Consider the single stage trickling filter plant from the solution in Example 9.1. The use of a single stage filter produced a plant efficiency of about 75%. To increase plant efficiency, the engineer decides to add an identical second stage filter in series to the first one. The wastewater flow rate is 2000 m3/d with a BOD5 concentration of 400 mg/L. Primary clarification removes 30% of the BOD5. The filters are each 12 m in diameter and 1.5 m in depth. The direct recirculation ratio for each stage is 2.0. Wastewater temperature is 20°C. Calculate the second stage hydraulic loading rate, organic loading rates, effluent BOD5 concentration, and overall plant efficiency. Comment on the advantages/disadvantages of using single stage versus two stage trickling filters.