Desulfurization Wastewater Treatment Research Articles

Current Status of Zero Liquid Discharge Technology for Desulfurization Wastewater

Desulfurization wastewater is industrial wastewater with a high salt content, high metal ions, and high hardness produced by flue gas desulfurization of the limestone-gypsum method in coal-fired power plants. This paper summarizes the source of desulfurization wastewater, water quality characteristics, water quality impacts, and other factors, combined with the current status of research worldwide to introduce the advantages and shortcomings of the existing desulfurization wastewater treatment technology. In addition, zero liquid discharge technology as a novel method to treat desulfurization wastewater is also summarized. It mainly includes evaporation and crystallization, flue gas evaporation, membrane distillation removal, etc. Finally, this manuscript looks forward to the future development direction of desulfurization wastewater based on its existing technology and emission standards.

Effect of charged spray evaporation of desulfurization wastewater on fine particle removal efficiency of electrostatic precipitator

The removal of fine particles from coal-fired power plants and the zero-discharge treatment of desulfurization wastewater (DW) from wet desulfurization are critical issues. In this study, we propose a charged droplet evaporation technology of DW for efficient electrostatic dust removal, aiming to achieve zero discharge of DW and effectively remove fine particles. We experimentally studied the effect of charged DW droplet evaporation on the dust removal efficiency of an electrostatic precipitator (ESP) and analyzed the internal mechanism. The results revealed that the removal efficiency of fine particles by ESP was affected by electrode voltage, atomization pressure, DW volume flow, and Cl− concentration. The main internal mechanisms that improved the removal efficiency of fine particles were agglomeration and pre-charging of the particles. Increasing the electrode voltage proved to be the most effective method in enhancing the removal efficiency of fine particles. Specifically, when the electrode voltage was increased from 0 to 12 kV, the removal efficiency of PM2.5 by ESP demonstrated an increase of greater 14 %. The removal efficiency in the penetrating window exhibited an increase of greater than 8 %. Furthermore, augmenting the atomization pressure and DW volume flow also contributed to the improvement in fine particle removal by ESP. In contrast, increasing the Cl− concentration had a detrimental effect on the removal process.

Study on Treatment Performance of Desulfurization Wastewater by Zero-Valent Iron Fenton-like Process

In this study, the zero-valent iron Fenton reagent (ZVI Fenton-like) system was combined with the chemical precipitation method for the deep treatment of desulfurization wastewater from coal-fired power plants, and the chemical oxygen demand (COD) was used as the evaluation criterion for organic matter in the desulfurization wastewater. The effects of reaction time, H2O2 dosage, zero-valent iron dosage, pH, and reaction temperature were also investigated. The results showed that the COD concentration of the effluent was the lowest when the running time of the ZVI Fenton-like reagent system was 1 h, the dosage of H2O2 was 33.3 mg·L−1, the dosage of iron was 0.075 g·L−1, the pH was 4.5~6.5, the reaction temperature was 35 °C, the COD concentration of the wastewater was the lowest and its operating conditions were the best, and the internal reaction mechanism was finally deduced. In summary, the zero-valent iron Fenton reagent system provides a new idea for the treatment of desulfurization wastewater from coal-fired power plants.

Mixed scaling deconstruction in vacuum membrane distillation for desulfurization wastewater treatment by a cascade strategy

Mineral scaling is one key obstacle to membrane distillation in hypersaline wastewater desalination, but the scaling or fouling mechanism is poorly understood. Addressing this challenge required revealing the foulants layer formation process. In this work, the scaling process was deconstructed with a cascade strategy by stepwise changing the composition of the synthetic desulfurization wastewater. The flux decline curves presented a 3-stage mode in vacuum membrane distillation (VMD). Heterogeneous nucleation of CaMg(CO3)2, CaF2, and CaCO3 was the main incipient scaling mechanism. Mg-Si complex was the leading foulant in 2nd-stage, during which the scaling mechanism shifted from surface to bulk crystallization. The flux decreased sharply for the formation of a thick and compacted scaling layer by the bricklaying of CaSO4 and Mg-Si-BSA complexes in the 3rd-stage. Bulk crystallization was identified as the key scaling mechanism in VMD for the high salinity and concentration multiple. The organic matter had an anti-scaling effect by changing the bulk crystallization. Humic acids (HA) and colloidal silica also contributed to incipient scaling for the high affinity to membrane, bovine serum albumin (BSA) acting as the cement of Mg-Si complexes. Mg altered the Si scaling from polymerization to Mg-Si complex formation, which significantly influence the mixed scaling mechanism. This work deconstructed the mixed scaling process and illuminated the role of main foulants, filling in the knowledge gap on the mixed scaling mechanism in VMD for hypersaline wastewater treatment and recovery.

Effects of nanofiltration on desalination of flue gas desulfurization wastewater by electrodialysis: Treatment effect, fouling property and techno-economic analysis

This study seeks to compare the treatment effect and fouling property of the nanofiltration (NF) – electrodialysis (ED) hybrid system and single ED system, and launches a techno-economic analysis for the flue gas desulfurization wastewater treatment. The optimal operation conditions of ED and NF process were determined, and the fouling properties of NF membranes and ion exchange membranes (IEMs) were explored. Morphology and chemical structure analysis concluded that NF membranes are more susceptible to fouling than IEMs, ascribing to the discrepancy of driving force and fouling mechanisms. The economic impact of membrane fouling was calculated in detail, including costs of increased membrane resistance and pressure drop of feed channel, decreased water permeability, membrane replacement and cleaning-in-place (CIP). We have found that the major factor of increased operating cost resulting from fouling comes from the membrane replacement cost (≥66%), followed by additional energy cost (≥4.1%) and with only a minor contribution from the CIP costs (≥0.8%). Overall, the total operating cost for the NF-ED system was 35.9% more expensive than the single ED system with a total cost of 2.95 ¥/m3. The results can provide a useful reference for the application of membrane technology in water and wastewater treatment.

The fate of selenium in the desulfurization wastewater evaporation process: Migration mechanisms and risk analysis

Owing to the implementation of the zero wastewater discharge policy in China, stricter supervision and technical requirements have been imposed. Hot flue gas evaporation technology exhibits significant advantages in desulfurization wastewater treatment. However, volatile constituents (such as selenium, Se) present in wastewater may be released, thus disrupting the power plant's original Se balance. In this study, the evaporation of three desulfurization wastewater plants is performed. The release of Se mainly begins from the threshold at which wastewater is evaporated to dryness, and Se release rates of 21.5, 25.1, and 35.6% are detected. Furthermore, the key components and properties of wastewater for Se migration are identified through experiments and density functional theory calculations. Lower pH values and Cl− contents are not conducive to Se stability, and this tendency is more pronounced in selenite. The suspended solid content temporarily traps the Se in the initial evaporation process, as confirmed via a decrease in the Se release rate and a high binding energy (−307.7 kJ/mol). Moreover, results of risk assessment reveal that wastewater evaporation results in a negligible increase in Se concentration. This study evaluates the risk of Se release during wastewater evaporation and provides a basis for Se emission control strategies.

Treatment of flue gas desulfurization wastewater by a coupled precipitation-ultrafiltration process

Flue gas desulfurization (FGD) wastewater is characterized by low pH, high content of hardness ions and COD. In this work, chemical precipitation and ultrafiltration (UF) membrane separation were corporately coupled to treat the FGD wastewater on a lab scale to remove the hardness as well as some organic compounds for further advanced treatment. Firstly, influential factors for precipitation to deal with the simulated wastewater, including reaction time, stirring speed, and dosage, were investigated by batch tests, while CaO and Na2CO3 were used as the first and second precipitants. The batch results showed that the removal rates of Mg2+ and Ca2+ could be both higher than 98% under the optimal reaction condition. Then a polyvinylidene fluoride tubular UF membrane was used to remove the precipitates without adding flocculants. Thirdly, the coupled process with the optimal operation parameters was adopted to treat real FGD wastewater. Almost all the hardness ions and most COD could be removed, while rapid permeability decline was observed in the UF process due to the high COD, which could be recovered by a simple cleaning. In summary, when the mass ratios of [CaO]/[Mg2+] and [Na2CO3]/[Ca2+] were 2.5 and 2.7, the flow velocity was around 5 m/s, the removal rates of the hardness ions can be above 98% and the membrane flux can be recovered by 98% with a backwash with pure water and an HCl solution of pH = 2. This work proved that the coupled process is a technically feasible technology for treating FGD wastewater to realize the ZLD.

Concentration effects of calcium ion on polyacrylamide fouling of ion-exchange membrane in electrodialysis treatment of flue gas desulfurization wastewater

Residual anion polyacrylamide (APAM) and fluctuating calcium ion (Ca2+) in flue gas desulfurization wastewater after pretreatment could result in ion-exchange membrane fouling during electrodialysis process. Concentration effects of Ca2+ on APAM fouling were systematically investigated and the mechanisms were illustrated. Results of desalination performance indicated that Ca2+ alleviated APAM fouling and the mitigating effect increased firstly and then declined, obtaining the mildest fouling phenomenon in the presence of 1.0 mM Ca2+. Zeta potential and particle radius of APAM in the feed solutions increased as Ca2+ changed the charge balance of APAM molecules and complexed with them. Morphology and chemical structure analysis concluded that APAM molecules were adsorbed on the membrane surface and the fouled layer changed with increasing Ca2+ concentration, from dense layer to reticular structure and then to sophisticated multilayer structure. Calculation of interfacial free energy based on Extended Derjaguin-Landau-Verwey-Overbeek theory confirmed that electrostatic interaction dominated the membrane fouling process. Concentration effects of Ca2+ were more remarkable on membrane-APAM attraction and APAM-APAM repulsion at 0.0–1.0 and 1.0–10.0 mM, respectively. The results contribute to establishing comprehensive understanding of the concentration effects of Ca2+ on polymer fouling of membranes and provide new insights into cleaning process optimization.

Experimental study on the treatment of desulfurization wastewater from coal-fired power plant by spray evaporation.

In this study, a pilot-scale evaporation tower system was built to treat the desulfurization wastewater by spray evaporation. The distribution characteristics of Cl- in the wastewater evaporation process were investigated. Besides, the morphology and physicochemical property of solid evaporation products from desulfurization wastewater were analyzed. In addition, the emission characteristics of fine particulates were evaluated. The results indicated that the increase of salt content in desulfurization wastewater increased the mass concentrations of Cl- in three phases, but the proportions of it remained almost unchanged, which were about 10%, 55%, and 35% in the gas phase, outlet solid phase, and bottom solid phase respectively. The increase of flue gas temperature can improve the content of Cl- in the gas phase, while the increase of wastewater pH inhibited the formation of gaseous HCl. The solid evaporation products from desulfurization wastewater had a prismatic crystal structure, which mainly included the sulfate and chloride salts, and the main elements including O, Na, Mg, S, Cl, K, and Ca. Besides, the peak values of particle size distribution in the bottom solid phase and outlet solid phase were 7.67 and 0.32μm, respectively. For the particulate matters in flue gas, the spray evaporation of desulfurization wastewater can reduce the particle concentration, promote particle agglomeration, reduce the number concentration of fine particles, and improve the removal effect of PM10. When the inlet particle concentration was 7.62g/m3, it can reduce the particle concentration at the tower outlet to 4.59g/m3 and reduce the number and mass concentrations of PM10 after ESP by about 43.8% and 36.8%.

Falling film evaporation of desulfurization wastewater with synergistic particle removal based on the dry-wet coupling electrostatic precipitator

Low temperature flue gas evaporation is an effective method for low-cost and efficient treatment of desulfurization wastewater (DW). However, due to the influence of low flue gas temperature and high salt content, it is easy to lead to scaling and blockage of evaporation flue, affect the stable operation of the system. In order to effectively use the waste heat of flue gas to treat DW and avoid the corrosion of DW to the flue, the falling film evaporation treatment technology of DW with synergistic particle removal is proposed. The effects of different operating parameters on the falling film evaporation and deposition characteristics of DW, and particle removal efficiency are studied. The results show that the increase of the electrostatic field voltage is conducive to the evaporation of DW, and inhibits its crystal deposition. The increase of the Cl- concentration is inconducive to the evaporation and crystal deposition of DW without electrostatic field, but is conducive to the evaporation and crystal deposition of DW in the electrostatic field. In the experiment of 120 ℃ flue gas, the evaporation capacity of liquid film decreases by 17.9% with Cl- concentration increasing from 0% to 5% without the voltage; but the evaporation capacity of liquid film increases by 30.9% with Cl- concentration increasing from 0% to 5% after applying 40 kV voltage. Replacing water with DW is conducive to the removal of particles by electrostatic field. The efficiency of particle removal increases from 79.9% to 84.8% with Cl- concentration increasing from 0% to 5% at 120 ℃ and 40 kV. In addition, increase on flue gas temperature is also conducive to the DW evaporation and particles removal by electrostatic field. Compared with other wastewater treatment technologies, this technology has the advantage of low treatment cost.

Reverse Osmosis Membrane Combined with Ultrasonic Cleaning for Flue Gas Desulfurization Wastewater Treatment

Flue gas desulfurization (FGD) wastewater treatment is currently of interest, as stringent standards have been released in order to limit the pollution emissions from the energy industry, and concerns about water scarcity are also increasing. Reverse osmosis (RO) membrane is a promising alternative for highly efficient FGD wastewater treatment. However, membrane fouling strongly limits its application. This study developed a suitable treatment system by combining RO membrane with ultrasonic cleaning. The introduction of low-frequency and high-intensity ultrasonic cleaning improved the cleaning efficiency of membrane fouling, as the permeate flux recovered 49% of the reduced value within 10 min of cleaning. The lifespan of the membrane was also extended, as the time of permeate flux declined to the same level, increasing from 2 h to 4 h after ultrasonic cleaning. The effluent of the system could meet the standard of desulfurization wastewater treatment. The treatment system is feasible for FGD wastewater treatment at a laboratory scale. These findings proved that the combination of RO membrane and ultrasonic cleaning could be applied to FGD wastewater treatment. The study provided an efficient, cost-saving, and convenient way to develop the FGD wastewater treatment system.

Solar-powered electrocoagulation treatment of wet flue gas desulfurization wastewater using dimensionally stable anode and induced electrode

Solar-powered electrocoagulation (EC) process is proven to be an alternative option for wet flue gas desulfurization (WFGD) wastewater treatment, due to simultaneous removal of multiple pollutants efficiently and reduce the operation costs significantly. Rapid and stable photoelectricity response is necessary for the removal efficiency of pollutants (eg. COD and turbudity), especially in low solar irradiation intensity. In this paper, dimensionally stable anode (DSA) and operation voltages in EC process driven by solar cells were investigated, for the purpose of the optimized removal of pollutants, including COD, turbidity, (free residual chlorine and chlorine dioxide). The results show that the removal efficiency of COD and turbidity can respectively reach 59.12% and 39.11% within 30 min of illumination time (the enhanced solar radiation = 915.8 W m-2), when Ti-based plates were adopted. The concentration of free residual chlorine and chlorine dioxide can reach 2.70 and 5.31 mg L-1, indicating that chlorine ions present in WFGD wastewater have been converted into active chlorine partly. Solar-powered EC equipped with Ti-based plates have a potential prospect in EC process for WFGD wastewater treatment.

Distribution and transformation of dissolved organic matters (DOMs) in membrane distillation for desulfurization wastewater in thermal power plant

The organic fouling mechanism and its control are patchy in membrane distillation (MD) process, as the distribution and transformation of dissolved organic matters (DOMs) in MD are poorly understood due to its application scenarios for high salinity wastewater. In this work, MD performance for desulfurization wastewater was evaluated over a 65 d long-term operation, with a focus on the composition, distribution, and transformation of DOMs. MD shows good tolerance to the high concentrations of salts and DOMs (salt rejection > 99%, organic matter rejection > 98%), with high flux of 15 kg/m2·h and high flux recovery as Fr was 99.7%. Polyaromatic hydrocarbon (PAHs), tryptophan- or protein-like, and autochthonous-sourced humic acids (FI was around 2) were main DOMs in feedwaters, and the spatio-temporal distribution and transformation appeared result from the membrane interception and microbial processes. Tryptophan/ tyrosine increased in the feedwaters, and becoming the dominant permeate component as the operation time prolonged. While proteins and PAHs also penetrated as the membrane was progressively wetted. Proteins was easily peeled off form membrane surface during cleaning, followed by PAHs, while tryptophan/tyrosine were protected by the biofilm. It demonstrating the vertical distribution of DOMs on foulants layer, which need further attention for membrane fouling control. This study demonstrates the potential of MD in desulfurization wastewater treatment and offers a new insight into the DOMs distribution and transformation, which could deepen the understanding of the organic fouling mechanism in MD.

Pilot-scale study on seeded precipitation assisted nanofiltration for flue-gas desulfurization wastewater softening.

In order to reduce the cost of chemical softening, the seeded precipitation assisted nanofiltration (NF) process was introduced into zero liquid discharge (ZLD) of flue-gas desulfurization (FGD) wastewater treatment. A pilot-scale system was developed and run for 168 h in a coal-fired power plant. The system mainly consists of lime softening, ambient temperature crystallizer (ATC) and NF, in which the raw water treatment capacity was 1 m3/h. The results indicated that the system operated stably, the softening cost was 13.30 RMB/m3, and the electricity cost was 3.39 RMB/m3 for the FGD wastewater in this pilot system. High quality gypsum was got from the ATC unit, of which the purity was 95.8%. Through this system, the hardness removal rate was higher than 98.9% and the water recovery rate reached 96%. In addition, the pressure and permeate flux kept stable in the ultrafiltration (UF) unit and NF unit, indicating no scaling occurred in the two units during 168 h test. Thus, a feasible and cost-effective process was provided by using the seeded precipitation assisted NF to deal with the FGD wastewater.

Treatment of flue gas desulfurization wastewater by bipolar membrane electrodialysis and its optimization by response surface methodology

Treatment of flue gas desulfurization wastewater by bipolar membrane electrodialysis and its optimization by response surface methodology

Concentration Effects of Calcium Ion on Polyacrylamide Fouling of Ion-Exchange Membrane in Electrodialysis Treatment of Flue Gas Desulfurization Wastewater

Concentration Effects of Calcium Ion on Polyacrylamide Fouling of Ion-Exchange Membrane in Electrodialysis Treatment of Flue Gas Desulfurization Wastewater

Experimental and theoretical study of a new CDI device for the treatment of desulfurization wastewater.

According to the characteristics of desulfurization wastewater, A new capacitive deionization (CDI) device was designed to study the desalination characteristics of desulfurization wastewater in this paper. The experiments investigated the desalination efficiency under different conditions which find that the best desalination efficiency is achieved at a voltage of 1.2V, pH=11 and 50°C. Besides, ion adsorption is more favorable under acidic and alkaline conditions. The anion and cation removal performance experiments showed that the order of cation removal is Mg2+>Na+>Ca2+>K+ and the order of anion removal is Cl->CO32->NO3->SO42->HCO3-. The mechanism of CDI was studied and analyzed by the isothermal adsorption model and COMSOL simulation software. It was found that the Freundlich model and Redlich-Peterson model have a good fit with the experimental results. The experiments show that the CDI device has excellent stability. CDI device was used to treat actual desulfurization wastewater. Furthermore, the study provides theoretical support for the industrial application of CDI for desulfurization wastewater treatment in the future. Graphical abstract.

Primary Research of a New Zero-Liquid-Discharge Technology of Wet Flue Gas Desulfurization Wastewater by Low-Rank Heat from Flue Gas

Wet flue gas desulfurization (WFGD) wastewater treatment is a key problem in coal-fired plants. Traditional chemical precipitation methods cannot reach zero-liquid discharge (ZLD). In this paper, a new technology using the low-rank heat from flue gas to concentrate the wastewater for ZLD is proposed. A scrubber was built to verify the concentrating process, and the characteristics of the concentrated water were analyzed. The concentrated water was neutralized by adding Ca(OH)2 to raise the pH value. The wastewater can be concentrated 10~25 times to reduce the flow rate. The characteristics of the concentrated wastewater were studied by dosing lime. Then, liquid and solids were separated by filter pressing, the liquid was mainly composed of CaCl2, which accounts for 73.6%. The sludge is composed of CaSO4 and Mg(OH)2, depending on the lime consumption of the dosing process. Finally, the filter liquor after the filter press was mixed with ash to reach zero liquid discharge, and the sludge could be burnt after mixing with the coal or disposed by third-part vendor. This technology is demonstrated in one 600 MW unit and shows a high system reliability. The clean water is recycled by the WFGD wastewater during the evaporation. Binding on the environmental policies and large market demand of the WFGD wastewater, this technology shows a great application prospect in the future.

Simulation Study on Centrifugal Spray Evaporation Characteristics and Process Optimization of Desulfurization Wastewater

As an advanced treatment of desulfurization wastewater, centrifugal spray drying technology, which can achieve a zero liquid discharge target, has attracted wide attention and great interest in recent years. However, the results of previous studies were based on the laboratory-scale centrifugal spray dryer. In order to study the evaporation characteristics of desulfurization wastewater and the parameter optimization of the dryer, the evaporation model of wastewater droplets was established. The effects of parameters such as the angle of the deflectors, gas–liquid ratio and atomizer speed on droplet evaporation were studied by numerical simulation. The results show that with the increase in the angle of the deflectors, the swirl effect of flue gas flow field is more obvious and the time and axial distance required for the complete evaporation of the droplets are shorter. Reducing the gas–liquid ratio will make the average evaporation time longer. Moreover, a higher atomizer speed is helpful for the evaporation of the droplets. The optimum gas–liquid ratio and rotational speed are found to be 9300 m3/Nm3 and 16,000 rpm, respectively.

Insight into the microbial distribution and succession and biofouling mechanism in membrane distillation for desulfurization wastewater treatment

The unrevealed mystery of biofouling obfuscates the understanding of fouling mechanism and the commercial application of Membrane distillation (MD). In this study, biofouling was revealed with respect to microbial morphology, distribution, succession, and function in MD for desulfurization wastewater. Heat- and salinity-stress driven the reconstruction of microbial community with a decrease in diversity, activity, and motility. Idiomarina and Phenylobacterium were enriched on membrane for higher cell motility and degradation ability. Horizontal distribution appeared with rising fouling tendency and longer but thinner cells, result from the Concentration polarization (CP), heat-, flow-, and nutrient-stress. Vertically, bacteria with higher motility, secretory ability, and activity like Chelativorans, Acinetobater, Salinarimonas attached to membrane surface firstly. Then pioneering bacteria with low microbial biosynthesis and cellular process but high degradation ability accumulated in the bottom layer, driven the DOM transformation for higher tryptophan and tyrosine metabolism. CP was a key reason for the accumulation of upper layer, in where the bacteria had low cellular process and motility. This work reveals the microbial succession and biofouling formation process, which provides an in-depth information to fill the knowledge gap of MD biofouling.