Desulfurization Wastewater Research Articles

Ammonia release characteristics during desulfurization wastewater evaporation: Mechanisms and implications

This study investigated the mechanisms of ammonia release during desulfurization wastewater evaporation and its potential environmental impacts. A single droplet evaporation device (SDD) assessed the wastewater evaporation and ammonia release characteristics. Approximately 8.5 % of ammonia was released during the free water evaporation period (0–35 s). As the droplet underwent shell inflation-deflation and core-shell drying, the remaining ammonia was mainly released due to increased vapor pressure and poor thermal stability of ammonium salts. The wastewater properties, especially pH value, greatly influenced the release of ammonia. Alkaline wastewater exhibited a significantly higher ammonia release rate. Ammonia migration and transformation were studied in a 600 MW power plant. Approximately 9.2–11.7 % of ammonia was released, while the rest was retained in solid form within the evaporation product. Characterization techniques and DFT simulations showed that the released NH3 probably combines with fly ash due to the water vapor, HCl, SO3, and other acidic gases in the flue gas. Risk analysis suggested that ammonia release during evaporation would not significantly increase ammonia concentration in flue gas or hinder fly ash comprehensive utilization. However, when handling desulfurization wastewater with high-concentration ammonia, it was essential to consider the potential corrosion of downstream equipment caused by released ammonia.

A sulfite/air fuel cell using cost-effective carbon-supported silver for hydrogen peroxide electrosynthesis

The development of highly selective, stable, and cost-effective electrocatalysts is a key step toward H2O2 electrosynthesis commercialization. Ag/C catalysts are developed for H2O2 production in the sulfite/air fuel cell here. An ammonia method desulfurization wastewater is applied as the fuel, which is a “waste to treasure” process. For low-cost catalysts and waste recycling, the Ag/C catalysts are also synthesized using an electroplating effluent. The rotating ring disc electrode tests and fuel cell tests exhibit high 2e--ORR activity and durable stability of the Ag/C catalysts. RRDE results indicate a maximum H2O2 selectivity in the H2SO4 medium of >85 %. Adopting the Ag/C catalysts, the sulfite/air fuel cell can achieve the highest open cell voltage of 0.44 V. It sheds light on the self-driven ability of the cell, attributed to the depolarized effects of both the sulfite oxidation anode and oxygen reduction cathode. At 20 mA cm−2, the initial current efficiencies are ∼96 %, related to a product concentration of ∼0.1 g L−1.

Insight into the influence of environmental factors on selenite removal from desulfurization wastewater by NZVI@AC: An experimental and theoretical study

Nano zero-valent iron (NZVI) technology has shown good potential for the treatment of selenium in wastewater. In this study, NZVI was loaded on activated carbon (AC) by carbothermal reduction method to synthesize high-efficiency adsorbent (NZVI@AC). The agglomeration of NZVI was suppressed and its reactivity was improved. The optimum preparation temperature of NZVI@AC (600 °C) was determined by comparing its purity. Moreover, the synergistic effect between the active component (NZVI) and the support (AC) was investigated on the basis of the density functional theory method. The smaller HOMO-LUMO gap (0.87 eV) and charge distribution of NZVI@AC indicated favorable electron transfer and enhanced chemical reactivity. The adsorption and reduction to Se(0)/Se(-II) were elucidated as the underlying mechanisms for the removal of selenite by comparative analysis of the morphological transformation of iron and selenium species. Furthermore, the selenite removal performance of NZVI@AC was investigated on account of the impact of dissolved oxygen and pH values, and the interaction mechanism of these factors was revealed. The decrease of solution pH and dissolved oxygen concentration are effective ways to improve the removal efficiency of selenite.

Investigation on Friedel’s salt precipitation method for chloride removal from flue gas desulfurization wastewater

Flue gas desulfurization wastewater (FGDW) contained high concentration of chloride, which made it difficult to recycle or achieve zero liquid discharge (ZLD). Friedel’s salt precipitation (FSP) method could effectively dislodge chloride from FGDW and was expected to achieve ZLD of FGDW. Effects of reaction conditions, reagents dosage and types on chloride removal efficiency of FSP method were investigated systematically by single factor tests. Results showed that chloride removal by FSP method was fast and basically completed in 60 min. A higher stirring speed (≥90 rpm) would enhance the dispersion and dissolution of reagents, which was beneficial to improve the chloride removal efficiency. Moreover, the dosage and types of reagents had significant influence on chloride removal and should be selected according to actual need. A two-stage FSP method was applied to avoid the negative effect caused by the presence of sulfate, by which the sulfate and chloride removal efficiency reached 98% and 60%, respectively, in the real FGDW treatment. Through SEM and XRD analysis, precipitates formed in Stage I and II were proved to be CaSO4 and friedel’s salt, which belonged to Ca-Al-layered double hydroxides. The kinetics of FSP method removed chloride was attempted to study, and inferred the reaction as third order reaction. FSP method has enormous potential to be applied in industrial wastewater treatment.

Technical innovation of Autoclaved Aerated Concrete preparation from Desulfurization Wastewater and Sludge and its Life Cycle Assessment

ABSTRACT The article presents an innovative technique for the production of autoclaved-aerated concrete using desulfurization wastewater. The experiments were conducted to explore the optimal formula that meets the requirements of high compressive strength(≥5MPa) and low oven-dry density (≤600 kg m−3). Combined with specific production cases, the environmental assessment within the scope of the total life cycle assessment and circular economy assessment were carried out. Using compressive strength and maximum dry density as indicators, the optimal formulation was found to be 73%:16%:11%:30%:45% for fly ash: cement: lime: desulfurization wastewater: recycled water (process water). And the optimum ratio was 72%: 14%: 12%: 45%: 30% for fly ash: cement: lime: nanofiltration water: recycled water. The life cycle assessment contains a total life-cycle inventory and willing to pay was 61.1CNY. In addition, the GWP = 144.83 kg per cubic meter of autoclaved aerated concrete, the carbon emission reduction efficiency is 72.4%, the water saving is 0.195CNY for one ton of water, and the water saving rate is 40%. The technology is also a low-cost solution for clean production and circular economy model, promoting green and low-carbon development and meeting the requirements of “waste-free cities” popular worldwide.

Insights into chloride sorption and phase transformation of the synthesized Ca-Al bimetallic oxides in flue gas desulfurization wastewater

Sorbents enriched with Ca3Al2O6 (C3A) and Ca12Al14O33 (C12A7) were successfully synthesized by a solid-state sintering method for Cl− removal from the flue gas desulfurization (FGD) wastewater. C3A and C12Al7-rich sorbents prepared at 1200 and 1100 °C achieved the highest Cl− removal of 83.3% and 73.1%, and the former had a higher aluminum utilization rate of 45.2%. Compositional analyses revealed that sorbents synthesized using α-Al2O3 had higher atomic density, higher ratio of absorbed oxygen to lattice oxygen, and higher AlO45−/AlO69− ratio than those using Al2O3, resulting in enhanced reactivity and superior Cl− removal performance. Higher calcination temperature also improved the crystallinity of bimetallic oxides. The sorption isotherms and thermodynamic studies confirmed that the sorption of Cl− on Ca-Al oxides was spontaneous and exothermic, and the maximum sorption capacities were 243.7 mg/g on C3A and 204.1 mg/g on C12Al7, respectively. Kinetics and characterizations suggested that the hydration-induced mineral phase transformation led to structural reconstruction, and the sorption mechanism involved a synergistic action of chemisorption (as the primary force) and physisorption. These results suggested that Ca-Al-based sorbents are highly promising alternatives for application in the zero liquid discharge process of FGD wastewater.

Thermodynamic insights into selenium oxyanion removal from synthetic flue gas desulfurization wastewater with temperature-swing solvent extraction.

Temperature-swing solvent extraction (TSSE) is a cost-effective, simple, versatile, and industry-ready technology platform capable of desalinating hypersaline brines toward zero liquid discharge. In this work, we demonstrate the potential of TSSE in the effective removal of selenium oxyanions and traces of mercury with the coexistence of high contents of chloride and sulfate often encountered in flue gas desulfurization wastewater streams. We compare the rejection performance of the two common solvents broadly used for TSSE, decanoic acid (DA) and diisopropylamine (DPA), and correlate those with the solvent physicochemical properties (e.g., dielectric constant, polarity, molecular bulkiness, and hydrophobicity) and ionic properties (e.g., hydrated radii and H-bonding). The results show that TSSE can remove >99.5% of selenium oxyanions and 96%-99.6% of mercury traces coexisting with sulfate (at a sixfold Se concentration) and chloride (at a 400-fold Se concentration) in a synthetic wastewater stream. Compared to diisopropylamine, decanoic acid is more effective in rejecting ions for all cases, ranging from a simple binary system to more complex multicomponent systems with highly varied ionic concentrations. Furthermore, the H-bonding interaction with water and the hydrated radii of the oxyanions (i.e., selenate vs. selenite) along with the hindrance effects caused by the molecular bulkiness and hydrophobicity (or lipophilicity) of the solvents play important roles in the favorable rejection of TSSE. This study shows that TSSE might provide a technological solution with a high deionization potential for the industry in complying with the Environmental Protection Agency regulations for discharge streams from coal-fired power facilities.

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 the Resource Utilization of Desulfurization Slurry Concentrate in Coal-fired Power Plants

In order to further solve the potential problem of zero discharge of existing desulfurization wastewater and improve the environmental and economic benefits of zero discharge technology, research on the resource utilization of desulfurization slurry concentrate was carried out. The basic magnesium chloride whisker prepared with it as raw material is a new composite material with broad application prospects and high economic value. The purified MgCl2 can be obtained by repeatedly eluting and purifying the concentrated solution of desulfurization slurry. Using it as raw material, we add 10mL of 2mol/L NaOH solution and 2mL of 1mol/L ammonia water into it, control the concentration of MgCl2 to 4 mol/L and the molar ratio of MgCl2 to ammonia water is 4:1, the temperature to 80 °C, and the aging time to 72 hours, and prepare a relatively ideal basic magnesium chloride whisker. This method can be used as a method for the resource utilization of the concentrated solution of desulfurization slurry.

Friedel’s Salts Synthesis and Adsorption Applications in the Removal of As(III) and Se(IV) from Desulfurization Wastewater

Friedel’s Salts Synthesis and Adsorption Applications in the Removal of As(III) and Se(IV) from Desulfurization Wastewater

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.

Review of Migration, Transformation, and Control of Volatile Components during Desulfurization Wastewater Evaporation: Advances and Perspectives

Review of Migration, Transformation, and Control of Volatile Components during Desulfurization Wastewater Evaporation: Advances and Perspectives

Investigating the Corrosive Influence of Chloride Ions on Slag Recovery Machine Shells in Power Plants.

An effective strategy for achieving cost-effective and environmentally friendly desulfurization wastewater in coal-fired power plants involves the incorporation of desulfurization wastewater into the slag water system. The objective of this study was to analyze the corrosion behavior of Q235-A slag-picker shell material upon the introduction of FGD wastewater into the slag water system. The dynamic weight loss method, electrochemical testing method and microscopic phase characterization were employed to investigate the impact of varying chloride ion concentrations (ranging from 1000 mg/L to 30,000 mg/L) of flue gas desulfurization wastewater (FGD wastewater) on the corrosion of Q235-A slag-picker shell material. The test results indicate that as the concentration of chloride ions increases, the corrosion rate increases from 1.1487 mm/a to 1.5590 mm/a when the concentration is less than 10,000 mg/L. However, when the concentration exceeds 10,000 mg/L, the corrosion rate decreases from 1.559 mm/a to 1.0393 mm/a. The corrosion rate is above 1 mm/a at all concentrations. As the Cl- concentration, the quality of the corrosion product film initially increases and then decreases. The primary components of the corrosion product are α- FeOOH, γ-FeOOH, β-FeOOH, Fe3O4 and γ-Fe2O3.

Incorporation of desulfurization wastewater to achieve ultra-low energy consumption in electrochemical lead recycling

Cleaner and more cost-effective battery recycling techniques are still in demand for improving battery's sustainability. Herein, a novel electrochemical spent lead-acid battery recycling approach with ultra-low energy consumption is proposed in this work, which is achieved via coprocessing with desulfurization wastewater. Desulfurization wastewater (containing sulfite ion, SO32−) is used as reducing agent for lead paste leaching process and electrolyte for the subsequent solid-state electrolysis process respectively, while the wastewater can be effectively treated. Morphology and crystal structure characterizations indicate the lead paste leached by simulated desulfurization wastewater is mainly composed of lead suboxide (Pb2O). Electrochemical analyses reveal that charge demand for cathodic electro-reducing desulfurization wastewater leached lead paste into metallic lead is significantly lower than original lead paste. Furthermore, sulfite ion is oxidated on anode during the solid-state electrolysis process, thereby decreasing the anodic potential compared to the traditional oxygen evolution reaction. Thus, the introduction of desulfurization wastewater significantly reduces the overall energy consumption of the solid-state electrolysis by influencing both of the anodic and cathodic processes. The energy consumption to recycle a ton of lead is 169.8–230.5 kWh under optimized operation conditions, which is only 21.2–51.8% of the traditional electrochemical lead recycling process, while 1.6–1.8 m3 desulfurization wastewater with 50,000 mg L−1 chemical oxygen demand can be treated. Therefore, the co-processing of spent lead-acid battery and desulfurization wastewater is proven to be a win-win waste disposal strategy.

A demonstration project for desulfurization wastewater evaporation technology: Field test and performance analysis

Desulfurization wastewater evaporation technology is an effective approach to achieve zero liquid discharge. However, limited information is available on the practical engineering performance and related risks of the technology. In this study, we conducted a field test of desulfurization wastewater evaporation technology in a demonstration project. The results indicated the technology was highly feasible and applicable to three operating conditions with varying desulfurization wastewater flow rates. The migration characteristics of Cl were investigated, revealing that less than 3 % of Cl was released into gaseous HCl. The concentrations of other typical pollutants, such as NOx and SO2, remained unchanged after treatment, indicating that the wastewater evaporation technology did not significantly affect the distribution of gaseous pollutants or the comprehensive fly ash utilization. Moreover, the study found that the evaporation process promoted the agglomeration of particulate matter, as confirmed by larger particle sizes and XRD analysis. The total operating cost of wastewater evaporation ranged from 25 to 30 yuan per ton of wastewater, primarily consisting of coal consumption for extracting flue gas. The data obtained in this work complements and verifies existing research on wastewater evaporation technology.

Effect of external magnetic field on mass transport of reactive species in the reaction between nano zero valent iron and selenate anions in a simulated flue gas desulfurization wastewater

The mechanism involved in the reaction of regulated ions with nano Zero-Valent Iron (ZVI) in the presence of an applied weak magnetic field (WMF) was investigated. The WMF effect on mass transport of reacting ions and morphology and composition of the oxide layer in nano ZVI was elucidated using Electron Energy Loss Spectroscopy (EELS). The magnetic gradient force produced by ferromagnetic ZVI particles had a greater influence on the rate of selenate diffusion in solution than the Lorentz force due to the externally applied weak magnetic field. Moreover, the magnetic gradient force was suggested to suppress ZVI corrosion reactions. Despite changes in the iron oxide layer under the WMF influence, the rate of selenate reduction has not been significantly affected over short term lasting several hours. Most crucially, WMF had a negligible effect on the rate of mass transport of selenate anions, as compared to the dominant effect of forced convection.

Experimental study on coal-fired flue gas HCl removal by injecting adsorbent into flue duct

Abstract Adsorbent injection into flue ducts is an effective technology for controlling gaseous pollutant in coal-fired power plants. This study proposed a new technique of injecting dechlorinater into flue duct for HCl removal in order to realize the wet flue gas desulfurization (WFGD) wastewater sequestration and upgrade the gypsum quality, known as the source dechlorination method. Four alkaline-based adsorbents of CaO, Ca(OH)2 + 5 % NaOH, ethanol-modified CaO, and NaHCO3 were developed and investigated in a pilot scale 6 kW coal-fired circulating fluidized bed (CFB) combustion system for capturing flue gas HCl. The physical and chemical properties of the adsorbents were characterized to explore the reaction mechanisms affected by the adsorbent size and its distribution, active component loading, micro-structure, morphology, and crystal structure. The influences of the injection amount, resident time and flue gas temperature on the HCl removal efficiency were carried out, the dechlorination mechanism of the ethanol-modified CaO were discussed. The distribution of flue gas chlorine species across the air pollutant control devices (APCD) were obtained. This study provides basis for developing the technology of injecting dechlorinater into flue gas for HCl removal.

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.

Use of Zero-Discharge Technology to Recycle Salt in Desulfurization Wastewater

Use of Zero-Discharge Technology to Recycle Salt in Desulfurization Wastewater

Research on optimization test of electrode material in desulfurization wastewater purification system of coal-fired power plant

The traditional coal-fired power plant wastewater treatment technology is faced with the problems of complex system, high operating cost, easy scaling and corrosion, etc. Therefore, coal-fired power plants need to adopt an integrated multi-functional coupling system, taking into account the desalination, anti-scaling, etc. function to remove pollutants from wastewater. Electro-adsorption technology is a technology that can realize water purification and water desalination. It is a new type of water treatment technology. It can effectively remove impurity ions in water without scaling under the premise of low energy consumption. In this paper, the development history of electrosorption theory, the principle of electrosorption, the main points of electric double layer theory, the structure of electrosorption and its working process are reviewed. Several main electrode materials and their advantages and disadvantages are introduced in this paper. Based on the increasingly stringent environmental protection requirements, electro-adsorption technology is expected to be widely used in the power industry due to its advantages of low energy consumption, low cost, and no secondary pollution.