Feedstock Profiles

Methane is 84 times more potent than carbon dioxide. Tossing food scraps and yard waste into the trash heats our climate. Instead, recycle food scraps and yard waste into green products.

Organic materials decompose in landfills and emit 20% of the state’s methane, a short-lived climate pollutant, 84 times more potent than carbon dioxide.

Recycling organic waste into compost, fertilizers, and biofuels reduces organic materials sent to landfills and cuts climate pollution.

Feedstocks

Feedstocks are the raw ingredients for composting – usually actively decomposing solid organic materials. Feedstocks determine the characteristics of the finished compost and influence the composting process.

Important properties of feedstocks include:

Moisture
Carbon and nitrogen content
Physical characteristics
Level of contamination

It’s easy to compost some common feedstocks, such as leaves, yard trimmings, and food material.

Composters can address more challenging feedstocks by understanding:

The physical and chemical characteristics
Available waste management technologies
Laws and regulations about specific feedstocks

Examples of feedstocks that composters may find challenging:

Cannabis
Compostable Plastics
Biosolids

California law defines organic waste as “food waste, green waste, landscape and pruning waste, nonhazardous wood waste, and food-soiled paper waste that is mixed in with food waste.”

Feedstock Profiles

These feedstock profiles focus on challenging feedstocks and methods to properly manage them.

This feedstock profile includes information about cannabis waste that consists solely of cannabis plant material (i.e., organic waste) that is subject to CalRecycle’s organic waste management laws and regulations. 

Select the tabs in this section to view additional information about this feedstock.

Name: Cannabis sativa L. – marijuana 

Legal description of feedstock 
California regulation defines cannabis waste as “any material intended for disposal that contains cannabis but is not otherwise considered hazardous waste. Cannabis waste consisting solely of plant material shall be considered an organic waste.”
California legalized the use of recreational cannabis for adults in 2018.

Physical and chemical characteristics of feedstock 

Cannabis Trichomes

Cannabis plants produce chemicals called cannabinoids that can cause mental and physical effects when consumed.

Cannabinoids are accumulated in trichomes that occur mostly on the flowering parts of the plant. Since cannabis goods are primarily produced from the flowers, cannabis grow residuals are mostly unusable plant waste, which can be up to 95% of the weight of the plant.

The major types of cannabis grow residuals are fan leaves, seeds, stems, stalks¹, and growing media/soil/roots.

Fan leaves, stems, and growing media

Residual Type

Nitrogen Content

Carbon Content

Moisture Content

Porosity

Fan leaf/seedlings

High

Low

High

Low

Stem (stalk)

Low

High

Low

High

Growing media/soil/root stock

Low

High

Low

Table 1 outlines the characteristics of cannabis grow residual types in terms of nitrogen, carbon, moisture, and porosity.

Source: BioCycle

1 – By definition, cannabis stalks are not considered cannabis waste because they are excluded from cannabis. “Cannabis” does not include the mature stalks of the plant, fiber produced from the stalks, oil or cake made from the seeds of the plant, any other compound, manufacture, salt, derivative, mixture, or preparation of the mature stalks (except the resin extracted therefrom), fiber, oil, or cake, or the sterilized seed of the plant which is incapable of germination.

Feedstock waste management plan 
California law requires a licensee to create and implement a written waste management plan that describes how they will dispose of cannabis waste.

Waste management technologies 
Some methods of effective cannabis waste management technologies can be found in the State of Montana’s Cannabis Waste Guidance.

Pre-processing 
Grinding is a pre-processing technique beneficial for composting cannabis waste, whether it is composted on-site or in another composting facility.

Chipper/shredder

While chipper/shredders cost less, they:
- Are loud
- Tend to clog when grinding wet feedstocks.
Slow-speed grinders:
- - Cost more
  - Good at grinding wet feedstocks and difficult materials like fibrous stems.
  - Produce smaller size particles that are better for composting.
Fibrous cannabis stems should be shredded to a fiber length of 1” or less for effective composting.

Composting 
Create an effective composting recipe:

Start with the type of feedstocks available for composting. Growers may recycle their cannabis byproducts to grow more plants.
Using complementary feedstocks, balance:
- Moisture
- Porosity
  - Fan leaves do not hold large amounts of air space in a compost pile, especially when shredded.
  - A carbon-rich bulking agent can be used to increase porosity in the compost pile.
- Carbon to nitrogen (C:N) ratio
  - Fan leaves have relatively high nitrogen content and low carbon content, with a relatively low C:N ratio of about 15-20:1.
  - Recommended practices for hot composting:
    - Have a starting C:N ratio of 25:1 or 30:1
    - Add carbon to facilitate an aerobic composting process.
Good sources of carbon and porosity are other grow residuals of a cannabis plant, such as stem, rootstock, and growing media, like coir, peat moss, and types of fertilizers, including compost.

Bokashi composting method
Bokashi method is an acidic, anaerobic fermentation process that can be used on-site to treat cannabis waste. When Bokashi compost activator is added to ground/shredded cannabis waste, the microorganisms begin to break down the organic matter. After two weeks of anaerobic fermentation, the resulting liquid can be used as a nutrient-rich fertilizer.

Benefits of Bokashi fermentation: 

Requires a very small footprint.
Can be done throughout the year.
Is easily scalable.
Produces no heat or gases.
The fermenting container will not attract flies because it is kept sealed.
Commonly practiced by small-scale growers.

Anaerobic digestion
Anaerobic digestion is an emerging best practice for managing plant waste on-site. This method creates a closed-loop system that provides 100% diversion and reuse. It also enables businesses to capitalize on an asset they already have access to, in addition to the added benefit of reducing waste removal costs. 

Anaerobic digestion uses plant waste to: 

Produce methane (CH4) for energy. 
Carbon dioxide (CO2) for the extraction or cultivation systems.  
Produce nutrient-rich fertilizer to reuse for cultivation.

Reuse 
Do not overlook the reuse potential of cannabis waste, which include:

Recycle plant waste by breaking down extremely fibrous material, like stalks, to create mulch for compost piles. 
Use cannabis plant biomass to make paper products, textiles, bioplastics, construction materials, composites, and livestock bedding.

Feedstock challenges
Keeping organic material clean of contaminations like RFID tags, plastic labels, nettings, and hazardous wastes like pesticides is a major challenge.

RFID tag on plant

Department of Cannabis Control issues Radio Frequency Identifier (RFID) tags to all statewide licensees to use the California Cannabis Track and Trace (CCTT) system. Known as ‘seed to sale’ tracking, it follows the movement of cannabis and its products through the supply chain.
- RFID tags often end up in cannabis waste and are a major source of contamination.
- While they are not a legal requirement in California, they will be around for a while because of how the track and trace contract is implemented.

Technological barriers to optimal cannabis growing have not been researched at the level of other agricultural products.

- - Cannabis growers cannot get the federal tax breaks other industries have for installing new technologies to improve their energy efficiency and minimize carbon dioxide emissions at cannabis cultivation facilities.
  - Cannabis does not yet have decades of agricultural research on optimizing growing conditions in greenhouses and indoor facilities.

Regulatory agencies that are responsible for handling cannabis waste management are: 

Department of Cannabis Control (DCC) is the California state agency that licenses and regulates cannabis businesses. 
Department of Toxic Substances Control  (DTSC) is committed to protecting Californians and their environment from exposure to hazardous wastes by enforcing hazardous waste laws and regulations. 
California Department of Food and Agriculture(CDFA) is responsible for protecting and promoting agriculture in California. CDFA was required by law to establish a certification program, OCal, for cannabis that is comparable to the National Organic Program and the California Organic Food and Farming Act.
California Department of Public Health (CDPH) works to protect the public’s health in the state of California and helps shape positive health outcomes for individuals, families, and communities. CDPH was mandated by state law to develop a program, OCal, for manufactured cannabis products that are comparable to the National Organic Program and California Organic Food and Farming Act.
California Department of Resource Recycling and Recovery (CalRecycle) brings together the state’s recycling and waste management programs and continues a tradition of environmental stewardship.

This feedstock profile includes information about food waste that is subject to CalRecycle’s organic waste management laws and regulations. 

Select the tabs in this section to view additional information about this feedstock.

Name: Food material, food waste

Legal Description of Feedstock
California regulation defines food material as “a waste material of plant or animal origin that results from the preparation or processing of food for animal or human consumption and that is separated from the municipal solid waste stream.” Food material is also referred to as food waste.
Food material includes, but is not limited to, food waste from:

Food facilities (such as restaurants)
Food processing establishments
Grocery stores
Institutional cafeterias
Residential food scrap collection

Food material does not include any material that is required to be handled by a rendering facility under the California Food and Agricultural Code and the corresponding regulations.

Physical and Chemical Characteristics of Feedstock
Food waste is a complex mixture that has general characteristics like high moisture content, varying protein, lipid, and carbohydrate concentrations, and significant amounts of volatile solids (VS). Its pH is generally acidic while its carbon-to-nitrogen (C/N) ratio varies depending on the food types.

The composition of food waste influences the characteristics depending on the place where it is produced. Food waste consisting mainly of rice, pasta and vegetables contains high quantities of carbohydrates, while meat, fish and eggs have high concentrations of protein and lipids.

The diverse nature of food waste makes it challenging to use as a resource and requires a comprehensive analysis of its physicochemical (physical and chemical) properties.

Physicochemical composition:

Moisture Content: Extremely high moisture content, compared to other organic waste like green waste. High moisture and lower dry matter breakdown easily and cause smell but are well suited for feedstock in anaerobic digestion (AD).
Volatile solids (VS): High VS content. It contains a high fraction of VS when compared with other types of organic waste. It has a high potential to produce methane. The VS fraction contributes to biomethane production which makes it a good substrate in AD processes.
pH: It has an acidic pH compared to other organic waste such as animal manure and green waste. During composting, low pH will slow down the microbes. For AD, pH is critical because microbes are very sensitive to change.
Carbon-to-Nitrogen (C/N) Ratio: Usually lower C/N ratio than optimal values recommended for the composting process resulting in N loss through ammonia (NH3) volatilization. To fix this, food waste needs to be mixed with high‑carbon materials like sawdust or straw.
C/N ratio helps control the composting process. Different materials have different C/N ratios depending on how much carbon and nitrogen they contain.
The optimal C/N ratio is maintained in the range of 20–30. For composting, the optimal initial C/N ratio should range from 25 to 35. During composting generally, the C/N ratio declines because microbes use carbon for energy and nitrogen assimilation.
Biochemical composition: Includes carbohydrates, proteins, and lipids, which are the three major macromolecules of organic matter. Of these, carbohydrates are generally higher than the other two fractions.
Biochemical Methane Potential (BMP): Relatively higher BMP than other municipal solid waste -derived organic waste, because of their high organic matter content. It offers several advantages including high biodegradability, and high potential for VS destruction.
BMP is defined as the maximum volume of methane produced per gram of VS substrate, and provides an indication of the biodegradability of a substrate and its potential to produce methane via AD.

Collection

3 bin collection system

Senate Bill (SB) 1383 (Lara, 2016) requires clean streams of organic material be collected, recovered, and recycled into end-products like compost or biofuel. Proper sorting and contamination monitoring are essential. The law allows jurisdictions the option of three, two, or one -container collection systems based on local infrastructure.

If organic waste is collected in the same container as recyclables or landfill materials, the mixed waste must be sent to a high-diversion organic waste processing facility to recover the organic material.

Pre-processing
The purpose of pre-processing organic materials before composting or AD is to improve efficiency and control. Preprocessing removes physical contaminants, reduces the size, and increases uniformity of the feedstock.
Preprocessing helps balance moisture, adjust C/N ratio, and improve porosity and aeration. For wet AD systems, including digesters at wastewater treatment plants (WWTP), preprocessing may involve turning food waste into a pumpable slurry.

Manual sorting
Manual picking or pick lines are commonly used to remove contaminants at composting, AD, and material recovery facilities to remove obvious contaminants, like plastic, wood, glass, cans, and bottles before (and sometimes after) processing.
However, manually removing food packaging is difficult, labor-intensive, and often inconsistent. To improve feedstock quality, facilities also rely on mechanical systems such as screens, separators, and de-packagers.

Depackaging Equipment
Food waste depackaging uses mechanical systems to separate food waste from its packaging. The recovered organics can be sent to composting or AD, while recyclable packaging is recovered. Non-recyclable materials, such as film plastic, are typically landfilled.

Others
There are a variety of other pre-processing methods to prepare feedstocks:

Grinders reduce food waste into a slurry typically sent to AD facilities or WWTPs for conversion to bioenergy.
Pulpers press liquid out and produce semi-dry pulps often sent to composting facilities.
Dehydrators use heat to remove liquid, creating dried-out material that can be compost or AD feedstock.
Aerobic digesters produce materials that usually need further processing, including semi-dry feedstocks or liquids sent to an AD facility or WWTP, or sometimes into the sewer system.

Visit the EPA Wasted Food Scale page to learn how to reduce the environmental impacts of wasted food.

Composting
A variety of methods are used to convert organic material into compost.
The fundamentals of composting are the same at any scale, but material volumes, feedstocks, and the methods and equipment used can vary.

Commercial and industrial composting in California are generally required to meet solid waste facility permitting requirements, and other local, state, or federal requirements.
In-vessel composting processes food or landscape waste, in enclosed containers to control emissions, temperature, and moisture.
Community composting takes place at the neighborhood or community level and may be located at schools, universities, community gardens, parks, and other spaces in urban, rural, and suburban areas, including on tribal lands.
Backyard composting occurs in residential settings – often in a backyard pile or a small, enclosed bin, and mostly handle food scraps (except for meat, bones, and dairy products) and yard trimmings.
Vermicomposting uses worms to break down organic material, including food scraps, and turn them into a nutrient-rich soil amendment.\

Anaerobic digestion (AD) and co-digestion
AD breaks down material without oxygen (i.e., anaerobically), producing biogas, and digestate.

Biogas can be purified to produce biomethane for fuel, pipelines, or electricity.
Digestate can be used as a soil amendment if it meets CalRecycle’s land application requirements.
Stand-alone AD facilities in California process source-separated organic materials, including food material and green material.

With Co-digestion of food waste at WWTPs food waste is typically pre-processed and mixed with sewage sludge.

Animal feed production and rendering
Food waste that was originally intended for human consumption or is a byproduct of human food production, such as food scraps, can be fed to animals either directly after harvesting or after processing.
Converting food waste to animal feed can lower animal feed cost, increase profitability, and reduce environmental impacts. For more information, see the California Department of Food and Agriculture’s Rendering Program and Commercial Feed Regulatory Program webpages.

Edible food recovery (SB 1383)
CalRecycle administers the competitive Edible Food Recovery Grant Program to support new and expanded food waste prevention/source reduction projects in California.
Funded projects either collect edible food to feed people or prevent food waste from being created at the source.

Upcycling
Upcycling food keeps it in the human food supply chain and avoids wasting the resources used to produce it. For example, fruit and vegetable byproducts can be processed into nutritious flours. Spent grains from brewing and fruit pomace can be turned into flours rich in fiber, protein, and micronutrients.
Another promising area of upcycling is the extraction of high-value compounds from food scraps. Researchers have successfully isolated antioxidants, antimicrobials, and other bioactive compounds from fruit peels, seed hulls, and vegetable trimmings.

Contamination and incompatible material
Under SB 1383, contamination of food waste occurs when non-food waste or other unacceptable materials are mixed with food waste in the designated organics bin, potentially ruining an entire load.

Plastic is one of the emerging contaminants of high concern that impact the quality of compost. The primary sources of plastic contamination in food waste streams are film plastic, produce stickers, food packaging and containers, and multilayer paper products coated in plastic, which are designed to provide a high level of resistance to water and gas transfer to the food they are meant to protect.