Coagulant dose

Streaming Current Detectors These units produce a measurement closely related to the zeta potential of a suspension and are used successfully in optimizing the coagulant dose in clarification applications. 

Figure 3. Dependence of radius of primary aggregates of BAS HPP on the coagulant dose and system alkalinity. OH/A1 ratio 2.5 (1) 2.0 (2) and 1.0 (3).

Figure 5. Dependence of E. coli extraction by AS vs. coagulant dose at pH 7.0 and 8.0.

Example 12.6 A raw water containing 140 mg/L of dissolved solids is subjected to a coagulation treatment using Fe2(S04)3. If the optimnm coagnlant dose as determined by a jar test is 40 mg/L, calculate the alkalinity of calcinm bicarbonate required. If the natural alkalinity is 100 mg/L as CaC03, is there enough alkalinity to neutralize the coagulant dose ... 

A raw water containing 140 mg/L of dissolved sohds is subjected to coagulation treatment using copperas. The alkalinity requirement is 18 mg/L as CaC03 and the natural alkalinity of the raw water is 100 mg/L as CaCO. The optimum dose of the coagulaut is 50 mg/L. Calculate the fractiou of the coagulant dose neutralized iu the preseuce of calcium bicarbouate. 

A raw water coutaiuiug 140 mg/L of dissolved solids is subjected to coagulatiou treatmeut usiug copperas. The hme used is 22.4 mg/L at a purity of 90%. Makiug appropriate assumptious aud calculate the optimum coagulant dose. 

A raw water is subjected to a coagulation treatment using FeC. The current acidity and pH are, respectively, 30 mg/L as CaC03 and 5.9. The sohds produced amount to 0.132 kg/m of water treated. What was the suspended solids content of the raw water, if the optimum coagulant dose is 40 mg/L ... 

From the change of the average floe diameter of the suspension as a function of the coagulant dose, a reference dose can be deduced. With the reference dose, the largest floes possibleh the given process conditions are obtained. This reference dose is a characteristic of the process, an objective parameter and useful as a basis for further research. 

The floes formed with the reference coagulant dose are itot only the largest floes possible in the corresponding conditions, but they have also proved to be the strongest. 

The zeta-potential of the formed hydroxide floes does not yield any information for a feed-back control of the coagulant dose. The adsorption behaviour of salts dissolved in the water is investigated. 

A fundamental study of the mechanisms of a coagulation-flocculation process requires knowledge about the characteristics of both the formed floes and the process. To investigate the influence of the different process parameters on the different characteristics, an objective coagulant dose must be used. Tbe majority... 

In an attempt to find an objective coagulant dose imposed by the process, we have measured the influence of the dosage on the floe dimensions and some other characteristics. 

An example of the calculated results obtained for flocculation under the conditions mentioned in Table 1 and with a coagulant dose of 3.738 mg(Al)/l is given in Figs. 3-6. 

The porosity of the flocculated suspensions in the experiments is always smaller than 0.005. This value is measured with a Malvern Particle Sizer type 2200 when very high coagulant doses were used. Therefore, the correction for the sedimentation velocity is always smaller than 1.02. 

The reproducibility of the experiment is very good. For 9 experiments under conditions given in Table 1, with a coagulant dose of 5.02 mg(AI)/l, the average of the maximum detected floe diameter was 3495 fJ.ni with a standard deviation of 134/im, i.e. 3.8% of the average. 

From Fig. 8 it is clear that the highest recovery factor occurs when floes formed with the reference coagulant dose. The relation between strength factor and coagulant dose is very smooth with a weak optimum for floes formed with the reference dose. 

Table 5 gives another list of results. In a kaolinite suspension prepared in distilled water, different salts were added together with the aluminium sulphate coagulant. The salt concentration in the suspension was always 10 M. The different cations had a chlorine counter-ion and the anions had a sodium counter-ion. In jar tests, the coagulant dose needed for a complete turbidity removal was determined, as was the corresponding E.M. of the floes. In the list of Table 5, only ions which can dissolve easily in the water are mentioned. At the given coagulant dose, the EJM. all had reached their constant values. 

With an increase of the coagulant dose, the coagulation and flocculation is speeded-up. This results in shorter floe built-up times. All the process parameters. 

Fig. 5 shows the plot of residual colour and a value vs. co t values. It actually shows the distribution of sedimentation rates of particles formed and the changes of the rate for t = 0, 50 minutes, and 24 hours. Coagulant dose 17 mg/L is lower than the optimum dose for t = 0 (Fig. 4). 

Fig. 8 illustrates the effect of the change in molecular weight distribution of HS in model water. Over 50% of HS2 (Fig. 2) can be taken for fulvic acid. The dose of 25 mg/L was determined by the same procedure used for Fig. 4. Fig. 8 is comparable to Fig. 6 with respect to optimal coagulant dose. The comparison of Fig. 6 with Fig. 8 reveals a lowered ability of separation of coloured substances... 

T = 100 g m ) involved flocculation and sedimentation of colloidal suspensions with precipitated calcium carbonate. The samples became clear after 30 minutes of sedimentation at a coagulant dose (both A and B) of 500 g m. There was no significant difference in the final removal efficiency between the two... 

The optimum doses of coagulants (both B and A) required to clarify a highly turbid colourless solution amounted to 400 and 500 g m , respectively. These large quantities were needed not only for the coagulation of colloids which occurred in great amounts and contributed to the high turbidity level, but also for the flocculation of precipitated calcium carbonate. At coagulants doses equal to,... 

A physico-chemical process based on coagulation-flocculation produces treated waste-water mainly composed of soluble and colloidal matter. A part of supracolloids responsible for TSS is always present, their remaining concentration depending on the coagulant dose. The stability of the treated wastewater is not well known, and it is not rare to see this type of sample aging with an increase in TSS concentration. 

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