On-site Composting of Restaurant Organic Waste: Economic, Ecological, and Social Costs and Benefits

On-site composting is examined as an alternative method of organic waste disposal in San Francisco Bay Area restaurants. Since 74% of an average restaurant’s waste stream is compostable material, composting and reuse of organic material would redirect a significant portion of the waste stream from landfills. Economic, ecological, and social costs and benefits of three methods of organic waste disposal are compared: landfilling, off-site composting, and onsite composting. A waste characterization of one large Emeryville restaurant is performed to determine the mass of the organic waste generated. An economic analysis of the three methods of organic waste disposal is made for the specifications of this particular restaurant and ecological and social considerations are proposed for each method. Two commercially available composting technologies are compared. For the more appropriate technology, present discounted value and payback period of the hypothetical investment are calculated based on the current expenditures for landfilling service. An ecosystem modeling method is performed as a means to visually represent ecological sustainability. A life-cycle approach is taken to determine the ecological impacts of the use of agricultural soil conditioners and fertilizers, impacts that would be curbed to the extent that restaurant compost is used in their place. Social costs and benefits are compared based on the goal of economic, ecological, and social sustainability as a follow-up to the scientific results. It is found that on-site composting is ecologically, socially, and economically more valuable than landfilling or off-site composting, although significant management constraints exist at this point in time when a composting infrastructure is not yet in place. It is also found that a significant market exists for a middleman firm that would incur the management responsibilities of on-site composting and benefit from the sale of restaurant compost. It is recommended that local governments exploit this market. Introduction Currently, the US commercial sector generates 24.6 million tons of food scraps and soiled, unrecyclable paper and cardboard annually (United States Environmental Protection Agency [EPA] 1999). In restaurants, organic materials make up an average of 74 percent of the total waste stream (EPA 1999). Composting redirects organic waste from landfills and transforms the waste into a product useful in landscaping, gardening, maintaining the structure and fertility of agricultural land, slope stabilization, and even brownfield remediation. The increasing sophistication of the available composting technology combined with the passage of AB 939, which mandates a 50% waste stream reduction goal for the state of California by the year 2000, have exposed widely used landfilling as a disposal method wasteful of both space and a potential resource. An anticipated rise in landfilling fees may lead businesses to seek alternative methods of food waste disposal. These combined factors have created an impetus for research on the relative economic, ecological, and social costs and revenues of organic waste composting in the Bay Area. Composting is a biological process in which microbes metabolize readily degradable organic matter into nutrient rich humus, a structural component of soil. Specific criteria must be met for composting to be successful, and meeting these criteria is especially important for large-scale industrial composting operations. Technology is currently available to allow low-maintenance pest and odor controlled on-site composting of organic residuals at restaurants. Organic residuals are plant and animal derived and include pre-consumer vegetable scraps, seeds, all animal product including bones, post consumer food waste, paper products, including waxed cardboard, and wood, including treated wood (Brandt, 1996). The addition of compost to agricultural land and urban landscaping areas provides many associated ecological benefits including reduced dependence on chemical fertilizers and reduced pollution by accumulation in landfills. Composted food waste is currently classified by the EPA as Class A material, rendering its land application unregulated (Miller and Miller 2000). 1 Microbial populations and species diversity change dramatically throughout the phases of the composting process. Initially, mesophilic bacterial and fungal activity cause the temperature of the organic matter to rise into the thermophilic range, >50°C. Thermophilic microbes, especially actinomycetes, maintain thermophilic conditions within the organic matter if provided with sufficient oxygen. This requirement is met through aeration of the organic material. Mesophylic microbes are present during the final curing stage at lower temperatures. The heat generated during the thermophilic phase of composting is intense enough to kill pathogens and seeds (EPA 1998). Food waste has been used as a soil amenity as far back as the middle ages in Europe, and evidence in Amazonia suggests that food processing wastes were added to soils around the same time (Miller and Miller 2000). By 1940, inexpensive inorganic fertilizers had become widely available and used due to their short-term results on crop yields; but more recent evidence of adverse ecological effects such as contamination of water supplies due to inorganic fertilizer application has led to a renewed interest in organic fertilizers. Various methods of organic residuals management should therefore be evaluated based on three categories: economic value, ecological value, and social value. Revealing categorized benefits and deficits of various methods allows for an in-depth, multilayered comparison of those methods. Economic costs and revenues are equal to the current actual costs and revenues of managing organic residuals in various existing or hypothetical ways. Ecological costs and revenues can be determined through the valuation of environmental externalities with regards to energy consumption, materials cycling and pollution generated and avoided. Social costs and revenues can be determined through an analysis of the longand short-term value inherent in initiating re-use behaviors vs. the maintenance of waste behaviors. Study Focus It is hypothesized that on-site composting is more ecologically and socially valuable and less economically valuable than landfilling organic waste in the San Francisco Bay Area. This study attempts to identify, compare and contrast the economic, ecological, and social values of three methods of food residuals management by the food service industry in relation to high-volume Bay Area restaurants. The first of three methods of food residuals management is landfilling, or the disposing of “waste” in specifically Bay Area containment facilities. The second method is city or county contracted commercial composting where responsibility for composting is assumed by a government body. On-site commercial composting is the third method: responsibility for composting and the resultant composted product is assumed privately by the individual restaurant. Materials and Methods Study Sites Specifically targeted is Chevy’s of Emeryville, CA whose current method of waste disposal is landfilling. The cost of its current method of organics residuals disposal will be compared with two alternate methods of disposal/reuse. Park Chow Restaurant will be studied as a reference for current costs to restaurants for a Bay Area city contracted organics composting program. Park Chow of San Francisco whose current method of waste disposal is composting of organics, recycling of recyclables, and landfilling of a minimum of materials pays a city contracted composting company to compost and recycle its pre-sorted waste. Waste Characterization In order to identify the organic waste component of Chevy’s waste stream, a waste characterization study was conducted. Average waste density was determined, and total waste volume generated per week was roughly determined. The quantity of organic waste generated per day was calculated using an EPA-determined percent organic waste by mass of an average restaurant’s waste stream. In order to determine the average density of the waste stream, each bag of trash was weighed upon being put into a single empty 3yd dumpster using a common bathroom scale. The dumpster was allowed to fill to the halfway mark, 1.15m(1.5yd) during the course of the day. Because the large volume of waste measured is a representative sample (trash bags were weighed from the opening of the restaurant until closing time) only one trial was made. Total waste volume data was taken over a week. Trash collection is four times weekly, and total waste volume was measured just before collection on each of the four collection days. Total waste volume generated per week was roughly determined. A rough determination of total waste volume generated was made due to the time and labor involved in a more accurate determination. An order of magnitude determination is of fundamental importance, but a very accurate determination is labor intensive. Due to the nature of the food service industry, business (and thus waste created) can fluctuate weekly, seasonally and annually. Furthermore, percentage of organics in waste streams varies among Bay Area restaurants, and although Chevy’s will be analyzed more specifically, it is also useful to provide a flexible model that can be applied to many Bay Area restaurants. Possible ranges of these values are given. It was important to this study to identify the compost machine capacity appropriate to the restaurant, and not necessarily a highly accurate waste characterization. Statistical significance tests were not appropriate to the type of data collected. Economic Analysis The cost of Chevy’s current method of landfilling will be compared with a theoretical model in which the restaurant adopts on-site composting. In the case that onsite composting proves to be a larger economic investment than landfilling, as hypothesized, circumstances that might make composting economically feasible, such as sale of the compost product, will be examined. In the case that on-site composting proves to be a lesser economic investment than landfilling, present discounted value and payback period of the initial capital investment will be calculated. Two commercially available composters will be compared in a theoretical scenario where Chevy’s would replace landfilling with composting and recycling. Green Mountain Technologies’ Earth TubsTM and Wright Environmental Management, Inc.’s small in-vessel automated composter are the two products under scrutiny. Data for each product were obtained through series of personal communications with representatives from each company. The writer endorses neither product. Life Cycle Approach “Lifecycle assessment (LCA) is used to measure the environmental inputs and outputs associated with a single product or service from the mining of raw materials, through production, distribution, use and re-use or recycling, to final disposal. This is carried out in terms of raw materials, energy use, emissions to air and water and solid waste” (Powel, et al 1998). It “is a technique for assessing the environmental aspects and potential impacts associated with a product, by: • compiling an inventory of relevant inputs and outputs of a product system; • evaluating the potential environmental impacts associated with those inputs and outputs; • interpreting the results of the inventory analysis and impact assessment phases in relation to the objectives of the study.” (Frankl and Rubik 2000) Finally, LCA consists of economic valuation of environmental impacts which assigns a dollar value to these impacts to effectively compare them to real market values. As the economic valuation process requires personnel and funding unavailable to this research, a full lifecycle analysis of the food service industry is beyond the scope of this paper. A limited “lifecycle approach” , which can be considered to consist of all components of LCA save economic valuation, will be conducted to provide a complete qualitative analysis of the ecological impacts created or curbed by the three aforementioned methods of organics residuals management. Ecosystem Modeling It is argued that modeling human industrial processes after natural ecosystems is necessitated both by an increasing human population in a finite material world and by the fact that decisions made on the basis of short-term criteria can produce disastrous longterm results on a global scale. Comparing industry to ecosystems with regards to materials and energy, then, allows an analysis of the degree of deviation of human activity from an ecologically sustainable biosphere (Graedel and Allenby 1995). Various organic restaurant waste management systems are represented visually and compared with regards to ecological sustainability. Social Costs and Revenues Social ramifications of the three methods of organics management are compared as trade-offs, although various social costs are in no way meant to be interpreted as equivalent to one another. Whether social ramifications are labeled as “costs” or “revenues” is highly subjective, but the labels are grounded in the writer’s concept of sustainability, and where ecological, economic, and social sustainability are perceived as goals. Results Waste Characterization The average density of Chevy’s waste stream was determined to be 207kg/m (7322lbs/21yd). The total waste volume generated was determined to be approximately 2.3m/day (21yd/wk). The EPA (1999) has determined that on average, the organic component of a restaurant’s waste stream is 74% by mass. Thus the mass of organic waste generated is 207 kg/m * 0.74 * 2.3 m/day = 352.3 kg/day This value is probably a slight overestimate: the total waste volume generated was determined by counting the number of filled dumpsters per week from which bottles and cans were not separated out. If this restaurant were to adopt on-site composting, which inherently involves source separation of waste, bottles and cans would be recycled rather than landfilled. Approximately 50 cases of glass bottles are ordered, and thus thrown away, per week. This amount of recyclable material occupies approximately 1m per week. Wright Environmental Management, Inc. (WEMI) makes two small-scale in-vessel composting units: a 273 kg/day (600lb/day) unit and a 455kg/day (1000lb/day) unit. Each unit can accommodate 66% of this mass in restaurant waste; the remaining mass comes from the added bulking agent. The larger of the two units, which can accommodate 300kg of organic restaurant waste per day is the appropriate size for a hypothetical Chevy’s on-site composting operation. This unit lists at $67 500. Economic Analysis Site: Chevy’s, Emeryville, CA Three scenarios of organic residuals management are analyzed and compared with regards to economic value only. Ecological and social considerations for each scenario are proposed. Scenario 1: All waste landfilled except cardboard The restaurant will operate as it does currently without separation of organics, and with all materials save cardboard being hauled and landfilled. Waste containers are owned by the hauling and landfilling company. Three 3 cubic yard containers are hauled four times weekly. The cost per year for pickup and landfilling is $ 23 052. Ecological considerations for Scenario 1: Lined and monitored landfills in the Bay Area present few immediate environmental impacts, but the fact remains that landfilling is an inherently nonsustainable practice. Disposing of waste materials in landfills renders materials impossible to separate and reuse due to the high degree of mixing and the presence of toxic contaminants. Furthermore, landfilling of materials is an immediate waste of potential resources and contributes to the unnecessary mining of raw materials and production of secondary materials which in turn creates pollution and disrupts the normal functioning of ecosystems. The anaerobic decomposition which food undergoes in an oxygen-poor landfill environment produces methane, a greenhouse gas. Social considerations for Scenario 1: “Waste” must be perceived as a natural resource for the maintenance of a sustainable society. Assuming that sustainability is a goal for human society, continuing to rely on the practice of landfilling for materials as readily degradable and reusable as food residuals serves to retard the attainment of this goal. Scenario 2: Off-site composting The cost of off-site city-wide commercial composting for a single restaurant is estimated to be approximately equivalent to the cost of landfilling for that restaurant. This result is extrapolated from the approximate equivalence in cost between landfilling and off-site composting incurred by Park Chow restaurant which recently underwent this switch (Hanek 2001, pers. comm.). Due to the high number of employees and the large amount of transportation necessary for such a composting program, this preliminary estimate is reasonable. Ecological considerations for Scenario 2: The transportation of organic residuals, which is a necessary intermediary between restaurant and composting facility, can tax the environment. Organic residuals are heavy, as they are composed of approximately 70% water. Currently, diesel trucks transport food residuals and compost in off-site composting programs. Figure 1 shows how total transportation can be significantly farther in an off-site composting scenario than an on-site composting scenario. Diesel trucks consume nonrenewable energy and contribute to non-point source pollution. Figure 1 A represents the restaurant, B represents the off-site composting facility, and C represents the site of compost use. The arrows represent distances traveled for different spatial arrangements. In case 1, distances traveled for off-site and on-site composting are equivalent. In case 2, the distance traveled for off-site composting is much farther than that for on-site. Scenario 3: On-site composting of all organics, recycling of cans, bottles, cardboard Organics will be separated from the rest of the waste stream at no extra cost. Chevy’s employees will carry out sorting as a new job routine. As sorting will be carried out, bottles and cans will be recycled at a minimal cost. Cardboard is currently recycled free of charge. In the design of a composting system for a high volume restaurant, several considerations must be made. First, organic waste must be stored for a minimum time period to maintain a pestfree restaurant. Each Green Mountain Technologies’ Earth Tubs require a fourteen-day period of mixing without loading (Bernard 2000, pers. comm.). A single-tub system would therefore require a fourteen-day organic waste storage time. Multiple-tub systems could reduce this storage time, but the space and labor required for such a system deem the system inappropriate to the scale of Chevy’s waste stream, and space and labor availability. The benefit of the Wright Environmental Management, Inc. in-vessel unit is that it has a continuous loading capability, such that organic waste storage is avoided altogether. The Wright unit is also extremely low in labor intensity compared with the Earth Tubs system. The Wright Environmental Management, Inc. system is evaluated here. Second, a bulking agent is required for all aerobic composting of food residuals. Two choices are available: shredded cardboard and wood chips. Corrugated cardboard is a waste A