch studies (550 L rotating drum composter) and the resulting best combination on a large scale (5000 L rotary drum composter). The pilot scale rotary drum reactor was commenced with cow manure and then treated for 3 months with 250 kg/day of homogenously mixed E. crassipes and dry leaves. The rotary drum's inlet and outlet temperatures were 60 °C and 39 °C, respectively, suggesting thermophilic conditions with a 7-day waste retention duration. Eisenia fetida was used for vermicomposting the outlet material for 20 days, raising the nitrogen content to 3.2%. Bacterial diversity (16S-rRNA) sequencing revealed that Proteobacteria and Euryarchaeota are the most predominant. After 27 days, the volume dropped by 71%, and the product was stable and soil-safe. Large-scale optimised biodegradation may be a better way to handle aquatic weed biomass.

Mobility and risk assessment of heavy metals in benthic sediments using contamination factors, positive matrix factorisation (PMF) receptor model, and human health risk assessment.

Metal pollution in benthic sediments was fractionated and modelled to quantify the risk of anthropogenic activities on river ecosystems. In this study, the individual contamination factor (ICF) and the global contamination factor (GCF) were used to measure the contamination levels in the sediments. On the other hand, the mobility factor (MF) was used to quantify the mobility of heavy metals in benthic river sediments. The factors used to assess pollution in benthic sediments employ bioavailable fractions of heavy metals, which have a greater chance of release into aquatic sediments and hence are more dangerous to the environment. Heavy metal mobility (MF) is highest in the post-monsoon season for Zn, Pb, Cu, and Co; Fe in winter; Mn in pre-monsoon; and Cd in monsoon. This means that heavy metals accumulate in benthic sediments during the post-monsoon season when river flows are less turbulent. ICF and GCF data show that pollution levels are higher post-monsoon than the rest season levels. Sediment samples were further subjected to the positive matrix factorization (PMF) model, which identified four factors that explained the variation in the study: factor 1 is concerned with anthropogenic Cu, Cd, and Co pollution, while factors 2, 3, and 4 are concerned with Fe, Mn, and Zn pollution. Finally, the total cancer risk (TCR) and hazard index (HI) are employed to quantify the risk to human health from accidental ingestion and dermal exposure. According to the risk outcomes from probabilistic and deterministic approaches, river exposure is dangerous to human health, with dermal absorption being the most significant concern of the exposure paths.

Thermal pretreatment of Lantana camara for improved biogas production: Process parameter studies for energy evaluation.

The rigid lignocellulosic structure of Lantana camara impedes the hydrolysis phase and reduces the biogas production during anaerobic digestion of Lantana camara. Hence, the current study focuses on the impact of various heating pretreatment techniques, viz., hot air oven (HAO), autoclave (ATC), hot water bath (HWB), and microwave (MCW) on L. camara to speed up hydrolysis and boost up biogas production. ATC pretreatment of L. camara was witnessed to be most efficient compared to HAO, MCW, and HWB pretreatment. ATC pretreatment enhanced the solubilization (45.44%), and an increment in volatile fatty acids (VFA) was observed (56.75%) at 110 °C for 80 min when correlated to the untreated (control). Cumulative methane production following ATC pretreatment had risen to 3656 mL in 5 weeks from 2895 mL in 7 weeks. Thermal pretreatment of Lantana camara broke down the rigid lignocellulosic structure, accelerating the hydrolysis stage and improving biogas production simultaneously. To the best of our knowledge, this is the first thermal pretreatment study conducted on Lantana camara for biogas production.

Development of function-specific indices for assessing water quality based on the proposed modifications of the expected conflicts on existing information entropy weights.

Water serves numerous purposes besides drinking, such as irrigation and industrial usage. Most water quality indices developed have primarily focused on drinking water quality. However, assessing other functionalities of water bodies is also equally essential. The present study proposes a novel technique to measure water quality for two highly specific water use, i.e., assessing heavy metal contamination and irrigation suitability. The ambiguities in the current practice of entropy weights were identified, and a novel method was proposed, considering a three-dimensional approach instead of the conventional two-dimensional procedure. Weights to different parameters were assigned based on the probability estimates obtained from the frequency of observed values within acceptable limits. The proposed method's reliability, correctness, and applicability were tested using Deepor Beel's water quality dataset. Results were highly consistent with the experimental values and correlated well with other established methods. The efficacy of the method was determined by employing sensitivity analyses. Both indices showed high reliability and correctness, as no single parameter was found to be highly sensitive compared to others. Therefore, the proposed methodology proved to be the most reasonable, incorporating all the factors required for a reliable water quality monitoring program.

Thermophilic-mesophilic biodegradation: An optimized dual-stage biodegradation technique for expeditious stabilization of sewage sludge.

The present study investigated the stabilization of fresh sewage sludge through a dual-stage biodegradation process; rotary drum composting in series with vermicomposting. After thermophilic exposure in a rotary drum composter, the partially degraded feedstock was separated into S1 without vermiculture, S2 and S3 with Eudrilus eugeniae and Eisenia fetida vermi-monocultures, respectively. The S3-derived vermicompost exhibited an 80% and 88% reduction in CO2 and ammonium-nitrogen evolution rates, respectively, demonstrating the expedient stabilization of sludge. The robust, more than 85% seed germination index supported S2 and S3 derived vermicompost viability. A significant decrease in heavy metals was evinced with S2 and S3-derived vermicompost; the S1-derived end product exhibited higher Zn, Cr, and Pb levels in the absence of vermicomposting. Furthermore, soil amended with 20% vermicompost from S3 displayed 50% more plant growth than S1. Thus, the optimized thermophilic-mesophilic dual-biodegradation technique stabilizes sewage sludge quickly, has a lot of potential in sludge management facilities around the world, and produces a marketable end product.

Biodegradation of an intrusive weed Parthenium hysterophorus through in-vessel composting technique: toxicity assessment and spectroscopic study.

Parthenium hysterophorus is a toxic terrestrial weed with its erratic behavior brought on by the presence of toxic compounds. A numerous works have been conducted on the complete eradication of this weed, but due to the residuals exists in soil, the weed re-grows. Current study therefore aims at examining the transformation of this weed by an in-vessel composting approach (rotary drum composter) and the evaluation of toxicity characteristics using Vigna radiata and Allium cepa as bioindicators. The nutritional content such as total Kjeldahl nitrogen (TKN), total phosphorus (TP), and total potassium were increased by 38.8, 39.1, and 49.5%, respectively, and the reactor was effective in reducing the biochemical content such as lignin, hemicellulose, and cellulose by 43.5, 50.7, and 57.3%, respectively, in the final compost. The thermophilic degradation phase in the reactor existed up to the 8th day of the composting process, which exhibits the highest degradation phase. Meanwhile, the degradation of phenolic, aliphatic, and lignocellulose was investigated and validated using Fourier transform infrared spectroscopy (FTIR) and powdered X-ray diffraction (PXRD) analysis. Although P. hysterophorus exhibited phytotoxic and cyto-genotoxic effects in plant models at the beginning of the composting process, the toxicity potential appeared to be reduced after 20 days of composting. Therefore, the study's findings proved that the in-vessel composting of P. hysterophorus can produce a nontoxic, nutrient-rich compost product that could be used as a soil conditioner in agricultural farmlands. The insights of the study are not limited to the nutritional, stability, and quality characteristics but also the toxicity characteristics during the composting process.

Performance assessment of in-vessel composter through heavy metal immobilization and humification of Parthenium hysterophorus.

The bioconversion of Parthenium hysterophorus was performed through rotary drum composter and examined the mechanism of humification and heavy metals immobilization in the process. The 20th day compost contains a significant increase in humic substances of 28.7% compared to the initial day mix. The bioavailable fractions of heavy metals have reduced by 30 to 55% in the 20th day compost compared to the initial day mix. The leaching potential of cadmium has been reduced by 69% in the 20th day compost. The immobile fractions (F5) of Cd, Ni and Pb have been increased to 100, 99 and 78% in the 20th day compost. The mitotic index was increased by 1.7 and 51.6% in 25% dosed compost extract compared to the control and P. hysterophorus extract respectively. The transition of heavy metals to immobile fraction indicated the biodegradation capability of P. hysterophorus through rotary drum composting.

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.

Interrelationships among critical success factors for the planning of municipal solid waste management PPP projects in India using structural equation modelling.

This research aims at investigating the interrelationships between critical success factors (CSFs) in municipal solid waste management (MSWM) projects taken up in public-private partnership (PPP) mode in India and studies the extent to which they can affect project success. A three-step procedure was followed to identify the CSFs in MSWM. A conceptual structural equation model (SEM) was developed using cluster groupings of the identified CSFs to show their interrelationships. Data collection from the public sector and private sector waste management managers was done through a questionnaire survey. The respondents' data were analysed in analysis of moment structures (AMOS) using structural equation modelling. The SEM analysis of the respondents' data gives the most exemplary fitting measurement model with the 17 CSFs taken as components of five latent variables: external environment, financial characteristics, project planning and procurement, project operation and management and project stakeholders. The model shows the relationships between the constructs of CSFs for project success. This study contributes to current ideas by empirically identifying the interrelationships between the MSWM CSFs, which can help waste management professionals handle the CSFs rationally. Furthermore, the study shows that all the groups have a direct and positive impact on project success. The findings may only portray the opinion of solid waste management managers in India.

Hydraulic performance, consolidation characteristics and shear strength analysis of bentonites in the presence of fly-ash, sewage sludge and paper-mill leachates for landfill application.

A rapid upsurge in urban and industrial developments leads to increased generations of solid wastes. The most accepted technique of waste discarding around the world is landfilling. Leaching chemicals from municipal dumping grounds can pollute the groundwater source and the surrounding environment without appropriate precautionary measures. Bentonite is a low-cost constituent used as a liner material in landfills due to its low permeability, high sealing ability, high specific surface area, and the ability to hold up the impurity migration through adsorption. However, leachate interaction with bentonite may alter its properties and reduce its usefulness as a barrier material in the long term. Also, bentonite having different chemical and mineralogical compositions will behave differently due to the leachate interaction. Therefore, it is necessary to compare the performance of various bentonites in the presence of leachates. In the present investigation, two Indian bentonites of different mineralogical compositions were studied for their change in the index properties, swelling, swelling potential, swelling pressure, hydraulic conductivity, consolidation parameters and shear strength properties in the presence of fly ash, sewage sludge and paper mill leachates. The outcomes showed that in the presence of all the leachates, liquid limit, free swell, compression index, swelling potential, swelling pressure, time to complete 90% of consolidation and shear strength dropped; whereas, hydraulic conductivity and coefficient of consolidation increased. Besides, the quality of bentonite prominently influenced the hydraulic, strength and swelling behaviour. The bentonite having a higher cation exchange capacity, liquid limit, specific surface area, and swelling capability undergoes a higher variability in the free swell (80.0, 73.8 and 76.9% decline), liquid limit (73.5, 61.7 and 69.2% decline), swelling potential (61.3, 55.7 and 51.0% decline), swelling pressure (53.3 and 56.4% decrease), and hydraulic conductivity (57.5, 8.6 and 41.1 times increase at a void ratio of 1.2) values when infused with fly ash, sewage sludge and paper mill leachates, respectively. The study also showed that the fly ash leachate interaction causes a higher variation in bentonite behaviour than sewage sludge and paper mill leachates. The study's findings would prove beneficial to design engineers for selecting bentonite types for landfill liners.

Enhanced methane production and hydrocarbon removal from petroleum refinery sludge after Pseudomonas putida pretreatment and process scale-up.

The influence of Pseudomonas putida 7525 strain on the pretreatment of petroleum refinery sludge was optimized at different dosages to maximize solubilization for improved biodegradability. Laccase-producing P. putida strain at a dosage of 108 CFU/mL resulted in 249% and 121.57% increments in soluble chemical oxygen demand and volatile fatty acids production respectively as compared to untreated within 6 days of incubation. 1L biochemical methane potential test conducted for optimization of different inoculum and pretreated substrate ratios (0.3, 0.4, 0.5, 0.7 and 1.0) revealed maximum methane augmentation (62%) and volatile solids degradation (66.7%) at ratio 0.5. Scaled-up study (20L) for ratio 0.5 resulted in 57.07% total petroleum hydrocarbon, 62.98% oil and grease and 91.9% phenol removal within 50 days of digestion of pretreated PS. Kinetic modelling of cumulative methane yield indicated that modified Gompertz model showed the best fit thereby, evincing the potency of bacterial species for bioremediation of PS.