4aerobic digesters (water depth = 15 ft) received waste from an mbr treatment plant. given conditions: q = 0.5 m. g.d., bod = 180 mg/l , soluble bod = 100 mg/l, t. s.s. = 200 mg/l, v. s.s. = 160 mg/l, mlss = 7000 mg/l, srt= 28 days, y= 0.8 and kd=0.04 (d-1 ). the target effluent soluble bod is zero. calculate the aeration basin volume, waste sludge, and volume of each aerobic digester required to meet class b requirements.

An external consultant recommends that a plant installs a bank of capacitors for power factor correction. this will reduce the peak electrical demand charges by an average of 93 kw every month. the plant current pays $13 per kw in peak demand charges. the capacitor bank will include 223 kw of fixed capacitors, and 183 of variable capacitors. the fixed capacitors cost $59 per kw, and the variable capacitors will cost $65 per kw. the consultant charges 21% of the equipment costs to install the capacitors. because this project will reduce the demand for the electric utility, they are prepared to provide a one-time rebate of $42 per kw of reduced demand. what is the simple payback period for this project (in years)?