Feasibility of Green Hydrogen Production at Lulu Island Wastewater Treatment Plant: Final Effluent Pathway and Ammonia Pathway

Introduction The production of hydrogen at wastewater treatment plants (WWTPs) is emerging as a promising avenue towards establishing a circular water economy. Electrolysis of water or ammonia can be integrated with wastewater treatment to produce hydrogen that can reduce carbon emissions, for example by powering vehicles using hydrogen as a fuel instead of diesel, and also provide residual heat for various purposes including heating buildings1-2. Metro Vancouver (MV) is conducting a feasibility study on green hydrogen production and utilization at Lulu Island WWTP. Lulu Island WWTP serves a population of 220,000 people and has a total capacity of 155 MLD, with average treated flowrate of 79 MLD. Treatment steps consist of pre-treatment, primary treatment, secondary treatment, disinfection and dechlorination and discharge. Methodology Two pathways were considered for production of green hydrogen by electrolysis of water or ammonia. 1. Final Effluent Pathway. Final effluent prior to chlorination is treated further to produce ultrapure water for electrolysis which in turn produces hydrogen and oxygen. Treatment includes pretreatment by screens, media filtration/DAF/ultrafiltration and then reverse osmosis (RO). Treated water is also passed through an ion exchange system to reduce the ionic concentration. 2. Ammonia Pathway. Ammonia is recovered from the centrate of mesophilic anaerobic digesters to produce nitrogen gas and hydrogen gas. Two technologies are evaluated for the recovery of ammonia from centrate: ion exchange and thermal stripping. (Another option, ammonia cracking using thermal hydrolysis to produce hydrogen and nitrogen, was not included in this study.) Flow diagrams depicting the treatment process for FE pathway (Figure 1) and ammonia pathway (Figure 2) are shown below. The hydrogen production is sized based on the availability of ammonia in the centrate to allow direct comparison between the two pathways. The average ammonia concentration in the centrate is 1,297 mg/L, 95% percentile is 1,390 mg/L, and the average flow ranges from 55,000 L/day to 885,000 L/day with average daily flow of 425,355 L/day. The result is a 1 MW electrolyzer operating at 80% to produce 350 kgH2/day. The carbon intensity of produced hydrogen for both pathways is largely dependent on the electricity demand. Notably, the ammonia pathways evaluated utilize considerably higher electricity consumption than the water electrolysis pathway. Utilizing a grid carbon intensity of 11.3 gCO2e/kWh for 2023 in BC 3, the lifecycle carbon intensity of produced hydrogen is expected to be approx. 5.6 gCO2e/MJ for the electrolysis pathway and between 10.1 to 12.7 gCO2e/MJ for the ammonia pathway, depending on the ammonia conversion technology is selected. The feasibility study is assessing different applications for using the hydrogen. Table 1 summarizes the pros and cons of the utilization options. Conclusions Metro Vancouver is currently evaluating the net present value (NPV) and levelized cost of hydrogen (LCOH) produced for the final effluent and ammonia pathways. Depending on the results, MV intends to build a pilot for the preferred technology onsite with industry partners to produce hydrogen for use in heavy-duty trucks or other end-use. The final effluent pathway distinguishes itself from the ammonia pathway primarily based on its technological readiness level. Technology for the final effluent pathway has reached an advanced stage of development and is readily available at scale. Ammonia separation technology is readily available but is still being developed specifically for hydrogen production. The TRL of the final effluent pathway is 9+ whereas TRL for the ammonia pathway is 5 to 7, contingent upon technology-specific variations. A key advantage of the ammonia pathway over the final effluent pathway is that ammonia can be recovered from the centrate, helping to meet final effluent ammonia regulatory requirements without the need for further investment in side-stream or main-stream ammonia treatment. The next steps will confirm the feasibility of hydrogen production at Lulu Island WWTP by:

*Coordinating with vendors to develop cost estimates for both processes.

*Completing a cost benefit analysis for both pathways.

*Determining NPV and LCOH for both pathways.

*Selecting a technology to advance to pilot project definition stage.