This report covers a study undertaken to determine the efficiency of operation and the parameters which measure the efficiency of at least three treatment unit processes used in small waste treatment plants. The first treatment unit is an upflow settling, digestion tank or anaerobic solids contact tank from which the solids are normally to be removed after several years accumulation. Liquid effluent from this primary unit is subjected to aeration in a secondary tank having two compartments, the first providing aeration and the second providing settling and sludge return to the first compartment. During the last six-month period of operation of this plant the raw sewage was placed directly into the aeration unit.