Effect of powdered activated carbon technology on short-cut nitrogen removal for coal gasification wastewater

Efficient flocculation pretreatment of coal gasification wastewater by halophilic bacterium Halovibrio variabilis TG-5

The isolated halophilic bacterial strain Halovibrio variabilis TG-5 showed a good performance in the pretreatment of coal gasification wastewater. With the optimum culture conditions of pH = 7, a temperature of 46 °C, and a salinity of 15%, the chemical oxygen demand and volatile phenol content of pretreated wastewater were decreased to 1721 mg/L and 94 mg/L, respectively. The removal rates of chemical oxygen demand and volatile phenol were over 90% and 70%, respectively. At the optimum salinity conditions of 15%, the total yield of intracellular compatible solutes and the extracellular transient released yield under hypotonic conditions were increased to 6.88 g/L and 3.45 g/L, respectively. The essential compatible solutes such as L-lysine, L-valine, and betaine were important in flocculation mechanism in wastewater pretreatment. This study provided a new method for pretreating coal gasification wastewater by halophilic microorganisms, and revealed the crucial roles of compatible solutes in the flocculation process.

Overview of enhancing biological treatment of coal chemical wastewater: New strategies and future directions

Coal chemical wastewater (CCW) is a type of refractory industrial wastewater, and its treatment has become the main bottleneck restricting the sustainable development of novel coal chemical industry. Biological treatment is considered as an economical, effective and environmentally friendly technology for CCW treatment. However, conventional biological process is difficult to achieve the efficient removal of refractory organics because of CCW with the characteristics of composition complexity and high toxicity. Therefore, seeking the novel enhancement strategy appears to be a favorable solution for enhancing biological treatment efficiency of CCW. This review focuses on presenting a comprehensive picture about the exogenous enhancement strategies for CCW biological treatment. The performance and potential application of exogenous enhancement strategies, including co-metabolic substrate enhancement, biofilm filler enhancement, adsorption material enhancement and conductive mediator enhancement, were expounded. Meanwhile, the enhancing mechanisms of different strategies were comprehensively discussed from a biological perspective. Furthermore, the prospects of enhancement strategies based on the engineering performance, economic cost and environmental impact (3E) evaluation were introduced. And novel enhancement strategy based on "low carbon emissions", "resource recycling" and "water environment security" in the context of carbon neutrality was proposed. Taken together, this review provides technical reference and new direction to facilitate the regulation and optimization of typical industrial wastewater biological treatment.

Copper-based Ruddlesden-Popper perovskite oxides activated hydrogen peroxide for coal pyrolysis wastewater (CPW) degradation: Performance and mechanism

Coal pyrolysis wastewater (CPW) contained all kinds of toxic and harmful components, which would seriously threaten the natural environment and human health. However, the traditional advanced oxidation processes frequently failed to remove phenolic substances. An A₂BO₄-type perovskite (La₂CuO₄) was successfully synthesized through sol-gel process and first applied in the treatment of CPW. More than 90% of 3, 5-dimethylphenol (DMP) was removed within 200 min at neutral conditions. Moreover, La₂CuO₄ also displayed excellent catalytic activity and stability in the actual CPW treatment process. Results demonstrated that DMP was removed through the attack of ∙OH, ∙O₂^- and ¹O₂ in La₂CuO₄/H₂O₂ system. The La₂CuO₄ were more favorable for H₂O₂ activation and have a lower adsorption energy than LaFeO₃. XPS of fresh and spent La₂CuO₄ illustrated that the decomposition of hydrogen peroxide (H₂O₂) was mainly due to the redox cycle between surface copper and oxygen species. Moreover, the possible degradation pathway of DMP was deduced by identifying degradation products and analyzing density functional theory (DFT) calculations. This research provided a novel strategy for the development of perovskite-based catalytic materials on the treatment of practical CPW.

Environmental contamination by heterocyclic Polynuclear aromatic hydrocarbons and their microbial degradation

Heterocyclic polynuclear aromatic hydrocarbons (PAHs) have been detected in all environmental matrices at few ppb to several ppm concentrations and they are characterized by high polarity. Some heterocyclic PAHs are mutagenic and carcinogenic to humans and various organisms. Despite being potent environmental pollutants, these compounds have received less attention. This paper focuses on the sources and occurrence of these compounds and their microbial degradation using diverse species of bacteria, fungi, and algae. Complete removal of 1.8 to 2614 mg/L of nitrogen heterocyclic PAH (PANH), 0.27 to 184 mg/L of sulfur heterocyclic PAH (PASH), and 0.6 to 120 mg/L of oxygen heterocyclic PAH (PAOH) compounds by various microbial species was observed between 3 h and 18 days, 8 h to 6 days, and 4 h to 250 h, respectively under aerobic condition. Strategies for enhancing the removal of heterocyclic PAHs from aquatic systems are also discussed along with the challenges.

Binary Dye Removal from Simulated Wastewater Using Reduced Graphene Oxide Loaded with Fe-Cu Bimetallic Nanocomposites Combined with an Artificial Neural Network

Reduced graphene oxide loaded with an iron-copper nanocomposite was prepared in this study, using graphene oxide as a carrier and ferrous sulfate, copper chloride and sodium borohydride as raw materials. The obtained material was prepared for eliminating hazardous dye carmine and the binary dye mixture of carmine and Congo red. The process of carmine dye removal by the nanocomposite was modeled and optimized through response surface methodology and artificial intelligence (artificial neural network-particle swarm optimization and artificial neural network-genetic algorithm) based on single-factor experiments. The results demonstrated that the surface area of the nanocomposite was 41.255 m2/g, the pore size distribution was centered at 2.125 nm, and the saturation magnetization was up to 108.33 emu/g. A comparison of the material before and after the reaction showed that the material could theoretically be reused three times. The absolute error between the predicted and experimental values derived by using artificial neural network-particle swarm optimization was the smallest, indicating that this model was suitable to remove carmine from simulated wastewater. The dose factor was the key factor in the adsorption process. This process could be described with the pseudo-second-order kinetic model, and the maximum adsorption capacity was 1848.96 mg/g. The removal rate of the mixed dyes reached 96.85% under the optimal conditions (the dosage of rGO/Fe/Cu was 20 mg, the pH was equal to 4, the initial concentration of the mixed dyes was 500 mg/L, and the reaction time was 14 min), reflecting the excellent adsorption capability of the material.

Effect of low-intensity electric current field and iron anode on biological nitrate removal in wastewater with low COD to nitrogen ratio from coal pyrolysis

Mixotrophic nitrate removal in wastewater from coal pyrolysis was achieved in microbial electrolysis cell with iron anode (iron-MEC). The effect of voltage, iron anode and conductivity were investigated. The effluent TN concentration was 8.35 ± 1.94 mg/L in iron-MEC when the conductivity of the wastewater was adjusted to 3.97 ± 0.08 mS/cm, which was lower than that in no-treated reactor. The increase of current density, which was resulted from the elevation of conductivity, promoted the iron corrosion and Fe2+ ion generation. Therefore, more Fe2+ ion was utilized by nitrate reducing ferrous oxidation bacteria (NRFOB) used to reduce nitrate. The microbial community analysis demonstrated that NRFOB, including Acidovorax and Bradyrhizobium, possessed a higher abundance in iron-MEC. The enrichment of Geobacter in iron-MEC might imply that the part of Fe(III) produced by ferrous oxidation was reduced by Geobacter, which established an iron cycle. Moreover, the production of N2O was decreased by the formation of Fe2+ ion.

Speciation and conversion of carbon and nitrogen in young landfill leachate during anaerobic biological pretreatment

There is an increasing need for landfill leachate pretreatment prior to discharge to wastewater treatment plants due to increasingly stringent sewer discharge limits. Lab-scale tests have shown that the anaerobic biological processes can effectively remove chemical oxygen demand and dissolved organic carbon from landfill leachate. Our work expands the knowledge in anaerobic leachate pretreatment by systematically studying the conversion of carbon and nitrogen species, particularly their recalcitrant fractions in a submerged anaerobic biofilm reactor using real-world leachate from a typical young municipal solid waste landfill. After reaching steady state, the reactor removed 41.7% of the fulvic acids (i.e., 1290 mg C/L). While compounds with a low degree of oxidation (O:C < 0.2) and compounds with a low degree of saturation (H:C < 1) were removed, compounds that were more oxidized (O:C > 0.2) and more saturated (H:C > 1) were produced. At steady state, 98% of recalcitrant dissolved organic nitrogen (i.e., rDON = 222 mg N/L) was removed. Compared to the DON in the raw leachate, the produced DON in the pre-treated leachate were more oxidized (O:C > 0.35) and more bioavailable (N:C > 0.07). The submerged anaerobic biofilm reactor may be an efficient leachate pretreatment method if rDON removal is needed.

Anaerobic biotransformation and potential impact of quinoline in an anaerobic methanogenic reactor treating synthetic coal gasification wastewater and response of microbial community

Phenolic and quinoline compounds are the most primary organic pollutants in coal gasification wastewater (CGW), but the biotransformation of quinoline compounds under methanogenic condition and their potential impacts on treatment performance of CGW are still unclear. Anaerobic biotransformation pathways of quinoline in an upflow anaerobic sludge blanket reactor treating synthetic CGW and response of microbial community were firstly investigated. The result indicated that the degradation of 2(1 H)-quinolinone was the rate-limiting step for the complete conversion of quinoline under methanogenic condition. The reactor performed stably at total phenols concentration of 1000 mg L^-1 with a gradual increase of quinoline concentration from 100 to 600 mg L^-1. However, the reactor performance was rapidly deteriorated from 98% of COD removal to about 80% at quinoline concentration of 1200 mg L^-1 resulting from the accumulation of 2(1 H)-quinolinone. Correspondingly, phenol utilization rate of sludge was significantly reduced by 61% while quinoline utilization rate of sludge was increased by 132%. As phenol degraders, Syntrophorhabdus gradually predominated along with the increase of quinoline concentration, but Syntrophus declined inversely. Compared with syntrophs, acetotrophic methanogens could quickly adapt to quinoline toxicity and tolerate higher quinoline stress. Therefore, anaerobic digestion is an effective method for eliminating quinoline and phenol in CGW.

Simultaneous nitrification and denitrification (SND) bioaugmentation with Pseudomonas sp. HJ3 inoculated for enhancing phenol and nitrogen removal in coal gasification wastewater

A simultaneous nitrification and denitrification (SND) bioaugmention system with Pseudomonas sp. HJ3 inoculated was established to explore the potential of simultaneous phenol and nitrogen removal in coal gasification wastewater (CGW). When the concentration of influent chemical oxygen demand (COD) and total phenols (TPh) was 1,765.94 ± 27.43 mg/L and 289.55 ± 10.32 mg/L, the average removal efficiency of COD and TPh at the stable operating stage reached 64.07% ± 0.76% and 74.91% ± 0.33%, respectively. Meanwhile, the average removal efficiency of NH₄ ⁺-N and total nitrogen (TN) reached 67.96% ± 0.17% and 57.95% ± 0.12%, respectively. The maximum SND efficiency reached 83.51%. Furthermore, SND bioaugmentation performed with good nitrification tolerance of phenol shock load and significantly reduced toxic inhibition of organisms. Additionally, the microbial community analysis indicated that Pseudomonas sp. HJ3 was the predominant bacterium in the SND bioaugmentation system. Moreover, the indigenous nitrogen removal bacteria such as Thauera, Acidovorax and Stenotrophomonas were enriched, which further enhanced the nitrogen removal in the SND bioaugmentation system. The results demonstrated the promising application of SND bioaugmentation for enhancing simultaneous phenol and nitrogen removal in CGW treatment.

Effect of low-intensity direct current electric field on microbial nitrate removal in coal pyrolysis wastewater with low COD to nitrogen ratio

The coupling of bioelectrochemical system with the biological denitrification process (R1) was constructed for nitrate removal in coal pyrolysis wastewater (CPW) and the effect of low-intensity direct current electric field was investigated. Compared with control reactor (R2), the total nitrogen (TN) removal efficiency in R1 at the optimized voltage of 0.9 V was 94.20 ± 2.14%, which was 14.42% higher than that in R2. The biofilm on the cathode of R1 enhanced the nitrate reducing, however, nitrite was only reduced by bacteria in suspended activated sludge, which was confirmed by cyclic voltammetry measurement (CV). Microbial community network analysis revealed that exoelectrogenic bacteria of Pseudomonas was enriched on the anode of R1, and the "small world", including Zoogloea, Pseudomonas and Arenimonas, was established under the stimulation of voltage. Therefore, Pseudomonas transferred electron to anode, and Arenimonas could utilize electron from anode to reduce nitrate, which enhanced TN removal in R1.

Enhanced nitrogen removal of coal pyrolysis wastewater with low COD to nitrogen ratio by partial nitrification-denitrification bioprocess assisted with polycaprolactone

The purpose of this study is to investigate the enhancement of polycaprolactone (PCL) on total nitrogen (TN) removal of coal pyrolysis wastewater (CPW) with low COD to nitrogen ratio by partial nitrification-denitrification bioprocess (PNDB) in one single reactor. With the innovative combination of PCL and PNDB, the TN removal efficiency in the experimental reactor (signed as R1) was 10.21% higher than control reactor (R2). Nitrite accumulation percentage (NAP) in R1 was 82.02%, which was 17.49% higher than R2 at the dissolved oxygen (DO) concentration of 0.9-1.5 mg/L, for the reason that the extra DO was consumed by PCL biodegradation at the aerobic period. Gel permeation chromatography (GPC) results demonstrated that organics with the molecular weight of 185 Da, which could serve as additional carbon sources for denitrifiers, were generated during the PCL hydrolysis process at the anoxic period. PCL was hydrolyzed by extracellular enzymes with the break of the ester bond which was confirmed by FT-IR spectrometer. Microbial community analysis revealed that Ferruginibacter was the dominant hydrolysis bacteria in R1. Nitrosomonas were the main ammonium-oxidizing bacteria (AOB) and Hyphomicrobium were the denitrifiers in this study.

Synergistic degradation on phenolic compounds of coal pyrolysis wastewater (CPW) by lignite activated coke-active sludge (LAC-AS) process: Insights into succession of microbial community under selective pressure

This study illustrated synergistic degradation of phenolic compounds by LAC-AS process via the insight into succession of microbial community under selective pressure. The results demonstrated that high phenols exhibited toxicity pressure to single AS process by eliminating non-tolerate bacteria, inducing vicious circulation by intermediates (catechol, nitrate, etc.) accumulation. However, LAC exerted another selective pressure and facilitated positive bio-community succession of moving biological bed reactor (MBBR). Firstly, it created rich microenvironments for diverse bacteria and promoted resilient adsorption for phenols with the assistance of biodegradation. Secondly, LAC enriched facultative bacteria, which developed multiple degradation paths on phenols and nitrogen based on multifunctional genes, counteracting the toxicity pressure. Specifically, phenols were degraded by the combination of anaerobic hydrolysis and oxidation, while conventional and shortcut nitrification-denitrification (SND) and nitrogen fixation all participated in nitrogen removal, achieving high removal of COD (93.49%), Tph (93.74%), TN (92.20%) and NH₄⁺-N (93.20%) under the highest phenols.

Two-stage air stripping combined with hydrolysis acidification process for coal gasification wastewater pretreatment

Coal gasification wastewater is mainly from gas washing, condensation and purification processes in the gas furnace with high NH₃-N (nitrogen in water in the form of free ammonia (NH₃) and ammonium ion (NH₄ ⁺)), TN (total nitrogen) and refractory organics content, which will inhibit the subsequent biological treatment. The 'air stripping - hydrolysis acidification - air stripping' process was proposed as the pretreatment for coal gasification wastewater to improve the biodegradability and nitrogen removal, which could reduce the subsequent biological treatment load. The first-stage air stripping process before hydrolysis acidification could achieve a significant removal of NH₃-N (97.0%) and volatile phenol (70.0%), reducing the corresponding toxicity on hydrolysis acidification. The group with air stripping had more abundant microbial communities and a more effective organic degradation performance in hydrolysis acidification than that without air stripping. The second-stage air stripping removed NH₃-N released from hydrolysis acidification, and significantly reduced the TN concentration in effluent. The whole process achieved a TN removal from 2,000 ± 100 mg/L to 160 ± 80 mg/L, and a total phenols removal from 700 ± 50 mg/L to 80 ±20 mg/L.

Selective adsorption and bioavailability relevance of the cyclic organics in anaerobic pretreated coal pyrolysis wastewater by lignite activated coke

This study originally investigated the selective adsorption of cyclic organics in APCPW by LAC, corresponding to the change of the bioavailability. As a product from low rank coal, LAC showed more oxygen (O)-containing groups and mesoporous structure than PAC. Adsorption mechanisms were analyzed by equilibrium isotherms and kinetics models combined with physicochemical properties of adsorbent and adsorbates. The results indicated that selectivity of LAC was dominated by chemical interaction and its mesoporous, and was enhanced by hydrophobicity of adsorbates. In addition, PAC and LAC were applied for the treatment of APCPW. Compared with PAC, LAC adsorption exhibited superior removal efficiency of Tph, TOC and TN at 85.90%, 91.15% and 51.64%, respectively. Furthermore, preferential adsorption of biotoxic and bioresistant cyclic organics by LAC was further proved by GC-MS analysis, resulting in increased bioavailability of APCPW. Specifically, LAC exerted sustained detoxication capacity until 86.50% reduction of TU by D. magna evaluation, and lowered toxicity rank (TU = 4.51, classIII) to T. pyriformis than that after PAC adsorption (TU > 10, ClassIV). Meanwhile, biodegradability was also improved by 9.17% after LAC adsorption. Lastly, LAC would exhibit great economic benefits as an alternative for PAC in subsequent process after anaerobic pretreatment.

The mechanism of synergistic effect between iron-carbon microelectrolysis and biodegradation for strengthening phenols removal in coal gasification wastewater treatment

A novel iron-carbon microelectrolysis (ICME) inoculated with activated sludge (AS) process was specifically designed to look into the roles of microelectrolysis and biodegradation as well as their synergistic effect on phenols removal in coal gasification wastewater (CGW) treatment. The results indicated that the removal efficiency of COD, phenols and TOC in integrated ICME-AS process reached 87.36 ± 2.98%, 92.62 ± 0.76% and 84.45 ± 0.65%, respectively. Moreover, phenols-degrading bacteria and electrochemical-active bacteria presented better adaptability to phenolic impact. Meanwhile their syntrophic interaction was driven under the simulation of microelectrolysis. Furthermore, electrochemical redox efficiency was significantly improved, and the corresponding maximum power output reached 0.043 ± 0.01 mW/cm². Apparently, the synergistic effect between microelectrolysis and biological action effectively strengthened phenols degradation and electricity generation. The results proved that the integrated ICME-AS process was a promising technology applied for CGW and other refractory industrial wastewater treatments.

Overview of the state of the art of processes and technical bottlenecks for coal gasification wastewater treatment

CGWW is major waste stream resulting from a number of activities of the low/medium temperature gasification unit that occurs during the production of natural gas. The resulting effluent contains a broad spectrum of organic and inorganic contaminants and exerts a negative influence on the environment, mainly due to the presence of toxic and refractory compounds. So far, various technologies have been applied for treatment of CGWW, while few reviews are available in the literature. Thus, this review attempts to offer a comprehensive picture about CGWW. An overview about pretreatment, biological and advanced processes for treatment of CGWW is presented, and the degradation mechanism of toxic and refractory pollutants is also elaborated. Technical bottlenecks existing in the operation of coal chemical industries, including foam proliferation, odors and biotoxicity risk, are detailed analyzed. Finally, the prospects of treatment for CGWW are discussed based on the concept of "wastewater is money". The review can be provided as an effective technical support for the construction and operation of coal gasification industries.

Microbial nitrate removal in biologically enhanced treated coal gasification wastewater of low COD to nitrate ratio by coupling biological denitrification with iron and carbon micro-electrolysis

Mixotrophic denitrification coupled biological denitrification with iron and carbon micro-electrolysis (IC-ME) is a promising emerging bioprocess for nitrate removal of biologically enhanced treated coal gasification wastewater (BECGW) with low COD to nitrate ratio. TN removal efficiency in R1 with IC-ME assisted was 16.64% higher than R2 with scrap zero valent iron addition, 23.05% higher than R3 with active carbon assisted, 30.51% higher than R4 with only active sludge addition, 80.85% higher than R5 utilizing single IC-ME as control. Fe²⁺ generated from IC-ME decreased the production of N₂O and enriched more Nitrate-reducing Fe(Ⅱ) oxidation bacteria (NRFOB) Acidovorax and Thiobacillus, which could convert nitrate to nitrogen gas. And the presence of Fe³⁺, as the Fe²⁺ oxidation product, could stimulate the growth of Fe(III)-reducing strain (FRB) that indicated by redundancy analysis. Microbial network analysis demonstrated FRB Geothrix had a co-occurrence relationship with other bacteria, revealing its dominant involvement in nitrate removal of BECGW.

Enhanced degradation of phenolic compounds in coal gasification wastewater by a novel integration of micro-electrolysis with biological reactor (MEBR) under the micro-oxygen condition

The aim of this work was to study an integration of micro-electrolysis with biological reactor (MEBR) for strengthening removal of phenolic compounds in coal gasification wastewater (CGW). The results indicated MEBR achieved high efficiencies in removal of COD and phenolic compounds as well as improvement of biodegradability of CGW under the micro-oxygen condition. The integrated MEBR process was more favorable to improvement of the structural stability of activated sludge and biodiversity of specific functional microbial communities. Especially, Shewanella and Pseudomonas were enriched to accelerate the extracellular electron transfer, finally facilitating the degradation of phenolic compounds. Moreover, MEBR process effectively relieved passivation of Fe-C filler surface and prolonged lifespan of Fe-C filler. Accordingly, the synergetic effect between iron-carbon micro-electrolysis (ICME) and biological action played a significant role in performance of the integrated process. Therefore, the integrated MEBR was a promising practical process for enhancing CGW treatment.

Enhanced nitrogen removal from coal gasification wastewater by simultaneous nitrification and denitrification (SND) in an oxygen-limited aeration sequencing batch biofilm reactor

Simultaneous nitrification and denitrification (SND) for treating coal gasification wastewater (CGW) was achieved successfully in a lab-scale sequencing batch biofilm reactor (SBBR) by oxygen-limited aeration. SND efficiency increased gradually with the concentration of dissolved oxygen (DO) decreased from 4.5mg/L to 0.35mg/L. The maximum SND efficiency of 81.23% was obtained at DO concentration of 0.35mg/L, and the corresponding removal efficiency of NH₄⁺-N and TN reached 76.91% and 70.23%, respectively. Meanwhile, COD was removed significantly and toxic compounds were degraded into biodegradable substances, which relieved effectively the inhibition on nitrogen removal. The results indicated that oxygen-limited condition performed greater toxic compounds and nitrogen removal compared with the aerobic condition. Furthermore, the results of scanning electron microscopic (SEM) and microbial community structure confirmed robust biofilm formation provided a suitable anoxic micro-environment for co-existence of nitrifying and denitrifying bacteria and organics degradation bacteria in the reactor at oxygen-limited condition.

Simultaneous removal of organic matter and salt ions from coal gasification wastewater RO concentrate and microorganisms succession in a MBR

A lab-scale membrane bioreactor (MBR) with intermittent aeration was operated to treat the reverse osmosis concentrate derived from coal gasification wastewater. Results showed intermittent aeration represented slight effect on organic matter reduction but significant effect on nitrite and nitrate reduction, with 6h aeration and 6h non-aeration, removal efficiencies of organic matter, chloride, sulfate, nitrite and nitrate reached 48.35%, 40.91%, 34.28%, -36.05% and 64.34%, respectively. High-throughput sequencing showed a microorganisms succession from inoculated activated sludge (S1) to activated sludge in MBR (S2) with high salinity. Richness and diversity of microorganisms in S2 was lower than S1 and the community structure of S1 exhibited more even than S2. The most relative abundance of genus in S1 and S2 were unclassified_Desulfarculaceae (9.39%) and Roseibaca (62.1%), respectively. High salinity and intermittent aeration represented different influence on the denitrifying genus, and non-aeration phase provided feasible dissolved oxygen condition for denitrifying genera realizing denitrification.

An advanced anaerobic biofilter with effluent recirculation for phenol removal and methane production in treatment of coal gasification wastewater

An advanced anaerobic biofilter (AF) was introduced for the treatment of coal gasification wastewater (CGW), and effluent recirculation was adopted to enhance phenol removal and methane production. The results indicated that AF was reliable in treating diluted CGW, while its efficiency and stability were seriously reduced when directly treating raw CGW. However, its performance could be greatly enhanced by effluent recirculation. Under optimal effluent recirculation of 0.5 to the influent, concentrations of chemical oxygen demand (COD) and total phenol in the effluent could reach as low as 234.0 and 14.2mg/L, respectively. Also, the rate of methane production reached 169.0mLCH4/L/day. Though CGW seemed to restrain the growth of anaerobic microorganisms, especially methanogens, the inhibition was temporary and reversible, and anaerobic bacteria presented strong tolerance. The activities of methanogens cultivated in CGW could quickly recover on feeding with glucose wastewater (GW). However, the adaptability of anaerobic bacteria to the CGW was very poor and the activity of methanogens could not be improved by long-term domestication. By analysis using the Haldane model, it was further confirmed that high effluent recirculation could result in high activity for hydrolytic bacteria and substrate affinity for toxic matters, but only suitable effluent recirculation could result in high methanogenic activity.

Comparative investigation on integrated vertical-flow biofilters applying sulfur-based and pyrite-based autotrophic denitrification for domestic wastewater treatment

Two parallel biofilters applying sulfur/pyrite-based autotrophic denitrification were investigated for removing COD, TP and TN by a coordinated process. Results demonstrated good performance by removing 86.32% vs 87.14% COD and 92.56% vs 89.65% NH4(+)-N. Biofilter with sulfur (BS) was superior on nitrate (89.74% vs 80.72%) and TN removal (83.18% vs 70.42%) while biofilter with pyrite (BP) was better on TP removal (82.58% vs 77.40%) and maintaining sulfate (27.56mgL(-1) vs 41.55mgL(-1)) and pH (7.13 vs 6.31). Water-permeable adsorbents lowered clogging risk and buffered loading. Clone library revealed reasons of diversities, pH variation and sulfate accumulation of both biofilters. Sulfur was efficient on denitrification but whose byproducts were troublesome, pyrite produced less byproduct but which was sensitive to organics. This research was the first attempt to systematically compare two promising alternatives and their merits/demerits for rural wastewater on-site treatment.

Promoting the bio-cathode formation of a constructed wetland-microbial fuel cell by using powder activated carbon modified alum sludge in anode chamber

MFC centered hybrid technologies have attracted attention during the last few years due to their compatibility and dual advantages of energy recovery and wastewater treatment. In this study, a MFC was integrated into a dewatered alum sludge (DAS)- based vertical upflow constructed wetland (CW). Powder activate carbon (PAC) was used in the anode area in varied percentage with DAS to explore its influences on the performance of the CW-MFC system. The trial has demonstrated that the inclusion of PAC improved the removal efficiencies of COD, TN and RP. More significantly, increasing the proportion of PAC from 2% to 10% can significantly enhance the maximum power densities from 36.58 mW/m² to 87.79 mW/m². The induced favorable environment for bio-cathode formation might be the main reason for this improvement since the content of total extracellular polymeric substances (TEPS) of the substrate in the cathode area almost doubled (from 44.59 μg/g wet sludge to 87.70 μg/g wet sludge) as the percentage of PAC increased to 10%. This work provides another potential usage of PAC in CW-MFCs with a higher wastewater treatment efficiency and energy recovery.

Influence of phenol on ammonia removal in an intermittent aeration bioreactor treating biologically pretreated coal gasification wastewater

A laboratory-scale intermittent aeration bioreactor was investigated to treat biologically pretreated coal gasification wastewater that was mainly composed of NH3-N and phenol. The results showed that increasing phenol loading had an adverse effect on NH3-N removal; the concentration in effluent at phenol loading of 40mgphenol/(L·day) was 7.3mg/L, 36.3% of that at 200mg phenol/(L·day). The enzyme ammonia monooxygenase showed more sensitivity than hydroxylamine oxidoreductase to the inhibitory effect of phenol, with 32.2% and 10.5% activity inhibition, respectively at 200mg phenol/(L·day). Owing to intermittent aeration conditions, nitritation-type nitrification and simultaneous nitrification and denitrification (SND) were observed, giving a maximum SND efficiency of 30.5%. Additionally, ammonia oxidizing bacteria (AOB) and denitrifying bacteria were the main group identified by fluorescent in situ hybridization. However, their relative abundance represented opposite variations as phenol loading increased, ranging from 30.1% to 17.5% and 7.6% to 18.2% for AOB and denitrifying bacteria, respectively.

Advanced treatment of biologically pretreated coal gasification wastewater using a novel expansive flow biological intermittent aerated filter process with a ceramic filler from reused coal fly ash

A novel expansive flow biological intermittent aerated filter (BIAF) process was employed for the advanced treatment of real biologically pretreated coal gasification wastewater (CGW) which had poor biodegradability and a low carbon/nitrogen ratio.

Effect of effluent recirculation rate on the performance of anaerobic bio-filter treating coal gasification wastewater under co-digestion conditions

In this study, anaerobic biofilter (AF) was adopted for anaerobic co-digestion of potato starch wastewater (PSW) and coal gasification wastewater (CGW).

The pollutants removal and bacterial community dynamics relationship within a full-scale British Gas/Lurgi coal gasification wastewater treatment using a novel system

The novel system of EBA (based on external circulation anaerobic (EC) process-biological enhanced (BE) process-anoxic/oxic (A/O) process) was applied to treat the British Gas/Lurgi coal gasification wastewater in Erdos, China. After a long time of commissioning, the EBA system represented a stable and highly efficient performance, particularly, the concentrations of COD, NH4(+)-N, total organic carbon, total nitrogen and volatile phenols in the final effluent reached 53, 0.3, 18, 106mg/L and not detected, respectively. Both the GC-MS and fluorescence excitation-emission matrix analyses revealed significant variations of organic compositions in the effluent of different process. The results of high-throughput sequencing represented the EBA system composed 34 main bacteria which were affiliated to 7 phyla. In addition, the canonical correspondence analysis indicated high coherence among community composition, wastewater characteristics and environmental variables, in which the pH, mixed liquid suspended solids and total phenols loading were the most three significant variables.

Determination of biological removal of recalcitrant organic contaminants in coal gasification waste water

Coal gasification waste water treatment needed a sustainable and affordable plan to eliminate the organic contaminants in order to lower the potential environmental and human health risk. In this paper, a laboratory-scale anaerobic-aerobic intermittent system carried out 66 operational cycles together for the treatment of coal gasification waste water and the removal capacity of each organic pollutant. Contaminants included phenols, carboxylic acids, long-chain hydrocarbons, and heterocyclic compounds, wherein the relative content of phenol is up to 57.86%. The long-term removal of 77 organic contaminants was evaluated at different hydraulic retention time (anaerobic24 h + aerobic48 h and anaerobic48 h +aerobic48 h). Contaminant removal ranged from no measurable removal to near-complete removal with effluent concentrations below the detection limit. Contaminant removals followed one of four trends: steady-state removal throughout, increasing removal to steady state (acclimation), decreasing removal, and no removal. Organic degradation and transformation in the reaction were analysed by gas chromatography/mass spectrometry technology.

Soil infiltration bioreactor incorporated with pyrite-based (mixotrophic) denitrification for domestic wastewater treatment

In this study, an integrated two-stage soil infiltration bioreactor incorporated with pyrite-based (mixotrophic) denitrification (SIBPD) was designed for domestic wastewater treatment. Benefited from excellent adsorption ability and water-permeability, soil infiltration could avoid clogging, shorten operating time and lower maintenance cost. Respiration and nitrification were mostly engaged in aerobic stage (AES), while nitrate was majorly removed by pyrite-based mixotrophic denitrification mainly occurred in anaerobic stage (ANS). Fed with synthetic and real wastewater for 120days at 1.5h HRT, SIBPD demonstrated good removal performance showing 87.14% for COD, 92.84% for NH4(+)-N and 82.58% for TP along with 80.72% of nitrate removed by ANS. TN removal efficiency was 83.74% when conducting real wastewater. Compared with sulfur-based process, the effluent pH of SIBPD was maintained at 6.99-7.34 and the highest SO4(2-) concentration was only 64.63mgL(-1). This study revealed a promising and feasible application prospect for on-site domestic wastewater treatment.

Treatment of coal gasification wastewater by membrane bioreactor hybrid powdered activated carbon (MBR–PAC) system

A laboratory-scale membrane bioreactor hybrid powdered activated carbon (MBR–PAC) system was developed to treat coal gasification wastewater to enhance the COD, total phenols (TPh), NH4+ removals and migrate the membrane fouling. Since the MBR–PAC system operated with PAC dosage of 4 g L−1, the maximum removal efficiencies of COD, TPh and NH4+ reached 93%, 99% and 63%, respectively with the corresponding influent concentrations of 2.27 g L−1, 497 mg L−1 and 164 mg N L−1; the PAC extraction efficiencies of COD, TPh and NH4+ were 6%, 3% and 13%, respectively; the transmembrane pressure decreased 34% with PAC after 50 d operation. The results demonstrate that PAC played a key role in the enhancement of biodegradability and mitigation of membrane fouling.

Nitrogen removal from coal gasification wastewater by activated carbon technologies combined with short-cut nitrogen removal process

A system combining granular activated carbon and powdered activated carbon technologies along with shortcut biological nitrogen removal (GAC-PACT-SBNR) was developed to enhance total nitrogen (TN) removal for anaerobically treated coal gasification wastewater with less need for external carbon resources. The TN removal efficiency in SBNR was significantly improved by introducing the effluent from the GAC process into SBNR during the anoxic stage, with removal percentage increasing from 43.8%-49.6% to 68.8%-75.8%. However, the TN removal rate decreased with the progressive deterioration of GAC adsorption. After adding activated sludge to the GAC compartment, the granular carbon had a longer service-life and the demand for external carbon resources became lower. Eventually, the TN removal rate in SBNR was almost constant at approx. 43.3%, as compared to approx. 20.0% before seeding with sludge. In addition, the production of some alkalinity during the denitrification resulted in a net savings in alkalinity requirements for the nitrification reaction and refractory chemical oxygen demand (COD) degradation by autotrophic bacteria in SBNR under oxic conditions. PACT showed excellent resilience to increasing organic loadings. The microbial community analysis revealed that the PACT had a greater variety of bacterial taxons and the dominant species associated with the three compartments were in good agreement with the removal of typical pollutants. The study demonstrated that pre-adsorption by the GAC-sludge process could be a technically and economically feasible method to enhance TN removal in coal gasification wastewater (CGW).

A soil infiltration system incorporated with sulfur-utilizing autotrophic denitrification (SISSAD) for domestic wastewater treatment

To enhance the denitrification performance of soil infiltration, a soil infiltration system incorporated with sulfur-utilizing autotrophic denitrification (SISSAD) for domestic wastewater treatment was developed, and the SISSAD performance was evaluated using synthetic domestic wastewater in this study. The aerobic respiration and nitrification were mainly taken place in the upper aerobic stage (AES), removed 88.44% COD and 89.99% NH4(+)-N. Moreover, autotrophic denitrification occurred in the bottom anaerobic stage (ANS), using the CO2 produced from AES as inorganic carbon source. Results demonstrated that the SISSAD showed a remarkable performance on COD removal efficiency of 95.09%, 84.86% for NO3(-)-N, 95.25% for NH4(+)-N and 93.15% for TP. This research revealed the developed system exhibits a promising application prospect for domestic wastewater in the future.