Overloaded sewer mains frequently rupture, requiring costly repairs or replacement, and causing serious inconveniences to affected neighbourhoods as well.
This study is focused on a local wastewater utility in the state of Oregon (United States) that contemplated replacing a 20,000-foot interceptor sewer pipe that forms the backbone of a city’s wastewater collection system. The interceptor was undersized for its service area, serving approximately 800 acres more than originally intended. The project aimed to replace a 50-year-old corroded, undersized, and seismically vulnerable concrete cylinder sewer line with a larger, flexible, high-density polyethylene pipeline. Planning, design, and construction was estimated to take over 10 years at a cost of US$95 million.
As the proposed interceptor project faced budgetary, visibility, permitting, and public acceptance issues, the utility sought alternative solutions, including a decentralized 23,600 m3/d (6.2MGD) facility that could be located close to wastewater sources.
Local, decentralized wastewater management has significant economic and operational advantages, allowing the utility to cost-effectively achieve its goals of relieving stress on the existing infrastructure (while simultaneously increasing capacity) and reducing combined sewer overflows to increase overall infrastructure reliability.
However, the concept generated two main concerns regarding social impacts of conventional onsite treatment solutions, such as a membrane bioreactor (MBR) system, with the proposed site was in a residential area. The first concern was raised around the large “psychological footprint” typical of conventional solutions due to unappealing aesthetics and odors. Secondly, land requirements to both construct a treatment facility and incorporate a surrounding buffer zone to combat the aforementioned visual and odor concerns results in a significant property acquisition.
To overcome these obstacles, a solution that can minimize both the psychological and physical footprint is essential. The utility considered the Organica solution as the most economical and socially-responsible alternative to addressing these concerns.
In contrast to the current infrastructure, decentralizing wastewater treatment with the Organica solution offers numerous advantages:
Aging sewer mains raise concerns with capacity, but also infiltration issues as stormwater and groundwater enters into cracking pipelines. As a result, the city’s sewers have overflowed in heavy rain for almost 20 years. Rain in excess of more than two inches a day can overwhelm the system and cause the interceptor sewer to back-up. The Department of Environmental Quality has repeatedly fined the utility for sewage overflows because the release of untreated sewage into a water body violates the federal Clean Water Act. The construction of an Organica-powered wastewater treatment facility would result in significantly fewer cases of sewer overflows, increasing operational reliability and minimizing negative environmental impacts.
Decentralizing the town’s wastewater management with Organica eliminates overload of existing sewer mains, resulting in lower maintenance and replacement costs. These savings can reach US$2 million per year, or up to US$77 million in total Net Present Value (NPV) relative to the Organica solution. Even in comparison to the alternative decentralised MBR option, Organica was able to provide NPV savings of approximately US$6 million, primarily due to reduced electricity consumption, sludge production, and eliminated need for membrane replacements.
With its minimal physical and psychological footprint, the Organica facility could be seamlessly integrated into the community with virtually no buffer zone, on a site as small as 4,400 m2 (48,000 ft2), without negatively impacting property values or requiring invasive access to the surrounding residential area.
Organica’s sustainability and appealing visuals, preserving “green space” within the community, greatly enhances the public image of the utility as well.
Assumptions: OPEX for both Organica and the alternative wastewater treatment option are assumed to increase at an annual rate of 3%. Replacement cost of the interceptor pipe is assumed to be 2% of the capital cost per annum. NPV is calculated over a 20-year time frame using a 10% discount rate.
Disclaimer: Financial estimates used are based on a hypothetical proposed alternative to replacing an interceptor sewer line in Oregon, US. Images are sample displays. This case study is created for informational purposes only, and should not be considered as a quote or offer of any kind. Financial data, OPEX, CAPEX, actual footprint, components (including but not limited to water reuse functionality), etc. may vary per project depending on the actual requirements.
Use our WWTP Design Generator to plan and compare multiple wastewater treatment plant options in 3 easy steps