Treatment Of Coal Gasification Wastewater Research Articles

Treatment of coal gasification wastewater by a two-phase anaerobic digestion

Coal gasification wastewater (CGW) is a refractory wastewater, whose anaerobic treatment has been a severe problem due to its toxicity and poor biodegradability. Using a two-stage anaerobic digestion as a control, the two-phase anaerobic digestion of real CGW was investigated. After 210 d of operation, the maximum removal efficiencies of COD and total phenols (TP) reached 50–60% and 55–60%, respectively, in the two-phase anaerobic digestion at total hydraulic retention time (HRT) of 48 h; the corresponding efficiencies were at low levels of 40–45% and 42–50%, respectively, in the two-stage anaerobic digestion. COD and TP removal efficiencies increased to 69.7 and 65.9%, when 50% of the effluent was recirculated to the hydrolytic acidogenic reactor. Phenol utilization rate and specific methanogenic activity (SMA) were decreased to 57.6 mg phenol/(gVSS d) and 394.3 mg COD-CH4/(gVSS d), respectively, as the HRT in the hydrolytic acidogenic reactor was reduced to 18 h. After the two-phase anaerobic digestion, the wastewater concentrations of the aerobic effluent COD could reach below 150 mg/l when compared to 237.2 mg/l if two-stage anaerobic digestion was done and 328.5 mg/l if sole aerobic pretreatment was done. The results suggested that the two-phase anaerobic digestion improved significantly both anaerobic and aerobic biodegradation of real CGW.

An advanced anaerobic expanded granular sludge bed (AnaEG) for the treatment of coal gasification wastewater

A state-of-the-art advanced anaerobic expanded granular sludge bed (AnaEG) was developed for the anaerobic treatment of coal gasification wastewater (typical industrial wastewater with poor biodegradability and high toxicity).

Bioaugmentation of biological contact oxidation reactor (BCOR) with phenol-degrading bacteria for coal gasification wastewater (CGW) treatment

This study was conducted to evaluate the performance of the biological contact oxidation reactor (BCOR) treating coal gasification wastewater (CGW) after augmented with phenol degrading bacteria (PDB). The PDB were isolated with phenol, 4-methyl phenol, 3,5-dimethyl phenol and resorcinol as carbon resources. Much of the refractory phenolic compounds were converted into easily-biodegradable compounds in spite of low TOC removal. The bioaugmentation with PDB significantly enhanced the removal of COD, total phenols (TP) and NH3-N, with efficiencies from 58% to 78%, 66% to 80%, and 5% to 25%, respectively. In addition, the augmented BCOR exhibited strong recovery capability in TP and COD removal while recovery of NH3-N removal needed longer time. Microbial community analysis revealed that the PDB presented as dominant populations in the bacteria consortia, which in turn determined the overall performance of the system.

Treatment of Lurgi coal gasification wastewater in pre-denitrification anaerobic and aerobic biofilm process

In this paper, a pre-denitrification biofilm process was conducted to investigate the degradation of Lurgi coal gasification wastewater (CGW). Under the HRT of 72h and recycle ratio (R) of 2, 80% of COD and 48.9% of NH4+N could be removed in AOAO system. In order to improve the pollutants removal efficiency, the order of aerobic reactor (O1) and anaerobic tank (A2) was reversed to build the A2O2 system. It was found that A2O2 had a better pollutant removal at the same operation conditions, the maximum removal rates of COD and NH4+N were 94.4% and 90.7%, respectively. Recycle ratio (R) had negligible effect on COD removal, but could strongly affect nitrification efficiency in A2O2. The NH4+N removal rate increased from about 75% at R was 1–90.72% at R was 2, but decreased to 80.31% at R was 3. Batch test results shown that the bio-degradability of nitrogenous heterocyclic compounds (pyridine, pyrrole and imidazole) could be improved as carbon source for denitrification under the condition of cosubstrate (phenol was used in this test) was introduced. Therefore, the results illustrated that the pre-denitrification biofilm process of A2O2 could treat the CGW effectively.

Technical and Economic Analysis of Supercritical Water Oxidation and Biochemical Process for Lurgi Coal Gasification Wastewater Treatment

The technical and economic analysis of supercritical water oxidation (SCWO) and biochemical process for Lurgi coal gasification wastewater (LCGW) treatment were carried out. The findings include the analysis of flow sheet, effluent quality and operation cost of the two processes. Studies show that the SCWO process is more simply and easier to control than the biochemical process. The effluent treated with SCWO process could reach national discharge standard I (GB 8978-1996) without other pretreatment and advanced processes, and could gain 2.3 yuan RMB/t(LCGW). While the operation cost of biochemical treatment is 41.8 yuan YMB/t(LCGW). The SCWO process shows a unique advantage in both technology and economy and will be a promising technique for LCGW treatment.

Recovery strategies for tackling the impact of phenolic compounds in a UASB reactor treating coal gasification wastewater

The impact of phenolic compounds (around 3.2g/L) resulted in a completely failed performance in a mesophilic UASB reactor treating coal gasification wastewater. The recovery strategies, including extension of HRT, dilution, oxygen-limited aeration, and addition of powdered activated carbon were evaluated in batch tests, in order to obtain the most appropriate way for the quick recovery of the failed reactor performance. Results indicated that addition of powdered activated carbon and oxygen-limited aeration were the best recovery strategies in the batch tests. In the UASB reactor, addition of powdered activated carbon of 1g/L shortened the recovery time from 25 to 9days and oxygen-limited aeration of 0–0.5mgO2/L reduced the recovery time to 17days. Reduction of bioavailable concentration of phenolic compounds and recovery of sludge activity were the decisive factors for the recovery strategies to tackle the impact of phenolic compounds in anaerobic treatment of coal gasification wastewater.

Effect of Diatomite Additive on Biomass Respiratory Activity in Activated Sludge

Laboratory and pilot scale experiments indicated that the diatomite additive could improve the stability of activated sludge process and the efficiency of COD removal for coal gasification wastewater treatment. In this paper, the effect of diatomite additive on biomass respiratory activity was studied to investigate the enhancing mechanism. Experimental results showed that diatomite additive could enhance biomass activity obviously when the biomass activity was inhibited by the wastewater with total phenols concentration of 188.9 mg/L -501.2 mg/L. It could be concluded that the mechanism of diatomite enhancing biomass activity were its adsorption of phenols and concentration of DO.

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.

Treatment of coal gasification wastewater by a two-continuous UASB system with step-feed for COD and phenols removal

A two-continuous mesophilic (37 ± 2 °C) UASB system with step-feed was investigated as an attractive optimization strategy for enhancing COD and total phenols removal of the system and improving aerobic biodegradability of real coal gasification wastewater. Through the step-feed period, the maximum removal efficiencies of COD and total phenols reached 55–60% and 58–63% respectively in the system, at an influent flow distribution ratio of 0.2 and influent COD concentration of 2500 mg/L; the corresponding efficiencies were at low levels of 45–50% and 43–50% respectively at total HRT of 48 h during the single-feed period. The maximum specific methanogenic activity and substrate utilization rate were 592 ± 16 mg COD-CH 4/(gVSS d) and 89 ± 12 mg phenol/(gVSS d) during the step-feed operation. After the anaerobic digestion with step-feed, the aerobic effluent COD concentration decreased from 270 ± 9 to 215 ± 10 mg/L. The results suggested that step-feed enhanced the degradation of refractory organics in the second reactor.

Process Development, Simulation, and Industrial Implementation of a New Coal-Gasification Wastewater Treatment Installation for Phenol and Ammonia Removal

Coal-gasification wastewater poses serious problems in the Lurgi process. It cannot be easily purified, as the high pH value of the wastewater limits the dephenolization efficiency of extraction. This work proposes a new process to remove ammonia and sour gas in order to reduce the pH value of the wastewater from 9 to below 7, and next to remove phenol with solvent extraction under acidic conditions. This new process consists of a wastewater stripper with side-draw to remove ammonia and sour gas, an extractor to remove phenol, and two distillation columns to recover extractant. Process simulation was conducted to study the performance of the new process and to perform a detailed design. The complex multicomponent system NH3−CO2−H2S−NaOH−phenol−H2O was analyzed when simulating the wastewater stripping. The new process has been successfully implemented in an industrial installation for coal-gasification wastewater treatment with a capacity of 2000 tons/day. Satisfactory agreement was obtained between the si...

Novel Single Stripper with Side-Draw to Remove Ammonia and Sour Gas Simultaneously for Coal-Gasification Wastewater Treatment and the Industrial Implementation

A large amount of wastewater is produced in the Lurgi coal-gasification process with the complex compounds carbon dioxide, ammonia, phenol, etc., which cause a serious environmental problem. Most o...

Conceptual design and retrofitting of the coal-gasification wastewater treatment process

Abstract The coal-gasification wastewater treatment is the most difficult pollution control task for coal-gasification plants. It is identified that there are two serious problems occurring in the current treatment process, i.e., low performance of phenols removal and plugging induced by ammonia salts. A new treatment process is proposed in this paper to solve these severe problems and pursue clean production. Three technical improvements are introduced in the coal-gasification wastewater treatment process. First, ammonia stripping is accomplished before phenols recovery to reduce pH value of the wastewater and to improve the phenols removal performance of extraction. Second, a complex stripper with a side draw is introduced to stripping ammonia and sour gas simultaneously. It is done to eliminate the ionic interaction during stripping and to improve the removal performance of ammonia and sour gas (carbon dioxide and hydrogen sulphide). Finally, methyl isobutyl ketone (MIBK) is used as extraction solvent instead of diisopropyl ether (DIPE) for further improvement of the phenols removal performance. Conceptual design of the proposed process is accomplished for a large-scale coal-gasification plant based on process simulation. With the proposed process, the concentration of carbon dioxide, hydrogen sulphide and ammonia in wastewater are reduced to trace, less than 10 mg/L, and about 30 mg/L, respectively. As a result, pH value of the wastewater is reduced from >9 to

Study on coal gasification wastewater treatment with aerated biological fluidized bed (ABFB) : Ye, Z. et al. Zhongguo Huanjing Kexue, 2002, 22, (1), 35-35. (In Chinese)

This paper introduces the fundamental principle and characteristics of the ABFB. The ABFB pilot plant with bulk effective volume of 1.5m3 has been made, and its fluidized medium is synthetic porous polymer material. Thephysical properties of the material are 25 times of water regain, specific surface area≥200m2/g, nitrogen content=6.72%, its holding of active groups -NH2, -COOH, -OH, epoxy etc., which are surtable for combination of support andmicroorganism as well as adoption of immobilized microorganism technology. The average biomass in the support is 28g/L (H2O), so it has quite high treating efficiency. There are COD=3450mg/L, NH4+-N=451mg/L and volatile phenol= 177mg/L in coal gasification wastewater while the water treated by ABFB has COD=57.7m2/g, NH4+-N= 0.285mg/L and volatile phenol=0.434mg/L. Its running effect is better than those of biological aerated filter (BAF) and contact oxidation and active carbon fluidized bed. ABFB has characteristics of steady running and powerful resistance to impact load, so it is a kind of advanced technology in wastewater treatment.

Anaerobic Treatment of Coal Gasification Wastewater

A sequence of unit processes consisting of a berl-saddle-packed anaerobic filter, an expanded-bed, granular activated carbon anaerobic reactor and an activated sludge nitrification system was employed for the treatment of synthetically prepared coal gasification wastewater. After acclimation, the coal gasification wastewater was fed to the treatment process train at three different chemical oxygen demand levels; these were 1,513. 3,027, and 7,567 mg/ℓ, respectively. No biological activity was observed in the first-stage filter, while excellent removal of organic matter was achieved in the second and third stages of the treatment systems. However, toxicity to the anaerobic culture in the second-stage reactor was observed during the second and third loading levels. This toxicity was overcome by employing a partial replacement schedule of the granular activated carbon medium in the reactor. This study represents an example of how biodegradation and physical adsorption may be successfully combined during the treatment of wastewaters containing toxic or inhibitory substances.

Anaerobic filters for the treatment of coal gasification wastewater

A process train consisting of the following sequence of unit processes, a berl-saddle-packed anaerobic filter, an expanded bed, granular activated carbon anaerobic filter, and an activated sludge nitrification system was evaluated for the treatment of a synthetically prepared coal gasification wastewater. The first-stage anaerobic filter resulted in very little removal of organic matter and no methane production. Excellent reduction in organic matter occurred in the granular activated carbon anaerobic filter. The removal mechanism was initially adsorptive and near the end of the study, removal of organic matter was primarily through conversion to methane gas. It is felt that the success of the activated carbon anaerobic filter was due to the ability of the activated carbon to sequester some components of the wastewater that were toxic to the mixed culture of anaerobic microorganisms. The activated sludge nitrification system resulted in complete ammonia oxidation and was very efficient in final effluent polishing.