Coal Gasification Wastewater Pretreatment with Coagulation and N_2 Flotation Combined System

A N 2 flotation tank combined with coagulation was developed as a pretreatment equipment of biological process to remove oil and other pollutants in coal gasification wastewater( CGW). With optimal PAC dosage of 20 mg / L,the sole coagulation process achieves removal efficiencies of 29. 34% and 26. 83% for oil and COD,respectively. For the sole N 2 floatation process,the optimal N 2 flux and HRT are 20 m3/ h and 20 min. Meanwhile,the oil and COD removal efficiencies are 35. 41% and 14. 26%,respectively. For the combined system of coagulation and N 2 floatation,the optimal parameter values are the same as the ones of separate processes. Correspondingly,the removal efficiencies are 46. 28% and 31. 89% for oil and COD, respectively. Besides,BOD 5 / COD of the effluent is improved. In contrast with conventional dissolved air floatation,the inert gas- N 2 prevents the formation of cyclopentenone, pyridine derivatives, and other heterocyclic aromatic hydrocarbons,thus improving the biodegradability of influent for the subsequent biological processes.

Degradation of Phenolic Compounds in Coal Gasification Wastewater by Biofilm Reactor with Isolated Klebsiella sp.

This study was conducted to evaluate the degradation of phenolic compounds by one strain isolated from coal gasification wastewater( CGW). 16S rRNA gene sequences homology and phylogenetic analysis showed that the isolate is belonged to the genus Klebsiella sp. The effect of different phenolic compounds on the isolate was investigated by determining OD600and phenoloxidase activity,of which the results showed that the isolate can utilize phenol,4-methyl phenol,3,5-dimethyl phenol and resorcinol as carbon resources. The biofilm reactor( formed by the isolate) can resist the influent concentration of phenolic compounds as high as750 mg /L when fed with synthetic CGW and incubated at optimum conditions. The capacity of improving the biodegradability of CGW through degrading phenolic compounds was testified with fed the biofilm reactor with real CGW. Thus,it might be an effective strain for bioaugmentation of CGW treatment.

A Pilot-scale Study on Coal Gasification Wastewater Reclamation Using Pretreatment Alternatives Combined with Ultrafiltration and Reverse Osmosis

Aims to investigate the performance of the pilot-scale reclamation plant for coal gasification wastewater( CGW) using ultrafiltration and reverse osmosis with appropriate pretreatment alternatives,different pre-treatment alternatives- coagulation,adsorption,and ozonation methods were employed to treat the secondary effluent of coal gasification wastewater( SECGW) in a pilot-scale pressurized membrane system. The performance was compared to choose the most suitable pre-treatment alternative for the SECGW reclamation.Ozone reaction achieved highest COD removal efficiency( 79.6%- 91.0%),resulting in the stable normalized parameters of the subsequent ultrafiltration and reverse osmoses. In contrast,the coagulation and adsorption processes achieved only 32. 8%- 45. 7% and 53. 1%- 64. 6% decreases in COD,respectively. The residual organic pollutants in the reverse osmosis feed water led to an increase in normalized pressure drop and a decrease in normalized permeability( or membrane transference coefficient). The hydrophobic fraction was the main constituent( approx. 70% of DOC) in pretreated SECGW, and the hydrophobic-neutral fraction contributed mostly to the UV absorbance( 53%). Fluorescence excitation emission matrices revealed that ozonation removed most of the hydrophobic and aromatic proteins such as tyrosine and tryptophan which dominated in raw wastewater. The recalcitrant compounds such as phenolic compounds, heterocyclic compounds,especially long-chain hydrocarbons,which were easily attached to the membrane surface and contributed to organic fouling,could be oxidized and mineralized by ozone. Among the three pretreatments,ozonation showed highest removal efficiencies of hydrophobic and aromatic proteins,therefore resulting in highest normalized permeability.

Performance of the Full-scale Loop Hybrid Reactor Treating Coal Gasification Wastewater under Different Recirculation Modes

This paper aims to investigate the simultaneous removal efficiencies of both COD and nitrogen in a single reactor treating coal gasification wastewater( CGW). A novel loop hybrid reactor was developed and operated under different recirculation modes in order to achieve simultaneous removal of refractory compounds and total nitrogen( TN) in a full-scale CGW treatment plant. Mid-ditch recirculation was superior to other operational modes in terms of the NH3-N and TN removal,resulting in a TN removal efficiency of 52. 3%.Although the system achieved equal COD removal rates under different recirculation modes,hydrophobic acid( HPO-A) fraction of effluent dissolved organic matter( DOMef) in mid-ditch recirculation mode accounted for35.7%,compared to the proportions of 59. 2%,45. 3% and 39. 4% for the other modes. The ultraviolet absorbance to dissolved organic carbon ratio test revealed that effluent under mid-ditch recirculation mode contained more non-aromatic hydrophilic components. Furthermore,appropriate recirculation and anoxic / oxic( A/O) partitions were also demonstrated to remove some refractory metabolites( phenols,alkanes,aniline,etc.),which reduced the chromaticity and improved the biodegradability.

Supported liquid membrane extraction to treat coal gasification wastewater containing high concentrations phenol

The hollow fiber supported liquid membrane extraction was introduced to treat coal gasification wastewater to recover phenolic compounds,with tributyl phosphate (TBP) as carrier,kerosene as the membrane solvent,sodium hydroxide solution as the stripping agent and PVDF as the membrane material. Factors having strong impact on the extraction efficiency were studied in detail,including the mass transfer mode,twophase flow rate,stripping phase concentration. As extraction system with 20% TBP-kerosene,parallel flow mass transfer,stripping phase concentration 0.1 mol/L,the optimal operating conditions could be obtained. Under the optimum operating conditions,the time required to reach equilibrium for the extraction is 50 min, and extraction efficiency of phenol is 86. 2% and the phenol concentration of effluent is 98.64 mg/L.

Analysis of organic compounds in coal gasification wastewater

A procedure for analysis of organic pollutants in coal gasification wastewater was developed, including a series extraction steps at different pH, followed by LC separation or resin adsorption, then analyzed by GC or GC/MS. More than 200 organic pollutants in 22 categories were determined. CH2CL2 extraction at NaHCO3 presence was used to separate carboxylic acids with phenolic compounds in aqueous. Derivatization with acetic anhydride was used for analyses of mono-, di-, poly-hydroxyl phenolic compounds. 21 mono-hydroxyl phenols and 13 di-hydroxyl phenols were determined from the coai gasification wastewater samples. Derivatization with BF3-CH3OH was used for analysis of carboxylic acid. 17 mono-carboxyl, 4 di-carboxyl acids and 6 aromatic acids were determined from coal gasification wastewater samples.

Enhanced anaerobic biodegradability of real coal gasification wastewater with methanol addition

Coal gasification effluent is a typical refractory industrial wastewater with a very poor anaerobic biodegradability due to its toxicity. Methanol was introduced to improve anaerobic biodegradability of real coal gasification wastewater, and the effect of methanol addition on the performance was investigated in a mesophilic upflow anaerobic sludge bed reactor with a hydraulic retention time of 24 hr. Experimental results indicated that anaerobic treatment of coal gasification wastewater was feasible with the addition of methanol. The corresponding maximum COD and phenol removal rates were 71% and 75%, respectively, with methanol concentration of 500 mg COD/L for a total organic loading rate of 3.5 kg COD/（m^3.day） and a phenol loading rate of 0.6 kg/（m^3.day）. The phenol removal rate was not improved with a higher methanol concentration of 1000 mg COD/L. Substrate utilization rate （SUR） tests indicated that the SURs of phenol were 106, 132, and 83 mg phenol/（g VSS.day） at methanol concentrations of 250, 500, and 1000 mg COD/L, respectively, and only 45 mg phenol/（g VSS.day） in the control reactor. The presence of methanol could reduce the toxicity of coal gasification wastewater and increase the biodegradation of phenolic compounds.

Inhibition and recovery of nitrification in treating real coal gasification wastewater with moving bed biofilm reactor

Moving bed biofilm reactor （MBBR） was used to treat real coal gasification wastewater. Nitrification of the MBBR was inhibited almost completely during start-up period. Sudden increase of influent total NH 3 concentration was the main factor inducing nitrification inhibition. Increasing DO concentration in the bulk liquid （from 2 to 3 mg/L） had little effect on nitrification recovery. Nitrification of the MBBR recovered partially by the addition of nitrifying sludge into the reactor and almost ceased within 5 days. Nitrification ratio of the MBBR achieved 65% within 12 days by increasing dilute ratio of the influent wastewater with tap water. The ratio of nitrification decreased to 25% when influent COD concentration increased from 650 to 1000 mg/L after nitrification recovery and recovered 70% for another 4 days.

Inhibitory effect of high phenol concentration in treating coal gasification wastewater in anaerobic biofilter

In this paper, the inhibition of methanogens by phenol in coal gasification wastewater（CGW）was investigated by both anaerobic toxicity tests and a lab-scale anaerobic biofilter reactor（AF）. The anaerobic toxicity tests indicated that keeping the phenol concentration in the influent under 280 mg/L could maintain the methanogenic activity. In the AF treating CGW,the result showed that adding glucose solution as co-substrate could be beneficial for the quick start-up of the reactor. The effluent chemical oxygen demand（COD） and total phenol reached1200 and 100 mg/L, respectively, and the methane production rate was 175 m L CH4/g COD/day.However, if the concentration of phenol was increased, the inhibition of anaerobic micro-organisms was irreversible. The threshold of total phenol for AF operation was 200–250 mg/L. The extracellular polymeric substances（EPS） and particle size distribution of anaerobic granular sludge in the different stages were also examined, and the results indicated that the influence of toxicity in the system was more serious than its effect on flocculation of EPS. Moreover, the proportion of small size anaerobic granular sludge gradually increased from10.2% to 34.6%. The results of high through-put sequencing indicated that the abundance of the Chloroflexi and Planctomycetes was inhibited by the toxicity of the CGW, and some shifts in the microbial community were observed at different stages.

On the fouling mechanism of polysulfone ultrafiltration membrane in the treatment of coal gasification wastewater

Membrane fouling has been investigated by using a polysulfone ultrafiltration membrane with the molecular weight cutoff of 20 kDa to treat crushed coal pressurized gasification wastewater. Under the conditions of different feed pressures, the permeate flux declines and rejection coefficients of pollutants referring to three parameters （total organic carbon （TOC）, chroma and turbidity） were studied. The membrane fouling mechanism was simulated with three classical membrane fouling models. The membrane image and pollutants were analyzed by scanning electron microscopy and gas chromatography-mass spectrography （GC-MS）. The results indicate that the permeate flux decreases with volume reduction factor before reaching a constant value. The rejection coefficients were also measured： fTOC = 70.5%,fc = 84.9% andfa- = 91%. Further analysis shows that the higher the feed pressure is, the sooner the permeate flux reaches constant value and the more sharply the permeate flux declines. Constant flux indicates a nonlinear growth with feed pressure （PF）： when Pr equals 1.2 bar, the mark for the critical flux, slight membrane fouling occurs; when PF exceeds 1.2 bar, cake layer pollution aggravates. Also the rejection coefficients of global pollutant increases slightly with PF, suggesting the possibility of cake compression when PF exceeds 1.2 bar. Through regression analysis, the fouling of polysulfone ultrafiltration membrane could be fitted very well by cake filtration model. The membrane pollutants were identified as phthalate esters and long-chain alkenes by GC-MS, and a certain amount of inorganic pollutants by X-ray photoelectron spectroscopy.

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 14.2 mg/L,respectively.Also,the rate of methane production reached 169.0 m L CH_4/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.

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 NH_3-N and phenol.The results showed that increasing phenol loading had an adverse effect on NH_3-N removal;the concentration in effluent at phenol loading of 40 mg phenol/（L·day） was 7.3 mg/L, 36.3%of that at 200 mg phenol/（L·day）. The enzyme ammonia monooxygenase showed more sensitivity than hydroxylamine oxidoreductase to the inhibitory effect of phenol, with32.2% and 10.5% activity inhibition, respectively at 200 mg 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.

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 GAG 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）.

An experimental investigation on phenol wastewater treatment from coal gasification by pervaporation with NaY molecular Sieve filling membrane

In the experiment,PDMS membrane with NaY molecular sieve filling were chosen as the experimental objects and the flux of phenol and removal efficiency of phenol as evaluation index,the effect of the system operating temperature,the flow rate,liquid membrane downstream pressure,operation time,and filling proportion of NaY molecular sieve on pervaporation treatment efficiency for wastewater from coal gasification were investigated. With the increase of temperature and feed flow rate,pervaporation flux and phenol removal efficiency increases. The decrease of the membrane downstream pressure and elevating NaY molecular sieve filling proportion may result in the increase of flux and then phenol removal efficiency improves. When NaY molecular sieve filling proportion is 45% ,treatment efficiency is the best for coal gasification wastewater containing 1850 mg/L phenol as the flux of phenol was 12948. 23 mg/(h·m2) .

Conceptual design of energy-saving stripping process for industrial sour water

Sour water contains ammonia,carbon dioxide,and hydrogen sulfides,producing from oil refining,coking,and coal gasification.To reduce the energy consumption in sour water stripping,a novel process is proposed which integrates with the bottom flashing mechanical vapor recompression heat pump(MVRHP)for treating such wastewater.Here,Aspen PlusTM as a powerful set of chemical process simulation software is utilized to investigate the economy and feasibility of the novel process.Comparison of the results of two process simulations,it can be seen that it is possible to reduce the total annual cost by nearly 45%to adopt the novel process,despite the capital investment increase 45%more than the conventional process.Thus,the provided conceptual design will play a guiding role in the industrialization of the process.