All man-made structures and materials have a design life. Across the United States there is a common theme for our water and wastewater treatment facilities and infrastructure. The design life of many of our mid 20th century water and wastewater infrastructures in the United States have reached or are reaching life expectancy limits (ASCE, 2010). To compound the financial crisis of keeping up with the degradation, meeting and exceeding quality standards has never been more important in order to protect local fresh water supplies. This thesis analyzes the energy consumption of a municipal water and wastewater treatment system from a Lake Erie intake through potable treatment and back through wastewater treatment then discharge. The system boundary for this thesis includes onsite energy consumed by the treatment system and distribution/reclamation system as well as the energy consumed by the manufacturing of treatment chemicals applied during the study periods. By analyzing energy consumption, subsequent implications from greenhouse gas emissions and financial expenditures were quantified. Through the segregation of treatment and distribution processes from non-process energy consumption, such as heating, lighting, and air handling, this study identified that the potable water treatment system consumed an annual average of 2.42E+08 kBtu, spent $5,812,144 for treatment and distribution, and emitted 28,793 metric tons of CO2 equivalent emissions. Likewise, the wastewater treatment system consumed an annual average of 2.45E+08 kBtu, spent $3,331,961 for reclamation and treatment, and emitted 43,780 metric tons of CO2 equivalent emissions.
The area with the highest energy usage, financial expenditure, and greenhouse gas emissions for the potable treatment facility and distribution system was from the manufacturing of the treatment chemicals, 1.10E+08 kBtu, $3.7 million, and 17,844 metric tons of CO2 equivalent, respectively. Of the onsite energy (1.4E-03 kWh per gallon treated) 74% is process energy and 26% is non-process energy. Sixty-six percent of the process energy is consumed by the main treatment facility and high service distribution. When analyzing seasonal variations, the highest amount of process energy treated the largest amount of potable water with the maximum revealing four Btu used per gallon treated while utilizing 54% of the design capacity. Compared to the periods when the lowest amount of the design capacity was utilized, 32 – 33%, the facility consumed the seasonal high in energy, approximately 6.7 Btu per gallon treated.
For the wastewater treatment and reclamation side, secondary treatment dominates all 3 categories by consuming 81,701,764 kBtu, $1.1 million, and 32,395 metric tons of CO2 equivalent. The total onsite energy was 2.79E-03 kWh per gallon treated, of which 43% was process energy, and the remainder was consumed by natural gas heating and `other non-process and process’ energy, 34% and 23%, respectively. Most significantly during the months of April and May, when the influent flow of wastewater doubles and is diluted due to the addition of seasonal rain water, the amount of energy spent per gallon of treated wastewater decreases by 48% and 34% from the maximum (5.03E-03 kWh/gallon).
By functioning closer to a forecasted design capacity, the efficiency of the potable water treatment facility could be dramatically improved. This can be achieved by implementing additional storage of ready-to-use potable water and/or by expanding the customer base and collaborating with other regional potable water utilities. For example, a county-wide approach to potable water planning falls into agreement with sustainable planning methods, providing regions of the county that have maximized treatment capacity of potable water and giving this region the opportunity to operate closer to the intended design capacity. On the wastewater treatment side, it is apparent that the more dense the BOD concentration in influent waters the more energy is spent in secondary treatment trying to remove it. Exploring more effective screening and pre-precipitation methods could also prove to save a significant amount in energy spent in the secondary treatment step, reducing the organic load prior to aeration. Coupling this with aeration blower and diffuser improvements can offer significant energy savings. Further water quality data and energy use data needs to be collected and analyzed on the individual wastewater treatment processes, especially regarding the impact and effectiveness of the preliminary and primary treatment steps on secondary treatment.