The Science of Composting

Eliot Epstein

• Editorial: CRC Press
• Año: 2017
• ISBN:
  9781351409124
• Edición: 1
• Categoría: Technology & Engineering
• Categoría: Environmental Management

FROM THE PREFACE
The main objective of composting is to transform organic materials into a stable usable product. Often organic materials which may have limited beneficial use in their raw state or have regulatory disposal constraints can be transformed by composting into marketable products. The limits on beneficial reuse may be regulations or they may be due to the potential for materials to be putrescible or pathogenic. Composting can be a solution for each of these.The implementation of composting on a large scale (in contrast to home or backyard composting) involves materials handling. Technological implementation of composting must be consistent with the biological demand of the system. If the biological system is violated, conditions will not be optimized for composting, and problems such as odor generation, insufficient aeration or moisture, or a combination of these conditions may result. Past problems and closure of facilities have been largely due to violations of the biological systems. Product quality with respect to particle size, inclusions, moisture content and other physical aspects are a function of engineering design. A well designed system must have the biological and engineering principles in harmony at all times.

1 Composting: A Prospective

Introduction

The subject of composting can be subdivided into two major areas: the composting process and the compost product. Composting as a process involves the biological decomposition of organic matter. This definition is all encompassing, from simplistic backyard composting to large composting facilities. In this text composting means: The biological decomposition of organic matter under controlled, aerobic conditions into a humus-like stable product. The term controlled indicates that the process is managed or optimized to achieve the objectives desired. Some of the major objectives are to

• decompose potentially putrescible organic matter into a stable state and produce a material that may be used for soil improvement or other beneficial uses
• decompose waste into a beneficial product; composting may be economically favorable as compared to alternative disposal costs and may be more environmentally acceptable than more conventional solid waste management methods
• disinfect pathogenically infected organic wastes so that they may be beneficially used in a safe manner
• bioremediate or biodegrade hazardous wastes by means of the composting process

This chapter provides a brief overview of the history of composting, its current status, and philosophical aspects regarding the role of composting in the treatment of wastes and their ultimate beneficial use.

The use of several general terms needs to be explained. Biosolids will be used throughout in lieu of sewage sludge. This term has been adopted by The Water Environment Federation and is currently used by the U.S. Environmental Protection Agency (USEPA) in their manual A Plain English Guide to the EPA Part 503 Biosolids Rule (USEPA, 1994). Many different sludges exist: some chemical and some biological. Biosolids indicate that the solid is a product of biological activity and is primarily organic. There are several types of biosolids, e.g., pulp and paper mill sludge; a better term would be municipal biosolids to distinguish from industrial biosolids.

The past literature often uses the terms garbage or refuse. In this text, the term municipal solid waste (MSW) is used since it is often difficult to distinguish in the literature what was the composition of the waste stream. Source-separated organic wastes or other types of separated wastes will be so designated to distinguish them from mixed MSW.

Composting and Recycling

In recent years our society has developed a hierarchy of waste management (USEPA, 1989). At the top of the hierarchy of integrated waste management and the most desirable is source reduction. This includes reduction of waste generated through improved packaging and reuse of materials. The second tier is recycling, including composting. Waste combustion and landfilling are placed at the bottom of acceptable technologies.

Composting is the highest form of recycling. An organic, discarded material is converted (recycled) for reuse in a manner that only can benefit mankind. The major use for compost is beneficial. Compost can improve soil conditions and plant growth, and reduce the potential for erosion, runoff, and non-source pollution. Compost is an organic matter resource. Properly produced compost adds humus to soils.

A considerable portion of the domestic waste stream is amenable to composting. Yard waste and biosolids are organic and are easily composted. In 1989 USEPA in the introduction to the 40CFR503 regulations estimated that the 15,300 publicly owned treatment works generated 7.7 million dry metric tons of biosolids. The volume of biosolids generated is expected to double by the year 2000 due to population growth. Distribution and marketing ofbiosolids products, primarily composting, but also including heat dried material, accounted for 9.1% of biosolids disposal at that time (USEPA, 1989).

Sixty-eight percent of the MSW waste stream is organic and therefore can be composted (Figure 1.1). Paper constitutes 37.5%. A considerable portion of the paper can be effectively recycled. However there is always a portion of the paper fraction that is soiled and cannot be recycled. Hyatt (1995) estimates that this fraction represents approximately 16%. USEPA estimated that, in 1990, 17% of the MSW waste stream was recycled or composted (USEPA, 1992). In 1990 over 177 million tons of MSW was generated in the United States. This represented approximately 1.95 kg/person/day. This number is projected to increase to 189 million tons or 2.05 kg/person/day by the year 2000.

Figure 1.1 Materials generated in MSW by weight and percentage, 1990. (From USEPA, 1992.)

Legislature by states to discourage landfilling will encourage recycling and composting. The only way communities can meet goals exceeding 35% (except in areas producing very heavy amounts of green material) is to compost a portion of the MSW stream. In addition to residential recovery of organic materials for composting, opportunities exist for large scale composting of food wastes generated in markets and restaurants.

History

Composting in the broadest sense undoubtedly was practiced in ancient times. The Israelites, Greeks, and Romans used organic wastes directly or composted them (Martin and Gershuny, 1992). The early civilizations of South America, China, Japan and India practiced intensive agriculture and used animal and human wastes as fertilizers (Howard, 1943). Many of these organic wastes were heaped and allowed to rot for long periods of time, producing compost.

Research on composting in the United States appears to have begun in the 1880s. One of the earliest publications on composting in the United States was Bulletin No. 61 by North Carolina Agricultural Experiment Station, published in December 1888, XI. Composts-—Formulas, Analyses, and Value (Figure 1.2). Maynard (1994) cites 70 years of research on waste composting and utilization at the Connecticut Agricultural Experiment station. Hyatt (1995) reported that during the period 1971 to 1993 the number of citations, both in the United States and internationally, relating to the subject of compost has grown to 11,353. This indicates strong interest and research effort on the subject.

The concept of large-scale composting in a methodical manner is often attributed to Sir Albert Howard and his Indore process at the Institute of Plant Industry, Indore, Central India, between the years 1924 and 1931 (Howard, 1935). Initially, the process was anaerobic, but was later modified to an aerobic process and renamed the Bangalore process. The basic concept was to utilize vegetable and animal wastes and night soil (human excrement), mixing them with an alkaline material for neutralizing acidity, and managing the mass through turning for aeration and water addition. The process used either shallow pits or piles, that at times contained 909 tonnes (1000 tons). The dimensions of some compost pits were 9 m (30 ft) by 4 m (14 ft) by 0.9 m (3 ft) with sloping sides. It is interesting to note that Sir Howard observed that “air percolates the fermenting mass to a depth of about 18 to 24 inches only, so for a height of 36 inches, extra aeration must be provided.” Only in recent years has it been documented that oxygen levels at the bottom of windrows are very limited and that this zone becomes anaerobic (see Chapter 2). Van Vuren (1949) published results of composting of urban wastes in 1939 in South Africa based on Sir Howard’s principles (Figure 1.3). He viewed the composting of urban wastes as a method of disinfection while producing organic matter which could restore soil humus. One ofthe earliest systems was patented by Beccari in 1922 (Beccari, 1922).

The first full-scale, refuse composting facility in Europe was established in the Netherlands in 1932. The process used was the Van Maanen process, that was a modification of the Indore method. The plant was operated by N.V. Vuilafvoer Maatschapii (VAM). Unground refuse was piled in large windrows and turned by overhead cranes (Breidenbach, 1971; Epstein, 1976). Following World War II composting increased in Europe, with practically no composting being conducted in the United States. In the Netherlands two large composting plants were constructed in Mierlo and Wijster using the VAM method. It was estimated that nearly one-third of the Dutch refuse was composted in these two plants. Unit trains from The Hague would bring the waste onto an elevated ramp and dump the waste forming large piles. Overhead or mobile cranes would move and turn the waste for several months. Screening would then produce several different grades of compost to be used in agriculture and horticulture. In 1976 the author visited the VAM, Wijster, facility. This method appeared to be well suited for developing countries since it was a relatively low technology utilizing easily available equipment. During a visit to South Yemen on behalf of United Nations Developing Programs, the author recommended that a modification of the VAM system be used in lieu of a high tech mechanical system originally proposed for that country. This low technology process was implemented.

Figure 1.2 An early publication by North Carolina Agricultural Experiment Station, Bulletin No. 61, XI. Composts-Formulas, Analyses, and Value. December 1888, January, 1889.

Figure 1.3 Composting by the Indore method in South Africa as described by Van Vuren, 1939-1942. (Photograph by Mr. R. Nicholson, Stellenbosch, from Van Vuren, 1949.)

Breidenbach (1971) indicated that there were more than 30 composting systems in 1969. Table 1.1 lists several major systems in the world at that time.

The only major research conducted on composting in the 1950s and 1960s was conducted at the Richmond Station of the University of California under the leadership of Drs. Gottas and Goulke.

In the 1960s U.S. P...

Índice

• Cover Page
• Title Page
• Copyright
• Contents
• A Sense of Humus
• Preface
• 1 Composting: A Prospective
• 2 Basic Concepts
• 3 Microbiology
• 4 Biochemistry
• 5 Stability, Maturity, and Phytotoxicity
• 6 Trace Elements, Heavy Metals, and Micronutrients
• 7 Organic Compounds
• 8 Pathogens
• 9 Bioaerosols
• 10 Odors and Volatile Organic Compounds
• 11 Soil Physical and Chemical Manifestations
• 12 Utilization of Compost
• 13 Compost Utilization II
• 14 Regulations
• Index