Kakar, Farokh Laqa

Dr. Farokh L Kakar is an environmental Engineer at Brown and Caldwell and Founder of Blue College of Water and Technology. Dr. Kakar is also the...

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About Kakar, Farokh Laqa

Dr. Farokh L Kakar is an environmental Engineer at Brown and Caldwell and Founder of Blue College of Water and Technology. Dr. Kakar is also the founder and president of Canadian Young Water Professionals and former Emerging Water Leader at International Water Association (IWA) also serving as Vice President of Young Professionals in Canadian Association for Water Quality (CAWQ). In addition, she is the Global Ambassador of the Society of Women Engineers empowering women in engineering internationally.

Kakar, Farokh Laqa

Titles from this speaker

Description: Effect of Hydrothermal Pretreatment on Resource Recovery From Thickened Waste...

Effect of Hydrothermal Pretreatment on Resource Recovery From Thickened Waste Activated Sludge

Abstract

INTRODUCTION
The world fossil fuel reservoirs are depleting and there is need for renewable energy resources. Sewage sludge is rich in organic carbon, and it can be utilized as a sustainable source for the production of value-added products such as Volatile Fatty Acids (VFAs) and biogas (CH4 and CO2). Anaerobic digestion (AD) is a technology that not only treats the waste, but it also turns the waste to value added products such as VFAs and/or methane. In addition of using methane as bioenergy source, the VFAs have variety of applications such as the production of biodegradable plastics, generation of bioenergy, and carbon source for biological nutrient removal [1]. Researches have evidenced that sludge pre-treatment is a viable strategy to accelerate the hydrolysis process which is the rate limiting step of the AD process [2]. Different pre-treatment technologies such as thermal, chemical, biological, and mechanical have been used to improve the hydrolysis step [2â€“4]. Among them Hydrothermal pretreatment (HTP) is one of promising techniques. The main objective of this research is to investigate the application of HTP of thickened waste activated sludge (TWAS) on the VFAs and methane production. Furthermore, evaluating the application of HTP as a pre- and inter-treatment on fermentation and AD of TWAS was examined. Moreover, combining chemical pretreament (free nitrous acid (FNA), acid, and alkaline) and HTP on the anaerobic digestibility of TWAS was investigated.
MATERIALS AND METHODS
Different HTP conditions were applied to the TWAS both individually and in combination with chemical pretreatment. HTP was conducted using Parr 4848 Hydrothermal Reactor. For the FNA pretreatment, the pH of the sample was adjusted at 5.5 and the required nitrate was added to achieve 1.8 mg HNO2-N/L, then the sample was mixed for 24-hour at 25Â°C. The pH of the sample was adjusted to 3.0 and 10.0 3M HCL and 3M NaOH for acid and alkaline pretreatment, respectively, then the sample was mixed for 24-hour at 25Â°C. Semi-continuous fermentation tests were conducted at 37Â°C and hydraulic retention time of 3 days. The biochemical methane potential (BMP) tests were conducted at 37Â°C and were designed based on F/M ratio of 1 g-TCOD/g-VSS.
RESULTS AND DISCUSSION
Effect of HTP on TWAS solubilization and methane production: The results of this study showed that the COD solubilization increase from 27% at lowest HTP condition of '150Â°C-30min' reaching its maximum value of 49 % at '200Â°C-10min' and it was almost constant afterwards, see Fig. 1. It was observed that lower retention time combined with higher temperatures demonstrated higher solubilization emphasizing that the temperature is the dominating parameter in the HTP process. However, the effect of both temperature and retention time on sludge solubilization were statistically significant (p<0.005). Additionally, the methane production improved by 12%-40% for the pretreatment samples, see Fig. 1. The highest methane yield was achieved at 170Â°C-10min. When the pretreatment condition reached to 220Â°C-30min, the methane yield gets lower than the raw TWAS. This reduction in methane production can be caused by the formation of toxic refractory compounds [5]. The results showed that there was no correlation between the increase in SCOD and the methane yield.
Effect of combined chemical (FNA, acid, and alkaline) and HTP on TWAS solubilization and methane production: Combined pretreatments resulted in higher COD solubilization of 39% compared to the individual pretreatment (average 12% for chemical pretreatment and 36% for HTP), see Figure 2. Furthermore, alkaline pretreatment was the most effective one out of the chemical pretreatments with doubing the COD solubilization compared to the acid and FNA pretreatment. Furthermore, all pretreated samples resulted in higher methane yield, see Figure 2. The results also revealed that combined pretreatments were associated with higher percentages increase (36%-53%) in methane production compared to the individual pretreatment (7%-30%). The highest increase in methane production of 53% was achieved for FNA + HTP. A preliminary economic analysis was performed considering the cost of pretreatment and the increase in methane production and the saving in solid disposal. The costs for the pretreatments per ton TWAS were estimated to be $4.6, $0.21, $0.6, and $0.46 for HTP, acid, alkaline, and FNA pretreatments, respectively. The net revenue/loss ranged from -$1.35/ton TWAS to + $3.64/ton TWAS. The highest net revenue of + $3.64/ton TWAS was observed for the combined HTP and FNA pretreatment.â€ƒ Evaluating the application of HTP as a pre- and inter-treatment on fermentation and AD: Two semi-continuous fermentations were used for raw and pretreated TWAS. The percentages solubilisation due to fermentation were calculated based on the data during the steady state. The results revealed that HTP only has better influence on solubilization compared to the fermentation only, 26% vs 17%. Moreover, combining HTP with fermentation with different configurations had similar effect in terms of solubilization, 44% for HTP plus fermentation and 45% for fermentation plus HTP. Furthermore, the percentage increase in the VFAs production for the HTP followed by fermentation was higher than that of the fermentation followed by HTP. Figure 3 shows the percentages increase in methane production compared to the raw TWAS for the different combinations of the HTP, fermentation, and thickening the samples. Percentage increase in methane production varied from 17% for the hydrothermally concentrate to 46% for the hydrothermally pretreated fermented. The fermented sample resulted in 34% increase in methane production compared to the raw sample, while the hydrothermally pretreated sample resulted in 22% increase in methane production compared to the raw sample.
Conclusions
The following conclusions can be drawn: - HTP improved the COD solubilization and the methane production significantly. The maximum solubilization of 49% was achieved at 200Â°C with 10min - The maximum methane production of 227 mLCH4/gTCODadded was achieved at 170Â°C with 10min. - Combining chemical and hydrothermal pretreatments improved methane yield but not the solubilization. - The highest methane yield of 275 mLCH4/gTCODadded was achieved for the combined pretreatment with FNA and HTP. - HTP increased the VFAs production by 40% compared to the raw TWAS. - There were no significant differences in the methane yield when HTP was applied prior to or after fermentation. - The percentage increase in methane production compared to the raw TWAS for the pretreatment or the inter-treatment were 46% and 44%, respectively.

The main goal of the current study was to investigate the impact of hydrothermal pretreatment on thickened waste activated sludge in terms of applied temperature, process configuration, and chemical addition. Results revealed intensification of temperature beyond 170 C adversely affects the fermentation and anaerobic digestion performance. Further, pretreatment demonstrated a slightly higher methane and VFA yield compared to intertreatment.

SpeakerKakar, Farokh Laqa

Presentation time

16:25:00

16:40:00

Session time

15:30:00

17:00:00

TopicIntermediate Level, Biosolids and Residuals, Energy Production, Conservation, and Management, Facility Operations and Maintenance

Author(s)

Kakar, Farokh Laqa

Author(s)Farokh Laqa Kakar1; Steven Liss1,2,3,4; Elsayed Elbeshbishy1

Author affiliation(s)Environmental Research Group for Resource Recovery, Department of Civil Engineering, Ryerson University, ON, Canada1; Department of Chemistry and Biology, Ryerson University, Ryerson University, ON, Canada2; School of Environmental Studies, Queen's University, ON, Canada3; Department of Microbiology, Stellenbosch University, South Africa4

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2022

DOI10.2175/193864718825158725

Volume / Issue

Content sourceWEFTEC

Word count13

Description: Effect of Hydrothermal Pretreatment on Volatile Fatty Acids and Methane Production...

Effect of Hydrothermal Pretreatment on Volatile Fatty Acids and Methane Production from Thickened Waste Activated Sludge

Abstract

The main goal of this study was to evaluate the impact of hydrothermal pretreatment (HTP) on fermentation and anaerobic digestion (AD) of the Thickened Waste Activated Sludge. For this purpose, all samples were subject to the HTP under 5 Severity indexes extending from 3.00 to 5.00. The HTP temperature, pressure and holding time ranged from 150 to 240oC, 69 to 488 psi, and 5 to 30 min, respectively. The batch mesophilic acidification and biomethane potential tests were conducted in triplicates for all hydrothermally pretreated and none pretreated samples considering the food to micro-organism ratio of 1 g-TCOD/g-VSS. Results revealed that HTP improves the fermentation and AD of TWAS significantly. The maximum solubilization, volatile fatty acids (VFAs) production, and methane yields were 49%, 5.4 g COD/L, 227 mL CH4/g TCODadded, respectively. Also, it was found that the optimum pretreatment condition varied from one parameter to another, for solubilization, it was“200°C-10min”, however, for VFAs production, it was “190°C-10min”, and for methane production, it was “170°C-10min”.

SpeakerKakar, Farokh Laqa

Presentation time

08:30:00

08:50:00

Session time

08:30:00

09:10:00

SessionPretreatment Enhancements and Impacts on Anaerobic Digestion

Session number311

TopicBiosolids and Residuals, Research and Innovation

Author(s)

F. KakarA. RazaviE. Hosseini KoupaieH. HafezE. Elbeshbishy

Author(s)F. Kakar1; A. Razavi1; E. Hosseini Koupaie1; H. Hafez2; E. Elbeshbishy1;

Author affiliation(s)Department of Civil Engineering, Ryerson University1; Greenfield Global2

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2020

DOI10.2175/193864718825157868

Volume / Issue

Content sourceWEFTEC

Word count17

Description: Fermentation Intensification with Vacuum-Assisted Technology: An Evaluation of...

Fermentation Intensification with Vacuum-Assisted Technology: An Evaluation of Full-Scale EBPR Alternatives Using a Calibrated Process Model Analysis

Abstract

IntensiCarb® is a vacuum-based intensification technology that provides process benefits in fermentation or anaerobic digestion. Applying this technology to fermentation allows for half the process volume to achieve improved yield of volatile fatty acids (VFA) for beneficial use. Generating VFA from fermentation provides a benefit to facilities that need supplemental carbon for nutrient removal targets in the liquid treatment process. VFA can be used by facilities to improve enhanced biological phosphorus removal (EBPR) performance, lowering effluent total phosphorus (TP) concentrations. An analysis was completed to evaluate the process performance and life-cycle costs of IntensiCarb® relative to chemical addition and conventional fermentation alternatives for TP removal. Experimental results on vacuum-assisted process intensification were used in the process performance analysis and GHG emissions were estimated to compare alternatives. The evaluation suggests IntensiCarb® is competitive with other alternatives to lower effluent TP with EBPR. FeCl3 chemical addition had the lowest life-cycle cost overall

IntensiCarbÂ® is a vacuum-based intensification technology that provides process benefits in fermentation or anaerobic digestion. An analysis was completed to evaluate the performance and life-cycle costs of IntensiCarbÂ® relative to chemical addition and conventional fermentation alternatives for the purposes of phosphorus removal. This paper describes bench-scale experimental results, presents model performance predictions, and compares life-cycle costs and greenhouse gas emission estimates.

SpeakerArmenta, Maxwell

Presentation time

16:10:00

16:30:00

Session time

15:30:00

17:00:00

SessionExtracting Carbon for Nutrient Removal

Session locationRoom S403a - Level 4

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

Author(s)

Armenta, Maxwell

Author(s)M. Armenta 1; F. Kakar 2 ; A. Al-Omari 3; C. Muller 4; K. Bell 5; G. Nakhla 6; D. Santoro 7; J. Boone 7; M. Armenta 1; R. Coleman 8;

Author affiliation(s)Brown and Caldwell 1; Brown and Caldwell 2 ; Brown and Caldwell 3; Brown and Caldwell 4; Brown and Caldwell 5; University of Western Ontario, London, ON 6; USP Technologies 7; PRAB, Kalamazoo, MI 7; Brown and Caldwell 1; Environmental Operating Solutions, Inc. 8;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2023

DOI10.2175/193864718825159027

Volume / Issue

Content sourceWEFTEC

Word count18

Description: Innovation Portfolio Management for Retrofitting Advanced Biotechnologies for...

Innovation Portfolio Management for Retrofitting Advanced Biotechnologies for Anaerobic Digestion Process at Lulu Island Wastewater Treatment Plant

Abstract

Metro Vancouver recently commissioned the Pilot Digestion Optimization Facility (PDOF) at its Lulu Island Wastewater Treatment Plant (LI WWTP) to facilitate the evaluation of different digestion optimization technologies without risk to full-scale plant operation. This study summarizes the integrated approach adopted at the pilot-scale preliminary design stage for two of these technologies. The first technology aims to increase biogas production rates by testing the Direct Interspecies Electron Transfer (DIET) process using electroconductive materials. The second technology utilizes a biological hydrogen methanation (BHM) process to convert the carbon dioxide portion of biogas into renewable natural gas (RNG) using hydrogen. Cost-effective pilot-scale conceptual designs are developed for testing the in-situ and ex-situ configurations of these technologies in order to reach a go/no-go decision quickly, while still producing replicable results for further scale-up. To guide the decision-making process for selecting these technologies for pilot testing, GHG emission reduction calculations and an energy balance model are used to evaluate the environmental impacts of implementing these technologies at full-scale. A Sumo model is used to evaluate the effects of implementing these technologies on process intensification.

Metro Vancouver, in collaboration with its partners, is developing innovative technologies that reduce greenhouse gas emissions and intensify existing digestion processes. Metro Vancouver will first assess the effectiveness and scalability of these technologies at the Lulu Island Pilot Digestion Optimization Facility. Metro Vancouver intends to incorporate these technologies into one of its treatment facilities if the technologies prove successful at pilot-scale.

SpeakerChegounian, Parisa

Presentation time

15:30:00

15:50:00

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)

Kakar, Farokh Laqa

Author(s)F. Kakar 1; C. Muller 2 ; T. Barber 3; F. Kakar 1; P. Chegounian 4; L. Zaremba 4; T. Gregonia 4; P. Kadota 4; S. Sorensen 4; A. Al-Omari 5;

Author affiliation(s)Brown and Caldwell 1; Brown and Caldwell 2 ; Brown and Caldwell 3; Brown and Caldwell 1; Liquid Waste Services Department, Metro Vancouver, Burnaby, BC, Canada 4; Liquid Waste Services Department, Metro Vancouver, Burnaby, BC, Canada 4; Liquid Waste Services Department, Metro Vancouver, Burnaby, BC, Canada 4; Liquid Waste Services Department, Metro Vancouver, Burnaby, BC, Canada 4; Liquid Waste Services Department 4; Brown and Caldwell 5;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2023

DOI10.2175/193864718825159034

Volume / Issue

Content sourceWEFTEC

Word count18

Description: Integrating Hydrothermal Pre-treatment and Vacuum Fermentation for Volatile Fatty...

Integrating Hydrothermal Pre-treatment and Vacuum Fermentation for Volatile Fatty Acids and Methane Recovery from Municipal Sludge

Abstract

Introduction Nowadays, there is an increase interest in recovering value-added products, such as volatile fatty acids (VFA), nutrients, and biomethane from the wastewater. Anaerobic digestion (AD) is a promising technology to reclaim energy from organic matter. Generally, methane produced from the last phase of AD is the main beneficial product. However, by excluding the methane-forming stage, valuable organic acids such as VFAs can be produced by anaerobic fermentation (hydrolysis and acidogenesis). However, relatively long hydraulic retention time (HRT) and low VFA yield are the main challenges associated with fermentation technology. pre-treatment technology with fermentation can be one of the solutions. Hydrothermal pre-treatment (HTP) has attracted industry attention as it accelerates the hydrolysis step, removes pathogens, reduces the viscosity of the sludge, facilitates smoother operation, improves dewatering, and improves the quality of biosolids in terms of odor (Taboada-Santos et al., 2019). Also, to increase organic loading rates without compromising biogas production and organics destruction, recuperative thickening, which involves solid separation of the digestate and solids recirculation to the digester, has been used to increase reactor capacity (Cobbledick et al., 2016a, 2016b; Li et al., 2020). On the other hand, other techniques such as vacuum evaporation is used for sludge dewatering (Yan et al., 2009) and it has been also employed for ammonia and volatile recovery (Nguyen et al., 2011) and hydrogen recovery from yeast fermentation broth (Sonnleitner et al., 2012). Applying a vacuum to the fermenter and or digester allows the decoupling of HRT from solid retention time (SRT) and can facilitate the separation and recovery of resources such as ammonia and VFA, while simultaneously enhancing sludge thickening. However, this technology is limited by low VFA production yield and rate. Therefore, the integration of HTP and vacuum fermentation is proposed and investigated. Integration of the HTP and vacuum fermentation is expected to enhance the degree of solubilization and increase the solids reduction. Furthermore, the effects of vacuum on the interaction of hydrolytic bacteria, fermentative bacteria, and acetogenic bacteria are largely unknown and therefore this study evaluates the microbial community changes in a vacuum and conventional fermentation systems and the integration of the HTP system. Materials and Methods Mixed sludge and anaerobically digested sludge from Ashbridge's wastewater plant were used to run four semi-continuous systems. Fours systems shown in Figure 1 include System (1) conventional fermentation fed with raw TWAS and PS; System (2) Vacuum fermentation fed with raw sludge; System (3) Conventional fermentation fed by pretreated TWAS + raw PS; System (4) Novel vacuum fermentation fed by pretreated TWAS + raw PS. Vacuumed high-grade VFAs and fermentate produced from these systems were further tested for biological nutrient removal (BNR) and AD, respectively. The optimum HTP condition obtained from our previous studies was used to pre-treat TWAS only (temperature: 170 °C, holding time: 30 min, pressure 6 bar) (Kakar et al., 2019). Fermentation tests were set up under thermophilic conditions, in a 3 L reactor. Conventional fermenters operated with HRT=SRT=3 days and vacuum-fermentation with SRT of 3 days and HRT of 1.5 days. Genomic DNA was extracted from the biomass using the PowerSoil DNA isolation kit (MoBio Laboratories Inc.). The DNA samples were sent to the Genome Quebec Research and Testing Laboratory in MontrÃ©al, QuÃ©bec for 16S rRNA gene sequencing (Illumina MiSeq). The DNA samples were amplified using PCR for amplicon preparations. The GenPipes version 4.0.0 (Bourgey et al., 2019) amplicon-seq pipeline was used to perform microbial community analyses. All the water quality analysis were measured according to the standard methods. Results Results revealed that hydrothermal pre-treatment integration with vacuum fermentation significantly improves the overall sludge hydrolysis (p>0.005), while its impact on fermentation was not significant. Figure 2 reports the average COD solubilization for all four systems. The figure shows that both vacuum fermentation systems, either fed by raw or pretreated sludge, had almost similar COD solubilization of 29% and 31% solubilization due to fermentation only. On the other hand, vacuum fermentation demonstrated about 30% improvement in COD solubilization compared to the conventional fermentation (24% vs 31%). As shown in Figure 3, pretreated feed demonstrates higher VFA yield for both cases (vacuum and conventional fermenters). Furthermore, feeding raw sludge exhibited superior results for vacuum fermenter compared to the conventional fermenter (See Figure 3). The average VFA yields in conventional reactors for raw and pretreated feed were 0.12 and 0.21 g COD/g VSS added, respectively, accounting for about 47% improvement due to HTP. The application of the vacuum led to a much higher VFA yield in fermentate compared to condensate. The average VFA yield in the steady-state phase for fermentate, condensate, and overall (fermentate + condensate) were 0.22, 0.011, and 0.23 g COD/g VSS added, respectively. Whereas, in the conventional reactor, the average VFA produced (0.125 g COD/g VSS added) was about 45% lower than the overall (fermentate + condensate) in vacuum fermenter. The microbial community results showed that the most abundant type of bacteria was Coprothermobacteraeota, followed by Synergistetes, Thermotogae, and Firmicutes which are mainly anaerobic bacteria growing in thermophilic conditions (55 „ƒ- 70 „ƒ). The vacuum application showed a great impact on the alpha diversity while for all the sample points the ASV for the vacuum reactors was lower than the conventional reactor by 15-20% (See Figure 4). Considering the steady-state data, the average ASV value for the vacuum and conventional reactors of 14 and 16, respectively, it was evidnced that the hydrothermal pre-treatment impacted the diversity of the microbial communities significantly. The dominant type of bacteria found for pretreated samples from both conventional and vacuum fermenters and raw for the vacuum system were Coprothermobacteraeota and Synergistetes, while on the other hand, Thermotogae and Synergestetes were the most abundant phyla for raw-conventional samples. The effluents of four different fermentation systems were tested to be used as a potential carbon source for denitrification. According to specific denitrification rate (SDNR) results using four effluents, the nitrite accumulation spike was lowest with the HTP vacuum condensate treatment, which indicates that the nitrite reduction (denitrification) started early in the bioreactor fed with HTP vacuum condensate. This is consistent with the above-mentioned finding where overall solubilized COD accumulation was highest in the HTP vacuum bioreactor. Nitrite accumulation was relatively fast with the raw vacuum fermentate (which indicates possibly nitrate removal rate was fast in this reactor). Furthermore, results revealed that condensate of the vacuum fermenters with and without pretreatment has the highest SDNR of 7.6 and 7.2 mg NO3-N/g VSS.h, compared to all other samples, and control (acetate, 6.8 mg NO3-N/g VSS.h), respectively. The results from the biochemical methane potential (BMP) tests of the fermentates that were produced from the four fermenters revealed that the integrated HTP and vacuum fermentation promotes hydrolysis and considerably enhance the methane production yield. The results showed that raw conventional fermented samples and raw vacuum fermented exhibited 28% and 36% increases in methane yield compared to raw (non-fermented sample). Additionally, integrating the HTP and vacuum fermentation increased the methane yields by 53% compared to raw (non-fermented sample). Conclusions Integration of vacuum in the fermentation reactor led to increasing the VFA yields by about 40% compared to the conventional fermentation, and it controlled the acid accumulation due to the continuous extraction of VFA from the system. While the integration of HTP with vacuum fermentation led to reducing the required HRT by 50% (from 3 days to 1.5 days), increasing the VFA yields to 330 mg COD/g VSS compared to 210 mg COD/g VSS for conventional (HTP) reactor, a higher degree of solubilization (45%), and enrichment of the thermophilic microbial communities such as Coprothermobacteraeota and Synergistetes phyla.

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

SpeakerKakar, Farokh Laqa

Presentation time

9:30:00

10:00:00

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

TopicResearch & Innovations

Author(s)

F. Kakar

Author(s)F. Kakar1, F. Okoye2, H. Aqeel3, S. Liss4, E. Elbeshbishy,

Author affiliation(s)Toronto Metropolitan University1; Brown and Caldwell2; Queen's University3; Stellenbosch University4

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date May 2023

DOI10.2175/193864718825158799

Volume / Issue

Content sourceResiduals and Biosolids

Word count17

Performance Evaluation of Pilot Digestion Optimization Facility (PDOF) for Digestion Intensification of Metro Vancouver Anaerobic Digestion Facilities

Abstract

Introduction Anaerobic digestion has proven effective and reliable for stabilizing sludge for decades1. As municipalities grow, digestion intensification can offset or defer major capital expenditures. Testing operational limits for existing systems and trialing new technologies at full-scale carries considerable risk as potential process failures can lead to long recovery times or not meeting regulatory requirements. One approach to address these challenges is conducting bench-scale tests; however, a direct transition to full-scale can impose risks that were not fully considered at bench-scale. Metro Vancouver has built a Pilot Digestion Optimization Facility (PDOF) to conduct tests at a representative scale without risk to full-scale operations. The PDOF consists of three 8 m3 digesters that can be fed with mixed sludge or any combination of primary and secondary sludge. This paper presents results of the first three tests of a multi-year test plan: baseline digestion, thermophilic digestion and temperature-phased anaerobic digestion (TPAD). The test plan for 2023—2024 is outlined in Figure 1. Baseline digestion aimed to replicate the full-scale mesophilic digesters and achieve stable PDOF operation at various hydraulic retention times (HRTs) to identify the most comparable HRT to the full-scale digesters and to develop a volatile solids removal (VSr) performance curve. Thermophilic digestion will run two pilot digesters at 55 degrees C and 60 degrees C while the third runs at 38 degrees C as a mesophilic control. Stress tests will determine HRT operating limits. TPAD involves separating the digestion process into a fermentation phase in a separate tank from methane production. Higher temperatures (55 degrees C) in the first stage increase the rate of hydrolysis, while lower temperatures (38 degrees C) for the methane forming stage reduce energy input and maximize process stability2. The results of baseline digestion test are complete and discussed here. Results for the other tests will be available at the time of paper submission. Methods The PDOF is located at Lulu Island Wastewater Treatment Plant (LIWWTP) in British Columbia, Canada where two 5,400 m3 mesophilic anaerobic digesters operate with 25-to-30-day HRT. The PDOF feeds the same mixed sludge as the full-scale digesters to three 8 m3 pilot digesters. The PDOF was commissioned in June 2023 and achieved steady state mesophilic digestion after 8 weeks. Baseline digestion testing was conducted from July to September 2023. Performance data includes organic loading rate (OLR), VSr and destruction (VSD), biogas and methane yields, volatile fatty acids (VFA), alkalinity, ammonia, and microbial consortia. Genomic samples are collected, extracted and sequenced using shallow shotgun sequencing. Results Baseline Digestion Key process parameters for the pilot digesters were within 5 to 15 % of the full-scale digesters, suggesting direct scalability between the two. Figures 2—4 highlight the similarity between TS, VFA, and ammonia concentrations. The start-up period used diluted digested sludge and can be seen from June 2023 to mid-August 2023 when the digesters achieved steady-state operation. PDOF metrics including VSr and biogas yield were comparable to the full-scale digesters (Table 1). As biogas data from the test was not completely reliable due to condensate issues, the data reported here relies on measured chemical oxygen demand (COD) and a theoretical conversion of 0.35 standard litres of methane per gram of COD destroyed3. Following baseline digestion, modifications to the gas meters improved the accuracy for further tests. There was good agreement between the microbial consortia population in the pilot and full-scale digesters (Figure 5). Thermophilic digestion with LIWWTP sludge in the PDOF is expected to develop a completely new population as it is not seeded from thermophilic digesters. Thermophilic Digestion A single digester was transitioned to thermophilic temperatures (55 degrees C) without a thermophilic digestate seed by increasing the temperature instantly, with no added feed. To ensure that the thermophilic transition was progressing as expected, VFA and alkalinity were monitored daily (Figure 6). A second digester will be converted to 60 degrees C using different methods where mixed mesophilic sludge will be continuously fed to the digester. The two transition methods will be compared once complete. TPAD The test for TPAD is anticipated to be complete by the time of paper submission. Conclusions The three PDOF digesters demonstrated distinct individual performances according to their HRT during the steady-state period. All three digesters were stable throughout the tests based on digested sludge characterization. The VSr results for Digester B with 20-day HRT were closest to the full-scale digester with 28-day HRT. This may indicate that a scalability factor or inefficiencies at full-scale need to be considered in future tests. With the shorter HRT of Digester C (15 days), the product still meets the Organic Matter Recycling Regulation (OMRR)4 requirements for Class B Biosolids. In addition, this study provides valuable insights into the performance and scalability of the PDOF, operational limits for various digestion processes at reduced HRTs, and potential redefines the minimum requirements to achieve biosolids reguirements.

Anaerobic digestion stabilizes sludge effectively, and optimizing this process can save costs as municipalities grow. Intensified anaerobic digestion enhances efficiency, biogas production, and pathogen reduction via thermophilic digestion, advanced reactor designs, and pre-treatment methods. To test these processes, Metro Vancouver built the Pilot Digestion Optimization Facility (PDOF) at Lulu Island WWTP. This paper summarizes the early results from thermophilic digestion at 55 and 60 degrees Celsius.

SpeakerChegounian, Parisa

Presentation time

16:30:00

16:50:00

Session time

15:30:00

17:00:00

SessionAdvances in Anaerobic Digestion

Session number219

Session locationRoom 344

TopicBiosolids and Residuals, Intermediate Level, Research and Innovation

Author(s)

Chegounian, Parisa, Barber, Tyler, Kakar, Farokh Laqa, Martin, Kelly, Choy, Chris, Zaremba, Lillian, Gregonia, Theresa, Muller, Christopher, Yesin, Michael, Flibotte, Stephane, Yik, Susanna

Author(s)P. Chegounian1, T. Barber2, F. Kakar3, K. Martin4, C. Choy5, L. Zaremba1, T. Gregonia1, C. Muller6, M. Yesin2, P. Chegounian1, T. Barber2

Author affiliation(s)1Metro Vancouver, BC, 2Brown and Caldwell, British Columbia, 3, ON, 4Metro Vancouver, 5Metro Vancouver, 6Brown and Caldwell, MA

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2024

DOI10.2175/193864718825159667

Volume / Issue

Content sourceWEFTEC

Word count18

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