Yarosz, Douglas

Douglas Yarosz was a speaker at the WEFTEC 2024 conference in New Orleans, LA October 5-9, 2024.

Titles from this speaker

A Journey of Upgrades and Innovations to Achieve Capacity Improvements at Metro Water Services' Central WRF

Abstract

Introduction The Central WRF has undergone significant upgrades to improve its treatment efficiency and capacity. With a rated capacity of 125 MGD and peak secondary flow of 350 MGD, the facility's treatment process includes preliminary treatment, PCs, aeration tanks (ATs), SCs, and UV disinfection. A key upgrade was the conversion of the aeration tanks from draft tube aerators to fine bubble diffused aeration and from two-pass, complete-mix reactors, to a plug-flow A/O process. This upgrade came with several unique challenges due to the sidewater depth of the tanks exceeding 30 ft. The draft tube aerators were inefficient at mixing resulting in pockets of low DO or anoxic conditions and thus reduced nitrification efficiency and promoted low DO filamentous bulking and foaming. The deep tanks were also followed by SCs with a sidewater depth of 16-ft. These conditions would result in nitrogen gas dissolving into the process water in the deep ATs that would evolve in the SCs causing poor settling and floating sludge blankets. The design criteria for diffused aeration at such depths were also not available from manufacturers or in the limited literature. The deepest diffuser submergence that manufactures could factory test their diffusers at was 23 ft. Therefore, assumptions of SOTE had to be made during design that accounted for potentially lower SOTE values than expected due to the air-side oxygen depletion during bubble transit. The assumed values were validated after startup and commissioning by performing off-gas testing. Methods Relevant tank improvements in each of the 8 ATs included anaerobic selector zones, baffle walls, a new aeration system, surface wasting stations, and degassing zones. The new aeration system included blowers, control valves and airflow meters, instrumentation, and fine bubble diffusers. The efficiency of fine-pore diffusers was calculated in clean water according to the ASCE (2006) standard and in wastewater via off-gas testing (ASCE, 2018). Plug-flow was achieved by installing RFP baffle walls in a serpentine manner and divided into 5 aeration zones as shown in Fig. 1. Since the PC effluent and RAS are added separately to the anaerobic zones, an influent chimney was used to direct the influent to the bottom of the anaerobic zone where it would come into close contact with the incoming RAS flow as shown in Fig. 2. To degas the mixed liquor before the SCs, a novel solution was implemented that included mid-depth coarse bubble aeration at the end of the aerobic zones as shown in Fig. 2. This system is critical at peak flows because the degassing that occurs in the aerated effluent channels between the ATs and SCs is significantly reduced at such short retention times. To help control and reduce nuisance foaming, surface wasting stations were installed in each AT as shown in Fig. 3. As the mixed liquor flows past the wasting station, a surface baffle directs any foam to the wasting station and is wasted from the system. Results and Conclusions The anaerobic selector zone has been instrumental in improving sludge settleability. Selector zones create an environment with a high F/M to out-select filamentous organisms, favoring floc-formers with high substrate uptake rates. The first two upgraded ATs were put in service in Jun 2022, resulting in an immediate drop in SVI as demonstrated in Fig. 4. The SVI continued to stabilize as additional pairs of upgraded ATs were put in service in Sep and Nov 2022. SVI averaged 235 +/- 92 mL/g for Oct 2021 — May 2022, and subsequently averaged 91 +/- 41 mL/g for June 2022 — Dec 2022. The SVI has also started to track with changes in F/M: when F/M is greater than 1, SVI averages 69 +/- 18 mL/g. This suggests that selector zone operation is critical for SVI stability. The new surface wasting stations also contributed to improved settleability by removing nuisance organisms accumulated in surface scum that cause foaming and bulking. Rapid reductions in the scum layer were observed after the first upgraded ATs were put in service. A comparison of the surface scum of the SCs before and after upgrades are provided in Fig. 5. As shown in Fig. 6, the average effluent ammonia concentration was approximately 2.5 mg /L (Jan 2021 — May 2022) and after the initiation of the upgrades fell to consistently below the detection limit of 0.4 mg/L (>95% of samples). As shown in the plot, the effluent ammonia has not peaked above 2 mg/L even though the plant operates at an aggressive SRT of 6-8 days year-round. Off gas testing of three ATs was carried out to assess the change in performance with different diffuser age (2, 6, and 10 months of operation). The off-gas testing results are compared to the design assumptions and clean water testing in Table 1. The assumed alpha and fouling factors used to correct the clean water performance for field conditions aligned well with the values measured in the AT with 2-month-old diffusers. The fouling factors decreased significantly for the 6- and 10-month-old diffusers. This information supported the recommendation that the diffusers should be inspected and cleaned at least annually to maintain adequate efficiency. In conclusion, the upgrades at the Central WRF, including the replacement of the draft tube aerators with a fine bubble aeration system, have significantly improved plant performance. The full paper and presentation will contain expanded discussions and all technical detail

Recent upgrades to the deep aeration tanks at the MWS Central WRF have improved sludge settleability, nitrification reliability, and reduced nuisance foam. Key improvements included anaerobic selector zones, baffle walls to reduce short-circuiting, a new aeration system, surface wasting stations, and degassing zones. To degas the mixed liquor before the clarifiers, an innovate solution was implemented that included mid-depth coarse bubble aeration at the end of the aerobic zones.

SpeakerMiller, Mark

Presentation time

16:30:00

17:00:00

Session time

15:30:00

17:00:00

SessionOptimizing Design for Increased Capacity

Session number228

Session locationRoom 349

TopicFacility Operations and Maintenance, Intermediate Level, Municipal Wastewater Treatment Design

Author(s)

Miller, Mark, Jimenez, Jose, Bauhs, Kayla, Yarosz, Douglas, Rosso, Diego

Author(s)M. Miller1, J.A. Jimenez2, K. Bauhs3, D. Yarosz3, D. Rosso4

Author affiliation(s)1Brown and Caldwell, NC, 2Brown and Caldwell, FL, 3Brown and Caldwell, TN, 4University of California, Irvine, CA

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2024

DOI10.2175/193864718825159630

Volume / Issue

Content sourceWEFTEC

Word count17

Bye-Bye Railcars! Nashville's 350 MGD UV Disinfection Facility is Online!

Abstract

Introduction Nashville Metro Water Services' (MWS) Central Water Reclamation Facility (WRF) has disinfected its treated plant effluent using gaseous chlorine since the facility was originally commissioned in 1958. Sixty-five years later, after 10+ years of planning, design, and construction, a new 350 MGD ultraviolet (UV) disinfection facility is online, and the last 90-ton rail cars were removed from the site. As of January 2024, the new UV facility has been operating as expected for six months, with E.coli values well within permit limits. The new UV facility is one of largest UV disinfection installation in the United States. Planning Driven by its Consent Decree, MWS commissioned the Central WRF Optimization Study (COPT Study) which recommended improvements to cost-effectively and reliably increase the peak wet weather capacity of its largest treatment facility from 220 MGD to 350 MGD via optimization; rather than by adding expensive new process tankage (Yarosz and Taylor, 2015). Figure 1 is an aerial photo of the Central WRF, which is located less than 2 miles from the heart of downtown Nashville. Since the Central WRF's existing gaseous chlorine disinfection system was unable to treat the large increase in capacity and MWS continued to have concerns with transporting, storing, and handling gaseous chemicals, MWS decided to evaluate alternative disinfection technologies as part of the COPT Study. The Central WRF also had two disinfection locations and desired to simplify operations by disinfecting optimized plant secondary effluent flows in a single location. A business case evaluation of multiple disinfection technologies was performed using both cost and non-cost considerations to determine the most beneficial long-term solution for MWS (BC, 2014). Capital costs, 15-year net present values (NPV) and 20-year NPVs were developed Non-cost factors include constructability, operability, reliability, safety, impact to traffic, and impact of potential future regulatory issues. UV disinfection was selected over sodium hypochlorite (bulk and onsite generation), peracetic acid (PAA), ozone. Table 1 includes the final results of this business case evaluation. Design of UV Facility Consistent with the project's goal to utilize existing structures, the design team determined it was feasible to construct the new UV disinfection facility within the footprint of the existing north chlorine contact tanks (CCT), which were designed to facilitate chlorine disinfection of 150 MGD. The following bullets briefly discuss some of the key design considerations. These and many other design considerations will be fully detailed in the full technical paper, if selected. The existing pile foundation of the CCTs was sufficient to support the new UV facility. The addition of concrete was offset by the reduction in water volume. The existing piles could also accommodate an enclosed pre-engineered metal building for shelter. CFD modeling was performed to confirm there was adequate mixing of north and south secondary effluent flows and determine a UV channel configuration that would not require flow straightening baffles as MWS has experienced algae issues with them at another WRF. Figure 2 shows output from the CFD model, which indicated that the flow split was within 2% of ideal at peak flow. There was limited headloss available to fit the UV facility into the Central WRFs hydraulic profile. Piping modifications upstream of the facility were required to reduce headloss. UV equipment O&M features were developed collaboratively in workshops with O&M staff where the engineers could listen, understand, and incorporate MWS' ideas and preferences into the design. The UV facility was designed around Trojan Technologies UVSigna(R) equipment because Trojan was able to propose multiple configurations that fit within the limited footprint of the existing chlorine contact tank structure, whereas several other leading UV manufacturers could not. Tables 2 and 3 include Design Flows and Permit Values and UV System Design Parameters, respectively. Additional discussion and supporting data related to the parameters in these tables will be included in the full technical paper, if selected. Construction Sequencing The UV facility layout and structural design had to facilitate construction sequencing that maintained plant effluent disinfection with flow routed through the structure throughout the duration of construction, except for several 2-to-5-day long shutdowns that generally occurred between different phases of construction. With the assistance of the Construction Manager at Risk (CMAR), a sequencing plan was developed in which the existing CCT structure was converted to the UV facility one half at a time. Figures 3 through 7 illustrate the sequence of construction, which was completed in approximately 3 years. Figures 8 is a photo from inside the UV facility. Status of Project/Significance of the Investigation All phases of this 10+ year long project are complete and the $35 million UV facility has been operating successfully for 6 months. This technical paper will include performance data, O&M experience, and 'if we could do it over again' insight from the Central WRF plant manager and the design engineer. Utilities, consultants, contractors, and others who are preparing to upgrade their water resource recovery facility (WRRF) disinfection systems can greatly benefit from this project's experience.

Nashville Metro Water Services' Central WRF has disinfected its plant effluent using gaseous chlorine since the facility was commissioned in 1958. Sixty-five years later, a new 350 MGD UV disinfection facility is online, and the last 90-ton rail cars were removed from the site. As of July 2024, the new $30 million UV facility has been operating successfully for almost one year with E. coli values well within permit limits. It is one of the largest UV facilities in the United States.

SpeakerYarosz, Douglas

Presentation time

11:30:00

12:00:00

Session time

10:30:00

12:00:00

SessionWhat's New in UV?

Session number518

Session locationRoom 238

TopicDisinfection and Public Health, Intelligent Water, Intermediate Level

Author(s)