Activated Sodium Persulfate Research Articles

Mechanism of Sulfate Radical Formation on Activation of Persulfate Using Doped Metal Oxide and Its Role in Degradation of Tartrazine Dye in an Aqueous Solution.

Degradation of tartrazine dye (TZD) was performed in this study using sulfate radicals (SO4•-) generated from the activated sodium persulfate (SPS) using Fe3O4@PDA nanoparticles (NPs). The NPs were characterized by Fourier transform infrared (FTIR), vibrating sample magnetometer (VSM), X-ray diffraction (XRD), high-resolution scanning electron microscopy (HR-SEM), X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HRTEM), and energy-dispersive X-ray spectroscopy (EDX). The average particle size of the NPs was 17.49 nm from XRD analysis. The presence of the C-N group at 1129 cm-1 in FTIR and 2.54% of the nitrogen element identified from the EDX plot was evidence of successful doping of polydopamine (PDA). Superparamagnetic nature with a decrease in the Ms value to 42.015 emu/g after doping was determined. Doping was further confirmed by XPS analysis with binding energies at 399.68 and 400.99 eV. The average particle size from HRTEM analysis was 21.47 nm with a lattice spacing of 0.30 nm. Turnover number (TON) and turnover frequency (TOF) values for Fe3O4@PDA were determined to be 3.72 and 0.0248 min-1 with respect to different systems, respectively. Optimum conditions for the Fe3O4@PDA/SPS system were 50 ppm TZD, 0.9 g/L catalyst, 12 mM SPS, and pH 4 with 94.68% efficiency in 150 min. The inhibition effect of ions in TZD degradation followed the order humic acid <NO3- < Cl- < CO32. The kinetic model fitting the Fe3O4@PDA/SPS system has pseudo-second-order kinetics. Excess formation of SO4•- produced hydroxyl radicals (•OH) that were identified by a scavenging test. Reusability of the NPs was performed for five cycles and showed acceptable degradation performance up to 82.47%. The intermediates identified from gas chromatography-mass spectrometry (GCMS) proved the cleavage of azo and sulfonate groups of TZD with the formation of nontoxic intermediates. Finally, the phytotoxicity assessment was studied using Vigna radiata (Green grams). The % decrease of the root, shoot, and seedling length for the degraded dye solution was negligible. Hence, this study proved that the Fe3O4@PDA/SPS system could effectively degrade TZD with nontoxic intermediate formation.

Role of surfactants in the degradation and sustainable dyeing for reactive dyeing wastewater

To enhance the decolorization rate of thermally activated sodium persulfate in dye wastewater, C.I. Reactive Black 5 (RB5) was investigated in this study, which was evaluated by the decolorization of the dye solution. The effect of surfactant concentration (including anionic surfactant sodium dodecyl sulfate (SDS), nonionic surfactant Tween 80 (TW-80) and amphoteric surfactant (BS-12)), SPS concentration, and reaction temperature on the degradation of RB5 was studied. Furthermore, the relationship between free radicals and RB5 degradation was investigated. The results showed that the addition of SDS and TW-80 would inhibit the decolorization of RB5. Correspondingly, the effect would enlarge as the surfactant concentration increased. Nevertheless, the addition of BS-12 wouldn’t affect the final decolorization of RB5 dye solution, despite it could increase the decolorization rate in the initial stage. After 10 min of decolorization, compared to the dye liquor without BS-12, the decolorization could increase by 9.07 % and 0.69 %, respectively, after adding 0.5 and 1.0 CMC of BS-12. Besides, when reactive dyes were degraded by thermally activated sodium persulfate, the SO4-· and ·OH would work together, and SO4-· played a major role while ·OH played an auxiliary part. When the treated wastewater was used for dyeing, the addition of BS-12 could effectively regulate the dyeing rate. The fixation and K/S value were increased by 1.1 % and 0.20, respectively. Furthermore, the dyed fabrics also exhibited improved uniformity, with negligible differences in color fastness. The effects of adding SDS were similar to BS-12, while it decreased the exhaustion and fixation rate of RB5. In addition, non-ionic TW-80 was unfavorable to dyeing. This work provides a new way for efficient treatment of dyeing wastewater as well as reuse, opening an environmentally friendly treatment concept.

Synergetic sludge conditioning by US enhanced Fe2+ activated sodium persulfate: Physicochemical properties and mechanisms

Efficient dewatering of sewage sludge is an energy- and carbon-saving procedure for sludge treatment in wastewater treatment facilities. The ultrasound-coupled divalent iron ion activated persulfate process can effectively promote sludge dewatering and improve organic substance content. Under the action of ultrasound (US 50 w/L), divalent iron ions (Fe2+) 200 mg/g (TS), and persulfate (PDS) 200 mg/g (TS) for 60 min, the capillary suction time (CST) was reduced by 79.74%, and the moisture content of the dewatered sludge cake reached 56.51 wt%. The organic carbon content of treated sludge was also four times higher than the original sludge and types were richer in short-chain volatile species in US/Fe2+/PDS. Moreover, the correlation analysis found that the relationship of between CST and SV30, Zeta and lactate dehydrogenase (LDH) were positive correlation, and the relationship of SCOD and TC were positively correlated with the PN (SB-EPS). Mechanistic studies showed that the US/Fe2+/PDS system could produce oxygen activators by US coupling Fe2+ to strengthen the effect of activated PDS strongly, while the sulfate radicals (SO4·-) radical was a dominant role. The cracking mechanism is divided into two pathways effectively degraded the macromolecule EPS into a small-molecule acid and further reduced the water-holding interfacial affinity as follow: (1) the radical path dominated by hydroxyl radicals (·OH), SO4·-, and superoxide radical (O2·-); (2) the non-radicals dominated by monoclinic oxygen (1O2). Afterwards, the electrostatic force and interfacial free energy were reduced, resulting in enhanced self-flocculation and mobility to enhanced dewaterability. These findings demonstrated the US/Fe2+/PDS system had significant advantages in sludge cracking and provided theoretical support for its practical application.

Structure-dependent degradation of phthalate esters with persulfate oxidation activated by thermal in soil

Phthalate esters (PAEs) have become one of the most concerned emerging organic pollutants in the world, due to the toxicity to human health, and hard to remove it efficiently. In this study, the degradation performance of DBP and DEHP in the soil by water bath heating activated sodium persulfate (PS) method under different factors were studied, in which the degradation rate of DBP and DEHP were improved with the increasing of temperature, PS concentration and water/soil ratio, and higher diffusion efficiency treatments methods, due to the improved mass transfer from organic phase to aqueous media. However, the degradation rate of DEHP was much lower than that of DBP, because DEHP in the soil was more difficult to contact with SO4•− for reaction on soil surface, and the degradation rate of PAEs in soil was significantly lower than that in water. Redundancy analysis of degradation rate of DBP and DEHP in water demonstrated that the key factors that determine the degradation rate is time for DBP, and cosolvent dosage for DEHP, indicating that the solubility and diffusion rate of PAEs from soil to aqueous are predominance function. This study provides comprehensive scenes in PAEs degradation with persulfate oxidation activated by thermal in soil, reveal the difference of degradation between DBP and DEHP is structure-dependent. So that we provide fundamental understanding and theoretical operation for subsequent filed treatment of various structural emerging pollutants PAEs contaminated soil with thermal activated persulfate.

Preparation of Nickel-Based Bimetallic Catalyst and Its Activation of Persulfate for Degradation of Methyl Orange

In this research, a new catalyst for activating persulfate was developed by loading iron and nickel ions onto powdered activated carbon (PAC) for treating methyl orange, and the preparation process was optimized and characterized. The efficacy of the treatment was evaluated using the Chemical Oxygen Demand (COD) removal rate, which reflects the impact of various process parameters, including catalyst dosage, sodium persulfate dosage, and reaction pH. Finally, the recovery and reuse performance of the catalyst were studied. The optimal conditions for preparing the activated sodium persulfate catalyst were determined to be as follows: a molar ratio of Fe3+ and Fe2+ to Ni of 4:1, a mass ratio of Fe3O4 to PAC of 1:4, a calcination temperature of 700 °C, and a calcination time of 4 h. This preparation led to an increase in surface porosity and the formation of a hollow structure within the catalyst. The active material on the surface was identified as nickel ferrite, comprising the elements C, O, Fe, and Ni. The magnetic property is beneficial to recycling. With the increase in catalyst and sodium persulfate dosage, the COD removal efficiency of the oxidation system increased first, and then, decreased. The catalyst showed good catalytic performance when the pH value was in the range of 3~11. Furthermore, Gas Chromatography–Mass Spectrometry (GC-MS) analysis indicated the complete oxidation of methyl orange dye molecules in the system. This result highlights the important role of the newly developed catalyst in activating persulfate.

Removal of p-nitrophenols by BC@nZVI activated persulfate: A study of key factors and mechanisms

Straw biochar loaded zero-valent iron nanoparticles were prepared by co-precipitation method using agricultural waste straw biochar as a carrier for the removal of p-nitrophenol (PNP) by activated sodium persulfate (PS). The physicochemical properties of BC@nZVI were characterized using SEM, EDS, FTIR, BET, and RAMAN. The effects of PS concentration, catalyst concentration, initial pH, coexisting anions, and different activation systems on the degradation of PNP were investigated. The results showed that the best activation effect was exhibited at pH= 7, BC@nZVI dosage of 2 g/L, and PS concentration of 1 mM, and the removal of 40 mg/L PNP reached 91.7 % in 10 min. The high concentration of PS (4 mM) triggered free radical competition to inhibit the degradation, and the removal rate was only 74.5 % at 1 mM. In addition, bicarbonate ions (0–20 M) had a significant inhibitory effect on this system. Electron spin resonance (ESR) demonstrated that SO4⋅− and·OH were the major radicals, and SO4⋅− was preferentially generated. The intermediate products were identified by LC-MS, XRD and XPS characterization, which showed that adsorption and redox were the main degradation mechanisms, with p-benzoquinone was the oxidized product and substances such as 4-heptanone and propionic acid were the reduced products. This study proves that BC@nZVI activated PS is an efficient and excellent means of removing PNP and a good way to reuse agricultural waste.

Mechanism of thermally activated sodium persulfate–biochar skeleton treatment to improve the dewaterability of waste activated sludge

Sludge dewatering is a necessary process in the disposal of waste activated sludge (WAS). In this study, thermally activated sodium persulfate–biochar skeleton pretreatment was performed to improve the dewaterability of sludge, and its internal mechanism was systematically elucidated. The experimental results showed that, under optimal operating conditions, the water content of WAS could be reduced from 89.7% to 61.3% of the raw sludge. Under these conditions, the capillary suction time and specific resistance to filtration were roughly 23.23% and 59.57% of those in the raw sludge, respectively. This study proposes a relationship between organic matter migration and sludge physical structure that explains the dewaterability improvement mechanism. Separate thermal treatment caused organic matter such as proteins, polysaccharides, and humic substances to dissolve, releasing their bound water. Simultaneously, changes in the surface structure (pore size reductions and BET surface area increases) deteriorated the dewaterability of WAS. The reactive oxygen species generated by the thermally activated sodium persulfate further mineralized the organic matter, simplifying the floc surface structure (pore size increases and BET surface area decreases) and finally improving the dewaterability. Under these conditions, the addition of biochar increased the pore size, and further improved sludge dewaterability.

The fate of extracellular proteins and polysaccharides of waste activated sludge oxidative in aqueous and granular sludge phase upon degradation using Fe(II)-persulfate conditioning

Dissolved organic matter, particularly proteins (PN) and polysaccharides (PS) in extracellular polymeric substances (EPS), are regarded as the key factors influencing the dewaterability of waste activated sludge (WAS). An investigation was conducted on the treatment of WAS by Fe(II) activated sodium persulfate (SPS) to evaluate the kinetics of oxidative degradation of EPS in the aqueous and granular sludge phase, and to quantify the oxidation of SPS in aqueous and granular sludge phase in Fe(II)-SPS system. The WAS was divided into granular sludge (GS) and raw sludge filtrate (RSF) by filtration and elutriation. The PN and PS components underwent rapid degradation on treatment with Fe(II)-SPS, which followed pseudo-first-order kinetics for both GS and RSF. EPS protein was preferentially oxidatively degraded over EPS polysaccharide in the same phase system. However, the degradation rates of PN and PS in GS were 1/6 and 16 times higher than those in RSF, respectively. 23% of the sodium persulfate was consumed by all the substances in the bulk solution where the GS was located, reducing the amount of “effective free radicals” that degrade EPS in the system. The mass balance of PN and PS indicated that the use of Fe(II)-SPS conditioning has an obvious degradative effect on EPS, and PN and PS in WAS were oxidized by 76.2% and 58.3%, respectively. These findings provide mechanistic insight into the oxidation and competitive reactions of PN and PS between sludge aqueous and granular sludge phases, which is beneficial to the selection and optimization of sludge conditioning.

Evaluation of alkaline activated sodium persulfate sustained release rod for the removal of dissolved trichloroethylene

The presence of trichloroethylene (TCE) dense non-aqueous phase liquid (DNAPL) in the subsurface can generate a dissolved phase plume in groundwater. This study developed an alkaline activated sodium persulfate (SPS) sustained release oxidation rod (alkaline SPS SR-Rod) for long-term in situ chemical oxidation accelerated treatment of TCE dissolved from TCE DNAPL, by creating a greater concentration gradient at the TCE DNPL boundary. The dissolution of TCE DNAPL (1 mL) in water (280 mL) generated ~700 mg L−1, with a volumetric mass transfer coefficient (kLa) of 0.0187 d−1. The alkaline SPS SR-Rod system had a kLa of 0.013 d−1 for TCE dissolution at early stage, and thereafter aqueous TCE concentration remained below ~10 mg L−1 over 60 d of reaction. An SPS SR-Rod life-span of 186 d, for 90% of SPS released from the rod, was estimated. In the soil-water system, aqueous TCE was maintained < 3 mg L− 1 throughout the reaction and the soil oxidant demand was determined to be ~4 g-SPS/kg-soil in the alkaline SPS SR-Rod system. These results revealed that the use of the alkaline SPS SR-Rod can be effective as a method of treating dissolved TCE released from DNAPL contamination, and thereby accelerating TCE DNAPL removal.

Regeneration of Granulated Spent Activated Carbon with 1,2,4-Trichlorobenzene Using Thermally Activated Persulfate.

Chlorinated organic compounds (COCs) are persistent organic pollutants often found in groundwater near industrial sites or in industrial wastewaters. Adsorption into activated carbon is a common strategy to remediate these waters, but spent activated carbon results in a toxic residue to manage. To avoid the transport of the chlorinated compounds out of the site, the in-situ regeneration of the spent activated carbon can be considered for reuse to implement a circular economy. In this work, the regeneration of a commercial granular activated carbon (GAC) has been carried out using thermally activated sodium persulfate (TAP). GAC was previously saturated in 1,2,4-trichlorobenzene (124-TCB) as the model compound. The initial adsorption value was 350 mg124-TCB·gGAC–1. First, the nonproductive consumption of sodium persulfate was studied at different temperatures using nonsaturated GAC. Then, the regeneration of the saturated GAC (5 g) was studied by an aqueous solution (166 mM) of TAP (1 L) at a temperature range from 20 to 80 °C. The possible recovery of the adsorption capacity was studied after 3 h of treatment in three successive adsorption–regeneration cycles at the selected temperature (60 °C). The physicochemical changes of the GAC were also investigated before and after the regeneration treatments. The results evidence the significant deposition of sulfate on the GAC after each treatment of regeneration, which avoids the recovery of the initial adsorption capacity. Therefore, each regeneration cycle was necessarily followed by a washing step at 60 °C to remove this sulfate. After that, the regeneration treatment achieved a stable and high recovery of the initial adsorption capacity of about 48.2%.

Effect of activated persulfate on the properties of contaminated soil and degradation behavior of PAHs

Sulfate radical-based advanced oxidation processes have been applied in the remediation of polycyclic aromatic hydrocarbons (PAHs) contaminated soil, during which sulfate can be activated in different ways. In this work, effects of four different ways (FeSO4, NaOH, H2O2, and Heat) activated sodium persulfate (PS) on PAHs removal and soil physicochemical properties (pH, organic matter, functional groups, surface morphology, and partial heavy metal elements) were compared, and the influencing factors and mechanism of soil PAHs removal by thermally activated PS were also studied. The results showed that at the dosage of 3% of persulfate, the removal efficiency of PAHs followed the sequences of Heat (91.4%) &gt; FeSO4 (86.6%) &gt; H2O2 (86.2%) &gt; NaOH (72.9%). However, thermal activation decreased the soil pH and organic matter content more significantly than other treatments. The reaction tended to reach equilibrium at 6 h when the dosage of persulfate was 3% and the activation temperature was 60 °C, and the reaction obeyed pseudo-first-order kinetics. Through quenching experiments, it was found that the free radicals playing a dominant role in the oxidation process were sulfate radicals. Compared with pH, liquid to soil (L/S ratio) and the temperature had more significant impacts on the degradation efficiency of PAHs.

Insights into the enhanced fluoranthene degradation in citric acid coupled Fe(II)-activated sodium persulfate system

Abstract Polycyclic aromatic hydrocarbons (PAHs), which are present in contaminated groundwater, have attracted increasing attention because of their serious harm to humans. In this study, the degradation performance of fluoranthene (FLT), a typical tetracyclic PAHs in organic contaminated sites, was investigated in the persulfate (PS)/Fe(II)/citric acid (CA) system. The effects of PS, CA, and Fe(II) doses on FLT degradation were tested. With the molar ratio at 60/20/5/1 of PS/Fe(II)/CA/FLT, FLT removal reached 96.3% in 120 min, much higher than 62% removal without CA at the same PS and Fe(II) doses, indicating that the addition of CA could remarkably enhance the FLT degradation. The water quality conditions (pH, anions and humic acid) were also investigated for their effects on FLT degradation. The results of probe tests, electron paramagnetic resonance detection and scavenging experiments showed that and acted predominantly on FLT degradation. The influence of surfactants on FLT degradation was examined. Furthermore, the primary degradation intermediates of FLT were detected by GC-MS and the possible degradation pathways of FLT were proposed. Finally, the effectiveness of the PS/Fe(II)/CA process for the FLT degradation in actual groundwater demonstrated that the process has a great prospect for the remediation of FLT-contaminated groundwater.

Enhanced treatment of oily ink wastewater using a modified degreaser by nano-Fe3O4/Na2S2O8: Efficient coagulation and sedimentation

Ink wastewater is hazardous because it contains oil and refractory pollutants, with high Chroma and turbidity. There are many aromatic compounds in the wastewater, such as benzene, toluene, xylene, and phthalocyanines, azos, and nitroso, which make high chemical oxygen demand (COD) and ammonia nitrogen content. The refractory pollutants are always encapsulated in diverse oil-water systems. Usually a massive degreaser has to be used to destroy the dispersant oil forms under preferred alkaline condition, and advanced oxidation is used for good removal of refractory pollutants under preferred acid condition, which commonly lead to a bad coagulation and sedimentation as a result. In this study, the nano-Fe3O4 (MNPs) activated sodium persulfate (SPS) has been testified to enhance degrease with efficient coagulation and sedimentation. The results showed that the removal of oil, COD, ammonia nitrogen, Chroma and turbidity reached respectively 96.40%, 98.35%, 88.00%, 99.70% and 98.22%, within 40–50 min. The mechanism shows that the catalytic oxidation significantly decreased the Zeta potential of the colloidal particles in the wastewater, which destroyed the steady-state of the colloid and enhanced the effect of coagulation sedimentation. Importantly, the combination of MNPs and colloidal particles successfully promoted the simultaneous production of SO4− and a large amount of HO under weakly alkaline (pH = 7.5–8.0) conditions, which made synergistic oxidation to remove micro-oil and organic pollution efficiently.

Insights into vacuum preloading consolidation of landfill sludge based on Fe2+-activated sodium persulfate.

To further reduce the in-situ sludge from landfill, Fe2+-activated sodium persulfate combined with vacuum preloading was first proposed. Firstly, the effects of optimal Na2S2O8 dosage on the landfill sludge (LS) were investigated by the vacuum filtration experiments. Then, vacuum preloading experiments were conducted on the sludge with different Na2S2O8 dosages to study the water content, water discharge, and settlement. Besides, sludge particle size diversification was carried out by particle size distribution and scanning electron microscopy (SEM) tests. The results were summarized as follows: the specific resistance of filtration (SRF) of LS could be reduced by 98.5% mostly when the Na2S2O8 dosage was 30%; the particle size became significantly smaller, and large particles were converted to small particles; the water content dropped from 86.9 to 58.3%; and the SEM test manifested the oxidation of sodium persulfate caused the destruction of the glial structure of the sludge and the recombination of partial particles.

Degradation of amoxicillin from water by ultrasound-zero-valent iron activated sodium persulfate

• Degradation of amoxicillin by ultrasound-zero valent iron activated persulfate was studied. • The effects of different influencing factors on the degradation rate were discussed. • The degradation mechanism and process are discussed. In this paper, studies were conducted on the degradation of amoxicillin by ultrasound-zero valent iron activated sodium persulfate. The effects of ultrasonic power, sulfate concentration, zero-valent iron dosage, pH value and reaction temperature on the degradation of amoxicillin (AMX) were studied. The intermediate products were measured and the degradation pathway was speculated and the optimal degradation conditions were given. It was found that when the ultrasonic intensity acting in the reaction system exceeded the cavitation threshold sound pressure of the cavitation bubbles, with the increase of power, the activation of persulfate and the reaction process of AMX are promoted and accelerated; With the increase of persulfate concentration, the removal effect of AMX is gradually enhanced. When the concentration reaches the optimal value, AMX is completely removed, and the removal time is shortened; Fe 0 can significantly improve the removal efficiency of AMX by persulfate. When the amount of zero-valent iron is added to the optimal value, AMX can be completely removed within a short time; The pH value in the solution has a large effect on the ultrasound-zero-valent iron activated persulfate system. In general, the best removal effect of AMX is achieved under acidic conditions; With the increase of reaction temperature, the removal effect of AMX is further improved. The results indicate that the ultrasonic-zero-valent iron activated persulfate system is of great potential application value in removal of organic pollution and environmental purification.

Characteristics and Mechanisms of Bacteriophage MS2 Inactivation in Water by UV Activated Sodium Persulfate

Viruses in the aquatic environment have strong resistance to common disinfection techniques. To contribute to the development of efficient virus inactivation technologies, the characteristics and mechanisms of virus inactivation in a UV activated sodium persulfate(UV/PS) system were studied. The inactivation rate and kinetic characteristics of bacteriophage MS2 in water samples by the UV/PS were studied. The effects of PS dosage, pH, and the initial concentration of bacteriophages on the inactivation effect were also investigated. Furthermore, the morphologies of phages before and after UV/PS treatment were observed by transmission scanning electron microscope, and the free radicals in the reaction system were identified by electron paramagnetic resonance spectroscopy. By means of a free radical quenching experiment, the contribution rate of various factors in the UV/PS system to phage inactivation was also analyzed and calculated. The results showed that when the UV irradiation intensity was 160 μW·cm-2, the phage MS2 of 4.39 lg could be removed after UV/PS treatment for 4 min, which was 1.44 lg higher than that of the same UV dose alone. The inactivation of phage MS2 by the UV/PS system was in accordance with the first-order kinetic model. Increasing the initial concentration of PS in the system significantly improved the inactivation rate of phages, while pH and the initial concentration of phages had little effect on the inactivation rate. UV/PS treatment damages the capsid of phages and promotes the aggregation of phage particles. The presence of SO4-· and·OH in the UV/PS system was an important factor for the inactivation of MS2 phages. Finally, ·OH contributed more to MS2 phage inactivation than SO4-·.

Adaptability of organic matter and solid content to Fe2+/persulfate and skeleton builder conditioner for waste activated sludge dewatering.

Sludge conditioning is important for improved dewatering, with the sludge characteristics impacting the effect of conditioning. A composite conditioner, Fe2+-activated sodium persulfate (Fe2+/SPS) combined with phosphogypsum (PG), was used to examine its impact on sludges with different organic contents (34.6-43.8%) or different solid contents (2.8-5.9%). Response surface optimization analysis shows that when the best conditioning is achieved, the reduction of the specific resistance to filtration (SRF) is not sensitive to organic matter content, but the dewatering performance of the sludge is greatly affected by the solid content. The oxidation role of Fe2+/SPS and the skeleton builder role of PG together affect the conditioning, oxidation playing a major role in conditioning, especially for greater organic matter content. The organic content (maximum ηSOL value was 0.32) also affects the effectiveness of the skeleton builder more than the solid content (Maximum ηSOL value was 0.25). Changes in PG significantly impacts the optimal molar ratio and dosage of Fe2+/SPS. Sludge with greater solid content requires greater Fe2+/SPS dosage to provide stronger oxidation to destroy flocs, and the maximum Fe2+:SPS molar ratio was 1.14 with solid content of 5.9 wt%. The composite conditioning decreases the content of extracellular polymeric substances and proteins/polysaccharides. This study provides new insight into the relationship between the oxidation role of Fe2+/SPS and the skeleton builder role of PG for sludge conditioning strategies according to the optimal conditions.

Optimization of thermally activated persulfate pretreatment of corn straw and its effect on anaerobic digestion performance and stability

The effect of thermally activated persulfate on anaerobic digestion is incompletely understood. An orthogonal test was used to optimize the pretreatment process of corn straw using thermally activated persulfate, a lab-scale batch anaerobic digester was used for exploring the effect of pretreatment on anaerobic digestion. The optimal pretreatment conditions were 50 °C, 16 h, 0.5% Na2S2O8, pH = 5, and solid–liquid mass ratio (S:L) = 1:10, which was the most crucial factor. Lignin pretreatment with thermally activated sodium persulfate (SPS) considerably decreased. The yield of reducing sugar (RS) and VFAs were observably higher than the untreated group. This trend occurred because the thermal activation of persulfate primarily destroys the benzene ring in lignin by generating and releasing active sulfate radical (SO4·−); moreover, hydroxyl radical (·OH) and SO4− work together during thermal activation. Furthermore, the daily biogas production of the groups pretreated for 16 and 48 h without elution were 22.78% and 26.80% higher than that of the group untreated, respectively. The degradation rates of total and volatile solids increased to 60% and 70% after the pretreatment. Therefore, thermally activated SPS could improve the performance and stability of anaerobic digestion, and the impact of dissolved organic matter loss exceeded that of residual Na+ and SO42−.

Novel insights into enhanced dewaterability and consolidation characteristics of landfill sludge and fresh sludge conditioned by Fe2+ activated sodium persulfate

Considering the reduction and resource utilization of landfill sludge (LS) and fresh sludge (FS), Fe2+ activated Na2S2O8 is proposed. The effects of the molar ratio of Fe2+/S2O82− and the addition of Na2S2O8 on the dewatering performance of sludge were studied by vacuum filtration experiments. Consolidation tests were conducted on the sludge with different Na2S2O8 dosage, and the compression, consolidation, and permeability characteristics of the sludge were researched. Besides, via particle size distribution (PSD) and scanning electron microscope (SEM) test, the variation of particle size of sludge was studied from the microscopic perspective. The results are as follows: the specific resistance of filtration (SRF) of LS and FS decreases by 99.3%, 95.2% at an optimal dosage (the molar ratio of (Fe2+/S2O82−) = 1, 30% Na2S2O8); the particle size of LS and FS is significantly smaller; the consolidation and permeability coefficients are increased by 1–2 orders of magnitude compared with non-conditioned sludge; the water content of LS and FS drops from 86.5% to 58.4%, 82.4%–59.7%. The research results have certain guiding significance for the in-situ treatment of sludge deep dewatering.

Enhanced dewaterability of waste activated sludge by UV assisted ZVI-PDS oxidation

Ultraviolet (UV) assisted zero-valent iron (ZVI)-activated sodium persulfate (PDS) oxidation (UV-ZVI-PDS) was used to treat waste activated sludge (WAS) in this study. The dewaterability performance and mechanism of WAS dewatering were analyzed. The results showed that UV-ZVI-PDS can obtain better sludge dewatering performance in a wide pH range (2.0-8.0). When the molar ratio of ZVI/PDS was 0.6, UV was 254nm, PDS dosage was 200 mg/g TS (total solid), pH was 6.54, reaction time was 20 min, the CST (capillary suction time) and SRF (specific resistance to filtration) were decreased by 64.0% and 78.2%, respectively. The molar ratio of ZVI/PDS used in this paper is much lower than that of literatures, and the contents of total Fe and Fe2+ in sludge supernatant remained at a low level, as 3.7 mg/L and 0.0 mg/L. The analysis of extracellular polymeric substances (EPS), scanning electron microscope (SEM) and particle size distribution showed that the EPS could be effectively destroyed by UV-ZVI-PDS, the sludge flocs broken down into smaller particles, cracks and holes appeared, and then the bound water was released. At the same time, the highly hydrophilic tightly bound-EPS (TB-EPS) were converted into loosely bound EPS (LB-EPS) and soluble EPS (S-EPS). During sludge pretreated by UV-ZVI-PDS, positively charged ions, such as Fe2+, Fe3+ and H+, produced in the reaction system could reduce the electronegativity of sludge surface, promote sludge particles aggregation, and then enhanced the sludge dewaterability.