Improving biogas usage at New York City’s WRRF
For my sustainability class, I had the opportunity to come up with theoretical designs of my choice that promotes sustainable practices. I selected to tackle energy usage and recovery in water resource recovery facilities (WRRFs) in New York City. More specifically, how can we optimize the biogas use from anaerobic digestion?
I began to ask myself what would this system look like? There are various technologies that exists to reuse biogas to produce reusable energy. Immediately, I thought of cogeneration (using the biogas to generate electricity and useful heat) and how interesting it would be for a WRRF to be completely self-reliant on the waste that it was designed to treat. Additionally, I have learned that circular economies can support sustainable infrastructure in a city, so I explored options where the energy produced can supply other infrastructure in New York City. Modifying the cogeneration system to supply the City quickly became an option I would explore, but also generating renewable natural gas (RNG) became an interesting option. The technology that goes into RNG production sounded very similar fundamentally, which is mostly removing contaminants and purifying the methane where the gas is similar to the natural gas in the pipes that fuels our stove, boilers, and heating systems in our home. By the end of this brainstorming phase, I had three alternatives to explore, plus a baseline which is the current state of the WRRF.
For each alternative, I designed a system using equipment that is supplied to industrial scale operations to get an idea of what information I would be expected to be given, or what information I should be able to provide as part of the design calculations. This experience is valuable as a future engineer who will have to consider suppliers and their equipment as a part of the design parameters which will lead to decision making.
As part of the decision making, I incorporated a cost-benefit analysis to see which of the four alternatives provided the best economical benefits. Various approximations were made from the New York State Energy Research and Development Authority (NYSERDA) in getting the capital and operational and maintenance (O&M) cost for the cogeneration and RNG equipment. With the capital and annual O&M costs, the net present value was calculated which was used to assess the overall economic benefits for each alternative.
Another aspect that went into the decision making was the overall greenhouse gas emission. Just like the cost-benefit analysis, the estimates were made based on approximations from studies conducted by the United States Environmental Protection Agency (USEPA) and the United State Energy Information Administration (USEIA).
Ultimately, I found that RNG was the best alternative to implement based on my analyses. In the cost-benefit analysis, the federal government incentives for producing fuels through the renewable identification number (RIN) system was a significant contributor the financial benefits gained. In the greenhouse as emission analyses, it was found that greenhouse gas emission was reduced by 40.9% as carbon dioxide, mainly due to the fact that the biogas is not burned on-site but only refined.
The complete report that I had submitted for my sustainability course can be found at this link.