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In this study, the traditional coagulation process was optimized and a method of vortex coagulation for wastewater treatment was proposed for the first time. The process discards the sedimentation method used in traditional coagulation and uses agitation to bring flocs up. These flocs can then be stuck by the filter cotton fixed in wastewater, and the filter cotton and flocs can act as net capturing several times under the action of agitation. It is worth noting that the filter cotton and flocs can synergistically adsorb the suspended and organic pollutants from wastewater. The results showed that the chemical oxygen demand (COD) removal of vortex coagulation could reach 82%, which was 10% higher than that of the traditional coagulation under the same coagulant dosing. In addition, the flocs in conventional coagulation and vortex coagulation were analyzed by IR spectroscopy and XRD, which showed that the mixing process did not destroy the chemical structure of the flocs. Compared with the conventional method, this process does not require a sedimentation tank, which can avoid the investment of equipment construction in this area. The effects of coagulant dosage, pH, stirring speed, and stirring time on the wastewater treatment effects were explored in the experiment.

Pressures related to urban growth and industrial activities exacerbated by climate change had an impact on water resources in Tunisia. The present study examines the application of cladode cactus mucilage (CCM) flocculants for hot alkaline chemical degreasing Zn-electroplating wastewater treatment and reuse (WWTR). The CCM flocculation process was selected through their environmental benefits, economic facilities, sustainable use of the natural biopolymer product, input biopolymers substitution, and on-site treated wastewater (TWW) reuse and recovery. The alum coagulation and CCM flocculation were performed by the jar test series. The suitability of treated wastewater quality (TWWQ) with alum/CCM was also assessed for reuse purpose in terms of corrosion-scaling indices (RSI, LSI, PSI, AI), oxidation-reduction potential (ORP), and microbiological community growth (Bacillus, Pseudomonas, Mesophilic bacteria and yeasts) for 28 days storage at 25 °C. The total alkalinity removal efficiency reached 95.8% with an optimum dosage of alum + CCM for hot alkaline chemical degreasing wastewater bath rinsing. The results showed that the stability of TWWQ has significantly deteriorated during storage leading to aggressive wastewater, pathogen growth, and biological malodor production which make them unsuitable for reuse. Therefore, there is a need for CCM processing alternatives that preserve the physico-chemical and microbial of TWW properties during storage.

Six kinds of dithiocarbamates (DTCs) were synthesized from three linear amines with different amino numbers, two polyether amines with different molecular weights, and one branched amine with benzene rings, respectively. The conditions affecting oil removal rate and floc rising time of DTC were studied using simulated oily wastewater. Furthermore, the effects of the molecular structure of DTC on oil removal efficiency, floc morphology, floc rising time, and floc adhesion were investigated. When the conditions were optimal, the oil removal efficiency of DTC synthesized from polyethylene polyamine was 95.14%, which was higher than other DTCs. Meanwhile, the ferrous ion was the most suitable chelating metal ion for DTC than other transition metal ions. The increase of amino groups in the initiators improves the oil removal efficiency of DTC, while the linear structural DTC exhibits a low oil removal efficiency due to a lack of network structural flocs. The introduction of polyether structure helps reduce the volume of the flocs and make them compact, but it also increases the adhesion of the floc on the metal surface. The introduction of bisphenol A phenol amino resin structure induces the generation of the flocs in oil wastewater and improves the oil removal efficiency.

The use of agricultural waste materials to remove heavy metals from wastewater is attractive due to its simplicity and economic efficiency. In this study, the applicability of calcined eggshell waste materials (CES) for heavy metals removal from real wastewater were examined via transport column experiment preceded by coagulation/flocculation process.A column packed with granular activated carbon (GAC) is operated in parallel to CES column to evaluate the adsorptive attributes of CES. The findings are assessed from another set of column experiments consisting of sand followed by CES column to evaluate the effect of particulate matter (PM) on CES performance toward heavy metals removal. In coagulation experiment, alum addition at an optimum dose (3.0 g/L) reduced the total suspended solids (TSS) by 80%, whereas the Fe, Pb, Zn, Cu, Ni, and Cr were reduced by 80%, 77%, 76%, 73%, 56%, and 49%, respectively. Under the current applied hydrodynamic conditions, using sand column before CES column improved the removal efficiencies of Fe, Pb, Cu, Zn, Ni, and Cr from 50% to 92%, 55% to 93%, 60% to 87%, 53% to 76%, 45% to 65%, and 41% to 60%, respectively. The whole results illustrate that CES can be competitive to GAC for heavy metals removal from landfill leachate, mainly if applied after PM removal by sand filtration. HIGHLIGHTS Total suspended solids and heavy metals are effectively decreased by adding 3.0 g/L alum.; Heavy metals are effectively eliminated from landfill leachate using calcined eggshells.; Particles facilitated heavy metal movement via the filter media.; Sand pretreatment improved the performance of calcined eggshell to remove heavy metals.; The research findings may lead to more cost-effective landfill leachate treatment technology.

The authors reported a potential candidate methylated mud snail protein (MeMsp) as an effective and eco-friendly flocculant to treat the high turbidity wastewater. MeMsp was obtained by extraction of mud snail protein (Msp) through isoelectric precipitation (PSC-IP) and then methylated via the esterification with side-chain carboxyl. Structural characterization of FT-IR, zeta potential and elemental analysis were carried out and further confirmed the successful of the methylation. Flocculation experiments with kaolin suspension simulated wastewater indicated that MeMsp-24 displayed more excellent flocculation efficiency at a low dosage. At the optimum dosage 27 mg/L, the maximum clarification efficiency of MeMsp-24 was 97.46% under pH 7.0. Furthermore, MeMsp-24 exhibited a wide flocculation window in the pH range 1.0–9.0, and faster sedimentation velocity and larger flocs size. In addition, MeMsp-24 exhibited 92.12% clarification efficiency in treating railway tunnel construction effluent. The flocculation kinetic and mechanism analysis revealed that the most effective particle collision occurred at the optimal dosage, with charge neutralization and adhesion playing irreplaceable roles in different environments, respectively. Therefore, through extraction and methylation modification, MeMsp could be a promising eco-friendly flocculant for high turbidity wastewater treatment. HIGHLIGHTS Synthesized a novel bio-flocculant methylated mud snail protein.; The protein-rich mud snail is fully utilized.; Methylation successfully improved the flocculation performance of mud snail protein.; Methylated mud snail protein achieved a significant turbidity removal for high turbidity wastewater treatment.; Methylated mud snail protein is completely environmentally friendly.

Coagulation kinetics and floc properties are of great fundamental and practical importance in the field of water treatment. To investigate the performance of Fe(VI) and Fe(III) salt on particle coagulation, Malvern Mastersizer 2000 was employed to continuously and simultaneously monitor the kaolin floc size and structure change, and population balance modeling was used to investigate the coagulation mechanism. The results show dosage increase had positive effect on collision efficiency and floc strength and negative effect on restructure rate. Low shear rate resulted in higher collision efficiency and stronger floc. Low water temperature had a pronounced detrimental effect on coagulation kinetics. Temperature increase showed the most significant positive effect on collision efficiency, floc strength and restructure rate. The optimum pH zone for the coagulation was found to be between 6 and 8. Further pH increase lowered the collision efficiency and floc strength and increased the restructure rate. FeCl3 resulted in a larger ratio of the mass to volume of kaolin flocs (compactness) than those induced by ferrate. HIGHLIGHTS Population balance modeling achieved excellent approximation of coagulation process.; FeCl3 produced larger, stronger and more compact flocs than those by ferrate(VI).; Dosage increase had positive effect on collision efficiency and floc strength.; High temperature resulted in high collision efficiency, floc strength and restructure.; Optimum pH for both coagulation systems was between 6 and 8.

The rapid expansion of global trade and human activities has resulted in a massive increase in wastewater pollution into the atmosphere. Suspended solids, organic and inorganic particles, dissolved solids, heavy metals, dyes, and other impurities contained in wastewater from various sources are toxic to the atmosphere and pose serious health risks to humans and animals. Coagulation–flocculation technology is commonly used in wastewater treatment to remove cell debris, colloids, and contaminants in a comfortable and effective manner. Flocculants, both organic and inorganic, have long been used in wastewater treatment. However, because of their low performance, non-biodegradability, and associated health risks, their use has been limited. The use of eco-friendly bioflocculants in wastewater treatment has become essential due to the health implications of chemical flocculants. Because of their availability, biodegradability, and protection, plant-derived coagulants/flocculants and plant-based grafted bioflocculants have recently made significant progress in wastewater treatment. This study will undoubtedly provide a clearer understanding of the current state, challenges, and solutions for bioflocculation in wastewater remediation using green materials for the sake of a cleaner climate. HIGHLIGHTS Plant mucilage as a cost-effective and eco-friendly natural bioflocculant.; It can serve as a potential bioflocculant for treatment of wastewaters released from different sources.; Significant removal of pollutants from wastewaters revealed the novelty of plant mucilage as a bioflocculant.; It throws light on their applications aiming to exploit the green materials for remediation of wastewater.

It is difficult to adjust the pH of oil acidized wastewater rich in Ca2+, thus hindering the polyacrylamide (PAM) flocculation. This study aims at accelerating the flocculation process by introducing CO2 into the water to induce the formation of CaCO3 nuclei. The order in which CO2 and NaOH were added affected the floc structures. Compared with CO2-NaOH-PAM, the flocs of NaOH-CO2-PAM were more compact and more CaCO3 crystals were formed. The aqueous Ca2+ involved in the reaction reached 20%, and CO2 utilization was enhanced. The settling time was shortened by half (from 20 to 3 min), and NaOH consumption was reduced by one-tenth (from 0.03 to 0.003 mol), hence significantly reducing the costs. Due to the higher settling rate and shorter contact time, the NaOH-CO2-PAM flocs adsorbed less so that the residual oil was 124 mg·L−1, while in the case of CO2-NaOH-PAM it was 88 mg·L−1. As a promising coagulation aid, CO2 can also be used to mineralize pollutants in wastewater.

In this study, the conditioning effect of cationic polyacrylamide (CPAM) with different charge densities on raw sludge (RS) and thermo-hydrolyzed sludge (HS) pretreated with or without ferric salt is studied through orthogonal experiments. In addition, this paper uses the principles of rheology and morphology to analyze and clarify the conditioning mechanism of RS and HS, and reveals the mechanism of thermal hydrolysis to improve the dewatering performance of sludge. Compared with the RS, the HS has smaller particle size, better filterability, stronger fluidity and more obvious thixotropy. However, due to the influence of filter pressing time, ferric salt should be added before conditioning. The orthogonal experiment shows that the optimal conditioner is CPAM with charge density of 60, and the specific resistance to filtration and capillary suction time of the adjusted thermo-hydrolyzed sludge are reduced to (1.11 ± 0.07) × 1012 m/kg and 16.1 ± 1.8 s; the particle size increased from 61.2 to 253.5 μm. The moisture content of the sludge cake is about 48%. The structural strength and thixotropy of HS are higher than those of the RS, and can be greatly improved by adding ferric salt. Morphological analysis confirms that thermal hydrolysis can lyse microbial cells in sludge, and the sludge treated with ferric salt will have more porous structure and stronger flocculation strength. HIGHLIGHTS Effects of CPAM on conditioning of raw sludge and thermal hydrolysis sludge were studied.; Thermal hydrolysis treatment will improve sludge dewatering capacity and fluidity.; Ferric salt treatment enhanced structural strength and thixotropy of conditioned thermal hydrolysis sludge.; Rheological analysis can be used as a new tool to reflect the dewatering capacity of sludge.

The effect of ethylated soy protein-based bioflocculant (EtSP) as a filter aid reagent was investigated. The efficiency of EtSP as a filter aid was evaluated in terms of the specific cake resistance, α, and was compared with chitosan and polyaluminum chloride (PAC). Diatomite and kaolin were used as model particles. Total filtration resistance, R, decreased with increasing flocculant dosage (wt.%, flocculant/particle) and was almost constant in the range of 1 wt.% or more for both particles. The α value was significantly decreased from 1.01 × 1011 to 9.01 × 1010 m/kg for diatomite and from 5.11 × 1010 to 5.20 × 109 m/kg for kaolin by the addition of EtSP in the case of 1.0 wt.%. The α value for cakes formed by EtSP was much smaller than that formed by chitosan and PAC. In the case of diatomite, in the dose range of 0.5–1.0 wt.%, the α value for cakes formed by EtSP and chitosan was almost the same. However, at the excess dose of 2.0 wt.% over, the α value formed by chitosan abruptly increased. In the case of kaolin, in the dose range of 1.0–2.0 wt.%, the α values of chitosan and PAC were mostly the same, however, these values were larger by ca. nine times than that of EtSP.

Sludge dewatering is an important step for wastewater treatment. Composite degradable flocculant (CDF) was prepared by cationic polyacrylamide (PAM) grafting onto modified starch with a novel initiator, and characterized by Fourier transform infrared spectroscopy. The microstructure of flocculated sludge was characterized by scanning electron microscopy. The study investigated the properties of CDF compared to PAM, which showed that the prepared CDF exhibited a highly effective flocculation on sludge dewatering, a higher transmittance and chemical oxygen demand removal rate, and a lower value of effluent ammonia nitrogen and total phosphorus. The fermentation process was also analyzed by testing the performance of dewatered sludge (temperature, pH, ammonia nitrogen, E4/E6 (humic acid absorbance at 465 nm (E4) and 665 nm (E6))). The dehydrated sludge with CDF could be easily compressed into cakes by belt-filter for easy transportation and storage. With the continuous addition of CDF and PAM, the corresponding index of capillary suction time (CST) increased. Moreover, the total value of CST with CDF was low, showing a good dewaterability. In addition, the sludge index of pumping time and moisture content with CDF were low in contrast with PAM. Fermentation experiments demonstrated that sludge with CDF had a comparatively high temperature and low value of E4/E6. Such novel CDF shows enormous potential in wastewater treatment and sludge fermentation.

In the present work the use of a promising novel coagulant aid, Guazuma ulmifolia, was optimized to treat synthetic water using central composite being highly efficient at rotatable design (CCRD). The factors evaluated for the coagulation-flocculation process were coagulants dosages and pH. A model to describe the coagulation-flocculation process was successfully obtained. The model was validated using 5 mg L−1 aluminum sulfate, 2.5 mg L−1G. ulmifolia and pH 9, achieving excellent agreement with observed values.

Higher standards in the European Water Framework Directive and national directive demand advanced wastewater treatment for removal of nutrients and organic micropollutants before the discharge into water bodies. Systematic investigations regarding relative dosage and filtration processes for removal of flocculated solids are currently lacking. In this study, the performance of technologies for advanced removal of total phosphorus down to 5 mol Me3+/mol sRP was necessary to achieve soluble reactive phosphorus (sRP) concentrations of

Flocculation is a common technique to harvest microalgae, where the negatively charged algal cells coalesce together to form larger flocs that settle under gravity. Although several inorganic flocculants have been applied for algal biomass recovery, the dosage varies depending on the algal strain-specific features. Thus, the selection of inorganic coagulant that can be applied at a low dosage for achieving the maximal biomass recovery under normal physiological conditions is necessary. The present study analyses the influence of different inorganic flocculants like ferric chloride (FeCl3), alum, calcium hydroxide, ferrous sulphate and copper sulphate on the biomass removal efficiency of a mixed microalgal consortium isolated from the open ponds of the National Institute of Technology Rourkela and further enriched with diluted human urine. Flocculation experiments were carried out with varying coagulant dosages, pH between 7.5 and 7.8, and 0.5 g L−1 algal concentration. The results revealed that FeCl3 at the dosage of 0.05 g L−1 and KAl(SO4)2 with the dosage of 0.04 g L−1 could be utilized to achieve the biomass recovery efficiency of 99.5% and 97.9%, respectively, within a duration of 5 min. An economic evaluation of the harvesting process showed KAl(SO4)2 to be the cheapest coagulant that could be feasibly used to recover algae at a large scale.

Chemical products traditionally used in the disinfection of water bodies often pose human health risks. For this reason, studies on natural coagulants such as Moringa oleifera Lam. represent an alternative for the inactivation of pathogenic microorganisms, among which is Escherichia coli. This study evaluated the effect of different concentrations of coagulants obtained from Moringa seed extracts and their protein fractions in the inactivation of E. coli during the coagulation/flocculation process. The coagulants studied were the aqueous extract, saline extract and protein fractions albumin and globulin, highlighting that the protein fractions were more effective on inactivating E. coli. The protein fraction globulin at a concentration of 10.0 mg L−1 showed bactericidal effects against E. coli within 18 min, whereas the albumin showed a bacteriostatic effect within 48 min because it isolated colonies in the sediment sample.

The aim of this work was to develop a method that allows the recovery of nutrients from aquaculture sludge, not only to alleviate the disposal problem, but also to address the future scarcity of non-renewable fertilizers. This method includes two steps: Nutrient mobilization using aerobic digestion followed by solids precipitation using chitosan as the flocculant. The aerobic digestion experiments were conducted in aerated batch reactors, while a jar test apparatus was used to assess the capacity of chitosan to remove total suspended solids (TSS) and turbidity. During aerobic digestion, the concentration of soluble N (sum of NH4-N, NO2-N, NO3-N) increased from 181 mg/L at the start to 890 mg/L after three weeks, and to 903 mg/L after four weeks and solids removal by chitosan flocculation. The corresponding concentrations for soluble P were 8.2 mg/L at start, 110 mg/L after three weeks of aerobic digestion, and 160 mg/L after four weeks of aerobic digestion and chitosan flocculation. Other macronutrients (K, Ca, Mg, S) and micronutrients (Fe, Mn, Zn, B, Cu, Mo) were mobilized to concentrations close to or higher than levels recommended for hydroponic growth of vegetables. Chitosan flocculation and precipitation using a dose of 15 mg/L resulted in a reduction of the turbidity by 96% from 156 to 6.5 FNU. After chitosan precipitation, 80% of the sludge could be reclaimed as a nutrient-rich clear phase, low in TSS and turbidity.

In the present study, real car wash wastewater was purified by different coagulation/flocculation methods. As coagulant, polyaluminum chloride (‘BOPAC’), conventional iron(III) chloride, iron(III) sulfate, and aluminum(III) chloride were used, while as flocculant non-ionic and anionic polyelectrolytes were investigated. The effects of added clay mineral (Na-bentonite) and cationic surfactant (hexadecyltrimethyl ammonium bromide – ‘HTABr’) were also investigated. The use of BOPAC was significantly more effective than conventional coagulants. Extra addition of clay mineral was also beneficial in relation to both the sediment volume and sedimentation speed, while polyelectrolyte addition enhanced further the sedimentation. Moreover, the simultaneous addition of HTABr significantly enhanced the color removal efficiency due to the successful in-situ generation of organophilic bentonite. In summary, the application of 100 mg L−1 Na-bentonite with 20 mg L−1 Al3+ (from BOPAC) and 0.5 mg L−1 anionic polyelectrolyte resulted in the efficient reduction of the turbidity (4–6 NTU), the COD (158 mg L−1) and the extractable oil content (4 mg L−1) with efficiencies of 98%, 59%, and 85%, respectively. By applying organophilic bentonite in high concentration (500 mg L−1) with identical concentrations of BOPAC and anionic polyelectrolyte, significant color removal (5 times lower absorbance at λ = 400 nm) and 27% lower sediment volume were achieved.

The biodegradability and safety of the bioflocculants make them a potential alternative to non-biodegradable chemical flocculants for wastewater treatment. However, low yield and production cost has been reported to be the limiting factor for large scale bioflocculant production. Although the utilization of cheap nutrient sources is generally appealing for large scale bioproduct production, exploration to meet the demand for them is still low. Although much progress has been achieved at laboratory scale, Industrial production and application of bioflocculant is yet to be viable due to cost of the production medium and low yield. Thus, the prospects of bioflocculant application as an alternative to chemical flocculants is linked to evaluation and utilization of cheap alternative and renewable nutrient sources. This review evaluates the latest literature on the utilization of waste/wastewater as an alternative substitute for conventional expensive nutrient sources. It focuses on the mechanisms and metabolic pathways involved in microbial flocculant synthesis, culture conditions and nutrient requirements for bioflocculant production, pre-treatment, and also optimization of waste substrate for bioflocculant synthesis and bioflocculant production from waste and their efficiencies. Utilization of wastes as a microbial nutrient source drastically reduces the cost of bioflocculant production and increases the appeal of bioflocculant as a cost-effective alternative to chemical flocculants.

One of the effective ways to remove halogenated disinfection by-products (DBPs) from drinking water is the application of ultrafiltration technology. However, membrane fouling is an important factor affecting the service life and treatment effect. In this study, the electrocoagulation/oxidation-ultrafiltration (EC/O-UF) process was used to remove the precursor substance that produced DBPs, i.e. dissolved organic matters (DOMs). Operating parameters were optimized from the matching of different flocculant morphology to low concentration DOM. The degree of membrane fouling was characterized by analyzing DOMs concentration and membrane flux. The results showed that the optimal conditions for the production of Alb were: current density 10 A/m2, hydraulic retention time 10 min, and initial pH 5.0–7.0. Under these conditions, the production of flocculant Alb could reach 58–61%, 94–97% DOMs were removed by EC/O-UF.

Staphylococcus sp. as Gram-positive and Escherichia coli as Gram-negative are bacterial pathogens and can cause primary bloodstream infections and food poisoning. Coagulation, flocculation, and sedimentation processes could be a reliable treatment for bacterial removal because suspended, colloidal, and soluble particles can be removed. Chemical coagulants, such as alum, are commonly used. However, these chemical coagulants are not environmentally friendly. This present study evaluated the effectiveness of coagulation, flocculation, and sedimentation processes for removing Staphylococcus sp. and E. coli using diatomite with standard jar test equipment at different pH values. Staphylococcus sp. demonstrated 85.61% and 77.23% significant removal in diatomite and alum, respectively, at pH 5. At pH 7, the removal efficiency decreased to 79.41% and 64.13% for Staphylococcus sp. and E. coli, respectively. At pH 9, there was a decrease in Staphylococcus sp. after adding diatomite or alum compared with that of E. coli. The different removal efficiencies of the Gram-positive and Gram-negative bacteria could be owing to the membrane composition and different structures in the bacteria. This study indicates that diatomite has higher efficiency in removing bacteria at pH 5 and can be considered as a potential coagulant to replace alum for removing bacteria by the coagulation process.

Polysilicate titanium salt (PST) is synthesized by using spent titanium solutions and polysilicic acid (PSiA) as raw materials. PSiA could improve the aggregation ability of titanium salt flocculants and also restrain the hydrolysis of Ti4+ to stabilize titanium salts. Meanwhile, replacing titanium salt with spent titanium solutions could reduce the cost of PST and solve the problem of wastewater treatment in the titanium industry, which makes valuable waste regeneration possible. Scanning electron microscopy (SEM) results show the morphology transformation (sheet, spheroid, and sphere) of PST with different Ti/Si molar ratios. The formation process of PST is analyzed by Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). This study investigates the effect of Ti/Si molar ratios on PST flocculation performance in humic–kaolin water and actual domestic wastewater treatment. The in situ floc size change of PST is measured by laser particle size analyzer in humic–kaolin water treatment. Additionally, the performance of PST is comprehensively evaluated on flocculation and sedimentation ability, rapid sweep netting ability and stability. In short, the prepared PST in this study is suitable for treating wastewater with high turbidity and chemical oxygen demand (COD) in a wide range of pH values.

The aim of this study was to assess the efficiency of mucilage extracted from the fruit of Dillenia indica for enhancing coagulation in the treatment of textile effluent. The mucilage extraction was carried out in water at room temperature. The pH, concentration of coagulant FeCl3.6H2O, and concentration of mucilage solution were optimized with star-type central composite design (CCD). We were able to analyze the synergistic effects between the FeCl3.6H2O and mucilage concentrations: the process of coagulation/flocculation (CF) for chemical oxygen demand (COD) removal was more efficient at a low chemical coagulant concentration (8.00 mg L−1) and a higher natural coagulant (NC) concentration (15.00 mg L−1). This demonstrated the potential of this mucilage to treat textile effluents, with 67.66%% COD removal, 96.86% turbidity removal and 91.12% apparent color reduction. The characterization of the mucilage of Dillenia indica was done using Fourier transform infrared spectroscopy (FTIR) and solid-state cross-polarization magic angle spinning carbon-13 nuclear magnetic resonance (CP/MAS 13C NMR), and the signals obtained indicated the presence of polysaccharides, which are responsible for enhancing the CF process.

The purpose of this study was to optimize the coagulation–flocculation effect of a wastewater treatment system using the response surface methodology (RSM) and three-step method to minimize phosphorus concentration in the distillate wastewater. In order to minimize the concentration of total phosphorus (TP), experiments were carried out using -factorial designs with three levels and three factors. A Box–Behnken design, which is the standard design of RSM, was used to evaluate the effects and interactions of three major factors (Fe:P (w/w) ratio, coagulation pH and fast mixing speed (FMS)) on the treatment efficiency. A multivariable quadratic model developed for studying the response indicated that the values for optimum conditions for Fe:P (w/w) ratio, coagulation pH and FMS were 2.40, 6.48 and 100 rev min−1, respectively. Under optimal process conditions, the TP concentration in the distillery effluent was reduced from 10 mg L−1 to 0.215 mg L−1, representing a removal efficiency of 97.85%. Based upon the statistical evaluation of results, it is inferred that RSM can be used as an appropriate approach to optimize the coag-flocculation process. Meanwhile, the study has shown that, for the equivalent dose of ferric chloride, the average three-step effect is better than that of the one-time addition.

There are residual polymers in the oily wastewater produced from polymer flooding (OWPF); keeping the residual polymer in the water during the flocculation is meaningful and challenging. In this paper, a selective flocculant (denoted as PDC10) which can remove the oil while keeping partially hydrolyzed polyacrylamide (HPAM) in water was prepared by copolymerization of decyl two methyl vinylbenzyl ammonium chloride (C10MVBA) and dimethyl aminopropyl methacryamide (DMAPMA). By using oil removal and HPAM retention as evaluation indexes, the synthesis condition of PDC10 was optimized. The optimum PDC10 exhibited oil removal of 98.0% and HPAM retention of 80.5%. Its HPAM retention is much higher than that of a regular cationic flocculant. Measurements of zeta potential, interfacial tension, interfacial dilational modulus and a dual polarization interferometry (DPI) test were carried out for investigating the flocculation mechanism of PDC10. The mechanism of PDC10 was that it can bridge and flocculate oil droplets by electrostatic interaction and hydrophobic interaction. It also preferred to distribute at the interface, and its interaction with HPAM in bulk water was weak, which confirms its selective flocculation properties.

In this study, the local and global sensitivity analyses of the Winterwerp model to the input parameters have been carried out using the Garson algorithm and the PaD2 method by virtue of an artificial neural network. The main results of the sensitivity analyses are that the model is most sensitive to the breakup parameter and that only two parameters (the floc aggregation and breakup parameters) are significant. The result that the model output is less sensitive to the choice of fractal dimension seems to imply that the modification work on the fractal dimension might be unnecessary.

This study has been carried out to evaluate the applicability of the pilot scale hybrid type of stormwater runoff treatment system for treatment of combined sewer overflow. Also, to determine the optimum operation parameter such as coagulation dosage concentration, effectiveness of coagulant usage, surface loading rate and backwashing conditions. The pilot scale stormwater filtration system (SFS) was installed at the municipal wastewater plant serving the city of Cheongju (CWTP), Korea. CWTP has a capacity of 280,000 m3/day. The SFS consists of a hydrocyclone coagulation/flocculation with polyaluminium chloride silicate (PACS) and an upflow filter to treat combined sewer overflows. There are two modes (without PACS use and with PACS use) of operation for the SFS. In case of no coagulant use, the range of suspended solids (SS) and turbidity removal efficiency were 72.0–86.6% (mean 80.0%) and 30.9–71.1% (mean 49.3%), respectively. And, the recovery rate of filter was 79.2–83.6% (mean 81.2%); the rate of remaining solid loading in filter media was 16.4–20.8% (mean 18.8%) after backwashing. The influent turbidity, SS concentrations were 59.0–90.7 NTU (mean 72.0 NTU), 194.0–320.0mg/L (mean 246.7mg/L), respectively. The range of PACS dosage concentration was 6.0–7.1mg/L (mean 6.7mg/L). The range of SS and turbidity removal efficiency was 84.9–98.2 (mean 91.4%) and 70.7–96.3 (mean 84.0%), respectively. It was found that removal efficiency was enhanced with PACS dosage. The recovery rate of filter was 92.0–92.5% (mean 92.3%) the rate of remaining solid loading in filter media was 6.1–8.2% (mean 7.2%) after backwashing. In the case of coagulant use, the particle size of the effluent is bigger than influent particle size. The results showed that SFS with PACS use more effective than without PACS use in SS and turbidity removal efficiency and recovery rate of filter.

A laboratory investigation of the treatment potential of a coagulation process in the context of stormwater treatment was undertaken. The initial 25 L road runoff generated from four rain events was collected and subjected to a jar-testing regime with two commercial coagulants. The treatment effect was assessed by analysing the runoff before and after treatment for turbidity, suspended solids and metal content. The coagulation process resulted in particle and total metal reduction of more than 90% compared to 40% for only sedimentation. Up to 40% reduction of dissolved Cr, Cu and Pb was also observed compared to 0% for sedimentation. This study shows that coagulation may be a useful process for stormwater treatment systems when the treatment requirements are high.

The difficulty of residual sludge dehydration is the major problem in sewage treatment. The reduction of moisture content in sludge can reduce the sludge volume significantly and is conducive to the subsequent disposal of sludge. As an organic polymer flocculant, chitosan (CTS) is widely used in water and waste water treatment. In this study, CTS was used in sludge treatment to improve the sedimentation and dehydration properties of sludge. When treated with CTS, the moisture content of sludge cake decreased from 85.9% to 83.0%, the SV30 decreased to about 1/2, and the sludge volume reduced to 82.9%. Further analysis showed that the zeta potential (ζ-potential) of the sludge changed from negative value to positive value, and the D50 of the sludge was larger than that of the raw sludge. In addition, when the moisture content of the sludge cake was reduced to the lowest, the concentration of extracellular polymeric substances (EPS) and SCOD was the largest and the |ζ| decreased to the lowest. CTS improved the dehydration and sedimentation performance of sludge mainly by factors of electrical neutralization, adsorption bridging and dissolution of EPS.

The implementation of carbon capture technologies such as high-rate activated sludge (HRAS) systems are gaining interests in water resource and recovery facilities (WRRFs) to minimize carbon oxidation and maximize organic carbon recovery and methane potential through biosorption of biodegradable organics into the biomass. Existing activated sludge models were developed to describe chemical oxygen demand (COD) removal in activated sludge systems operating at long solids retention times (SRT) (i.e. 3 days or longer) and fail to simulate the biological reactions at low SRT systems. A new model is developed to describe colloidal material removal and extracellular polymeric substance (EPS) generation, flocculation, and intracellular storage with the objective of extending the range of whole plant models to very short SRT systems. In this study, the model is tested against A-stage (adsorption) pilot reactor performance data and proved to match the COD and colloids removal at low SRT. The model was also tested on longer SRT systems where effluents do not contain much residual colloids, and digestion where colloids from decay processes are present.

The coagulation/flocculation process is an essential step in drinking water treatment. The process of formation, growth, breakage and rearrangement of the formed aggregates is key to enhancing the understanding of the flocculation process. Artificial neural networks (ANNs) are a powerful technique, which can be used to model complex problems in several areas, such as water treatment. This work evaluated the evolution of the fractal dimension of aggregates obtained through ANN modeling in the coagulation/flocculation process conducted in high apparent color water (100 ± 5 PtCo), using alum as coagulant in dosages varying from 1 to 12 mg Al3+ L−1, and shear rates from 20 to 60 s−1 for flocculation times from 1 to 60 minutes. Based on raw data, the ANN model resulted in optimized condition of 9.5 mg Al3+ L−1 and pH 6.1, for color removal of 90.5%. For fractal dimension evolution, the ANN was able to represent from 95% to 99% of the results.

In recent years, electrocoagulation has been extensively studied on the removal of refractory pollutants. However, the application of electrocoagulation in actual flocculation tank is limited because of its high energy consumption, especially under the condition of large electrode plate spacing. In this study, the computational fluid dynamics (CFD) software – ANSYS Fluent had been used to simulate the flow state of grid flocculation tank, for the purposes of optimizing the design parameters. The simulation results showed that vortex velocity gradient was stronger, the grid plate spacing was smaller when the velocity was 0.13 m s−1, perforation size was 25 × 25 mm, porosity was 31.25%. And the optimal grid plate spacing was 250 mm. Moreover, in order to prove the reasonableness of simulation results, the humic acid wastewater was treated by electrocoagulation process in the specific device which was built based on simulation results. The results showed that the optimal condition of orthogonal test were as follows: the initial pH was 8, the concentration of sodium chloride was 5 mmol L−1, the voltage was 15 V; and the power time was 60 min. This study greatly narrowed the grid plate spacing, optimized design parameters under the circumstances of strong turbulent intensity and provided a theoretical basis for the combination of electrocoagulation and hydraulic flocculation.

The aim of the present study was to investigate the performance of a novel coagulant, i.e. ZrOCl2, for the removal of anthraquinone-based reactive dye from aqueous solution. An ideal experimental setup was designed based on central composite design using response surface methodology to determine the individual and interactive effects of different operational variables (i.e. pH, coagulant dose and dye concentration) on treatment performance in terms of dye and chemical oxygen demand (COD) removal efficiencies. Total 92.58% dye and 85.33% COD removal were experimentally attained at optimized conditions at low coagulant dose, i.e. 156.67 mg/L for the dye concentration of 105.67 mg/L at pH 2. To validate the working pH of the metal coagulant, the static charge of ZrOCl2 was measured using Eh value. The performance of the coagulant was validated with experimental and predicted values in the selected data set, and R2 values for both responses were found to be 0.99 and 0.95 respectively, which shows the reliability of the experimental design. Further, the toxicity of the coagulant was assessed and no such toxicity was found even up to the concentration of 500 mg/L, proclaiming the disposal of sludge may not exhibit any threat to humans. Experimental results suggested that the ZrOCl2 could be used as an eco-friendly coagulant for dye wastewater treatment.

The efficiency of chemical oxygen demand (COD) and color removal from raw coffee processing wastewater (CPWW) using batch electrochemical coagulation (BECC) treatment process using stainless steel (SS) and iron (Fe) electrode combinations are investigated. Of the combinations: four SS, four Fe, Fe-Fe-SS-SS, Fe-SS-Fe-SS, SS-SS-Fe-Fe, and SS-Fe-SS-Fe; four SS electrodes operated at 23 V having 120 A/m2 current density was found as a good operating condition to achieve ∼87% COD removal from its initial COD of 1,984 mg/L and corresponding color removal of 97.1% (initial color 7,000 PCU). The second best electrode combination, SS-SS-Fe-Fe, had COD and color removals of 75% and 91%. When using polyaluminum chloride (PAC) as aid with different dosages of 20–100 mg/L, 50 mg/L PAC showed maximum COD and color removals of 80% and 92%. Comparison of proximate and ultimate analyses of various solid fuels with CPWW ECC sludge showed its usefulness as a soil supplement and as an adsorbent for reutilization. The solid residue obtained after BECC was characterized using energy dispersive X-ray spectroscopy and other analyses. Summarizing the results, it was concluded that BECC can be effectively used for maximum removal of organics from raw CPWW with clean water reclamations of up to ∼90% using ECC as a novel treatment technique.

Settling of activated sludge particles has long been the key to successfully achieving secondary treatment. While soluble products can be converted to particulate components via microbial reactions in the activated sludge process, it is the subsequent removal of these particulate components that is the key to achieving ultimate water quality criteria. An understanding of the operating parameters for selecting good settling activated sludge particles was first documented in the 1970s and 1980s. An understanding of the growth pressures that can be imposed on filamentous organisms, and the impacts of selector zones in general, allowed the design and operation of activated sludge processes to routinely achieve good sludge settleability. More recently, research has identified what could be the next evolution in flocculant growth, with the growing interest in aerobic granular sludge. Aerobic granular sludge is purported to provide superior settling properties, and many of the growth pressures identified for aerobic granular sludge are also present in activated sludge systems. These enhanced settling sludge systems are gaining significant interest, but the factors leading to enhanced sludge settleability could be present in historical and existing systems. Three facilities were evaluated that exhibited enhanced settleability (i.e. sludge volume indices of less than 70 mL/g the majority of the time) to determine how these enhanced settling sludges compare to typical settling curves from the literature. The enhanced settling sludge facilities exhibit key differences related to surface overflow rate, return activated sludge (RAS) pumping requirements, and sensitivity to solids concentration that are critical for developing effective settling designs for enhanced settling sludge facilities. As more facilities aim to achieve enhanced settling sludge for intensification of infrastructure, it will be important to carefully consider historic settling curves and to develop site-specific settling criteria when possible.

In activated sludge (AS) process, the impact of the operational parameters on process efficiency is assumed to be correlated with the sludge properties. This study provides a better insight into these interactions by subjecting a laboratory-scale AS system to a sequence of operating condition modifications enabling typical situations of a wastewater treatment plant to be represented. Process performance was assessed and AS floc morphology (size, circularity, convexity, solidity and aspect ratio) was quantified by measuring 100,000 flocs per sample with an automated image analysis technique. Introducing 3D distributions, which combine morphological properties, allowed the identification of a filamentous bulking characterized by a floc population shift towards larger sizes and lower solidity and circularity values. Moreover, a washout phenomenon was characterized by smaller AS flocs and an increase in their solidity. Recycle ratio increase and COD:N ratio decrease both promoted a slight reduction of floc sizes and a constant evolution of circularity and convexity values. The analysis of the volume-based 3D distributions turned out to be a smart tool to combine size and shape data, allowing a deeper understanding of the dynamics of floc structure under process disturbances.

In this study, the effects of lysozyme, protease and α-amylase pretreatments for improving the hydrolysis and biodegradability of waste activated sludge (WAS) were investigated. The results showed that lysozyme was more effective in increasing the soluble chemical oxygen demand (SCOD) concentration in the liquid phase of sludge and improving the release of protein and carbohydrate from sludge flocculation to enhance sludge hydrolysis. After 8 h hydrolysis, the net SCOD increase in a reactor with lysozyme was 2.23 times and 2.15 times that of the reactors with protease and α-amylase, respectively. Meanwhile, lysozyme and protease could improve the lysis of microorganism cells and the dissolution of extracellular polymeric substances (EPS) to a certain extent, and lysozyme was more effective. Furthermore, the compositional characteristics of dissolved organic matter (DOM) and EPS were analyzed by EEM fluorescence spectroscopy and fluorescence regional integration (FRI) analysis. Tryptophan-like protein was the main component of sludge, which accounted for 31% and 38% of DOM and EPS, respectively. Lysozyme could decrease the percentage of non-biodegradable materials in sludge, such as humic acid-like substances and fulvic acid-like substances, so it could improve the biodegradability of sludge. This study can provide valuable information for future studies about hydrolytic enzyme pretreatments for WAS disposal.

Organic material is considered as a main component of oilfield fracturing wastewater (OFW). The work is intended to optimize the experimental conditions for the maximum oxidative degradation of organic material by coagulation and UV/H 2 O 2 /ferrioxalate complexes process. Optimal reaction conditions were proposed based on the chemical oxygen demand (COD) removal efficiency. The overall removal efficiency of COD reached 83.8% for dilution ratio of raw wastewater was 1:2, pH of 4 and the FeCl 3 loading of 1,000 mg/L in the coagulation process; dosage of H 2 O 2 (30%,v/v) was 0.6% (v/v) and added in three steps, the n(H 2 O 2 )/n(Fe 2+ ) was 2:1, n(Fe 2+ )/n(C 2 O 4 2− ) was 3:1and pH of 4 in the UV/H 2 O 2 /ferrioxalate complexes process; pH was adjusted to 8.5-9 by NaOH and then cationic polyacrylamide(CPAM) of 2 mg/L was added in neutralization and flocculation process. The decrease in COD during the coagulation process reduced the required H 2 O 2 dosage and improve efficiency in the subsequent UV/H 2 O 2 /ferrioxalate complexes process. Furthermore, more than 13.4% of COD removal efficiency significantly increased with the introduction of oxalate compared with UV/Fenton. Experimental results show that the coagulation and UV/H 2 O 2 /ferrioxalate complexes process could efficiently remove theorganic material dissolved in OFW. An optimal combination of these parameters produced treated wastewater that met the GB8978-19969Integrated Wastewater Discharge Standard’ level III emission standard.

In this study, Couette flow experiments were performed to estimate the temporal evolution of the 2D and perimeter-based fractal dimension values of kaolinite flocs during flocculation. The fractal dimensions were calculated based on the projected surface area, perimeter length and length of the longest axis of the flocs as determined by sampling observation and an image-processing system. The 2D fractal dimension, which relates the longest axis length and projected surface area of flocs, was found to decrease with the flocculation time, corresponding to the production of some porous flocs from the flow shear. This fractal dimension finally reached a steady state, which resulted from a dynamic equilibrium among the floc growth, floc breakage and floc restructuring. The perimeter-based fractal dimension, which characterizes the relationship between the projected surface area and the perimeter of flocs, increases with flocculation time because the flow shear increases the collisions among the primary particles, and some irregular flocs are formed. The perimeter-based fractal dimension reaches a steady level because of the balance among floc aggregation, breakage and restructuring. In addition, a stronger turbulent flow shear makes the steady state of fractal dimensions occur early during flocculation.

The technical performance of a precoat filter was compared with that of a traditional sand filter. Particle concentration and size distribution were measured before and after the filtration of swimming pool water. Both the sand and precoat filters could reduce the particle concentration in the effluent. However, higher particle removal efficiency was generally observed for the precoat filter, especially for particles smaller than 10 μm in diameter. Adding flocculant improved the removal efficiency of the sand filter, resulting in removal efficiencies comparable to those of the precoat filter. Three powders, i.e., two types of perlite (Harbolite® and Aquatec perlite) and cellulose fibers (Arbocel®), were tested for the precoat filter, but no significant difference in particle removal efficiency was observed among them. The maximum efficiency was reached within 30–40 min of filtration. The energy required for the pumps increased by approximately 35% over a period of 14 days. The energy consumption could be reduced by replacing the powder on the filter cloth. The sand filter was backwashed once a week, while the powder on the precoat filter was replaced every two weeks. Under these conditions, it was possible to reduce the water used for cleaning by 88% if the precoat filter was used instead of the sand filter.

Hydroxypropyl guar gum is considered to be a main component of oilfield fracturing wastewater (OFW). This work is intended to optimize the experimental conditions for the maximum oxidative degradation of hydroxypropyl guar gum by the coagulation and UV/H2O2/ferrioxalate complexes process. Optimal reaction conditions were proposed based on the chemical oxygen demand (COD) removal efficiency and UV_vis spectra analysis. The overall removal efficiency of COD reached 83.8% for a dilution ratio of raw wastewater of 1:2, pH of 4 and FeCl3 loading of 1,000 mg/L in the coagulation process; the dosage of H2O2 (30%,v/v) was 0.6% (v/v) and added in three steps, the n(H2O2)/n(Fe2+) was 2:1, n(Fe2+)/n(C2O42−) was 3:1 and pH was 4 in the UV/H2O2/ferrioxalate complexes process; pH was adjusted to 8.5–9 by NaOH and then cationic polyacrylamide (CPAM) of 2 mg/L was added in the neutralization and flocculation process. The decrease in COD during the coagulation process reduced the required H2O2 dosage and improved efficiency in the subsequent UV/H2O2/ferrioxalate complexes process. Furthermore, COD removal efficiency significantly increased by more than 13.4% with the introduction of oxalate compared with UV/Fenton. The UV_vis spectra analysis results indicated that the coagulation and UV/H2O2/ferrioxalate complexes process could efficiently remove the hydroxypropyl guar gum dissolved in OFW. An optimal combination of these parameters produced treated wastewater that met the GB8978-1996 Integrated Wastewater Discharge Standard level III emission standard.

Analyses of rheological properties and electrical conductivity (σdc) at direct current have been employed in order to investigate the effects of calcium oxide on the coagulation process during sludge treatment in the textile industry. In this context, rheological and electrical measurements were performed on five samples – one that contained raw sludge and the other four that were prepared from the raw sludge and different amounts of calcium oxide: 2, 3, 4, 5% (w/w). Rheological behavior of these samples was analyzed using the Herschel–Bulkley modified model. The influence of calcium oxide content on the rheological parameters such as infinite viscosity, the yield stress, the consistency coefficient, and the consistency index, are presented and discussed. The impact of the calcium oxide content on pH and conductivity were also examined. Similar behaviors have been seen in the evolution of conductivity and infinite viscosity as a function of the calcium oxide content. These latter characteristics were modeled by an equation using two power laws. This equation was able to fit very well the evolution of electrical conductivity and also the viscosity versus the percentage of calcium oxide to predict the optimal amount of calcium oxide (3%) to achieve the coagulation step during sludge treatment.

In order to meet the latest Environmental Protection Law of China on wastewater discharge standards, this paper studied a pilot-scale micro-flocculation filtration pretreatment process for the treatment of oilfield wastewater. The experiment showed that the removal rate of oil and suspended solids (SS) respectively increased from 91.52% to 95.38% and from 66.42% to 97.19%. After the treatment by the micro-flocculation filtration device, the relevant characteristics of the discharge wastewater satisfied the latest standards continuously. Moreover, the polyaluminum chloride (PAC) dosage was reduced from 200 mg/L to 100 mg/L (50 mg/L in micro-flocculation device and 50 mg/L in the cyclone reactor) at the same time. In order to decrease the degree of scaling in the filter, ceramsite was chosen as the filter material instead of quartz sand that is widely applied in the oilfields. The scaling experiment showed that the HCO3−, Ca2+ and Mg2+ contents in the extract from quartz sand after the scaling study were increased by 38.05, 35.91 and 0.28 mg/L, respectively. Meanwhile, the HCO3−, Ca2+ and Mg2+ contents in the extract from ceramsite were only increased by 13.14, 6.26 and 0.27 mg/L, respectively. Therefore, the ceramsite is not so prone to scaling as compared to quartz sand under identical test conditions, which avoided a hardened and impervious filter after operating for some time. These results suggest that the micro-flocculation filtration with the ceramsite as filter media is a suitable pretreatment process for the oilfield wastewater treatment.

Algae are considered water pollutants because they form algal blooms in stagnant water. Algae harvesting technology, however, can help convert them into a useful industrial material like biomass. The core technique (flocculation) separates microalgae from other flocculants, allowing for the harvest of clean and pure algal biomass. This study aims to estimate and evaluate algal separation (removal or harvesting) efficiency (X) to concurrently obtain the objectives of algal bloom management and algal particle collection. To simulate algal separation by auto-flocculation (no flocculants) related flotation, the population balance in turbulence (PBT) model is used. Model simulations are conducted under optimal conditions provided by previous studies about the biological impact factors of algae, operating parameters of the flotation process, and so on. This modeling study determines the efficiency (X) of separating algae from the water body in the separation zone after forming auto-flocculated bubble–floc agglomerates by making them collide and attach to each other in the contact zone of the flotation tank. The X is examined as a function of size distribution of agglomerates and bubbles and of the number of initially injected bubbles. Optimal conditions for forming and harvesting the agglomerates may be found through further modeling studies.

A coagulation–flocculation process was applied to wastewater of paint and construction chemicals producing factory in Turkey. Ferric chloride was used as coagulant and several natural based materials, namely limestone, pumice, sepiolite, bentonite and mussel shell were used as flocculant aids. The effects of dosage of flocculant aids on the pH, color and electrical conductivity of wastewater were studied. The experimental results showed that the treatment with all substances was very effective. The pHs of treated wastewater were obtained in the range of 5–7 without needing pH adjustment process. Fifteen Pt-Co color values were obtained on average, which is similar to pure water clarity. The amount of solute in the wastewater was evaluated by the electrical conductivity values. According to the results, under the optimum treatment conditions, chemical oxygen demands were determined. As a result of the work, the cost of chemicals for the wastewater treatment processes has been reduced by about 90%.

The flocculation–column flotation with hydraulic loading (HL, >10 m h−1) was studied for the treatment of oil-in-water emulsions containing 70–400 mg L−1 (turbidity = 70–226 NTU) of oil and salinity (30 and 100 g L−1). A polyacrylamide (Dismulgan, 20 mg L−1) flocculated the oil droplets, using two floc generator reactors, with rapid and slow mixing stages (head loss = 0.9 to 3.5 bar). Flotation was conducted in two cells (1.5 and 2.5 m) with microbubbles (MBs, 5–80 μm) and nanobubbles (NBs, 50–300 nm diameter, concentration of 108 NBs mL−1). Bubbles were formed using a centrifugal multiphase pump, with optimized parameters and a needle valve. The results showed higher efficiency with the taller column reducing the residual oil content to 4 mg L−1 and turbidity to 7 NTU. At high HL (27.5 m h−1), the residual oil concentrations were below the standard emission (29 mg L−1), reaching 18 mg L−1. The best results were obtained with high concentration of NBs (apart from the bigger bubbles). Mechanisms involved appear to be attachment and entrapment of the NBs onto and inside the flocs. Thus, the aggregates were readily captured, by bigger bubbles (mostly MBs) aiding shear withstanding. Advantages are the small footprint of the cells, low residence time and high processing rate.

An inorganic-organic hybrid flocculant Al(OH)3-polyacrylamide (Al-PAM) with narrow molecular weight distribution was synthesized using inverse microemulsion polymerization. The hybrid polymer Al-PAM was characterized by Infrared spectroscopy, thermogravimetric analysis, transmission electron microscopy and scanning electron microscopy, and it was found that it had a ‘star-like’ structure in which Al(OH)3 colloidal particles acted as cores linking PAM chains. The properties of Al-PAM were investigated in flocculating 10 wt% cyanide tailing suspensions. It was found that as the amount of Al-PAMM1 with high molecular weight and aluminum content increased, the initial settling rate of particles accelerated, achieving the maximum 6.6 m/h, 17.3 times the rate of the control without flocculants. The turbidity of the supernatant decreased to 35 ± 2 NTU accordingly, compared to 353 ± 2 NTU of that in the control, which meant that 90.0% of turbidity was removed from the cyanide tailing suspensions. The flocculation mechanism was further explored by floccule size and ζ potential measurements. The superior performance of cationic Al-PAM in flocculating negatively charged particles compared to commercial non-ionic GG indicated that electrostatic repulsion between tailing particles was a crucial factor in deciding the flocculation performance of the polymer. The study demonstrated that both charge neutralization and bridge adsorption were conductive to the particle flocculation.

The enhancement of sludge dewaterability is of great importance for facilitating the sludge disposal during the operation of wastewater treatment plants. In this study, a novel oxidative conditioning approach was applied to enhance the dewaterability of waste activated sludge by the combination of zero-valent iron (ZVI) and peroxymonosulfate (PMS). It was found that the dewaterability of sludge was significantly improved after the addition of ZVI (0–4 g/g TSS) (TSS: total suspended solids) and PMS (0–1 g/g TSS). The optimal addition amount of ZVI and PMS was 0.25 g/g TSS and 0.1 g/g TSS, respectively, under which the capillary suction time of the sludge was reduced by approximately 50%. The decomposition of sludge flocs could contribute to the improved sludge dewaterability. Economic analysis demonstrated that the proposed conditioning process with ZVI and PMS was more economical than the ZVI + peroxydisulfate and the traditional Fenton conditioning processes.