This study documents the energy intensity and environmental impacts from operation of water and wastewater treatment systems through case-studies in US. Life-cycle energy and impact assessments were conducted for the Ann Arbor Water Treatment Plant (WTP) and Ann Arbor Wastewater Treatment Plant (WWTP) in Michigan. The framework for assessment was modified to assess the environmental burdens from Laguna WWTP in California and Ypsilanti Community Utility Authority (YCUA) WWTP in Michigan.
From the comparative assessment of the three WWTPs, it is found that the life-cycle energy for the YCUA WWTP is the highest- 21 GJ/MG; out of which, 46% is from electricity used for operation, 44% from natural gas used for the sludge incinerator and 10% from production of chemicals used for treatment. For Ann Arbor WWTP, electricity utilized accounts for 50%, natural gas use for 25%, sludge-hauling for 16% and chemicals used for 9% of the total life-cycle energy of 16 GJ/MG. The life-cycle energy for the Laguna WWTP is the lowest - 11 GJ/MG, as it meets the total requirement for natural gas and 40% of the electricity required from methane produced upon anaerobic sludge digestion. Hence, 91% of the life-cycle energy for Laguna WWTP is from electricity, 8% from chemicals and a mere 1% from sludge-disposal.
From the assessment of the Ann Arbor 'water and wastewater' system, it is found that the Ann Arbor 'water and wastewater' treatment system accounts for 54% of the total electricity required by the Ann Arbor municipal government sector. Further, the lifecycle energy required for the system is 40 GJ/MG of clean water, out of which 60% is from the operation of the Ann Arbor WTP. The system also generates 5,230 kg CO2 eq. /MG clean water or 3.57 million kg CO2 eq. per year. Electricity required for operation of the Ann Arbor WTP and WWTP contributes significantly to the total life-cycle energy and emissions. Thus, energy conservation at the plants, adoption of renewable energy and an anaerobic sludge digestion system coupled with co-generation unit would prove to be useful for reducing the total life-cycle energy and environmental burdens from the