9.3 A wastewater treatment plant uses a single stage rock-media trickling filter for secondary treatment, as illustrated in Figure 9.5(a). The wastewater flow rate is 2000 m3/d with a BOD5 concentration of 400 mg/L. Primary clarification removes 30% of the BOD5. The filter is 12 m in diameter and 1.5 m in depth. Direct recirculation pump operates at 2.78 m3/min to the filter. It is observed, as shown in the solution to Example 9.1, that the use of a single filter produces a plant efficiency of about 75%, with very high hydraulic and BOD loading rates.To reduce the loading rates and increase plant efficiency, the engineer decides to add an identical filter in parallel to the first one. The direct recirculation ratio is maintained at 2.0. Wastewater temperature is 20°C. Calculate the new hydraulic loading rate, organic loading rate, effluent BOD5 concentration, and overall plant efficiency. Is the new design better than the old one?