This document contains instructions for 4 homework problems related to environmental engineering calculations. Problem 1 asks to calculate the volume of an aeration tank given parameters like flow rate, BOD loading, and MLVSS concentration. Problem 2 asks to calculate hydraulic retention times for continuous flow stirred tank and plug flow reactors treating wastewater. Problem 3 provides data to calculate organic loading rate, F/M ratio, and sludge wasting rate for an activated sludge process. Problem 4 gives specifications for a trickling filter to estimate hydraulic loading rate and effluent BOD.