How to Select a Chemical Coagulant and Flocculant

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In many water treatment processes the selection of the chemical regime is of critical importance. The mechanical equipment will remove water contaminants to a reasonable level, but to meet the increasingly stringent Federal and Provincial licensing requirements chemical coagulation, flocculation, and disinfection are necessary. This paper will address several topics that will help the water treatment plant operator select the most appropriate chemical treatment programme for the needs of the community that the plant services.

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... Inorganic coagulants are cheap, available and effective in removing different contaminates. The choice of coagulant depends on wastewater characterization, type of particulate to be removed, quantity of wastewater, cost, sludge treatment, and the quality of effluent required [12] [15]. Coagulation/flocculation is an instantaneous process accomplished by adding coagulants into wastewater. ...
... Consequently, rapid cleavage or aggregation of particles or rearrangement takes place. This is carried out through four stages: 1-electrical double layer condensation, 2-adsorption and charge neutralization, 3precipitation, and 4-adsorption and antiparticle bridging [15 ] [ 16]. The coagulation and flocculation mechanisms depend on the type of charge of suspended solids in wastewater. ...
... Where, if the suspended solids have the same charge of surface then a repulsion force will be established when they come close to each other. Consequently, the treatment process could not be completed [9[ ] 10[ ] 15]. However, the treatment process could be carried out efficiently through the presence of the coagulant chemicals (CC). ...
Countries with arid and semi-arid climates suffer from scarcity of drinking water sources. Therefore, treated sewage water is an unconventional source of water. The separation of sewage into grey and black water reduces the pollution water. Grey water becomes simpler to treat. The treated effluent can be reused to irrigate many crops. The aim of this work was to apply the sedimentation process enhanced by chemical coagulants (FeCl3/lime), followed by a hybrid constructed wetland to treat grey water. The Horizontal constructed wetland was subsurface flow (SSF-CW) and followed by vertical flow constructed wetland (VF-CW). The hydraulic loading rate (HLR) of 170, 85, and 56.6 corresponding to organic loading rates (OLR) of 717.4, 358.70, and 239.13 kg BOD5 at (1, 2, and 3 days), respectively was applied. The COD, BOD5, and TSS were reduced by 90.42, 90.65, and 91.4% at hydraulic residence time (HRT) of 3 days while at HRT of 2 days the removal rates were 90.83, 89.82, and 91.1%, respectively. The treatment efficiency at two and three days was in accordance with the laws of discharging the treated wastewater into the sewerage networks, as well as the Egyptian code for treated effluent reuse.
... These results suggested that BFB is likely to be a natural metal-based organic coagulant. The blending of the different species of bones increased the alignments of the metal ions in reasonable proportions in the structure, thereby increasing the potential of BFB to induce coagulation when the positive-charged metallic ions are precipitated from the surface and diffuse into the water medium [9,26,27,28]. ...
... Hence, we concluded that the finish water is stable and will neither be corrosive. The optimal pH was determined to help reduce coagulant wastage and cost of services [4,27]. ...
... The optimization results presented in Figs. 3 and 4 of ESM show that the optimum dosages were 0.1 g/L for ABC and 0.4 g/L for BFB, respectively. The optimal values of the dosages were considered to be minimal since these values of dosages are less than 0.5 g/L [27]. An optimal dosage value lesser than 0.5 g/L is an indication that minimal residues were produced during the coag-flocculation period, thus resulting in smaller volumes of residual turbidity. ...
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This research is centered on the optimization of coagulation–flocculation treatment of cosmetic wastewater. It analyzes blends of fishbone (BFB) and aluminum-based coagulant (ABC) to determine the efficacy of BFB as a potential coagulant–flocculants aid at optimum conditions using response surface methodology (RSM). The experiment was carried out employing the standard nephelometric procedure at 1000 rpm stirring rate. The central composite design (CCD) was used to examine the interactions of pH, dosage, and settling time to maximize the turbidity removal efficiency of the ABC- and BFB-driven coag–flocculation. The optimal pH, dosage, and settling time for ABC were obtained as 10, 0.1 g/L, and 2 min, while pH 6, 0.4 g/L, and settling time of 4 min were recorded for BFB following the established quadratic model of the RSM. The removal efficiency of ABC and BFB plots 80% and 88%, respectively; this corresponds to 262 NTU and 288 NTU of removal from the wastewater at optimal conditions. The kinetics result indicated that the rate constant ( K f ) 3 × 10 ⁻³ (L/g min) of BFB surpassed 5 × 10 ⁻⁵ (L/g min) recorded for ABC following second-order coag–flocculation reaction, with correlation coefficients ( R ² ) values of 0.999 and 0.9985, respectively. The research also applied cost–benefit analysis for the determination of the efficacy of BFB. The figure obtained shows that the benefit of using BFB will save $5.50 compared to ABC based on this work. At optimal conditions, BFB satisfied the environmental protection agency pH standard for industrial wastewater discharge, promising coagulant–flocculants aid for industrial wastewater purification purpose and the preservation of the environment.
... The characteristics of the coagulants are presented in Table 1. The strength of solutions was as recommended by Greville (1997). ...
... Thus, for comparison, the same dosage range was initially used in the flocculation test for each of the selected coagulants after which adjustments were made. Preparation of solutions for each coagulant was adapted from Greville (1997). Alum acted as the control for the tests. ...
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Drinking water treatment at Harare's main water works, Morton Jaffray Water Treatment Works (MJWTW), has been a challenge due to source (Lake Chivero) pollution, and the efficacy of some of the processes and chemicals including aluminium sulphate (alum) has been questioned. This study investigated the use of an alternative coagulant to the traditional use of alum at MJWTW. The effectiveness of five coagulants, namely Anhydrous Poly Aluminium Chloride (APAC), Poly Aluminium Chloride (PAC), Primco 100, Zetafloc 4030 and alum (control) was investigated by flocculation tests in a laboratory using Lake Chivero water. Parameters analysed included pH, turbidity, Electrical Conductivity (EC) and chlorophyll-a for raw water and treated water. Raw water mean pH was 7 ± 0.4, turbidity (3.3 ± 0.2 NTU), EC (337 ± 5.0 μS/cm) and chlorophyll-a concentration (2.28 μg/L). Primco 100 had the best performance with the lowest optimum dosage of 25 mg/L while alum had the highest dosage of 55 mg/L. APAC, PAC, Primco 100 and Zetafloc 4030 did not change the pH of water significantly but alum did. The study concluded that Primco 100 was the most suitable coagulant and could be an alternative to alum. Highlights Provides insight on developing technology on coagulants for treatment plants.; Closes research gap on use of alternative coagulants at water treatment plants in Zimbabwe.; Provides practical guidelines on how to select a new coagulant, especially in developing countries.; Provides insights on cost saving measures in water treatment process at MJWTW.; Provides extensive methods of laboratory tests in assessing efficacy of coagulants.;
... Generally, jar test is the most common test for optimizing the coagulant dose for water treatment plants (WTPs) (Zainal et al. 2012;Koohestanian et al. 2008;Malian et al. 2017). However, jar test still suffers from several drawbacks (Greville and Environmental 1997;Almeida et al. 2017). These drawbacks include using a small volume of water to represent the whole water quantity throughout the day. ...
The optimum alum dose has been estimated electrically based on the difference between the electrical charges in the treated and the raw water under the same conditions. For each level of turbidity and algae, a direct relationship was obtained between the alum dose and the difference values of the electrical charges in the raw and treated water under the same conditions. It was found that the electrical charges inside the same water come down directly with the reduction in the turbidity and algae values, especially under insignificant algae levels. Therefore, relationships between the electrical charge differences and turbidity and algae removal were obtained with error values of 0.0, 5, and 10.0 for algae concentration of 0.0, 103, and 106, respectively. Finally, the electrical charge difference between the turbid and treated water has been amplified and used instantaneously to control the required alum dose of the water. Further, an additional feedback signal has been set after settling process to ensure that there are no residual charges in the settled water. As a result, dynamic and instantaneous control of the alum dose has been achieved accurately. This technique can be used successfully in water treatment plants that have variable turbidity levels throughout the day to overcome the most human mistakes associated with alum feeding.
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Petroleum refinery effluent (PRE) containing a high concentration of colloidal particles causing turbidity is a point source pollutant. There is currently no baseline for the residual concentration of colloids in industrial effluent. In the present study, the performance of land snail shells (LSS) characterized using FTIR and XRD techniques used for the treatment of PRE was investigated. The effluent collected from the outlet train of the industrial facility contains 220NTU of turbidity corresponding to 520mg/L of colloidal particles. Analysis of the industrial effluent yielded a COD to BOD ratio > 3.5 eliminating the option of a biological method of treatment. Coagulation-flocculation treatment of the PRE was carried-out following a standard nephelometric test. To clarify the applicability of LSS beyond removal efficiency, machine learning (ML), adsorption, and coag-flocculation kinetics were applied to investigate the treatment process. The predictive capacities of the ML models were compared using statistical metrics. The synergetic effects of operating variables were equally studied. The predicted optimum operating conditions of the treatment process were pH 6, dosage of 0.1g/L, and a settling time of 30 minutes. The pseudo-second-order and coag-flocculation kinetics result confirmed the reduction of the colloidal particles that occurred via adsorption and inter-particle bridging mechanism. The flocculation outcome proved that the mixing regime 20s⁻¹≤ G≤120s⁻¹ promoted aggregation rate over breakage coefficient transcending to 90% removal efficiency. The finding shows that the stability of the finished water corresponds to the 23 mg/L threshold of residual colloidal particles, and 10NTU, which satisfied the EPA guideline for environmentally sustainable recovery.
The main problem that the world is facing today is the scarcity of natural resources, including freshwater, due to ramping environmental pollution. It is primarily due to rapid industrialization posing a serious threat to the entire ecosystem. Most of the industries discharge effluents to the nearby wetlands and water bodies. As a result, the amount of usable water reduces drastically due to surface and ground waters contamination. The discharged effluents contain various toxic impurities in the form of metals, organic and inorganic particles, suspended solids, etc. If without proper treatment, the water is used, serious health hazards can occur. It is, therefore, necessary to treat the water before it is used for domestic and drinking purposes. There are many stages of treating natural wastewaterWaste water for removal of organic, inorganic, and suspended loads. The primary process is to remove suspended inorganic solids and for that flocculationFlocculation is generally used as it is one of the most convenient and cheapest unit operations. At the same time, it has also been found that polymeric flocculants are more effective than conventional inorganic flocculants for settling inorganic suspensions. It works both by charge neutralization and bridging mechanisms to settle the flocs in a reasonably quick time. This chapter vividly described the treatment of wastewaterWaste water containing suspended inorganic solids with polysaccharide grafted hyperbranched copolymersGraft copolymer as flocculants. Hyperbranched polymers have unique properties like higher solubility, higher hydrodynamic volume, more functional ends hence higher zeta potential for charge neutralization and more inner voids for bridging of flocs, which make them a better flocculant than conventional linear polymers. Along with hyperbranched polymer-based natural flocculants, future scope for incorporating various nanoparticles into the polymeric network for further improvement in flocculationFlocculation efficiency, has also been discussed in this chapter.
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The present study was conducted to assess the performance of the treatment plant installed on the main effluent drain of Hayatabad Industrial Estate (HIE) for reducing pollution load. The objective of the study was to know about the pollution removal efficiency and suggest changes in the existent treatment plant, if required. For this purpose, samples were taken from the effluent, before and after it went through the treatment plant. It was found that the treatment was not sufficient to remove various physical and chemical parameters including Suspended solids (SS), Biological Oxygen Demand (BOD), Chemical Oxygen Demand (COD) and Sulfide (S) in order to comply with Pakistan National Environmental Quality Standards (Pak-NEQS).The collected samples were then treated in the laboratory in order to identify and suggest suitable coagulant. For this purpose three different treatments .i.e. Lime, Alum and Alum+Lime were applied. The optimum doses identified were 25, 35 and 26:13 ml respectively. The settling time was 25, 35 and 20 minutes respectively for lime, alum and alum+lime. The results revealed that the combine treatment (Alum + Lime) effectively removed suspended load up to 90%, along with 82% BOD, and 80% COD respectively. Therefore, it was concluded that the installed small scale treatment plant is not enough in its present form and needs to be upgraded by adding a coagulation step.
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