Sulphate-reducing bacterial community structure from produced water of the Periquito and Galo de Campina onshore oilfields in Brazil

Nitrate and oxygen significantly changed the abundance rather than structure of sulphate-reducing and sulphur-oxidising bacteria in water retrieved from petroleum reservoirs

Sulphate-reducing bacteria (SRB) are the main culprits of microbiologically influenced corrosion in water-flooding petroleum reservoirs, but some sulphur-oxidising bacteria (SOB) are stimulated when nitrate and oxygen are injected, which control the growth of SRB. This study aimed to determine the distributions of SRB and SOB communities in injection-production systems and to analyse the responses of these bacteria to different treatments involving nitrate and oxygen. Desulfovibrio, Desulfobacca, Desulfobulbus, Sulfuricurvum and Dechloromonas were commonly detected via 16S rRNA gene sequencing. Still, no significant differences were observed for either the SRB or SOB communities between injection and production wells. Three groups of water samples collected from different sampling sites were incubated. Statistical analysis of functional gene (dsrB and soxB) clone libraries and quantitative polymerase chain reaction showed that the SOB community structures were more strongly affected by the nitrate and oxygen levels than SRB clustered according to the sampling site; moreover, both the SRB and SOB community abundances significantly changed. Additionally, the highest SRB inhibitory effect and the lowest dsrB/soxB ratio were obtained under high concentrations of nitrate and oxygen in the three groups, suggesting that the synergistic effect of nitrate and oxygen level was strong on the inhibition of SRB by potential SOB.

Effect of environmental factors on accumulation of trace metals in a typical shale gas exploitation area: A comprehensive investigation by machine learning and geodetector models

Whether a certain relationship is exist between shale gas exploitation and accumulation of trace metals in soil is a controversial issue in recent years. To date, few study clearly reveal the intrinsic contributions of natural and anthropogenic factors to accumulation of trace metals in soil. In this study, machine learning and geodetector models were integrated to investigate to contribution of environmental factors to variations of trace metals concentration. Before modeling, there are 10.33%-25.87% of soil considered as metal pollution, and the value of Pn further suggest that the Ba contribute the most to the comprehensive pollution index of trace metals in soil. The initial prediction of trace metals concentration by machine learning models is less effectively indicating the need for alternative approaches. To address this problem, post-constraints approach was used, and the post-constraint MSLR model demonstrates superior performance (R2 = 0.81) Additionally, through the utilization of geodetector model, the explanatory power (q) of CEC and SOM were identified as dominant natural factors with value of 0.055 and 0.089. respectively. Moreover, distance from working sites and working status were identified as the dominant anthropogenic factors associating to the spatial heterogeneity of trace metals in soil. The interaction between natural and anthropogenic factors showed a siginifacnt nonlinear enhancement effect on accumulation of Cr, Ba and Sr, and the highest value of q was 0.38 for SOM and distance. This study indicated that the potential metal contamination was related to shale gas exploitation and provide reference for controlling soil pollution in shale gas exploitation area and making management strategy.

An integrated approach to identify the source apportionment of potentially toxic metals in shale gas exploitation area soil, and the associated ecological and human health risks

Public awareness of the potential environmental risks of shale gas extraction has increased in recent years. However, the status and environmental risks of potentially toxic metals (PTMs) in shale gas field soil remain unclear. A total of 96 topsoil samples were collected from the first shale gas exploitation area in China. The sources of nine PTMs in the soils were identified using positive matrix factorization and correlation analysis, and the ecological and human health risks of toxic metals from different sources under the two land use types were calculated. The results showed that mean pollution load index (PLI) values for farmland (1.18) and woodland (1.40) indicated moderate pollution, As, Cd and Ni were the most serious contaminants among all nine PTMs. The following four sources were identified: shale gas extraction activities (43.90%), nature sources (31.90%), agricultural and traffic activities (17.55%) and industrial activities (6.55%). For ecological risk, the mean ecological risk index (RI) values for farmlands (161.95) and woodlands (185.27) reaching considerable risk. The contribution ratio of shale gas extraction activities for farmlands and woodlands were 5.70% and 8.90%, respectively. Regarding human health risk, noncarcinogenic risks for adults in farmlands and woodlands were negligible. Industrial activities, agricultural and traffic activities were estimated to be the important sources of health risks. Overall, shale gas extraction activities had little impact on the ecological and human health risk. This study provides scientific evidence regarding the soil contamination potential of shale gas development activities.

Characteristic pollutants and microbial community in underlying soils for evaluating landfill leakage

Leachate leakage poses a serious environmental risk to the safety of surrounding soils and groundwater. A much faster approach to reflect landfill leakage is the premise to mitigate the ecological risk of landfills. In this study, two landfills (BJ and WZ) were selected to investigate the leaching characteristics of various pollutants along the vadose soil depths. The physiochemical properties of underlying soils including NO₃^--N, NO₂^--N, NH₄⁺-N, OM, TN, EC and Cl^- exhibited a typical leaching dynamic along the depths. Among them, TN, NH₄⁺-N, OM, NO₃^--N, and EC might be used as characteristic pollutants to evaluate the leachate leakage issues in landfilled sites. The genera Thiopseudomonas, Acinetobacter, Pseudomonas, and Hydrogenispora dominated in underlying soils. Compared to BJ samples, a more diverse and active microbiome capable of carbon and nitrogen cycles was observed in WZ samples, which was mainly ascribed to nutrients and elements contained in different types of soils. Among the environmental factors, nitrogenous compounds, SO₄^2-, pH and EC had significant effects on the microbial community structures in the underlying soils. The relative abundances of Hydrogenispora and Caldicoprobacter might be used as characteristic microorganisms to evaluate the leachate leakage issues in landfilled sites. These results provided a deep insight into effects of leachate leakage in underlying soils, especially the pollutants vertical distribution and the corresponding microbial community structures.

Produced Water Treatment and Valorization: A Techno-Economical Review

In recent years, environmental concerns have urged companies in the energy sector to modify their industrial activities to facilitate greater environmental stewardship. For example, the practice of unconventional oil and gas extraction has drawn the ire of regulators and various environmental groups due to its reliance on millions of barrels of fresh water—which is generally drawn from natural sources and public water supplies—for hydraulic fracturing well stimulation. Additionally, this process generates two substantial waste streams, which are collectively characterized as flowback and produced water. Whereas flowback water is comprised of various chemical additives that are used during hydraulic fracturing; produced water is a complex mixture of microbiota, inorganic and organic constituents derived from the petroliferous strata. This review will discuss the obstacles of managing and treating flowback and produced waters, concentrating on the hardest constituents to remove by current technologies and their effect on the environment if left untreated. Additionally, this work will address the opportunities associated with repurposing produced water for various applications as an alternative to subsurface injection, which has a number of environmental concerns. This review also uses lithium to evaluate the feasibility of extracting valuable metals from produced water using commercially available technologies.

Assessing Alternative Supporting Organic Materials for the Enhancement of Water Reuse in Subsurface Constructed Wetlands Receiving Acid Mine Drainage

Acid mine drainage (AMD) is a global problem with severe consequences for the environment. South Africa’s abandoned mines are a legacy from the country’s economic dependence on the mining sector, with consequent negative impacts on ecosystems. AMD remediation includes active and passive techniques. Constructed wetlands (a passive technique) have lower operational costs but require larger spaces and longer timeframes to achieve the remediation of AMD, and are supported by anaerobic sulphate-reducing bacteria (SRB), which capable of remediating high-sulphate-laden AMD while precipitating dissolved metals from the AMD. Organic substrates supporting these activities are often the limiting factor. When enhancing existing passive AMD remediation technologies, alternative waste material research that may support SRB activity is required to support the circular economy through the reduction in waste products. Chicken feathers show potential as a substrate enhancer, boosting organic carbon availability to SRB, which sustains passive AMD treatment processes by achieving pH elevation, sulphate and metal reductions in AMD water for reuse. Microbial biodiversity is essential to ensure the longevity of passive treatment systems, and chicken feathers are proven to have an association with SRB microbial taxa. However, the longer-term associations between the AMD water parameters, microbial diversity and the selected substrates remain to be further investigated.