Comprehensive review on toxicity of persistent organic pollutants from petroleum refinery waste and their degradation by microorganisms

Selective pressure leads to an improved synthetic consortium fit for dye degradation

Microorganisms have great potential for bioremediation as they have powerful enzymes and machineries that can transform xenobiotics. The use of a microbial consortium provides more advantages in application point of view than pure cultures due to cross-feeding, adaptations, functional redundancies, and positive interactions among the organisms. In this study, we screened about 107 isolates for their ability to degrade dyes in aerobic conditions and without additional carbon source. From our screening results, we finally limited our synthetic consortium to Gordonia and Rhodococcus isolates. The synthetic consortium was trained and optimized for azo dye degradation using sequential treatment of small aromatic compounds such as phenols that act as selective pressure agents. After four rounds of optimization with different aims for each round, the consortium was able to decolorize and degrade various dyes after 48 h (80%-100% for brilliant black bn, methyl orange, and chromotrop 2b; 50-70% for orange II and reactive orange 16; 15-30% for chlorazol black e, reactive red 120, and allura red ac). Through rational approaches, we can show that treatment with phenolic compounds at micromolar dosages can significantly improve the degradation of bulky dyes and increase its substrate scope. Moreover, our selective pressure approach led to the production of various dye-degrading enzymes as azoreductase, laccase-like, and peroxidase-like activities were detected from the phenol-treated consortium. Evidence of degradation was also shown as metabolites arising from the degradation of methyl red and brilliant black bn were detected using HPLC and LC-MS analysis. Therefore, this study establishes the importance of rational and systematic screening and optimization of a consortium. Not only can this approach be applied to dye degradation, but this study also offers insights into how we can fully maximize microbial consortium activity for other applications, especially in biodegradation and biotransformation.

The influence of benzene on the composition, diversity and performance of the anodic bacterial community in glucose-fed microbial fuel cells

Bioelectrochemical systems offer unique opportunities to remove recalcitrant environmental pollutants in a net positive energy process, although it remains challenging because of the toxic character of such compounds. In this study, microbial fuel cell (MFC) technology was applied to investigate the benzene degradation process for more than 160 days, where glucose was used as a co-metabolite and a control. We have applied an inoculation strategy that led to the development of 10 individual microbial communities. The electrochemical dynamics of MFC efficiency was observed, along with their 1H NMR metabolic fingerprints and analysis of the microbial community. The highest power density of 120 mW/m2 was recorded in the final period of the experiment when benzene/glucose was used as fuel. This is the highest value reported in a benzene/co-substrate system. Metabolite analysis confirmed the full removal of benzene, while the dominance of fermentation products indicated the strong occurrence of non-electrogenic reactions. Based on 16S rRNA gene amplicon sequencing, bacterial community analysis revealed several petroleum-degrading microorganisms, electroactive species and biosurfactant producers. The dominant species were recognised as Citrobacter freundii and Arcobacter faecis. Strong, positive impact of the presence of benzene on the alpha diversity was recorded, underlining the high complexity of the bioelectrochemically supported degradation of petroleum compounds. This study reveals the importance of supporting the bioelectrochemical degradation process with auxiliary substrates and inoculation strategies that allow the communities to reach sufficient diversity to improve the power output and degradation efficiency in MFCs beyond the previously known limits. This study, for the first time, provides an outlook on the syntrophic activity of biosurfactant producers and petroleum degraders towards the efficient removal and conversion of recalcitrant hydrophobic compounds into electricity in MFCs.

Desorption of Polycyclic Aromatic Hydrocarbons from Microplastics in Human Gastrointestinal Fluid Simulants-Implications for Exposure Assessment

Microplastics have been detected in various food types, suggesting inevitable human exposure. A major fraction may originate from aerial deposition and could be contaminated by ubiquitous pollutants such as polycyclic aromatic hydrocarbons (PAHs). While data on the sorption of pollutants to microplastics are abundant, the subsequent desorption in the gastrointestinal tract (GIT) is less understood. This prompted us to systematically investigate the release of microplastics-sorbed PAHs at realistic loadings (44-95 ng/mg) utilizing a physiology-based in vitro model comprising digestion in simulated saliva, gastric, and small and large intestinal fluids. Using benzo[a]pyrene as a representative PAH, desorption from different microplastics based on low density polyethylene (LDPE), thermoplastic polyurethanes (TPUs), and polyamides (PAs) was investigated consecutively in all four GIT fluid simulants. The cumulative relative desorption (CRD) of benzo[a]pyrene was negligible in saliva simulant but increased from gastric (4 ± 1% - 15 ± 4%) to large intestinal fluid simulant (21 ± 1% - 29 ± 6%), depending on the polymer type. CRDs were comparable for ten different microplastics in the small intestinal fluid simulant, except for a polydisperse PA-6 variant (1-10 μm), which showed an exceptionally high release (51 ± 8%). Nevertheless, the estimated contribution of microplastics-sorbed PAHs to total human PAH dietary intake was very low (≤0.1%). Our study provides a systematic data set on the desorption of PAHs from microplastics in GIT fluid simulants.

Remediation of groundwater polluted with lindane production wastes by conductive-diamond electrochemical oxidation

This work studies the remediation of groundwater saturated with dense non-aqueous phase liquid (DNAPL) from lindane production wastes by electrochemical oxidation. DNAPL-saturated groundwater contains up to 26 chlorinated organic compounds (COCs), including different isomers of hexachlorocyclohexane (HCH). To do this, polluted groundwater was electrolysed using boron-doped diamond (BDD) and stainless steel (SS) as anode and cathode, respectively, and the influence of the current density on COCs removal was evaluated in the range from 5 to 50 mA cm-2. Results show that current densities higher than 25 mA cm-2 lead to the complete removal and mineralisation of all COCs identified in groundwater. The higher the current density, the higher the COCs removal rate. At lower current densities (5 mA cm-2), chlorobenzenes were completely removed, and degradations above 90 % were reached for COCs with more than five chlorine atoms in their molecules. The use of BDD anodes promotes the electrochemical generation of powerful reactive species, such as persulfate, hypochlorite or hydroxyl radicals, that contribute to the degradation and mineralisation of COCs. The applied current density also influences the generation of these species. Finally, no acute toxicity towards Vibrio fischeri was observed for the treated groundwater after the electrochemical oxidation performed at 5 and 10 mA cm-2. These findings demonstrate that electrochemical oxidation with BDD anodes at moderate current densities is a promising alternative for the remediation of actual groundwater contaminated with DNAPLs.

Enhanced reduction of COD in water associated with natural gas production using iron-based nanoparticles

The natural gas production industry faces the problem of the proper disposal of produced water and its treatment with significantly advanced technologies to meet the minimum quality standard for irrigation activities, commercial purposes, and consumption by living organisms. This study describes an effective method for reducing the COD (chemical oxygen demand) content in formation water using different metal oxide nanoparticles such as iron oxide (FO), iron zinc oxide (FZO), and iron vanadium oxide (FVO) nanoparticles. These nanoparticles were synthesized and fully characterized using powder X-ray diffraction (XRD) analysis, Fourier transform infrared (FT-IR) spectroscopy, field emission scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis, dynamic light scattering particle size (DLS) analysis and zeta potential analysis. The experimental results revealed that the maximum reduction of COD content was 42.18% using FVO nanoparticles with a dose of 3 g L-1 at 25 °C and pH = 6. Compared to commercial products [Redoxy and Oxy(OXYSORB)], the synthesized FO, FZO, and FVO nanoparticles demonstrated their superiority by achieving excellent results in decreasing the COD content of wastewater associated with natural gas production by more than 86%. This study introduces a promising technique for decreasing the COD content using metal oxide nanoparticles, which are eco-friendly, bio-safe, cheap, and nontoxic materials, and improving the quality of wastewater associated with natural gas production for its safe disposal through sewage and treatment plants.

Correlation between microbial communities and volatile organic compounds in an urban soil provides clues on soil quality towards sustainability of city flowerbeds

Soil functionality is critical to the biosphere as it provides ecosystem services relevant for a healthy planet. The soil microbial composition is significantly impacted by anthropogenic activities, including urbanization. In this context, the study of soil microorganisms associated to urban green spaces has started to be crucial toward sustainable city development. Microbes living in the soil produce and degrade volatile organic compounds (VOCs). The VOC profiles may be used to distinguish between soils with various characteristics and management practices, reflecting variations in the activity of soil microbes that use a variety of metabolic pathways. Here, a combined approach based on DNA metabarcoding and GC-MS analysis was used to evaluate the soil quality from urban flowerbeds in Prato (Tuscany, Italy) in terms of microbial biodiversity and VOC emission profiles, with the final aim of evaluating the possible correlation between composition of microbial community and VOC patterns. Results showed that VOCs in the considered soil originated from anthropic and biological activity, and significant correlations between specific microbial taxa and VOCs were detected. Overall, the study demonstrated the feasibility of the use of microbe-VOC correlation as a proxy for soil quality assessment in urban soils.

Soil Microbiome in Conditions of Oil Pollution of Subarctic Ecosystems

The present study aimed to investigate the recovery of soil quality and the bacterial and fungal communities following various recultivation methods in areas contaminated with oil. Oil spills are known to have severe impacts on ecosystems; thus, the restoration of contaminated soils has become a significant challenge nowadays. The study was conducted in the forest-tundra zone of the European North-East, where 39 soil samples from five oil-contaminated sites and reference sites were subjected to metagenomic analyses. The contaminated sites were treated with different biopreparations, and the recovery of soil quality and microbial communities were analyzed. The analysis of bacteria and fungi communities was carried out using 16S rDNA and ITS metabarcoding. It was found that 68% of bacterial OTUs and 64% of fungal OTUs were unique to the reference plot and not registered in any of the recultivated plots. However, the species diversity of recultivated sites was similar, with 50-80% of bacterial OTUs and 44-60% of fungal OTUs being common to all sites. New data obtained through soil metabarcoding confirm our earlier conclusions about the effectiveness of using biopreparations with indigenous oil-oxidizing micro-organisms also with mineral fertilizers, and herbaceous plant seeds for soil remediation. It is possible that the characteristics of microbial communities will be informative in the bioindication of soils reclaimed after oil pollution.

Characteristics of dissolved organic matter in point-source wastewaters at a petrochemical plant: Molecular constituents and contributions to the influent of wastewater treatment plant

Dissolved organic matter (DOM) in point-source petrochemical wastewaters (PCWs) from different operating units is closely linked to the efficiency of wastewater treatment plant (WWTP). However, systematic studies on DOM characters of point-source PCWs and their influences on WWTP influents were seldom conducted. In this study, DOM in three low-salinity point-source PCWs and four high-salinity point-source PCWs at a typical petrochemical plant were comprehensively characterized at a molecular level. Orbitrap mass spectrometry results indicated that point-source PCWs had diverse DOM constituents tightly related to the corresponding petrochemical processes. Phenols in oily wastewaters (OW), phenols and N-containing compounds in coal partial oxidation wastewater (POXW), and naphthenic acids (NAs) and aromatic acids in crude oil electric desalting unit wastewater (EDW) were characteristic DOM constituents for low-salinity point-source PCWs. While S-containing compounds (mercaptans, thiophenes) and NAs in spent caustic liquors (SCL), alcohols and esters in butanol-octanol plant wastewater (BOW), high molecular weight aromatic ketones in phenol-acetone plant wastewater (PAW), and oxygenated NAs as well as short chain N-containing compounds in concentrate from reverse osmosis unit (ROC) were characteristic DOM constituents for high-salinity point-source PCWs. Spearman correlation analysis indicated that though with relative low pollutant contents (OW) and discharge volume (EDW), N/O/S-containing compounds of OW and EDW greatly contributed to the polar DOM constituents of low-salinity influent in WWTP (R > 0.5, P < 0.001). While N-containing compounds of ROC mainly contributed to the polar DOM of high-salinity influent (R > 0.5, P < 0.001). Though N-/S-containing species in PAW had low contents, they also posed obvious impacts on DOM constituents of high-salinity influent. Interestingly, some O-/S-containing species were newly formed during the confluent process of high-salinity point-source PCWs. The results strengthened the combined contributions of pollutants contents, discharge emission and DOM constituents of point-source PCWs to the water matrix of WWTP influents, which would provide reference for the management of PCW streams.

Polycyclic Aromatic Hydrocarbons in Soil and Vegetation of Niger Delta, Nigeria: Ecological Risk Assessment

The Niger Delta, Nigeria, is noted for crude oil exploration. Whereas there seems to be a handful of data on soil polycyclic aromatic hydrocarbon (PAH) levels in this area, there is a paucity of studies that have evaluated soil and vegetation PAHs simultaneously. The present study has addressed this information gap. Fresh Panicum maximum (Jacq) (guinea grass), Pennisetum purpureum Schumach (elephant grass), Zea mays (L.) (maize), and soil samples were collected in triplicate from Choba, Khana, Trans-Amadi, Eleme, Uyo, and Yenagoa. PAHs determination was carried out using GC-MS. The percentage composition of the molecular weight distribution of PAHs, the molecular ratio of selected PAHs for identification of possible sources, and the isomeric ratio and total index of soil were evaluated. Pennisetum purpureum Schumach (elephant grass) from Uyo has the highest (10.0 mg·kg^-1) PAH while Panicum maximum (Jacq) (guinea grass) has the highest PAH (32.5 mg·kg^-1 from Khana. Zea mays (L.) (maize) from Uyo (46.04%), Pennisetum purpureum Schumach (elephant grass) from Trans-Amadi (47.7%), guinea grass from Eleme (49.2%), and elephant grass from Choba (39.9%) contained the highest percentage of high molecular weight (HMW) PAHs. Soil samples from Yenagoa (53.5%) and Khana (55.3%) showed the highest percentage of HMW PAHs. The total index ranged 0.27-12.4 in Uyo, 0.29-8.69 in Choba, 0.02-10.1 in Khana, 0.01-5.53 in Yenagoa, 0.21-9.52 in Eleme, and 0.13-8.96 in Trans-Amadi. The presence of HMW PAHs and molecular diagnostic ratios suggest PAH pollution from pyrogenic and petrogenic sources. Some soils in the Niger Delta show RQ_(NCs) values higher than 800 and require remediation to forestall ecohealth consequences.

In-depth comparative transcriptome analysis of Purpureocillium sp. CB1 under cadmium stress

Fungal bioremediation is a very attractive tool to cope with environmental pollution. We aimed to decipher the cadmium (Cd) response of Purpureocillium sp. CB1, isolated from polluted soil, at transcriptome level by RNA-sequencing (RNA-seq). We used 500 and 2500 mg/L of Cd²⁺ concentrations at two time points (t_6;36). RNA-seq determined 620 genes that were co-expressed in all samples. The highest number of differentially expressed genes (DEGs) was obtained within the first six h of exposure to 2500 mg/L of Cd²⁺. Several genes encoding transcriptional regulators, transporters, heat shock proteins, and oxidative stress-related genes were differentially expressed under Cd²⁺ stress. Remarkably, the genes that encode salicylate hydroxylase, which is involved in naphthalene biodegradation pathway, were significantly overexpressed. Utilization of diesel as the sole carbon source by CB1 even in the presence of Cd²⁺ supported concomitant upregulation of hydrocarbon degradation pathway genes. Furthermore, leucinostatin-related gene expression levels increased under Cd²⁺ stress. In addition, leucinostatin extracts from Cd²⁺-treated CB1 cultures showed higher antifungal activity than the control. Notably, Cd²⁺ in CB1 was mainly found as bound to the cell wall, thus confirming its adsorption potential. Cd²⁺ stress slightly reduced growth and led to mycelial malformation due to Cd²⁺ adsorption, especially at a concentration of 2500 mg/L at t₃₆. A strong correlation was recorded between RNA-seq and reverse-transcriptase-quantitative polymerase chain reaction (RT-qPCR) data. In conclusion, the study represents the first transcriptome analysis of Purpureocillium sp. under Cd²⁺ stress, providing insights into the primary targets for rational engineering to construct strains with remarkable bioremediation potency. KEY POINTS: • Upregulation of genes encoding salicylate hydroxylases under Cd²⁺ stress • Maximum Cd²⁺ adsorption at 500 mg/L at t₃₆ as tightly bound to the cell wall • Concordant bioremediation potential of CB1 on Cd²⁺ and diesel.

Emission characteristics of benzene series in FCC flue gas

Benzene series are considered as air pollutants in refineries. However, the emissions of benzene series in fluid catalytic cracking (FCC) flue gas are poorly understand. In this work, we conduct stack tests on three typical FCC units. Benzene series, including benzene, toluene, xylene and ethyl benzene, are monitored in the flue gas. It shows that the coking degree of the spent catalysts affect the emissions of benzene series significantly, and there are four kinds of carbon-containing precursors in the spent catalyst. A fixed-bed reactor is used to conduct the regeneration simulation experiments, and the flue gas is monitored by TG-MS and FTIR. The emissions of toluene and ethyl benzene are mainly emitted in the early and middle stage of the reaction (250-650 °C), while the emission of benzene is mainly detected in the middle and late stage of the reaction (450-750 °C). Xylene group is not detected in the stack tests and regeneration experiments. Higher emissions of benzene series are released from the spent catalyst with lower C/H ratio during regeneration process. With the increase of oxygen content, the emissions of benzene series decrease, and the initial emission temperature is advanced. These insights can improve the refinery's awareness and control of benzene series in the future.

Sorption of organic contaminants by biochars with multiple porous structures: Experiments and molecular dynamics simulations mediated by three-dimensional models

Interactions between organic pollutants and carbon-based particles are critical for understanding and predicting the fate of organic contaminants in the environment. However, traditional modeling concepts did not consider three-dimensional (3-D) structures of carbon-based materials. This prevents a deep understanding of the sequestration of organic pollutants. Therefore, this study revealed interactions between organics and biochars by combining experimental measurements and molecular dynamics simulations. Biochars displayed the best and worst sorption performances for naphthalene (NAP) and benzoic acid (BA), respectively, among the five adsorbates. The kinetic model fitting suggested that biochar pores played a vital role during sorption and led to the fast and slow sorption of organics on the biochar surface and in pores, respectively. Active sites on the biochar surface predominantly sorbed organics. Organics were only sorbed in pores when the surface's active sites were fully occupied. These results can guide the development of efficient organic pollution control strategies to protect human health and improve ecological security.

Ecological and human health risk assessment of polycyclic aromatic hydrocarbons (PAH) in Tigris river near the oil refineries in Iraq

Recent Iraqi battles against ISIS in 2014 and 2015 resulted in the destruction or severe damage to several refineries' infrastructure. This, along with other factors, has led to the release and accumulation of a wide range of hazardous chemicals into the environment, for instance, polycyclic aromatic hydrocarbons (PAH). Thus, for the first time, a comprehensive 16 PAHs measurements campaign over the course of six months near the oil refineries along the Tigris River and its estuaries was investigated. The 16 PAHs concentrations in surface water and the sediments for the following oil refineries: Baiji, Kirkuk, Al-Siniyah, Qayyarah, Al-Kasak, Daura, South Refineries Company, and Maysan were examined. The overall findings indicated that the 16 PAHs concentrations ranged from 567.8 to 3750.7 ng/L for water and 5619.2-12795.0 ng/g for sediment. Water samples in South Refineries Company recorded the highest PAH concentrations while Baiji oil refinery registered the highest PAH concentrations in the sediment samples. The percentages of high molecular weight PAH (5-6 rings) in water and sediment samples were the highest, ranging from 49.41% to 81.67% and from 39.06% to 89.39% of total PAH for water and sediment, respectively. The majority of 16 PAHs measured in water and sediment samples of the Tigris River were derived from pyrogenic sources. Based on sediment quality guidelines (SQGs), most sites showed a possible effect range with occasional biological effects of most of the PAH concentrations in all sediments' samples. The calculated incremental lifetime cancer risk (ILCR) value was high risk with adverse health effects, including cancer.

Bioengineering for the Microbial Degradation of Petroleum Hydrocarbon Contaminants

Petroleum hydrocarbons are relatively recalcitrant compounds, and as contaminants, they are one of the most serious environmental problems. n-Alkanes are important constituents of petroleum hydrocarbons. Advances in synthetic biology and metabolic engineering strategies have made n-alkane biodegradation more designable and maneuverable for solving environmental pollution problems. In the microbial degradation of n-alkanes, more and more degradation pathways, related genes, microbes, and alkane hydroxylases have been discovered, which provide a theoretical basis for the further construction of degrading strains and microbial communities. In this review, the current advances in the microbial degradation of n-alkanes under aerobic condition are summarized in four aspects, including the biodegradation pathways and related genes, alkane hydroxylases, engineered microbial chassis, and microbial community. Especially, the microbial communities of “Alkane-degrader and Alkane-degrader” and “Alkane-degrader and Helper” provide new ideas for the degradation of petroleum hydrocarbons. Surfactant producers and nitrogen providers as a “Helper” are discussed in depth. This review will be helpful to further achieve bioremediation of oil-polluted environments rapidly.

Degradation of alkane hydrocarbons by Priestia megaterium ZS16 and sediments consortia with special reference to toxicity and oxidative stress induced by the sediments in the vicinity of an oil refinery

Petroleum hydrocarbon is a critical ecological issue with impact on ecosystems through bioaccumulation. It poses significant risks to human health. Due to the extent of alkane hydrocarbon pollution in some environments, biosurfactants are considered as a new multifunctional technology for the efficient removal of petroleum-based contaminants. To this end, Yamuna river sediments were collected at different sites in the vicinity of Mathura oil refinery, UP (India). They were analysed by atomic absorption spectrophotometry and gas chromatography-mass spectrometry (GC-MS) for heavy metals and organic pollutants. Heptadecane, nonadecane, oleic acid ester and phthalic acid were detected. In total 107 bacteria were isolated from the sediments and screened for biosurfactant production. The most efficient biosurfactant producing strain was tested for its capability to degrade hexadecane efficiently at different time intervals (0 h, 7 d, 14 d and 21 d). FT-IR analysis defined the biosurfactant as lipopeptide. 16S rRNA gene sequencing identified the bacterium as Priestia megaterium. The strain lacks resistance to common antibiotics thus making it an important candidate for remediation. The microbial consortia present in the sediments were also investigated for their capability to degrade C₁₆, C₁₇ and C₁₈ alkane hydrocarbons. By using gas chromatography-mass spectrophotometry the metabolites were identified as 1-docosanol, dodecanoic acid, 7-hexadecenal, (Z)-, hexadecanoic acid, docosanoic acid, 1-hexacosanal, 9-octadecenoic acid, 3-octanone, Z,Z-6,28-heptatriactontadien-2-one, heptacosyl pentafluoropropionate, 1,30-triacontanediol and decyl octadecyl ester. Oxidative stress in Vigna radiata L. roots was observed by using Confocal Laser Scanning Microscopy. A strong reduction in seed germination and radicle and plumule length was observed when Vigna radiata L. was treated with different concentrations of sediment extracts, possibly due to the toxic effects of the pollutants in the river sediments. Thus, this study is significant since it considers the toxicological effects of hydrocarbons and to degrade them in an environmentally friendly manner.

Competitive interactions between culturable bacteria are highly non-additive

Microorganisms are found in diverse communities whose structure and function are determined by interspecific interactions. Just as single species seldom exist in isolation, communities as a whole are also constantly challenged and affected by external species. Though much work has been done on characterizing how individual species affect each other through pairwise interactions, the joint effects of multiple species on a single (focal) species remain underexplored. As such, it is still unclear how single-species effects combine to a community-level effect on a species of interest. To explore this relationship, we assayed thousands of communities of two, three, and four bacterial species, measuring the effect of single, pairs of, and trios of 61 affecting species on six different focal species. We found that when multiple species each have a negative effect on a focal species, their joint effect is typically not given by the sum of the effects of individual affecting species. Rather, they are dominated by the strongest individual-species effect. Therefore, while joint effects of multiple species are often non-additive, they can still be derived from the effects of individual species, making it plausible to map complex interaction networks based on pairwise measurements. This finding is important for understanding the fate of species introduced into an occupied environment and is relevant for applications in medicine and agriculture, such as probiotics and biocontrol agents, as well as for ecological questions surrounding migrating and invasive species.

Tricks and tracks in waste management with a special focus on municipal landfill leachate: Leads and obstacles

Landfilling is the most widely used disposal method for municipal solid waste around the world. The main disadvantage of this strategy is formation of leachate, among other aspects. Landfill leachate contains highly toxic and bio-refractory substances that are detrimental to the environment and human health. Hence, the risk(s) of discharging potentially harmful landfill leachate into the environment need to be assessed and measured in order to make effective choices about landfill leachate management and treatment. In view of this, the present review aims to investigate (a) how landfill leachate is perceived as an emerging concern, and (b) the stakeholders' mid- to long-term policy priorities for implementing technological and integrative solutions to reduce the harmful effects of landfill leachate. Because traditional methods alone have been reported ineffective, and in response to emerging contaminants and stringent regulations, new effective and integrated leachate treatments have been developed. This study gives a forward-thinking of the accomplishments and challenges in landfill leachate treatment during the last decade. It also provides a comprehensive compilation of the formation and characterization of landfill leachate, the geo-environmental challenges that it raises, as well as the resource recovery and industrial linkage associated with it in order to provide an insight into its sustainable management.

Impact of Atmospheric Polycyclic Aromatic Hydrocarbons (PAHs) of Falling Dust in Urban Area Settings: Status, Chemical Composition, Sources and Potential Human Health Risks

The present work is considered to investigate the sources, concentration, and composition of polycyclic aromatic hydrocarbons (PAHs) and associated health risk assessment of road dust in Riyadh City, Saudi Arabia. The study region included an urban area, strongly affected by traffic, a bare and an industrial area. A total of 50 locations were selected for sampling and 16 different PAHs were determined. The concentration of PAHs in road dust and their estimated lifetime average daily dose (LADD) for adults (human) ranged from 0.01 to 126 ng g−1 and 1950 to 16,010 mg kg−1 day−1, respectively. The ADDing was calculated separately for children (>6), teenagers (6−12), and adults (>12) for all PAHs with each collected sample. Moreover, the average daily exposure dose by ingestion (ADDing) and average daily exposure dose by dermal absorption (ADDder) were more in children (<6 years) as compared to teenagers (6−12 years) and adults (>12 years). Likewise, total equivalency factor based on BaP (TEQBaP) calculations pointed out that PAHs having more benzene rings or having high molecular weight showed high TEQBaP as compared to low molecular weight PAHs. The data revealed that the children population is at high risk for asthma, respiratory and cardiovascular diseases, and immunity suppression as compared to adults in the particular area of investigated region. These outcomes of this study can be used to deliver significant policy guidelines concerning habitants of the area for possible measures for controlling PAHs contamination in Riyadh City to protect human health and to ensure environmental sustainability.

Comparative chemical analysis, mutagenicity, and genotoxicity of Petroleum refinery wastewater and its contaminated river using prokaryotic and eukaryotic assays

Concern on the toxicity of final wastewater generated by the petroleum refining industry has increased in recent years due to the potential health threats associated with their release into the waterways. This study determined the mutagenic and genotoxic potential of petroleum refinery wastewater and a receiving river using the Ames fluctuation test on Salmonella typhimurium strains TA100 and TA98, SOS chromotest on Escherichia coli PQ37, and piscine peripheral micronucleus (MN) assay. Analyses of the physicochemical parameters, heavy metal, and organic contents of the samples were also performed. Ames test result showed that the two tested samples were mutagenic with TA100 strain as the more responsive strain for both the refinery wastewater and the river sample in terms of the calculated mutagenic index. A similar result was obtained in the SOS chromotest; however, the E. coli PQ37 system recorded a slightly higher sensitivity for detecting genotoxins than the Salmonella assay in the two samples. MN data showed induction of a concentration-dependent significant (p < 0.05) increase in the frequency of MN by both samples when compared with the negative control. Generally, the refinery wastewater induced the highest mutagenicity and genotoxicity compared to the river sample in the three assays used. Haemoglobin, platelets, red blood cells, mean corpuscular volume, total white blood cells, heterophils, haematocrit, and eosinophils reduced significantly with increased lymphocytes, basophils, mean corpuscular haemoglobin, and mean corpuscular haemoglobin concentration in fishes exposed to both samples. Total petroleum hydrocarbon, benzene, toluene, phenol index, polycyclic aromatic hydrocarbons, cadmium, mercury, nickel, lead, and vanadium contents analysed in the samples were believed to be responsible for the observed genotoxicity and mutagenicity. The findings of this study revealed that petroleum refinery wastewater is a potential mutagenic and genotoxic risk to the environment.

Soft Magnetic Microrobots for Photoactive Pollutant Removal

"Soft" robotics based on hydrogels appears as an alternative to the traditional technology of "hard" robotics. Soft microrobots are employed for drug delivery and cell manipulation. This work develops magnetic hydrogel-based microrobots using chitosan (CHI) as the body of the micromotor and Fe₃ O₄ nanoparticles to allow for its magnetic actuation. In addition, ZnO nanoparticles are incorporated inside the CHI body of the microrobot to act as an active component for pollutants photodegradation. CHI@Fe₃ O₄ -ZnO microrobots are used for the efficient photodegradation of persistent organic pollutants (POPs). The high absorption of CHI hydrogel enhances the POP photodegradation, degrading it 75% in just 30 min. The adsorption-degradation and magnetic properties of CHI@Fe₃ O₄ -ZnO microrobots are used in five cycles while maintaining up to 60% photodegradation efficiency. The proof-of-concept present in this work represents a simple way to obtain soft microrobots with magnetic actuation and photodegradation functionalities for several water purification applications.

Petroleum refinery effluent contribution to chemical mixture toxic pressure in the environment

Petroleum refinery effluents (PRE) are wastewaters from industries associated with oil refining. Within Europe, PREs are regulated through local discharge permits and receive substantial treatment before emission. After treatment, PREs can still contain low levels of various pollutants potentially toxic to organisms. Earlier work, including whole-effluent toxicity assessments, has shown that the toxicity of permitted PREs is often limited. However, the extent to which PREs contribute to chemical pollution already present in the receiving environment is unknown. Therefore, our study aimed to assess the contribution of PREs to mixture toxic pressure in the environment, using the multi-substance potentially affected fraction of species (msPAF) as an indicator. Based on measured chemical concentrations, compiled species sensitivity distributions (SSD) and a mechanistic solubility model, msPAF levels were estimated for undiluted effluents at discharge points and diluted effluents downstream in receiving waters. Median msPAF-chronic and msPAF-acute levels of PREs at discharge points were 74% (P50) and 40% (P95), respectively. The calculated msPAF levels were reduced substantially to <5% downstream for most effluents (82%), indicating low to negligible toxicity of PREs in receiving environments beyond the initial mixing zone. Regardless of differences in endpoints and locations, hydrocarbons (mainly total petroleum hydrocarbons) and inorganics (mainly ammonia) explained at least 85% of the mixture toxic pressure. The msPAF levels of PREs were on average 2.5-4.5 orders of magnitude lower than msPAF levels derived from background pollution levels, suggesting that PREs were minor contributors to the toxic pressure in the environment. This study presents a generic methodology for quantifying the potential toxic pressure of PREs in the environment, identifying hotspots where more effective wastewater treatment could be needed. We explicitly discuss the uncertainties for further refinement and development of the method.

Patent mining on soil pollution remediation technology from the perspective of technological trajectory

Recent years have seen a marked growth in soil environmental problems, however, the research & development (R&D) direction of soil pollution remediation technology (SPRT) for addressing related challenges to the global ecosystem is still unclear. Patent is the most effective carrier of technological information. Therefore, this study investigates the status and future direction of SPRT through the analysis and mining of 14,475 patents from 1971 to 2020. In 2006-2020, 14,435 SPRT patents (79% of the total) were published, which is in the development stage. By measuring the proportion of high-value patents, determined by the ratio of the number of patent families containing two or more patents (PF2) to that containing at least one patent (PF1), we found that United States (PF2/PF1 = 0.711), Japan (PF2/PF1 = 0.500), and South Korea (PF2/PF1 = 0.431) hold a monopoly. International patent organizations serve as a bridge for technology transfer. Patent CN101947539-A measured by structural hole index (Effective size = 98.194, Efficiency = 0.926) has the most significant technological influence. Therefore, in order to accomplish the technological transition and improve the soil remediation capacity, more attention should be paid to the microbial-assisted phytoremediation technology related to inorganic pollutants, hyperaccumulators and stabilizers. Additionally, patents CN102834190-A (Effective size = 23.930, Efficiency = 0.855, Constraint = 0.141, Hierarchy = 0.089) and CN105855289 (Effective size = 21.453, Efficiency = 0.795 Constraint = 0.149, Hierarchy = 0.086) are both at the location of structural holes. So, more research should be carried out on green and cost-effective solutions for reducing organic pollutants in soil remediation. The current study identifies opportunities for innovations and breakthroughs in SPRT and offers relevant information on technological development prospects.

Use of Taguchi design for optimization of diesel-oil biodegradation using consortium of Pseudomonas stutzeri, Cellulosimicrobium cellulans, Acinetobacter baumannii and Pseudomonas balearica isolated from tarball in Terengganu Beach, Malaysia

A consortium of bacteria capable of decomposing oily hydrocarbons was isolated from tarballs on the beaches of Terengganu, Malaysia, and classified as Pseudomonas stutzeri, Cellulosimicrobium cellulans, Acinetobacter baumannii and Pseudomonas balearica. The Taguchi design was used to optimize the biodegradation of diesel using these bacteria as a consortium. The highest biodegradation of diesel-oil in the experimental tests was 93.6%, and the individual n-alkanes decomposed 87.6-97.6% over 30 days. Optimal settings were inoculum size of 2.5 mL (1.248 OD_600nm); 12% (v/v) the initial diesel-oil in a minimal salt medium of pH 7.0, 30.0 gL^-1 NaCl and 2.0 gL^-1 NH₄NO₃ concentration, incubated at 42 °C temperature and 150 rpm agitation speed. Parameters significantly improved diesel-oil removal by consortium as shown by the model determination coefficient (R² = 90.89%; P < 0.001) with a synergistic effect of agitation speed significantly contributing 81.03%. Taguchi design determined the optimal settings for the parameters under study, which significantly improved diesel-oil removal by consortium. This can be used to design a novel bioremediation strategy that can achieve optimal decontamination of oil pollution in a shorter time.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s40201-022-00812-3.

Spatial distribution, composition, and source analysis of petroleum pollutants in soil from the Changqing Oilfield, Northwest China

Petroleum contamination surrounding oilfields has attracted more concerns. However, the levels, distribution and source of petroleum of Changqing Oilfield soil still remain lots of knowns, which is important for local environmental protection. Given soil contamination issues in Changqiong Oilfield were investigated. The maximum concentrations of total petroleum hydrocarbons (TPHs), N-alkanes (TNAs) and polycyclic aromatic hydrocarbons (PAHs) were determined to be 1960.29, 96.13 and 0.82 mg/kg, respectively. TPHs were higher in the north than the south of the study area. TPHs decreased in the horizontal and vertical distribution as soil depth and distance from oil wells increased. Source analysis showed that TNAs mainly originated from petroleum, PAHs were controlled by petroleum spills, combustion and traffic. Correlation analysis implied that TPHs residues had an effect on soil environmental quality. This study have important implications for understanding the environmental behavior of petroleum and can provide support for petroleum remediation and risk control.

Prospective review on bioelectrochemical systems for wastewater treatment: Achievements, hindrances and role in sustainable environment

Bioelectrochemical systems (BESs) are a relatively new arena for producing bioelectricity, desalinating sea water, and treating industrial effluents by removing organic matter. Microbial electrochemical technologies (METs) are promising for obtaining value-added products during simultaneous remediation of pollutants from wastewater. The search for more affordable desalination technology has led to the development of microbial desalination cells (MDCs). MDC combines the operation of microbial fuel cells (MFC) with electrodialysis for water desalination and energy generation. It has received notable interest of researchers in desalination and wastewater treatment because of low energy requirement and eco-friendly nature. Firstly, this article provides a brief overview of MDC technology. Secondly, factors affecting functioning of MDC and its applications have been accentuated. Additionally, challenges and future outlook on the development of this technology have been delineated. State-of-the-art information provided in this review would expand the scope of interdisciplinary and translational research.

Pollution pressure and soil depth drive prokaryotic microbial assemblage and co-occurrence patterns in an organic polluted site

Organic polluted sites have become a global concern of soil contamination, yet little is known about microbial vertical distribution and community assembly in organic polluted sites. Here, high-throughput sequencing technology was employed to investigate prokaryotic microbial diversity and community assembly along soil profile in an abandoned chemical organic contaminated site. Results showed that there was no significant difference (P > 0.05) observed in microbial alpha diversity among different soil layers, whereas the structure of microbial communities presented significantly different (P < 0.05) in the superficial layer (0-0.5 m) compared with intermediate (1-1.5 m) and bottom (2.5-3 m) layers. Soil prokaryotic microbial community evolved to possess the potential of degrading organic pollutants under long-term organic pollution stress. A relatively homogeneous environment created by the organic polluted site mainly induced the ecological process of homogeneous selection driving community assembly, while dispersal limitation gained importance with the increase of soil depth. Organic contaminants were identified as the key driver of destabilizing co-occurrence networks, while the frequent cooperative behaviors among species could combat organic pollution stress and sustain prokaryotic community stability. Collectively, pollution pressure and soil depth jointly affected prokaryotic microbial assemblage and co-occurrence that underpinned the spatial scaling patterns of organic contaminated sites microbiota.

New Insights in factors affecting ground water quality with focus on health risk assessment and remediation techniques

Groundwater is considered as the primary source of water for the majority of the world's population. The preponderance of the nation's drinking water, as well as agricultural and industrial water, comes from groundwater. Groundwater level is becoming increasingly challenging to replenish due to climate change. Fertilizer application and improper processing of industrial waste are the two major anthropogenic drivers of groundwater pollution. Arsenic and cadmium are two of the principal heavy metal pollutants that have affected groundwater quality by human activity. When people are exposed to both non-carcinogenic and carcinogenic contaminants for an extended period, toxic effects might occur. It can have detrimental health effects from long-term exposure to contaminants, even in low amounts. As a result, metal contamination concentrations and fractions can be used to determine potential health concerns. At the same time, contaminants also need to be removed or converted to harmless products by groundwater remediation. Remediation of groundwater quality can be accomplished in several ways, including natural and artificial means. The purpose of this review is to explore a wide range of factors that affect groundwater quality, including their possible health effects. This communication provides state-of-the-art information about remediation approaches for groundwater contamination including hindrances and perspectives in this area of research. The in-depth information provided in different sections of this communication would expand the scope of interdisciplinary research.

Exploring the Function of Quorum Sensing Regulated Biofilms in Biological Wastewater Treatment: A Review

Quorum sensing (QS), a type of bacterial cell–cell communication, produces autoinducers which help in biofilm formation in response to cell population density. In this review, biofilm formation, the role of QS in biofilm formation and development with reference to biological wastewater treatment are discussed. Autoinducers, for example, acyl-homoserine lactones (AHLs), auto-inducing oligo-peptides (AIPs) and autoinducer 2, present in both Gram-negative and Gram-positive bacteria, with their mechanism, are also explained. Over the years, wastewater treatment (WWT) by QS-regulated biofilms and their optimization for WWT have gained much attention. This article gives a comprehensive review of QS regulation methods, QS enrichment methods and QS inhibition methods in biological waste treatment systems. Typical QS enrichment methods comprise adding QS molecules, adding QS accelerants and cultivating QS bacteria, while typical QS inhibition methods consist of additions of quorum quenching (QQ) bacteria, QS-degrading enzymes, QS-degrading oxidants, and QS inhibitors. Potential applications of QS regulated biofilms for WWT have also been summarized. At last, the knowledge gaps present in current researches are analyzed, and future study requirements are proposed.

Migration Behavior and Influencing Factors of Petroleum Hydrocarbon Phenanthrene in Soil around Typical Oilfields of China

Petroleum spills and land contamination are becoming increasingly common around the world. Polycyclic aromatic hydrocarbons (PAHs) and other pollutants found in petroleum are constantly migrating underground, making their migration in soil a hot research topic. Therefore, it is of great significance to evaluate the migratory process of petroleum hydrocarbons in petroleum-polluted soil to clarify its ecological and environmental risks. In this study, Phenanthrene (PHE) was used as a typical pollutant of PAHs. The soil was gathered from three typical oilfields in China, and a soil column apparatus was built to simulate the vertical migration of PHE in the soil. The migration law and penetration effect of PHE in various environmental conditions of soil were investigated by varying the ionic strength (IS), pH, particle size, and type of soil. According to the literature, pH has no discernible effect on the migration of PHE. The migration of PHE was adversely and positively linked with changes in IS and soil particle size, respectively. The influence of soil type was mainly manifested in the difference of organic matter and clay content. In the Yanchang Oilfield (YC) soil with the largest soil particle size and the least clay content, the mobility of PHE was the highest. This study may reveal the migration law of PAHs in soils around typical oilfields, establish a new foundation for PAH migration in the soil, and also provide new ideas for the management and control of petroleum pollution in the soil and groundwater.

Nano-remediation technologies for the sustainable mitigation of persistent organic pollutants

The absence of novel and efficient methods for the elimination of persistent organic pollutants (POPs) from the environment is a serious concern in the society. The pollutants release into the atmosphere by means of industrialization and urbanization is a massive global hazard. Although, the eco-toxicity associated with nanotechnology is still being debated, nano-remediation is a potentially developing tool for dealing with contamination of the environment, particularly POPs. Nano-remediation is a novel strategy to the safe and long-term removal of POPs. This detailed review article presents an important perspective on latest innovations and future views of nano-remediation methods used for environmental decontamination, like nano-photocatalysis and nanosensing. Different kinds of nanomaterials including nanoscale zero-valent iron (nZVI), carbon nanotubes (CNTs), magnetic and metallic nanoparticles, silica (SiO₂) nanoparticles, graphene oxide, covalent organic frameworks (COFs), and metal organic frameworks (MOFs) have been summarized for the mitigation of POPs. Furthermore, the long-term viability of nano-remediation strategies for dealing with legacy contamination was considered, with a particular emphasis on environmental and health implications. The assessment goes on to discuss the environmental consequences of nanotechnology and offers consensual recommendations on how to employ nanotechnology for a greater present and a more prosperous future.

Current technologies and future perspectives for the treatment of complex petroleum refinery wastewater: A review

Petroleum refinery wastewater (PRW) is a complex mixture of hydrocarbons, sulphides, ammonia, oils, suspended and dissolved solids, and heavy metals. As these pollutants are toxic and recalcitrant, it is essential to address the above issue with efficient, economical, and eco-friendly technologies. In this review, initially, an overview of the characteristics of wastewater discharged from different petroleum refinery units is discussed. Further, various pre-treatment and post-treatment strategies for complex PRW are introduced. A segregated approach has been proposed to treat the crude desalting, sour, spent caustic, and oily wastewater of petroleum refineries. The combined systems (e.g., ozonation + moving bed biofilm reactor and photocatalysis + packed bed biofilm reactor) for the treatment of low biodegradability index wastewater (BOD₅/COD < 0.2) were discussed to construct a perspective map and implement the proposed system efficiently. The economic, toxicity, and biodegradability aspects are also introduced, along with research gaps and future scope.

Sustainable management of municipal solid waste through waste-to-energy technologies

Increasing municipal solid waste (MSW) generation and environmental concerns have sparked global interest in waste valorization through various waste-to-energy (WtE) to generate renewable energy sources and reduce dependency on fossil-derived fuels and chemicals. These technologies are vital for implementing the envisioned global "bioeconomy" through biorefineries. In light of that, a detailed overview of WtE technologies with their benefits and drawbacks is provided in this paper. Additionally, the biorefinery concept for waste management and sustainable energy generation is discussed. The identification of appropriate WtE technology for energy recovery continues to be a significant challenge. So, in order to effectively apply WtE technologies in the burgeoning bioeconomy, this review provides a comprehensive overview of the existing scenario for sustainable MSW management along with the bottlenecks and perspectives.

Biochar production with amelioration of microwave-assisted pyrolysis: Current scenario, drawbacks and perspectives

In recent years, biomass has been reported to obtain a wide range of value-added products. Biochar can be obtained by heating biomass, which aids in carbon sinks, soil amendments, resource recovery, and water retention. Microwave technology stands out among various biomass heating technologies not only for its effectiveness in biomass pyrolysis for the production of biochar and biofuel but also for its speed, volumetrics, selectivity, and efficiency. The features of microwave-assisted biomass pyrolysis and biochar are briefly reviewed in this paper. An informative comparison has been drawn between microwave-assisted pyrolysis and conventional pyrolysis. It focuses mainly on technological and economic scenario of biochar production and environmental impacts of using biochar. This source of knowledge would aid in the exploration of new possibilities and scope for employing microwave-assisted pyrolysis technology to produce biochar.

Performance evaluation of rhamnolipids addition for the biodegradation and bioutilization of petroleum pollutants during the composting of organic wastes with waste heavy oil

Environmental pollution caused by petroleum hydrocarbons is being paid more and more attention worldwide. Surfactants are able to improve the solubility of petroleum hydrocarbons, but their effects on petroleum hydrocarbon degradation in composting systems are still unclear. In this study, the effects on microbial community succession were investigated by adding petroleum hydrocarbons and rhamnolipids during composting of organic wastes. The results showed that the compost and the addition of rhamnolipids could effectively reduce the petroleum hydrocarbon content with an efficiency of 73.52%, compared to 53.81% for the treatment without addition. Network analyses and Structural Equation Model suggested that there were multiple potential petroleum degraders microbes that might be regulated by nitrogen. The findings in this study can also provide an implication for the treatment of petroleum hydrocarbon pollutants from oil-polluted soil, and the technology can be potentially applied on an industrial scale in practice.

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Effects of rhamnolipids on the removal of petroleum hydrocarbons were investigated

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The relationship between PDM, APDM, and environmental factors was revealed

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There was a significant correlation between nitrogen and PDM and APDM

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Rhamnolipids are bio-resources for effectively removing petroleum hydrocarbons

Rhodococcus oxybenzonivorans sp. nov., a benzophenone-3-degrading bacterium, isolated from stream sediment

A Gram-stain-positive, facultative aerobic, oxidase-negative, catalase-positive, non-sporulating, and non-motile bacterium, which degraded benzophenone-3, was isolated from stream sediment collected in the Republic of Korea and designated as strain S2-17T. Cells of this strain were rod-shaped during the early growth phase but became coccoid after the late exponential growth phase. Bacterial growth was observed at 15–37 °C (optimum, 25–30 °C) and pH 6.0–9.5 (optimum, pH 7.5–8.5) and in the presence of 0–9.0 % (w/v) NaCl (optimum, 0–1.0 %). Menaquinone-8 (H2) was the sole isoprenoid quinone, and C16 : 0, C17 : 1  ω8c, summed feature 3 (comprising C16 : 1  ω7c/C16 : 1  ω6c) and C18 : 1  ω9c were the major fatty acids. The cell wall of strain S2-17T contained meso-diaminopimelic acid, and arabinose, galactose and mycolic acid were found in whole-cell hydrolysates, suggesting a chemotype IV cell wall. The G+C content of the genome was 65.6 mol%. Phylogenetic analyses revealed that strain S2-17T formed a phyletic lineage within the genus Rhodococcus and was most closely related to Rhodococcus jostii DSM 44719T (99.2 % 16S rRNA gene sequence similarity). Average nucleotide identity and digital DNA–DNA hybridization values between strain S2-17T and R. jostii DSM 44719T were 82.6 and 26.5 %, respectively, indicating differences between the species. Based on its phenotypic, chemotaxonomic and molecular features, strain S2-17T represents a novel species of the genus Rhodococcus , for which the name Rhodococcus oxybenzonivorans sp. nov. is proposed. The type strain is S2-17T (=KACC 19281T=JCM 32046T).

Nontarget Screening Exhibits a Seasonal Cycle of PM2.5 Organic Aerosol Composition in Beijing

The molecular composition of atmospheric particulate matter (PM) in the urban environment is complex, and it remains a challenge to identify its sources and formation pathways. Here, we report the seasonal variation of the molecular composition of organic aerosols (OA), based on 172 PM_2.5 filter samples collected in Beijing, China, from February 2018 to March 2019. We applied a hierarchical cluster analysis (HCA) on a large nontarget-screening data set and found a strong seasonal difference in the OA chemical composition. Molecular fingerprints of the major compound clusters exhibit a unique molecular pattern in the Van Krevelen-space. We found that summer OA in Beijing features a higher degree of oxidation and a higher proportion of organosulfates (OSs) in comparison to OA during wintertime, which exhibits a high contribution from (nitro-)aromatic compounds. OSs appeared with a high intensity in summer-haze conditions, indicating the importance of anthropogenic enhancement of secondary OA in summer Beijing. Furthermore, we quantified the contribution of the four main compound clusters to total OA using surrogate standards. With this approach, we are able to explain a small fraction of the OA (∼11-14%) monitored by the Time-of-Flight Aerosol Chemical Speciation Monitor (ToF-ACSM). However, we observe a strong correlation between the sum of the quantified clusters and OA measured by the ToF-ACSM, indicating that the identified clusters represent the major variability of OA seasonal cycles. This study highlights the potential of using nontarget screening in combination with HCA for gaining a better understanding of the molecular composition and the origin of OA in the urban environment.

Carbon-based catalyst for environmental bioremediation and sustainability: Updates and perspectives on techno-economics and life cycle assessment

Global rise in the generation of waste has caused an enormous environmental concern and waste management problem. The untreated carbon rich waste serves as a breeding ground for pathogens and thus strategies for production of carbon rich biochar from waste by employing different thermochemical routes namely hydrothermal carbonization, hydrothermal liquefaction and pyrolysis has been of interest by researchers globally. Biochar has been globally produced due to its diverse applications from environmental bioremediation to energy storage. Also, several factors affect the production of biochar including feedstock/biomass type, moisture content, heating rate, and temperature. Recently the application of biochar has increased tremendously owing to the cost effectiveness and eco-friendly nature. Thus this communication summarized and highlights the preferred feedstock for optimized biochar yield along with the factor influencing the production. This review provides a close view on biochar activation approaches and synthesis techniques. The application of biochar in environmental remediation, composting, as a catalyst, and in energy storage has been reviewed. These informative findings were supported with an overview of lifecycle and techno-economical assessments in the production of these carbon based catalysts. Integrated closed loop approaches towards biochar generation with lesser/zero landfill waste for safeguarding the environment has also been discussed. Lastly the research gaps were identified and the future perspectives have been elucidated.

Elucidating the biodegradation pathway and catabolic genes of benzophenone-3 in Rhodococcus sp. S2-17

A new bacterium, Rhodococcus sp. S2-17, which could completely degrade an emerging organic pollutant, benzophenone-3 (BP-3), was isolated from contaminated sediment through an enrichment procedure, and its BP-3 catabolic pathway and genes were identified through metabolic intermediate and transcriptomic analyses and biochemical and genetic studies. Metabolic intermediate analysis suggested that strain S2-17 may degrade BP-3 using a catabolic pathway progressing via the intermediates BP-1, 2,4,5-trihydroxy-benzophenone, 3-hydroxy-4-benzoyl-2,4-hexadienedioic acid, 4-benzoyl-3-oxoadipic acid, 3-oxoadipic acid, and benzoic acid. A putative BP-3 catabolic gene cluster including cytochrome P450, flavin-dependent oxidoreductase, hydroxyquinol 1,2-dioxygenase, maleylacetate reductase, and α/β hydrolase genes was identified through genomic and transcriptomic analyses. Genes encoding the cytochrome P450 complex that demethylates BP-3 to BP-1 were functionally verified through protein expression, and the functions of the other genes were also verified through knockout mutant construction and intermediate analysis. This study suggested that strain S2-17 might have acquired the ability to catabolize BP-3 by recruiting the cytochrome P450 complex and α/β hydrolase, which hydrolyzes 4-benzoyl-3-oxoadipic acid to benzoic acid and 3-oxoadipic acid, genes, providing insights into the recruitment of genes of for the catabolism of emerging organic pollutants.

Organic solid waste: Biorefinery approach as a sustainable strategy in circular bioeconomy

Waste generation is associated with numerous environmental consequences, making it a point of discussion in the environmental arena. Efforts have been made around the world to develop a systematic management approach coupled with a sustainable treatment technology to maximize resource utilization of organic solid waste. Biorefineries and bio-based products play a critical role in lowering total emissions and supporting energy systems. However, economic viability of biorefineries, on the other hand, is a stumbling hurdle to their commercialization. This communication provides a thorough study of the concept of biorefinery in waste management, as well as technological advancements in this field. In addition, the notion of techno-economic assessment, as well as challenges and future prospects have been covered. To find the most technologically and economically viable solution, further techno-economic study to the new context is required. Overall, this communication would assist decision-makers in identifying environmentally appropriate biorefinery solutions ahead of time.

Municipal solid waste management: Dynamics, risk assessment, ecological influence, advancements, constraints and perspectives

Global energy consumption has been increasing in tandem with economic growth, putting pressure on the world's supply of renewable energy sources. Municipal Solid waste (MSW) has been reported contributing immensely to the improvement of a secure environment and renewable sources. Energy scarcity and conventional MSW disposal methods in developing countries lead towards many environmental and economic issues. Scientists have been able to experiment with various waste-to-energy conversion technologies in light of this situation. This communication highlights and reviews WtE technologies to convert MSW and other feedstocks into electricity, hydrogen gas, bioethanol along with other value added products like fertilizer(s), platform chemicals as an environmentally friendly products. This review comprehensively summarized the dynamics, risk assessment, ecological influence, advancements, constraints and perspectives altogether in field of municipal solid waste management and treatment. Stare-of-the-art information on ecological influence and risk assessment in handling and transportation of municipal solid waste has been provided. Advanced trends involved in remediation of emerging pollutants and resources obtained from municipal solid wastes have been uncovered. Lastly, this paper comprises constraints and perspectives for uncovering MSW based circular bioeconomy aspects.

Trends in mitigation of industrial waste: Global health hazards, environmental implications and waste derived economy for environmental sustainability

Majority of industries, in order to meet the technological development and consumer demands generate waste. The untreated waste spreads out toxic and harmful substances in the environment which serves as a breeding ground for pathogenic microorganisms thus causing severe health hazards. The three industrial sectors namely food, agriculture, and oil industry are among the primary organic waste producers that affect urban health and economic growth. Conventional treatment generates a significant amount of greenhouse gases which further contributes to global warming. Thus, the use of microbes for utilization of this waste, liberating CO₂ offers an indispensable tool. The simultaneous production of value-added products such as bioplastics, biofuels, and biosurfactants increases the economics of the process and contributes to environmental sustainability. This review comprehensively summarized the composition of organic waste generated from the food, agriculture, and oil industry. The linkages between global health hazards of industrial waste and environmental implications have been uncovered. Stare-of-the-art information on their subsequent utilization as a substrate to produce value-added products through bio-routes has been elaborated. The research gaps, economical perspective(s), and future research directions have been identified and discussed to strengthen environmental sustainability.

Exploring the role of microbial biofilm for industrial effluents treatment

Biofilm formation on biotic or abiotic surfaces is caused by microbial cells of a single or heterogeneous species. Biofilm protects microbes from stressful environmental conditions, toxic action of chemicals, and antimicrobial substances. Quorum sensing (QS) is the generation of autoinducers (AIs) by bacteria in a biofilm to communicate with one other. QS is responsible for the growth of biofilm, synthesis of exopolysaccharides (EPS), and bioremediation of environmental pollutants. EPS is used for wastewater treatment due to its three-dimensional matrix which is composed of proteins, polysaccharides, humic-like substances, and nucleic acids. Autoinducers mediate significantly the degradation of environmental pollutants. Acyl-homoserine lactone (AHL) producing bacteria as well as quorum quenching enzyme or bacteria can effectively improve the performance of wastewater treatment. Biofilms-based reactors due to their economic and ecofriendly nature are used for the treatment of industrial wastewaters. Electrodes coated with electro-active biofilm (EAB) which are obtained from sewage sludge, activated sludge, or industrial and domestic effluents are getting popularity in bioremediation. Microbial fuel cells are involved in wastewater treatment and production of energy from wastewater. Synthetic biological systems such as genome editing by CRISPR-Cas can be used for the advanced bioremediation process through modification of metabolic pathways in quorum sensing within microbial communities. This narrative review discusses the impacts of QS regulatory approaches on biofilm formation, extracellular polymeric substance synthesis, and role of microbial community in bioremediation of pollutants from industrial effluents.

Gas-phase advanced oxidation (GPAO) for benzene-containing gas by an ultraviolet irradiation/hydrogen peroxide vapour (UV/[H2O2]g) process

Hydrogen peroxide (H2O2) is a remarkably strong oxidant, and its vapour ([H2O2]g) has further advantages, such as a low cost and good light transmission. However, there has been very little research on its removal through gas-phase advanced oxidation (GPAO). In the present study, the photochemical oxidation of a gas that contains a series of benzene derivatives using ultraviolet (UV) irradiation and [H2O2]g was investigated in a transparent bag made of fluorinated ethylene propylene (FEP). UV and [H2O2]g barely reduced the pollutant within 5 h when used alone, and the reactant was also stable. When the pollutant concentration was high (248 to 756 mg/m3) and the residence time was short (3 s) compared with related studies on the removal of benzene, toluene and xylene, the apparent removal rate by UV/[H2O2]g/(powder active carbon, PAC) was higher than when other methods (UV/[H2O2]g, UV/[H2O2]g/TiO2 and UV/[H2O2]g/ZnO), were used. However, it was found that the mineralization by UV/[H2O2]g significantly decreased, which in turn decreased the conductivity after the reaction. Increasing the pollutant concentration and the pH of the H2O2 had a negative effect on the treatment, but the UV radiation had a positive effect at powers of up to 40 W. In addition, the characteristic absorbance of three benzene derivatives showed that the key structure of the pollutant molecules was damaged during GPAO.

A study of the flexibility of the carbon catabolic pathways of extremophilic P. aeruginosa san ai exposed to benzoate versus glucose as sole carbon sources by multi omics analytical platform

Polyextremophilic, hydrocarbonoclastic Pseudomonas aeruginosa san ai can survive under extreme environmental challenges in the presence of a variety of pollutants such as organic solvents and hydrocarbons, particularly aromatics, heavy metals, and high pH. To date, the metabolic plasticity of the extremophilic P. aeruginosa, has not been sufficiently studied in regard to the effect of changing carbon sources. Therefore, the present study explores the carbon metabolic pathways of polyextremophilic P. aeruginosa san ai grown on sodium benzoate versus glucose and its potential for aromatic degradation. P. aeruginosa san ai removed/metabolised nearly 430 mg/L of benzoate for 48 h, demonstrating a high capacity for aromatic degradation. Comparative functional proteomics, targeted metabolomics and genomics analytical approaches were employed to study the carbon metabolism of the P. aeruginosa san ai. Functional proteomic study of selected enzymes participating in the β-ketoadipate and the Entner-Doudoroff pathways revealed a metabolic reconfiguration induced by benzoate compared to glucose. Metabolome analysis implied the existence of both catechol and protocatechuate branches of the β-ketoadipate pathway. Enzymatic study of benzoate grown cultures confirmed the activity of the ortho- catechol branch of the β-ketoadipate pathway. Even high concentrations of benzoate did not show increased stress protein synthesis, testifying to its extremophilic nature capable of surviving in harsh conditions. This ability of Pseudomonas aeruginosa san ai to efficiently degrade benzoate can provide a wide range of use of this strain in environmental and agricultural application.

Bioremediation of Hydrocarbon-Polluted Soil: Evaluation of Different Operative Parameters

The bioremediation of soils polluted with hydrocarbons demonstrated to be a simple and cheap technique, even if it needs a long time. The current paper shows the application of statistical analysis, based on two factors involved in the biological process at several levels. We focus on the Design of Experiments (DOE) to determine the number and kind of experimental runs, whereas the use of the categorical factors has not been widely exploited up to now. This method is especially useful to analyze factors with levels constituted by categories and define the interaction effects. Particularly, we focused on the statistical analysis of (1) experimental runs carried out at laboratory scale (test M, in microcosm), on soil polluted with diesel oil, and (2) bench scale runs (test B, in biopile), on refinery oil sludge mixed with industrial or agricultural biodegradable wastes. Finally, the main purpose was to identify the factor’s significance in both the tests and their potential interactions, by applying the analysis of variance (ANOVA). The results demonstrate the robustness of the statistical method and its quality, especially when at least one of the factors cannot be defined with a numerical value.

Bioaugmentation as a green technology for hydrocarbon pollution remediation. Problems and prospects

Environmental pollution mitigation measure involving bioremediation technology is a sustainable intervention for a greener ecosystem biorecovery, especially the obnoxious hydrocarbons, xenobiotics, and other environmental pollutants induced by anthropogenic stressors. Several successful case studies have provided evidence to this paradigm including the putative adoption that the technology is eco-friendly, cost-effective, and shows a high tendency for total contaminants mineralization into innocuous bye-products. The present review reports advances in bioremediation, types, and strategies conventionally adopted in contaminant clean-up. It identified that natural attenuation and biostimulation are faced with notable limitations including the poor remedial outcome under the natural attenuation system and the residual contamination occasion following a biostimulation operation. It remarks that the use of genetically engineered microorganisms shows a potentially promising insight as a prudent remedial approach but is currently challenged by few ethical restrictions and the rural unavailability of the technology. It underscores that bioaugmentation, particularly the use of high cell density assemblages referred to as microbial consortia possess promising remedial prospects thus offers a more sustainable environmental security. The authors, therefore, recommend bioaugmentation for large scale contaminated sites in regions where environmental degradation is commonplace.