CWC Technology Brief

COMPOSTING PRODUCE WASTE AND WAX COATED CARDBOARD: BEST MANAGEMENT PRACTICES

A best management practices manual for implementing a low technology grocery waste composting program has been produced. The manual was produced to promote the development of programs for composting produce waste and wax coated cardboard generated by grocery stores. The specific reasons for developing the manual are presented as follows:

1. The composting of produce waste at yard debris composting facilities has significant potential for improving the nutrient content, overall value and marketability of yard debris compost products.
2. Compost producers, waste haulers and grocery stores in the Puget Sound Area have begun to implement produce waste and wax coated cardboard composting programs and express interest in the expansion of such programs.
3. The low technology approach presents a very feasible and economical means of recycling produce waste and wax coated cardboard.
4. Grocery stores can achieve significant savings in disposal costs by participating in a composting program.
5. Regulatory and solid waste agencies are requesting more technical information regarding this waste recycling technology.

Composting source separated grocery wastes can be an attractive, cost effective waste recycling strategy. The first step in developing a grocery waste composting program is to determine whether composting is a feasible recycling alternative. In general, the feasibility of a grocery waste composting program is dependent on the following items:

· Corporate support of the program
· Availability of specialized waste hauling services
· Availability of permitted composting facility with expertise in produce waste composting
· Economic feasibility of the program.

Specialized composting and waste hauling services must be available to implement a composting program. The collection, hauling and composting of grocery waste pose numerous challenges. It is important that the hauler and composter understand the challenges and are willing to address them prior to initiating the program. If specialized services are not readily available, the grocery store, waste hauler and composting facility will need to work together to determine the feasibility of developing these services. In many instances public agencies have assisted with identifying and developing the specialized hauling and composting services required.

The long term success of the program is dependent on planning and initial implementation activities.

The essential source separation and collection elements of a program include:

· Retaining hauling and composting services
· Grocery waste collection system design
· Preparation for alleviating potential problems
· Employee training.

The collection system is a critical component of the grocery waste composting program. The collection system consists of the procedures and materials used to source separate compostables in the store and transport the materials to the primary collection containers. The primary objectives of the collection system are to:

· Maximize capture rate of compostable materials
· Eliminate inert contaminants such as: plastic wraps, rubber bands, glass, and metal
· Minimize in-store labor and space requirements.

Throughout the country, source separated grocery wastes are commonly being processed at yard debris composting facilities using a low technology approach. However, for many facilities to successfully implement this approach, a higher level of process management is required. The development of operational guidelines is significant as the number of facilities composting produce waste is increasing rapidly. The low technology alternative offers the advantage of lower capital and operating costs compared to other more capital and labor intensive processes. Low technology composting is defined as a process by the following traits:

· Relies on windrow turning for aeration
· Utilizes uncovered composting area
· Limits use of capital equipment.

Overall, produce waste has a higher nitrogen, moisture, and readily available carbon (sugars, starches and proteins) content than yard debris. As a result, composting grocery wastes using a low technology approach presents the following challenges:

· Generation of odors
· Nuisance animal and insect attraction
· High free water content
· Decomposition of cardboard

These potential problems can be controlled through a variety of process management techniques. These techniques include: · Absorbing free water with adequate bulking material
· Selection of bulking materials and mix rations
· Thorough mixing of the composting feedstocks
· Incorporation of a process monitoring program
· Maintaining adequate conditions for composting

A basic tenet of effective site operations and odor control requires that feedstocks arriving at a composting facility are immediately processed and placed into windrows, this is especially important for produce waste. The drainage of free water from produce waste can be readily controlled at the facility by mixing in bulking materials such as yard debris, mixed waste paper and sawdust to absorb the water.

The provision of optimum composting conditions starts with the development of the initial compost mix. Porosity is the single most important component of an initial mix. A mix with insufficient porosity will limit aeration. This is especially significant when using a low technology composting approach that relies entirely on windrow turning and convection for aeration. Porosity is provided in a mix by large particle size materials such as chipped brush and wood chips. Porosity is also influenced by the moisture content. If the moisture content is excessive, pore spaces are filled with water instead of air.

The maintenance of aerobic conditions during the composting process is crucial for minimizing odor production and maximizing the decomposition process. As a result of the high energy content of produce waste, the aeration requirements for composting produce waste are typically greater than for yard waste alone. Maintaining adequate aeration requires an increased turning frequency or a process modification to enhance convection.

Compost processing information presented in the manual was conducted with the assistance of Iddings, Inc. a compost processor located in Kent, Washington.

This technology brief was prepared by the Clean Washington Center. The Clean Washington Center is the Managing Partner of the Recycling Technology Assistance Partnership (ReTAP). ReTAP is an affiliate of the national Manufacturing Extension Partnership (MEP), a program of the U.S. Commerce Department's National Institute of Standards and Technology. ReTAP is also funded by the U.S. Environmental Protection Agency and the American Plastics Council.

Report Dated: October 1994

Fact Sheet Update: October 1994