Dyes are common pollutants in textile wastewaters, and the treatment of the wastewater has now attracted much attention due to its wide application and low biodegradability. In this study, Fe0/C/Clay ceramics, a kind of novel micro-electrolysis filler, were sintered and employed in a dynamic micro-electrolysis reactor for synthetic Acid Red 73 (AR73) and Reactive Blue 4 (RB4) wastewater treatment. The effects of influent pH, hydraulic retention time (HRT), and aeration on the decoloration efficiencies of AR73 and RB4 were studied. The optimum conditions for wastewater treatment were: AR73, influent pH of 4, HRT of 2 h and aeration; RB4, influent pH of 5, HRT of 6 h and aeration. Under the optimum conditions, decoloration efficiency of AR73 and RB4 wastewater was 96% and 83%, respectively. Results of UV-vis spectrum scanning demonstrated that the chromophores were broken. Continuous running tests showed that improvement of micro-electrolysis system with Fe0/C/Clay ceramics for AR73 and RB4 synthetic wastewater treatment could avoid failure of micro-electrolysis reactor, which indicated great potential for the practical application of the ceramics in the field of actual industrial wastewater treatment.

The coupling mechanism between wave absorption and microwave metal discharges is very important in the application of microwave heating for the treatment of waste electronic scraps, tires, and other refuse of a similar nature. In this work, microwave absorbing material, metal strips, and their mixture embedded in quartz sands were irradiated by microwaves and an indirect calorimetric method was used to measure their heating effect to explore their coupling mechanism. Numerical study was also carried out to validate the experimental results and explain the mechanism in theory. The results indicate that the amount of microwave absorber directly influences the stimulation and the intensity of microwave metal discharges. An appropriate amount of microwave absorber is advisable for an efficient heating process by microwaves. The coupling mechanism of wave absorption and microwave metal discharges varies from collaborative to competitive with the increased amount of microwave absorber. Overuse of microwave absorber can counteract the improvement of microwave energy efficiency.

To solve the disposal problems of solid wastes, dehydrated sewage sludge and Yellow River sediments were tested as components for production of ultra-lightweight ceramsite. The effects of Yellow River sediments addition on the characteristics of ceramsite were investigated. Ceramsite with different Yellow River sediments additions was characterized using thermal analysis, X-ray diffraction, morphological structures analyses, pore size distributions and porosity analyses. Chemical components, especially ratios of SiO2 + Al2O3/Flux, were used to explain the glassy shell formation, physical properties and pores distribution of ultra-lightweight ceramsite; physical forces for instance expansion force and frictional resistance which combined with SiO2 + Al2O3/Flux ratios were used to explain the bloating mechanism. Results showed that the maximum addition of Yellow River sediments for making ultra-lightweight ceramsite was 35%. Macropores (between 0.226 μm and 0.554 μm) of ultra-lightweight ceramsite were dominant in the pore structures of ultra-lightweight ceramsite and its porosity was up to 67.7%. Physical force of expansion force was constant with the variation of Yellow River sediments content and physical force of frictional resistance was decreased with the increase of Yellow River sediments addition. The relationship between expansion and frictional resistance could determine the expansion rate of ceramsite. Larger pores inside the ceramsite bodies could be obtained as Yellow River sediments additions ranged from 10% to 30%. Ceramsite with higher Yellow River sediments additions of 40% (SiO2 + Al2O3/Flux ratios ⩽ 4.25) became denser and have lower porosity. Crystal components analysis proved that the sintering process made some components of raw materials transfer into other crystals having better thermostability.

The research aimed to evaluate present and potential phosphorous pollution due to high sedimentary phosphorus load and release from sediment, when external phosphorus was reduced in downstream Nansi Lake. Pollution load of the sediment and overlying water was investigated. Kinetics and isotherms of adsorption/release of sedimentary phosphorus were studied to determine equilibrium phosphate concentration (EPC0) and release potential. Kinetics of phosphorus adsorption on sediment and release from sediment were well described by both the pseudo-first-order rate equation and the pseudo-second-order rate equation, but more appropriate to the pseudo-second-order rate equation with the adsorption/release capacity more close to the measured values, suggesting that the processes were chemically rate controlled and dependent on adsorption capacity. Soluble reactive phosphorus (SRP) sorption isotherms on sediment were best fitted by the modified Langmuir model indicating a monolayer adsorption. By comparing EPC0 and SRP of water, the status (adsorption, releasing or in equilibrium) of sediment phosphorus could be determined. The sediments at site S1, S3, S4, S5, and S7 where the EPC0s were greater than the SRPs, had a potential to release phosphorus into the water column. However, those sediments at S9, S10, and S12, where the EPC0s were approximately equal to the SRPs, were in impermanent equilibrium with overlying water in status of phosphorus, the sediments can be likely to release phosphorus to the water column once the equilibrium was broken. Therefore, sedimentary phosphorus can be a secondary pollution source in downstream Nansi Lake.

In this work we investigated the chemical, thermal and toxic properties of dried sewage sludge (DSS), the preparation and properties of lightweight sludge ceramic (LSC) and the mechanisms of action of the organic and inorganic foaming agents (OFAs and IFAs). The chemical components and thermal properties of the raw materials were studied by Energy Dispersive X-ray Detection (EDX) and Thermogravimetric Analysis and Differential Scanning Calorimetry (DSC/TGA). The mineral phases of the raw materials and the formed ceramics were determined by X-ray Diffraction (XRD). The leaching characteristics of heavy metals were investigated with Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES). Different ratios of DSS and clay were mixed and pressed into raw pellets. After drying and preheating treatment, the raw pellets were sintered at 1150°C for 10 min. The physical properties of LSC (50 wt% DSS added) were tested. The results showed that when the addition of DSS was above 50 wt%, LSC began to shrink, and a maximum density occurred. The environmental safety of LSC was satisfactory. XRD showed that some new mineral phases formed in the LSC. Observation of the microstructure by Scanning Electron Microscope (SEM) indicated that the body of LSC was porous.

A new adsorbent modified from wheat residue was synthesized after reaction with epichlorohydrin and triethylamine by using the modifying agents of diethylenetriamine in the presence of organic medium of N,N-dimethylformamide. The performance of the modified wheat straw (MWS) was characterized by Fourier transform infrared spectroscopy and point of zero charge analysis. The adsorption was investigated in a batch adsorption system, including both equilibrium adsorption isotherms and kinetics. Results showed that MWR had great anion-adsorbing capacity, due to the existence of a large number of introduced amino groups, and the value of pHPZC was around 5.0. Equilibrium data were analyzed using the Langmuir, Freundlich, and Temkin isotherm models and were found to be best represented by the Freundlich isotherm model. Evaluation of the adsorption process identified its endothermic nature. The maximum adsorption capacity of MWS for the removal of Cr(VI) was 322.58 mg/g at 328 K, indicating that MWS has high chromium removal efficiency, compared to other adsorbents reported. The kinetics of adsorption followed the pseudo-second-order kinetic equation. The mechanism of adsorption was investigated using the intraparticle diffusion model. Thermodynamic parameters (free energy change, enthalpy change, and entropy change) revealed that the adsorption of Cr(VI) onto MWS was endothermic and spontaneous; additionally, the adsorption can be characterized as an ion-exchange process. The results suggest that MWS is an inexpensive and efficient adsorbent for removing Cr(VI) ions from aqueous solution.The functional groups introduced into wheat residue and modified wheat straw were determined by infrared spectra analysis.

Polyferric chloride (PFC) was used to remove natural organic matter (NOM) from the surface water with low concentration of organic matter to evaluate coagulation behavior and floc parameters. The relationship between PFC dosages and chlorine decay was also investigated and the chlorine demand for reacting with organic compounds was estimated by a chlorine model. Under the raw water conditions, the NOM removal efficiency increased within the dosage investigated. The lower specific UV absorbance (SUVA) values were achieved in the dosage range 10–16 mg/L of PFC. Adsorption, entrapment, and complexation played important roles for PFC in removing NOM besides charge neutralization in the coagulation process. Large flocs formed with a PFC dosage of 22 mg/L were better resistant to increasing shear but showed poor recoverability. Small flocs at a PFC dosage of 3 mg/L were little influenced by the increasing shear and showed full reversibility. Coagulation treatment with 22 mg/L of PFC resulted in higher chlorine decay rate, more free chlorine residuals and less total chlorine demand in the effluent when compared to coagulation with dosages of 14 and 3 mg/L. Furthermore, minimal amount of disinfection by-products (DBPs) would be possibly produced after treatment with 22 mg/L of PFC.Research highlightsRemoval of natural organic matter (NOM) has become an increasingly important issue in drinking water treatment because of the formation of disinfection by-products (DBPs) which are caused by the incompletely removed NOM. In this study, PFC was used to treat the surface water with low concentration of OM. The coagulation efficiency was studied as well as the floc properties in terms of floc strength and regrowth in the coagulation process.Additionally, delivery of safe and potable water throughout a distribution system requires free chlorine residuals to be maintained at acceptable levels. In order to comply with DBPs regulations, higher levels of NOM removal should be achieved which can change the water quality and in turn affect the chlorine decay kinetics. In this paper, the relationship between dosage and chlorine decay process was also discussed. The values of chlorine demand for organic compounds were calculated through a chlorine model to estimate the formation of DBPs.

The interaction of disperse blue SBL (DBSBL) with bovine serum albumin (BSA) was investigated using fluorescence, UV–visible and far-UV circular dichroism (CD) spectroscopy. The results showed that the fluorescence of BSA was quenched by DBSBL through static quenching after correcting for the inner filter effects (IFE). The binding constant Kb of DBSBL with BSA at 288, 298 and 303 K were 0.116×106, 3.18×106 and 12.3×106 L mol−1, respectively. The thermodynamic parameters, standard enthalpy change (ΔH0) and standard entropy change (ΔS0), for the reaction were evaluated to be 227.2 kJ mol−1 and 886 J mol−1 K−1 according to the van’t Hoff equation. The above data suggested that the forces acting between DBSBL and BSA were predominantly hydrophobic interactions. The results of UV–visible absorption and far-UV CD spectroscopy also revealed that the conformation and microenvironment of BSA molecule were changed after DBSBL binding to BSA. At 288 K one binding site was present but at higher temperatures a second binding site was detected between DBSBL and the BSA molecule. The lower bound for the distance between the bound dye and the Trp residue is 2.35 nm as calculated from Forster energy transfer.

Two polyferric chloride–polyamine (PFC–EPI–DMA) dual-coagulants with different dosing methods were comparatively investigated in terms of color removal performance and floc aggregation in the treatment of synthetic disperse yellow and reactive red wastewater, and in comparison with PFC and EPI–DMA. The coagulation efficiency was studied by Jar-test, and Photometric Dispersion Analyzer 2000 (PDA 2000) was used to investigate floc aggregation process. The results showed that in two dual-coagulants treatment, PFC dosing followed by EPI–DMA dosing (PFC/EPI–DMA) achieved higher color removal rate for synthetic disperse yellow 201 wastewater, whereas reverse dosing order compared to the former (EPI–DMA/PFC) obtained better color removal performance for synthetic reactive red 24 wastewater. The optimal color removal efficiencies for treating disperse yellow 201 by PFC/EPI–DMA and reactive red 24 by EPI–DMA/PFC were both 97.5% at pH 6.0. The floc aggregation process showed that the floc growth rate of PFC/EPI–DMA was higher than that of EPI–DMA/PFC at the same dosage, whereas both Ratio and the time-weighted ratio variance (TWV) of PFC/EPI–DMA were almost lower than those of EPI–DMA/PFC in the treatment of disperse yellow 201. For reactive red 24 treatment, both floc growth rate and Ratio of EPI–DMA/PFC were higher than those of PFC/EPI–DMA, whereas TWV of EPI–DMA/PFC was lower than that of PFC/EPI–DMA. For disperse yellow 201 treated by PFC/EPI–DMA, the maximums of floc growth rate and Ratio were both reached at pH 6.0, whereas TWV was decreased as the increase of pH. For reactive red 24 treated by EPI–DMA/PFC, the maximums of three parameters were all reached at pH 4.5.

The adsorption of humic acid (HA) on kaolin particles was studied at various conditions of initial solution pH, ionic strength and solid-to-liquid ratio. The resulting affinity of interactions between humic acid and kaolin was attributed to the surface coordination of HA in ambient suspensions of mineral particles and the strong electrostatic force at low pH. Addition of inorganic salt can also influence the adsorption behavior by affecting the HA molecular structure, the clay particle zeta potential and so on. Equilibrium data were well fitted by the Freundlich model and implied the occurrence of multilayer adsorption in the process. In addition, the enthalpy dependent of system temperature was 79.17 kJ/mol, which proved that the mechanism of HA adsorption onto kaolin was comprehensive, including electrostatic attraction, ligand complexation and hydrogen bonding.

Activated carbon was prepared from the sewage sludge of municipal wastewater treatment plant by chemical activation (activation reagent is ZnCl2) and was used for the adsorption of dye (reactive brilliant red K-2BP). The impact of adsorbent amount, adsorption time and pH value on adsorption effect, the adsorption kinetics, and the adsorption thermodynamics were discussed according to batch adsorption tests. The results indicated that the activated carbon developed from sewage sludge (ACSS), which was mesoporous, possessed opened porous structures. The iodine number of the ACSS was 326 mg·g−1. The rate of achievement was 51.31%. The BET surface area was 298 m2·g−1 and the contents of heavy metals in the leachate didn’t exceed the contents limit. The adsorption kinetics of reactive brilliant red K-2BP on the ACSS was accorded with the two-step kinetics rate equation and pseudo-second-order kinetics equation. Compared to the Freundlich isotherm equation, the Langmuir isotherm equation showed better applicability for the adsorption. The adsorption which was favorable was an endothermic (enthalpy ΔH > 0) and spontaneous (free energy ΔG < 0) process and was accompanied by an increase in entropy (ΔS > 0).

The characterization of polyepicholorohydrin-dimethylamine/bentonite and the kinetics of adsorption of four disperse dyes, namely, Disperse Yellow Brown S-2RFL (DYB S-2RFL), Disperse Red S-R (DR S-R), Disperse Blue SBL (DB SBL) and Disperse Yellow (DY SE-6GFL) onto organophilic bentonite (polyepicholorohydrin-dimethylamine/bentonite) have been studied at various solution concentrations and temperatures. The adsorption kinetics was studied in terms of a two-step first-order kinetic rate equation and intra-particle diffusion model. The adsorption process has been found to follow with two different rate constants (k1 and k2) for two-step first-order kinetic rate equation and also two different intra-particle diffusion rate constants (kint1 and kint2) for intra-particle diffusion model. For both the kinetic steps, the energies of activation of adsorption (Ea1 and Ea2) and other thermodynamic parameters (ΔH1* and ΔH2*, ΔS1* and ΔS2*, ΔG1* and ΔG2*) have been calculated using Arrhenius's and Eyring's equation, respectively. It has been found that for both the adsorption kinetic steps, Ea1 and Ea2 are corresponding to the values of k1 and k2 and ΔH1*<−Tav ΔS1*, ΔH2*<−Tav ΔS2* and ΔG* > 0, which means that the influence of entropy is more remarkable than enthalpy in activation reaction and the adsorption process is not spontaneous.

•A new hybrid coagulants-polysilicate titanium sulfate was synthesized.•PST achieved better NOM removal, especially PST20.-PST generated larger flocs than TS；floc breakage and recovery factor were improved by PST.•PST5 and PST10 flocs were stronger than TS flocs, while PST20 and PST50 flocs were weaker.•Sludge can be reused to prepare TiO2.Polysilicic acid (PSiA) has been used to improve the coagulation behavior of metal coagulants (such as aluminum salts and iron salts), while there is not much research on the combination of polysilicic acid and titanium salts. This study was aimed to evaluate the effect of Ti/Si molar ratios on the titanium salt coagulation performance and floc properties in humic–kaolin water treatment. Polysilicate titanium sulfate (PST) was synthesized by mixing different amounts of PSiA and titanium sulfate (TS) solution. According to experiment results, PST20 (Ti/Si molar ratio = 20) exhibited the best natural organic matter removal efficiency (%). The effluent residual turbidity was also improved by PST at proper Ti/Si molar ratio. Floc size of titanium sulfate was enlarged by the addition of PSiA. Additionally, floc strength was enhanced by PST20 and PST50, while PST10 and PST5 flocs were weaker than TS floc. Floc strength and recovery ability were also improved by PSiA. However, flocs produced by PST were much loosely constructed with lower fractal dimension. Sludge of PST coagulation system was collected and calcined at 700 °C to prepare TiO2.

•Coagulation performance of PFC/DAM–ECH was better than PFC at proper dosage.•Adding sequence of coagulants was critical for HA removal and floc properties.•Better removal efficiencies of HA by PFC/DAM–ECH achieved at acidic condition.•DAM–ECH improved the floc properties by enhancing charge neutralization mechanism.•Effects of DAM–ECH on floc properties reduced membrane fouling.Polyferric chloride (PFC) and epichlorohydrin–dimethylamine (DAM–ECH) with different PFC (as Fe3 +)/DAM–ECH mass ratios (MR) and dose methods were used in the treatment of humic acid–kaolin (HA–kaolin) simulated water under different pH conditions. Coagulation performance, floc characteristics and membrane fouling of PFC/DAM–ECH in coagulation–ultrafiltration (C–UF) process were investigated in this study. Results showed that the optimum coagulation performance was achieved when PFC dose was 15 mg/L with PFC/DAM–ECH MR of 2:1 under pH 6.0. Opposite adding sequence (DAM–ECH/PFC) would reduce UV254 (ultraviolet adsorption at 254 nm) and DOC (dissolved organic carbon) removal efficiency. Addition of DAM–ECH on the basis of PFC produced larger and stronger flocs with better regrowth ability. Proper dosage of DAM–ECH under certain coagulation condition could achieve the best coagulation performance and keep the UF membrane operating under a preferable status. Results of this study would be beneficial for application of composite coagulant PFC–DAM–ECH and DAM–ECH as coagulant aid in water treatment processes.

Giant reed (GR) was modified into giant reed quaternary amino anion exchanger (GR-QE) for the removal of phosphate by reacting with epichlorohydrin, ethylenediamine (EDA) and triethylamine in the presence of N,N-dimethylformamide (DMF). Factors like GR dosage, temperatures and volumes of organic liquid chemicals were used in single-factor experiments and orthogonal experiments for determining optimal conditions, with phosphate removal efficiency and zeta potentials as indicators. The results indicated that the optimal conditions obtained in the orthogonal experiments were consistent with those in the single-factor experiments. The GR utilization on a large-scale was realized, and the dosage of EDA was considered as the key influential factor in the preparation of GR-QE. Under these conditions, the nitrogen content in GR-QE was about 7.78%, while it was 0.9% in GR. The phosphate removal was about 82.1%, zeta potential was 23.2 mV.

•PD aid in alum and PACl coagulations could improve HA removal by C–UF process.•Floc size had more important effect on UF than compact degree.•PD–alum/PD–PACl led to the highest fluxes but was most susceptible to high shear.•Rc and Ra were chiefly affected by floc size and Df, respectively.Effects of polydimethyldiallylammonium chloride (PD) on coagulation behaviors of different Al-based coagulants were investigated in coagulation–ultrafiltration (C–UF) hybrid process, regarding the impurity removal efficiency, floc properties and membrane foulings. Floc characteristics, including floc size, compact degree, strength and re-growth ability were studied using a laser diffraction particle sizing device. Resistance analyses were implemented to explore the membrane fouling mechanisms. The results indicated that PD aid could increase the purification efficiency of C–UF, especially at low coagulant doses. PD–alum/PD–PACl contributed to large flocs, while alum–PD/PACl–PD gave rise to flocs with high Rf and Df values. The results of ultrafiltration experiments showed that conventional coagulant, i.e., alum led to a flux reduction of 52%; while the reductions for alum–PD and PD–alum were 53% and 34%, respectively. The flux reductions for PACl, PACl–PD and PD–PACl were 60%, 57% and 39%. Flux declines became more severe when the coagulated suspensions were exposed to increased shears and the suspensions coagulated by aluminum plus PD resulted in the least reductions in fluxes.Resistance analyses of the investigated systems: coagulations by different alum-based and PACl-based coagulants with and without floc breakage and re-growth phases.Download high-res image (130KB)Download full-size image