ELECTRICITY USE IN SMALL WASTE-WATER TREATMENT PLANTS

Electrical energy consumption was documented for five wastewater treatment facilities with average flows of less than 0.2 m3/s. Three of the plants employed activated sludge, one used trickling filter/solids contact, and one had parallel activated-sludge and trickling-filter trains. All digested sludge aerobically. Most of the larger motors at the facilities (5 kW or more) were operated within a load range giving optimum efficiency. Smaller motors were generally operated in very inefficient load ranges. Aeration for secondary processes or (aerobic) sludge digestion was the greatest single consumer of electrical energy, accounting for 49-97% of total plant requirements. Unit energy consumption at the facilities ranged from 0.39 to 1.17 kWh/m3 of wastewater treated, and from 3.7 to 7.2 kWh/kg BOD5 removed. This parameter varied inversely with the percentage of design capacity at which the plants were operated. The peaking factor for electrical demand ranged from 1.2-1.9.