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Lowering Phosphorous with Stainless-Steel Filtration



Regulating phosphorous and nitrogen in water has become and increasing concern of local governments and dischargers. Excessive amounts of phosphorous and nitrogen are known to have far-reaching effects on public health, the environment and the economy. These nutrients are natural parts of aquatic ecosystems, but when too much nitrogen and phosphorus enter the environment the air and water can become polluted. Nutrient pollution impacts all types of water sources, such as streams, rivers, lakes, and bays. Phosphorous and nitrogen make their way into water ways via rain, surface runoff, including urban and agricultural ground water drainage, and municipal and industrial wastewater.


Removing phosphorous from water at municipal and industrial plants can be done in a number of ways (chemically, biologically, tertiary filtration treatment, etc.) Our team takes pride in partnering with innovative and proven technologies to address environmental issues and help facilities move forward into the future.


Project Background


Our team was approached by a consulting engineer with an upcoming phosphorous removal project for a Wisconsin municipality. The wastewater treatment facility is subject to Wisconsin River Total Maximum Daily Load (TMDL) effluent phosphorus limits and would be subject to increasingly stringent limits, which will become effective in July 2023. Additionally, a new wastewater treatment facility is being designed due to issues with flooding and overloading at the existing site. Construction for the new site is anticipated to take place beginning in spring of 2024.


Currently, the wastewater treatment facility uses chemical phosphorus removal with ferric chloride to comply with their phosphorus limit of 1 mg/L. Once the new wastewater treatment facility is built, the City intends to utilize biological phosphorus removal followed by tertiary filtration for long-term compliance with phosphorus limits.


Nuove Energie USA, Inc. was contracted by the City to perform a tertiary filtration study. The pilot arrived at the wastewater treatment facility on June 6th, 2022 and testing commenced on June 10th. Once the needed connections to power and water were completed, and the unit was readied for service. The unit was setup and operated per the design conditions provided to follow and a meeting was held with the facility in cooperation with their consulting engineer prior to the testing commencement.


The Nuove team operated the pilot over the course of the study and compiled the report with results. The pilot program was overseen by the consulting engineer and the facility’s operation staff, who aided with pilot setup, as well as addressing day to day needs, and performed regular check-ins for coordination.


Request for Quote: Design Conditions


In the RFQ, the consulting engineer detailed the design conditions:

  • The pilot study must show that effluent phosphorus can be removed to the following levels.

- Anticipated lowest effluent phosphorus concentration: 0.25 mg/L

- Maximum hydraulic loading to the filters shall be 5 gpm/sf

  • The study should include sufficient testing to document the required coagulant and flocculent doses for the lowest effluent concentration and the range of additional effluent concentrations presented.

  • It is anticipated that influent phosphorus concentrations to the filter will range between 0.6 mg/L to 1.5 mg/L.

Given that the wastewater facility currently utilizes ferric chloride for chemical treatment and will continue to do so at the new wastewater treatment facility, it is the City’s desire to continue using ferric chloride for a coagulant. Nuove Energie provided chemicals, mixing tanks, or other associated equipment necessary for the pilot test. Mixing tanks were sized to have sufficient volumes for detention times needed for range of concentrations above.


The new wastewater treatment facility will be designed for the following flows, which must be treated by the filtration equipment, up to the Design Maximum Day flow. Provisions will be made for bypassing of the Design Peak Hourly Flow.

  • Current Annual Average (2015-2020) – 2.355 MGD

  • Design Annual Average – 2.907 MGD

  • Design Maximum Month – 4.192 MGD

  • Design Maximum Day – 7.098 MGD

  • Design Peak Hourly Flow – 10.416 MGD


Pilot Unit Description


The Ultrascreen® Model UY1001 pilot unit is a self-contained disk filtration system consisting of a filter containing one pair of disks with a total filtration area of 17 square feet, utilizing 316L stainless steel 20-micron woven filtration media. Typical filtration rates of up to 16 gpm/ft2 are achievable depending on influent water quality and process requirements for a total peak capacity as high as 272 gpm.


The pilot unit was equipped with a self-priming influent pump, as well as the needed hoses for supplying and discharging water from the unit. The influent was drawn from the clarifier effluent and fed into the Ultrascreen® flocculation tank for chemical precipitation/flocculation via ferric chloride and an anionic high molecular weight emulsion polymer (Neo Solutions NS 6350 – 30% Anionicity.) The filter skid was equipped with an influent flow meter, local control panel, and an automated self-contained backwashing system, which draws its wash water from the effluent of the

unit.


The unit was provided with coagulant & polymer day tanks along with peristaltic chemical dosing pumps for feeding each chemical. The coagulant ferric chloride, when utilized, was dosed to an inline static mixer directly following the influent feed pump and conveyed to a 795-gallon baffled flocculation tank via a 50-foot long 4-inch flexible hose. The polymer was dosed to the first stage of flocculation with carry-water for better floc formation, as well as improved TP removals. The flocculation tank was equipped with adjustable dual paddle wheel flocculators to deliver chemical mixing.


Data was collected in an operational log of the pilot’s operating parameters and is presented in full in Appendix A. Samples were collected as needed for process optimization via grab sampling and supplemented with an influent and effluent refrigerated composite sampler for the eight hour runs per the protocol established.


Samples for process optimization were tested onsite for Total Phosphorus (TP) and Dissolved Total Phosphorus by the Nuove staff member for making process related adjustments and recorded. A Hach DR5000 photospectrometer, DRB200 Batch Reactor were utilized for the Total Phosphorus analysis and a 0.45-micron filtration membrane syringe was provided for filtering the samples for Dissolved Total Phosphorus prior to analysis. Determination of Total Phosphorus and Dissolved Total Phosphorus was by the PhosVer® 3 Ascorbic Acid method with Acid Persulfate Digestion, which is EPA Compliant per Hach Method 8190 with a Range: 0.06 - 3.50 mg/L PO4.


A duplicate sample from each composite run was given to the wastewater treatment facility for Total Phosphorus testing confirmation in their onsite lab. The wastewater treatment facility also ran each of the samples for Total Suspended Solids (TSS.)


Pilot Setup: a.) Pilot Unit with Clarifier in the background, b.) Two-Stage Flocculation Tankage, c.) Internal View of Flocculation Tank, d.) Ultrascreen Pilot Overall, e.) View of Ultrascreen Disks and Backwash System


How the Ulstrascreen® Filter Works


The Ultrascreen® Disk Filter uses Dynamic Tangential Filtration® to physically remove biological and inorganic solids as well as chemically precipitated solids like Phosphorus from wastewater. The filtering disks are constructed using a woven 316 stainless steel mesh as the filtration medium. Dynamic Tangential Filtration® is a unique, patented concept that uses the combination of constant disk rotation and an influent flow pattern where water passes across the disks tangentially, rather than orthogonally. This reduces the effective openings of the stainless-steel mesh and allows for very efficient separation of micro particles contained in the influent water. The efficiency achieved with tangential filtration allows the system to handle total suspended solids (TSS) upsets up to 150 mg/L and leads to a smaller overall footprint for the system and filtration rates of up to 16 gpm per square foot of disk area.


The filtering disks work in pairs. The influent water enters between a pair of disks and water passes outward across the disks. The filtered water then flows by gravity into a common collection well and exits the unit though the outlet pipe.


As water passes across the rotating disks, solids accumulate on the disk surface, which creates head-loss. This causes the water level between the pairs of disks to increase. When the water reaches a predetermined level, a level sensor activates an automatic spray wash cleaning sequence. Each disk has its own spray header to ensure efficient disk cleaning. The spray wash wastewater (backwash reject) from each set of disks is collected in a common channel and then purged from the unit through a dedicated drain. The reject water is then typically returned to the headworks of the facility for

continued treatment.



The Ultrascreen® Disk Filter offers the lowest possible total cost of ownership. The robust, all stainless-steel construction of the filtering disks means less changing of the filtering elements. Typically, the filtration media has an average lifespan greater than 10 years. None of the mechanical bearings within the tank are submerged, which drastically increases the bearing’s lifespan. The design allows for a simple, “plug and play” startup process and easy access to the unit internals when maintenance is required.


Optimizing the performance of the system is possible because the disk rotation speed, wash cycle timing, and water level in the feed zone are all adjustable. Process adjustments like these are not possible with other static disk filter systems.


The Ultrascreen® Disk Filter is simple to integrate, and it comes as a complete filtration package including the backwash system, disk drive system, local control panel, and connecting flanges factory installed (unless specified otherwise.) With the local control panel being factory assembled to the filter, the interconnecting wiring from the local control panel to the associated filter components and sensors is shipped complete and factory tested, meaning installation and startup typically only requires siting/securing the filter in place, bringing power to the local control panel, connecting the

associated piping, and connecting to SCADA for remote monitoring and operation capability.


The Ultrascreen® Disk Filter’s compact footprint, robust stainless steel filtration media, and ease of installation combined with its low total cost of ownership and easy to maintain design make it the right choice for your tertiary filtration needs.




Phosphorous Removal Results with Nuove Energie


Below is a summary of the operating conditions for each of the composite runs completed and the lab results of the 8 hour or greater composite sample per the testing protocol established. The influent Total Phosphorus to the filter system varied quite dramatically during the course of the pilot, reaching levels of over 3 mg/L TP at the start of the study to less than 0.2 mg/L at the midpoint of the study. The study was paused on June 16-22, to allow the facility to optimize their clarified effluent for the design conditions and once again on July 1-18. This resulted in three ranges of influent TP tested, which were established as High Influent TP (approx. 2-3 mg/L), Low Influent TP (approx. 0.2-0.3 mg/L), Moderate Influent TP (approx. 0.4-0.5 mg/L) which was the closest to the intended design parameters.


The results of the pilot testing proved the Ultrascreen® disk filter can efficiently and effectively reduce Total Phosphorus at the wastewater treatment facility to well within the anticipated TMDL’s.

  • The Ultrascreen® filter removed on average 58% of the particulate Total Phosphorus throughout the duration of the study with a maximum removal of 1.8 mg/L of Total Phosphorus across the filter.

  • With chemical precipitation, the filter effluent TP over the duration of the study averaged 0.12 mg/L, well exceeding the 0.25 mg/L TP effluent goal.

  • Also, it should be noted this 0.12 mg/L TP average included the testing during the high influent TP period at the beginning of the study.

Conclusion


The results of the pilot testing proved the Ultrascreen® disk filter can efficiently and effectively reduce Total Phosphorus at the wastewater facility to well within the anticipated TMDL’s. Phosphorus precipitation of Soluble Reactive Phosphorus can be accomplished either via increased Ferric Chloride dosing to the main facility system with polishing of the remaining particulate Phosphorus via filtration, or with Ferric Chloride and Anionic Polymer dosing to a flocculation system just prior to the Ultrascreen® filters.


Even with a system upset and the loss of BNR phosphorus removal, the Ultrascreen®

filter was able to remove an astounding 1.8 mg/L of particulate phosphorus directly through the filter after chemical precipitation. Throughout the duration of the study, removal of particulate phosphorus averaged 58% for the composite runs recorded. With chemical precipitation over the duration of the study, including the high influent TP period, the Ultrascreen filter averaged 0.12 mg/L, easily exceeding the 0.25 mg/L TP effluent goal set forth in the RFQ.


Testing on 6/15/2022 and then on 6/23-24 were conducted at slightly lower filter loading rates vs. the remainder of the tests due to hydraulic restrictions between the flocculation tank and the filter unit. This was rectified for the additional tests conducted by adjusting the piping configuration. The remainder of the tests were performed at 5 gpm/ft2 average loading rate and one run was performed at 7 gpm/ft2 peak loading rate at the conclusion of the testing.


Overall, the pilot testing of the Nuove Energie Ultrascreen® went extremely well. With chemical precipitation prior to the Nuove system, the filter effluent TP over the duration of the study averaged 0.12 mg/L, easily exceeding the 0.25 mg/L TP effluent goal. Also, it should be noted this 0.12 mg/L TP average included the testing during the high influent TP period at the beginning of the study.


The Ultrascreen® filter operated flawlessly over the course of the study and the conclusion of the study the stainless steel Ultrascreen filtration media was readily cleaned with a simple application of household bleach followed by a commercially available ZEP brand rust and stain remover to remove any residual chemical and biological accumulation.


Once again Nuove Energie would like to thank the City and their consulting engineer for the invitation and support for piloting testing the Ultrascreen® filtration technology. The Ultrascreen’s robust all stainless-steel filtration design is an excellent fit for the planned tertiary improvements to enable the facility to meet the effluent permit requirements, while providing years of trouble-free operation and maintenance.


Want to view the full report?

Contact the ICS Group to request the pilot data, optimized operational parameters and results.





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