What To Do With It?

The City of Milwaukee’s priorities for food waste reduction, set out in the Climate and Equity Plan, are influenced by the EPA’s hierarchy for managing food waste. In order of priority:

Edible wasted food should go to feeding people, then animals.
Remaining food waste should be sent to biodigestion or compost.
Sending food waste down the drain or to an incinerator is a last resort.

Edible Food to People:

Feeding America tracks the number of meals needed by county to eliminate food insecurity on an annual basis. The USDA estimated the weight of a nutritious meal in the US

Edible Food to Animals

Interviews with Feeding America identified shelter and rescue operations that they have been supplying and their unmet needs

Facility Sizing

Feeding America’s Milwaukee facility was used as a baseline to determine the number of square feet of new facilities required - however, the total is likely larger, as smaller facilities are less efficient, but dispersion of them can improve distribution

Composting

Windrow composting cannot handle more than a 1:1 volume ratio of yard waste to food waste
The 9,800 tons of compostable yard waste going to landfill in MKE sets the upper limit on the amount of food waste that can be composted using traditional methods

Facility Sizing

The 2017 SARE Composting Study reviewed composting facilities and processing capabilities, finding an average processing rate of 3,850 cubic yards of material per year per acre (larger facilities are more efficient than smaller ones)

City of Milwaukee MSD

Large scale usage of kitchen disposals to process food waste would overwhelm the city’s current infrastructure, and is less desirable
Planned increases to processing facilities could handle up to 3,000 additional tons of food waste per year through the sewer system, beyond population growth
MMSD also has a high-strength digester that can handle up to 2,000 more tons of food waste

Facility Sizing

Barring changes to the 2035 and 2050 plan, these figures set the maximum the MMSD can take

Basic digester sizing diagram, care of Biocycle

Biodigestion

All other outlets limited by demand or capacity, biodigestion would have to take on the remaining food waste
Milwaukee’s energy demand far exceeds the maximum generation capabilities, so digestion is not limited in capacity, though may have issues with profitability, low-production inputs may need to be sent to vermicomposting facilities instead

Facility Sizing

Facility design guidance from BioCycle suggests that a 1 million gallon digester can process around 26,300 tons of food waste per year, given 80 tons of input per day and a 90% run time

Biodigestion Benefits:

4.2 million gallons of processing at digestion facilities would produce roughly 2.3 million cubic feet of biogas per day, at 60% methane content
This would displace approximately 1.38 million cubic feet per day of natural gas usage in Milwaukee, ~0.3% of the current RNG demand

Vermicomposting

Using worms to process food waste is a bridge between composting and digestion

Facility Sizing

Vermicomposting can help balance Milwaukee’s equation, but we did not factor it into our sizing calculations due to its overlap with both digestion and composting

Quantities to handle:

11,550 tons of wasted edible food can be redistributed to humans
75 tons of wasted edible food can be redistributed to animals
17,650 tons can be managed with composting
112,735 tons will need to be managed through biodigestion

Facilities Required:

240,000 sq ft of food banks will be needed to redistribute edible food to people and animals
35 acres of composting will be needed to process a mix of food and yard waste
5 million gallons of digestion facilities will be needed to handle the remaining food waste