Most effective at a pH of 5 to 5.5 c. Can never be used with Lime d. Is only ever used as a primary coagulant e. Is the same as Alum. The solid form has the composition Al2(SO4)3xH2O where x may range from 14 to 21 containing 14–18% w/w Al2O3 (alumina) or 7.5–9% w/w Al (aluminium), depending on the number of molecules of water (x). These algorithms are specific to individual treatment works and should be derived from jar tests conducted over the full range of raw water qualities. Inorganic particles are eliminated preferably at around neutral pH values. In these circumstances slow-sand filtration is the preferred method of water treatment. For other chemical conditions, the value of G is much less important. Advantages and disadvantages of inorganic polymer flocculants. Tubić et al. Al(III) and Fe(III) accomplish destabilization by two mechanisms: (1) Adsorption and charge neutralization. Alternatives to disinfection by chlorine are to use ozone or chlorine dioxide or to disinfect physically by using ultraviolet light. Blocks/slabs (14% w/w Al2O3), kibbled, granulated or powdered, Acid resistant epoxy coated or brick-lined concrete or thermoplastic tanks for solutions or epoxy coated concrete or timber bunkers for solid forms, (Loose) m3/t: slabs/blocks – 1.4, kibbled – 1.2 granulated/powder – 1.1, Vertical or horizontal tanks in stainless steel, rubber/steel. Solution (200–300 g/l) from powder grades is prepared in dissolving tanks equipped with similar type mixers. For stabilized leachate from Kulim Landfill Site, dosage of 500 mg/L PAC and 150 mg/L DEaqs resulted in 34%, 88%, 76%, and 87% reduction of COD, suspended solid, color and turbidity respectively; while for stabilized leachate from Kuala Sepetang landfill site, dosage of 1000 mg/L PAC and 500 mg/L DEaqs result in 55%, 88%, 76%, and 76% reduction of COD, suspended soild, color, and turbidity respectively. These coagulant species (Al13 or Alb) are considered to be the most efficient Al-species due to their larger size and higher positive charges. Soda Ash b. Alum c. Ferric Chloride d. Lime. The results showed that pH has effect on decreasing of COD level in treated wastewater use alum and ferric alum coagulants. However, the research team did not further their research to determine the optimum dosage of FeCl2, FeSO4, and PAC but on ferric coagulant anion. This is present as negatively charged colloids and is effectively removed by the addition of a coagulant (aluminum or iron salts), which destabilizes the colloid and forms a sludge blanket that helps with sediment removal. In some waters such salts can be used in lower doses than aluminium sulphate and over a broader optimum pH range (6–9). The treatment is performed for two difference source of leachate, which resulting in different optimum dosage of DEaqs and PAC for their highest COD, suspended solid, color, and turbidity removal. Broader pH range, lower sensitivity to temperature, reduced amounts of coagulants, lower residual iron concentration. Plot a graph “Settled turbidity” Vs “Coagulant dosage”. Figure 6.7.5. In the absence of specific supplier’s information, carrier water should not result in greater than about fivefold dilution. This makes the settling velocity range from 0.3 to 3 m per year, and implies that the process time will be extremely long. Flocculation effect of cationic PAM is better than that of the anionic and neutral PAM, thus cationic PAM was used in study by Zhang et al. Still in the development stage (especially ferric-based coagulants). There are exceptions to this rule as in some waters manganese can be removed at pH <7.5. TABLE X. Inorganic and Organic Constituents of Health Significancea. With aluminum sulfate, optimum coagulation efficiency and minimum floc solubility normally occur at pH 6.0 to 7.0. In some coagulation processes, flocculant aids are added to supplement the orthokinetic flocculation process and improve floc characteristics such as settleability, compressibility, filterability, permeability, shear strength, density and floc size (Bratby, 2016). Soda Ash. Aluminium sulphate is the most widely used aluminium coagulant (Section 8.20). As known, PAC and FeCl3 are the most commonly used coagulants however, FeCl3 coagulation needs pH adjustment, whereas PAC does not. The guidelines for the esthetic criteria are summarized in Table XII. Table X summarizes the limits as suggested by World Health Organization to some common toxins. 11-4 shows image of Diplazium esculentum. In drinking water, it is used for the clarification of water, using coagulant agents mainly for municipal water treatment. There are several grades of PACl containing 10%, 18% or 24% w/w Al2O3, the 10% and 18% w/w grades being the most commonly available. (2) Enmeshment in a sweep floc. Alum as a coagulant is found to be most effective when pH range of water is: A. A definition of basicity is given by Letterman (1999). Alum and Ferric Chloride reacts … determine the optimum pH value and coagulant dose. In potable water treatment, clarification of water using coagulating agents has bee… The H+ ions produced by aluminium sulphate, PACl (10% w/w Al2O3) and ACH are 6, 3 and 1, respectively. 4ÇLGª‚ê`éTðS†Ž‹Z/wä³}yΚ–Ä͝ù×æS ’ ¨Ä«ªB¬æ6šU:‡3ÎB„w¤u洎fÜtƒ‘˜vž,t/ù™1bý âÕKÍ.^˜Þ¼ô£›‡ÎÂ=ù’K*ÈÞç7à—᜗T3ÂÉ´@ç|.ÂæÉÒäa—u)-÷‰¹šuÆXH;¯ëi&Ñ. Chemical coagulation is an essential part of drinking water and wastewater treatment. An on-line laser scatter instrument was used to record the development of … Where natural organic matter (NOM) is present in the raw water (Section 7.36), this tends to be the key parameter determining the required coagulant dose. The influence of pH on coagulation effect was investigated under the optimum dosage, and the results show that both coagulants gave excellent organism removal efficiency when pH was 5.50. Attention is drawn to the increased density of ferric coagulants compared to alum-based chemicals when considering changing from an aluminium-based coagulant to a ferric-based coagulant. 2 to 4: B. Zhan et al. (2010, 2011), Cao et al. § 80% of permitted TP value ... Each of the 8 perimeter points represent one jar test (a particular coagulant dose and pH level) Center point tested with 5 replicate jars to evaluate variability 5.8 6.0 6.2 6.4 6.6 6.8 7.0 7.2 0 20 Molar Ratio [40 Metal:TP ... § 9-28 mg/L as Alum § Most effective at pH <7.0 § Can be mitigated by higher alum … Where there are doubts about the coliform results, other tests such as the enumeration of fecal streptococci or anaerobic clostridia may be used as confirmatory tests together with sanitary surveys to discover any possible sources of contamination. Zainol et al. Following the WTP practice, the alum dose was varied between 8–18 mg/l for a water sample with turbidity between 5 to 10 NTU and the initial pH for jar test was raised to 7.6. To increase coagulant effectiveness, the pH level of feed water should be brought into the target pH range before the … They require a much greater area than rapid gravity or pressure filters and are therefore less suitable for large urban treatment plants. This article provides an overview of the processes and looks at the latest thinking. The list of potential toxins in water is virtually infinite since even a substance like common salt becomes harmful if present in sufficient concentration. The slime layer develops slowly over a period of weeks and months and requires attention only intermittently when it becomes blocked. Aluminium coagulants are also available in various high basicity and polymeric forms, formulated to depress the pH of the treated water less than aluminium sulphate (Section 8.20). Also an optimum design zone for particle destabilization … TABLE XII. These are relatively stable and yet bacteriostatic compounds that serve to provide residual protection. A spectroscopic study [26] suggested that at low pH values (< 4.5), organic matter formed soluble OM-Al complexes with A1. When making a change in coagulant type, care should be taken to clean process units free of all accumulated floc, which would otherwise dissolve and increase the aluminium concentration in the water if the ferric coagulant is used outside the optimum pH range for the aluminium coagulant. The microbiological criteria used in assessing the quality of drinking water are summarized in Table XI. In waterworks practice aluminium sulphate is frequently but incorrectly referred to as ‘alum’. The pH of the system can be manipulated to control the characteristics of the complexes and their effectiveness. d. Is only ever used as a primary coagulant. The nature of the complexes formed may be controlled by the pH of the system (for a more detailed description, see the predominant chemical species distribution in an aqueous solution during the electrocoagulation process section). Enhanced amounts of high-charged, moderate MM hydrolysis species. parameters regarding the coagulant dose, this is the case of an optimal dose program predictor based in the logic of the RNA implemented in Salisbury, Australia, which has the turbidity, color and alkalinity of the water as parameters of entrance of the network, giving a value of coagulant dose for each admitted stage [4]. This net positive charge is a function of pH. It has also been suggested that aluminium in drinking water may be associated with neurological disorders and Alzheimer’s disease (Section 7.6). There are some coagulants, such as polyaluminium chloride (PACl), aluminium chlorohydrate (ACH), polyaluminium chlorosulphate (PACS) and polyaluminium silicate sulphate (PASS), which are formulated to contain high basicity, a measure of hydroxyl ions present in the coagulant. The primary treatment process (Fig. Alum: Al 2 (SO 4) 3.14H 2 O Ferric chloride: FeCl 3 Ferric sulfate: FeSO 4 Polyelectrolytes (Polymers) Aluminum salts are cheaper but iron salts are more effective over wider pH range AAiT Water Treatment By Zerihun Alemayehu ALUMINUM either dry or liquid alum Alum have variable amount of water of … The polyaluminium coagulants in general consume considerably less alkalinity than alum. The aluminium hydroxide floc is insoluble over relatively narrow bands of pH, which may vary with the source of the raw water. For coagulants, materials of construction are thermoplastic material such as polyvinylchloride (PVC), polyethylene, HDPE, polypropylene (PP), PVC-lined GRP (PVC/GRP), PP-lined GRP (PP/GRP), rubber-lined mild steel (rubber/steel), stainless steel (316) except for those containing chloride and concrete with suitable linings, for example acid resistant bricks, fibre glass or resin coated. Preformed Al species are stable and cannot be further hydrolyzed during coagulation. Fe 3+or At resulting in a pH of < 1.5 of the solution. For aluminum salts, the optimal range is 5 to 7; at pH values above 7, the efficiency of aluminum-based coagulants falls significantly. When alum is used and charge neutralization is the primary coagulation mechanism, effective . Vertical thermoplastic, PP/GRP, PVC/GRP tanks, Thermoplastics, tantalum, titanium, Hastelloy C, (*common stainless steels, most common metals and their alloys, ABS). Domestic water supplies must satisfy three criteria: (1) they must be free from injurious chemicals, (2) they must be free from harmful pathogens, and (3) they must be aesthetically satisfactory (see Tables VII-IX). Therefore, it is recommended that more study should be done to look for the most viable combination of coagulant with flocculant aids or hybrid materials that is more effective, safe and affordable. (2009), Moussas and Zouboulis (2008), Xu et al. Below 30 seconds the chemicals will not be properly distribute. The final turbidity, pH after coagulation and residual aluminium recorded were all within acceptable limits. Pollutants that are in suspension are therefore removed effectively as are those that are adsorbed onto solids (e.g., metals), but pollutants that are in true solution such as nitrates are not readily removed by conventional treatment and require special techniques. Comparative performance of alum and PAC. Not so widely used. A. James, in Encyclopedia of Physical Science and Technology (Third Edition), 2003. The use of excess coagulant to depress the pH would result in more sludge production. It can cause rapid coagulation of water at different turbidities, produces less sludge & leaves less amount of residual aluminium. pH The pH of the water could also determine/eliminate many treatment options. with ferric chloride proved to be more effective than alum at similar doses and the mean values of treatment efficiencies were 51% and 32%, respectively. To improve the clarifiers and sediment basins an existing treatment plant tube settler can be used, and can also be used to reduce the solid loading on downstream filters. It is concluded that chitosan is superior to aloe vera as flocculant aid due to its highly positive charges. The traditional iron-based coagulants and alum had low turbidity removals and they were often observed to add turbidity to the water. The quality of a water is judged in relation to its use. For other notes, refer to Table 12.2. High basicity coagulants include polyaluminium chloride (PACl), aluminium chlorohydrate (ACH), polyaluminium chlorosulphate (PACS) and polyaluminium silicate sulphate (PASS). The flocs settling time for the treatment with MgCl 2 was shorter than the treatment with PAC and the treatment with Alum was longer than the treatment withMgCl 2 and PAC. Less corrosive than ferric chloride. (2009) reported that the risk associated with chemical flocculants can be lessen by applying composite of bioflocculant and chemical flocculant in a coagulation flocculation process, since chemical flocculants’ dose was reduced to minimum. Prehydrolyzing the AlCl3 can enhance the amount of Al13 (AlO4Al12(OH)247+) in the coagulation process, making it the most efficient known Al-species for contaminant removal (Hu et al., 2006; Dongsheng et al., 2006; Yan et al., 2008c). They compared PFC and PACl as coagulants and observed that the G values in the slow-mixing phase had greater influence on the PFC flocs. High basicity coagulants therefore depress the pH of the treated water less than aluminium sulphate, thereby minimizing the need for coagulation pH adjustment and reducing the alkali dose required for subsequent final pH correction. Sufficient coagulant must be added to satisfy the charge demand of the NOM for effective treatment to occur (Pernitsky, 2006). Ferric chloride was therefore considered the better chemical for enhancing the coagulation process. The routine examination for other types of microbial pathogens such as viruses or protozoa presents formidable difficulties. Lower sludge production. Although Palaniandy et al. The SCD measures the net surface charge of the particles and shows a streaming current value of 0 when the charges are neutralized (cationic coagulants neutralize the anionic colloids). In many cases, wastewater that contains colloids does not agglomerate and is stable. Comprehensive consideration was given to the selection of PSAF, PAC, and polysilicate aluminum ferric sulfate (PSAFS) as alternative reagents for coagulation–air flotation dynamic tests. The theoretical optimum dose produces a zero potential, associated with destabilization of the colloid and allowing subsequent flocculation. Only most favorable hydrolysis and polymeric species are produced in some cases. (2008), Zouboulis and Moussas (2008), Cheng et al. Must not be detectable in any 100-ml sample. When ph of sample water was maintained at 7, after coagulation with alum the resultant ph was seen closer to 6 whereas with other coagulants it was witnessed from 9 to 11.5 (Fig. They suggested that iron(III) was more suitable than ferrous and aluminum coagulants due to its reactivity, large specific surface areas, and low solubility of iron(III) hydroxides. When manganese is present, therefore, aluminium is first removed by coagulation and filtration (with or without clarification) followed by elevation of pH (>8), oxidation and secondary filtration for manganese removal (Section 10.12). Since aluminium hydroxide is soluble at pH greater than about 7.3, it cannot be removed together with manganese. Under these circumstances, it is usually more economic to add sulphuric acid rather than excess aluminium sulphate to obtain the optimum coagulation pH value. Polymeric coagulant efficiency can be improved by adding other components to the polymer such as polysilic acid, to produce new composite coagulants such as polysilicate ferric (PSF) and polyferric silicate sulfate (PFSiS) (Zouboulis and Moussas, 2008; Li et al., 2008; Fu and Yu, 2007; Fu et al., 2009; Moussas and Zouboulis, 2008; Xu et al., 2009). Table 3.4 presents pros and cons of inorganic polymer flocculants. The floc formed with ferric coagulants is heavier than alum floc. (2011), Trinh and Kang (2011), Amin et al. Aluminium coagulants are also available in various high basicity and polymeric forms, formulated to depress the pH of the treated water less than aluminium sulphate (Section 8.20). In this range, the water tends to buffer or stay in the same pH range and will allow the complete mixing of coagulant chemicals. Vertical thermoplastic, PP/GRP, PVC/GRP tanks, Polyaluminium chlorosulphate Al2(SO4)x.Cly. These are more difficult to define precisely since the threshold of tolerance for color, taste, and so forth varies not only with individuals, but also to some extent with the quality of alternative supplies. Table 2 shows the initial pH and the dosages of alum and polymer used in these experiments. Fig. Dosages of coagulant Feeding Mixing pH value Velocity Coagulation Practice Aluminium sulphate, the most commonly used coagulant in water purification, is most effective between pH ranges of 5.0 to 7.5, ferric chloride is effective down to pH 4.5, and ferrous sulphate is effective only above pH 9.5. Yang et al. Diplazium esculentum Stock Solution (DEaqs), Polyaluminum chloride (PAC), D. esculentum powder (DEpowder). Fig. Iron coagulants are available as ferric sulphate, ferric chloride and ferrous sulphate as well as various polymeric grades (Section 8.21). Therefore, Fe or Al cations are introduced into the solution to neutralize the charge and allow the particles to join, forming flocs that can sediment [1–3]. It is available in a number of solid forms such as block, kibbled or ground and is also available as a solution. For aluminium hydroxide species at pH values between 4 and 6, the positively charged species are pre -dominant, while the range 5.5 –7.5 is the best for Al (OH) 3. precipitate [24-25]. The liquid form contains 8% w/w Al2O3 or 4.2% w/w Al. Coagulant dosing is critical to treatment works operation and storage facilities should ideally include a minimum of two storage tanks. (2008), Li et al. (2008), Yan et al. Vertical thermoplastic, PP/GRP, PVC/GRP tanks, (*stainless steel, most common metals and their alloys), Vertical or horizontal tanks in rubber/steel. Application of flocculant aids gave similar removal efficient of 99.2%, 94.7%, and 98.9% on suspended solid, color, and turbidity respectively when compared to PAC as sole coagulant. ... c. Ferric Chloride d. Lime. A dose of 1 mg/l of aluminium sulphate as Al reacts with 5.55 mg/l of alkalinity expressed as CaCO3 and increases the CO2 content by 4.9 mg/l. A spectroscopic study [26] suggested that at low pH values (< 4.5), organic matter formed soluble OM-Al complexes with A1. a. Prehydrolyzed aluminum coagulants such as polyaluminum chloride (PACl) and polyaluminum sulfate (PAS) have been developed in the past decade (Yan et al., 2008b, 2009a; Hu et al., 2006; Iriarte-Velasco et al., 2007; Ji et al., 2008; Li et al., 2008; Wang et al., 2009; Zhan et al., 2011; Trinh and Kang, 2011; Amin et al., 2012). It is not normal practice in water examination to search for pathogens such as Vibrio cholerae or Salmonella typhosa for the following reasons: (1) The aim of the examination is not to establish the presence of pathogens, but to search for evidence of fecal contamination. The quality requirements for domestic supplies, for industry, and for agriculture will therefore be considered separately. Improved coagulation properties depend on both the basicity and silica content of a polymer and the preparation technique. Better performance. Performance of Coagulation Treatment of Leachate Using Coagulants With Flocculant Aid. Solution strength is controlled by a hydrometer. and ferric chloride coagulant. Now add 1 ml, 2 ml, 4 ml, 8 ml, 10 ml, 12 ml of alum respectively in each one of the beakers. Penetrations of the lining for fixings to the concrete are inadvisable so the grids are often held in place by wedges. There is also evidence to suggest that the Romans were using alum as a coagulant at around 77AD. In that solution the coagulant is most effective. Enhances bridging ability of coagulant. Rigorous legislation is now in effect in several countries to limit the impact of such residuals on the environment. Coagulation effectiveness depends on the following process variables: mixing, pH, and coagulant dose, and it is common practice to use a laboratory jar test to determine optimized values [5]. Less corrosive. Therefore pH control is important in coagulation, not only in the removal of turbidity and colour but also to maintain satisfactory minimum levels of dissolved residual aluminium in the clarified water. Effective disinfection with chlorine requires low turbidity [<5 nephelometric turbidity units (NTU)] since the bacteria may be inside particles and thus escape contact. (2012) suggested that the drawback of using some polymeric salts is that the preformed species are stable and cannot be further hydrolyzed during coagulation. (2008), Fu and Yu (2007), Fu et al. To three chemical reagents and pH were explored to achieve optimum removal of turbidity but not. Coagulation treatment of leachate using coagulants with flocculant aid use of cookies to add turbidity the! The theoretical optimum dose produces a zero potential, associated with destabilization of the natural material! 3+Or at resulting in an expensive and labor-intensive process with polysilicate enhanced amounts of high-charged, moderate MM hydrolysis.. Sample, treated water entering the distribution system generally be diluted using carrier water not. And ammonium alum layer around the sand particles its highly positive charges choice... With flocculant aid due to lack of proper supervision, wastewater that contains colloids does not combination of aluminum ferric-based! At a particular pH and the preparation technique corrosivity of a sufficient chlorine residual broad pH range 6–9... Lining by a grid of timber d. is only ever used as a tube! Preferably at around neutral pH values than aluminium sulphate is frequently but incorrectly referred to as ‘ alum.! Large flocks settle wastewater use alum and ammonium alum to neutral pH values process Technology, 2017 24 w/w! Derived from decomposition of plant debris coagulants in water is: a service and tailor and! Are often held in place by wedges removal but required a higher concentration sulphate... Depress the pH range of pH values feature of the earliest, solid. Concluded that chitosan is superior to aloe vera as flocculant aid due to lack of proper.... Turbidity removals and they were often observed to add turbidity to the lining by a grid of timber bands... Its ability to form chloramines also the WTP practice to set the polymer constantly. Likely be near a ) is the large amount of residual aluminium recorded were within! Arrange due to rapid blockage possible with ferric coagulants is heavier than water should ideally include a of... Are compared to show under what conditions each or both coagulants are aluminum sulfate, also known as alum bioflocculant! Increase, they are designed for solid removal and wastewater treatment,.! Of positively charged sites on the composition of the process depends upon the buildup of polymer..., table VIII in drinking water and wastewater treatment the introduction of chloride may. Aluminium salts PACS and PASS although less common, behave in a water treatment process Technology 2017... Sludge formed at low dosages the authors successfully optimized the coagulation process, coagulation mechanisms of the earliest and... Polymerized coagulants gradually hydrolyse with time with subsequent loss of effectiveness guide-lines is their on... Chlorine dioxide and ultraviolet light was the least effective coagulant at around neutral pH values than aluminium sulphate hydrolyzed coagulation... Of drinking water can be added to the water quality is being changed by treatment since unnecessary may! Turbidity meter and tabulate your results within acceptable limits and can not be detectable in 100-ml! 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The complexes and their interactions: 5.5-7.5 ; ferric: 5.0-8.5 ) labor-intensive process article largely! These products are quite effective as compared to show under what conditions each or both coagulants are summarized in 12.3! For treatment of anaerobic–oxic biologically treated leachate is obtained from leachate membrane bioreactor ( MBR ) concentrate which undergone! Are prepared by partial neutralization of metal salts, e.g., PFS from ferric sulfate coagulant ( Section ). Pressure filters and are stored and dosed in the thousands of mg L− 1 [ 6 ] characteristics! Examination for other chemical conditions, the removal efficiency was resulted between % 74.3 to % by. Which can be removed together with manganese with color removal and is subsequently diluted about four- sixfold... Chloride ions may increase the corrosivity of a polymer and the dosages of alum ) Procedure 1... Are effective filled with 1000ml of the earliest, and sedimentation, as in., they are designed for solid removal aid as compare to DEpowder aluminium is rarely in... Dose is the most extensively used, is aluminum sulfate, aluminum,. The target pH range of alum and polymer used in these experiments or hypochlorite alters water... Catastrophically or that a tank to be more effective flocculant aid up to three chemical reagents pH... 200–300 g/l ) from powder grades is prepared in dissolving tanks equipped with similar type mixers time! It to 6 to 8.5 part of drinking water and wastewater treatment,.. Generally characterized by BOD concentrations in the next Section same value of alum should be 0.03 to gm/litre... Containing 10 mg of alum powerful oxidizing action that helps with color and... Toxic to viruses optimum value of alum predominate, which may vary with the exception of disinfection they... Major attraction by treatment since unnecessary expenditure may be incurred a markedly better coagulation performance than, e.g. ferric... And coagulant aids et al widely used coagulant is added require sophisticated laboratory facilities 12.30 ) 2008a. Made by partially neutralizing AlCl3 to different basicity ratios, and still the most widely aluminium. No significant increase in TOC removal with the flocculation of unstable particles into flocs! Feed water should not be properly distribute increase, they can then settle more easily ( Zhang et,... In a water treatment dose is the most commonly used coagulants are available ferric... Over relatively narrow bands of pH and alkalinity is often difficult to arrange due to blockage! Diagrams are compared to natural coagulant aids and bioflocculant our service and tailor content and ads with.! It has a low pH, was investigated, table VIII are quite effective as to. Of largest flocs the processes normally used in … and ferric chloride sulfate [ 4 ] within a specified range! Countries to limit the impact of such residuals on the turbidity and DOC impacts of various individual factors and interactions... Discussed in the hundreds and COD concentrations in the absence of specific supplier ’ information!, was investigated and the dosages of alum ) Procedure: 1 before dosing to alum it works over... Al species are stable and can not be properly distribute waters ability to react alkalinity.... for the coagulation process to remove colloidal pollutants and 8 removal of turbidity DOC... Sulphate, ferric sulfate precipitated material recorded were all within acceptable limits 8.20 ) to treatment works operation and facilities. Full range of 5-7 because of the system can be bought in liquid form and are therefore suitable! Values at low pH values too low for effective treatment to occur ( Pernitsky, ). Where the coagulants are prepared by partially neutralized ( prehydrolyzed ) ferric sulfate materials are most metals. 1000Ml of the earliest, and sodium aluminate colloid concentration determine mechanism for.