Utilizing the Revolving Algal Biofilm (RAB) As An Industrial Pretreatment Process to Meet Plant Loading Reduction Targets and City Sustainability Goals

Sioux City is home to more than 30 industrial wastewater contributors. Each one of these industries discharges wastewater to the City's WWTP. This wastewater is more concentrated in nutrients than typical domestic wastewater. Due to the additional loading and strain these industrial contributors put on the WWTP, they must pay surcharge costs to the City to treat this wastewater. Although these costs can be a burden to the industries, the greater concern is the lack of additional capacity at the City's WWTP. The City's WWTP frequently exceeds their design TKN loading coming into the plant. This limits Sioux City in its ability to expand and serve more citizens or bring in new industries and with them, jobs, revenue, and infrastructure. To extend the life of the existing plant infrastructure the City is evaluating ways to reduce the total plant loading. One of the largest contributors to plant loading comes from a cluster of industrial users that discharge wastewater to the WWTP. These users combined make up nearly 20% of the City's WWTP designed TKN loading. The City has conceptualized an industrial pretreatment facility that can reduce this loading before it reaches the main WWTP. This will free up capacity for the plant to operate as it was designed and make room for new users to be brought online.
Gross-Wen Technologies' (GWT), Revolving Algal Biofilm (RAB) treatment system has been shown to be an effective technology to help communities' cost effectively and sustainably treat industrial wastewaters to reduce plant loading. Furthermore, during the treatment process, algae biomass is produced. This algae has value and can be sold to create a variety of produces such as fertilizers or biogas. The RAB system is an easy to construct and operate solution to reduce plant loading as an industrial pretreatment facility. Overall, the RAB solution allows the City to effectively utilize the existing infrastructure without the need for significant plant retrofits and allows for more capacity at the WWTP. Furthermore, using algae for wastewater treatment greatly boosts the City's commitment to sustainability. The City of Sioux City is currently facing stricter effluent permits at their WWTP. Due to anticipated increases in the plant loading the plant has reached the limit of what it is able to treat. To extend the lifetime of the existing plant infrastructure the City is evaluating ways to reduce the overall plant loading. Some of the greatest contributions to the plant come from the industrial users that discharge wastewater to the plant. In order to evaluate the RAB's effectiveness at treating this wastewater a pilot-scale RAB system was deployed to the site to gather real-world treatment data. In this 9 month pilot study (December 2020 – September 2021) a GWT pilot-scale RAB system was used to treat several of the industrial user's wastewater to reduce the loading before it was discharged to the plant. In this application the RAB functioned as an industrial pretreatment treatment system to remove plant loading before it reached the treatment plant. Over the course of the pilot study, the RAB system was able to demonstrate that it can effectively reduce the industrial user's wastewater to domestic level concentrations. The system reduced the BOD from ~1000 mg/L to less than 250 mg/L. Additionally, the RAB system was able to simultaneously treat the wastewater for TKN, reducing the TKN from ~350 mg/L to less than 100 mg/L. Lastly, the system was able to reduce the phosphorous concentration by ~50%, setting the WWTP up for future nutrient limits that may be placed on the plant. By installing the RAB system as an industrial pretreatment system, the City not only is selecting the lowest cost alternative to meet their loading reduction goals but also the most sustainable. The RAB system utilizes algae to treat the wastewater and as the algae is grown it removes carbon dioxide from the atmosphere. This, plus the RAB's low energy usage makes it the most sustainable way to treat this industrial wastewater in Sioux City. In order to meet the treatment needs of the City, GWT has proposed that 36 RAB modules are required to treat the combined industrial wastewater. Not only will the RAB capture carbon in the process of growing algae but it will also offset electrical usage at the WWTP. By removing the load upstream of the WWTP, through a more energy efficient process than energy intensive aeration, the plant's total oxygen demand can decrease. By reducing the plant's oxygen demand their electrical usage will drop, offsetting the release of CO2 into the atmosphere. Collectively, these modules have the potential to capture and offset more than 1,000 tons of CO2 from the atmosphere annually. The algae grown in this process has value that can be used to offset operational costs of the RAB system. Furthermore, the carbon that is captured in the growth process can also be valued through carbon credit programs. If a 36 RAB module system were installed in Sioux City as an industrial pretreatment facility the estimated revenue from algae sales and carbon credits is more than $100,000 annually. This cost will offset the operational costs associated with personnel and maintenance of the equipment. This makes the RAB the lowest cost alternative for the community due to the revenue generated by installing this system.
In this pilot study, Sioux City utilized the RAB treatment system as an effective industrial pretreatment technology. The RAB system was able to effectively reduce the combined industrial flow to 'domestic level' concentrations. This shows that the RAB has the potential to greatly reduce the overall plant loading at the City's WWTP. By reducing the plant loading, the WWTP will be able to operate within its design loading and will not struggle to meet the discharge permit. Additionally, the City will be able to bring in new industrial or domestic users that will lead to an increase in revenue for the City. Furthermore, by using algae to treat the wastewater the City is selecting the most sustainable way to treat wastewater and solidifying their commitment to sustainability.