Treatability Factor Determination

The method of obtaining treatability factors and n values (media specific) involves the use of complex equations. For practical design purposes, a graph is more convenient. Figure 7.23.4 is a design chart for a trickling filter that uses synthetic media with an n value of 0.5 for various treatability factors.

Environmental engineers must obtain the treatability factors by field testing for specific wastewater. Figure 7.23.4 relates the raw hydraulic loading (Q, without recirculation) for a depth (D) to the design performance required. For example, obtaining a BOD removal of 80% with a specific raw hydraulic dosage rate (Q) and depth (D) a wastewater with a K factor of 0.020 requires four times as much filter area as a wastewater with a treata-bility factor of 0.08.

Trickling filters can provide roughing or complete treatment of wastewater. Roughing treatment does not reduce the treatability of the filter effluent in a subsequent, activated-sludge, process step. A synthetic-media trickling filter is suited for roughing treatment when high temperature is involved because the cooling effect of the filter makes the effluent more amenable to activated-sludge treatment.

Synthetic-media trickling filters are not economically suitable to obtain high treatment levels for soluble organic matter with low treatability factors (below 0.05) because of the large filter volume required.

(1 + 0.1R)2 where R is the recirculation ratio

FIG. 7.23.4 Effect of residence time on BOD removal efficiency. The n is a dimensionless exponent function of the trickling filter media. Its value is 0.67 for conventional rock media, 0.50 for most synthetic media, and intermediate values for other types of trickling filter media.

FIG. 7.23.4 Effect of residence time on BOD removal efficiency. The n is a dimensionless exponent function of the trickling filter media. Its value is 0.67 for conventional rock media, 0.50 for most synthetic media, and intermediate values for other types of trickling filter media.

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