Case Study: Is A Digester The Answer? It Depends.


A top-tier hotel in San Francisco.


Many businesses try to cut waste costs by decreasing the number of waste services they pay for, without fully understanding the big picture, and how their waste management costs are really calculated and incurred.

With a comprehensive understanding of the local industry and the way waste is processed and billed in the city, Great Forest was able to quickly identify the client's miscalculation, and apply a comprehensive solution that took full advantage of local waste management discounts. Over the first year, Great Forest was able to increase the hotel’s diversion rate to 74 percent, reduce trash by 2 yards daily, and reduce costs by 30 percent. Waste costs for the hotel went down from $20,000 to $14,000 a month.


In San Francisco, the rate and discount structure is set up to charge the most for trash service and offer discounts for subscribed levels of recycling and compost service. Businesses in San Francisco stand to reduce their waste costs the most if they not only reduce the amount of trash generated, but also increase their recycling and composting.

The hotel had implemented a seemingly adequate waste management program, and in a misguided effort to cut costs by eliminating composting service, the client added a high tech digester. But that decision was made in isolation, without a complete understanding of their business environment, and without a through cost-benefit analysis. The full impact of that decision soon became clear.

  • Because the digester was not able to handle some materials that could go into the compost stream–such as paper towels, tissues, napkins, pizza boxes, wooden stirring sticks, waxed produce boxes, and plant starch-based cups and utensils– all these materials still had to be separated out and collected for composting. So not only did the hotel NOT eliminate their need for composting service with the digester, but they lost a valuable composting discount from Recology, the city’s waste processor, because a good portion of the hotel’s valuable organic waste now went into the digester, and was being literally flushed down the drain.
  • On top of the cost of the machine, the hotel also had to pay a $500 monthly maintenance fee. They also did not realize that the machine’s operation would incur higher energy and water costs until it was revealed to them through a Great Forest analysis. (Digesters can use up to 180 gallons of water a day and create a liquid residual that many city’s wastewater treatment systems cannot handle effectively.)
  • The digester was also purchased and installed without consulting kitchen staff, or providing adequate training. As a result, there was confusion about what compostable materials could and could not go into the machine. Staff was uncertain about how the program worked and did not embrace the change.

As a result, the hotel’s diversion rate plateaued, their disposal costs remained high, and the city issued a 50 percent  surcharge on their waste services due to noncompliance. Staff morale was low, and the hotel’s culture of support for sustainability was diminishing.


1) Address the digester

  • To take full advantage of the local waste management playing field, Great Forest recommended that the hotel stop using the digester and rely on better sorting methods to increase the volume of recyclables and compostables, while decreasing the amount of trash. This produced positive results almost immediately.

2) Make adjustments to the hotel’s equipment

  • To decrease the frequency of waste pickups, Great Forest recommended that the hotel reactivate an aging 3-yard vertical trash compactor that the hotel’s engineering department was able to repair and put back into service.
  • The hotel, however, was unable to save an old recycling compactor. Great Forest worked to find a suitable replacement as rapidly as possible to avoid any price increases that might come with the steel tariffs, and ensured that it was right-sized to the hotel’s average needs. This meant that the new compactor would be able to handle seasonal increases in volume from large banquets and celebratory events. Having new, reliable equipment increased operational efficiency and also boosted morale of the hotel’s staff.

3) Educate all stakeholders

  • To ensure adjustments to the program were successful, Great Forest launched an education campaign that included all departments, with custom interactive presentations to the culinary staff.
  • To reengage the hotel staff and redevelop a culture of sustainability, hotel management, with assistance of their corporate affiliate, convened a team of departmental representatives for a week-long exercise. They also identified an internal point of contact for all waste management issues. Great Forest arranged for this team to tour Recology’s Recycle Central sorting facility so that the team could connect the dots in waste management and convey how waste management works to colleagues.
  • Great Forest also provided a tutorial to the hotel’s finance director to provide an understanding of Recology’s invoicing and discount system.

4) Continuing oversight

  • Great Forest continues to provide a monthly key waste financial indicators report aimed at management and budget development, as well as a monthly weight and volume report to track actual waste management performance and to set goals.
  • Great Forest also continues to provide weekly on-site monitoring and periodic refresher training sessions for all departments, and conducts waste training in monthly new hire orientations.


The new system implemented by Great Forest enabled the hotel to reduce the trash stream by 2 yards daily and increase the materials composted to 4 yards daily. As a result, the hotel’s diversion rate rose from 64 percent to 74 percent in a year and is expected to be close to 80 percent during the second year of Great Forest’s partnership.

In San Francisco, this means that the hotel is now receiving the most favorable rates from Recology, which charges the most for trash, and offers discounts that increase with the amount of recycling and composting. With Great Forest’s recommendations, the hotel now earns a monthly discount from Recology for providing valuable compostable material. Waste costs for the hotel went down from $20,000 to $14,000 a month and the city eliminated the 50 percent surcharge on waste services.


*NOTE:  In general, when composting is available, digesters may not be the best option. Every organics program should be designed to best fit the needs of the business and the operating rules of its location. In San Francisco, digesters represent misapplied technology that answers the wrong question.

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(Photo: Lewis Fagg, Unsplash)

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