PROJECT CREATION AND MANAGEMENT
COMPOSTING 12,000 TONS OF FOOD RESIDUALS A YEAR
With food residuals comprising almost one-third of its waste stream, the New York State Department of Correctional Services has built 30 composting facilities since 1990.
Jim Marion

Thirty-six tons of food residuals per day with a disposal cost of $120/ton add up to a large enough amount to attract the attention of the New York State Department of Correctional Services. That’s why ten years ago, the department began an initiative to divert recyclables and organic residuals from the landfill-bound waste stream. The creation of a resource management position was key to focusing both human and fiscal resources on identifying and implementing waste diversion strategies in the 70 state prisons located in 31 counties across the state.

The program was launched partly in response to the Solid Waste Management Act of 1988 requiring all state agencies to develop mandatory waste management and recycling programs, but the underlying motivation was to control the soaring waste disposal costs for the rapidly expanding correctional system with a year 2000 population of 72,000 inmates. Cost avoidance through on-site separation and processing of waste materials emerged as a valid strategy given the availability of inmate workers and ample site space in most prisons.

Early waste audits revealed that the food service area of correctional facilities was a prime generation site for recoverable materials. Corrugated cardboard, plastics, steel cans and other packaging materials were accumulated in abundance in kitchen environments.

Audits also indicated a significant percentage of the waste steam was in the form of food residuals. In fact, over 30 percent by weight of a typical prison disposal stream was organic residuals from the kitchen area. Further investigation showed approximately one lb/day of food scraps was recoverable per inmate, and that the food scraps were not coming from inmates’ plates but from food preparation areas.

Vegetable peelings, coffee grounds, stale bakery products, leftover starches such as rice, macaroni, and potatoes, soups, stews and casseroles accounted for more than three-quarters of a pound per inmate per day. Actual quantities varied from prison to prison depending on inmate activity and feeding styles. Prisons with a large number of special housing units where inmates are confined 23 hours a day had considerably higher daily by-pass (i.e. more food residuals generated — up to 2 lbs/day). Compared to other institutions such as hospitals and nursing homes that produce three to four pounds of food residuals per day per resident, the prisons were doing a good job of feeding efficiency.

The recovered food scraps contained about 75 percent water and weighed in at 1,800 lbs/cubic yard. It became obvious that the food scrap stream was a target for reducing disposal costs. Several prisons utilize pulpers to dispose food directly to the municipal wastewater treatment facility. Although very economical, the practice has recently caused problems in several Department of Correctional Services and municipal treatment plants by raising the biological oxygen demand (BOD) beyond the capacity of the plants. Two New York prisons are under order to remove raw food residuals from the wastewater stream; several others have been notified of the problem. An alternative was needed to divert food residuals from the landfill and waste-water streams.

ENTER COMPOSTING

On-site composting of food scraps and ground wood residuals has been shown to be an effective strategy to mitigate two very expensive waste streams. Since 1990, 30 prison compost facilities have been built in New York. Five more facilities are under construction or funded. New York prison composting sites handle from 300 lbs/day up to five tons/day with a total of nearly 12,000 tons of material composted annually. A new facet of the composting initiative will be to incorporate wastewater sludge in the recipe from selected department-operated treatment plants. Permitting issues and facility design for biosolids/food cocomposting are being engineered at the present time.

Determining the appropriate technology for prison compost operations entails analysis of variables unique to each site. The prevailing policy in New York has been to utilize the lowest cost-effective technology to maximize avoided costs and minimize capital amortization of equipment and buildings. As a general rule, compost facilities must achieve a capital payback of less than five years. To date, most installations have a gross cost return from avoided disposal costs of three years.

SELECTING A TECHNOLOGY

Prior to deciding on a technology style for an individual prison, site planners look at a number of characteristics of the prison.

1. What is the prison population and housing type? Traditional walled facilities with maximum security inmates were frequently built on large tracts of land with active or former prison farm operations. However, maximum security facilities may not have inmates with security clearance to operate a composting unit outside the security perimeter. Facilities constructed in the rapid expansion period of the 1970s and 1980s were often built on smaller parcels of land with the security perimeters expanded to property lines, but often have minimum security inmates that are available for outside duties.

The number of inmates a prison complex houses will determine the avoided cost potential of composting. Based on economy of scale, a larger facility may allow more efficient material handling equipment and process control while offering a reasonable payback period. In planning compost sites, nearby or shared site prison facilities may be combined to increase volume or enable appropriate inmate workers. Transporting food residuals more than a few miles has not proven to be economical when considering driver wages, equipment requirements and staffing availability.

2. Leachate and runoff treatment. Every compost facility must be concerned with water leaving the site. Open windrow facilities must deal with rain and snowmelt and the stained water it generates. Covered facilities may have more concentrated leachate with high BOD values that require treatment or disposal. In some cases, depending on local precipitation, a simple solids holding tank with a managed infiltration system will suffice. More concentrated materials will require closed capture systems that can be recirculated or moved to a wastewater treatment facility. Ideally, the drain system of a covered facility or composting vessel can be connected directly to the facility’s sanitary sewer system.

3) Odor. Well designed and operated food residuals composting facilities rarely have odor problems; however, the contingency must be addressed. A malodorous, anaerobic episode can have long lasting public and staff relations impact. Support for food residuals composting is fleeting when a nuisance to a confined population is inherent.

Successful siting will include consideration of visual buffers, prevailing wind, seven day/week operating procedures and technology that has appropriate process control. Drainage design and elimination of standing liquids have been the key to successful odor control in New York facilities.

4) Accessibility. Composting facilities need to have seven day/week, year-round access by trucks, material handling equipment and labor. Access roads and approaches need to be installed with snow removal, wet weather and appropriate vehicles in mind. In many cases, semitrailer trucks will visit the site to deliver bulking materials and remove compost product. Hiding a facility at the far extremes of the property may be more expensive than upgrading technology for aesthetics and process control. In areas of extreme snow and rain, institutions may consider a covered facility to simplify material handling and site runoff.

5) Aesthetics. Although waste managers may find composting and recycling facilities innocuous and perhaps a thing of beauty, that view is often not shared by institution administrators. Site selection should include review by institution planners with view to public image, traffic patterns and long range plans for institution expansion.

6) Regulatory oversight. Most states and many localities have regulatory permitting and operational oversight agencies that will have an impact on siting, environmental and operational protocols. In New York, the Department of Environmental Conservation provides permitting exemptions for institutions composting their own material on-site up to a cubic yardage threshold. Interpretations of regulations may allow inter-facility transport of food residuals by an agency.

7) Economic efficacy. Assuming a major incentive for composting is to avoid waste disposal fees, technology and facility capacity decisions will ultimately be guided by the long-term direct cost savings that on-site organic residuals processing can generate. Cost per ton capital, operating and indirect costs when totaled must compare favorably to the combined costs of landfilling including tipping, hauling and storage equipment.

COMPARISON OF FACILITIES

In an effort to summarize relative cost of technology and facility options, the New York State Department of Correctional Facilities compared four food residuals composting facilities constructed in 1998-99. Since construction labor and operational labor vary depending on inmate participation and availability, the comparison was based on capital construction and equipment costs.

Although direct costs are a basis for technology comparison, individual site constraints will affect the ultimate choice as obligated by institution characteristics as outlined above. The following discussion will highlight the pros and cons of our compost systems as well as cost avoidance and return of investment for each.

OPEN WINDROW ON PAD

Butler Correctional is a minimum security facility housing approximately 550 inmates. It is located in rural upstate New York with a number of acres of land outside the security perimeter. A 160 foot by 60 foot concrete pad with a 90 foot by 60 foot concrete curing area and 50 foot by 40 foot bulking agent storage bunker were built approximately 600 foot from the compound. A one-inch water line and gravel road were built to the site. Runoff control included a compound sloped pad with a single drain basin emptying to a stone and grass filter strip. Capital equipment was limited to a 75 HP skid steer loader.

Capital construction and equipment costs totaled $96,000 for the facility. The three ton/day capacity amortized over 15 years provides a capital cost of $5.80/ton. The potential disposal cost avoidance for the facility is $125,925/year based on a $115/ton disposal cost. The pad area was intentionally oversized in anticipation of facility expansion.

An open windrow design offers advantages of flexibility of feedstocks, mid-course corrections of recipes and windrow management. An open pad facility also allows maximum use of pad space where a covered facility limits proximity of equipment to walls. Economies of an open pad include minimal utilities and maintenance overhead.

Liabilities of open windrows revolve around exposure to the elements where runoff, process moisture control and potential animal vectors must be aggressively managed to avoid odors and maximize compost throughput. Machine time and labor costs may be higher in an uncovered operation in reacting to weather related windrow moisture management.

COVERED WINDROWS

Gowanda Correctional facility is located in southwestern New York in the lee of Lake Erie. The facility is heavily developed with little visually screened area. In addition, heavy winter lake effect storms inundate the area with several feet of snow each winter. The site includes two correctional facilities with a combined inmate population of 4,000 medium security residents.

A covered windrow compost unit was constructed with a 60 foot by 160 foot pole barn over a sloped concrete pad. A 16 foot eave height allowed trucks to dump feedstock directly on the pad. A 40 foot by 50 foot bulking agent bunker is adjacent to the pole structure. Leachate is drained to a concrete settling tank and the liquid fraction infiltrated through a stone and grass filter strip. A two foot ventilated “sugar house” ridge vent was included in the structure to avoid condensate problems. Material handling equipment included a three yard articulated loader, 18 cubic yard PTO driven agricultural feed mixer and a 75 HP farm tractor. A one-inch water line was installed to the site running approximately 700 feet from the nearest main.

The two ton/day facility was built for $178,000 with an anticipated 20-year useful life. The amortized capital cost per ton is $12.19. The potential avoided cost at $115/ton disposal fees is $83,959 annually.

Covered windrows offer advantages in process control by eliminating environmental influences and enable increased composting rates in severe winter weather. Negligible leachate production allows for modest control investment. Protection from the elements facilitates equipment cover and better working conditions, encouraging better management. The aesthetic acceptance of the pole structure was not an issue to nearby buildings.

With the addition of a building perimeter and confined roof, ventilation becomes a concern as well as the maintenance of push walls and limitations to floor space use with a loader unit. Provisions for lighting and irrigation of windrows are also added building expenses.

COVERED AERATED STATIC BAY

Located in the heart of the six million acre Adirondack Forest Preserve, Adirondack Correctional facility offered new challenges for design of a compost site. The Adirondack Park Agency stringently oversees all development within the park boundaries regarding aesthetics, viewsheds, environmental impact and land clearing. Harsh, long winters and limited development space were complicating factors. An added challenge was to include the food scraps of the neighboring Federal Correctional Institution at Raybrook in return for recycling services. The combined federal and state inmate population is nearly 2,100.

In order to meet park regulations, deal with site limitations and be in close proximity to the security compound, an aerated static bay design was built at Adirondack. It is the first compost facility of any type permitted by the Adirondack Park Agency.

The 60 foot by 110 foot pole structure over concrete includes an integrated bulking agent bunker, trommel screen, curing area and stationary agricultural mixer under one roof. A covered concrete access ramp allows downloading of food residuals from trucks directly into the mixer. Eight 8 foot by 10 foot compost bays are aerated by individual wall mounted blowers through four-inch perforated PVC pipe. An electronic timer control allows automated blower intervals for each bay. The pad is drained directly to the municipal wastewater system. Material handling is accomplished by a 75 HP skid steer loader.

Capital construction and equipment expenditures for the Adirondack facility were $172,000 with a one ton/day capacity. A 20-year amortization of the facility yields a cost of $23.56/ton. The annual avoided cost potential is $54,750/year with a local net disposal cost of $150/ton.

The covered aerated bay facility offers increased process control with minimal material handling in a minimum amount of space. Environmental influences are minimal with resulting liquid discharge negligible. The integrated process under one roof provides an aesthetically innocuous facility with good access and year round working conditions.

The aerated facility necessitates increased management and attention to process control with staff training and maintenance of great importance. Increased utility costs with three-phase power, light and water are minor but constant. Accurate recording of process times, volume received and bulking:feedstock ratios add to the staff time requirement. There is little overlap allowance for bay space to balance intake and output. Screening, mixing and bay exchange are daily activities.

IN-VESSEL

Self-contained in-vessel composting was the logical choice for Auburn Correctional. The state’s oldest prison, located in central New York, houses 1,785 maximum-security inmates in an urban setting. No adjacent land was owned by the prison system, mandating the compost operation to be within the acre 25-foot walled security enclosure. Odor, appearance and space were of critical consideration in a compost design.

The 1,500 lb/day Wright Environmental unit installed at Auburn has 12 foot by 40 foot footprint with an adjacent 30 foot by 40 foot curing area. The 28-day residency compost cycle incorporates mixing, aeration, biofilter, agitation and water irrigation functions. Three-phase power and direct connection to facility wastewater service made installation easy. A 75 HP skid steer loader was the only material handling equipment required as 80-gallon totes are used for food residuals delivery. Two inmate workers spend approximately two hours each day working with the unit to load and unload material.

With an anticipated 15-year useful life, the $150,000 construction and purchase cost of the unit results in a per ton charge of $36.63. The potential of $40,950/year in disposal savings relates to an acceptable 3.6- year payback on the investment.

Total process control, odor management and low profile are selling points for the in-vessel system. The space saver design and minimal handling of material also are positive aspects. The self-contained unit is indeed a good neighbor. With the convenience of looks and control come some management considerations. Daily maintenance checks are required, and the possibility of total shutdown due to mechanical failure is a real risk. Contingency plans for waste disposal are advised. The complexity of the machine requires comprehensive operator training and attention to detail while operating the unit.

APPROPRIATE CHOICE

While cost of construction and related cost avoidance are the primary factors in most compost installations, no one system is appropriate for all sites. All the systems described (see Table 1) are capable of producing a high quality product with minimal nuisance or environmental impact. All will also provide an acceptable payback period for capital investment. Labor, space, aesthetics and volume are major factors in technology decisions.

Jim Marion is resource management director for the New York State Department of Correctional Services. His office at the ENYCF-Division of Industries is in Napanoch, New York.