Bruce I Dvorak
Date of this Version
Hansen, A. (2023). "Reducing Infiltration and Inflow in Small Collection Systems: Environmental, Economic, and Other Impacts." MS Thesis, University of Nebraska-Lincoln.
Wastewater treatment facilities (WWTFs) and the collection systems (CSs) which feed them provide essential services to society by collecting sewage (aka wastewater), biologically treating it, and minimizing risks to human health as well as the impact of waste on the environment. However, as collection systems age, increasing infiltration and inflow (I/I) from groundwater and stormwater can negatively affect the system. I/I is often mitigated to reduce flow and eliminate other negative impacts to the system.
Ten total case studies, seven mechanical water resource recovery facilities (WRRFs) and three lagoon facilities, were examined for the environmental, economic, and other impacts/benefits from I/I mitigation. Life Cycle Assessment (LCA) was used to evaluate the environmental impacts resulting from the construction and operation phases of original (WWTFs and CSs) and new infrastructure designed to mitigate I/I in small communities (less than 10,000 people) in the Great Plains region. Inventory data was gathered from facilities’ original engineering design documents, operation and maintenance manuals, utility bills, and monthly discharge monitoring reports (DMRs). Open LCA (v1.10.3) was used to convert inventory data into ten output impact categories (defined by TRACI 2.1) using Ecoinvent (v3.6).
It was found that mitigating I/I is one of the most significant things an existing WRRF can do to reduce its environmental impact. Overall environmental impacts for mechanical WRRFs were reduced in 6 of 7 case studies, conversely, overall environmental impacts from lagoons were more complex (reduced in one of three case studies). Overall reduction in environmental impact was frequently tied to reduced operational energy or reduced water emissions. The additional environmental impact of materials used in mitigation measures was observed to be proportionally small compared to embedded material impacts. Generally, the costs of I/I mitigation are small, but still larger than energy cost savings. Additionally, “other” impacts and site-specific benefits were often cited as highly important to facilities (e.g., grit reduction, avoiding regulatory non-compliance). Consistent with existing literature, initial per capita flow was predictive of when I/I mitigation is an environmentally and economically sound decision. I/I mitigation projects with initial flows greater than 120 GPCD were economically and environmentally advantageous.
Advisor: Bruce I. Dvorak