Wastewater Treatment Units Research Articles

Membrane Processes for Dye Wastewater Treatment: Recent Progress in Fouling Control

The textile industry generates large volumes of effluents on a daily basis, which contains substantial loads of organic compounds, inorganic salts, and suspended impurities. Membrane filtration has become an essential part of advanced treatment plants for dye wastewater treatment. Prevention of membrane fouling is one of the critical objectives for making the overall treatment process commercially viable. Development in this area during the past decade is critically evaluated in this review. Recent developments in the primary, secondary, and tertiary treatment steps in textile wastewater treatment are outlined. The methods employed for measuring, modeling, and understanding membrane fouling processes are discussed. Specific efforts toward fouling control by (a) pretreatment stages of textile wastewater and (b) modifying and optimizing the membrane separation process parameters such as feed composition, hydrodynamic conditions, and membrane properties are then assessed. Fouling related investigations for microfiltration/ultrafiltration membranes, membrane bioreactors, reverse osmosis, and nanofiltration membranes with special focus on textile wastewater treatment are discussed. Recent efforts toward developing new membranes and cleaning processes for fouled membrane activation are also discussed. Pilot plant studies involving membrane separation in combination with other treatment processes are also summarized. Strategies evolved and experiences gained from the industrial scale textile wastewater treatment plants in India are discussed. The authors also summarize the opportunities and the challenges remaining at different stages of industrial textile wastewater treatment units.

Contribution of siloxanes to COD loading at wastewater treatment plants: Phase transfer, removal, and fate at different treatment units

Cyclic volatile methylsiloxanes (cVMSs) are entering to waste stream in increasing quantities due to their increasing use in personal care products (i.e., shampoos, creams). The cVMSs have high vapor pressures and low solubilities and are mostly transferred into the gaseous phase via volatilization; however, some are sorbed onto biosolids. The purpose of this study was to track and estimate the phase transfer (water, solids, gas), fate, and contribution to COD loading of selected siloxanes (D4, D5 and D6) which are the most commonly found cVMSs in the wastewater systems. Removal efficiencies of the wastewater treatment units were evaluated based on the partitioning characteristics of the cVMSs in gas, liquid, and biosolids phases. The contributions of the siloxanes present in the influent and effluent were estimated in terms of COD levels based on the theoretical oxygen demand (ThOD) of the siloxanes. Siloxanes constitute approximately 39 and 0.001mgL−1 of the COD in the influents and effluent. Oxidation systems showed higher removal efficiencies based COD loading in comparison to the removal efficiencies achieved aeration tanks and filtration systems. Treatment systems effectively remove the siloxanes from the aqueous phase with over 94% efficiency. About 50% of the siloxanes entering to the wastewater treatment plant accumulate in biosolids.

Multi‐objective optimisation for design and operation of anaerobic digestion using GA‐ANN and NSGA‐II

AbstractBACKGROUNDDue to the complexity of nonlinear and biochemical phenomena involved in anaerobic wastewater treatment units, efficient operation and control is limited and difficult. The objective of this study was to implement a new multi‐objective control strategy to simultaneously optimise the effluent chemical oxygen demand (CODeff) and the biogas flow rate (Qgas) in an anaerobic bioreactor using non‐dominated sorting genetic algorithms‐II (NSGA‐II) and genetic algorithm–artificial neural network (GA‐ANN). The novel approach considered two operational objectives, i.e. control of the effluent quality and control of the maximum production rate of biogas, and took advantage of the difference between the dynamics of the liquid and gas phases using variables from both phases.RESULTSBased on the relatively lower values for the mean square error, the root mean square normalised error, and the mean absolute percentage error, as well as higher values for the correlation coefficient, GA‐ANN models achieve better performances than ANN models. Based on GA‐ANN and NSGA‐II, a more flexible and precise optimisation process was allowed, and an optimal balance between effluent quality and biogas flow rate of the anaerobic bioreactor can be achieved.CONCLUSIONThe proposed GA‐ANN models were shown to be capable of dynamically predicting CODeff and Qgas. Meanwhile the optimisation system developed may offer a useful tool for simulation, design, control and optimisation of anaerobic biodigesters. © 2014 Society of Chemical Industry

Water Network Optimization with Wastewater Regeneration Models

The conventional water network synthesis approach greatly simplifies wastewater treatment units by using fixed recoveries, creating a gap for their applicability to industrial processes. This work describes a unifying approach combining various technologies capable of removing all the major types of contaminants through the use of more realistic models. The following improvements are made over the typical superstructure-based water network models. First, unit-specific shortcut models are developed in place of the fixed contaminant removal model to describe contaminant mass transfer in wastewater treatment units. Shortcut wastewater treatment cost functions are also incorporated into the model. In addition, uncertainty in mass load of contaminants is considered to account for the range of operating conditions. Furthermore, the superstructure is modified to accommodate realistic potential structures. We present a modified Lagrangean-based decomposition algorithm in order to solve the resulting nonconvex mixed-integer nonlinear programming (MINLP) problem efficiently. Several examples are presented to illustrate the effectiveness and limitations of the algorithm for obtaining the global optimal solutions.

Synthesis of biodiesel from vegetable oils wastewater sludge by in-situ subcritical methanol transesterification: Process evaluation and optimization

Biodiesel are gaining increased public and scientific attention as an alternative to petroleum diesel fuel, driven by factors such as oil price spikes, energy security and environmental concerns. In this study, low grade wastewater sludge originated from wastewater treatment unit of vegetable oil factory as a viable alternative lipid source for biodiesel production was evaluated. The lipid mass fraction of the dry and ash-free sludge was 12.44 ± 0.87%, which mainly comprised of C16–C18 fatty acids. The in-situ transesterification process under subcritical water and methanol conditions was applied as a green pathway to convert lipids into fatty acid methyl esters (FAMEs). The reaction parameters investigated were temperatures (155–215 °C), pressures (5.5–6.5 MPa) and methanol to lipid mass ratios (1:1, 5:1 and 9:1). The highest FAME yield of 92.67 ± 3.23% was obtained at 215 °C, 6.5 MPa and methanol to lipid mass ratio of 5:1. Statistical analysis based on response surface methodology in 3-factor-3-level central composite designed experiments and analysis of variance were applied to examine the relation between input parameters and the response and to locate the optimum condition. Results showed that 98% of the variability in the response could be adequately explained by the second-order polynomial model. The optimum FAME yield (90.37%) was obtained at 215 °C, 6.5 MPa and methanol to lipid mass ratio of 5.12:1. Experimental validation (N = 3) demonstrated satisfactory agreement between the observed and predicted values with an error of at most 3.3%.

Monitoring metal ions present in the effluent discharged from a surface treatment plant: Analytical results

Precise data concerning the metals occurring in industrial discharge water from the surface treatment sector as well as their qualitative and quantitative fluctuations have to our knowledge never been reported. In the present study, we monitored 28 metals in the effluent from a surface treatment plant every week for about a year. The effluent studied was taken at the outlet of a depollution plant that removed a large proportion of the metals as insoluble forms. We report and discuss the analytical results obtained on a total of 49 samples. The results, expressed both as concentrations and as fluxes, showed high levels of polymetallic contamination of the effluent. Of the 28 metals tested for, 13 were detected and 6 (Co, Cr, Fe, Mn, Ni, and Zn) were systematically present at quantifiable levels. Our findings also indicated how Cr, Fe, Ni and Zn levels were strongly dependent on certain conditions prevailing at the inlet of the wastewater treatment unit. Even though the levels of each metal were under the regulatory limits when taken individually, overall pollution from metals was far from negligible, with a calculated total of 264 kg of metals being discharged each year.

ADSORPSI PENCEMARAN LIMBAH CAIR INDUSTRI PENYAMAKAN KULIT OLEH KITOSAN YANG MELAPISI ARANG AKTIF TEMPURUNG KELAPA

Chitosan has been used as biosorbent. In addition to having advantages, chitosan as biosorbent also has disadvantages. Chitosan is very soluble in low pH, so it cannot adsorb Cr (total) at low pH. It is because the active site (amine group) of chitosan undergoes protonation, and its adsorption capability is easily influenced by anions in waters. Therefore, this research studied the use of chitosan coating on active charcoal of coconut shell to increase the adsorption capability of Cr (total), BOD, and COD. This research was done to evaluate the characteristics of the liquid waste quality with or without Wastewater treatment unit (IPAL), and compare them with the Regulation of DIY Governor number 7/2010. It also studied the effect of pH and Concentration of chitosan coating on active charcoal as adsorbent on the decrease of Cr (total), BOD, and COD concentration in the liquid waste of leather tanning. The results indicate that the liquid waste of the leather tanning industry with and without Wastewater treatment unit (IPAL) have exceeded the quality standard for the liquid waste of leather tanning industry. An ANOVA statistical test indicated that Cr (total), BOD, and COD are significant at 0.05 (p < 0.05), with various pH influencing the decrease in Cr (total), BOD, and COD. The highest removal percentage resulting from the effect of chitosan concentration coating on active charcoal is obtained in adsorbent C (K3A1), with Cr (total) (91.9%); BOD (99.5%); and COD (98.47%).;

Optimal design for heat-integrated water-using and wastewater treatment networks

This work proposes a novel general superstructure and a simultaneous optimisation model for the designing of a heat-integrated water-using and wastewater treatment network (HIWTN) by combining a water-using network (WN), a wastewater treatment network (WTN), and a heat exchanger network (HEN). The proposed work is an extension of our previous studies that considered only heat-integrated water networks (HIWNs) or combined WN and HEN without WTN. The new proposed superstructure of this work combines water integration (water-usage, wastewater treatment, and recycling) and heat integration (direct and indirect heat exchanges) within an overall network. The simultaneous optimisation model of the proposed superstructure is formulated as a non-convex mixed integer non-linear programming (MINLP) problem for minimising the total annual network cost (TAC). This model enables appropriate trade-offs between freshwater usage, hot and cold utilities consumption, and capital cost of heat exchangers (HEs) and wastewater treatment units (TUs). Three literature examples are used to test the proposed model. The improved results of the first two examples are given whilst for the third modified example a novel network design is presented in order to include wastewater treatment.

Estimation of Contamination Sources of Human Enteroviruses in a Wastewater Treatment and Reclamation System by PCR–DGGE

A polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) method was employed to estimate the contamination sources of human enteroviruses and understand how their dominant strains vary in a wastewater treatment and reclamation system consisting of sewage collection, wastewater treatment with membrane bioreactor and open lakes for reclaimed water storage and reuse. After PCR-DGGE using a selected primer set targeting enteroviruses, phylogenetic analysis of acquired enterovirus gene sequences was performed. Enteroviruses identified from the septic tank were much more diverse than those from grey water and kitchen wastewater. Several unique types of enterovirus different from those in wastewater samples were dominant in a biological wastewater treatment unit. Membrane filtration followed by chlorination was proved effective for physically eliminating enteroviruses; however, secondary contamination likely occurred as the reclaimed water was stored in artificial lakes. Enterovirus 71 (EV71), a hand-foot-and-mouth disease (HFMD) viral pathogen, was detected mainly from the artificial lakes, implying that wastewater effluent was not the contamination source of EV71 and that there were unidentified non-point sources of the contamination with the HFMD viral pathogen in the reclaimed water stored in the artificial lakes. The PCR-DGGE targeting enteroviruses provided robust evidence about viral contamination sources in the wastewater treatment and reclamation system.

Simultaneous optimization of water and energy within integrated water networks

This contribution presents the synthesis of heat-integrated water-using and wastewater treatment networks (HIWTNs). The superstructure proposed includes process water-using units, wastewater treatment (regeneration) units, and heat exchangers (HEs) as well as all the new opportunities for water and heat integration within the overall network. A two-step solution strategy is proposed for the subsequent solving of two nonlinear models and the identifying of a set of good locally optimal solutions. The targeting model is solved during the first synthesis step thus minimising the operating cost of the network and providing an initialisation, as well as good upper-bounds for freshwater and utilities consumption for the second model. The objective of the second synthesis step is to synthesise HIWTNs simultaneously by minimising total annual cost (TAC). This research was an extension of our previous works and a follow-up on our recent studies, where we addressed the synthesis problems of HIWTNs but now using a different superstructure (e.g. multiple choices mixing and the splitting of streams allowing for additional heat integration within the overall network) and a more efficient solution strategy from the point of generating of multiple solutions. We solved two literature and two newly introduced examples in order to demonstrate the applicability of the proposed strategy. Improvements in the results were achieved using the studied literature examples of HIWTNs.

Controlled Re-emission of Mercury in Waste Water Treatment

This paper introduces a novel process for the controlled re-emission and immobilization of Mercury (Hg) in waste water treatment plants of wet flue gas desulfurization (FGD). The aim is to create a highly concentrated sink for Hg for further processing. Experiments are carried out with a continuously operated lab-scale wet FGD system and a batch-wise operated waste water treatment unit. By aeration of the liquid phase, the controlled desorption of Hg during the alkalization process of the waste water treatment is enhanced. It is demonstrated, that Hg is emitted in its elemental form (Hg0). Thus, a chemical reduction of Hg2+ takes place prior to its desorption. Linear dependency of Hg0 formation on Sulfite- (SO32-) and Hydroxide-ion (OH-) concentration indicates first order dependency of reaction kinetics. Decreasing concentration of Hg0 in the exhaust air for increasing Cl--concentration is observed. The results show exponential dependence of Hg0 mass transfer on stirring speed and almost constant re-emissions for the aeration flow rates investigated. Thus, the application of low air flux is beneficial in terms of energy demand of the fan and also for the purpose of creating a highly concentrated sink for Hg in the process. The concentration decrease of Hg2+ in the waste water is proportional to the savings in terms of precipitating agent consumption of the further processing steps.

A Quantitative Model for Measuring the Project and Feeding Buffers in CCM Method by Fuzzy Approach (Case Study: Construction of Industrial Wastewater Treatment Unit at Lorestan Petrochemical Company, Iran)

A Quantitative Model for Measuring the Project and Feeding Buffers in CCM Method by Fuzzy Approach (Case Study: Construction of Industrial Wastewater Treatment Unit at Lorestan Petrochemical Company, Iran)

Isolation, Identification of a Halotolerant Acid Red B Degrading Strain and its Decolorization Performance

One salt-tolerant strain (named P-1) which can efficiently degrade azo dye acid red B was isolated and screened from activated sludge of a wastewater treatment unit of a dye plant. On the basis of morphological observation, physiological and biochemical test, 26S rDNA gene sequence and phylogeny analysis, the strain P-1 was identified as Pichia kudriavzevii strain. The effect of salinity, initial concentration of acid red B solutions, temperature and pH on decolorization performance was investigated to optimize decolorization conditions. The results showed that, the optimal conditions for degradation of acid red B by strain P-1 were: salinity, 10%; initial concentration of acid red B solutions, 100mg/L; temperature, 33oC; pH, 5.0. Under the optimal conditions, the degradation rate of acid red B reached 94.29%.

Removal of Some Hydrocarbon Pollutants from Baiji Oil Refinery Wastewater Using Granular Activated Carbon Column

Petrochemical industry, specially oil refineries produces large quantities of wastewater that isstrongly polluted with hydrocarbon compounds. Although Baiji oil refinery has wastewatertreatment plant, it discharges water to Tigris river that is strongly polluted with hydrocarboncompounds that exceed the Iraqi permissible limits. Thus the aim of the present work is toremove phenol, parachlorophenol, and benzene from the wastewater of Baiji oil refinery usinggranular activated carbon(GAC)column. A laboratory scale apparatus is designed andconstructed in order to perform this study taking into account the ability to control the mostimportant parameters affecting adsorption process. Actual wastewater samples taken from thefinal discharge point of wastewater treatment unit of Baiji oil refinery are used to conduct allexperiments.The results indicated that these pollutants could be removed completely. Moreover, it indicatesthat breakthrough and exhaustion time are directly proportional with GAC thickness and inverselyproportional with pollutants concentration and liquid hourly space velocity (LHSV). The resultsshow that maximum breakthrough time is 39.26, 21.35, and 16.58 hours at LHSV of 0.5 hr-1 and35cm of GAC thickness for phenol, parachlorophenol, and benzene respectively. Thecorresponding minimum breakthrough time is 9.24, 5.23, and 6.08 hours at LHSV of 129 hr-1.However, the corresponding maximum exhaustion time is 49.6, 48.7, and 43.84 hours, while theminimum exhaustion time are 27.5, 16.54, and 10.89 hours. The results show that breakthroughtime for phenol is 27.23 hours when the phenol inlet concentration is 5.212 mg/l, it decreased to13.83 hours at inlet phenol concentration of 19.31 mg/l. The corresponding exhaustion time is68.83 and 37.22 hours. Other two pollutants have similar trend. Based on the experimental data,dynamic adsorption capacities are calculated and found to be increased with the increase ofpollutants concentration and LHSV. It is also found that calculated adsorption zone thickness isproportional with LHSV. The calculated maximum dynamic carbon adsorption capacity are 115.4,67.62, and 12.628 mg/g for phenol, parachlorophenol, and benzene respectively at LHSV of 129hr-1. The corresponding minimum capacity at LHSV of 0.5 hr-1 are found to be 1, 0.99, and 0.257mg/g. Calculated values of minimum and maximum adsorption zone thickness for the threepollutants at LHSV of 0.5 and 129 hr-1 are (0.0729, 0.1965, and 0.2176) and (0.2324,0.2118,and 0.1545)cm respectively.Application of the most famous the adsorption models shows that only Freundlich model givesexcellent agreement with experimental data. Finally, new three models are developed. The firstand second relate breakthrough and exhaustion time with LHSV, wastewater pollutantsconcentration, and GAC thickness while the third relates adsorption velocity with LHSV and inletpollutant concentration.

Prediction of polar oil and grease contamination levels in refinery wastewater through multivariate statistical modeling

A dynamic mass balance was implemented for polar oil and grease contamination in a petroleum refinery wastewater circuit through developing a predictive model for a kerosene caustic washing unit, identified as the major source of polar substances into the industrial wastewater effluent. The model was developed following the Projection to Latent Structures (PLS) approach. Comparison between analytical data for polar oil and grease concentrations in refinery wastewater in the Dissolved Air Flotation (DAF) effluent and the predictions of the dynamic mass balance calculations are in a very good agreement and highlights the dominant impact of spent caustic in increasing the oil and grease contamination levels. The results of this work have led to implementation of the dynamic mass balance in the refinery as an online tool, which allows for prevision of possible contamination situations and taking the required preventive actions, and can serve as a basis for establishing relationships between the oil and grease contamination in the refinery wastewater with the properties of the refined crude oils and the process operating conditions. The PLS model developed could be of great asset in both optimizing the existing and designing new refinery wastewater treatment units or reuse schemes.

Molecular Weight Distribution of DOC in Effluent of Petrochemical Wastewater Treatment Units

The results showed that DOC, UV254 and SUVA all presented a characteristic that organics was mainly concentrated on molecular weight <1kDa.Except organics with molecular weight <1kDa, the molecular weight of organics in Influent and effluent of Hydrolytic Acidification respectively distributed in the range of <1kDa, 30~100kDa and 1~3kDa, 10~30kDa. Organics in effluent of Anaerobic, Aerobic, Secondary sedimentation tank and Contact oxidation occupied proportions in all ranges of molecular weight distribution but relatively lower.

Experimental Study and Adsorption Modeling of COD Reduction by Activated Carbon for Wastewater Treatment of Oil Refinery

Application of Granular Activated Carbon (GAC) in adsorption process has been studied for the advanced treatment of municipal and industrial wastewater. Because of entering poisonous compounds such as furfural, phenol and sulfides into the oily wastewater of Tehran refinery, biological aeration basins of wastewater treatment unit may not have the desired performance of COD reduction. In this study, GAC is examined for reduction of COD effluent from the Dissolved Air Flotation (DAF) unit to achieve to the environmental and design regulations.The equilibrium batch experiments as well as dynamic adsorption tests were performed to determine the maximum adsorption capacity and the breakthrough curves of COD, respectively. The data derived from equilibrium studies were modeled using Langmuir theory and the isotherm parameters were determined at two different temperatures of 25 and 40 C. Dynamic adsorption modeling was carried out considering the axial dispersion model in the bed of GAC with the assumption of lump kinetic mass transfer and linear driving force into the solid phase. The model results of COD breakthrough curve concentration have shown a fairly good agreement with experimental results. The sensitivity analysis of the dynamic model was carried out at different temperatures, bed lengths, feed flow rate and feed concentration to have a proper insight for appropriate design of a GAC fixed bed.It is concluded that GAC fixed bed could be an auxiliary unit for biological treatment of wastewater to overcome the problems of biological basin in oil refineries.

Bayesian Modeling of Enteric Virus Density in Wastewater Using Left-Censored Data

Stochastic models are used to express pathogen density in environmental samples for performing microbial risk assessment with quantitative uncertainty. However, enteric virus density in water often falls below the quantification limit (non-detect) of the analytical methods employed, and it is always difficult to apply stochastic models to a dataset with a substantially high number of non-detects, i.e., left-censored data. We applied a Bayesian model that is able to model both the detected data (detects) and non-detects to simulated left-censored datasets of enteric virus density in wastewater. One hundred paired datasets were generated for each of the 39 combinations of a sample size and the number of detects, in which three sample sizes (12, 24, and 48) and the number of detects from 1 to 12, 24 and 48 were employed. The simulated observation data were assigned to one of two groups, i.e., detects and non-detects, by setting values on the limit of quantification to obtain the assumed number of detects for creating censored datasets. Then, the Bayesian model was applied to the censored datasets, and the estimated mean and standard deviation were compared to the true values by root mean square deviation. The difference between the true distribution and posterior predictive distribution was evaluated by Kullback-Leibler (KL) divergence, and it was found that the estimation accuracy was strongly affected by the number of detects. It is difficult to describe universal criteria to decide which level of accuracy is enough, but eight or more detects are required to accurately estimate the posterior predictive distributions when the sample size is 12, 24, or 48. The posterior predictive distribution of virus removal efficiency with a wastewater treatment unit process was obtained as the log ratio posterior distributions between the posterior predictive distributions of enteric viruses in untreated wastewater and treated wastewater. The KL divergence between the true distribution and posterior predictive distribution of virus removal efficiency also depends on the number of detects, and eight or more detects in a dataset of treated wastewater are required for its accurate estimation.

Waste sludge reduction with a pilot-scale membrane bioreactor for point source pollution management

It is an important subject to reduce the amount of waste sludge from small-/middle-scale wastewater facilities for the establishment of point source pollution management. In this work, we focused on the development of sludge decomposition system which did not increase organic loading ratio into wastewater treatment units. The excess sludge produced from wastewater treatment plant of a food factory was decomposed by an aerobic digestion technology with a membrane bioreactor (MBR) system. It was composed of digestion tank (500 L) and a membrane filtration unit (350 L). Sludge was decomposed under the following conditions: 25 g L-1 of MLSS, 36.9 d of HRT, average temperature 32.3°C, and 0.565 kg-SS m-3 d-1 of sludge loading rate. The system decomposed 77.2% of the fed sludge to inorganic carbon, and all of average TOC, CODMn and CODCr in the effluent were less than 50 mg L-1. However, the effluent contained T–N and T–P at 200 mg N L-1 and 150 mg-P L-1, respectively. The quinone profile analysis indicated that the consortia of sludge in the reactor were different from the fed sludge.

Microbial Electrolysis of Synthetic Acids for Biohydrogen Production: Influence of Biocatalyst Pretreatment and pH with the Function of Applied Potential

Bioelectrolysis of synthetic acids (acetate, butyrate and propionate) was evaluated in a single chamber Microbial Electrolysis Cell (MEC) to produce biohydrogen (H2). The influence of culture pretreatment (untreated and acid pretreated) and pH (6 and 7) conditions on electrolytic process were studied. MEC was operated at three optimized potentials viz., 0.2, 0.6 and 1.0 V along with control operated without any applied potential. Maximum Hydrogen Production Rate (HPR), Cumulative Hydrogen Production (CHP) and Specific Hydrogen Yield (SHY) were registered at 0.6 V followed by 1.0 and 0.2 V operations under all the experimental conditions studied. Culture pretreatment and pH variation showed influence on the MEC process. Pretreatment (PTr) operation at pH 7 showed good process performance than pH 6. MEC with untreated (UTr) at pH 6 and 7 showed lower performance compared to PTr operations. About 53% removal of synthetic acids was registered during the process which is a good sign for MEC as a wastewater treatment unit. Electrokinetic evaluation through Tafel slope showed that MEC operations with PTr and UTr at pH 6 recorded lower redox slopes and lower polarization resistance (Rp) at 0.2 V and 0.6 V whereas pH 7 recorded lower redox slopes and Rp at 0.6 V and 1.0 V.