Enhanced coagulation process for removing dissolved organic matter, microplastics, and silver nanoparticles.

Dissolved organic carbon (DOC), microplastics (MPs), and silver nanoparticles (AgNPs) in water are of major concern because of their direct and indirect toxic effects on aquatic organisms and human exposure via water. This work investigated the effect of poly aluminum chloride (PACl) coagulation for reducing DOC, MPs, and AgNPs. This work used water from a canal in Thailand with a DOC of 5.2 mg/L in the experiment. AgNPs of 5-20 mg/L were added to canal water to create synthetic water for the PACl coagulation. Polyethylene and polypropylene (PP) type MPs were identified in the raw water with Fourier transform infrared spectroscopy. Coagulation with 15 mg/L of PACl performed better in the PP removal. The PACl coagulation at dosages of 15, 40, and 70 mg/L removed DOC by 16-20%, 44-52%, and 46-63% and AgNPs by 34-90%, 53-93%, and 81-95%, respectively. The presence of AgNPs at high levels could inhibit the efficiency of DOC reduction by the PACl coagulation. The FESEM identified the adsorption of silver-containing nanoparticles onto the flocs with increased dosages of PACl. So, PACl is a coagulant in the removal of AgNPs that can reduce health hazards and eco-toxicological risks in water sources due to the release of silver.

Reduction by enhanced coagulation of dissolved organic nitrogen as a precursor of N-nitrosodimethylamine.

Raw water from the Banglen (BL) water treatment plant (WTP) and Bangkhen (BK) WTP in central Thailand and Hatyai (HY) WTP in southern Thailand was investigated for dissolved organic nitrogen (DON) reduction. The DON(mg N/L) and the dissolved organic carbon (DOC)/DON ratio were 0.34 and 21, 0.24 and 18, and 1.12 and 3 for the raw waters from BL, BK, and HY WTPs, respectively. Polyaluminum chloride (PACl) dosages of 150, 80, and 40 mg/L at pH 7 were the optimal coagulation conditions for the raw waters from BL, BK, and HY WTPs, respectively, and could reduce DON by 50%, 42%, and 42%, respectively. PACl and powder activated carbon (PAC, both in mg/L) at 150 and 20, 80 and 20, and 40 and 60 could reduce DON in the raw waters from BL, BK, and HY WTPs by 71%, 67%, and 29%, respectively. DOC/DON values of water treated with PACl were similar to those of raw water. DOC/DON values of water treated with PACl and PAC were lower than those of raw water. N-nitrosodimethylamine (NDMA) formation potentials of raw water, water treated with PACl, or both PACl and PAC, and organic fractions of BL, BK, and HY WTPs were below the detection limits of 542 and 237 ng/L, respectively. Reductions in fluorescence intensities of tryptophan-like substances at peaks 240/350 and 280/350 (nmEx/nmEm) were moderately (correlation coefficient, R = 0.85 and 0.86) and fairly (R = 0.59, 0.67, and 0.75) correlated with DON reduction.

Performance comparison of three methods for detection of Giardia spp. cysts and Cryptosporidium spp. oocysts in drinking-water treatment sludge.

Detecting pathogenic protozoa in drinking-water treatment sludge is a challenge as existing methods are complex, and unfortunately, there are no specific technical standards to follow. Selecting an efficient analytical method is imperative in developing countries, such as Brazil, in order to evaluate the risk of parasite infection. In this context, three methods to detect Giardia spp. cysts and Cryptosporidium spp. oocysts were tested in sludge generated when water with protozoa and high turbidity was treated. Jar testing was carried out using polyaluminium chloride as a coagulant to generate the residue to be analyzed. The results showed that calcium carbonate flocculation with reduced centrifugation and immunomagnetic separation obtained the highest recoveries in the tested matrix showing 60.2% ± 26.2 for oocysts and 46.1% ± 5 for cysts. The other two methods, the first using the ICN 7× cleaning solution and the second considering the acidification of the sample, both followed by the immunomagnetic separation step, also presented high recoveries showing 41.2% ± 43.3 and 37.9% ± 52.9 for oocysts and 11.5% ± 85.5 and 26% ± 16.3 for cysts, respectively. Evidently, these methods and others should be studied in order to make it possible to detect protozoa in settled residue.

[Determination of 7 elements in chemical treatment agent polyaluminium chloride and iron sulfate by inductively coupled plasma mass spectrometry].

OBJECTIVE: To establish a new rapid method for determination of 7elements( arsenic, selenium, mercury, cadmium, chromium, lead and silver) in two kinds of chemical water treatment agents polyaluminium chloride and iron sulfate by inductively coupled plasma mass spectrometry( ICP-MS). METHODS: Pure water was added to two kinds of chemical water treatment agents. Nitric acid was added to the solution, and the solution was incubated by water bath for 1 h. Matrix effects was eliminated by the employment of Sc, Y, In and Bi as internal standards. The concentrations of 7 elements were determined. RESULTS: The linear ranges for 7 elements were between 0 and 50. 0µg/L with a correlation coefficient for each element of higher than 0. 999. The detection limits were between 0. 05 and 0. 96 µg/L, the recoveries were between 90. 1% and106. 4%, the relative standard deviations were between 1. 6% and 5. 7%. The concentration of arsenic, selenium, and lead in certain samples of the 40 samples tested did not meet the health standards. The large majority of the unqualified samples were caused by the concentration of element lead. CONCLUSION: This method is simple, rapid, accurate and sensitive. It is very suitable for the determination of multi-elements inchemical water treatment agents.

Comparison of a novel polytitanium chloride coagulant with polyaluminium chloride: coagulation performance and floc characteristics.

Polymerized inorganic coagulants are increasingly being used in the water supply and wastewater treatment process, yet there is limited research on the development of polytitanium coagulants. The aim of this study is to synthesize polytitanium chloride (PTC) coagulants and investigate their coagulation behavior and floc characteristics for humic acid removal in comparison to polyaluminum chloride (PAC). The PTC samples with different B (molar ratios of OH/Ti) values were prepared using an instantaneous base-feeding method, employing sodium carbonate as the basification agent. The coagulation efficiency was significantly influenced by different B values. The results suggest that the humic acid removal increased with the increasing B value for PAC, while the inverse trend was observed for PTC. The optimum B value was chosen at 1.0 and 2.0 for PTC and PAC, respectively. Under the optimum coagulant dose and initial solution pH conditions, the PTC coagulant performed better than the PAC coagulant and the floc properties were significantly improved in terms of floc growth rate and floc size. However, the PAC coagulants produced flocs with better floc recoverability than the PTC coagulants.

The coagulation characteristics of humic acid by using acid-soluble chitosan, water-soluble chitosan, and chitosan coagulant mixtures.

Chitosan is a potential substitute for traditional aluminium salts in water treatment systems. This study compared the characteristics of humic acid (HA) removal by using acid-soluble chitosan, water-soluble chitosan, and coagulant mixtures of chitosan with aluminium sulphate (alum) or polyaluminium chloride (PACl). In addition, we evaluated their respective coagulation efficiencies at various coagulant concentrations, pH values, turbidities, and hardness levels. Furthermore, we determined the size and settling velocity of flocs formed by these coagulants to identify the major factors affecting HA coagulation. The coagulation efficiency of acid- and water-soluble chitosan for 15 mg/l of HA was 74.4% and 87.5%, respectively. The optimal coagulation range of water-soluble chitosan (9-20 mg/l) was broader than that of acid-soluble chitosan (4-8 mg/l). Notably, acid-soluble chitosan/PACl and water-soluble chitosan/alum coagulant mixtures exhibited a higher coagulation efficiency for HA than for PACl or alum alone. Furthermore, these coagulant mixtures yielded an acceptable floc settling velocity and savings in both installation and operational expenses. Based on these results, we confidently assert that coagulant mixtures with a 1:1 mass ratio of acid-soluble chitosan/PACl and water-soluble chitosan/alum provide a substantially more cost-effective alternative to using chitosan alone for removing HA from water.

Reduction of DOM fractions and their trihalomethane formation potential in surface river water by in-line coagulation with ceramic membrane filtration.

This research was aimed at investigating the reduction of DOM fractions and their trihalomethane formation potential (THMFP) by in-line coagulation with 0.1 µm ceramic membrane filtration. The combination of ceramic membrane filtration with a coagulation process is an alternative technology which can be applied to enhance conventional coagulation processes in the field of water treatment and drinking water production. The Ping River water (high turbidity water) was selected as the raw surface water because it is currently the main raw water source for water supply production in the urban and rural areas of Chiang Mai Province. From the investigation, the results showed that the highest percent reductions of DOC, UV-254, and THMFP (47.6%, 71.0%, and 67.4%, respectively) were achieved from in-line coagulation with ceramic membrane filtration at polyaluminum chloride dosage 40 mg/L. Resin adsorption techniques were employed to characterize the DOM in raw surface water and filtered water. The results showed that the use of a ceramic membrane with in-line coagulation was able to most efficiently reduce the hydrophobic fraction (HPOA) (68.5%), which was then followed by the hydrophilic fraction (HPIA) (49.3%). The greater mass DOC reduction of these two fractions provided the highest THMFP reductions (55.1% and 37.2%, respectively). Furthermore, the in-line coagulation with ceramic membrane filtration was able to reduce the hydrophobic (HPOB) fraction which is characterized by high reactivity toward THM formation. The percent reduction of mass DOC and THMFP of HPOB by in-line coagulation with ceramic membrane filtration was 45.9% and 48.0%, respectively.

An effective algaecide for the targeted destruction of Karenia brevis.

We address the targeted destruction of Karenia brevis using the algaecide calcium peroxide, in tandem with the flocculation and sinking of the species. The specific aspect of the approach is the incorporation of the algaecide within the floc to rapidly kill K. brevis, thus minimizing escape of cells from the floc and reentry to the water column. CaO2 gradually produces H2O2, which diffuses through cell membranes and induces oxidative stress, leading to cell death via excessive reactive oxygen species (ROS) formation. The effect of varying doses of calcium peroxide on K. brevis cells was measured with pulse amplitude modulated fluorometry and indicated that doses as low as 30 mg/L when integrated into flocs are effective in suppressing photosynthesis. Cell viability assays also indicate that such low levels are sufficient to cause cell death in a 3-6 hour time period. Thus, the proposed technology involving the incorporation of calcium peroxide in a cationic flocculating agent (polyaluminum chloride, PAC) leads to an inexpensive and scalable technology to mitigate harmful algal blooms of K. brevis.

Improvement of humic acid (HA) removal using a new inorganic-organic composite coagulant: α-costic acid as a modifier of polyaluminum chloride properties.

In this work, α-costic acid (αCA), a plant sesquiterpenoid from Dittrichia viscosa, was grafted into polyaluminum chloride (PAC), forming a new eco-sustainable composite coagulant PAC-αCA with improved functionality. The α-costic acid fraction grafted into the PAC and the distribution of aluminum forms in the composite coagulant were evaluated for their effectiveness in removing bentonite and humic acid from synthetic water. The interaction mechanism between PAC and α-CA was examined by the Al-Ferron time spectrophotometric method, density functional theory (DFT), and FTIR analysis. By monitoring the aluminum speciation in the composite coagulant PAC-αCA, it was discovered that the introduction of α-CA impacted the distribution of various aluminum forms, including mononuclear Ala, highly polymeric Alb, colloidal, and medium polymeric Alc. The theoretical analysis identified the Alb species as particularly sensitive to reacting with α-CA. Furthermore, coagulation performance tests demonstrated that increasing the percentage of α-CA and promoting the prevalence of Alb and Alc species over Ala species in PAC-αCA led to improved removal of turbidity and UV254. This study provides an attractive and practical option for water treatment plants to remove colloidal suspensions in raw water effectively.

The use of coagulant and natural soil to control cyanobacterial blooms in a tropical reservoir.

Cyanobacterial blooms have been a growing problem in water bodies and attracted attention from researcher and water companies worldwide. Different treatment methods have been researched and applied either inside water treatment plants or directly into reservoirs. We tested a combination of coagulants, polyaluminium chloride (PAC) and iron(III) chloride (FeCl3), and ballasts, luvisol (LUV) and planosol (PLAN), known as the 'Floc and Sink' technique, to remove positively buoyant cyanobacteria from a tropical reservoir water. Response Surface Methodology (RSM) based on Central Composite Design (CCD) was used to optimize the two reaction variables - coagulant dosage (x1) and ballast dosage (x2) to remove the response variables: chlorophyll-a, turbidity, true color, and organic matter. Results showed that the combination of LUV with PAC effectively reduced the concentration of the response variables, while PLAN was ineffective in removing cyanobacteria when combined to PAC or FeCl3. Furthermore, FeCl3 presented poorer floc formation and lower removal efficiency compared to PAC. This study may contribute to the theoretical and practical knowledge of the algal biomass removal for mitigating eutrophication trough different dosages of coagulants and ballasts.

The role of bioturbation triggered by benthic macroinvertebrates in the effectiveness of the Floc & Lock technique in mitigating eutrophication.

Anthropogenic activities have led to excessive loading of phosphorus and nitrogen into water bodies, leading to eutrophication and promoting the growth of cyanobacteria, posing a threat to the health of humans and aquatic animals. Techniques such as Floc & Lock have been developed to mitigate eutrophication by reducing phosphorus concentrations in water and preventing algal blooms. However, little attention has been given to the impact of phosphorus resuspension by sediment-associated organisms such as benthic macroinvertebrates, on the effectiveness of this technique. Here, we experimentally evaluated whether the presence of snails Melanoides tuberculata (Müller, 1774) and larvae of Chironomus sancticaroli (Strixino and Strixino, 1981) affects the efficiency of the Floc & Lock technique. Snails and chironomid larvae are benthic macroinvertebrates commonly found in high abundance in eutrophic reservoirs. Specifically, we tested the hypotheses that (i) the presence of benthic macroinvertebrates reduces the efficiency of coagulants and clays in removing phosphorus and algal biomass from the water column, and (ii) this effect is species-dependent, as some organisms such as the snails, revolve the substrate and resuspend sedimented particles, while other ones, such as chironomid larvae, aid in the removal of phosphorus from the water column by depositing them in the sediment. Our findings revealed that the impact of benthic macroinvertebrates on the effectiveness of the Floc & Lock technique is species-dependent. Chironomid larvae positively influenced the efficiency of the technique by aiding in the removal of total phosphorus, soluble reactive phosphorus, and algal biomass from the water column, depositing them in the sediment. In contrast, the presence of snails had the opposite effect, resulting in increased phosphorus concentration and algal biomass in the water. Surprisingly, the snails consumed the flocs formed by the coagulant and clay within a short time interval of 72 h, raising concerns due to the presence of toxic cyanobacterial biomass in these flocs. Our study emphasizes the importance of considering benthic macroinvertebrates and their impact on the effectiveness of eutrophication management techniques.

Application of a new HMW framework derived ANN model for optimization of aquatic dissolved organic matter removal by coagulation.

Removing dissolved organic matter (DOM) with polyaluminium chloride is one of the primary goals of drinking water treatment. In this study, a new HMW framework was proposed, which divided the factors affecting coagulation into three parts consisting of hydraulic condition (H), metal salt (M), and background water matrix (W). In this framework, H, M and W were assumed to be interacted with each other and combined to determine coagulation efficiency. We investigated the feasibility of the framework to determine the treatment efficiency through mathematical models. Results showed that non-linear artificial neural network (ANN) model was a better fit to the experimental data than the linear partial least squares (PLS) model: the ANN model could explain 76% of the total variations while the PLS could only explain 71%. The PLS did not follow the variations of observed values adequately. These experiments showed that the interaction between the HMW framework components were not simple linear relationships. The ANN model was able to optimize the composition of the HMW framework improving the efficiency of DOM removal through the components of HMW such as velocity gradient (G value), coagulant dosage, solution pH, and background water matrix. Overall, HMW framework is a new classification of factors affecting coagulation, leading to a better understanding of the coagulation process and sensitivity to influencing variables.

Coagulating potential of Iranian oak (Quercus Branti) extract as a natural coagulant in turbidity removal from water.

Because of the presence of tannin in the molecular structure of oak extract, this substance is used as a natural coagulant to remove turbidity from water. The aim of this study was to determine the efficiency of this coagulant alone and in combination with polyaluminium chloride (PACl) in turbidity removal from water under optimal conditions. In this experimental study, Iranian oak extract was prepared by maceration method using ethanol 96% as an extractor. Kaolin was used to prepare synthetic turbid water samples. Using the jar test, the optimum concentrations of oak extract and PACl were determined in various concentrations of initial turbidity and pH. Moreover, the central composite design (CCD) method was utilized to design experiments and RSM was applied for analyzing the obtained results. Optimum concentrations of oak extract and PACl were 62.6 mg/L and 52.6 mg/L, respectively. An increase in initial turbidity and pH led to an increase in turbidity removal by the two coagulants. The efficiency of turbidity removal by oak extract and PACl was 63.5% and 66.5%, respectively. The simultaneous application of oak extract and polyaluminium chloride increased removal efficiency (85%) and reduced the total organic carbon concentration (TOC) in water (42.3%). The results showed that the simultaneous application of Iranian oak extract and polyaluminium chloride had an acceptable performance in removing turbidity from water.

Effects of polyaluminium chloride addition on community structures of polyphosphate and glycogen accumulating organisms in biological phosphorus removal (BPR) systems.

Polyaluminium chloride (PAC) was added into the biological phosphorus removal (BPR) systems to investigate the populations of polyphosphate and glycogen accumulating organisms (PAOs and GAOs). Typical BPR performed under Al:P of 1:1, while BPR almost disappeared at Al:P of 4:1. Even with high PAC addition, PAOs still existed in systems. Compared to the BPR with no PAC addition, the relative abundance of Accumulibacter, Tetrasphaera and Commnadaceae slightly increased with PAC addition. The relative abundance of Dechloromonas was improved from 0.87% to 3.82%, becoming the most dominant PAOs. The specific structures of Accumulibacter and Tetrasphaera changed little, but that of Dechloromonas and Comamonadaceae significantly altered. Regarding the GAOs, the relative abundance of Competibacter and Defluviicoccus significantly declined. Additionally, PAC addition effectively inhibited the proliferation of filamentous bacteria, indicating its potential in inhibiting the sludge filamentous bulking. This study provided guidance for the selection of the phosphorus removal process and operational conditions.

Removal efficiency of phosphorus, cyanobacteria and cyanotoxins by the "flock & sink" mitigation technique in semi-arid eutrophic waters.

Geoengineering techniques have been used to control phosphorus and cyanobacteria in lakes promising greater and quicker chemical and ecological recovery. Techniques that use coagulants and clays to remove particulates and dissolved phosphorus from the water column have received great. In this study, bench-scale "flock & sink" assays were carried out to evaluate the efficiency of the coagulants aluminium sulphate (SUL), polyaluminium chloride (PAC) and chitosan (CHI), alone and combined with natural bentonite clays (BEN) and lanthanum-modified bentonite (LMB), to remove of phosphorus from a eutrophic reservoir in a semi-arid region of Brazil. In addition, the study seeks to assess the effects on the cyanobacteria density and the intra- and extracellular concentrations of cyanotoxins after the application of these geoengineering materials. The SUL and PAC coagulants effectively reduced the total phosphorus (TP), reactive soluble phosphorus (SRP), turbidity, chlorophyll-a, cyanobacteria density and intracellular microcystin, whereas CHI showed a low removal efficiency. Lanthanum-modified bentonite proved to be more effective than BEN; however, the application of the coagulants only was sufficient to successfully remove phosphorus and cyanobacteria from the water column. In addition, the efficiency of the "flock & sink" technique in cell removal varied among the cyanobacteria species. Small colonial species such as Aphanocapsa delicatissima, Merismopedia glauca and Merismopedia tenuissima were removed regardless of the treatment used, including those with CHI and BEN. As for the filamentous cyanobacteria, Cylindrospermopsis raciborskii, Geitlerinema amphibium, Planktothrix agardhii and Pseudanabaena catenata, removal was achieved only using PAC, SUL and LMB alone or when combined. The intracellular concentrations of saxitoxin and cylindrospermopsin and the extracellular fraction of these cyanotoxins and of microcystin were not influenced by the application of coagulants and clays. This indicates that cell lysis did not occur with the addition of the geoengineering materials. These results demonstrate that the "flock & sink" technique could be used for restoration of eutrophic waters.

Optimization of flocculation conditions for soluble cadmium removal using the composite flocculant of green anion polyacrylamide and PAC by response surface methodology.

In this work, we describe a flocculation performance evaluation of a novel anionic polyacrylamide (APAM) synthesized using low dose γ-ray initiation. The APAM structure and morphology were characterized using Fourier transform-infrared spectroscopy (FTIR), High performance liquid chromatography (HPLC), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM) techniques. In comparison to commercially purchased APAM (Mw = 1.0 × 107), γ-ray initiation was demonstrated to be a more effective method to increase molecular weight, decrease the residual acrylamide monomer, and improve thermal stability. Flocculant performance was evaluated by assessing their ability to remove Cd(II) from water. We utilized the Plackett-Burman (PB), steepest ascent, and response surface methodology (RSM) experimental design to identify the optimal flocculating conditions for the removal of soluble Cd(II). Under optimal conditions [26.84 mg L-1 CaO, 71.28 mg L-1 polyaluminium chloride (PAC) and 2.87 mg L-1 APAM], the maximum percent removal of Cd(II) was observed to reach 93.65%. A potential flocculation mechanism for the Cd(II) removal from water was further studied by evaluating the colloid Zeta potential. Results from these studies demonstrated that PAC had a greater capability to change the Zeta potential of collide under alkaline conditions, while APAM played a critical role in the bridging, enmeshment, and sweeping effect. The composite of two types of predominance makes considerable sense in regards to enhancing flocculating efficiency, decreasing secondary pollution, and reducing flocculant cost.

Differences in behaviour of three biopolymer constituents in coagulation with polyaluminium chloride: Implications for the optimisation of a coagulation-membrane filtration process.

Coagulation is often applied as a pre-treatment for membrane processes to reduce dissolved organic matter and to prevent membrane fouling. Biopolymers (BPs) have repeatedly been reported as major organic foulants, and coagulation conditions such as pH or dose have been optimised to minimise the remaining BPs. Optimisation however remains problematic because of the complex and heterogenetic nature of BP. In this study, the behaviour of several BP fractions in a coagulation process was investigated by excitation-emission matrix-parallel factor analysis (EEM-PARAFAC) following liquid chromatography (LC)-fractionation. Using a series of jar tests, we found that BP removal depends on the type of source water, reflecting differences in charge neutralisation conditions in three samples of natural water despite nearly identical processes for removing humic substances. This result demonstrates the complexity of optimisation for BP coagulation. Fractionation of EEM-PARAFAC to BP by LC showed that at least three organic component groups (C1, C2 and C3) constitute BP. C1 is tryptophan-like organic matter that is often found in wastewater effluent, C2 is tyrosine-like organic matter that has a phenolic chemical structure, and C3 is a humic-like substance. C1 was removed thoroughly at acidic pH but not at neutral pH, while the removal of C2 was inefficient even with a significant change in pH or dose, indicating similar difficulties in a coagulation process. The difference in components C1 and C2 may partly explain the difference in efficiencies of removal of BP in water from different sources. Our investigation suggests that the optimisation or selection of appropriate pre-treatment processes for membrane systems should be substantially based on the composition of BPs (e.g., C1 and C2 components).

Comparison of coagulation pretreatment of produced water from natural gas well by polyaluminium chloride and polyferric sulphate coagulants.

This study aimed to optimise coagulation pretreatment of the produced water (PW) collected from a natural gas field. Two coagulants, polyferric sulphate (PFS) and polyaluminium chloride (PACl), were applied separately for the organics, suspended solids (SS), and colour removal. Treatment performance at different coagulant dosages, initial pH values, stirring patterns, and the addition of cationic polyacrylamide (PAM) was investigated in jar tests. The optimal coagulation conditions were dosage of PACl 25 g/L or PFS 20 g/L with that of PAM 30 mg/L, initial pH of 11, and fast mixing of 1.5 min (for PACl) or 2 min (for PFS) at 250 rpm followed by slow mixing of 15 min at 50 rpm for both coagulants. PACl performed better than PFS to remove chemical oxygen demand (COD), total organic carbon (TOC), SS, and colour, and achieved a removal efficiency of 90.1%, 89.4%, 99.0%, and 99.9%, respectively, under the optimal condition; while PFS efficiency was 86.1%, 86.1%, 99.0%, and 98.2%, respectively. However, oil removal was higher in PFS coagulation compared to PACl and showed 98.9% and 95.3%, respectively. Biodegradability, ratio of the biological oxygen demand (five-day) (BOD5)/COD, of the PW after pretreatment increased from 0.08 to 0.32 for PFS and 0.43 for PACl. Zeta potential (Z-potential) analysis at the optimum coagulant dosage of PACl and PFS suggests that charge neutralisation was the predominant mechanism during coagulation. Better efficiency was observed at higher pH. The addition of PAM and starring pattern had a minor influence on the removal performance of both coagulants. The results suggest that PACl or PFS can be applied for the pretreatment of PW, which can provide substantial removal of carbon, oil, and colour, a necessary first step for subsequent main treatment units such as chemical oxidation or biological treatment.

Cinética da floculação: um estudo comparativo no uso do cloreto de polialumínio com alta e baixa basicidade e o sulfato de alumínio / Flocculation kinetics: a comparative study on the use of polyaluminium chloride with high and low basicity and alum

RESUMO O sulfato de alumínio (SA) é amplamente utilizado como coagulante no tratamento de água de abastecimento via ciclo completo. Coagulantes alternativos estão disponíveis no mercado, dentre eles o cloreto de polialumínio (PAC). Porém, estudos comparativos entre o SA e os PACs de alta (PAC-AB) e baixa (PAC-BB) basicidade em relação à cinética de floculação ainda são escassos. Nesse sentido, o intuito deste trabalho foi comparar o uso de PAC-BB, PAC-AB e SA via coagulação, floculação e sedimentação, bem como avaliar o efeito na condutividade elétrica, na formação de lodo, na alcalinidade, no pH e na remoção de turbidez baseado na cinética de floculação e morfologia do floco formado. Os resultados indicaram aumento de 8,1% na condutividade elétrica e de 30,6 mg.L-1 na formação de lodo; não houve diferença significativa entre os coagulantes. O PAC-AB apresentou menor consumo de alcalinidade e, consequentemente, menor redução no pH. A remoção de turbidez foi estatisticamente igual entre o PAC-BB (91,8 ± 3,7%) e o PAC-AB (91,5 ± 1,1%), porém maior que no SA (82,2 ± 6,4%). Essa diferença se acentua com o aumento da velocidade crítica de sedimentação. A constante de agregação dos flocos (K A ) apresenta resultados estatisticamente iguais entre os coagulantes, e o melhor desempenho de remoção de turbidez dos PACs em relação ao SA se deve à menor constante de ruptura do floco (K B ), podendo-se inferir, portanto, que os flocos formados com o PAC-AB e o PAC-BB são mais fortes que os formados com o SA.

ABSTRACT Aluminum sulfate (AS) is widely used as a coagulant in conventional drinking water treatment facilities. Alternative coagulants are commercially available, including polyaluminium chloride (PAC). However, comparative studies between AS and PAC with high (PAC-AB) and low (PAC-BB) basicity regarding flocculation kinetics are still scarce. In this sense, the aim of this work is to compare the use of PAC-BB, PAC-AB, and AS via coagulation, flocculation, and sedimentation as well as to evaluate the effect on electrical conductivity, sludge formation, alkalinity, pH, and turbidity removal based on flocculation kinetic and floc morphology. The results indicated that the increase in electrical conductivity was 8.1% and the sludge formation was 30.6 mg.L-1, and that there was no significant difference between coagulants. PAC-AB presented the lowest alkalinity consumption and, consequently, the lowest pH reduction. Turbidity removal was statistically equal between PAC-BB (91.8 ± 3.7%) and PAC-AB (91.5 ± 1.1%), but higher than in AS (82.2 ± 6.4%). This difference is accentuated with the increase in critical settling velocity. The floc aggregation constant (K A ) is statistically equal among the coagulants, and the better turbidity removal performance of the PACs in relation to the AS is due to the lower floc breaking constant (K B ) and may, therefore, infer that the flocs formed with PAC-AB and PAC-BB are stronger than those formed with SA.

Clarificação de águas de lavagem de filtros em estações de tratamento de água por coagulação, floculação e flotação por ar dissolvido / Clarification of spent filter backwash water in water treatment plants by coagulation, flocculation and dissolved air flotation

RESUMO Este artigo apresenta estudos de coagulação, floculação e flotação por ar dissolvido que foram conduzidos com o objetivo de promover a clarificação de águas de lavagens de filtros (ALF) em uma estação de tratamento de água (ETA) com base em experimentos de bancada e piloto. A efetividade da coagulação-floculação foi analisada pela flotabilidade dos agregados obtidos sob diferentes níveis de pH e dosagem de cloreto de polialumínio, enquanto ensaios de flotação foram investigados com base na eficiência de saturação em bancada e na taxa de recirculação. Os resultados indicaram que o pH e a concentração do coagulante representaram condições críticas na etapa de coagulação. A variação do pH da ALF condicionada com 8 mg.L-1 de Al+3 destacou a formação de espécies hidrolisáveis e a elevada atividade das cargas dos coloides indicou a ocorrência de mecanismos diferentes da neutralização de cargas na coagulação. A máxima clarificação da água ocorreu com dosagem de 12 mg.L-1 de Al+3, razão de recirculação de 10%, tempo de floculação de 15 min e pH 6,5. Em configuração otimizada, a técnica alcançou remoção de 88% de turbidez e 86% de sólidos totais, o que pode resultar em mais de 11 quilogramas de sólidos removidos do sistema de tratamento em cada ciclo de lavagem em comparação com a sedimentação, implicando aumento de 33% da carreira de filtração e, consequentemente, redução de custos e melhor desempenho da estação.

ABSTRACT This article presents studies on coagulation, flocculation and dissolved air flotation that were conducted with the aim of promoting the clarification of spent filter backwash water (SFBW) in a Water Treatment Plant (WTP) based on bench and pilot experiments. The effectiveness of coagulation-flocculation was analyzed according to the buoyancy of the aggregates obtained from different levels of pH and dosage of polyaluminium chloride, whereas flotation tests were investigated based on bench saturation efficiency and recirculation rate. According to the results, the pH and the concentration of the coagulant represented critical conditions in the coagulation. The pH variation of the SFBW conditioned with 8 mg.L-1 of Al + 3 highlighted the formation of hydrolyzable species, and the high activity of the colloid indicated the occurrence of different mechanisms for neutralization in the coagulation. The maximum clarification of the SFBW occurred with a dosage of 12 mg.L-1 of Al+3, recirculation rate of 10%, flocculation time of 15 min, and pH 6.5. In an optimized configuration, the technique achieved removal of 88% turbidity and 86% total solids, which can result in more than 11 kilograms of solids removed from the WTP in each backwashing cycle compared with sedimentation. This would imply an increase of 33% in the backwashing interval and, consequently, in the reduction of costs and in the better performance of the WTP.