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North Liberty Biosolids Improvements

Phase II Wastewater Treatment Plant

The wastewater treatment plant in North Liberty, Iowa, is undergoing the Phase II expansion to increase treatment capacity for a projected population of approximately 27,000. Part of Phase II includes improvements to the biosolids handling facilities.

Facility planning in 2012 evaluated liquid storage vs. dewatering. To reduce solids handling costs and storage requirements, biosolids dewatering was selected as the preferred method. During the design phase, several different technologies were evaluated. FOX Engineering worked closely with plant staff to determine the most beneficial, operator-friendly, and cost-effective system. Through this evaluation, plant staff could select two preferred technologies: screw press and rotary press.

To further evaluate these technologies, on-site pilot testing was conducted during the summer of 2015. The goals were to evaluate the dewaterability; confirm operational parameters such as solids loading, flow, speed, and pressures; determine optimum polymer dose and full-scale design conditions; and evaluate operation and maintenance requirements. The pilot studies also provided an ideal opportunity for plant staff to get first-hand operational and maintenance experience with the equipment.

FOX used the pilot study data to compare the life-cycle-cost of each technology. The life-cycle-cost evaluation included capital costs, operating costs (power, polymer, water, manpower), maintenance costs, and sludge disposal costs. Based on this evaluation and the plant operator’s preference for operational and maintenance features, the rotary press technology was selected for full-scale design.

The design included construction of a new building to house one rotary press with space to add one more unit in the future, and a new biosolids storage facility. The rotary press is designed to handle up to 108,000 gallons (18,000 lbs) per week.

The new dewatering and storage facilities, which were part of the $15.5 million Phase II plant expansion, started operation in December 2016. Plant staff have been diligently optimizing the process over the past several months to obtain the most efficient use of polymer and highest solids content possible.

Plant staff have been pleased with performance and results of the new dewatering facilities. During the first hauling event this spring (2017), biosolids disposal costs were significantly reduced compared to previous liquid land application methods, resulting in a savings of nearly $54,000.

FOX Engineering is an environmental engineering firm based in Ames, Iowa. We specialize in water and wastewater solutions for our diverse municipal and industrial clients. Our work varies in size and scope and can be found throughout the Midwest and beyond.