Inorganic Coagulants Research Articles

Application of xanthan gum as coagulant-aid for decolorization of synthetic Congo red wastewater

In recent years, utilization of polysaccharides as natural coagulant and coagulant-aid has become a topic of interest, due to the nature of biopolymers that are renewable, biodegradable, and non-toxic. In this study, Congo red, as a model dye substance, was treated using polyaluminium chloride (PAC) as the main coagulant and xanthan gum as the coagulant aid. For this purpose, the effect of pH (3–9), xanthan gum dose (0.5–4 mg/L), and the initial concentration of Congo red dye (50–100 mg/L) to the dye removal and sludge volume were investigated. The outcome of this investigation indicates that the best pH for Congo red coagulation occurred at pH 3, due to the charge neutralization mechanism. The addition of coagulant-aid dose increases the %-removal and sludge volume until reaching the best coagulant-aid dose of 2 mg/L that results in a %-removal value of 93.81% and a sludge volume of 23.5 mL/L. Further addition of xanthan gum reduced the %-removal and sludge volume due to the inter-polymer force causing more difficult floc formation. The best initial concentration of dye occurred at a Congo red concentration of 50 mg/L, with a %-removal value of 93.81% with PAC (15 mg/L) and xanthan gum (2 mg/L) coagulants. This value is considerably higher than PAC and xanthan gum only which amounts to 81.16 and 7.18%, respectively. Based on these results, it is apparent that xanthan gum can positively contribute to dye coagulation while reducing the use of harmful inorganic coagulant.

Study of the Sedimentation Parameters of an Iron Ore Tailing from Fundão Dam Using a Tannin-Based Coagulant

From the rupture of the Fundão dam in Mariana–MG, there are tailings still present at the bottom of the plant that must be recovered. The flocculation followed by sedimentation operation can be applied as a unit operation in this recovering process. Instead of using conventional inorganic coagulants, bio-based coagulants offer some advantages, due to their low toxicity and biodegradability. Nonetheless, the use of bio-based coagulants in the mining industry is not established yet, due to the complex parameters that must be taken in consideration. This study analyzes the influence of the pH and flocculant concentration, which are the variables of the 22 full factorial design. The pH value for the batch sedimentation process was defined ranging from 5 to 9. Tanfloc, a tannin-based coagulant, was used as a coagulant agent. The results indicate a strong dependence on the coagulant concentration, and a recommended 15 g/L dosage with pH varying from 6 to 8. From batch sedimentation, it was possible to determine an exponential model for the sedimentation with an excellent fitting (R2 = 0.997). The sedimentation efficiency calculated is 65.6%. These results confirm the potential use of bio-based materials in mining tailing treatments. In addition, they can be used in equipment sizing and simulations of the sedimentation operation.

QSAR model and microscopic mechanism analysis of dye removal by coagulation of aluminum chloride under alkaline conditions

Introduction: The inorganic coagulant AlCl3 is used in the traditional coagulation method for the decolorization of industrial dye wastewater. We studied its effectiveness in 41 kinds of dye with different structures, including azo, anthraquinone, arylmethane, and indigo dyes.Discussion: The optimal conditions for the removal of dye in the AlCl3 coagulation system were alkaline > neutral > acidic conditions. Under alkaline conditions, the hydrolysis colloid of AlCl3 is positively charged and easily combined with negatively charged anionic dyes by electrostatic adsorption. Therefore, the relationships between the dye removal behavior and molecular parameters under alkaline conditions were analyzed.Methods: Quantitative structure–activity relationship (QSAR) models were built for the color removal rates (Rexp) of 41 dyes and 46 molecular parameters computed by the density functional theory (DFT). Internal validation, external validation, statistical tests, Y-randomization, and applicability domain tests indicated that the optimal models are stable, accurate, reliable, and predictive.Results: The optimal QSAR model showed that surface area (approx.) (SAA) and molecular weight (MW) are two key molecular parameters. Moreover, electrostatic forces and hydrogen bonding are the predominant adsorption forces in this coagulation process.

Preparation of inorganic nanocomposite coagulant and its application in oilfield sewage treatment

Carbon nanotubes (CNTs), as a new type of carbon material with complete molecular structure, have great application potential in the field of nanocomposites. In this study, carbon nanotubes were first surface modified to give them good hydrophilicity. Subsequently, the nanocomposite coagulant (PASS-T) with different modified CNTs (m-CNTs) contents was prepared by alkaline titration method. The CNT, m-CNT, PASS and PASS-T were characterized by FTIR, XRD and XRF. Then the coagulant was applied to oily sewage, and the coagulation results showed that the PASS-T (0.1%) had the best oil reduction rate (92%) and turbidity reduction rate (97%). Appropriate addition of m-CNT can increase the local concentration of coagulant at the molecular level, making the flocs of oily sewage larger. It can be found by SEM that PASS-T produces large and knotted flocs in oily sewage. Finally, the residual turbidity and oil removal rate of the different coagulants were statistically analyzed.

Improving the Dewaterability of a Filter Press through Optimization of the Coagulation Conditions of Sewage Sludge

This study applied a filter press for dewatering that uses pressure to reduce the water content of sludge generated in sewage treatment plants and evaluated the improvement of dewaterability under various coagulation conditions according to the type of coagulants, amounts, and pH conditions. The improvement of dewaterability was evaluated by measurement of time to filter (TTF), change in zeta potential, and sludge cake generated after filter press dewatering. It was found that under the applied coagulation conditions, inorganic coagulants were suitable for filter press dewatering. The optimum conditions were PAC with a dose of 70 mg/gTS, pH 10 for mixed sludge, and PAC with a dose of 100 mg/gTS, pH 6 for anaerobically digested sludge. Under optimal coagulation conditions, the water content of the sludge cake was 57% and 65%, respectively, marking a reduction by 19-27% compared to conventional centrifuge dewatering.

Inorganic composite coagulant for wool scouring wastewater treatment: Performance, kinetics and coagulation mechanism

Wool is perceived to be a clean and green natural fibre. However, raw wool contains substantial amounts of contaminants that must be removed in a wool scouring process before the wool can be used as a textile fibre. Coagulation is the first step for scouring wastewater treatment. But the role of inorganic coagulants in increasing sludge density for scouring wastewater treatment remains unclear. This work systematically prepared a series of inorganic composite coagulants (polyaluminium ferric silicate (PAFS)) and investigated their efficiency for treating wool scouring wastewater. Compared with conventional coagulants, polyaluminium chloride (PAC) and polyferric sulfate (PFS), PAFS showed improved coagulation performance over a wider pH range (3–7), achieving higher removal rates of 97 % and 99 % for chemical oxygen demand (COD) and turbidity, respectively. In addition, PAFS showed its advantages for practical wastewater treatment, including fast floc settling rate, increased sludge density (with a reduced sludge volume) and low floc moisture content. This optimized PAFS was successfully obtained in a scaled-up process. Zeta potential tests revealed that PAFS coagulated colloidal particles by the synergistic action of electro-neutralization and adsorption bridging. This work has practical implications for increasing the efficiency of wastewater treatment and reducing the environmental impact of wool scouring.

Combined conditioning of inorganic coagulant and polyamine to improve the dewaterability of municipal sludge, minimize dosage and reduce the influence of filtrate.

Efficient dewatering of sludge is necessary for its cost-effective transportation and final disposal. However, the common method of using polyferric sulfate (PFS) and polyacrylamide (PAM) requires a large amount of dosage and produces high iron ion content in the filtrate. This study examined a solution of applying polyamine (PA) coupled with inorganic coagulant PFS. The results demonstrated that using PFS + PA together could achieve the same or similar filtering rates as using PFS + PAM. The capillary suction time (CST) of PFS + PA (89.0 s) was equivalent to that of PFS (75.1 s) and better than that of PA (117.1 s) and raw sludge (RS, 403.8 s). Compared with PFS + PAM, the combination of PFS and PA efficiently removed Fe ions and chemical oxygen demand (COD) in sludge water content, with Fe ions in the sludge filtrate reduced by 97.8% and COD reduced by 78.9%, respectively. By analyzing the basic physicochemical properties of the sludge system, including the synergistic effect of coagulation and flocculation, sludge hydrolysis and flocculation, it indicated that PA + PFS could reduce bound water. These results demonstrated that combining PFS and PA to improve sludge dewatering performance is more beneficial than utilizing a coagulant or flocculant alone, even PFS + PAM.

Conceptualizing Cavigulation Methodology by Integrating Cavitation and Coagulation and Application to Dye Wastewater Treatment

The present work provides a proof of concept for a new hybrid process, cavigulation, by combining cavitation and coagulation and its application to dye wastewater treatment. Both acoustic and hydrodynamic cavitations were evaluated. Removal of a commonly used dyes such as Congo red was investigated by cavigulation in the concentration range of 50 to 500 ppm. A broad spectrum of coagulants including two inorganic coagulants; poly aluminium chloride, iron (III) chloride, and natural biocoagulants derived from Moringa oleifera, Cicer arietinum and Acanthocereus tetragonus were employed to substantiate the concept of cavigulation. A vortex diode device employing vortex flow for cavitation, was used for the hydrodynamic cavitation (HC) -based cavigulation. Cavigulation in the form of acoustic cavitation + coagulation, showed significant improvement over individual processes; acoustic cavitation alone was largely ineffective for dye removal. Increase over conventional coagulation to the extent of 24% and 48% was observed for the two inorganic coagulantsIron (III) chloride and PAC SAB 18, while for Moringa oleifera, Acanthocereus tetragonus, and Cicer arietinum the increase was 27%, 33%, and 29% respectively. The pH has a large impact on the cavigulation process, similar to coagulation and the coagulant dose could be reduced by more than half by adjusting pH to 3. Auramine O dye removal was effective using hydrodynamic cavitation compared to coagulation. The developed cavigulation process, especially using biocoagulants, could be an effective alternative to the conventional chemical coagulation in the form of a green process in dye wastewater treatment

The influence of coagulant type on the biological treatment of sewage sludge

Anaerobic digestion (AD) and composting are commonly utilized sludge management methods however, the influence of different coagulant types on these biological processes and their stabilized biomass characteristics have not been fully explained. In this study, the effect of the coagulant used in municipal wastewater treatment on the biological stabilization of sludge was investigated. Fully controlled and monitored small-scale AD and composting bioreactors were utilized. The coagulants tested included an inorganic coagulant (IC), polyaluminium chloride (PAC), and organic coagulants, (OC) polyamine (pAmine) and chitosan (Chit). Overall, the coagulant applied showed a measurable influence on the biological stabilization of sludge. The presence of complex organics compounds from OC in the sludge biomass was found to decrease biomass biodegradability while increasing gas production. During AD, Chit-sludge achieved higher biogas production than pAmine- and PAC-sludges (13 % and 16 %, respectively, in Nm3 CH4 t−1VS). In composting, pAmine-sludge achieved the highest feedstock temperature (34–35 °C) and CO2 gas emissions, followed by Chit- (33 °C) and PAC-sludges (32 °C). Generally, tot-P concentration in PAC-sludge was higher than in pAmine and Chit-sludges both before (20, 17 and 15 g/kg DM, consecutively) and after AD (23, 21 and 20.5 g/kg DM, consecutively), and during the composting (31, 29.5 and 26 g/kg DM, consecutively) process. Tot-N concentrations (g/kg DM) showed a substantial increase after AD (pAmine and PAC ca 50 % and Chit 81 %), while a decrease was observed after composting, specifically in PAC-sludge (PAC 28 %, pAmine and Chit ⁓5 %). The selection of the most suitable coagulant by wastewater treatment facilities depends on the objective of the biological stabilization process. In cases where AD is applied and biogas yield is selected as the target output, the semi-natural OC Chit was found to be the best option among the coagulants tested. Comparably, when the nutrient content of resulting biosolids (AD or composting) is more relevant, it was found that OC-produced sludge contained higher N concentrations, while IC-produced sludge contained slightly higher P concentrations.

Behavior of Sludge Dewaterability and Nutrient Contents after Treatment with Cellulose-Based Flocculants with Combined PTS and Catalytic Behavior of Sludge towards Tetracycline Degradation

Wastewater treatment plants are increasingly interested in adopting inorganic coagulants and organic flocculants in their sludge treatment process since sludge disposal costs more than half of the overall operational costs. This study synthesized poly titanium sulfate (PTS) by different molar ratios and used the best one with cellulose-based flocculants for sludge conditioning. PTS synthesized with a 1:2 molar ratio showed the lowest capillary suction time (CST) of sludge and was selected for further studies with cellulose-based flocculants. As bio-based flocculants have gained popularity due to current environmental problems, cationized cellulose-based flocculants (Ce-CTA) were used in this work with or without PTS for sludge treatment. After coagulation–flocculation, dewaterability of sludge enhanced, and the Lowry and Anthrone method was used to assess proteins and polysaccharides. Next, metal content and nutrients such as total phosphorus, phosphate, and nitrate were measured by ICP-OES and IC, and we found promising results of phosphate especially at pH 3. Higher total phosphorus content was found at pH 3 and 9, and even at pH 6 after PTS or PTS+Ce-CTA treatment. In addition, PTS-treated sludge materials also showed catalytic behavior, suggesting a new research avenue for future development. Based on this study, the PTS+Ce-CTA combination is promising for sludge treatment and nutrient recovery, along with the possibility for the further valorization of the sludge materials.

Experimental Study of Effluent Salty Wastewater Treatment from a Solar Desalination Pond

In this research, the quality of the wastewater discharged into the environment has been investigated. The effluent from solar desalination pond contains large amounts of TDS (3.68 grams per liter) and TH (6.50 grams per liter). Since the use of filter is not economical in this case, three types of commercial coagulants such as aluminum sulfate, ferric chloride and ferric sulfide have been used in this study. The main parameters such as effectiveness of three inorganic coagulants, ammonium sulfate, ferric sulfate, and ferric chloride, which separately help to remove hardness, have been studied. According to the results, using laboratory test, 25/g of ferric sulfate as coagulant is best coagulant mass and the ratio of 4 to 3 for auxiliary coagulant (sodium carbonate and sodium hydroxide) to coagulant will be best ratio. Also, the mixing rate of 120 rpm in the first reactor will give the best mixing speed. These conditions will lead to 0.348 grams per liter of TDS, 0.345 grams per liter of TH and 0.195 grams per liter of calcium hardness and 300 micro Siemens electrical conductivity of the purified sample.

Evaluation of Turbidity and Color Removal in Water Treatment: A Comparative Study between Opuntia ficus-indica Fruit Peel Mucilage and FeCl3.

Natural coagulants derived from by-products have gained popularity as sustainable alternatives to inorganic coagulants in water/wastewater treatment due to their abundant availability, biodegradability, low cost, easy disposal and low sludge volumes. In this study, the mucilage obtained from the peel of Opuntia ficus-indica fruit was evaluated as a biocoagulant for treating synthetic turbid water and compared with a traditional chemical coagulant (FeCl3). The effects of coagulant dosage and pH on the turbidity and color-removal efficiency of synthetic turbid water were analyzed. To estimate the coagulation mechanism, the flocs produced under optimal values were characterized structurally (FTIR and zeta potential) and morphologically (SEM). The optimal condition for the removal of turbidity and color was a coagulant dose of 12 mg/L at pH 13. For the optimal values, the biocoagulant and the FeCl3 presented a maximum removal of 82.7 ± 3.28% and 94.63 ± 0.98% for turbidity and 71.82 ± 2.72% and 79.94 ± 1.77% for color, respectively. The structure and morphology of the flocs revealed that the coagulation mechanism of the mucilage was adsorption and bridging, whereas that of FeCl3 was charge neutralization. The results obtained showed that the mucilage could be used as an alternative coagulant to replace FeCl3.

Preparation of polyaluminium silicate sulphate by gravity supercritical method and its coagulation in oily sewage

In this work, different synthetic methods of polymeric aluminum silicate sulfate (PASS) and their coagulability to oily sewage were comparatively studied. PASS was synthesized by two methods: gravity supercritical method and basic titration method, denoted as PASS-B and PASS-S, respectively. The results show that the PASS prepared by gravity supercritical method has better Alb and stability. By applying two coagulants to oily sewage, it was found that PASS-B exhibited better turbidity and oil removal. It was found that PASS-B still has good coagulation by testing its coagulation after placing the coagulant for 2 months. In acidic test water, PASS-B exhibited stronger deprotonation ability. Finally, the polymerization mechanism and coagulation mechanism of PASS-B were analyzed in combination with Al morphology distribution and coagulation experiments. Gravity supercritical method as a new polymerization method may replace the traditional preparation method of inorganic polymer coagulants in the future, especially in large-scale applications.

An all-organic conditioning method to achieve deep dewatering of waste activated sludge and the underlying mechanism

Among the common treatment/disposal routes of excessive activated sludge from municipal wastewater treatment plant, dewatering process functions as an essential pre-/post-treatment for volume minimization and transportation facilitation. Since inorganic coagulants have long been criticized for their high dosage and solid residue in sludge cake, there is an urgent need for investigations regarding the potential of applying organic chemicals as the conditioner. In this study, combined use of poly dimethyldiallylammonium chloride (PDMD) and tannic acid (TA) were investigated as an all-organic co-conditioning method for sewage sludge pre-treatment. Results showed that this all-organic conditioning strategy can effectively improve the dewaterability of sewage sludge. The capillary suction time reduced from 128.8 s to 23.1 s, and the filtration resistance reduced from 1.24 × 1012 cm/g to 7.38 × 1010 cm/g. The moisture content of dewatered sludge cake decreased to as low as 55.83%, showing the highest dewatering efficiency reported so far. In addition, the combination of PDMD and TA maximized the treating efficiency with very limited consumption of conditioners (added up to 4% of total solid). Based on the physic-chemical and rheological property investigation, it was proposed that the intermediate molecular weight polymer-based flocculation process and the TA agent-based protein precipitation process, could remarkably strengthen the compactness and structure robustness of sludge. In all, this PDMD-TA-based conditioning method suggested practical significance in consideration of its cost-effectiveness and disposal convenience of sludge cake.

Enhanced removal of trace pesticides and alleviation of membrane fouling using hydrophobic-modified inorganic-organic hybrid flocculants in the flocculation-sedimentation-ultrafiltration process for surface water treatment

Pesticide concentrations in surface water occasionally exceed regulated values due to seasonal events (rainy season in high intensity agricultural areas) or intermittent discharges (leakage, spillage, or other emergency events). The need to remove pesticide compounds in these situations poses a challenge for drinking water treatment plants (DWTPs). In this work, the performance of dosing hydrophobic-modified inorganic-organic hybrid flocculants (HOC-M; lower acute toxicity than corresponding metal salt coagulants; acceptable economic costs when M=Al or Fe; prepared in large-scale quantities), for the removal of four different pesticides (each initial concentration: 0.25 μg/L) from Yangtze River water, and in mitigating membrane fouling, by an integrated flocculation-sedimentation-ultrafiltration (FSUF) process, was evaluated over a period of 40 days; the FSUF is well-established in many DWTPs. The mechanisms underlying the treatment were unveiled by employing a combination of instrumental characterizations, chemical computations, material flow analyses, and statistical analyses. Efficient pesticide removal (80.3%∼94.3%) and membrane fouling reduction (26.6%∼37.3% and 28.3%∼57.6% for reversible and irreversible membrane resistance, respectively) in the FSUF process were achieved by dosing HOC-M, whereas conventional inorganic coagulants were substantially inferior for pesticide removal (< 50%) and displayed more severe fouling development. Hydrophobic association between the pesticides and the hydrophobic organic chain of HOC-M played a predominant role in the improvement in pesticide removal; coexisting particulate/colloid inorganic minerals and natural organic matter with HOC-M adsorbed on the surface, acting as floc building materials, provided sites for the indirect combination of pesticides into flocs. The observed fouling alleviation from dosing HOC-M was ascribed to both the pre-removal of fouling-causing materials in the flocculation-sedimentation prior to UF, and a stable hydrophilization modification effect of residual HOC-M in the UF unit. The latter effect resulted from a hydrophobic association between the PVDF substrate of the membranes and the hydrophobic organic chains of the HOC-M, causing the hydrophilic ends of the HOC-M to be exposed away from the membrane surface, thereby inhibiting foulant accumulation. This work has not only demonstrated the superior performance of dosing HOC-M in the FSUF process for trace pesticide removal in DWTPs, but also clarified the underlying mechanisms.

Solid–Liquid Separation of Dairy Barn by Electrocoagulation with Cationic Polymer Coagulant

High–molecular-weight polymer coagulants are widely used in wastewater treatment combined with traditional inorganic coagulants to improve the solid–liquid separation efficiency. However, it is desirable to keep chemicals used in treatments at minimum levels for economic and safety reasons. This study aimed to increase the efficiency of two-stage electro- and chemical-coagulation treatment with a minimum chemical dosage for the separation of solids and liquid in dairy manure slurry for the safe composting of solids and safe discharge of wastewater. Accordingly, dairy manure slurry was treated with aluminum (Al) coagulants, such as polyaluminum chloride (PAC), aluminum chloride (AlCl3), and aluminum sulfate (Al2(SO4)3), PAC combined with the cationic polyacrylamide (CPAM), and PAC and CPAM combined with electrocoagulation (EC). Results revealed that PAC was the best among the Al coagulants evaluated for the reduction in turbidity in the liquid fraction at a dosage of 100 mg/L. PAC dosage was reduced to 40 mg/L when the treatments were combined with CPAM at a dosage of 40 mg/L, which was further reduced to 30 mg/L when treatments were combined with 5 min EC and 20 mg/L of CPAM dosage.

The last 25 years of research on bioflocculants for kaolin flocculation with recent trends and technical challenges for the future.

The generation of kaolin-containing wastewater is an inevitable consequence in a number of industries including mining, wastewater treatment, and bitumen processing. In some cases, the production of kaolin tailings waste during the production of bitumen or phosphate is as high as 3 times greater than the actual produced product. The existing inventory of nearly five billion barrels of oil sands tailings alone represents a massive storage and reclamation challenge, as well as a significant economic and environmental liability. Current reclamation options like inorganic coagulants and organic synthetic polymers may settle kaolin effectively, but may themselves pose an additional environmental hazard. Bioflocculants are an emerging alternative, given the inherent safety and biodegradability of their bio-based compositions. This review summarizes the different research attempts towards a better bioflocculant of kaolin, with a focus on the bioflocculant source, composition, and effective flocculating conditions. Bacillus bacteria were the most prevalent single species for bioflocculant production, with wastewater also hosting a large number of bioflocculant-producing microorganisms while serving as an inexpensive nutrient. Effective kaolin flocculation could be obtained over a broad range of pH values (1-12) and temperatures (5-95°C). Uronic acid and glutamic acid were predominant sugars and amino acids, respectively, in a number of effective bioflocculants, potentially due to their structural and charge similarities to effective synthetic polymers like polyacrylamide. Overall, these results demonstrate that bioflocculants can be produced from a wide range of microorganisms, can be composed of polysaccharides, protein or glycoproteins and can serve as effective treatment options for kaolin. In some cases, the next obstacle to their wide-spread application is scaling to industrially relevant volumes and their deployment strategies.

Synthesis and characterization of polyamine-based polyelectrolytes for wastewater treatment in the sugar industry

The treatment of sugar industrial effluent is an enormous task because of the very high load of turbidity, chemical oxygen demand (COD), biological oxygen demand (BOD), total suspended solids (TSS), high or low pH value and oil & grease. The polyelectrolyte in conjunction with inorganic coagulant was used successfully for its treatment. Four new polyamine-based cationic polyelectrolytes have been synthesized. These polyelectrolytes were characterized by FTIR, 13C NMR, 1H NMR, gel permeation chromatography (GPC), and were exploited in the sugar industry wastewater. Cationicity of polyelectrolytes was also determined, and the polyelectrolytes’ efficiency was calculated at different coagulants and flocculants dosages. Based on the result obtained by four polyelectrolytes, it was observed that polyelectrolytes with a 1.5:1 molar ratio of epichlorohydrin: diphenylamine has given the best result in the removal of pollutants from sugar industry wastewater. The result was found to be consistent in all kinds of pollutants of sugar industry suspension with a 1.5:1 molar ratio of epichlohydrin: diphenylamine polyelectrolytes.

High-efficiency leaching of Al and Fe from fly ash for preparation of polymeric aluminum ferric chloride sulfate coagulant for wastewater treatment

Preparation of inorganic polymer coagulants from circulating fluidized bed (CFB) fly ash is one of the most significant value-added and environment-friendly approaches. Nevertheless, CFB fly ash presents relatively low solubility in acidic systems, which limits its utilization efficiency. In this paper, enhanced metal leaching from CFB fly ash using combined HCl-H2SO4 leaching process for polymeric aluminum ferric chloride sulfate (PAFCS) preparation was proposed. PAFCS with the different molar ratios of Al3+/SO42− and Al3+/Fe3+ were prepared from as-obtained leaching liquors and characterized by SEM, XRD, FTIR, and coagulation experiments. The leaching efficiencies of Al and Fe in CFB fly ash were up to 96.75% and 97.64% by combined HCl-H2SO4 leaching process. The optimal molar ratios of Al3+/SO42− and Al3+/Fe3+ for the turbidity and UV254 removal were 10:1 and 10:1, respectively, due to the three-dimensional chain-net structure and the highest [Al + Fe]b content. When applied to biochemical effluent of coking wastewater treatment, PAFCS exhibited excellent removal performance on both humic acid-like and fulvic acid-like matters. The resultant flocs of PAFCS presented the largest recovery factor (Rf = 0.37) and strength factor (Sf = 0.79) in contrast with PAC and PAFC. This work provides a novel and high-efficient Al and Fe leaching strategy from CFB fly ash to prepare Al-Fe coagulant.

STUDY OF THE PROCESSES OF WASTEWATER TREATMENT FOR REUSE IN THE PULP AND PAPER INDUSTRY

Nowadays, more than 80% of cardboard and paper products of Ukrainian mills are made from waste paper – secondary fibers that differ in their chemical and physical properties from primary cellulosic fibers. Characteristic feature of secondary fibers is the presence of a large number of small fibers, which negatively affects the quality of finished products, mass retention on the grid during the formation of paper or cardboard, which leads to pollution of wastewaters. Despite its environmental friendliness and economy, waste paper is also characterized by the presence of various pollutants, the formation of which is associated with the process of paper formation, storage of finished products, and their use. As a result of the preparation of the mass from secondary fibers, there is a transition of pollutants from the waste paper to the wastewater in the form of colloidally dispersed and soluble substances, which lead to the pollution of circulating water. Purification of water and its reuse in technological processes is an important task of paper industry mills. The results show that more than 90% of the secondary fibers have a length that does not exceed 1 mm, while in the primary cellulose fiber from coniferous wood about 53% of the fibers have a length of more than 1 mm. The high content of short fibers in the paper mass affects the processes of paper formation, worsening them, and a decrease in the retention of the fiber on the grid of the paper or cardboard machine is observed, causing the pollution of wastewater. The results of the study of coagulation of industrial wastewater with the content of suspended solids 1520 and 3200 mg/dm3 from the production of cardboard from recycling paper show that the best coagulants are A1(OH)C12 and A12(OH)5C1. The maximum efficiency of water purification of only 92.5% was achieved at the suspended solids content of 1520 mg/dm3, while for wastewater with a suspended solids concentration of 3200 mg/dm3 98.0% was obtained. To develop a scheme for deep purification of wastewaters, it is important to understand which components are removed from water more easily and which are more difficult during coagulation. For this purpose, studies on coagulation of model suspensions of starches, bentonite and kaolin using inorganic coagulants were conducted. It was established that coagulation of native corn starch suspension with inorganic coagulants is effective. However, in the case of using modified starches, the removal of cationic starches is reduced. The efficiency of water purification in the removal of bentonite by sedimentation-filtration with the use of coagulants is quite high. The degree of purification reaches 80.8-98.1%. The filtering stage allows the degree of purification to be further increased. Research on the processes of purification of model kaolin suspensions shows that mechanical and physico-chemical methods are ineffective in removing this mineral filler.