Critical elements of flocculation in drinking water treatment
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Abstract The specific focus of this study was on the effects of flocculation duration, intensity, and scheme (i.e., single or multistage) on floc formation (time and size) and treated turbidity (settled and filtered). The results showed that floc formation times were 2–8 times longer under charge neutralization conditions compared with sweep flocculation conditions for the low‐turbidity and low‐organics water studied. Settled turbidity removals were dependent on the applied mixing conditions. Filtered turbidity was found to be independent of the investigated flocculation conditions, which calls into question the true value of mixing conditions with substantial implications on facility design, operation, and regulation. While at least 9 min of flocculation time was necessary under some coagulation conditions, the intensity and scheme of flocculation were not critical to overall treatment efficiency under the studied conditions. These findings might offer potential savings to water utilities in terms of design, construction, operation, and maintenance costs.Keywords:
Turbidity
Intensity
This study aimed to determine the effects of three different high molecular weight (HMW) flocculants (anionic, cationic and non-ionicflocculants) on the fine particles removal from natural stone (foid-bearing rock) processing plant wastewater at alkaline pH conditions.The test results were investigated in terms of turbidity values depending on pH of the medium, flocculant concentration and time (0–60min). According to the results obtained, the turbidity values of the wastewater in the absence of the flocculants were pH dependent anddecreased as the pH increased, resulted in the minimum turbidity values at pH 12. In the presence of the flocculants, the pH dependedturbidity removal efficiencies varied with flocculant type, flocculant concentration and time. The best results were obtained at highlyalkaline pH values (pH 12) with the turbidity removal efficiency of ≤99% in the presence of non-ionic flocculant. In the case of anionicand cationic flocculants, the minimum turbidity values were also obtained at pH 12 with turbidity removal efficiencies over 90%.
Turbidity
Cationic polymerization
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Since there are many factors which influence the process of flocculation by polymeric flocculant, the scientific understanding of the flocculation mechanism is still under discussion. We have proposed a simple bridging model which expresses flocculation under various additive manners of the flocculant and enables visual understanding of qualitative trends of the flocculation system. In this study, from the simulated results based on the model and experimental data, we obtained the following knowledge. 1) The intermittent addition of polymeric flocculant gives better and reproducible turbidity removal. 2) The optimum dosage, which shows the minimum turbidity at a given manner of addition, increases as the number of doses under the intermittent addition increases. 3) In much lower (or higher) dosage than the optimum dosage, the reproducibility of turbidity removal is satisfactory. All these findings are originated from the difference of probability of bridging formation among particles under various additive manners.
Turbidity
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The performance of two flocculants on turbidity reduction was studied. The two flocculants were: a biopolymeric flocculant which was extracted from fruit waste and a commercial industrial flocculant. The effect of the flocculants’ average molecular weight on turbidity treatment, the treatment efficiency of both flocculants and the flocculants’ degradability were investigated. Response surface methodology was carried out using Box Behnken design to find the optimal pH, cation concentration, and flocculant dosage to maximize the turbidity reduction. The results showed that the maximum turbidity reduction by industrial flocculant occurs between pH 7.5 and pH 8.2, cation concentration between 0.02 and 0.06 mM, and industrial flocculant dosage between 6.5 and 8.0 mg/L. While with biopolymeric flocculant, maximum turbidity reduction occurred between pH 4.6 and pH 7.5, cation concentration between 0.60 and 0.95 mM, and biopolymeric flocculant dosage between 4 and 6 mg/L.
Turbidity
Box–Behnken design
Industrial waste
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The efficiencies of turbidity removal of PDMDAAC flocculant series used to treat the test water of kaolinite have been studied. By the microelectrophoretic technique, the flocculation mechanism of PDMDAAC flocculant series is discussed. Their efficiencies of turbidity removal used with PAC have also been tested. The experimental results show that PDMDAAC flocculant series have excellent efficiencies of turbidity removal, especially to the water with high turbidity. The greater the intrinsic viscosity and cationicity of flocculants, the better the efficiency of turbidity removal. The flocculation mechanism of PDMDAAC flocculant series is the combination of charge neutralization and adsorption bridge formation. Used with PAC, PDMDAAC flocculant series can make the efficiency of turbidity removal better and lower the cost of treatment.
Turbidity
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Рассмотрена эффективность самостоятельного применения катионного флокулянта Праестол 650 для очистки мутных вод в зависимости от мутности исходной воды и условий флокуляции. Показано, что приоритетными параметрами, определяющими эффективность самостоятельного применения катионного флокулянта Праестол 650 для очистки мутных природных вод, является интенсивность и длительность перемешивания в камере хлопьеобразования. При длительности не менее 20 минут и среднем градиенте скорости перемешивания G = 340 с-1 эффективность снижения мутности составляет 96% (конечная мутность 7 мг/л). Установлена 96%-ная эффективность неионного флокулянта с молекулярной массой 5–7 млн в неоптимальном режиме хлопьеобразования при длительности перемешивания 5 минут и G = 65 с-1. The efficiency of the individual use of the cationic flocculant Praestol 650 for the purification of turbid water is considered, depending on the turbidity of the source water and the conditions of flocculation. It is shown that the priority parameters that determine the effectiveness of the individual use of the cationic flocculant Praestol 650 for the purification of turbid natural water are the intensity and duration of mixing in the flocculation chamber. With a duration of at least 20 min and an average gradient of mixing rate G= 340 s-1, the efficiency of turbidity reduction is 96% (final turbidity being 7 mg/l). A 96% efficiency of the non-ionic flocculant with a molecular weight of 5–7 million was determined in a suboptimal flocculation mode with a mixing period of 5 min and G = 65 s-1.
Turbidity
Cationic polymerization
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The flocculating effects of the flocculants produced by the flocculant-creating bacteria HHE-P7, HHE-P8, HHE-P21, HHE-P24 and HHE-A26 on the high-turbidity wastewater from building material production are studied respectively, and the main factors affecting the flocculation are discussed. The results of the flocculation showed that the removal rates of the turbidity of the wastewater, whose turbidity was 2 227 NTU, from the production of building materials by the bacteria-containing inoculums were all above 92%.
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The polysilic aluminum ferric flocculants were prepared from bauxite sledge.Its flocculating effects were studied by coagulating test.The properties of the flocculant,including color removal rate and turbidity removal rate were discussed.The effect of Al/Fe/Si,pH and the dosage were presented.The turbidity removal rate was above 80% in n(Al)/n(Fe)=2.0～4.0,n(M)/n(SiO2)=0.7～1.3 for treatment of the mould turbidity water.The decolorization rate was above 80% in condition that the pH was 7～9 and flocculant was 1.5 mL/L for treatment of the simulated dyingwaste water.During the n(M)/n(SiO2)=1,n(Al)/n(Fe)=2.0～3.0 in the polysilic aluminum ferric flocculants,the decolorization rate reached 90% for treatment of the industrial dyingwaste water.
Turbidity
Alum
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This chapter contains sections titled: Role of Coagulation and Flocculation Processes in Water Treatment Stability of Particles in Water Coagulation Theory Coagulation Practice Coagulation of Dissolved Constituents Flocculation Theory Flocculation Practice Problems and Discussion Topics References
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Abstract The specific focus of this study was on the effects of flocculation duration, intensity, and scheme (i.e., single or multistage) on floc formation (time and size) and treated turbidity (settled and filtered). The results showed that floc formation times were 2–8 times longer under charge neutralization conditions compared with sweep flocculation conditions for the low‐turbidity and low‐organics water studied. Settled turbidity removals were dependent on the applied mixing conditions. Filtered turbidity was found to be independent of the investigated flocculation conditions, which calls into question the true value of mixing conditions with substantial implications on facility design, operation, and regulation. While at least 9 min of flocculation time was necessary under some coagulation conditions, the intensity and scheme of flocculation were not critical to overall treatment efficiency under the studied conditions. These findings might offer potential savings to water utilities in terms of design, construction, operation, and maintenance costs.
Turbidity
Intensity
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This paper discusses the functions and properties of coagulation and flocculation. Coagulation and flocculation are related terms describing the process of preparing colloidal materials for removing by sedimentation. Coagulation is the process used to reduce the energy forces present around particles that tend to keep them from joining together to form a larger mass. Flocculation refers to the process used to bring the coagulated particles together so that they can combine to form larger, settleable, and filterable masses of particles called floc. Zeta potential is defined and its role in coagulation described. The importance of flash mixing and slower agitating processes in flocculation are also emphasized.
Sedimentation
Zeta potential
Colloidal particle
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