## Mg precipitant added pr liter of waste water

Figure 11.9. COD (mg/l) of effluent versus dosage of three different précipitants used on waste water from a brewery are shown. 1. corresponds to the use of iron III chloride at pH = 4.2, 2 the use of glucose-tri-sulfate at the same pH and 3 the use of lignosulphpnic acid at pH = 4.5. Note that the initial COD is 3300 mg/l.

Figure 11.10. The figure gives the quality of the effluent obtained by precipitation with lignosulphonic acid (lower curve) and glucose-tri-sulfate (upper curve) on brewery waste water. Optimum dosage of chemicals according to Fig. 11.9 is presumed.

Figure 11.10. The figure gives the quality of the effluent obtained by precipitation with lignosulphonic acid (lower curve) and glucose-tri-sulfate (upper curve) on brewery waste water. Optimum dosage of chemicals according to Fig. 11.9 is presumed.

The temperature influences the solubility of mangesium-ammonium-phosphate and of proteins. The solubility decreases for both with increasing temperature, but it is hardly possible to regulate the temperature to obtain better conditions for the precipitation.

The settling rate is also dependent on the temperature,too. Various expressions have been suggested to describe this relationship:

where Vs,T is the settling rate at the absolute temperature T, and Vs,Tr is the settling rate at the absolute reference temperature Tr.

Tetra Tech (1980) uses:

157.5

where T = temperature in °C and fs(T) is a temperature adjustment function. 0.018

0.016

where T = temperature in °C and fs(T) is a temperature adjustment function. 0.018

0.012

0.010

0.008

Figure 11.11.Viscosity, v, plotted versus temperature. A regression analysis will show the following relationship: = 0.178 / (1 + 0.0337 * T + 0.00022*T2)

Straskraba and Gnauck (1985) suggest another method for considering the influence of temperature on the settling rate. They use the known relations between viscosity and density of water on the one hand and the temperature on the other; see Figs 11.11 and 11.12.

These relations have been used in the construction of a diagram giving the settling rate versus the temperature, as it is known that the sedimentation rate, U, is proportional to da - dw / ¿/w. The larger da, the more strongly pronounced is the temperature dependence, da is the density of the particles, dw the density of water and ¿/w is the viscosity of water.

Figure 11.12 Density of water, dw, plotted versus temperature. A regression analysis will show the following relationship: dw = 0.999879 + 6.02602 * 10"5 * T®.

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