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• An existing activated sludge system was upgraded to a continuous-flow AGS system. • Shear forces, combined with feast/famine conditions, induced granulation. • Organic matter and nutrients were removed simultaneously within microaerobic tanks. • A 38.2 % reduction in footprint and one-third savings in reflux energy were achieved. Aerobic granular sludge (AGS) has been successfully used in sequencing batch reactors. However, their application to existing continuous-flow systems remains challenging. In this study, a novel microaerobic-aerobic configuration with internal separators was implemented in a full-scale municipal wastewater treatment facility with a nominal capacity of 2.5 × 104 m3 d−1. Sludge characteristics, pollutant removal and associated pathways, shifts in the microbial community, and underlying granulation mechanisms were investigated. Following a two-month operation period, the transition from flocculent-activated sludge to well-defined AGS with distinct boundaries and compact structures was successfully achieved. The average size of sludge increased from 31.9 to 138.5 μm, with granules larger than 200 μm constituting 28.9 % of the total sludge and SVI 30 averaging 51.4 ± 8.2 mL g−1. The 95th percentile effluent COD, NH 4 +-N, and TN concentrations were 35.0, 1.2, and 13.3 mg L−1, respectively. The primary pathways for pollutant removal were identified as simultaneous nitrification, denitrification, and phosphorus removal within the microaerobic tanks. The enrichment of denitrifying phosphorus-accumulating organisms, including Hydrogenophaga, Accumulibacter, Azospira, Dechloromonas , and Pseudomonas , provides an essential microbial foundation. Furthermore, computational fluid dynamics modeling revealed that the incorporation of internal separators in aerobic tanks induced shifts in the flow pattern, transitioning from a single-circulation cell to multiple vortical cells. This alteration amplified the local velocity gradients, generating the required shear forces to drive granulation. Moreover, mass balance analysis revealed that the microaerobic and aerobic tanks operated under feast and famine conditions, respectively, creating a microbial selection pressure that favored granulation. This process eliminates the need for external clarifiers, resulting in a footprint reduction of 38.2 % and one-third energy savings for sludge reflux. This study offers valuable insights into the application of continuous-flow AGS to upgrade existing activated sludge systems with limited retrofitting requirements. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • A pilot scale chemically enhanced high-loaded membrane bioreactor was operated for over 8 months. • Stable filtration (flux 8–10 LMH) was achieved at SS over 15 g/L. • Over 75% soluble organics and phosphorous were removed by CE-HLMBR. • 27–80 times concentration and over 85% concentration efficiency of COD were achieved. A-stage technology is acknowledged as a promising process for organic recovery. Due to its superior separation performance, the high-loaded membrane bioreactor (HLMBR) is a competitive variant of the A-stage. In this study, a pilot-scale chemically enhanced HLMBR (CE-HLMBR) was established to enhance the practical feasibility of the process. Polyaluminium chloride (PAC) and activated carbon (AC) were added to address membrane fouling, dependence on intensive aeration, and inadequate concentration factors. Eight conditions were designed to investigate the role of chemicals and aeration in filtration, pollutant removal, and organic recovery. Stable filtration (8–10 LMH) was achieved at SS concentrations of 15–20 g/L, benefiting from the dynamic formation and shedding of the protective cake layer, as well as the reduction of extracellular polymer substances (EPS). Over 75 % soluble organics and 80 % soluble phosphorous were removed by CE-HLMBR, mainly subject to the chemicals. Simultaneous nitrification–denitrification occurred due to uneven oxygen distribution. The influent organics were concentrated by factors ranging from 27 to 80 and the loss rate was less than 15 %. Meanwhile, methane production may not be an efficient method of resource extraction. The practical feasibility of the proposed CE-HLMBR was confirmed based on an additional three-month stable operation. This study will open new possibilities for the application of HLMBR systems. [ABSTRACT FROM AUTHOR]

Methanosaeta strains are frequently involved in the granule formation during methanogenic wastewater treatment. To investigate the impact of Methanosaeta on granulation and performance of upflow anaerobic sludge blanket (UASB) reactors, three 1-L working volume reactors noted as R1, R2, and R3 were operated fed with a synthetic wastewater containing sodium acetate and glucose. R1 was inoculated with 1-L activated sludge, while R2 and R3 were inoculated with 200-mL concentrated pre-grown Methanosaeta harundinacea 6Ac culture and 800 mL of activated sludge. Additionally, R3 was daily dosed with 0.5 mL/L of acetyl ether extract of 6Ac spent culture containing its quorum sensing signal carboxyl acyl homoserine lactone (AHL). Compared to R1, R2 and R3 had a higher and more constant chemical oxygen demand (COD) removal efficiency and alkaline pH (8.2) during the granulation phase, particularly, R3 maintained approximately 90 % COD removal. Moreover, R3 formed the best granules, and microscopic images showed fluorescent Methanosaeta-like filaments dominating in the R3 granules, but rod cells dominating in the R2 granules. Analysis of 16S rRNA gene libraries showed increased diversity of methanogen species like Methanosarcina and Methanospirillum in R2 and R3, and increased bacteria diversity in R3 that included the syntrophic propionate degrader Syntrophobacter. Quantitative PCR determined that 6Ac made up more than 22 % of the total prokaryotes in R3, but only 3.6 % in R2. The carboxyl AHL was detected in R3. This work indicates that AHL-facilitated filaments of Methanosaeta contribute to the granulation and performance of UASB reactors, likely through immobilizing other functional microorganisms. [ABSTRACT FROM AUTHOR]

• In-situ H 2 -assisted biogas upgrading was applied to anaerobic wastewater treatment. • CH 4 content of product gas was consistently over 90% at all OLRs. • H 2 -rich syngas could replace pure H 2 during the in-situ biogas upgrading process. • Syntrophy of bacteria and methanogens facilitated biogas upgrading with syngas. • Aceticlastic Methanothrix species were the dominant methanogens in the reactors. The H 2 -assisted biogas upgrading approach has recently attracted much interest as a low-cost and environmentally friendly alternative to commonly used ex-situ/ physiochemical biogas upgrading techniques. However, most studies conducted to date have been limited to anaerobic solid-waste treatment characterized by flocculant sludge and low organic loading rates (OLR). In an attempt to expand its application to high-rate anaerobic wastewater treatment, an innovative two-stage up-flow anaerobic sludge blanket reactor system was employed using anaerobic granular sludge. We found that the CH 4 content of product gas was consistently >90% and that H 2 and CO 2 concentrations stayed below 5%, even when OLR was increased from 1 to 5 g L−1 d−1 and H 2 feeding rates were increased from 0.13 to 0.63 g L−1 d−1. We were also able to show that CO (5–10%) in H 2 -rich syngas didn't inhibit methanogenesis or had significant impact on microbial community structure, suggesting that H 2 -assisted biogas upgrading with H 2 -rich syngas is feasible. [ABSTRACT FROM AUTHOR]

This work aimed to enrich a denitrifying bacterial community for economical denitrification via nitrite to provide the basic objects for enhancing nitrogen removal from wastewater. A sequencing batch reactor (SBR) with continuous nitrite and acetate feeding was operated by reasonably adjusting the supply rate based on the reaction rate, and at a temperature of 20 ± 2 °C, pH of 7.5 ± 0.2, and dissolved oxygen (DO) of 0 mg/L. The results revealed that the expected nitrite concentration can be achieved during the whole anoxic reaction period. The nitrite denitrification rate of nitrogen removal from synthetic wastewater gradually increased from approximately 10 mg/(L h) to 275.35 mg/(L h) over 12 days (the specific rate increased from 3.83 mg/(g h) to 51.80 mg/(g h)). Correspondingly, the chemical oxygen demand/nitrogen (COD/N) ratio of reaction decreased from 7.9 to 2.7. Both nitrite and nitrate can be used as electron acceptors for denitrification. The mechanism of this operational mode was determined via material balance analysis of substrates in a typical cycle. High-throughput sequencing showed that the main bacterial community was related to denitrification, which accounted for 84.26% in the cultivated sludge, and was significantly higher than the 2.16% in the seed sludge. [ABSTRACT FROM AUTHOR]

The idea of sewage concentration is gradually being accepted as a promising and sustainable way of wastewater resource recovery. In this study, Hybrid coagulation microfiltration (HCM) with air backflushing (AB) was investigated to effectively concentrate organic matter. Compared to direct sewage microfiltration, the addition of coagulation process improved the filtration performance with less fouling trends and better concentration efficiency. The use of AB exhibited even better performance within the same 7-h preliminary concentration period by reducing to one tenth of the resistance and collecting around four times as much organic matter into the product concentrate as in direct sewage microfiltration. During 93-h lab-scale continuous concentration by HCM with AB, a product concentrate with the COD concentration over 15,000 mg/L was achieved and around 70% of total influent organic matter could be recovered. Compared to Direct Membrane Filtration (DMF) with Chemically Enhanced Backwash (CEB), HCM with AB achieved better concentration efficiency with higher concentration extent and concentration velocity along with less organic matter mineralization and the more concentrated product despite with lower organic matter retention. HCM with AB could be a promising effective sewage organic matter concentration for resource recovery under optimization. [ABSTRACT FROM AUTHOR]

A systemic strategy was proposed to improve aerobic granular sludge (AGS) stability and nitrogen (N) removal efficiency by optimizing feeding mode and substrate aiming at complicated wastewater characteristics. Key functional groups at the genus level identified by high-throughput sequencing were evaluated as well. The results showed that anaerobic feeding mode and acetate promoted the compact AGS formation with excellent total nitrogen (TN) removal efficiency (averaging 91.7% ± 4.1%) at various dissolved oxygen conditions. While the aerobic feeding mode led to a loose AGS structure with a vulnerable anaerobic core and poor TN removal efficiency (averaging 58.8% ± 7.4%). Simultaneous nitrification and denitrification process played the dominant role in N removal in compact AGS over the alternating nitrification and denitrification process. High-concentration glucose undermined feast–famine condition with filamentous bacteria growth out of granule and decreased TN removal efficiency to 67.3% ± 15.2%. Lower food to microorganism ratio may result in a lower N removal rate attributed to the sharply increased biomass concentration fed by glucose. Ammonia-oxidizing bacteria, nitrite-oxidizing bacteria, denitrifying bacteria, and denitrifying phosphorus accumulation organisms enriched during AGS granulation also contributed to the efficient N removal. The proposed strategy provided insights into the relationship between various factors and stable AGS formation, and systemic operation methods for various complicated wastewater treatment. Unlabelled Image [ABSTRACT FROM AUTHOR]

Abstract Energy neutrality in municipal wastewater (MW) treatment is an ambitious sustainability goal that is hampered by MW's low organics concentration. A potential method is to pre-concentrate MW to recover the organics and use them to produce energy via anaerobic decomposition. This study conducted a pilot-scale operation using an enhanced membrane-based pre-concentration (MPC) technique to efficiently recover organics from actual MW. Stable and highly efficient organics recovery (72–75%) was achieved during two-month operations. Concentrated organics demonstrated high COD (above 20,000 mg/L) and good anaerobic biodegradability (360–367 mL CH 4 /g VS). Organics recovered by MPC exhibited the potential of net electrical energy production of 0.029–0.050 kWh/m3, depending on the fouling situation. The energy consumption of MPC was limited by avoiding continuous intensive aeration. With effective fouling control, as much as 2.91 times more energy could be produced than that was consumed. This suggests MPC-based processes have the potential to transform MW treatment plant from energy consumers to net producers. Graphical abstract Image Highlights • Stable and efficient organics recovery (72–75%) during pilot-scale operations. • Recovered organics exhibited high COD and good anaerobic biodegradability. • The energy consumption of MPC was limited by avoiding intensive aeration. • Net electrical energy production of 0.029–0.050 kWh/m3. • MPC-based processes have the potential to transform MW treatment to net producers. [ABSTRACT FROM AUTHOR]

This work investigated ammonia pre-concentration from low-strength municipal wastewater by flow-electrode capacitive deionization (FCDI) cell. A variety of operating conditions, including applied voltage, flow rate, graphite powder dosage, pH value and initial ammonia concentration, were investigated systematically. The results indicated that removal efficiency was greatly improved by increasing the working voltage (from 0.2 V to 1.2 V) and flow rate (from 5.00 to 7.75 mL/min), adding 1.5 wt% graphite powders and decreasing pH to 4. The maximum ammonia removal efficiency (87.00 ± 0.79%) was obtained with adsorption capacity of 1.43 ± 0.01 mg NH 4 Cl/g. Based on these optimum operation conditions, enrichment experiments were conducted with the desired concentration multiple times of 20 and an initial ammonia concentration of 20 mg N/L, which led to a final ammonia concentration of 322.06 mg N/L in the aqueous phase of flow electrodes. Additionally, valence, initial concentration, hydrate radius and diffusion efficiency also notably affected the alternative electro-performance of the FCDI cell because of co-existing cations. The study provides new insights into the emerging FCDI technology, which is expected to improve the methods of performing cost-effective ammonia removal and pre-concentration from low-strength municipal wastewater with moderate ion selectivity and wide ranging influent quality. [ABSTRACT FROM AUTHOR]

Sequence batch reactors (SBR) with simultaneous feeding/draw mode and low-strength wastewater were used for the cultivation of aerobic granules, and analysis of bacterial community diversity were conducted. Results revealed that the ratio of chemical oxygen demand/total nitrogen removal amount for R1 with real wastewater and R2 with synthetic wastewater decreased from 9.9 to 8.7 and, 29.9 to 21.1, respectively, when volumetric exchange ratio (VER) decreased from 90% (stage I) to 50% (stage II), indicating that organic matter in real and low-strength wastewater was fully utilized with lower VER by denitrifying bacteria. Relative abundances of the genus Dechloromonas , Pseudomonas , Bacillus in R1, which are responsible for denitrifying phosphorus removal, were much higher than that in R2, accounting for the high efficiency of nitrogen and phosphorus removal from real wastewater with low influent C/N ratio of 3.6 on average. These results provide useful information for improving wastewater treatment efficiency in the future. [ABSTRACT FROM AUTHOR]

From the perspective of mass flow, the conventional municipal wastewater treatment based on active sludge process (CAS) removes pollutants by aerobically converting organic carbon (C) into useless CO 2 with excess sludge as a by-product and removing nitrogen (N) in the form of N 2 by nitrification/denitrification with aeration energy and the carbon source input. To improve sustainability, in this paper, we propose a novel process based on the coagulation adsorption enhanced membrane (CAEM) method, which redesigns the C and N mass flows for energy-neutral wastewater treatment. A pilot-scale operation conducted over two months demonstrated that up to 85.6% chemical oxygen demand (COD) was rejected by CAEM, which could be directed into the anaerobic energy recovery unit in a concentrated form with high biodegradability. Meanwhile, 74.9% nitrogen was kept in the mainstream for the subsequent autotrophic deammonification. Modelling results based on steady-state mass balance and stoichiometric calculations indicated the changes in the C and N mass flows induced by CAEM. The amount of organics (COD) used for energy production increased remarkably compared with that in the CAS process. Combined with mainstream deammonification, this CAEM-based process also avoided the COD consumed by denitrification and heterotrophic oxidation, leading to less aeration and energy consumption (0.22 kWh/t in the CAS process vs. 0.05 kWh/t in the CAEM-based process). The proposed CAEM-based process redesigned a larger C mass flow to the anaerobic energy recovery unit than energy-intensive aerobic oxidation and more N removal by autotrophic deammonification than by heterotrophic deammonification, making it feasible to achieve energy neutrality. [ABSTRACT FROM AUTHOR]

Membrane-based pre-concentration (MPC) process has been regarded as an attractive approach to sustainable municipal wastewater (MW) treatment. The aim of this study is to verify the techno-economic feasibility of pilot-scale MPC demonstrations and to design a complete technical route for MPC-based MW treatment and resource recovery. Three pilot MPC demonstrations (50–500 t/d) were operated for several months with different strategy combinations of chemicals and aeration. The filtration performance, pollutant removal performance, and concentrate characteristics were investigated and a techno-economic assessment was conducted. Based on the characteristics of each MPC effluent, biofilters, reverse osmosis (RO) and membrane capacitive deionization (MCDI) were selected as post-treatment units. Comparisons were carried out from 6 perspectives, including effluent quality, energy consumption, capital investment, operating cost, by-products, and recovery potential. In MPC_C, the combination of intermittent aeration and "50 mg/L Polyaluminium chloride +25 mg/L activated carbon" ensured a stable filtration (flux >10 LMH over 3 months) and an exceptional pollutant removal (soluble organics removal rate >75%) performance. The highest energy recovery potential (0.35 kWh/m3) was also achieved in MPC_C with the lowest energy consumption (0.12 kWh/m3) and an acceptable operating cost (0.53 CNY/m3). As for post-treatment units, RO showed advantages in effluent quality, technological maturity, and economic cost. An "MPC (intermittent aeration + high strength dosage) + RO + anaerobic digestion" system was proposed for synchronous water-energy reclamation. The net energy consumption and operating cost were estimated as 0.273 kWh/m3 and CNY 1.132/m3, respectively. This study will open new possibilities for the establishment of revolutionary wastewater treatment routes for carbon neutrality and sustainable development. [Display omitted] • Techno-economic feasibility of "membrane-based pre-concentration (MPC) + post-treatment" was verified. • Intermittent aeration + high-strength chemical dosage is a promising operating strategy in MPC. • Reverse osmosis (RO) is a favorable technology for treating MPC permeate currently. • A combined system (MPC-RO) was proposed for synchronous water-energy reclamation. [ABSTRACT FROM AUTHOR]

Biologically treated cephalosporin pharmaceutical wastewater is a complex industrial wastewater that is toxic and refractory for further biological treatment. For this purpose, a novel sonoelectrochemical catalytic oxidation-driven process using a nanocoated electrode has been developed to treat such wastewater. In the process, the synergy and mechanism of the sonoelectrochemistry using ultrasound enhancement of the nanocoated electrode activity to treat the wastewater was studied. The nanocoated electrode generated more radicals than the traditional coated electrode did; in the presence of ultrasonic waves, the mass-transfer effects on the nanocoated electrode surface were enhanced, resulting in rapid diffusion of the generated hydroxyl radicals into the solution, and quickly reacted with organic pollutants. Compared with the traditional coated electrode, the effect of the nanocoated electrode used on the wastewater treatment process was more enhanced by ultrasound under the same conditions. The biotoxicity of the wastewater in the sonoelectrochemical catalytic oxidation process was monitored and shown as having first increased and then decreased. The optimum operating conditions resulted in a 94% removal efficiency for COD and consisted of a current of density 8 mA/cm 2 and an ultrasound frequency of 45 kHz. All of the results showed that the sonoelectrochemical catalytic oxidation-driven process was found to be a very efficient method for the treatment of non-biodegradable cephalosporin pharmaceutical wastewater. [ABSTRACT FROM AUTHOR]

• A pilot-scale enhanced magnetic separation equipment (300 m3/d) was proposed for up-concentration. • Adsorption further enhanced the ability to capture soluble organics of magnetic separation. • Over 60% of organics were removed within 10 min with satisfactory energy consumption. • The energy potential of the produced sludge was competitive. The up-concentration process has been demonstrated as an attractive approach to carbon-neutral wastewater treatment. Innovation in the separation processes can help eliminate the current heavy dependence on gravity, and credible pilot-scale verification is crucial for application promotion. We hereby proposed a pilot-scale enhanced magnetic separation (EMS) system as an up-concentration step to maximize energy recovery from municipal wastewater. The design of EMS was based on the hypothesis that magnetic-driven separation could be a breakthrough in separation speed, and adsorption could further enhance the separation efficiency by capturing soluble substances. Jar tests confirmed the feasibility of activated carbon adsorption, which could also roughen the surface of aggregates. Further, over one-year operation of a 300 m3/d EMS equipment provided optimum operation strategies and evidence of system effectiveness. More than 80% of particulate organics and 60% of soluble organics were removed within 10 min at an energy consumption of only 0.036 kWh/m3. The characteristics of sludge were clarified in terms of organic concentration, extracellular polymeric substances composition, and micro-community analysis. The anaerobic experiments further demonstrated the potential value of the concentrated products. Surprisingly, the developed EMS system exhibited significant advantages in time consumption and space occupation, with competitive operating cost and energy consumption. Overall, the results of this study posed the EMS process for up-concentration as a potential approach to organics recovery from municipal wastewater. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • A pilot-scale MCDI system was designed for ammonia recovery from municipal wastewater. • Different working conditions were optimized for ammonia recovery. • Competitive adsorption between Ca2+, Mg2+ and NH 4 + were discussed. • The MCDI system showed high stability in long-term operation. • MCDI showed preferential electrosorption of NH 4 + in short adsorption periods. With the depletion of energy, renovation of wastewater has attracted wide attention around the world, among which the recovery of ammonia has also been an ongoing topic. Membrane capacitive deionization (MCDI) has emerged as a promising technology for nutrient removal and recovery. However, limitations of both scale-up and treatment of practical wastewater still restrict its real application. This study aims to investigate the feasibility of ammonia removal from real wastewater by MCDI on a pilot scale. The MCDI module used in this study was expanded to a 2-unit facility (15 pairs of electrodes per unit). Firstly, synthetic wastewater was used as feed water to optimize different kinds of operating parameters, including applied voltage (0–2.5 V), flow rate (7–30 L/h), and initial concentration (20–100 mg/L). Further experiments investigated the competitive adsorption performance under complex inflow conditions. Results indicated that the presence of co-existing cations significantly reduced the removal efficiency and adsorption capacity of ammonia. With the same inflow concentration, the removal efficiency of NH 4 +, Mg2+, and Ca2+ was 39.12 ± 5.31%, 47.56 ± 2.68%, and 33.33 ± 1.90% respectively. The interplay of initial ion concentration, charge valence, and hydrated radii led to the different electro-sorption performances. Subsequently, practical municipal wastewater after the up-concentration of organics was used as feed water to evaluate the feasibility of the pilot-scale MCDI. Under the optimized condition, a long-term experiment was carried out for 15-day to deal with actual wastewater. Besides, ion removal performance, the energy consumption, and desorption efficiency were also analyzed. The system maintains a stable removal efficiency for all cations, with low energy consumption (1.16 kWh/m3) and high desorption efficiency (around 90%). Overall, the results of this study posed the MCDI process as a potential approach to ammonia removal and recovery from municipal wastewater. [ABSTRACT FROM AUTHOR]

• SBR with anoxic reflux and nanofloc® used for daily operation of sewage treatment. • High pollutants removal was obtained in laboratory and pilot-scale modified SBRs. • Periodic addition of nanofloc® benefited in pollutants removal especially for TP. • Efficient sludge sedimentation was achieved with low SVI, comparable with AGS. • Nutrients removal mechanism of this innovative technology was discussed. This study aims to develop a novel technology for actual municipal wastewater treatment to achieve rapid sludge sedimentation and high pollutants removal efficiency. The SBRs were modified and operated with periodic addition of 20 μL·L−1 nanofloc®. Results revealed that NH 4 +-N and chemical oxygen demand (COD) was efficiently removed in both laboratory- and pilot-scale SBRs, and the average removal efficiency of total nitrogen (TN) and total phosphorus (TP) was as high as 72.43 ± 2.66% and 98.63 ± 0.74%, respectively, with hydraulic retention time (HRT) of 8 h. Besides, the sludge volume index at 30 min (SVI 30) was only 40.06 ± 1.99 mL·g−1, comparable with aerobic granular sludge (AGS). This novel technology could be proposed as a competitive method to upgrade, reconstruct and delay the expansion of municipal wastewater treatment plants (WWTPs) due to its rapid sludge sedimentation and efficient pollutants removal with low HRT. [ABSTRACT FROM AUTHOR]

• Pretreatment is needed as trichloroacetaldehyde enters biological treatment units. • Trichloroacetaldehyde influenced key enzymes and extracellular polymeric substances. • Biological acidification only presented highly limited ability of dechlorination. • The removal pathways of trichloroacetaldehyde are bio-oxidation and bio-reduction. Biological acidification plays a crucial role in biological removal of organic compounds during petrochemical wastewater treatment. Trichloroacetaldehyde is a typical organic pollutant in petrochemical wastewater, however, no studies have been conducted on its effect on biological acidification. In this study, batch bioassays of volatile fatty acids were conducted to explore the inhibitory effect of trichloroacetaldehyde on biological acidification, the variations of key enzymes and extracellular polymeric substances under trichloroacetaldehyde shock, and the mechanism of trichloroacetaldehyde removal. The results of these bioassays indicated that trichloroacetaldehyde inhibited the acid yield at higher concentrations (EC 50 112.20 mg/L), and butyric fermentation was predominant. Moreover, the contents of extracellular polymeric substances and several key acidifying enzymes greatly decreased when the trichloroacetaldehyde concentration exceeded 100 mg/L, which was due to the toxicity that trichloroacetaldehyde poses to the microbes involved in biological acidification. The trichloroacetaldehyde mechanism was as follows: first, trichloroacetaldehyde was adsorbed by extracellular polymeric substances and anaerobic granular sludge, and then transformed into trichloroethanol, trichloroethane, dichloroacetaldehyde, and dichloroethanol under the combined action of the aldehyde reductase and reductive dehalogenases secreted from the microbial consortium. The ability of biological acidification to remove trichloroacetaldehyde was limited; therefore, trichloroacetaldehyde should be pretreated before it enters biological treatment systems. [ABSTRACT FROM AUTHOR]

Petrochemical wastewater is a major industrial source of pollution that produces a variety of refractory and toxic organic pollutants that are detrimental to animals and plants in natural water bodies; it is especially harmful to biological treatment systems. Regardless of these threats, studies on these specific organic pollutants are limited at present. Consequently, it is extremely essential to promote relevant problem solving efficiently. Currently, only limited processes are available for pretreatment of high-concentration wastewater, and advanced treatment of secondary effluent as compared to the conventional treatment are introduced by current studies. Therefore, in this review, we have systematically generalized the characteristics of petrochemical wastewater; we have particularly summarized and compared different methods (recent developments, influencing factors, etc.) which are applied in pretreatment and advancement of current methods. Additionally, the interaction mechanisms of microbes under a wide range of concentrations of specific organic pollutants and associated degradation pathways have been described comprehensively. Moreover, we have analyzed bioenergy recovery from the degradation/removal of specific organic pollutants with environmental-friendly and economically methods because it can help realize the goal of circular resource utilization during the process of detoxification and minimization. Image 1 • A good toxicity reduction of petrochemical wastewater pretreatment is hydrolysis acidification. • Specific organic pollutants removal is the key of petrochemical wastewater advanced treatment. • The function of microbial community mainly influencing pretreatment effect. • Bioenergy recovering from petrochemical wastewater is economic and viable measure. [ABSTRACT FROM AUTHOR]