Due to ongoing nitrogen contamination of the Deschutes River Basin in central Oregon, an extensive Deschutes County report was developed detailing the need for groundwater protection in the area, which consist largely of onsite and decentralized wastewater systems. During the study period, larger decentralized wastewater facilities without nitrogen-reduction systems were flagged as key projects requiring upgrades.
During the evaluation period for a large recreational vehicle (RV) resort servicing over 200 connections, it was determined that a detailed technology and economic analysis was necessary to identify the most sustainable alternative to replace the failing system. Many factors were key in the comparative analysis of technologies, none more critical than the Total Nitrogen (TN) limit of 10 mg/L and the isolated location of the resort. Other key elements in the evaluation include the ease of operation, energy consumption, process complexity, and capital costs.
The nitrogen-removal processes evaluation included analysis of 7 technologies: textile packed-bed filter, membrane-aerated biofilm reactor (MABR), simultaneous BNR activated sludge, sequencing bioreactor, pressurized membrane bioreactor, submerged membrane bioreactor, multi-stage activated sludge.
A capital cost analysis was completed with assistance from various equipment manufacturers and suppliers. This extensive analysis required comprehensive design work for all seven technologies. The design analysis included capital costs, O&M requirements, and long-term R&R cost analysis.
In order to compare capital costs of technologies, there was a need to determine which components in each system needed to remain the same throughout the comparison. The material specified for the enclosure and tankage was consistent throughout the analyses, which allowed for an accurate comparison of the individual technologies. It was also assumed that the building materials for the control shelter would remain consistent between technologies. With specific components of the design remaining constant, the equipment supplied by each manufacturer and estimated installation time were added for capital cost analysis. For additional comparison, a select few manufacturers were requested to provide quotes on full package system, which are typically installed within steel containers (often used shipping containers). It was, however, determined that steel containers were not optimal for the long-term sustainability of this project and quotes with steel containers were not included in the final comparison. After evaluating the capital costs for each treatment option, the range in up-front capital costs for all systems varied by as much as18%.
The O&M comparison included the hours recommended by each manufacturer and the energy and chemical consumption of the treatment processes. The evaluation of O&M costs showed an annual variation of $5,500 between the least intensive and most intensive operating requirements (roughly 35% variation). Although O&M expenses appear to be of relatively low economic value compared to capital expenditures, the frequency of visits required each week for various technologies and the availability of trained service providers in the area played a vital role in the final selection of appropriate technologies for the project.
R&R costs were then evaluated as part of the long-term sustainability analysis. Overall, R&R costs varied little, with annual budgets differing by only $2,200 among the technologies evaluated. However, the importance of discussing R&R costs at the onset of a project cannot be emphasized enough. Providing the necessary information for owners to be prepared for setting aside funds to sustain the system is critical in the operation of any business.
At the end of the analysis, the final decision was most influenced by the capital and O&M costs, with a heavy emphasis on the availability of trained operators in this isolated area and their comfort level with the preferred technology. The technology selected based on these factors was the MABR system, due mainly to capital costs, performance reliability, and ease of operations.
The MABR system utilize a breakthrough technologies to optimize energy efficient nutrient removal. MABR Technology is a low energy advanced aerobic biological treatment, based on Membrane Aeration Biofilm Reactor process, using an enclosed patented spiral membrane aerated biofilm reactor that reduces power significantly by eliminating the need to use compressed air for aeration of the wastewater. The bioreactor is formed of breathable membranes assembled in a continuous spiral. A constant stream of low-pressure air distributes oxygen to the wastewater through a laminated succession of membrane and spacers wound into spirals. This structure produces optimal oxygen transfer efficiency using natural gas diffusion from one side of the membrane to the wastewater on the other side. This process optimizes a simultaneous nitrification/denitrification. In addition, the system is a simple to operate, robust, and requiring minimal operator attention saving the end user money with lower energy and operating costs.