Performance and microbial community analysis of combined bioreactors in treating high-salinity hydraulic fracturing flowback and produced water

Novel microbial fuel cell integrating anoxic/oxic-membrane bioreactor design for simultaneous energy recovery and carbon-nitrogen removal from shale oil and gas wastewater

Shale oil and gas wastewater (SOGW), rich in pollutants, poses an environmental threat. A novel microbial fuel cell (MFC) resembling an anoxic/oxic-membrane bioreactor (A/O-MBR), called AOMM, was developed to treat SOGW and recover energy. AOMM required no expensive ion-exchange membrane and incorporated a custom suspended-rotating biocathode, reducing the reliance on high-cost and hard-to-scale components. Furthermore, AOMM achieved a maximum power density of 61.6 mW/m2 and, under optimized operating conditions, removed 98.3% of chemical oxygen demand (COD), 99.6% of ammonium nitrogen (NH4+-N), and 82.2% of total nitrogen (TN) from simulated SOGW. Microbial and gene analyses revealed enrichment of key bacteria and functional genes associated with electron transfer, carbon degradation, and nitrogen removal in both the anode and cathode. Moreover, AOMM demonstrated greater organic removal with a simpler process than an actual SOGW treatment project. This study provides an alternative with high application potential for efficient treatment and resource recovery of SOGW.

Current status, potential assessment, and future directions of biological treatments of unconventional oil and gas wastewater

Unconventional oil and gas (UOG) extraction techniques typically involve the production of large volumes of so-called flowback and produced water (FPW), a site-specific wastewater stream characterized by complex organic and inorganic composition. Sustainable and cost-effective management of FPW, as well as mitigation of its environmental risks and impacts, represents substantial challenges for governments, industries, and societies worldwide. Among various treatment technologies, biological processes have gained interest due to their low installation and operational costs. However, the interaction of FPW's complex composition with microorganisms poses challenging scientific and engineering questions. This review examines the water quality characteristics and sources of FPW from twelve UOG extraction sites in China and North America, revealing strong spatio-temporal heterogeneity of organic, inorganic, and microbial components across different reservoirs. The complex and variable water quality, large wastewater volumes, and high treatment demands have driven the exploration of biological treatments for FPW. This work systematically reviews and analyzes the operating conditions, treatment efficiency, and technical applicability of suspended sludge reactors, attached sludge reactors, mixed systems, and resource/energy recovery systems. Developing skid-mounted equipment based on suspended sludge reactors to handle variations in wastewater quantity and innovating the form of attached sludge reactors, especially in enriching salt-tolerant microbes for in-situ FPW treatment, are deemed essential. The dominant microorganisms playing a key role in the biological treatment are also discussed, with focus on two different inoculation sources (activated sludge and FPW). Roseovarius from FPW and Pseudomonas from activated sludge have strong adaptability to different reactors. The review further underscores the need to integrate biological treatments with complementary technologies. Finally, it advocates for the establishment of robust and scalable biological treatments through research in three main directions: (i) exploring microbial resources in original FPW; (ii) using omics technologies to elucidate microbial function and species interaction; (iii) pre-designing environmental and operational conditions to optimize treatment efficiency.

Effects of salinity and betaine addition on anaerobic granular sludge properties and microbial community succession patterns in organic saline wastewater

In this study, the effects of different salinity gradients and addition of compatible solutes on anaerobic treated effluent water qualities, sludge characteristics and microbial communities were investigated. The increase in salinity resulted in a decrease in particle size of the granular sludge, which was concentrated in the range of 0.5-1.0 mm. The content of EPS (extracellular polymeric substances) in the granular sludge gradually increased with increasing salinity and the addition of betaine (a typical compatible solute). Meanwhile, the microbial community structure was significantly affected by salinity, with high salinity reducing the diversity of bacteria. At higher salinity, Patescibacteria and Proteobacteria gradually became the dominant phylum, with relative abundance increasing to 13.53% and 12.16% at 20 g/L salinity. Desulfobacterota and its subordinate Desulfovibrio, which secrete EPS in large quantities, dominated significantly after betaine addition.Their relative abundance reached 13.65% and 7.86% at phylum level and genus level. The effect of these changes on the treated effluent was shown as the average chemical oxygen demand (COD) removal rate decreased from 82.10% to 79.71%, 78.01%, 68.51% and 64.55% when the salinity gradually increased from 2 g/L to 6, 10, 16 and 20 g/L. At the salinity of 20 g/L, average COD removal increased to 71.65% by the addition of 2 mmol/L betaine. The gradient elevated salinity and the exogenous addition of betaine played an important role in achieving stability of the anaerobic system in a highly saline environment, which provided a feasible strategy for anaerobic treatment of organic saline wastewater.

UHPM dominance in driving the formation of petroleum-contaminated soil aggregate, the bacterial communities succession, and phytoremediation

This study focused on the effects of urea humate-based porous materials (UHPM) on soil aggregates, plant physiological characteristics, and microbial diversity to explore the effects of UHPM on the phytoremediation of petroleum-contaminated soil. The compositions of soil aggregates, ryegrass (Lolium perenne) biomass, plant petroleum enrichment capacity, and bacterial communities in soils with and without UHPM were investigated. The results showed that UHPM significantly increased soil aggregate content by 0.25 mm-5 mm, resulting in higher fertilizer holding capacity, erosion resistance capacity, and plant biomass and microbial number than the soil without UHPM mixed. In addition, UHPM decreased the absorption of petroleum by plants in the soil while increasing the abundance of degrading bacteria and petroleum-degrading-related genes in the soil, thereby promoting the removal of hard-to-degrade petroleum components. RDA showed that, compared with the unimproved soil, each soil indicator was positively correlated with a high abundance of degrading bacteria in the improved soil and was significant. UHPM can be regarded as a petroleum-contaminated soil remediation agent that combines slow nutrient release with soil improvement effects.

Efficient nitrogen removal from real municipal wastewater and mature landfill leachate using partial nitrification-simultaneous anammox and partial denitrification process

Anaerobic ammonia oxidation (anammox) of municipal wastewater is a research focus, especially the combined treatment with mature landfill leachate is a current research hotspot. In this study, municipal wastewater was treated by partial nitrification via sequencing batch reactor (SBR), and its effluent and mature landfill leachate were then mixed into an up-flow anaerobic sludge blanket (UASB) for simultaneous anammox and partial denitrification reaction. Through partial nitrification, a high nitrite accumulation rate (93.0 ± 3.8 %) was achieved by low dissolved oxygen (0.5-1.6 mg/L) and controlled aerobic time (3.5 h) in SBR. The UASB system was responsible for 78.8 ± 2.1 % nitrogen removal of the entire system with a hydraulic reaction time (HRT) of 3.8 h, accompanied by the anammox contribution up to 89.4 ± 6.0 %. The overall partial nitrification-simultaneous anammox and partial denitrification (PN-SAPD) system was controlled at a total COD/TIN of 2.8 ± 0.3 and a total HRT of only 10.2 h, achieving the nitrogen removal efficiency and effluent TIN were 95.2 ± 2.2 % and 3.4 ± 1.5 mg/L, respectively. The qPCR results showed functional genes (hzsA(B), hdh) associated with anaerobic ammonia-oxidizing bacteria (AnAOB), whose high gene copy abundance and transcription expression ensured the removal of major nitrogen from municipal wastewater and mature landfill leachate. 16S amplicon sequencing showed that the Ca. Brocadia (9.72-12.6 %) was further enrichment after sodium acetate was added, and the transcription expression of Thauera (0.5-7.0 %) caused nitrate to nitrite. The high abundance of related enzymes (hao, hzs, hdh, narGHI) involved in anammox and partial denitrification processes were found in the macrogenomic sequencing, and only Ca. Brocadia was involved in multi-pathway nitrogen metabolism in AnAOB. Based on the efficient nitrogen removal by AnAOB and denitrifying bacteria, this modified PN-SAPD process provides a new option for the co-treatment of mature landfill leachate in municipal wastewater treatment plants.