Song, Wonho

Wonho Song is a senior engineer in the Wastewater Research Section at the Los Angeles County Sanitation Districts (LACSD), with over 30 years of technical experience at the LACSD and private consulting companies. He is also an adjunct professor at the University of Southern California (USC), where he has been teaching courses on water and wastewater treatment plant design. Wonho holds B.S. and M.S. degrees in civil engineering from Korea University, a M.S. degree in environmental engineering from City University of New York, and a Ph.D. degree in environmental engineering from USC.

Titles from this speaker

Description: Enhancing Secondary Clarifier Capacity through Hydrocyclone Implementation at...

Enhancing Secondary Clarifier Capacity through Hydrocyclone Implementation at Full-Scale Wastewater Treatment Plants

Abstract

BACKGROUND Hydrocyclone technology was tested at the Los Angeles County Sanitation Districts' (Districts) Whittier Narrows Water Reclamation Plant (WNWRP). The WNWRP is a Modified Ludzack Ettinger (MLE) facility with a permitted design capacity of 15 mgd. However, the facility currently operates below its rated flow capacity due to secondary clarifier loading limitations. Additionally, the plant faces seasonal challenges with high sludge volume index (SVI), particularly during winter, which impacts system performance. The plant's location within a floodplain further complicates matters, as construction beyond the existing facility footprint is prohibited. To address the secondary clarifier capacity constraints and winter SVI challenges, the World Water Works inDENSEÂ® hydrocyclone system, equipped with five cyclones, was evaluated at the WNWRP (Figure 1). The hydrocyclone system, applied to the return activated sludge (RAS) stream, separates lighter biomass (overflow) from denser biomass (underflow). The denser fraction is recycled back into the RAS, while the lighter fraction is discarded, enhancing sludge settleability. RESULTS AND DISCUSSION The hydrocyclone's performance was assessed by measuring the solids concentration and SVI in the hydrocyclone inflow, underflow, and overflow streams (Figure 2). Overall, the results revealed a consistent pattern across samples: SVI values followed the order of overflow > inflow > underflow, while TSS concentrations were ranked as underflow > inflow > overflow. Long-term impacts on the full-scale activated sludge process were evaluated by monitoring SVI over time. Figure 3 illustrates SVI trends for the three MLE aeration units (Units 1, 2, and 3) throughout 2024. Hydrocyclone implementation improved sludge settleability, reducing SVI from approximately 175 to 125 mL/g within a few weeks of operation. Continued use further decreased SVI to about 50 mL/g; however, this unexpectedly resulted in higher TSS and turbidity levels in the secondary effluent (Figure 4). In response, the hydrocyclone system was temporarily shut down until effluent quality improved, after which four out of the five cyclones were reactivated. The deterioration in effluent quality was attributed to a loss of extracellular polymeric substances (EPS) within the sludge flocs. EPS forms a matrix that binds microbial cells and traps pinpoint flocs, promoting the formation of cohesive flocs. The high-speed centrifugal forces within the hydrocyclone disrupt the EPS matrix (Xu and Wang, 2019; Xu et al., 2019), weakening cell adhesion. This disruption results in the formation of smaller, fragmented flocs and untrapped fine particles, both of which settle poorly and are more likely to be carried over into the secondary effluent. Scatter plots in Figure 5 illustrates the relationship between average SVI for the three aeration units and TSS and turbidity in the secondary effluent. Figure 5a reveals a positive correlation: higher SVI, indicative of poorer sludge settling, results in increased TSS and turbidity in the effluent. This trend remained consistent after hydrocyclone implementation (Figure 5b). Conversely, excessively low SVI also correlated with elevated effluent solids, likely due to smaller, fragmented flocs and untrapped pinpoint flocs caused by EPS disruption. This U-shaped relationship suggests that maintaining SVI within an optimal range is critical for minimizing effluent solids. Microscopic analysis of biological flocs in the inflow, underflow, and overflow samples (Figure 6) further elucidated these observations. Initial hydrocyclone operation improved settling (~125 mL/g SVI) by regulating filamentous bacteria populations (Figures 6a, 6c, and 6e) within three weeks. However, extended hydrocyclone operation reduced or eliminated filament bridging within flocs (Figures 6b, 6d, and 6f), which contrasts with typical biological flocs where filamentous bridging provides structural integrity. Table 1 summarizes the size distribution of biological flocs across inflow, underflow, and overflow samples collected on four dates. Mid-sized flocs (100—500 Âµm) were dominant. Over time, smaller flocs (<100 Âµm) increased, while larger flocs (>500 Âµm) decreased, indicating that hydrocyclone shear forces break larger, fragile flocs into smaller, denser ones. SUMMARY AND RECOMMENDATIONS Hydrocyclone technology has demonstrated its value as a cost-effective solution for enhancing secondary clarifier capacity by improving sludge settleability. This improvement has allowed the WNWRP to sustain efficient operations at higher flow rates. However, optimizing hydrocyclone operating conditions is essential to balance improved settling performance with maintaining effluent quality. In 2024, the hydrocyclone system was intermittently shut down to address effluent quality concerns, with only four of the five cyclones in operation during the latter half of the year. Beginning in 2025, the system will transition to continuous operation using three cyclones, and findings from this updated configuration will be presented. Building on this success, the Districts are advancing the installation of two additional hydrocyclone systems at the Pomona and San Jose Creek WRPs. Performance data from these installations is expected by mid-2025, and the presentation will include key insights and results from these new applications.

This paper was presented at WEFTEC 2025, held September 27-October 1, 2025 in Chicago, Illinois.

Presentation time

16:00:00

16:30:00

Session time

15:30:00

17:00:00

SessionSqueezing the Tube to the End: Maximizing Capacity

Session locationMcCormick Place, Chicago, Illinois, USA

TopicOptimization of Municipal Facility Operations

Author(s)

Song, Wonho, Ackman, Philip, Weiland, Thomas, Mansell, Bruce

Author(s)W. Song1, P. Ackman1, T. Weiland1, B. Mansell1

Author affiliation(s)LA County Sanitation District1

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Sep 2025

DOI10.2175/193864718825159918

Volume / Issue

Content sourceWEFTEC

Word count13

Description: Optimizing Hydraulic Efficiency of Anoxic Zones through Computational Fluid Dynamics...

Optimizing Hydraulic Efficiency of Anoxic Zones through Computational Fluid Dynamics Modeling and Residence Time Distribution Analysis

Abstract

A combined approach of computational fluid dynamics (CFD) modeling and residence time distribution (RTD) analysis was utilized to optimize and validate the hydraulic efficiency of anoxic zones. Baseline CFD simulations satisfactorily assessed the hydraulic conditions of the anoxic zones, leading to the identification of areas requiring improvement. To address these identified issues, the CFD model explored various modification options, aiming to enhance volumetric efficiency and mixing efficiency. Through CFD simulations, cost-effective hydraulic improvement options were identified for each anoxic zone. Once the selected modifications are implemented, the performance of the modified system was verified through RTD analysis. This involved fitting a hydraulic model to the RTD data obtained from field tracer analysis, providing a comprehensive assessment of hydraulic performance before and after the modifications. The combined use of CFD modeling and RTD analysis presents numerous benefits, such as cost and time savings by avoiding costly trial-and-error installations, while ensuring dependable results.

Computational fluid dynamics (CFD) simulations assessed the hydraulic conditions of anoxic zones and explored various modifications to identify cost-effective improvements for each anoxic zone. Residence time distribution (RTD) analysis validated modified system performance by fitting a hydraulic model to field tracer data, providing a comprehensive assessment before and after modifications. This approach saves costs and time by avoiding trial-and-error installations, ensuring reliable results.

SpeakerSong, Wonho

Presentation time

14:30:00

15:00:00

Session time

13:30:00

15:00:00

SessionSweat Your Assets Off: BNR Optimization

Session locationRoom S403b - Level 4

TopicIntermediate Level, Nutrients

Author(s)

Song, Wonbo

Author(s)W. Song 1; P. Ackman 2 ; N. Melitas 3; W. Song 1;

Author affiliation(s)Los Angeles County Sanitation Districts 1; Los Angeles County Sanitation Districts 2 ; Los Angeles County Sanitation Districts 3; Los Angeles County Sanitation Districts 1;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2023

DOI10.2175/193864718825159007

Volume / Issue

Content sourceWEFTEC

Word count17

Description: Pilot-Scale Comparison of Synthetic Biotrickling Filter Media: Implications for...

Pilot-Scale Comparison of Synthetic Biotrickling Filter Media: Implications for Design of Full-Scale Odor Control Facilities

Abstract

The performance of pilot-scale biotrickling filters (BTFs) for hydrogen sulfide (H2S) removal was evaluated to compare three synthetic media for use within the BTF: (i) polyurethane foam cubes (PU foam), (ii) polyethylene mesh (PE mesh), and (iii) calcium silicate foamed glass (foamed glass). Under low H2S loading conditions, the three media achieved nearly complete removal and showed no difference in their performance. However, clear differences were observed under high loading conditions. PU foam achieved the highest and most consistent H2S removal across diurnal and seasonal variations, followed by PE mesh, then foamed glass. The differences appear to be influenced by media properties, including specific surface area and media porosity, which enable biological growth and affect contact time, respectively. The findings of this study were used to identify cost-effective BTF media for proposed and existing odor control facilities, based on the estimated H2S loading, and to predict the BTF performance with the selected media.

Hydrogen sulfide (H2S) removal was evaluated in pilot-scale biotrickling filters using three synthetic media: polyurethane foam (PU foam), polyethylene mesh (PE mesh), and foamed glass. All media achieved complete removal at low H2S loadings. However, at high loadings, PU foam achieved the highest and most consistent H2S removal across diurnal and seasonal variations, followed by PE mesh and foamed glass. Media properties such as surface area and porosity likely contributed to the differences.

SpeakerSong, Wonho

Presentation time

16:00:00

16:20:00

Session time

15:30:00

17:00:00

SessionManaging the Third Effluent Part I

Session locationRoom N426b - Level 4

TopicIntermediate Level, Municipal Wastewater Treatment Design

Author(s)

Song, Wonho

Author(s)W.W. Song 1; N. Munakata 2 ; P.W. Ackman 3; M. Sullivan 1; A. Malik 1; W.W. Song 1;

Author affiliation(s)Los Angeles County Sanitation Districts 1; Los Angeles County Sanitation Districts 2 ; Los Angeles County Sanitation Districts 3; Los Angeles County Sanitation Districts 1; Los Angeles County Sanitation Districts 1; Los Angeles County Sanitation Districts 1;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2023

DOI10.2175/193864718825159038

Volume / Issue

Content sourceWEFTEC

Word count16

Description: Pilot-Scale Comparison of Synthetic Biotrickling Filter Media for Hydrogen Sulfide...

Pilot-Scale Comparison of Synthetic Biotrickling Filter Media for Hydrogen Sulfide Removal at the Los Coyotes Water Reclamation Plant

Abstract

INTRODUCTION
The Los Angeles County Sanitation Districts (Districts) have operated full-scale odor control systems at their facilities for many years, using either stand-alone biotrickling filters (BTFs) or a combination of a BTF and carbon adsorber. In the combined system, the BTF removes most of the hydrogen sulfide (H2S) and the carbon adsorber polishes the air to remove the remaining odor and volatile organic compounds. Lava rock has been used as the media in the Districts' BTFs since 2005. At the Districts' Joint Water Pollution Control Plant (JWPCP), the H2S removal performance with lava rock media was excellent initially but declined after several years of service. This decline, along with concerns about stress on the media support structure from the weight of the lava rock, prompted consideration of synthetic media for the BTFs. Synthetic media have been installed in several full-scale BTFs at the Districts' facilities, but comparing their performance is difficult due to the differing conditions at each facility. A side-by-side comparison of synthetic media is required to evaluate the relative performance of different media under the same air quality/flow and operational conditions. BTF performance is typically evaluated based on the H2S percent removal efficiency for a specific reactor, or more generally as the H2S removal rate normalized by the media bed volume, i.e., the elimination capacity (EC, in units of g-H2S removed/m3-h). As H2S loading increases, the biofilm within the BTF is expected to grow, resulting in increased EC. Planning is currently underway for an odor control facility consisting of BTFs and carbon adsorbers at the Districts' Los Coyotes Water Reclamation Plant (LCWRP). To support the design of the proposed system, pilot-scale BTFs were constructed and operated for approximately two years to compare three synthetic media that have been considered or used recently in the Districts BTFs: (i) polyurethane foam cubes (PU foam), (ii) polyethylene mesh (PE mesh), and (iii) calcium silicate foamed glass (foamed glass). The objectives of this study were to establish the relationship between the H2S loading and removal/EC for each of the three synthetic media, and to identify any potential issues after extended operation, such as media deformation or loss.

METHODOLOGY
Figure 1 shows the schematic diagram of the pilot-scale BTF system. Each BTF was constructed from a PVC column with a nominal diameter of ~12 inches, filled to a packing height of 4 feet, and operated with an empty bed residence time (EBRT) of ~14 seconds. A recirculation system pumped water from a recirculation tank through a spray nozzle at the top of the BTF at a flow rate of 1.7 gpm, or a hydraulic loading rate of 2.4 gpm/sf of media bed. The pH of the recirculation water was maintained between 1.5 and 2.5 by adding make-up water to the recirculation tank. The make-up water was prepared by adding nutrients to plant washwater, stored in a make-up water tank (shared by the three BTFs), and pumped as needed to each BTF's recirculation tank. An OdaLog meter continuously monitored H2S concentrations and temperatures at the BTF inlet and outlet.

RESULTS
The EC increased linearly with H2S loading (Figure 2), with the PU foam showing the steepest increases, followed by PE mesh, then foamed glass. Figure 3 presents the H2S removal efficiency under varying H2S loadings; to more clearly show trends, data have been averaged in loading increments of 10 g/m3-h, up to a loading of 500g/m3-h. The H2S removal efficiency decreased as H2S loading increased for all three synthetic media. PU foam exhibited the highest H2S removal (â‰¥93% across all tested loadings), followed by PE mesh (â‰¥94% at loadings up to 200 g/m3-h, and 88-93% at loadings higher than 200 g/m3-h), then foamed glass (â‰¥95% at H2S loadings up to 35 g/m3-h, and 80-90% removal at loadings higher than 100 g/m3-h). Upon completing approximately two years of operation of the BTFs, the packing material was removed from the BTF columns and visually inspected and photographed. No signs of compression, deformation, or deterioration were identified. The media were cut in half and the cross sections were visually inspected for biofilm build-up on internal surface or pores. Biofilms were observed throughout the PU foam and PE mesh media, and some of the internal fine structures were encapsulated by biofilm build-up. However, biofilm was primarily found on the external surface of the foamed glass, not within the fine pores of the media.

DISCUSSION
The absolute rate of H2S removal increased with H2S loading (Figure 2); this result suggests that higher H2S loadings and/or concentrations result in more biomass, better mass transfer of H2S into the biofilm, and/or faster removal kinetics. However, the concurrent decrease in H2S percent removal (Figure 3) indicates that any increase in biomass, mass transfer, or kinetics does not completely compensate for the increased loading, i.e., the biomass or contact time is insufficient to completely handle the higher H2S loadings. According to the manufacturer specifications, PU foam has a higher specific surface area than the PE mesh (140-160 vs 114 square feet/cubic foot), which enables more growth of sulfide-oxidizing biomass. PU foam also has a slightly higher porosity than the PE mesh (96-97% vs 92-94%) and therefore provides more void volume and a slightly longer actual contact time for the same EBRT. The better performance by the PU foam may be attributable to a higher biomass, in combination with the slightly longer contact time. The manufacturer specifications for foamed glass list a slightly lower porosity (80-90%) and a much higher specific surface area (600 square feet/cubic foot) than the other two media. However, the visual observation of biomass on only the external surface of the foamed glass (compared to growth throughout the PU foam and PE mesh media) indicates that the pore volume and surface area within the media are inaccessible to the foul air, recirculation water, and/or sulfide-oxidizing bacteria. Consequently, much of the nominal pore volume and surface area are not available for sulfide removal, likely resulting in the observed lower performance by the foamed glass. Of the three media, foamed glass has the lowest cost; PU foam costs ~2-3 times more, and PE mesh costs ~5 times more. Consequently, foamed glass may be the 'best' choice under low loadings, while PU foam or PE mesh may be more appropriate at higher loadings. The performance of the foamed glass media at low loadings has been confirmed at full-scale in one of the Districts' odor control facilities at the JWPCP, where the H2S loading is ~13 g/m3-h. Over the past two years, the foamed glass media in these BTFs has provided > 98% to > 99.7% removal, generally reducing inlet concentrations of 50-300 ppmv down to less than 1 ppmv. However, the expected H2S loading at the LCWRP is much higher, ~60 g/m3-h. Consequently, PU foam or PE mesh is recommended at LCWRP; the higher cost of these two media is expected to be offset by better H2S removal performance, reduced H2S loadings to the second stage carbon adsorber, and decreased costs for carbon regeneration/replacement.

This paper was presented at the WEF Odors and Air Pollutants Conference, May 16-19, 2023.

SpeakerSong, Wonho

Presentation time

13:30:00

14:00:00

Session time

13:30:00

15:00:00

SessionBacteria and Synthetic Media: A Match Made in Odor Heaven

Session number9

Session locationCharlotte Convention Center, Charlotte, North Carolina, USA

TopicOdor/Air Research and Optimization

Author(s)

W. Song

Author(s)W. Song 1; N. Munakata 1; P. ackman 1; N. Melitas 1; M. Sullivan 1; A. Malik 1

Author affiliation(s)LA County Sanitation District1

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date May 2023

DOI10.2175/193864718825158745

Volume / Issue

Content sourceOdors and Air Pollutants

Word count19

Description: Systemwide Evaluation of Iron-Based Sulfide Control Across Wastewater Collection and...

Systemwide Evaluation of Iron-Based Sulfide Control Across Wastewater Collection and Treatment Systems

Abstract

BACKGROUND The Los Angeles County Sanitation Districts (Districts) operate a regional wastewater system serving approximately 850 square miles, including more than 1,400 miles of sewers and 11 treatment plants. Upstream sewers converge into three major Joint Outfall Systems-JOA, JOB, and JOD-that convey wastewater to the A.K. Warren Water Resource Facility (WF), the Districts' largest facility, treating approximately 250 mgd (Figure 1a). To control sulfide-related corrosion and odors, the Districts operate five sulfide control facilities (SCFs) that dose ferrous chloride (FeCl₂) within the wastewater collection system (WCS) (Figure 1a). FeCl₂ is also added at the WF anaerobic digesters to control hydrogen sulfide (H₂S) in digester gas (Figure 1b). Over the past decade, FeCl₂ unit costs have increased approximately 2.5-fold, with 2025 procurement alone totaling about $40 million. Iron dosed upstream directly affects iron and sulfide loading to the WF, with reductions in WCS doses increasing iron demand at the digesters (Figure 2), highlighting the need for systemwide optimization rather than facility-specific optimization. The objectives of this study were to evaluate the Districts' iron-based sulfide control practices across the WCS and WF, quantify the systemwide fate of iron and sulfur, and assess competing iron reaction pathways. The results of this work serve as a foundation for future studies to identify and evaluate opportunities for coordinated systemwide optimization. METHODOLOGY Historical flow, sulfate, sulfide, and iron usage data were analyzed to quantify iron loading and sulfide control practices across the WCS and WF. These data were also used to develop a systemwide mass balance. GIS hotspot analysis of H₂S monitoring data identified spatial patterns and recurring sulfide problem areas. Targeted upstream and downstream sampling at selected SCFs was used to calibrate a chemical equilibrium model (CEM) and then simulate near-field and downstream iron reactions and solids formation. RESULTS AND DISCUSSION Analysis of historical data for the WF influent sewers shows that JOB had the highest sulfate concentrations (Figure 3), largely attributable to wastewater from battery recycling and other industrial sources. Sulfate can be reduced to sulfide under anaerobic sewer conditions. Consequently, JOB was dosed with the most iron, resulting in the highest iron loads (Table 1) and the highest concentrations of total iron and insoluble sulfide (Figure 4), a proxy for sulfide precipitates such as ferrous sulfide (FeS). Calculated and observed iron concentrations showed reasonable agreement for all three sewers, with doses in JOA and JOB frequently exceeding 20 mg-Fe/L and even 30 mg-Fe/L in some years -above the typical sulfide-control range of 5–20 mg-Fe/L (WEF, 2017; Gutierrez et al., 2010). These results suggest upstream iron dosing in JOA and JOB may not be fully optimized. A GIS hotspot analysis of H₂S monitoring data (Figure 5) identified statistically significant sulfide clusters in three areas that are consistent with operator observations. These clusters were confirmed to have elevated sulfide levels, based on 90th-percentile H₂S concentrations aggregated by manhole (Figure 6) for representative low (2019) and high (2022) sulfide years, as measured at the WF. Near-field sampling downstream of the South Gate JOA SCF shows close agreement between measured and CEM-predicted total and dissolved iron concentrations (Figure 7a), confirming model calibration. Modeling indicates approximately 30% of dosed iron reacts rapidly with carbonate and orthophosphate to form siderite and vivianite, while FeS formation is limited immediately after dosing due to low dissolved sulfide availability (Figure 7b). Reductions in orthophosphate and alkalinity across multiple sampling events further support rapid near-field iron scavenging (Figure 8). Serial CEM simulations (Figures 9–11) show iron solids form progressively as sewage flows downstream in JOA, JOB, and JOD, with shifting contributions of FeS, vivianite, and siderite driven by evolving sulfide, phosphate, carbonate, and pH conditions. Aggregated systemwide, nearly all iron dosed upstream reaches the WF as solid-phase minerals (Figure 12). The systemwide iron mass balance (Figure 13) indicates that most iron within the WF influent is retained in solids and exits the WF in biosolids. The iron alone (ignoring any co-precipitated anions) comprises an estimated 10% of the biosolids mass, highlighting the strong linkage between upstream sulfide control and downstream solids handling and cost. Model results were compared to a sewer deposit sample collected from a location downstream of the Beach Avenue JOD SCF. Characterization of the deposit was broadly consistent with the model-predicted precipitation of FeS and siderite: the elemental composition was dominated by iron, sulfur, carbon, and oxygen, and sulfur was co-located with iron. (Figure 14). SUMMARY AND FUTURE WORK Results show iron dosing for sulfide control in the collection system is often conservative, with substantial iron consumed by carbonate and phosphate reactions and transported to the WF as solids. Findings support the need for coordinated, systemwide sulfide control. Future work will evaluate alternative control strategies, sulfate source control from industrial dischargers, and optimized iron dosing using integrated BioWin modeling.

This paper was presented at WEFTEC 2026 in New Orleans, Louisiana.

Presentation time

09:30:00

09:45:00

Session time

8:30:00

10:00:00

SessionOdor and Corrosion Control: Transformation and Optimization

Session locationErnest N. Morial Convention Center

TopicAir Quality and Odor Management, Collection Systems, Facility Operations and Maintenance, Municipal Wastewater Treatment Design, Public Communication and Outreach

Author(s)

Song, Wonho, Jimenez, Karina, Fitamo, Temesgen, Hsia, Patricia, Munakata, Naoko, Mansell, Bruce

Author(s)W. Song1, K. Jimenez1, T. Fitamo1, P. Hsia1, N. Munakata1, B. Mansell1

Author affiliation(s)LA County Sanitation District, 1LA County Sanitation District, 1LA County Sanitation District, 1LA County Sanitation District, 1LA County Sanitation District, 1LA County Sanitation District, 1

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Sep 2026

DOI10.2175/193864718825160313

Volume / Issue

Content sourceWEFTEC

Word count13