Provide answers to the following questions related to pH control, ion exchunge, reverse osmosis and the activated sludge process. (i) Explain one (1) key operating approach and one (1) monitoring method to ensure the effective performance of the application of each technology applied to water or wastewater treatment: (3) (a) pH control (e.g., Cr and Cu in wastewater) (4) (b) ion exchange (e.g., surface water softening for Ca or Mg ) (3) (c) reverse osmosis (e.g., remove total dissolved solids from groundwater) (ii) An activated sludge plant is to treat 100,000m3/d of municipal wastewater. You have been asked to assist the senior process design engineer by calculating the tollowing: (3) (a) The required aeration tank volume V in m3 and the aeration tank hydraulic retention time () in hours; (4) (b) the quantity of sludge to be wasted daily (Qw) in kg/d; and (3) (c) the return sludge recycle ratio (Qr/Qo). Use the following process information: - Influent BOD5 and TSS=200mg/L : - effluent BOD5 and TSS=15mg/L; - yield coefficient, Y=0.6; - decay rate, kd=0.04d1 : - average MLSS in the aeration tank, X=4,000mg/L : - waste MLSS from the clarifier, Xw=10,000mg/L; and - mean cell residence time, c=10 days