Wastewater treatment plants serve an important role in society to purify water. Primary treatment at wastewater facilities begins with screens to filter out larger items like sticks and rags, then a grit chamber where sand and small stones settle, followed by the sedimentation tank allowing suspended solids to sink. Most systems also include a secondary treatment process to filter out additional organic particles. Sewer systems also get inflow from other sources like yard drains, cooling towers, street wash water, and groundwater infiltration. Excessive infiltration and inflow (I&I) can dilute the sewage that goes to the wastewater treatment plant, reducing the efficiency and possibly overloading the system. This results in an additional maintenance burden, potential environmental impact, and can impact the facilities’ life expectancy. Some small wastewater facilities have been overdesigned to accommodate treatment of excessive I&I, but they use significantly more energy. Life-cycle assessment has proven to be an effective tool in comparing environmental impacts on systems, but there has been little research using LCA on real world projects related to the performance of wastewater facilities and I&I mitigation.
Researchers Andrew Hansen, Susan Moussavi, and Bruce Dvorak analyzed the environmental implications of I&I mitigation projects using case studies of both wastewater resource recovery facilities and lagoon systems. The objectives of their research, “Reducing Infiltration and Inflow in Small Collection Systems: Environmental, Economic, and Additional Impacts,” were threefold: to use LCA to calculate the environmental impact, to perform cost modeling and understand the economic impact before and after I&I mitigation, and to identify any additional impacts. The results of this study in the Journal of Environmental Engineering can be applied to wastewater facilities and their systems regardless of size and will have a major impact on sustainability. Learn more about their research at https://doi.org/10.1061/JOEEDU.EEENG-7446. The abstract is below.
Wastewater treatment facilities and sewage collection systems provide essential services to society that can be negatively affected by increased infiltration and inflow (I&I). Ten case studies examined the construction and operation phases of wastewater infrastructure serving small communities (<4,000 people); the case studies were used to analyze the environmental, economic, and additional impacts and benefits from I&I mitigation using life-cycle assessment (LCA), cost data, and anecdotal information. Consistent with existing literature, I&I mitigation projects completed where initial flow was greater than 454 L (120 gal.) per capita per day were economically and environmentally advantageous. It was found that mitigating I&I is often one of the most significant practices existing facilities can implement to reduce environmental impacts. Overall environmental impacts for mechanical wastewater resource recovery facilities (WRRFs) were reduced in six of seven case studies. Conversely, overall environmental impacts from lagoons were reduced for one of three case studies. Environmental impact reductions were typically tied to reduced operational energy and/or water pollutant emissions. Generally, I&I mitigation costs are small compared to estimated original facility costs. Additional impacts and benefits include improved wet weather resilience and reduced maintenance, which were commonly cited by staff as highly important.
Consider these findings in detail and how they can benefit wastewater processing in the ASCE Library: https://doi.org/10.1061/JOEEDU.EEENG-7446.