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Common methods for treating surface waters involve chemical flocculation, for which a significant factor contributing to the total cost and climate impact is the consumption of chemicals, chiefly coagulants and pH-adjusting chemicals. The amount of chemicals required for treating surface waters and achieving suitable flocculation pH depends greatly on the alkalinity of the source water. This study investigates the viability of mixing two surface waters with different chemical properties with the aim of reducing the amount of chemicals used during chemical flocculation. Bench-scale experiments were carried out, and the results were compared with full-scale operations at a surface water treatment plant (WTP). The WTP uses ferric chloride as a coagulant, which effectively removes natural organic matter, but consumes large amounts of hydroxide to manage pH before and after flocculation. As an alternative process, this study tested the use of aluminum sulfate, polyaluminum chloride and ferric chloride at varying dosages in combination with different source water mixtures to achieve suitable flocculation pH. The results showed that pH-adjusting chemicals could be omitted by adding a small amount of high alkalinity surface water to the primary source water, thereby reducing costs and climate impact substantially. HIGHLIGHTS Mixing raw waters with different properties could substantially reduce costs and climate impact.; Aluminum sulfate offered potential cost savings of up to 40% and a reduction in climate impact by up to 36% compared to conventional ferric chloride precipitation.; Polyaluminum chloride with high basicity offered a broader coagulant dosage range, reducing the need for pH adjustment and potentially allowing for higher dosages.;

This study aims to recover the used coagulants from two water treatment plants via acidification technique. The water treatment sludge (WTS) was acidified with sulfuric acid (H2SO­4) at variable normalities (0.5, 1, 1.5, 2.0 and 2.5 N). The surface morphology and functionalities of both recovered coagulants were analysed using scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR). The performance of recovered coagulants was tested for turbidity removal in surface water treatment at different coagulant dosages and pH. It was found that the optimum normality of H2SO4 for recovered alum was 1.5 N, where 66% turbidity removal was recorded. The recovered PAC treated with 1.0 N H2SO4 indicated high turbidity removal percentage, which was 50.5%. The turbidity removal increased with increasing coagulant dosage. More than 80% turbidity removal was achieved with 40 mg/L dosage of recovered alum and recovered PAC. Maximum removal (85%) was observed with 50 mg/L dosage of recovered alum. For commercial coagulant, the turbidity removal was higher, with a difference of up to 6% in favor of recovered alum. The potential reuse of coagulants can be explored in order to reduce the operating costs and promotes the reduction of WTS disposal. HIGHLIGHTS Coagulation in water treatment process generates a large amount of sludge.; Water treatment sludge (WTS) are commonly discharged into rivers.; Coagulant recovery from WTS can reduce environmental impact.; Coagulant recovery is a great approach to support water circular economy.;

Currently, a reliable and easy-to-use method to monitor flocculation in the water treatment process is highly demanded, especially for small water purification stations. For this problem, in situ images were used to analyze the flocculation process under different conditions via jar tests. A texture feature of the gray level co-occurrence matrix was found to be helpful for monitoring the floc status, such as growth rate and settling velocity. To further verify this finding, we established the correlation between the texture time sequence curve (TTSC) and its corresponding floc status. The slope of the TTSC during the growth phase and during the settling phase can describe the growth rate and the settling velocity, respectively, i.e., the higher the slope, the higher the growth rate and settling velocity. In addition, significant differences between the TTSCs in various abnormal conditions and the normal condition of coagulation can be identified. By using the TTSC for detecting abnormal conditions, we again verified that the texture feature can reliably reflect the flocculation process. Our study helps to develop a low-cost, stable, and simple method for monitoring flocculation and detecting abnormal conditions, which can effectively be used in the operation and management of water treatment plants. HIGHLIGHTS Compared with the morphological features, the texture features are more stable.; The texture time sequence curve (TTSC) can describe flocculation.; Variation characteristics of TTSC can detect abnormal coagulation conditions.; TTSC-based methods can be readily applied online.;

Diatom is a unicellular photosynthetic microalga that is found in diverse environments. These are decorated with siliceous cell walls called frustules. Diatoms have long been favoured by grazers such as microscopic protozoa and dinoflagellates. However, grazers typically remain intact in laboratory culturing and feed on diatom in culturing vessels and reducing biomass yield. The isolation and cultivation of diatoms in laboratories hamper diatoms’ diversity and vast industrial potential. Chitosan, a biopolymer, has been widely used with other polyelectrolytes to flocculate various organic and inorganic colloids at acidic pH. Dissolved chitosan (acidic pH) has been used in various natural water samples and wastewater system for dewatering. However, untreated chitosan flakes have never been evaluated in a heterogeneous natural water environment. Since diatoms have silica surfaces, we tested chitosan for diatom separation and optimized chitosan concentration and other parameters to obtain grazer-free diatom starter culture from raw water. We also elucidated the mechanism for chitosan flakes-mediated diatom flocculation through adsorption kinetics and molecular dynamic simulation analysis. The results of this study are statistically optimized and validated, with a significant R2 value of 0.99 for the proposed model. HIGHLIGHTS Flocculation-based separation of diatoms from natural water samples is presented here.; The possibility of enrichment for less abundant diatom species is done by this method.; The method will reduce the labour associated with the serial dilutions and pure culture preparation.;

A mechanical flocculation system with multi-chambers in series is commonly used as the advanced phosphorus removal technology for wastewater treatment. This work aims to numerically investigate the inner states and overall performance of industrial-scale mechanical flocculators in series. This is based on our previously developed computational fluid dynamics (CFD) flocculation model which is extended to consider the key chemical reactions of phosphorus removal. The effects of the number of flocculation chambers, locations, and sizes of the flocculation chamber connection as well as operational combinations of impeller speeds are investigated. With a decreasing number of flocculation chambers, the main vortexes and chemical reactions are weakened, while the small flocs form. Both the phosphorus removal efficiency η and the average floc size dp reduce as the number of flocculation chambers decreases. The connection location of flocculation chambers directly determines the turbulent flow, thus influencing the key performance indicators. However, the phosphorus removal efficiency η and average particle size dp are little affected by the size of the flocculation chamber connection. As the impeller speeds in series gradually increase, the gradient of floc size distribution in each chamber is enlarged and the chemical reaction is enhanced over the working volume. HIGHLIGHTS Effects of geometry and operational conditions on mechanical flocculators in series are investigated.; This work is done by further developing a CFD flocculation model which is extended to consider the key chemical reactions of phosphorus removal.; The fluid flow, chemical reactions and flocs dynamics are captured successfully.; Results are analyzed in terms of the internal states and overall performance.;

Floc-particle size in drinking water treatment is an important parameter for designing and operating clarification and filtration units. However, advanced techniques for floc characterization are not affordable in drinking water utilities in developing countries because they are expensive and require qualified and training personnel. Therefore, the main objective of this research was to develop and test a nonintrusive low-cost methodology for floc size characterization using a regular HUAWEI P30 cell phone equipped with 40 megapixels camera, which is significantly less expensive than a sophisticated high-speed high-resolution camera used for floc characterization based on image analysis. This technique does not require sample processing, which keeps unaltered floc/particles aggregates for analysis. The methodology was calibrated using four different source waters with low turbidity (≤5.95±0.48 NTU) and relatively low alkalinity (≤52.4± 4.12 as CaCO3), which are typical from the Andina Region in Colombia. This methodology demonstrated to be useful for obtaining the mean floc size (based on average Feret diameter), floc area, floc perimeter and circularity of aggregates formed by the addition of alum [Al2(SO4)3*18H2O] after 15 minutes of flocculation in a regular jar tester. The methodology also proved to be valuable for measuring floc sizes in a range between 33 μm and 1,200 μm. HIGHLIGHTS Development of a low-cost methodology for flocs size characterization in developing countries.; Determination of floc physical characteristics, mean diameter, perimeter, area, and circularity.; Impact of raw water turbidity and coagulant dose on flocs size.; Calculation of the floc settling velocity in sedimentation units.;

Recent research has shown that the equilibrium between aggregation and breakup in flocculation kinetics modelling may not hold due to irreversible floc breakup. This work investigated the influence of the coagulant/particle ratio and average velocity gradient () in the occurrence of this phenomenon with a different water matrix than previous research. Jar test assays were conducted with low (≈15 NTU), medium (≈50 NTU) and high (≈100 NTU) turbidity synthetic raw water, using alum as coagulant and kaolin as primary particles. Results were analyzed using Argaman and Kaufman's model and values for KA (aggregation constant) and KB (breakup coefficient) were determined with the evolutionary convergence method. Model fitting was satisfactory when the Al/particle ratio varied between 10 and 27 mg Al3+/g. Outside this range, residual turbidity increased after equilibrium, attributed to the irreversible floc breakup process and not adequately described by the model. A two-factor analysis of variance (ANOVA) was conducted, and the results indicated a plausible correlation between pKA (–log KA) and Al/particle ratio. As for pKB (–log KB), the results indicated a possible correlation with both Al/particle ratio and . The results suggest that the irreversible floc breakup may occur regardless of the water matrix composition. HIGHLIGHTS Equilibrium between aggregation and breakup processes in Argaman and Kaufman's original model may not hold.; Residual turbidity increase was observed and attributed to the irreversible floc breakup process.; This phenomenon was not adequately captured by Argaman and Kaufman's original model.; Coagulant/particle ratio may play a critical role.; The irreversible floc breakup may occur regardless of the water matrix.;

This research aimed to create a novel technique for recovering fertilizers from aquaculture effluent to overcome potential non-renewable fertilizers shortages. There are two steps: a photocatalyst technique for nutrient mobilization, succeeded by solids precipitating with two natural and one synthetic flocculants. The photocatalytic degradation of organonitrogen compounds in batch experiments started under the irradiation of sunlight. Following that, photocatalytic breakdown of organonitrogen compounds produces inorganic nitrogen constituents like NH4+, NO2−, and NO3−, which could be used as manure. It was found that, after 12 h of circulation, the concentration of inorganic nitrogen became NH4+ = 17.2 g/L, NO2− = 18.1 mg/L, and NO3− = 15.9 mg/L. The jar test was adopted to assess the capacity of two natural compounds (tamarind kernel polysaccharide (TKP) and tannin-based substance (TBS)) and synthetic water-soluble polymer cationic polyacrylamide (SWP) to reduce turbidity, total suspended solids (TSS), chemical oxygen demand (COD) and colour. The findings revealed that with a dose of 20 mg/L of TBS, 20 mg/L of TKP, and 50 mg/L of SWP, the maximum turbidity reductions were 95, 93, and 94%, respectively. The TBS was slightly better than TKP and much better than SWP in terms of coagulation activities with TSS, COD and colour maximum removal efficiencies. HIGHLIGHTS Remediation aquaculture effluent to overcome potential non-renewable fertilizers shortages.; In this work, the photocatalytic degradation of organonitrogen was studied.; Two natural flocculants were used in the treatment process.;

Coagulation and sedimentation process is one of the most popular processes in drinking water treatment. Hydrodynamic breakage has a significant impact on the evolution of floc characteristics and the efficiency of turbidity removal. In this work, the effects of hydrodynamic breakage on floc size, fractal dimension, and floc morphology were investigated with an in-situ recognition system. The experiments were conducted in a continuous flocculation and sedimentation reactor equipped with perforated plates to provide different hydrodynamic breakage conditions. The experimental results indicated that the hydrodynamic conditions significantly influenced the floc destabilization and restructuring processes. A low hydrodynamic shear force provided by P1 led to the increase of both bigger sized flocs but accompanied with small particles (0–10 μm). Excessive velocity gradient provided by P3 produced smaller and looser flocs. An appropriate velocity gradient (i.e., the flow velocity through the perforated plate P2 at 18.9 × 10−3m s−1) was conducive for the formation of larger and more compact structures, with higher average floc size and fractal dimension. This flocculation condition in turn resulted in effective improvements in the turbidity removal efficiency. Floc evolution models were described based on the mechanism of the breakage and restructuring process. HIGHLIGHTS Hydrodynamic effects on flocs properties were revealed in a flocculation and sedimentation reactor.; Evolutions of flocs was recorded by an in-situ recognition system.; Moderate breakage (G = 69 s−1) promoted the generation of larger flocs.; Moderate breakage helped to increase the settleability of flocs.;

Alginates are quite abundant in nature as they occur both as a structural component in marine brown algae (Phaeophyceae) comprising up to 40% of dry matter and as capsular polysaccharides in soil bacteria. Alginic acid is the only polysaccharide, which naturally contains carboxyl groups in each constituent residue, and possesses various abilities for functional materials. Experiments were carried out for water of turbidity 300 NTU. Alginate as such doesn't act as a coagulant, instead it should be converted to calcium alginate by adding calcium ions. Calcium chloride was used for imparting calcium ions necessary for the reaction. The dosage of calcium was fixed as 50 mg/L, 75 mg/L, 100 mg/L, 150 mg/L, 200 mg/L, and alginate doses between 2 to 10 mg/L. Calcium dosage below 50 mg/L was not sufficient for the formation of the egg-box structure which is responsible for the coagulation and flocculation process. For the mechanism of charge neutralization to take place effectively, calcium should be added first followed by alginate. pH and conductivity of the sample remain constant before and after the treatment. The dosage of alginate required for the treatment is less, so the cost of treatment also will be much less, thus alginate can replace the usage of chemical coagulants like alum. HIGHLIGHTS Alginate, a natural and renewable bio-flocculant, produces no secondary pollution and hence can be used as potential coagulant for drinking water purposes.; Unlike other coagulants, the pH and conductivity of the treated water do not change.; The concentration of Ca ions is well within the desirable limit after treatment.;

The method of flocculation of biomass from the water depth to the bottom can be applied in case of local algae blooms. In our research, the combined application of FeCl3 and Polyethyleneoxide-based cationic flocculant was applied for the first time for the harvesting of the enrichment culture obtained from the reservoir during eutrophication. The effects of coagulant (FeCl3·6H2O), various flocculants based on polyacrylamide (PAA), polyethylenoxide (PEO) and flocculated biomass as ballast agent, dosage and sedimental time on flocculation efficiency of harvesting enrichment culture obtained from Pond Chernoistochinsky during eutrophication have been studied. The results show that the flocculation efficiency achieved about 90% after 5 min of sedimentation when adding coagulant and flocculant mixture (FeCl3 30 mg/L + PEO based Sibfloc-718 2.5 mg/L) or flocculant with ballast agent (FeCl3 30 mg/L + Sibfloc-718 2.5 mg/L + 1,7% flocculated biomass). PAA, PEO and FeCl3·6H2O did not demonstrate a sufficient flocculation capacity with enrichment culture containing different types of microalgae. HIGHLIGHTS Combined application of FeCl3 and polymeric flocculant was successfully applied for sedimentation of enrichment culture obtained from an eutrophic pond.; The use of flocculants has been shown to be a promising method of biomass concentration in water bodies.; Application of flocculated biomass as ballast agent for further biomass flocculation was shown to be effective.;

In the pursuit of a treatment approach that is both cost-effective and environmental-friendly, the applicability of microscreen (MS) techniques coupled with a primary sedimentation tank (PST) as a physical advanced primary treatment (APT) to enhance the removal of particulate organic carbon (POC) from municipal wastewater was investigated. A pilot unit, including a modified MS, adjustable to different meshes (including 20 and 15 μm) was operated continuously downstream to the PST at the Büsnau wastewater treatment plant in Stuttgart, Germany, and monitored for more than half a year. A strategy involving time-dependent backwashing and recirculation of MS permeate was employed to remove as much POC as possible from primarily treated wastewater, thereby extending the application of the MS. The optimal configuration, PST + 15-μm MS, achieved maximum removal efficiencies of 90% for turbidity, 90% for total suspended solids (TSS), and 80% for total chemical oxygen demand (TCOD). These results are significant, as comparable removal levels for these parameters were conventionally achieved using less eco-friendly methods such as physiochemical APT, including coagulation-flocculation with iron or aluminum salts followed by microscreening or sedimentation. However, this study's findings ascertained that solo physical APT applications could produce equivalent effluent quality with a much smaller footprint while keeping the advanced primary treated wastewater suitable for biological treatment.

This study involved synthesising new hybrid polymers called ZOPAT, made up of zinc oxide, acrylamide, and tannin, using a blended technique. The effectiveness of ZOPAT in treating textile wastewater was then tested by measuring floc growth rate, flocculation index, strength factor, and recovery factor under optimised conditions. The study also identified the zeta potential, morphology, elemental composition, and functional groups of the polymers. Response surface methodology determines the optimal pH and ZOPAT dose, resulting in 93% colour, 80% chemical oxygen demand (COD), 100% turbidity, and suspended solids (SS) removal at pH 9.22 and 737 mg/L ZOPAT. The study found that ZOPAT was more effective than commercial Polyaluminium chloride in reducing colour and COD, producing larger and stronger flocs, and requiring a shorter coagulation time of 17.5 min. ZOPAT was also easy to homogenise and operate due to its one-unit dosing system. The study attributes the success of ZOPAT to the presence of Zn, N, and K, which create electrostatic attraction with opposite charged particles, and the formation of dye-particle-dye with amide, hydroxyl, and carboxyl groups in ZOPAT, which remove colour, turbidity, COD, and SS. Overall, the study concludes that ZOPAT has significant potential for textile wastewater treatment.

A treatment and volume reduction process for a spent uranium-antimony catalyst has been developed. Targeted removal, immobilization and disposal of the uranium component has been confirmed, thus eliminating the radiological hazard. However, significant concentrations of antimony ([Sb]≥25-50 mg L-1) remain in effluent from the process, which require removal in compliance with Korean wastewater regulations. Antimony(III/V) removal via co-precipitation with iron has been considered with optimal pH, dose and kinetics being determined. The effect of selected anions -- Cl-, SO42- and PO43- -- have also been considered, the latter present due to a prior uranium removal step. Removal of Sb(III) from both Cl- and SO42- media and Sb(V) removal from Cl- media to below release limits were found to be effective within 5 minutes at an iron dose of 8 mM (molar ratio, [FeIII]/[Sb] = 20) and a target pH of 5.0. However, Sb(V) removal from SO42- was significantly hampered requiring significantly higher iron dosages for the same removal performance. Phosphate poses significant challenges for the removal of Sb(V) due to competition between PO43- and Sb(OH)6- species for surface binding sites, attributed to similarities in chemistries and a shared preference for an inner vs outer binding mechanism. [ABSTRACT FROM AUTHOR]

In this paper, the removal performance and mechanism of xanthated chitosan (XCTS) towards heavy metal ions are investigated. XCTS possesses both strong chelating abilities and excellent flocculation properties, which can effectively remove several kinds of heavy metal ions, such as Cr3+, Cu2+, Mn2+, Ni2+, Pb2+ and Zn2+. It has a good potential for practical application. In a flocculation test of a mixed component solution, the removal rates of Cr3+, Cu2+ and Cd2+ reach 100%, 100% and 99.1%, respectively. The removal rates are significantly greater than that of a single component solution. It indicates that there is a synergistic effect between different metal ions. Moreover, the selectivity of XCTS for Cr3+ and Cu2+ is obviously superior to that for Cd2+; XCTS is easier to combine with the heavy metal ions belonging to hard acids. [ABSTRACT FROM AUTHOR]

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 33-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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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), 194.0-320.0 mg/L (mean 246.7 mg/L), respectively. The range of PACS dosage concentration was 6.0-7.1 mg/L (mean 6.7 mg/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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Particles are a concern regarding tunneling wastewater, but gaps remain in understanding metal(loid)s content and coagulation efficiency. In this research, characterization of the wastewaters before and after treatment was investigated by chemical analysis and various techniques for particle characterization. Then, laboratory work was conducted to evaluate effectiveness of sedimentation and use of coagulants to remove particles and particle-associated contaminants. Both natural (chitosan) and chemical coagulants (ferric chloride sulfates and polyaluminium chloride solution), were applied in a jar test system. The results indicated that short-time sedimentation alone substantially reduced the particle content and particle-associated pollutants, including metal(loid)s, while subsequent chemical coagulation was required to comply with discharge limits. The optimum dosages of chitosan, PIX, and PAX for water 1 after pre-treatment (15 min sedimentation) were 1 mg/L, 3 mg Fe/L, and 3 mg Al/L, respectively, while a dosage of 2 mg Al/L gave the best results in water 3. Furthermore, chemical coagulation significantly decreased the volume density of particles in the diameter range of 1-100 μm, showing that coagulants are efficient for the removal of smaller particles not removed by conventional sedimentation.

A series of carboxymethyl starches (CMSs), with various degrees of substitution from 0.1 to 0.79, were synthesized and selected as a model to study the feasibility of using natural polymers as flocculants for oil sand tailings treatment. The flocculation performance of modified CMS in kaolin clay suspensions and oil sand tailings was evaluated in terms of settling rate, solids content, capillary suction time, and specific resistance to filtration of the sediment phase. It was found that the synthesized CMS effectively accelerates settling of kaolin suspensions and oil sand fine tailings, thus demonstrating the feasibility of this application. [ABSTRACT FROM AUTHOR]

The purpose of this study was to monitor the presence of Cryptosporidium spp. and Giardia duodenalis in a water treatment plant (WTP) using settling sludge and backwash water (BW) samples in previous and post the deflocculation of polyaluminium chloride (PAC) flacks. Eleven collections were performed. BW and settling sludge (SSF) were concentrated by calcium carbonate flocculation, and another aliquot of settling sludge (SSC) by centrifugation. The samples were divided as follows: Group A, containing 33 samples without degradation of PAC flakes, and Group B, with degradation by alkalinization with 10 M NaOH. Sample DNA was extracted with a commercial kit, and nested polymerase chain reaction (PCR) was used to detect Cryptosporidium and G. duodenalis. All samples from Group A were negative for Cryptosporidium spp., and 6.1% (2/33) were positive for G. duodenalis in SSC samples. While the absence of Cryptosporidium may be due to a low contamination level of the water resource, the presence of G. duodenalis indicates contamination of the raw water. The detection of G. duodenalis in SSC samples indicates that this detection method was the most effective. The 33 samples from Group B were negative for both protozoa, probably due to the presence of aluminium and humic substances. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The objective of this study was to investigate the ability of cactus Opuntia ficus-indica, used as a natural flocculant in the treatment of phosphate clay as an industrial wastewater. It is a new process that has proven very promising in the removal of high turbidity from industrial effluents. The volume of clear water recovered (supernatant) is one of the characteristic features which allow us to judge the effectiveness of this bioflocculant. The following of the settling velocity on the one hand and the analysis of supernatant and sludge on the other hand allow us to compare the cactus-based flocculant effectiveness with that of a chemical flocculant (CF) of anionic polyacrylamide nature. The optimum pH required for maximum settling velocity was found to be 12. Obtained results indicated that after 900 seconds of settling, the highest volume of clear supernatant was obtained with the natural flocculant (740 mL/L), against 666 mL/L obtained with CF. Several analyses on recovered clear water (pH, turbidity, Cu, Zn, Fe, Cd and Cr) and on dry sludge (P2O5, CaO, MgO, organic C, SiO2 and Cd) are highlighted. [ABSTRACT FROM AUTHOR]

The pH value of oil acidized wastewater is relatively low (pH = 6.1), which seriously affects the flocculation of polyacrylamide (PAM). NaOH was used to adjust the pH value, but the maximum was only 7.5. The regulation was limited as the Ca2þ in aqueous phase up to 1,350 mg L-1 consumed OH-. A novel formulation of Na2CO3 þ PAM was proposed to form CaCO3 floc core to facilitate PAM coagulation. When the concentration was above 400 mg L-1, the PAM precipitation tended to be maximum, followed by NaOH adjustment of pH to 8.0 that could enhance PAM flocculation successively. The sewage sludge (SS) remained and residue oil reduced to 25 mg L-1 and 34 mg L-1 respectively. The analysis of the species and composition of fatty acids indicated that the coagulation-flocculation selectively effected the sedimentation of saturated fatty acids (SAT). This provides a new idea for recovery of high value-added residual oil. The optimal additive of Na2CO3 is expected as promising coagulant aid to improve the PAM coagulation-flocculation of oil acidized wastewater. [ABSTRACT FROM AUTHOR]

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 perimeterbased 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. [ABSTRACT FROM AUTHOR]