Worldwide Composting Technologies with Special ... - ACS Publications

Chapter 23

Worldwide Composting Technologies with Special Reference to Biodegradable Plastics Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on June 9, 2016 | http://pubs.acs.org Publication Date: February 15, 2001 | doi: 10.1021/bk-2001-0786.ch023

Eliot Epstein E&A Environmental Consultants, Inc., 95 Washington Street, Suite 218, Canton, MA 02021

There are more than 50 different types of composting technologies operating worldwide. These can be classified generically into static, turned, or combined systems. In the U.S., static systems are predominantly used for biosolids composting, whereas turned systems are primarily used for municipal solid waste and yard materials composting. In Europe, many static systems are used for biowaste and agitated systems for solid waste. There are more than 274 biosolids, 3,484 yard materials, and 142 food/institutional composting facilities operating in the U.S. today; there are only 15 municipal solid waste composting facilities. The potential for utilization of biodegradable plastics in composting operations is in the use of bags for source -separated solid waste and yard material, coated papers, and packaging materials. There are several factors that could affect the rate and extent of biodegradation of polymers/plastics. The efficiently of biodegradation is dependent upon the feedstock, the system, and maximizing the microbial system.

Composting is the biological decomposition of organic matter under controlled, aerobic conditions. It can involve both mesophilic and thermophilic temperatures. Over 80 different microorganisms have been identified in composting . There are many factors which affect the composting process: r/;

• • • •

Oxygen Moisture Temperature pH Nutrients, especially carbon, nitrogen, and phosphorus

© 2001 American Chemical Society

Gross and Scholz; Biopolymers from Polysaccharides and Agroproteins ACS Symposium Series; American Chemical Society: Washington, DC, 2001.

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Particle size and surface area Chemical and physical nature of the feedstock material These factors greatly affect the rate and extent of microbial decomposition of organic compounds. The ultimate goal in composting is to produce a humus-like material, which is an excellent soil conditioner and can be used for numerous horticultural and agricultural applications. As a soil conditioner, this stable organic material improves soil moisture content, water retention, infiltration and permeability of water, soil structure, soil temperature, cation exchange capacity, and other soil chemical properties. Constraints to product use have been related to heavy metal content exceeding regulatory levels; pathogens as a result of improper composting; unstable material, resulting in odors; rapid decomposition in soil causing nutrient deficiency in plants; presence of undesirable organic compounds (e.g., PCBs); contamination with inerts, such as glass, metals, and plastics; lack of product standards, resulting in inconsistent product quality and consistency; and lack of educational programs to target the market. Many components of the waste stream can be composted. The materials listed below are some of the feedstocks that have been composted. Municipal solid waste, unsorted or sorted Biosolids (sewage sludge) Septage or night soil Animal wastes Leaves/yard materials Food wastes (restaurants) and food processing waste Industrial waste - pulp and paper mill sludge - organic polymer sludge - petroleum waste, tank bottoms - munitions waste (TNT, H M X , R D X ) - pharmaceutical wastes Coated paper and cardboard Biodegradable polymers Artificial blood In the U.S., there are over 247 biosolids, 3,484 yard material, 147 food/institutional, and 15 municipal solid waste composting facilities. The extent of composting in North America has primarily been a function of the economics of disposal for a particular feedstock and regulatory restrictions on various management options. There are three major feedstocks that are composted: municipal solids waste, biosolids (sewage sludge), and yard materials. Traditionally, municipal solid waste has been managed by the private sector, while biosolids management has been the responsibility of public entities (wastewater treatment plants). Yard material is managed by both private and public organizations. Until the mid-1980s, there was little composting of unseparated or source-separated municipal solid waste in North America or Europe. In the 1930s and 1940s, several attempts were made to compost municipal solid waste. One proprietary method, Fairfield-Hardy, was used at several plants, the largest of which was in Altoona, Gross and Scholz; Biopolymers from Polysaccharides and Agroproteins ACS Symposium Series; American Chemical Society: Washington, DC, 2001.

389 Pennsylvania. In the 1960s, the U.S. Public Health Service funded two projects in Johnson City, Tennessee and Gainesville, Florida. Two municipal solid waste composting facilities were constructed and operational, but both of these facilities were subsequently closed. However, by 1971,14 of the 18 largescale composting facilities constructed in the U.S. were closed/ In 1991, there were 18 municipal solid waste composting facilities, and there has been virtually no growth in the number of facilities in recent years. This can be attributed to the low cost of landfilling in the U.S. as well as the poor performance of existing municipal solid waste composting facilities. Table I lists the solid waste composting facilities in the U.S. Three large facilities in Portland, Oregon; Dade County, Florida; and Pembroke Pines, Florida have closed within the past four years. The facilities were closed primarily because of odor problems caused by poor design. This has given municipal solid waste composting a bad reputation. Currently, the largest co-composting (municipal solid waste and biosolids) facility is being designed in Edmonton, Alberta, Canada. This facility will compost approximately 1,000 tonnes of municipal solid waste and 90 dry tonnes of biosolids per day. Prior to 1975, there was an insignificant amount of biosolids composting. In 1973, the U.S. Department of Agriculture embarked on a major research program at the Beltsville Agricultural Research Station in order to find a biosolids management option for Washington, D . C . In 1974, the Aerated Static Pile composting method was developed/^ This method can be used for the composting of either undigested (raw) or digested biosolids. From that period forward, biosolids composting increased. This continued increase was the result of several factors:


2;

• • • •

The economics of biosolids composting is very competitive with other technologies, such as land application, heat drying, incineration, and landfilling. Regulations in the U.S. favor beneficial use, such as composting, heat drying, and land application. The public generally favors composting over other management options. Federal funds appropriated through the Clean Water Act of 1978 provided funds for composting facilities and other technologies.

It is expected that this growth will continue, even though no more Federal funds for project development are available. There has been an increased involvement by the private sector in financing and operating biosolids composting facilities. The greatest growth of composting has been in yard material management. It is estimated that there are over 3,484 yard material composting facilities, both private and public, currently operating in the U.S. There were very few yard material composting facilities until the late 1980s because landfilling was inexpensive and convenient. When local and state governments became concerned about ground water contamination from landfills and diminished landfill capacity, states began restricting landfill disposal of yard materials. The U.S. E P A imposed more strict regulations on landfill construction and monitoring, making this technology more expensive. A t this point, it appears that the growth in yard material composting has peaked. Many private companies, such as Browning Ferris Industries; Waste Management, Inc.; and Scotts Environmental entered the yard waste composting business for profit, but Gross and Scholz; Biopolymers from Polysaccharides and Agroproteins ACS Symposium Series; American Chemical Society: Washington, DC, 2001.

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Table I. Some Solid Waste Composting Facilities in the United States Location

Year

Capacity (tonnes/day)

Technology

Status

New Castle, D E

1984

205

Fairfield

Closed

Pennington Co., M N

1985

22

Lundell

Closed

Fillmore Co., M N

1987

5

Engineered/ aerated windrow

Operating

St. Cloud, M N

1988

228

Recomp

Closed

Sumter Co., F L

1988

46

Retrofitted to Bedminster

Operating

--

114

Addington

Closed

Mora, M N

1992

270

Static pile

Restarting

Pinetop-Lakeside, A Z

1991

8

Bedminster

Operating

Cobb Co., G A

1995

273

Bedminster

Restarted after fires

35

Engineered/ windrow

Operating

Engineered/ windrow

Operational

Ashland, K Y

Buena Vista Co., IA

-

Swift Co., M N

1992

5

Truman, M N

1992

91

OTVD

Operational

Lexington, K Y

-

91

Agranom

Operational

East Hampton, N Y

--

27

Engineered/ IPS

Operational

Sevierville, T N

1993

209

Bedminster

Operational

Wright Co., M N

1992

150

Buhler

Closed

Pembroke Pines, F L

1992

546

Buhler

Closed

Toronto, C N

1978

41

Fairfield-Hardy

Closed

Altoona, P A

1951

23

Fairfield-Hardy

Closed

Portland, O R

1991

546

DANO

Closed

-

64

Engineered

Operational

Columbia Co., WI


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recently, several of these large waste corporations have discontinued their organics operations, citing low or negative profit margins. Collection costs are an important factor. Early attempts at biodegradable plastic bags failed, and paper bags are costly. Removal of plastics from the waste stream has also been problematic and costly. Some facilities have solved this problem by restricting bagging of yard material; others have restricted bagging to paper only. Odor has also been a problem for yard material facilities, especially those that process large volumes of grass.

Factors Affecting the Growth of Composting The major factors affecting growth and development of the composting industry are: Economics of waste management Public attitudes towards recycling/composting Incentives Regulations Product markets Past experience Environmental and public health issues

Economics of Waste Management In most of the U.S., the least expensive method of waste management has always been landfilling. Landfill costs have increased in recent years as a result of regulations that require leachate and gas emissions control. In several parts of the U.S., particularly the northeast where landfill costs can exceed $60 per ton, municipal solid waste composting can compete and succeed. Composting can generally compete in cost with waste-to-energy facilities. The economics of biosolids composting is competitive with most biosolids management options, as landfilling of low-solids material is often not allowed. Incineration or heat drying is more expensive; direct land application is often less expensive.

Public Attitude Towards Recycling Composting is recycling. The U.S. E P A and many state agencies have established a hierarchy of solid waste management options. Reuse, recycling, and composting are rated as the most desirable, and waste-to-energy, incineration, and landfilling are ranked as least desirable. Recycling goals and mandates have had much influence on the development of composting facilities, particularly yard materials facilities. Many states have instituted recycling goals of up to 50 percent diversion from landfills. Composting plays an essential role in attaining these goals.


392 The publie generally favors composting over other waste management options. However, many individuals, as well as communities, do not want composting facilities or other waste handling industries in their neighborhoods. This has mostly been a result of odor problems experienced at some facilities.


Incentives Financial incentives from both the U.S. Federal and state governments have encouraged composting. The U.S. Federal government has provided money through Clean Water Act funding for the development of biosolids composting facilities. Several states have provided financial incentives in the form of grants for composting development and facilities. For example, the state of Minnesota has provided up to $2 million for construction of municipal solid waste composting facilities. Thus, this state has the highest number of municipal solid waste composting facilities. Several states tax waste going into landfills and use the moneys to provide grants for composting, recycling, and other activities.

Regulations Regulations can impact the economics of waste disposal as well as the availability of options. Regulations regarding air emissions from waste-to-energy facilities increase the cost of combustion of wastes. Regulations on leachate control and gas emissions from landfills increase the cost of landfill construction and operation. The U.S. E P A has promulgated regulations that have significantly increased the cost of incineration and landfilling. The Clean Water Act, which specifically banned ocean dumping of biosolids, left many wastewater treatment plants searching for options. The U.S. E P A 40 C F R Part 503 regulations, encouraging and regulating the beneficial reuse of biosolids, make composting a more attractive alternative than many other options. Canadian regulations of trace elements can discourage composting by limiting its use and distribution. In the Netherlands, composting has shifted from solid waste composting to composting of yard material and biowaste. Although landfilling has decreased significantly, incineration of solid waste has increased. Improved technology for effective separation and refining of products could have resulted in less incineration and more composting.

Product Markets The availability of markets for compost encourages composting. Before financing a private facility, lending institutions want assurance that a market for the finished product exists. Past experience has shown that a high quality product is easily marketed. Prices vary from $7 to over $20 per cubic meter. The principal paying markets in the U.S. are landscapers, nurseries, greenhouses, turf grass growers, and soil blenders.


393


Past Experience A community or industry evaluating different waste management strategies can only base its judgment on previously built facilities. Unfortunately, the failure of facilities reflects badly on the industry and can make siting new facilities difficult. This has been especially true with respect to municipal solid waste facilities. The principal reason for the failure of several large municipal solid waste composting facilities was the poor design of materials handling systems and odor control. Facilities were sited near residential communities, and odorous emissions caused complaints and concern about public health. Most of the biosolids composting systems that have failed have been vertical systems. The failures were due to mechanical problems, the inability to process the waste properly, creation of odors, and inadequate odor control. It is doubtful that new vertical systems will be designed and accepted in the U.S.

Environmental and Public Health Issues Environmental and public health aspects have often restricted the development of composting facilities. The most important issues regarding facilities are odors and bioaerosols. The presence of odors suggests to the public that the air being emitted may contain unhealthy compounds or material. The potential for odors exists, regardless of the technology or system. The key to odor control is proper design of the facility and proper operation. Enclosing facilities can result in better odor management. However, this raises the cost of the facility. Odors have also been the major cause of failure at yard material facilities. Although brush and leaves are relatively easy to handle, grass, which arrives at facilities in concentrated batches, can quickly create an odor problem i f left unmanaged. The major potential use of biodegradable polymer bags is in source-separated municipal solid waste, such as dry/wet or blue bag systems or the collection of yard materials.

Composting Technology

Basic Concepts Composting systems fall into one of several categories: static, turned, or a combination of both. Within these categories, there are several different basic designs: •

Static systems - aerated static pile - vertical silos or bins - tunnels


394


Turned systems - windrow - agitated bed Different systems are more appropriate for different feedstocks. Depending on the feedstock, more structures, odor control, or special material handling equipment may be required. For example, biosolids are best composted in an aerated static pile or agitated bed system. Both of these systems can be enclosed with effective odor control. The aerated static piles can often be built outdoors with negative forced air that is piped into a biofilter for treatment. Turned systems can be more effective in reducing particle size and are generally more suitable for municipal solid waste or yard materials. Table II lists numerous composting system that we have evaluated. These systems are based on static or turned technologies and would be very different in their ability to biodegrade feedstocks.

Table II. Various Composting Systems Composting Systems

Aerated Static Pile (non-proprietary)

Windrow (non-proprietary)

International Processing System (IPS)

Bedminster

Longwood

OTVD

DANO

Buhler

Taulman-Weiss

ABV-Purac

BAV

Daneco

Arus-Ruthner

P L M Selbergs

EBARA

Japan Steel Works

Paygro

AmeriCycle

American BioTech

Ashbrook Tunnel

Enadisma

Gicom Tunnel

Seerdrum

Fairfield

Agripost

Heidelberg Silo

VAM

Sorain Cecchini

Weser Bio-waste

Koch Bio-waste


395 Composting of organic material involves three basic processes:


•

Pre-processing Composting Post-processing

Pre-processing involves the preparation of the feedstock for composting. It may involve shredding, removal of non-desirable materials (plastics, metals), or blending of amendments or bulking agents. Table II lists the various systems that have been investigated. The first stage of composting involves a high rate of decomposition, which results in high temperatures and rapid breakdown of the organic matter. This stage has a higher potential for odor generation. The length of this stage depends on the feedstock. The second stage involves curing. Curing is a continuation of composting, but since materials are partially stabilized, heat generation is lower and there is less oxygen demand in the composting medium. Curing produces a stable and mature compost product. Post-processing involves the production of a material for marketing. This stage can involve screening, destoning, and other refining processes. Figures 1,2, and 3 show general process flow diagrams for municipal solid waste, biosolids, and yard materials composting facilities.

Composting as Related to Biodegradable Polymers/Plastics There is considerable potential for the use of biodegradable plastics, especially in yard material, food waste, and solid waste composting. The different systems could greatly affect the rate and extent of the biodégradation of polymers and plastics. Composting conditions will vary within each system. For example, anaerobic conditions are much more prevalent in windrow or unaerated static systems. This can be overcome by installing aeration systems. Aerobic conditions accelerate composting and reduce the potential for odors. Moisture content will vary. Windrow and agitated bed systems will tend to dry unless water is applied at frequent intervals. Temperatures will generally be higher in static systems, often approaching high thermophilic temperatures exceeding 60°C. The rate of biodégradation is a function of particle size. Different systems affect physical properties, especially particle size and surface area. A l l these factors affect the microbial population both, in types and numbers, and they, in turn, influence the rate and extent of biodégradation. There is a need for improved technology in debagging, separation of inerts, and other product refining systems in order to produce high quality products.



PRE-PROCESSING Source-Separation: Manual or Mechanical

Rejects: Plastics, Metals

COMPOSTING High-Rate Composting And Curing

I POST-PROCESSING Screening Bagging

Rejects Product Marketing

Figure 1. Process Flow for Municipal Solid Waste Composting.


397

PRE-PROCESSING Mixing, Homogenizing


Bulking Agent Addition

COMPOSTING High-Rate Composting And Curing

ï POST-PROCESSING Screening Bagging

Bulking Agent Recycling Product Marketing

Figure 2. Process Flow for Biosolids Composting.

PRE-PROCESSING Debagging Sorting Grinding

Rejects. Plastics, Metals

Ï COMPOSTING High-Rate Composting And Curing

Air Water

ï POST-PROCESSING Screening Bagging

Figure 3. Process Flow for Yard Materials Composting.


398

Literature Cited 1. 2. 3.

Epstein, E. The Science of Composting; Technomic Publishing Co., Inc.: Lancaster, P A , 1997. Stickelberger, D . "Survey of City Refuse Composting;" W H O International Reference Centre, 1974. Epstein, E.; Willson, G.B.; Burge, W.D.; Mullen, D.C.; Enkiri, N . K . J. Water


Pollut. Control Fed. 1976, 48,688-694.


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