Coking Wastewater Treatment Plant Research Articles

Catalytic Wet Air Oxidation of Coke-Plant Wastewater on Ruthenium-Based Eggshell Catalysts in a Bubbling Bed Reactor

Catalytic wet air of coke-plant wastewater was studied in a bubbling bed reactor. Two types of supported Ru-based catalysts, eggshell and uniform catalysts, were employed. Compared with the results in the wet air oxidation of coke-plant wastewater, supported Ru uniform catalysts showed high activity for chemical oxygen demand (COD) and ammonia/ammonium compounds (NH3-N) removal at temperature of 250 degrees C and pressure of 4.8 MPa, and it has been demonstrated that the catalytic activity of uniform catalyst depended strongly on the distribution of active sites of Ru on catalyst. Compared to the corresponding uniform catalysts with the same Ru loading (0.25 wt.% and 0.1 wt.%, respectively), the eggshell catalysts showed higher activities for CODcr removal and much higher activities for NH3-N degradation. The high activity of eggshell catalyst for treatment of coke-plant wastewater can be attributed to the higher density of active Ru sites in the shell layer than that of the corresponding uniform catalyst with the same Ru loading. It has been also evidenced that the active Ru sites in the internal core of uniform catalyst have very little or no contribution to CODcr and NH3-N removal in the total oxidation of coke-plant wastewater.

Treatment of coke plant wastewater by SND fixed biofilm hybrid system

In this article, coke plant wastewater was treated by a simultaneous nitrifying and denitrifying (SND) fixed biofilm hybrid system. The results showed that suitable parameters of the system were important for the performance of the bio-degradation system. The chemical oxygen demand (COD) removal efficiency in this system was satisfactory, higher than 94%, and ammonia nitrogen was higher than 95%. The effluent COD concentration could meet the discharge standard, except for very few situations. The results showed that a sufficient carbon source was important for making ammonia nitrogen concentration meet the discharge standard. Then the TN removal efficiency in this system can be brought higher than 94%. Dissolved oxygen (DO) is very important to the performance of the SND bio-degradation system, and the suitable DO is about 3.5–4.0 mg/L at the forepart of reactor. In addition, the performance of the system was almost not affected by pH value. The results show that the system is feasible to treat coke plant wastewater.

End-point detection of the aerobic phase in a biological reactor using SOM and clustering algorithms

The estimation of the aerobic phase end-point is usually used to improve the operating capacity in a sequencing batch reactor. In this paper, a software tool and a configuration of the dissolved oxygen control closed loop are proposed to achieve the aerobic end-point detection of a sequencing batch reactor in a coke wastewater treatment plant. The proposed software tool consists of self-organizing map (SOM) and clustering algorithms. Moreover a validation method for SOM training is outlined and a predefined criterion to determine the SOM size is tested.

Treatment of coke plant wastewater by A/O fixed biofilm system

Coke plant wastewater was treated by an anaerobic-aerobic (A/O) biofilm system. A lab-scale experiment, during which semi-soft media were packed in both the anaerobic and the aerobic reactors, was carried out. The influence parameters, such as HRT, C/N ratio, OLR, and the recycling flow rate on the performance of the system, were studied. The results showed that a sufficient carbon source was important to the performance of bio-degradation system. The COD removal rate increased from 64.15% to 83.28% by raising C/N in wastewater from 2.5 (no external carbon source) to 5. But the effluent COD concentration was still a little higher than the discharge standard. In order to make it meet the discharge standard, a deep treatment, coagulation, was applied, which was proved as an effective method. Then the effluent COD concentration can be brought to lower than 200 mg·L−1. The NH4-N removal rate in this system was satisfactory, being higher than 99%. In addition, it was almost not affected by both C/N ratio and coagulation treatment. The results show that the system is feasible to treat coke plant wastewater.

Optimized sequence retrieval from single bands of temperature gradient gel electrophoresis profiles of the amplified 16S rDNA fragments from an activated sludge system

Sequence retrieval from single bands of polymerase chain reaction (PCR)-denaturing gel electrophoresis (DGE) profiles is an important but often difficult step for molecular diversity analysis of complex microbial communities such as activated sludge systems. We analyzed the temperature gradient gel electrophoresis (TGGE) profiles of PCR-amplified 16S rDNA fragments from an activated sludge sample of a coking wastewater treatment plant. Single bands were excised, and a clone library was constructed for each. Sequence heterogeneity in each single band was found to be significantly overestimated due to single-stranded DNA (ssDNA) contamination formed during the PCR amplification, since only 10–60% of library clones of each single TGGE band had identical migration behavior compared with the parent band. Three methods, digestion with mung bean nuclease, optimization of PCR amplification, and purification via denatured polyacrylamide gel electrophoresis (d-PAGE), were compared for their ability to minimize ssDNA contamination, with the last one being the most efficient. After using d-PAGE to minimize ssDNA to a nearly nondetectable level, 70–100% of library clones for each single TGGE band had identical migration compared with the parent band. Several sequences were found in each of six single bands, and this co-migration could be predicted with the Poland software. The predominant bacteria of the activated sludge were assessed via a combination of sequence retrieval from each single TGGE band and band intensity analysis. Only beta and alpha subclasses of the Proteobacteria were detected, 93.8% and 6.2%, respectively. Our work suggests that prior to constructing a clone library to retrieve the actual sequence diversity of a single DGE band, it is advisable to minimize ssDNA contamination to a nondetectable level.

Treatment of coke-plant wastewater by biofilm systems for removal of organic compounds and nitrogen

Coke-plant wastewater was treated by an anaerobic–anoxic–aerobic (A 1–A 2–O) biofilm system and an anoxic–aerobic (A/O) biofilm system, respectively. At same or similar levels of hydraulic retention time (HRT), the two systems had almost identical chemical oxygen demand (COD) and NH 3 removals, but a different organic-N removal. Set-up of an acidogenic stage benefited for the removal of organic-N and the A 1–A 2–O system was more useful for total nitrogen removal than the A–O system. HRT did not have a substantial effect on the COD and NH 3–N removal efficiencies, but considerably influenced the organic-N removal and distribution of oxidized nitrogen in the final effluent. The GC/MS analysis demonstrated that some refractory compounds were decomposed at the acidogenic stage and resulted in the production of some intermediates, which were more readily degraded in the subsequent aerobic stage. Hence, the A 1–A 2–O system had better effluent quality than the A–O system in terms of effluent composition.

Development of nanofiltration/steam stripping sequence for coke plant wastewater treatment

The present work proposes the optimisation of an integrated process that consists in the coupling of Nanofiltration (NF) with Steam Stripping for the treatment of ammoniacal wastewaters contaminated by cyanides ions and phenols. These wastewaters are fractionated by NF into an ammonium concentrate and an ion-containing permeate stream. The concentrates are further fractionated in the steam stripping column. The NF experiments were performed with a DSS plate and frame Lab-Unit 20, equipped with a HR-98-PP membrane. The NF experiments were run in concentration mode to optimise the concentrate ammonium content/permeate flux as a function of water recovery ratio (RR). The optimisation of the NF/steam stripping integrated process was carried out with a sequential process simulator. The optimisation study showed that the NF should work at a recovery ratio of 40%. At this RR the ammonium can be efficiently concentrated and purified from cyanides at reasonable permeate flowrates. The column steam consumption was also optimised as a function of the NF concentrates flowrate. The integrated process leads to an increase of the stripping efficiency and to significant energy savings (0.698 EURO/m 3 treated water).

Hybrid neural network modeling of a full-scale industrial wastewater treatment process.

In recent years, hybrid neural network approaches, which combine mechanistic and neural network models, have received considerable attention. These approaches are potentially very efficient for obtaining more accurate predictions of process dynamics by combining mechanistic and neural network models in such a way that the neural network model properly accounts for unknown and nonlinear parts of the mechanistic model. In this work, a full-scale coke-plant wastewater treatment process was chosen as a model system. Initially, a process data analysis was performed on the actual operational data by using principal component analysis. Next, a simplified mechanistic model and a neural network model were developed based on the specific process knowledge and the operational data of the coke-plant wastewater treatment process, respectively. Finally, the neural network was incorporated into the mechanistic model in both parallel and serial configurations. Simulation results showed that the parallel hybrid modeling approach achieved much more accurate predictions with good extrapolation properties as compared with the other modeling approaches even in the case of process upset caused by, for example, shock loading of toxic compounds. These results indicate that the parallel hybrid neural modeling approach is a useful tool for accurate and cost-effective modeling of biochemical processes, in the absence of other reasonably accurate process models.

COMPARISONS OF PROCESS IDENTIFICATION METHODS AND SUPERVISORY DO CONTROL IN THE FULLSCALE WASTEWATER TREATMENT PLANT

Dissolved oxygen (DO) control in the wastewater treatment plant (WWTP) has been the most critical factor in terms of improving the wastewater treatment efficiency and energy saving. However, the result of DO control with simple PID controller is not satisfactory since the dynamics of DO show some time-varying and nonlinear characteristics. The objectives of this study are as follows. First aim is to apply and compare some process identification methods of PID autotuning for stable DO control in a real coke WWTP. Second, a simple algorithm for the supervisory control of set point decision is proposed to decide a proper DO set point for the current operation condition of the aeration basin by estimating the respiration rate simultaneously during process identification step. The key idea in this method is that the DO set point is proportional to the respiration rate, which is the indicator of the biologically degradable load. In the experimental results, process identification methods have been practiced and compared at the modeling and control performance and supervisory control reduced the aeration cost in the full-scale WWTP.

Closed-loop identification and control application for dissolved oxygen concentration in a full-scale coke wastewater treatment plant

The objective of this paper is to apply a closed-loop identification to actual dissolved oxygen control system in the coke wastewater treatment plant. It approximates the dissolved oxygen dynamics to a high order model using the integral transform method and reduces it to the first-order plus time delay (FOPTD) or second-order plus time delay (SOPTD) for the PID controller tuning. To experiment the process identification on the real plant, a simple set-point change of the speed of surface aerator under the closed-loop control without any mode change was used as an activation signal of the identification. The full-scale experimental results show a good identification performance and a good tracking ability for set-point change. As a result of improved control performance, the fluctuation of dissolved oxygen concentration variation has been decreased and the electric power saving has been accomplished.

99/03370 Automatic control for DO and pH in the activated sludge process in a coke wastewater treatment plant

99/03370 Automatic control for DO and pH in the activated sludge process in a coke wastewater treatment plant

98/03387 Posttreatment of effluent from coke-plant waste-water treatment system in sequencing batch reactors: Yu, H. et al. J. Environ. Eng., 1997, 123 (3), 305–308

98/03387 Posttreatment of effluent from coke-plant waste-water treatment system in sequencing batch reactors: Yu, H. et al. J. Environ. Eng., 1997, 123 (3), 305–308

Automatic control for DO and pH in the activated sludge process in a coke wastewater treatment plant

The objective of this study is to develop an automatic control system for dissolved oxygen (DO) and pH of the activated sludge process in a coke wastewater treatment plant. A discrete type autotuned proportional-integral (PI) controller using an auto-regressive exogenous (ARX) model as a process model was developed to maintain the DO concentration in aerators by controlling the speed of surface aerators. Also a nonlinear pH controller using the titration curve was used to control the pH of influent wastewater. This control system was tested in a pilot scale plant. During this pilot plant experiment, there was small deviation of pH and the electric power consumption of surface aerators was reduced up to 70% with respect to the full operation when the DO set point was 2 mg/l. For real plant operation with this system, the discrete PI controller showed good tracking for set point change. The electricity saving was more than 40% of the electricity consumption when considering surface aerators. As a result of maintaining the DO constantly at the set point by the automatic control system, the fluctuation of effluent quality was decreased and overall improvement of the effluent water quality was achieved.

Coke plant wastewater treatment by fixed biofilm system for COD and NH 3-N removal

Coke plant and coal gasification wastewater have similar characteristics. There are high concentrations of ammonia and organic compounds especially refractory and inhibitory organics in them. Coal is the main energy resource in China hence pollution caused by coke plant and coal gasification wastewater has been severe for decades. The anaerobic-anoxic-oxic (A 1-A 2-O) fixed biofilm system was used for coke plant wastewater treatment in this study. The experimental results showed that this system was efficient and stable in NH 3-N and COD reductions. The effluent NH 3-N and COD were 3.1, 114 mg/l with removal efficiencies of 98.8 and 92.4%, respectively, when the total HRT of the whole system was 31.6 hours. Microorganisms were enumerated and organic transformation in the system was analyzed by GC/MS equipment. Batch tests were also conducted and it was found that anaerobic treatment of coke plant wastewater differed from anoxic treatment. Biodegradable phenolics were removed at lower efficiencies while complicated and high molecular weight organics were removed at higher efficiencies by anaerobic treatment in comparison with anoxic treatment. The biodegradability of anaerobic effluent was higher than that of anoxic effluent.

Automatic control for do and pH in the activated sludge process in a coke wastewater treatment plant

The objective of this study is to develop an automatic control system for dissolved oxygen (DO) and pH of the activated sludge process in a coke wastewater treatment plant. A discrete type autotuned proportional-integral (PI) controller using an auto-regressive exogenous (ARX) model as a process model was developed to maintain the DO concentration in aerators by controlling the speed of surface aerators. Also a nonlinear pH controller using the titration curve was used to control the pH of influent wastewater. This control system was tested in a pilot scale plant. During this pilot plant experiment, there was small deviation of pH and the electric power consumption of surface aerators was reduced up to 70% with respect to the full operation when the DO set point was 2 mg/1. For real plant operation with this system, the discrete PI controller showed good tracking for set point change. The electricity saving was more than 40% of the electricity consumption when considering surface aerators. As a result of maintaining the DO constantly at the set point by the automatic control system, the fluctuation of effluent quality was decreased and overall improvement of the effluent water quality was achieved.

98/00752 Methods for improving biochemical treatment of coke plant wastewater

98/00752 Methods for improving biochemical treatment of coke plant wastewater

Comparison between Anaerobic-Anoxic-Oxic and Anoxic-Oxic Systems for Coke Plant Wastewater Treatment

Coke plant wastewater produces severe pollution throughout China because coal is the main energy resource. The anoxic-oxic (A2-O) system can be used to treat this type of wastewater for simultaneous removal of NH3-N and COD. A comparative study between an anaerobic-anoxic-oxic (A1-A2-O) system and an A2-O system for coke plant wastewater treatment under the same operational conditions was undertaken to examine removal efficiencies of COD and NH3-N, denitrification performance, and transformation of organic pollutants in each system. The experimental results showed that the A1-A2-O system was comparatively more effective not only in nitrification but also in denitrification performance. The total NH3-N removal efficiency and the anoxic NOx-N removal rate of the A1-A2-O system were about 20% higher and more than twice that of the A2-O system, respectively. Coke plant wastewater subjected to anaerobic treatment resulted in less inhibitory effect on the subsequent nitrification process, and provided a more biodegradable and suitable carbon substrate for denitrifying bacteria. The anaerobic stage played an important role in nitrogen reduction in coke plant wastewater treatment.

Kinetics of phthalic acid ester degradation by acclimated activated sludge

Activated sludge obtained from a coke-plant wastewater treatment plant was acclimated and used as seeding microbes to investigate the kinetics of biodegradation of di- n-butyl phthalate (DBP), one of the most frequently identified phthalic acid esters in diverse environments and the most widely used plasticizer in China. DBP biodegradation conformed to the first-order model with respect to its concentration and the rate constant was independent of the initial concentration when the initial DBP concentration was less than 200 mg/litre.

Posttreatment of Effluent from Coke-Plant Wastewater Treatment System in Sequencing Batch Reactors

The performance of sequencing batch reactors (SBRs) for the treatment of effluent from a conventional coke-plant wastewater biological treatment system has been evaluated. The results showed that an operating mode that incorporated two anoxic portions, one ahead of the aeration period and one after the aeration, was superior to the other modes (prearranged denitrification and postarranged denitrification) for nitrogen removal. The 4-h anoxic fill probably allowed some substrates in the influent to be stored in the biomass and led to subsequent storage-induced denitrification in the second anoxic portion during the reaction period. Under these conditions, the ammonia nitrogen (NH{sub 3}-N) and chemical oxygen demand (COD) reductions were 83.5 and 65.2%, respectively. During the fill period of an SBR, the organics concentration was reduced, probably due to the adsorption of organics onto activated sludge and dilution of the mixed liquor. Some readily biodegradable organics in the influent, such as phenol and o-cresol, were utilized by denitrifiers as a carbon source. A 16-h aeration significantly reduced the concentrations of o-cresol, 3,4-dimethyl phenol, and 2-quinoline alcohol, while reductions in quinoline, isoquinoline, indol, and methyl quinoline were limited.

96/00934 Electrochemical oxidation process for the treatment of coke-plant wastewater

96/00934 Electrochemical oxidation process for the treatment of coke-plant wastewater