A two stage high rate trickling plant is to treat a municipal wastewater having a flow of 2.0mgd. pertinent data: influent BOD5 = 200mg/l, BOD5 removal by primary clarifier = 33%, filter bed depth = 5 to 7ft, first and second stage filter are equal in diameter, and depth, recycle ratio = 1.0 for each filter and effluent BOD5 = 20mg/l. using the NRC equation, determine the volume of stone required for each filter. and determine the effluent BOD5