Thermally Activated Persulfate Research Articles

Thermally activated persulfate (TAP)-enhanced tris(2-chloroethyl) phosphate removal in real-world waters based on a response-surface approach as well as toxicological evaluation on its degradation products

As a typical organophosphorus flame retardant, tris(2-chloroethyl) phosphate (TCEP) is refractory in aqueous environment. The application of TAP is a promising method for removing pollutants. Herein, the removal of TCEP using TAP was rigorously investigated, and the effects of some key variables were optimized by the one-factor-at-a-time approach. To further evaluate the interactions among variables, the response surface methodology (RSM) based on central composite design was employed. Under optimized conditions (pH 5, [PS]0: [TCEP]0 = 500:1), the maximum removal efficiency (RE) of TCEP reached up to 90.6%. In real-world waters, the RE of TCEP spanned the range of 56%− 65% in river water, pond water, lake water and sanitary sewage. The low-concentration Cl- (0.1 mM) promoted TCEP degradation, but the contrary case occurred when the high-concentration Cl-, NO3-, CO32-, HCO3-, HPO42-, H2PO4-, NH4+ and humic acid were present owing to their prominently quenching effects on SO4•-. Both EPR and scavenger experiments revealed that the main radicals in the TAP system were SO4•- and •OH, in which SO4•- played the most crucial role in TCEP degradation. GC-MS/MS analysis disclosed that two degradation products appeared, sourcing from the replacement, oxidation, hydroxylation and water-molecule elimination reactions. The other two products were inferred from the comprehensive literature. As for acute toxicity to fish, daphnid and green algae, product A displayed the slightly higher toxicity, whereas other three products exhibited the declining toxicity as compared to their parent molecule. These findings offer a theoretical/practical reference for high-efficiency removal of TCEP and its ecotoxicological risk evaluation.

Field test of thermally activated persulfate for remediation of PFASs co-contaminated with chlorinated aliphatic hydrocarbons in groundwater

The co-occurrence of per- and polyfluoroalkyl substances (PFASs) and chlorinated aliphatic hydrocarbons (CAHs) in groundwater has drawn increased attention in recent years. No studies have been conducted concerning the oxidative degradation of PFASs and/or CAHs by in situ thermally activated persulfate (TAP) in groundwater, primarily due to the difficulty in cost-effectively achieving the desired temperature in the field. In this study, the effects and mechanisms of PFASs degradation by in situ TAP at a site with PFASs and CAHs co-contaminants were investigated. The target temperature of 40.0–70.0 °C was achieved in groundwater, and persulfate was effectively distributed in the demonstration area – the combination of which ensured the degradation of PFASs and CAHs co-contaminants by in situ TAP. It was demonstrated that the reductions of perfluoroalkyl carboxylic acids (PFCAs) concentration in all monitoring wells were in the range of 43.7 %–66.0 % by in situ TAP compared to those maximum rebound values in groundwater, whereas no effective perfluoroalkane sulfonic acids (PFSAs) degradation was observed. The conversion of perfluoroalkyl acids (PFAAs) precursors was one of the main factors leading to the increase in PFCAs concentrations in groundwater during in situ TAP. CAHs were effectively degraded in most monitoring wells, and furthermore, no inhibitory effects of CAHs and Cl− on the degradation of PFASs were observed due to the presence of sufficient persulfate. Additionally, there were significant increases in SO42− concentrations and reductions of pH values in groundwater due to in situ TAP, warranting their long-term monitoring in groundwater. The integrated field and laboratory investigations demonstrated that the reductions in PFCAs and CAHs concentrations can be achieved by the oxidative degradation of in situ TAP.

Degradation of sulfamethazine in water in thermally activated persulfate process

BackgroundThe thermally activated persulfate (TAP) process was utilized to degrade sulfamethazine in water. MethodsThe effects of temperature, Na2S2O8 dosage, initial concentration of sulfamethazine, and the presence of salt (NaCl and NaNO3) and natural organic matter (humic acid) on the degradation of sulfamethazine in the TAP process were studied. Significant FindingsThe degradation of sulfamethazine in the TAP process was closely fitted by a pseudo-first-order kinetic model. At pH 6, the degree and rate of degradation of sulfamethazine at 70 °C considerably surpassed those at 40 °C with diverse Na2S2O8 dosages. At 70 °C and pH 6, raising the Na2S2O8 dosage from 1 mM to 8 mM increased the degree and rate of degradation of sulfamethazine; but excess Na2S2O8 (16 mM) limited them. However, lower temperatures eliminated this limitation. The degree and rate of degradation of sulfamethazine were higher at 70 °C and pH 6 when the initial concentration of sulfamethazine was lower. The Arrhenius equation was utilized to calculate the apparent activation energy at diverse Na2S2O8 dosages. The apparent activation energy for the degradation of sulfamethazine increased from 91 kJ/mol to 150 kJ/mol as the Na2S2O8 dosage was raised from 1 mM to 8 mM. However, the apparent activation energy for the degradation of sulfamethazine was reduced to 120 kJ/mol as the Na2S2O8 dosage was raised further to 16 mM. Radical quenching tests indicate that the most important radical in the degradation of sulfamethazine at 70 °C and pH 6 was SO4•−. At 70 °C and pH 6, the presence of salt (NaCl and NaNO3) and humic acid (HA) exhibited various influences on the degradation of sulfamethazine. The degree of degradation of sulfamethazine (10 mg/L) in the TAP process (70 °C and pH 6) reached 100% at 3 min at an Na2S2O8 dosage of 8 mM with a corresponding rate constant of 1.4003 min−1. Accordingly, the TAP process can be utilized in the effective treatment of sulfamethazine-contaminated water.

Enhanced disintegration mechanism of surplus activated sludge to improve dewatering by thermally activated persulfate oxidation under mild temperature.

The dewatering treatment is an essential process for the treatment and disposal of surplus activated sludge (SAS), and improving sludge dewatering performance is still a challenge and has become a research hotspot in recent years. The oxidation and disintegration of bacterial cells and extracellular polymeric substances (EPS) by active radicals produced by advanced oxidation processes (AOPs) were extremely promising to achieve deep sludge dewatering. This paper systematically studied the efficiency and mechanism of thermally activated persulfate (TAP) oxidation technology to the improvement of SAS dewatering performance. The results showed that the relative filterability (CST0/CST) was increased 2.52 times with 2.0 mmol/g VSS potassium peroxydisulfate (PDS) at 80 °C in 90 min. Under this condition, the Zeta potential of SAS significantly decreased from - 14.8 to - 1.44 mV, while the average particle size (dp50) decreased from 52.981 to 48.259 μm. Thermal treatment disrupted the sludge structure to release large amounts of EPS including polysaccharides and protein. Meanwhile, the results of three-dimensional excitation-emission matrix (3D-EEM) fluorescence spectra showed that the TAP treatment could expedite the disintegration of sludge, facilitating the decrease of total EPS content and conversion of tightly bound EPS (TB-EPS) to loosely bound EPS (LB-EPS) and soluble EPS (S-EPS). The mechanism of TAP process to improve SAS dewatering performance was revealed, which could contribute to breaking the bottleneck of sludge depth dewatering and provide a theoretical and technical basis for its practical application.

Thermally activated persulfate oxidation of Basic Fuchsin dye: Effect of different operating parameters, kinetic, and thermodynamic study

AbstractThe present paper aims to investigate the efficiency of thermal activation persulfate in eliminating the organic dye “Basic Fuchsin” (BF). In addition, the study attempts to elucidate the effect of different operating parameters, such as persulfate dosage (0.44–4.4 mM), the initial solution pH of (3–10), and temperature (25–50°C), on the process. The effects of various anions and water matrices on BF discoloration were investigated. Thus, the findings revealed that 94.15% of BF can be eliminated using persulfate at a concentration of 4.4 mM and a temperature equal to 50°C. It occurs under the following operating conditions: oxidation time of 60 min, initial pH equal to 6, the pollutant concentration of 10 ppm, and stirring speed equal to 300 rpm. Furthermore, the kinetic study indicated that the degradation of the BF dye using PS followed a first‐order pattern with rate constants varying within a range of 15.3 × 10−3–43.2 × 10−3 min−1. Based on the Arrhenius equation, the activation energy of the studied process was determined to be 29 kJ mol−1, suggesting that a moderate activation energy is required for BF discoloration. The results of the thermodynamic study confirm that the oxidation process is non‐spontaneous and endothermic. Coexisting inorganic anions delayed BF discoloration to varying degrees, and the inhibitory action followed the following order: carbonate > chloride > sulfate > nitrate. Organic pollutants oxidation by the thermal activation of the persulfate is a simple and effective method for the depollution of waste textile water.

UV-photoaging behavior of polystyrene microplastics enhanced by thermally-activated persulfate

Aging of microplastics (MPs) under natural conditions takes several months or even years. In this study, polystyrene MPs (PS-MPs) were used as the target MPs, and these were subject to artificially accelerated aging by UV irradiation (UV254) and UV/heat-activated persulfate (UV+K2S2O8). The physicochemical characteristics of aged MPs and the interaction with tetracycline hydrochloride (TH) were investigated. Simultaneously, the fluorescence characteristics, total organic carbon content (TOC), and toxicity effects of aging filtrate were also evaluated. Furthermore, the aging path of PS-MPs was derived with reactive species analysis using an electron paramagnetic resonance (EPR) test. The results showed that obvious cracks appeared on the surface of the aged PS-MPs, with the average particle size decreasing from 83.95 ± 19.93 µm to 60.41 ± 19.58 µm in the UV treatment and to 48.02 ± 18.83 µm in the UV+K2S2O8 treatment. The oxygen-containing functional groups of aged MPs were detected after the UV and UV+K2S2O8 treatment; the carbonyl index (CI) values were 0.44 and 0.62, respectively. The TH adsorption capacity of UV-treated MPs and UV+K2S2O8-treated MPs increased from 0.176 mg g−1 for pristine MPs to 0.193 mg g−1 and 0.225 mg g−1, respectively. Especially, the TOC and luminescent inhibition toxicity of the filtrate increased after aging. EPR analysis demonstrated that SO4•− and ROS played a key role in accelerating the aging of PS-MPs. This study provided a reference for UV photoaging behavior of MPs enhanced by activated K2S2O8, which is meaningful for a comprehensive understanding of MPs behavior and the risks they introduce into the environment.

Decomplexation of Ni-EDTA by thermally activated persulfate: Efficiency and mechanism

The thermally activated persulfate (TAP) advanced oxidation process is a promising technology for treating complex heavy–metal wastewater because of its environmental friendliness and high efficiency. However, previous studies have not fully explored the potential mechanisms involved in removing complex heavy metals. Herein, we investigated the effects of temperature, initial pH, peroxydisulfate (PDS) dosage, and the initial concentration of Ni-EDTA on the removal of Ni-EDTA using TAP. Results showed that increasing the activation temperature and PDS dosage enhanced the removal rate of Ni-EDTA, whereas decreasing the pH and initial concentration of Ni-EDTA were more conducive to Ni-EDTA removal. In addition, the quenching experiment indicated that OH and SO4− were the main active species, with OH being the most important contributor in the Ni-EDTA removal process. The degradation mechanism of Ni-EDTA was also explored through ultra performance liquid chromatography–mass spectrometry (UPLC–MS) analysis and density functional theory (DFT) calculations. These showed that the TAP-based degradation of Ni-EDTA is a step-by-step decarboxylation process due to increased bond lengths of CN or NCCN bonds of Ni-EDTA, resulting in the destabilization of Ni-EDTA. Overall, this study provides unique insights into the degradation of complex heavy metals in industrial wastewater using TAP.

Degradation efficiency and mechanism of 2,2′,4,4′-tetrabromodiphenyl ether (BDE-47) by thermally activated persulfate system

Polybrominated diphenyl ethers (PBDEs) as a typical brominated flame retardant (BFR) have attracted worldwide attention due to the high environmental risk and resistance to conventional remediation processes. In this study, thermally activated persulfate (TAP) process was applied to degrade 2,2′,4,4′-tetrabromodiphenyl ether (BDE-47), which is the most toxic and representative PBDEs in e-waste dismantling sites. Impact factors such as PDS dosage, heating temperature, and initial pH were evaluated. Results showed that BDE-47 can be 100% degraded within 180 min under the condition of PDS:BDE-47 = 1000:1, 60 °C, and pH = 7. Quenching experiments combined with EPR analysis further proved the important role of SO4·− in oxidating BDE-47. According to high-resolution mass spectrometry (HRMS) analysis, only one oxidation product of low toxicity was detected during the oxidation process. Theoretical calculations further revealed that the oxidation process mainly involved radical attack at C–Br bond, cleavage of C–Br bond, and fission of ether bond, and HSO4· may also play an important role in BDE-47 degradation in TAP system. In addition, TAP system exhibited universality as all selected PBDE congeners can be degraded, and the degradation rate of PBDEs was greatly affected by the number of substituted Br atoms in a negative trend. Overall, these findings indicate that TAP can be applied as an effective method for removal of PBDEs, and we provide a new insight for the practical application of TAP technology in BDE-47 degradation from experimental and theoretical aspects.

Degradation of antiviral drug acyclovir by thermal activated persulfate process: Kinetics study and modeling

Pharmaceutical and personal care products (PPCPs) pose a great threat to water environment security. In this study, acyclovir (ACV) was efficiently degraded by thermally activated persulfate (TAP) system. The ACV degradation increased with rising reaction temperature and persulfate dosage. With the existence of inorganic anions and humic acid, ACV removal was retarded to varying degrees. Under strong alkaline condition, it was observed that the degradation of ACV was significantly inhibited. In addition, Kintecus software was employed to simulate ACV removal and achieved a good fit with the experimental results. The contribution rates of main reactive radicals under acidic, neutral, and alkaline conditions were investigated, and the contribution of hydroxyl radical (⋅OH) increased significantly under alkaline condition. The main active species were identified as sulfate radical (SO4⋅-) and ⋅OH through quenching experiment, and the second-order reaction rate constants of SO4⋅- and ∙OH reacted with ACV were calculated to be 9.17 × 109 M−1 s−1 and 2.74 × 109 M−1 s−1, respectively. The main degradation pathways included addition of free radicals, oxidation of branch chain and ring opening. The acute and chronic toxicity of intermediates to organisms predicted by ECOSAR were significantly reduced compared with that of ACV.

Dexamethasone degradation in aqueous medium by a thermally activated persulfate system: Kinetics and transformation products

Dexamethasone (DEX) is a synthetic steroid hormone that, owing to its endocrine disruptive effects, has the potential to be detrimental. DEX must be successfully removed during drinking water treatment to preserve human and aquatic animals' health. This study investigates the thermally activated persulfate (TAP) process for the efficient decomposition of DEX. The effectiveness of several variables such as pH, persulfate dose, DEX concentration, reaction temperature, and water matrices was studied. Removal of 500 μg/L DEX reached 100 % by using 100 mg/L of persulfate in ultrapure water (pH = 7) at 50 °C, within 45 min of reaction time. DEX removal usually followed exponential decay. The removal efficiency of DEX in the TAP process was pH-dependent, as 61 % of DEX was removed at a pH value of 9. In contrast, complete degradation was achieved under acidic and near neutral conditions.Moreover, environmentally relevant degradation experiments showed that, in principle, the presence of bicarbonate ions and humic acid had a negative effect on DEX decomposition by reducing the percentage removal of the target compound by >50 %. Six transformation products derived from DEX oxidation were identified using high-resolution LC-MS. TAP system could be proposed as a promising application for removing steroid hormones n real water matrices after process optimization in real conditions.

Treatment of wood by sulfate and hydroxyl radical oxidation produced from thermally-activated persulfate: VOC emission and wood property evaluation

ABSTRACT Wood emits volatile organic compounds (VOCs) that can affect people’s health and air quality. Based on advanced oxidation processes (AOPs), sulfate radicals produced via thermally-activated persulfate (Na2S2O8, KHSO5) can minimize VOCs. This research aims to apply this technique to minimize the VOC content in Pinus radiata. The results showed that terpenes and alcohols were the main VOCs emitted from Pinus radiata, which were greatly minimized using four treatments; however, acetic acid and 3-furaldehyde emissions increased. Furthermore, the temperature and oxidizing agent contributed to VOC degradation. Characterization results, including FTIR, XRD, color tests, and compressive strength indicated that the AOP treatment caused only a slight decline in the wood properties, while effectively reducing VOC emissions by as much as 32.75–61.05%.

Evaluation of watermelon peel, banana peel and bay leaves hydrochars as green catalysts in the degradation of malachite green by thermally activated persulfate oxidation method

Water is essential for the continuation of life, moreover, clean water is of great importance on the basis of a healthy life. However, one of the biggest problems of our age is water scarcity and the rapid pollution of existing water resources. Besides, solid food wastes are becoming a growing problem day by day. Therefore, both environmentally friendly, effective and innovative techniques are required in the reuse of solid waste in the treatment of wastewater that is generated at enormous levels. In this study, the thermally activated persulfate (TAP) oxidation method was applied to remove the color and total organic carbon (TOC) of an industrial dye, malachite green (MG). The effects of different levels of experimental variables such as concentration of the oxidising agent, K2S2O8, (0.048 mM–0.55 mM), temperature (336 K–370 K) and treatment time (1.6 min–18.4 min) on the color and TOC removal of MG were investigated. Color removal efficiencies of 97.3% and TOC removal efficiencies of 56.4% were achieved. Evaluation of the effects of the experimental variables on the responses and the optimisation of the TAP method was performed using the response surface method (RSM). The accuracy of the method was assessed by ANOVA. Catalytical efficiencies of hydrochars synthesized in the subcritical water medium (SWM) and obtained from solid food wastes such as banana peel (BP) and watermelon peel (WM) as well as bay leaf (BL) were evaluated. The synthesized hydrochars were characterised by scanning electron microscope (SEM) and (Brunauer–Emmett–Teller) BET analyses. The most effective hydrochar in the catalysis of K2S2O8 was BP hydrochar as 83.6% of color removal was obtained using 0.048 mM K2S2O8 and 2 g/L BP hydrochars at 353 K in 10 min.

Degradation of tris(2-chloroethyl) phosphate (TCEP) by thermally activated persulfate: Combination of experimental and theoretical study

Organophosphorus esters (OPEs), one kind of the emerging contaminants with high frequency of detection, is rather refractory in natural environment, thus posing great threat to human health. This study investigated the feasibility and mechanism of tris(2-chloroethyl) phosphate (TCEP) degradation in thermally activated persulfate (TAP) system. Influence of impact factors, such as PDS dosage, temperature, initial pH, and presence of natural water matrix (Cl−, NO3−, H2PO4−, NH4+, humic acid), were evaluated. Results showed that 100% degradation of TCEP can be achieved in TAP system in 40 min at 60 °C. SO4·− as the dominant oxidant for TCEP degradation was proved by quenching experiment and verified by EPR analysis. Alkaline condition exerted great inhibitory effect by affecting the constituents of oxidative radicals. It is suggested that Cl− and H2PO4− at lower dosages promoted the degradation by stimulating ·OH production and forming oxidative radicals with better selectivity. Intermediates identified by high resolution mass spectrometer was suggested less toxic than TCEP by ECOSAR program. Meanwhile, the illustrated oxidation mechanism mainly involved radical attack at CCl bond and cleavage of CO bond, as further confirmed by frontier electron density calculation and wavefunction analysis. Moreover, cyclic degradation of TCEP indicated the constant release of SO4·− in 450 min, suggesting high efficiency and stability of PDS in TAP system. Four selected OPEs achieved complete removal in TAP system and their degradation discrepancy was further discussed based on the distinctive structures. Altogether, TAP technology can be used as an efficient method in TCEP removal with great potential for application.

Decomposition of perfluorooctanic acid by carbon aerogel with persulfate

Thermally-activated persulfate (PS) has been recognized as one of the most effective Advanced oxidation processes (AOPs) to oxidize Persistent perfluorooctanoic acid (PFOA). Applications of Carbon aerogel (CA)-activated PS for PFOA decomposition at 25, 40, 50 and 60 °C were evaluated. With the presence of CA in PS oxidation, 85.7% of PFOA was decomposed to fluoride ions and intermediates of short-chain perfluorinated carboxylic acids (PFCAs) with a 34.5% defluorination efficiency at 60 °C after 8 h. PFOA was decomposed and mineralized to fluoride ions in the CA + PS system following a stepwise degradation process of C6F13COOH → C5F11COOH → C4F9COOH → C3F7COOH → C2F5COOH → CF3COOH at 60 °C. The decomposition and defluorination rates of the combined CA + PS system at 60 °C were approximately 1.83 and 1.61 times faster than those of the PS-only system, respectively. With CA in the PS system, activation energies of PFOA removal and defluorination were significantly reduced from 66.8 to 37.2 and 97.3 to 49.2 kJ/mol, respectively. It implies that applying CA could effectively promote the PFOA degradation that leads to significant savings in energy consumption and reductions in process time. Characteristics of CA used were evaluated by using N2 adsorption, zeta potential, Raman, SEM, XRD, XPS and FT-IR techniques. A quenching test was conducted by using methanol as an inhibitor and Electron spin resonance (ESR) spectra of free radicals were analyzed for development of proposed reaction mechanisms.

Degradation and mechanism of hexafluoropropylene oxide dimer acid by thermally activated persulfate in aqueous solutions

Hexafluoropropylene oxide dimer acid (HFPO-DA), an alternative of perfluorooctanoic acid (PFOA), has been detected frequently in environmental media worldwide. It has been reported that HFPO-DA is equal to or more toxic than PFOA, as well as more recalcitrant to degradation. In this study, the efficient degradation of HFPO-DA was achieved by the thermally activated persulfate (TAP) system, but the influence of co-contaminants in the field can be significant. The degradation pathways of HFPO-DA were proposed through an integrated approach of experiment and density functional theory (DFT) calculations. CF3CF2COO− and CF3COO−, were the stable intermediates identified by ultra-performance liquid chromatography-quadrupole-time-of-flight-mass spectrometry (UPLC-Q-TOF-MS). Electron transfer, decarboxylation, H abstraction, HF elimination using H2O as a catalyst and hydrolysis occurred in different steps of HFPO-DA degradation process, with –COO− as the initial oxidative site attacked by SO4−. In addition, the acute toxicity assessment for HFPO-DA degradation in the TAP system performed by Escherichia coli suggested that HFPO-DA was degraded to a level having no adverse effect on the growth of E. coli, and no more toxic intermediates were formed. Overall, this work provides insights for the degradation of HFPO-DA contamination by the TAP system.

Treatment of soil contaminated with petroleum hydrocarbons using activated persulfate oxidation, ultrasound, and heat: A kinetic and thermodynamic study

This study focuses on the remediation of petroleum hydrocarbons in the soil matrix. Factors such as the persulfate dosage, initial pH, temperature, ultrasonic power, and soil water ratio were investigated by using ultrasonic and thermal energy to activate persulfate. The results showed that the degradation efficiency of the total petroleum hydrocarbon (TPH) content was 78.2% and 72.64% within 72 h for the ultrasonically/thermally-activated persulfate (“US/Heat/PS”) and thermally-activated persulfate (“Heat/PS”) systems, respectively, whereas it was 56.41% for the ultrasonically-activated persulfate system. The results of the kinetics analysis suggested that the degradation of petroleum hydrocarbons well-fitted the pseudo-second-order reaction, and that the rate constants increased with increasing temperature and initial persulfate dosage but with decreasing pH over a certain range. Moreover, three reaction phases comprising two rapid phases and an intermediate phase were observed for the TPH degradation. The measured thermodynamic parameters justified the spontaneity of the degradation process. Furthermore, a possible mechanism of petroleum hydrocarbon degradation in the US/Heat/PS system was determined through gas chromatography–mass spectrometry analysis, and the degradation priority of different components was ranked as: alkenes > alcohols > esters > alkanes > aromatics.

Biopolymer transformation and antibiotics degradation of wastewater sludge using thermally activated persulfate oxidation for dewaterability enhancement

Wastewater sludge is mainly comprised of microorganisms and extracellular polymeric substances (EPS). The gel-like network structure of EPS traps bound water, resulting in poor dewaterability of sludge. In this work, the thermally activated persulfate (TAP) oxidation was used in sludge treatment to improve dewaterability. The transformation of proteins and phosphorus were systematically investigated to understand the mechanisms of sludge conditioning with TAP at molecular levels. The results showed that TAP oxidation produced SO4- and OH radicals which decomposed the macromolecular proteins, causing uncoiling of protein secondary structures and exposure of inner hydrophobic sites. The polypeptide, amino acid, and ammonia nitrogen were generated, and sludge dewaterability was enhanced. A mechanism was proposed to explain the synergistic effects of thermal hydrolysis and TAP oxidation on the transformations of nitrogen and phosphorus containing biopolymers. Furthermore, 30%-100% of antibiotics were degraded in TAP treatment. TAP performed well in macrolide and tetracycline degradation (>80%), while most of quinolone antibiotics were more refractory to oxidation.

Membrane concentrate management for textile wastewater with thermally activated persulfate oxidation method

AbstractIn this study, concentrated textile wastewater using NF270 membrane was further treated by thermally activated persulfate (TAP) oxidation method. First, the effluent of the textile wastewater treatment plant was treated using NF270 membrane, and the concentrated stream was obtained. Second, the TAP method was applied using the central composite design (CCD) optimization method. The steady‐state permeate flux of NF270 was obtained as 3.4, 6.8, 17.4 L/m2.h, respectively, for 10, 15, 20 bars pressure. COD concentration and color in concentrated stream increased from 880 mg/L and 2960 Pt‐Co to 1120 mg/L and 4860 Pt‐Co, respectively, when operating pressure increased from 10 to 20 bars. The results obtained from the CCD optimization method showed that the experimental and predicted values showed a good fit in both chemical oxygen demand (COD) and color removals models. The maximum experimental values of COD and color removal efficiencies were obtained 69% and 95%, respectively, at 370 K temperature, 60 mM K2S2O8 concentration, and 80 min treatment time. The NF270 concentrated stream was also filtrated from the 2nd stage of NF270 membrane after TAP treatment. The results showed that TAP degradation of concentrated stream improved the 2nd stage of NF270 membrane flux compared without degradation. The proposed TAP method was successfully used to further the treatment of textile wastewater concentrated stream for NF270 membrane.

Treatment of agrochemical wastewater by thermally activated persulfate oxidation method: Evaluation of energy and reagent consumption

Agrochemical wastewater is a potential danger to public health, the environment, and other livings, as it contains hazardous compounds that can harm plants and animals and cause many diseases in humans. In this work, the thermally activated persulfate (TAP) oxidation method, which is an effective and practical approach for degradation of agrochemical wastewater, was carried out. Optimization and modeling of total organic carbon (TOC) and decolorization of the agrochemical wastewater were studied using a central composite design. Persulfate was thermally activated and the effect of the temperature, treatment time, and persulfate concentration on the TAP method was detailed. Temperature and persulfate concentration were the most effective process parameters for TOC removal. Results, model coefficients, and analysis of variance (ANOVA) showed that the resulting model was precise and acceptable for predicting TOC and color removals. The feasibility of energy and reagent consumption was proposed. Under conditions where TOC and color removal rates were reached 70.2% and 100%, the electrical energy and persulfate consumption were 529.5 kWhm−3 and 21.6 kgm−3, respectively. Chemical composition analysis of wastewater and treated samples showed that the TAP method was able to degrade almost all compounds found in this study, including those resistant to oxidation. Ion chromatography analysis showed that the ion concentration of the wastewater samples changes with the applied temperature and the oxidant concentration.

Improving dewaterability of waste activated sludge by thermally-activated persulfate oxidation at mild temperature

The mass production of waste activated sludge in wastewater treatment plants may lead to environmental pollution and sludge dewatering is an essential process during its treatment. The oxidation of extracellular polymeric substances (EPS) was the core step to achieve deep sludge dewatering. In this study, thermally-activated sodium persulfate (SPS) process was managed to improve the dewaterability of waste activated sludge (WAS) and its internal mechanism was systematically elaborated. Experimental results showed that with 2.0 mmol/g VSS SPS at 80 °C, capillary suction time (CST) was roughly 59.74% of that in raw sludge. Under this condition, 14.66 ± 0.10 × 1011 kg/m of specific resistance to filtration (SRF) and 61.8% ± 0.1% of water content (WC) was determined, respectively. A solubilization/oxidation process was proposed to unravel the mechanism of the enhanced dewaterability of WAS in thermally-activated SPS process. Mild temperature efficiently disrupted the sludge flocs and broke cell walls, releasing large amounts of EPS into bulk phase. Meanwhile, mild temperature accelerated the decomposition of SPS to generate sulfate radicals (SO4−) and hydroxyl radicals (OH) for oxidizing EPS, facilitating the conversion of bound hydrated water into free water and achieving solid-water separation. The higher reaction temperature favored sludge dewatering, whereas overdosing SPS posed no significant impact. Further analysis illustrated that tyrosine protein-like, tryptophan protein-like, fulvic acid-like and humic acid-like substances in various EPS fractions together exerted the influence on sludge dewatering. Furthermore, the synergy process could alter the secondary structure of protein, which caused a loose structure of EPS and the exposure of hydrophobic sites, facilitating the dehydration of sludge flocs. The details of how thermally-activated SPS process enhanced sludge dewaterability provided the theoretical and technical basis for the application of the process under a real-world situation.