Luo, Hao

Hao Luo, PhD, earned his doctorate in Mechanical Engineering from the University of Alberta, specializing in UV air disinfection and indoor air quality. Currently, as a Postdoctoral Researcher at USP Technologies and Western University, he focuses on optimizing wastewater disinfection processes with advanced mathematical and computation modeling. As Co-chair of the IUVA Task Force on Air and Surface Treatment, Hao is dedicated to advancing UV technology and improving environmental control systems across various sectors.

Titles from this speaker

Description: Alternate: Effects of Primary Sludge Blending and Alum Addition on Thermal...

Alternate: Effects of Primary Sludge Blending and Alum Addition on Thermal Hydrolysis-Enhanced Anaerobic Digestion of Waste Activated Sludge and Recalcitrant Dissolved Nitrogen Formation

Abstract

Introduction The waste activated sludge (WAS) produced in Washington Suburban Sanitary Commission's (WSSC Water) Water Resource Recovery Facilities (WRRFs) is historically known to have relatively poor digestibility, even with thermal hydrolysis pretreatment (THP). In agricultural waste management, it has been a common practice to co-digest a poorly biodegradable feedstock with an easily biodegradable feedstock to improve the overall digestibility of the former (Karki et al., 2021). Since primary sludge (PS) generated in WRRFs usually possesses much better digestibility over that of the WAS, this study tested the hypothesis whether blending PS with WAS can increase the biodegradability of WAS. Because WRRFs need to use more coagulants such as alum to precipitate more PS for the blending, the impact of alum on the WAS biodegradability was also taken into consideration. Therefore, this study investigated the effects of PS:WAS blending ratio and alum doses on the WAS digestibility in a THP-anaerobic digestion system. Meanwhile, this study also tested the hypothesis that blending PS with WAS may produce more recalcitrant dissolved organic nitrogen (rDON) as a result of Maillard reaction in THP (Zhang et al., 2020). Maillard reaction occurs between the carbonyl groups of reducing sugar and the amino groups of proteins (Hodge, 1953). Since PS and WAS are mainly composed of carbohydrates and proteins, respectively, and the typical THP temperature at 165 0C is ideal for Maillard reaction, it is a reasonable prediction that more rDON may form within THP fed with PS and WAS blending than without. Materials and Methods Experimental design Dewatered WAS and PS cake samples with around 20% total solids (TS) were collected from two WRRFs of WSSC Water. Depending on the Al that came with each type of cakes, additional Al was supplemented according to the Al doses designed in Table 1. Basically, more Al was supplemented when more PS was blended to simulate the scenario when more alum was consumed for more PS production. A jar test was performed to estimate the Al dose it took to produce enough PS for the blending ratio in Table 1. Then, the PS and WAS cake samples were either individually processed in THP-anaerobic digester (AD) systems as controls or blended according to the blending ratio as summarized in Table 1 to study the blending effects during this three-phase study. All cake feedstocks were diluted to 16% TS prior to feeding into the CAMBI pilot THP system operated at 165 oC for 30 min. The THP effluent was further diluted to 9% prior to being fed into the four pilot mesophilic AD systems. These ADs were inoculated with fresh effluent sludge from a full-scale THP-fed mesophilic AD at DC Water. The steady-state digestates were analyzed for understanding the impacts of PS:WAS blending ratio and alum doses on WAS digestibility. In general, four phases of studies described in Table 1 were performed with controls to understand the effects of 1:1 blended with low Al in phase I, 1:1 Blended with high Al in phase II, and 3:1 Blended with high Al in phase III. rDON determination The four AD effluent samples from Phase II study in Table 1 were subjected to a rDON test. This test was divided into two steps including air stripping and aerobic incubation. The goal of air stripping was to reduce the total ammonia nitrogen (TAN) of the AD effluent to lower than 200 mg/L. This is because the TAN concentration is significantly greater than that of dissolved organic nitrogen (DON) and thus may overshadow the DON level readings which are calculated as the difference between soluble Kjeldahl nitrogen and TAN. The aerobic incubation aimed to remove the biodegradable DON, and in turn the remaining DON in the system can be regarded as rDON. Results WAS digestibility The volatile solid reduction (VSR) has been used as an indicator of sludge digestibility (Luo et al., 2022). Hence, the steady-state VSR of all digesters were determined. Assuming the VSR of PS does not change with and without blending, the blended WAS VSR can be calculated and compared to the control WAS VSR without blending and Al supplementation to assess whether the WAS digestibility has been improved. As can be seen from Figure 1, the WAS VSR did not change with and without blending with PS at a 1:1 ratio without external Al addition. This means blending PS at this low ratio does not improve the WAS digestibility. When a low dose of Al was added to increase the blended sludge background Al level from 1.49 to 1.95%, it can be seen that WAS VSR decreased about 2%, indicating the inhibitory effect of Al on WAS digestion. The reduced hydrolysis rate as a result of binding between Al and protein in WAS has been regarded as the reason accounting for the WAS digestibility decrease (Luo et al., 2022). This conclusion was reinforced by the fact that WAS VSR substantially decreased to 15% when further increasing the background Al level from 1.95 to 2.85% without changing the blending ratio (Figure 1). It is interesting to see that tripling the PS blending ratios can bring WAS VSR back to 28% even when the same high Al dose (2.85%) was used in the sludge mixture. These observations suggest that co-digesting PS with WAS does not directly improve WAS digestibility; however, adding more PS does mitigate the Al inhibition on WAS digestion. It was reported in a previous study that Al is expected to play greater binding effects on WAS than on PS because the affinity of Al to proteins in WAS is higher than that to the polysaccharides in PS (Luo et al., 2022). Therefore, PS might be able to prevent the binding between Al and protein in WAS by acting as a barrier. Hence, the reduced binding potential between Al and protein in WAS could mitigate the Al inhibition on WAS digestion. rDON The centrates containing DON generated from all four digesters in phase II study (Table 1) were exposed to aerobic incubation for 14 days. Profiles in Figure 2a showed that centrates from PS only and blended sludge with high Al addition contained the least DON. PS does not contain much protein and thus is reasonable to produce less DON. Al ¬ is known to be capable of precipitating DON (Zhang et al., 2020), which may explain the low DON level in centrate with high Al addition. In contrast, the DON levels in both WAS only and blending sludge without external Al addition were two times greater. The same trends were also observed with the residual DON, namely rDON in Figure 2b. It should be pointed out that the rDON level in blended sludge was actually substantially greater than the average level from the two individual sludge without blending, indicating extensive Maillard reaction might have occurred when PS and WAS were blended. Conclusions It can be concluded from this study that blending PS does not directly improve the WAS digestibility. Instead, blending more PS did mitigate the inhibitory effect of Al on WAS digestion. However, blending PS with WAS promoted rDON formation due to Maillard reaction between the two types of sludges.

This paper was presented at the WEF/IWA Residuals and Biosolids Conference, May 16-19, 2023.

SpeakerLuo, Hao

Presentation time

13:30:00

16:45:00

Session time

13:30:00

16:45:00

SessionSession 07: Intensifying Digestion

Session number07

Session locationCharlotte Convention Center, Charlotte, North Carolina, USA

TopicDigestion & Stabilization

Author(s)

H. Luo

Author(s)H. Luo1, C. Nguyen2, M. Taylor3, Z. Wang4,

Author affiliation(s)Virginia Tech1; Washington Suburban Sanitary Commision2

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date May 2023

DOI10.2175/193864718825158833

Volume / Issue

Content sourceResiduals and Biosolids

Word count24

Description: Buckingham-π Dimensional Analysis for Chemical Disinfection in Wastewater...

Buckingham-π Dimensional Analysis for Chemical Disinfection in Wastewater Reactors

Abstract

This study presents a novel dimensionless framework for evaluating and scaling chemical disinfection reactors based on Buckingham-π analysis. By defining key π groups and deriving a generalized performance equation, both idealized and real-world systems can be evaluated or optimized efficiently. The model was validated through CFD simulations under varying geometries and disinfectants. A practical case study demonstrated how the framework can be applied for upgrading flow capacity or switching disinfectants while maintaining performance. The proposed approach supports more flexible and cost-effective design and scale-up strategies for wastewater disinfection systems. To facilitate implementation, we developed a decision-making flowchart that incorporates the dimensional analysis into the scale-up and optimization process. This tool offers a flexible, cost-effective alternative for guiding reactor design and performance assessment in both research and industry settings.

MATERIALS AND METHODS
Disinfection efficiency depends on microbial inactivation kinetics and the overall chemical dose, represented by the integral contact time (ICT), which is a function of disinfectant decay and reactor hydraulics. For an ideal plug flow reactor (PFR) with a double-exponential disinfection kinetic model (capturing rapid and tailing phases), the microbial survival fraction at the outlet is expressed as [1]:
Where β, kd, kp, and m are the particle-associated microbial fraction, inactivation rate constants for dispersed and particle-associated microbes (Lm/(mg min)m and L/(mg min)), and the shoulder effect exponent, respectively.

Eleven key parameters influencing disinfection performance-covering reactor geometry, flow characteristics, and reaction kinetics-were identified, and dimensionless groups were constructed using the Buckingham-π theorem (Table 1). Three repeating variables, Dhy, ρ, and v, were selected to derive the rest nine π groups.

These π groups characterize reactor geometry (π1), hydrodynamics (π2), chemical disinfectant decay (π3 and π4), and microbial inactivation kinetics (π5—π7). Substituting these into Eq. (1) yields a generalized, non-dimensional form:
This reformulation allows disinfection efficiency to be evaluated using dimensionless inputs, independent of specific reactor size or operating conditions. Notably, the hydrodynamic group π2 (which includes 1/Re) is not explicitly included in Eq. (2), due to the PFR assumptions of negligible axial dispersion, uniform radial mixing, and steady, unidirectional flow. In real systems like chlorine contact channels, turbulent conditions are typically maintained to preserve plug-flow behavior. Thus, as long as turbulence is sustained, changes in Re have a minimal influence on performance. However, if flow transitions to laminar or poorly mixed regimes, Re becomes more influential and may require explicit consideration, which is outside of the scope for this study.

RESULTS
To validate Eq. (2), CFD simulations were conducted under four hypothetical reactor scenarios (Table 2). Geometry and operating parameters were systematically varied, while dimensionless groups were kept consistent. Case #1 served as the reference, while Cases #2—#4 introduced changes in reactor length, diameter, and cross-sectional shape (square vs. round) to test the dimensional framework.

Results (Figure 1) show that despite significant differences in physical dimensions and flow velocities, the outlet microbe concentrations remained similar across all cases (52.34, 52.04, 52.09, and 52.13, respectively), confirming that matching π groups leads to equivalent disinfection outcomes. These results support the use of the proposed dimensionless formulation for design and scale-up.

While similarity-based scale-up preserves dimensional consistency, it is often infeasible in practice. For example, changing disinfectants alters kinetic parameters (kc, kd, kp, and m), making it impossible to preserve all π groups (π4—π7). To address this, a performance-based scale-up method was developed using Eq. (2) to guide parameter selection when full similarity cannot be maintained.

A decision-making flowchart (Figure 2) outlines both approaches:
- If full similarity is possible, use π group preservation to calculate new design parameters.
- If multiple parameters change (e.g., disinfectant or flowrate), use performance-based scale-up by holding π9 constant and solving for the required dose or operating conditions using numerical optimization.

To demonstrate the framework, a case study was conducted using the secondary wastewater effluent disinfection system at the Great Lakes Water Authority (GLWA). The facility includes four parallel chlorine contact conduits (~140 m long, 4.57 m x 4.72 m cross-section), a junction chamber (8.6 m x 8.84 m x 20.12 m), and a 1.5-km-long outfall pipe (5.49 m diameter). Under dry weather conditions, the plant operates at an average flow of 510 MGD with an influent E. coli concentration of ~21,000 CFU/100mL. Chlorine disinfection is currently used, with ongoing evaluations of PAA and PFA as alternatives. Reaction kinetics for each disinfectant in GLWA wastewater were obtained through batch testing (Table 3).

We first simulated the baseline case (Case #5, Table 3) using chlorine at 0.7 mg/L (after demand), yielding an effluent E. coli concentration of ~70 CFU/100 mL-meeting regulatory limits (<200 CFU/100mL).

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

Presentation time

08:30:00

09:00:00

Session time

08:30:00

10:00:00

SessionOptimizing Disinfection Systems for Efficiency and Reliability

Session locationMcCormick Place, Chicago, Illinois, USA

TopicDisinfection & Public Health

Author(s)

Luo, Hao, Santoro, Domenico

Author(s)H. Luo1, D. Santoro2

Author affiliation(s)Western University1, USP Technologies2

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

DOI10.2175/193864718825160054

Volume / Issue

Content sourceWEFTEC

Word count10

Description: Does Thermal Hydrolysis Alter the Efficiency besides the Rate of Anaerobic...

Does Thermal Hydrolysis Alter the Efficiency besides the Rate of Anaerobic Digestion?

Abstract

Introduction Thermal hydrolysis pretreatment (THP) can intensify the anaerobic digestion process by applying high temperature and pressure to the municipal sludge prior to the anaerobic digestion in the water resource recovery facilities (WRRFs). Many advantages of THP have been reported in previous studies including the improvement of sludge dewaterability, digestion rate acceleration, higher anaerobic digester (AD) organic loading rate, pathogen-free in biosolids, and foaming potential reduction (Higgins et al., 2011). Many studies have been conducted to understand the mechanisms behind the enhancement of anaerobic digestion by THP (Barber, 2016). It is generally accepted that THP increases the sludge anaerobic digestion rate rather than biodegradability. A long enough solids retention time (SRT) of anaerobic digestion is believed to produce the same amount of CH4 with and without THP. In other words, it is not the accumulative but the rate of CH4 that can be presumably improved by THP. However, to our best knowledge, this hypothesis still remains to be tested. The most commonly used method to evaluate the anaerobic biodegradability of municipal sludge is the biological methane potential (BMP). Therefore, the main objective of this study is to evaluate the effect of THP on municipal sludge anaerobic biodegradability via BMP tests. Materials and Methods Experimental design A process flow chart of the experimental design is provided in Figure 1. Dewatered cake collected from a local WRRF with primary sludge and wasted activated sludge blended at a 3:2 v/v ratio was diluted from 30% total solids (TS) to 16% TS prior to feeding into THP. The treated sludge from the THP unit with TS around 9% was then used as the influent for three pilot mesophilic ADs operated at SRTs of 10d. 12.5d, and 15d, respectively. After that, BMP tests were performed on the three digestates to measure their remaining methane potential. Conventionally, the remaining biomass that can survive BMP tests are regarded as non-readily biodegradable. In this study, these biomasses were further processed in a 2nd round of THP to test the hypothesis whether THP can turn the non-readily biodegradable fraction into readily biodegradable. After that, a second round of BMP were performed on the same sludges to measure if more readily biodegradable fractions have been created by the THP. THP and anaerobic digester setup A five-gallon capacity THP system shown in Figure 2 was procured from CAMBI. The THP unit was heated by hot steam to 165 oC for 30 min. The treated sludge was cooled down to room temperature prior to feeding into bench-scale mesophilic ADs. Three units of mechanically mixed ADs with 10 L working volume were operated in parallel with temperature maintained at 36.5 ± 0.3 ËšC. These ADs were inoculated with fresh effluent sludge from a full-scale THP-fed mesophilic AD at DC Water. BMP test setup A respirometer system was used to perform BMP tests with a triplicate design for each digestate sample. The 1st BMP test was performed without inoculation because the samples tested were active digestate. After 1st BMP test, residues of all triplicate groups for each sample were combined and then treated with 2nd round of THP (160 °C, 30 min) prior to the 2nd BMP test. In the 2nd BMP test, inoculum collected from another local WRRF's full-scale mesophilic AD effluent was used as the seed. Blank bottles were prepared with only inoculum for two BMP tests. Control bottles were also prepared by adding glucose to check the inoculum activity in both BMP tests. All the experimental groups were placed in an incubator shaker with temperature controlled at 35.5 °C. During the two rounds of BMP tests, the CO2 and H2S in biogas produced from each bottle were scrubbed by an inline KOH scrubber. The residual biogas after KOH scrubbing was regarded as CH4 and quantified by a bubble counter in each respirometer channel. The CH4 production from each bottle was real-time monitored throughout the two rounds of BMP experiments until the CH4 accumulation profile reach a plateau in each BMP experiment. Results CH4 production during two rounds of BMP tests As can be seen in Figure 3a, profiles in both BMP tests reached plateaus after 40 days. It is noteworthy that the maximum specific methane production rates measured by the profile slopes in the first 2 days of the BMP tests were much greater in the 2nd BMP than that in the 1st BMP. Undoubtedly, more much readily biodegradable biomass has been created by the 2nd round of THP prior to the 2nd BMP. Moreover, the less methane was produced from the digestates collected from ADs with longer SRTs (Figure 3a), which is reasonable because more biodegradable residuals remained under shorter SRTs. The methane yields from unit VS processed in AD and two rounds of BMP tests are shown in Figure 3b. As can be seen, about 0.08 to 0.1 L g-1 VS fed remained even though 0.49 to 0.55 g-1 VS fed has been recovered from THP-AD. Moreover, the methane production in AD and 1st BMP were increased and decreased with the AD SRTs, respectively, which is expected. It is surprising to see that the even more methane was produced from the 2nd BMP test than from the 1st one as a result of the 2nd round THP (Figure 3b). Theoretically, 1st BMP should have exhausted all methane potential remained in the digestates remaining from AD. The fact that even more methane produced from the 2nd BMP after 2nd THP points to an important discovery, i.e., THP does have the capacity to turn non-readily biodegradable fraction of the sludge biomass into readily biodegradable. COD turnover The organic fraction remaining in the sludge samples can be quantified by COD, and thus their organics biodegradability can be measured by the COD removal. Since very similar trends were shown from all samples, the COD turnover in sludge digested under a 15-d SRT was selected as a representative biomass in Figure 4. Both soluble COD (sCOD) measured after 0.45 µm filtration and the particulate COD (pCOD) calculated as the difference between total COD (tCOD) and sCOD were monitored before and after each treatment. As can be seen, THP mainly turned pCOD into sCOD with minor tCOD alternation. A little bit more tCOD reduction observed in the 2nd THP can be attributed to the greater volitation of volatile fatty acids (VFAs) as a result of the VFA enrichment in samples before 2nd THP (Figure 5), which was not the case in the 1st THP when raw cake was fed. This volatile COD loss can be avoided in full-scale THP-AD when the two systems are directly connected. In line with methane production profiles in Figure 3b, majority of COD was removed in the AD. The parallel removal of sCOD and pCOD in the 1st BMP indicates that the much of the residual COD of both types in AD were readily biodegradable. In contrast, only sCOD was removed in the 2nd BMP leaving the pCOD unchanged. It should be realized that the residual sCOD after 2nd BMP is almost equal to that of the 1st BMP(Figure 4). Hence, it is a reasonable inference that all sCOD removed during the 2nd BMP might be the fraction of sCOD created in the 2nd THP from pCOD (Figure 4). Therefore, the role of THP might be turning the non-readily biodegradable portion of pCOD into readily biodegradable sCOD but leaving the biodegradability of inert sCOD unchanged. This is very plausible because one of the main mechanisms in THP is solubilization of biomass (Phuong Linh et al., 2021). For example, microbial cells grown in AD and 1st BMP are usually not biodegradable because of cell wall protection. The breakdown of cell wall by high temperature and pressure in THP can release the soluble intracellular organics thus increasing the biodegradability of the sludge (Phuong Linh et al., 2021). On the other hand, the unchanged pCOD in 2nd BMP corroborates that the non-readily biodegradable pCOD that can survive THP was indeed recalcitrant to biodegradation. These inert pCOD accounts for 13% tCOD in the original cake. Conclusions This study proved that THP not only elevated the rate but also the efficiency of AD by turning a portion of non-readily biodegradable COD into biodegradable. Specifically, it looks like that the sludge biodegradability improvement was from the sCOD created by THP from pCOD but not the portion of recalcitrant sCOD remained.

This paper was presented at the WEF/IWA Residuals and Biosolids Conference, May 16-19, 2023.

SpeakerLuo, Hao

Presentation time

8:30:00

9:00:00

Session time

8:30:00

11:15:00

SessionSession 21: Advances and Innovations in Thermal Processes II

Session number21

Session locationCharlotte Convention Center, Charlotte, North Carolina, USA

TopicThermal Processes and Biochar

Author(s)

H. Luo

Author(s)H. Luo1, F. Haile2, M. Strawn3, Z. Wang4,

Author affiliation(s)Virginia Tech1; Arlington County Water Pollution control Bureau2

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date May 2023

DOI10.2175/193864718825158782

Volume / Issue

Content sourceResiduals and Biosolids

Word count13

Description: Effect of Primary and Secondary Sludge Blending on Recalcitrant Nitrogen Formation...

Effect of Primary and Secondary Sludge Blending on Recalcitrant Nitrogen Formation in Thermal Hydrolysis Pretreatment

Abstract

1. Introduction Thermal hydrolysis pretreatment (THP) of sewage sludge prior to anaerobic digestion is known to be able to enhance the sludge digestibility. For that reason, higher total solids (TS) contents and shorter solids retention times (SRTs) have been commonly used for anaerobic digesters (ADs) fed with sludge processed with THP. Yet, it is also known that the sludge digestibility should decrease with the increase of TS and decrease of SRTs. Whether the application of THP can justify the sludge digestibility loss at higher TS and shorter SRTs remains to be addressed. Moreover, whether blending waste activated sludge (WAS) with primary sludge (PS) can further enhance the digestibility of the WAS following THP is another unknown. Therefore, this study is aimed to understand the effect of TS, SRTs, and PS /WAS blending on sludge digestibility with THP. 2. Materials and Methods Thermal hydrolysis pretreatment A five-gallon capacity THP system shown in Figure 1 was procured from CAMBITM . The THP unit was heated by hot steam to 165 oC for 30 min (6 bar). The treated sludge was cooled down to room temperature prior to feeding into bench-scale mesophilic ADs shown in Figure 2a. Anaerobic digester setup Six units of mechanically mixed ADs as shown in Figure 2a were operated in parallel with temperature maintained at 36.5 ± 0.3 oC using two thermal tents as illustrated in Figure 2b. Another six units of gas recirculation mixed ADs were set up and operated as described in a previous study (Zhang et al., 2020). These ADs were inoculated with fresh effluent sludge from a full-scale THP-fed mesophilic AD at DC Water. The TS feeding into these mechanically mixed ADs was 9% while the TS feeding into these gas recirculation mixed ADs was 4% (Table 1). Blended sludge (PS:WAS, 31:19, w/w dry) collected from a local wastewater treatment plant, (WWTP) was processed through THP and then fed into three mechanically mixed ADs to study the SRT effect on volatile solids reduction (VSR) at 9% TS. The same blended sludge without THP was also fed into another six gas recirculation mixed ADs to study the SRT effect on VSR at 4% TS. PS, WAS, and blended sludge (PS:WAS ,1:1, w/w dry) collected from another local WWTP were processed through THP to feed another three mechanically mixed ADs operated at a TS of 9% and SRT of 15 days to study the effect of sludge blending on the sludge digestibility improvement in terms of VSR. Detailed SRTs, TS, and PS:WAS ratios used in the study can be found in Table 1. 3. Results and Discussion VSR has been used as an indicator of sludge digestibility (Schnaars, 2012). Results in Figure 3a revealed that VSR is positively related to the SRT used in the THP-enhanced ADs. This relationship is more prominent at high TS. For example, at 9% TS, VSRs dropped by 4% as SRTs were reduced from 15 days to 10 days. In contrast, at 4% TS, VSRs dropped the same 4 % when SRTs were reduced from 50 to 15 days. It is noteworthy that, at the SRT of 15 days, VSR dropped another 4% when TS was switched from 4% to 9% even with THP (Figure 3a). The decline of VSR as TS increases is expected because of the high loading rate that was imposed on the AD system. However, the THP enhancement on the sludge digestibility is still prominent in that the loading rate has been increased for 225% when TS was increased from 4% to 9% while the VSR only dropped for 4% at a SRT of 15 days. Even at the SRT of 10 days, such a VSR drop was only 8% in sludge with THP as compared to the sludge without THP at the SRT of 15 days. As shown in Figure 3b, although the VSR of WAS was only as low as 36%, after blending it with PS at a 1:1 ratio, the overall VSR turned out to be as good as 49% which is very similar to that of the PS. This result indicates that blending WAS into PS can significantly improve the digestibility of WAS in THP enhanced AD system for 13%. 4. Conclusions The following concluding remarks can be drawn from this study: 1) The drop of VSRs as a result of SRT decrease from 50 days to 10 days can be explained by the loading rate increase as a result of the THP. 2) Blending WAS with PS can increase the digestibility of WAS by 15% at 9% TS with THP.

This paper was presented at the WEF Residuals and Biosolids Conference in Columbus, Ohio, May 24-27, 2022.

SpeakerLuo, Hao

Presentation time

13:30:00

14:00:00

Session time

13:30:00

16:45:00

Session number12

Session locationGreater Columbus Convention Center, Columbus, Ohio

TopicAnaerobic Digestion, Thermal hydrolysis

Author(s)

H. Luo

Author(s)H. Luo1; M. Taylor2; C. Nguyen3; M. Strawn4; L. Racey5; B. Balchunas6; C. Moline7

Author affiliation(s)Virginia Tech; 1Washington Suburban Sanitary Commision; 2Residuals and Biosolids Speaker; 3Arlington County Water Pollution Control Bureau; 4Arlington County Water Pollution Control Bureau; 5HDR Inc; 6HDR Inc; 7

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date May 2022

DOI10.2175/193864718825158423

Volume / Issue

Content sourceResiduals and Biosolids

Word count16

Description: Identifying the Source, Cause, and Solution of Biosolids Odor at a Maryland Water...

Identifying the Source, Cause, and Solution of Biosolids Odor at a Maryland Water Resource Recovery Facility

Abstract

INTRODUCTION Recently, the Western Branch (WB) Water Resource Recovery Facility (WRRF), one of the five major WRRFs of Washington Suburban Sanitary Commission (WSSC), has the immediate challenge with the biosolids odor produced during the processes of storage, dewatering, and transport of biosolids. The dewatered biosolid cake in WB-WRRF is disposed in landfills now, but the landfills have expressed concerns over excessive odors and in some instances stopped accepting the dewatered biosolid cake. This problem will be continued for the next 3 years. WSSC is looking for some solutions to reduce the biosolids odor issue. According to the processes operated in WB-WRRF, there are several possible reasons causing the odor emission issue. First of all, the blending of sludges with different characteristics may contribute to biosolids odor development. At WB-WRRF, three separate streams of waste sludge, namely high-rate activated sludge (HRAS), nitrification activated sludge (NAS), and denitrification activated sludge (DNAS) are combined in WAS Wet-Well and thickened using a dissolved air flotation (DAF) system. It is likely that the combination of these sludges has augmented the biosolids odor production. Second, the anaerobic condition created during the sludge holding time in the sludge holding tank may be another possible factor contributing to the biosolids odor emission issue. The dewatering centrifuges were shut down during the weekend, leading to 15 ft deep blended sludge accumulation in the two holding tanks for around 48 hours. The bottom of the holding tank may be considered anaerobic, and many offensive odor compounds could be produced during the holding time. It was reported that the major odor-causing compounds emitting from anaerobically digested sludge are mainly H2S, and volatile organic sulfur compounds (VOSCs) including methanethiol (MT) and dimethyl sulfide (DMS) (Novak et al., 2006). Therefore, it is our hypothesis that process such as aeration may maintain a relatively high oxidization reduction potential (ORP) in the sludge holding tanks and mitigate the odor generation. The objectives of this research include: 1. Measure ORP profiles throughout all treatment trains in WB-WRRF to infer the suspicious spots that have high odor generation potential. 2. Test various combinations of the blending of HRAS, NAS, and DNAS to study their effects on the odor emission following sludge dewatering. 3. Evaluate the effect of aeration in the sludge holding tank on odor emission from dewatered cake. METHODS Fresh HRAS, NAS, DNAS and blended sludge were collected from WB-WRRF and blended based on the actual blending ratios used in the WB-WRRF. A laboratory dewatering protocol was established to mimic the full-scale centrifuge dewatering processes following three key steps: (1) polymer conditioning under controlled mechanical shearing at G t value of 105, where G is the mean velocity gradient and t is the retention time taken for sludge to be exposed to shear force; (2) centrifugal sedimentation using a lab centrifuge; (3) cake compressing using a piston under controlled pressure to obtain a cake around 20% total solids which is similar to that in the full scale. The dewatered cake was stored in a glass jar with a septum stopper. The contents of odor compounds such as H2S, MT, DMS in the headspace of the jar were measured using a gas chromatograph (GC). Headspace gas samples were collected on a timely basis and manually injected into the GC. Meanwhile, the ORP profiles across the entire WB-WRRF were measured using two ORP probes. RESULTS ORP profiles along with the treatment trains of WB-WRRF. The three types of sludge in WB-WRRF, namely HRAS, NAS, and DNAS, were firstly combined in a WAS wet-well and then thickened in DAF prior to being stored in holding tanks in preparation for dewatering. As shown in Figure 1, we measured the ORP profiles along with these treatment tanks and found that the ORP quickly dropped from 113 mV in HRAS reaction tank to -81.55 mV in WAS wet-well. Thereafter, the ORP further dropped to -218.95 mV in the sludge holding tank, creating ideal conditions needed for formation of odorous compounds such as H2S, MT and DMS. High-rate activated sludge is the major source of odor generation The headspace peak concentrations of H2S, MT, and DMS measured during the storage time for seven combinations of the three types of sludge are shown in Figure 2. As can be seen, whenever HRAS was blended in, the peak concentrations of the sulfur-containing odorous gas were always prominently high. In contrast, only negligible peak concentrations of H2S, MT, and DMS were observed in NAS, DNAS, and NAS + DNAS. Since the blending ratios used in this study were based on the actual blending ratio in the WB-WRRF, it can be concluded that HRAS accounts for the odor generation during the dewatered cake storage, and NAS and DNAS appear to have little to do with odor generation. Aeration effect on the odor emission from dewatered cake (bench-scale). Aeration of thickened solids in the sludge holding tank was tested at bench-scale as an odor mitigation strategy. As can be seen in Figure 3, all control groups and the mechanical mixing groups demonstrated the higher peak concentrations of odorous compounds than corresponding aeration groups during the storage time (Figure 3). Particularly, the cake from the control group had the highest MT peak concentration, while the aeration group had the lowest one (Figure 3b). Likewise, the aerated sample gave the lowest DMS level (13.86 mg m-3 g-1) which is approximately 30% lower than those in the other two conditions (Figure 3c). Undoubtedly, the aeration in the simulated holding tanks substantially attenuated the extent of H2S, MT, and DMS emission from dewatered cake. Aeration effect on the odor emission from dewatered cake (full-scale). After obtaining the favorable result in the bench-scale SHTs aeration test, full-scale testing of aeration in SHTs as an odor mitigation strategy was conducted, as well. As shown in figure 4, the dewatered sludge with aeration pretreatment during the sludge holding time in the SHTs generated less H2S than the group without aeration pretreatment during the storage time (Figure 4a). There was not much difference between these two groups in terms of MT concentration (Figure 4b). Moreover, only minor levels of DMS were produced (Figure 4c), indicating that the major odorous compounds emitted from the full-scale dewatered cake were H2S and MT. We can conclude that aeration during the sludge holding time can reduce odorous compounds generated from the dewatered cake.

The following conference paper was presented at Residuals and Biosolids 2021: A Virtual Event, May 11-13, 2021.

SpeakerLuo, Hao

Presentation time

13:00:00

13:20:00

Session time

13:00:00

14:00:00

SessionOdor Control and Digestion Intensification Solutions

Session number4

Session locationSimu-Live

TopicAnaerobic Digestion, Biosolids, Odor/Air Emissions

Author(s)

H. LuoD. ZhangM. TaylorC. NguyenS. QuansahZ. Wang

Author(s)H. Luo1; D. Zhang2; M. Taylor3; C. Nguyen4; S. Quansah5; Z. Wang6

Author affiliation(s)Virginia Tech 1; Stantec 2; Washington Suburban Sanitary Commission 3; Washington Sub San Commission 4; Washington Suburban Sanitary Commission 5; Virginia Tech 6;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date May 2021

DOI10.2175/193864718825157957

Volume / Issue

Content sourceResiduals and Biosolids Conference

Word count17

Description: To What Extent Can Solids Retention Time Be Reduced Without Deteriorating the...

To What Extent Can Solids Retention Time Be Reduced Without Deteriorating the Performance of the Thermal Hydrolysis Pretreatment-enhanced Mesophilic Anaerobic Digestion

Abstract

The solids retention time of anaerobic digesters is one of the most important parameters for operational and design purposes. It has been believed to have the potential for process intensification with thermal hydrolysis pretreatment upstream. To assess the extent and impact of digester solids retention time reduction, the digestibility and dewaterability of three pilot-scale, continuous flow, mesophilic anaerobic digesters operating at 15-, 12.5-, and 10-day SRT were evaluated. These 10-liter digesters were fed with 9% total solids CAMBITM THP-processed primary and wasted activated sludge every day for nearly a year. The study revealed that shortening the solids retention time from 15 to 10 days linearly decreased volatile solids reduction from 60.7% to 53.6%, highlighting the reduction in hydrolysis rate as the major drawback. However, other digester performance parameters such as methane yield, rheology, and dewaterability largely remained unchanged.

The solids retention time in anaerobic digesters has long been considered as a potential parameter for process intensification, particularly with the installation of thermal hydrolysis pretreatment upstream. This pilot study aims to assess the impact of further reducing digester SRT from 15 to 12.5 days and then to 10 days on the digestibility and dewaterability. It is anticipated to provide engineering guidance for utilities that consider pursuing process intensification of THP-AD systems.

SpeakerLi, Yitao

Presentation time

09:00:00

09:20:00

Session time

08:30:00

10:00:00

SessionIntensifying and Optimizing Anaerobic Digestion

Session locationRoom S503 - Level 5

TopicIntermediate Level

Author(s)

Li, Yitao

Author(s)Y. Li 1; H. Luo 1 ; M. Strawn 2; L. Racey 2; F. Haile 3; B. Balchunas 4; C. Moline 4; L. Hentz 4; Z. Wang 1; Y. Li 1;

Author affiliation(s)Department of Civil and Environmental Engineering, Virginia Tech 1; Department of Civil and Environmental Engineering, Virginia Tech, Blacksburg, Virginia 24061, United States 1 ; Arlington County Water Pollution Control Bureau 2; Arlington County Water Pollution Control Bureau 2; Arlington County Water Pollution Control Bureau 3; HDR 4; HDR Engineering, Inc. 4; HDR Engineering 4; Department of Biological Systems Engineering, Virginia Tech 1; 1;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2023

DOI10.2175/193864718825159151

Volume / Issue

Content sourceWEFTEC

Word count22

Description: To What Extent Can Thermal Hydrolysis Improve the Biodegradability of Municipal...

To What Extent Can Thermal Hydrolysis Improve the Biodegradability of Municipal Sludge

Abstract

Thermal hydrolysis Pretreatment (THP) has been full-scale implemented as a pretreatment means to expedite the rate of municipal sludge anaerobic digestion (AD). However, it is generally unknown how much methane potential remains after the primary TH-AD, and whether a secondary TH can further enhance the recovery of the residual methane potential. In this study, a biological methane potential (BMP) test was first performed on the digestate collected from a pilot-scale TH-AD process to exhaust its digestibility. After that, the sludge was processed in a secondary TH again and then run through another round of BMP test to check whether the TH has conferred new biodegradability on the sludge. Results showed that another 15% more methane can be further recovered. It was interesting to observe that this extra methane was recovered from the soluble COD produced during the secondary TH. Hence, it can be concluded that TH is capable of turning recalcitrant particulate biomass into biodegradable soluble organics. Several mechanisms responsible for the secondary TH enhancement was discussed

This paper was presented at WEFTEC 2023 in Chicago, IL.

SpeakerLuo, Hao

Presentation time

16:00:00

16:20:00

Session time

15:30:00

17:00:00

SessionImproving Biosolids Treatment Efficiency

Session locationRoom S403b - Level 4

TopicEnergy Production, Conservation, and Management, Intermediate Level, Research and Innovation

Author(s)

Luo, Hao

Author(s)H. Luo 1; Z. Wang 1 ; M. Strawn 2; F. Haile 3; H. Luo 1;

Author affiliation(s)Depratment of Biological Systems Engineering, Virginia Tech 1; Depratment of Biological Systems Engineering, Virginia Tech 1 ; Arlington County Water Pollution Control Bureau, 3402 S Glebe Rd, Arlington, VA 22202 2; Arlington County Water Pollution Control Bureau, 3402 S Glebe Rd, Arlington, VA 22202 3; Depratment of Biological Systems Engineering, Virginia Tech 1;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2023

DOI10.2175/193864718825159035

Volume / Issue

Content sourceWEFTEC

Word count13