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1 March 2017

Biogas energy recovery at a California wastewater treatment plant – Lessons learned

Bernardini, Jessica (1)I recently worked on a very interesting project in California to design a biogas energy recovery system for a wastewater treatment plant (WWTP). The system recovers nearly 100 percent of the methane produced from anaerobic digestion of wastewater sludge and conditions it for heat and power generation and transportation fuel. The design integrates a BioCNG™ gas conditioning system, microturbines, hydronic boiler, and BioCNG fueling station. This was a unique and rather innovative project – and one of the more involved projects of its kind. I thought others might be interested in some of the lessons our team learned.

First a bit about the facility

bernardini-wwtp1The WWTP digester produces biogas at an average of 32 standard cubic feet per minute (scfm). The average methane content of the biogas is 63 percent.

The system we developed allows the WWTP to produce biogas in two different modes: Renewable natural gas (RNG) mode and conditioned digester gas (CDG) mode. In the RNG mode, an RNG storage tank acts as a buffer. The RNG is used by the fueling station and/or the hydronic boiler. One microturbine is operating with near full heat/electrical generation during this mode of operation. When the RNG storage tank is full, the system switches to CDG mode, with no RNG consumption. Two microturbines are operating at approximately 75 percent of full capacity while the system operates in CDG mode, with the microturbines producing both electrical and heat output.

Funding opportunities made it possible

One of the things that made the project feasible is new renewable energy funding opportunities now available in California. So far, the project has secured over $1 million in funding from the California Energy Commission, as well as sales tax exclusion funding from the California Alternative Energy and Advanced Transportation Financing Authority. Other possible options for projects like this include credits through the California Low Carbon Fuel Standard (LCFS), as well as utility company rebates.bernardini-lasg1-completed1

Special project considerations

Biogas projects have a list of “special considerations” that are unique to these projects. Here are a few special project considerations that are applicable to projects that have biogas sources ranging from landfills to anaerobic digesters:

  • Distances and enclosures required by National Fire Protection Association (NFPA).
  • Potential expansion/increase in available gas, including receipt of fats, oils, and grease (FOG), increased feedstock, food slurry, landfill expansion.
  • The need to obtain permits and approvals from multiple agencies.
  • Dealing with the shutdown of the existing system while transitioning to the new system.
  • Decommissioning of existing equipment with new equipment installed and ready to take its place.
  • Purging of existing pipelines for the new system.
  • Pipeline routing – At other projects we have  had to deal with conflicts with other utilities, right-of-way issues, permitting with third parties, stream crossings, construction access and phasing.
  • Interconnect with existing utilities – At other projects we have had challenges with an existing fueling station, existing WWTP operations, and of course the electrical grid.

Here are a few lessons we learned

  1. Be sure to evaluate funding opportunities ahead of time so you can get a realistic picture of costs.
  2. Avoid unnecessary fast-pace schedules – they can really increase project costs.
  3. Verify available biogas quantity and quality and keep seasonal and feedstock variations in mind.
  4. Availability of space for all the components can be a killer. Keep the equipment footprint in mind and consider suitable access for operations and maintenance activities that go on at the site. And let’s not forget those NFPA distances and clearances and the potential for system expansion I mentioned earlier.
  5. Make sure the entire team agrees on project goals and constraints during the conceptual phase before the project is too far along.
  6. The fuel you produce will be substantially lower cost than traditional vehicle fuels. It is definitely cost competitive with conventional CNG at today’s NG prices.
  7. Use modules that can allow for flexible growth as biogas increases, capital becomes available, and/or CNG vehicle fuel demand rises.
  8. It’s a good idea to have an available supply of utility natural gas to blend with the biogas you produce to boost methane or for increased demand, or as a backup fuel if your biogas source is interrupted.
  9. Biogas quality makes a difference – while possible to produce high-quality fuel, even if the gas source has contaminants, the concentration and type of contaminants affect operating costs and the types of conditioning processes that are needed.

Have you worked on any unique energy recovery projects and if so, what are some of the challenges you faced?

Jessica Bernardini, PE, is a project manager with more than nine years of experience in a range of solid waste related projects on a local, regional, and national level.

Categories: Air Quality, Alternative Energy, Biogas and Landfill Gas, Environmental Planning & Compliance
Posted By Jessica Bernardini, PE at 11:30 AM  |  No Comments on Biogas energy recovery at a California wastewater treatment plant – Lessons learned

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