Government of New Brunswick
 

1.0 Introduction


Composting of the organic fraction of municipal solid waste is receiving increasing interest in the province. Presently there are some composting operations in the province which are handling a variety of materials including leaves, fish waste, sewage sludge and animal manures. Typically these projects are evaluated on a case by case basis by the Department of Environment in terms of environmental approval. However, as composting efforts increase in terms of both scale and number it is becoming necessary to provide those involved in composting operations with some guidance with regard to the composting process and environmental protection.

The aim of these guidelines is to provide some basic information on the composting process as well as to offer guidelines relating to the siting and operation of composting facilities in the province. These guidelines will help ensure that compost can be produced without adversely affecting human and animal health, food production and the natural environment.


Objectives:

To allow for the evaluation of composting operations while ensuring that the environment is protected.

To bring all composting operations, whether new or existing, into conformity with the provisions and recommendations of these Guidelines so that environmentally undesirable practices will be avoided.

To assist individuals involved in composting operations to comply with the conditions and recommendations of these Guidelines by avoiding unacceptable environmental conditions which could lead to legal disputes concerning pollution.

 

 

2.0 Background


Composting has been used for hundreds of years to convert organic waste to a rich, humus-like soil amendment used in agriculture and horticulture. Composting speeds up the natural decomposition processes to break down waste. In order for this to occur the micro-organisms need the proper amounts of air, water and nutrients.

During the decomposition process organic matter is returned to simple chemical compounds which plants can use. Heat, water vapour, and carbon dioxide are released during the process. The heat release also causes the destruction of harmful pathogens and weed seeds in compost. Successful composting depends primarily on adequate temperature and moisture control, oxygen supply and nutrients to feed the microbial populations.

Potential raw materials for composting include the compostable fraction of municipal solid waste, yard, garden and leaf wastes, agricultural crop residues and animal manures, fish waste, food processing wastes, forest products and paper product wastes and other biodegradable wastes from industry and other sectors. The primary objective of composting is to recover and recycle a valuable resource in an economic and environmentally acceptable manner.

The quality of the compost produced depends upon controlling the type of waste composted to minimize potential contaminants such as heavy metals and hazardous organic material. These control measures may include picking out potential problem materials prior to the composting process, excluding industrial sludge and source separation of organic material.

It is important to maintain quality control over the compost. The quality of the compost produced will affect marketability of the material and has the potential to impact on the environment.

 

 

3.0 The Composting Process


Essentially there are three basic steps to composting. The raw material is prepared, the composting process takes place and then the final product is graded and prepared for sale. There are four basic kinds of process technologies: turned windrow; static pile (forced aeration); in-vessel; and a hybrid version which is a combination of the above systems.

The difference between the systems is the way aeration of the material is accomplished. There are various methods of aeration including agitation, injection and a combination of the two.

Agitation can be accomplished by turning, tumbling or stirring. Air injection, or forced aeration, is accomplished by forcing or drawing air through the composting mass. Injection often is used in combination with agitation. Individual in-vessel compost systems may depend entirely on agitation or injection, or may use them in combination.

Of the composting technologies, the turned windrow and forced aeration methods are usually classified as "open" systems as typically they are not contained in a structure. This does not exclude enclosing the operation in a shelter or building. Both of these systems use elongated piles, referred to as windrows, to manage the composting material.

In-vessel composting systems can be categorized as an "enclosed" system as the compost is mixed mechanically in a structure. Many of these systems use a vessel to accomplish the mechanical mixing of the compost and the other stages occur in windrows. Such combinations can be referred to as hybrid systems.

 

 

4.0 Operating and Control Parameters


In order to better understand the description of the operating and control parameters, a brief explanation of the composting process is included here. There are two stages to the biological activity associated with composting. The first stage is the active stage in which there is a high rate of biological activity taking place. The temperature of the compost mass increases to 60 degrees Celsius. During this time the readily biodegradable material is decomposed to less readily degradable components. As this occurs the temperature of the mass drops because of a slowing of microbial activity. This second stage is known as curing or the maturation stage and ends when the material reaches the required degree of stability. Hence, an important consideration in the evaluation of a compost system is the fact that the compost process is finished only upon completion of the curing stage.

4.1 Time Requirements

The compost process is complete when the original organic material cannot be identified and the compost has a fresh earthy smell. At this point, the mass has been stabilized to a point where it can be stored without causing nuisances and can be used without inhibiting plant growth. The curing interval is particularly important because it must be long enough for the composting material to have reached the final level of stability.

The length of time required to complete the composting process will depend upon the nature of the waste and the system employed. For example, yard and park debris, including grass clippings and leaves with the proper balance between the nutrients of carbon and nitrogen (C/N), composting can be accomplished in four to eight weeks. Leaves without the proper C/N ratio can take two to three years to compost. Municipal solid waste, with or without sewage sludge, can take eight to 24 weeks. Sewage sludge alone (with suitable bulking) can take six to eight weeks. Animal manure and assorted food processing wastes (that have been appropriately bulked) can take six to eighteen weeks to produce compost.

4.2 Temperature Requirements

Unless there is an obvious problem no effort is required to ensure the adequate temperature is achieved. The pile reaches the highest temperature, between 55 to 60 degrees Celsius, when the degree of microbial activity is greatest. The temperature of the pile will rise quickly as this is the most active stage of microbial activity, which is referred to as the thermophilic stage.

Eventually the microbial activity decreases and the temperature cools. This return to ambient temperature is referred to as the mesophyllic stage.

Typically the highest temperature is achieved in the first 10 days of the composting process and then gradually returns to the initial temperature over a period of six to eight weeks depending upon the nature of the material.

If the temperature of the pile is too high, microbial activity will be impaired and efforts may have to be taken to lower the temperature depending upon the type of system being used. The usual approach is to increase the rate and extent of aeration.

If the temperature rises too slowly or there is no temperature rise then not enough microbial activity is taking place. The attainment and maintenance of thermophilic temperatures for a time period is required for weed and pathogen control. If the temperature rise is inadequate the reason may be an operational or other problem.

4.3 Moisture Requirements

Ideally the moisture content should be between 45 and 55 percent. If the moisture content of the mass is eight percent or lower, microbial activity will cease.

Too much moisture prevents air from being supplied to the microbes. For this reason it is necessary to add bulking agents such as wood chips, straw, or leaves to wastes that have a high moisture rate such as cannery wastes, sewage sludge, and fresh manure.

4.4 Oxygen Requirements

Although composting can occur without oxygen (anaerobic systems), composting systems which use oxygen (aerobic systems) are considered more efficient, reliable and can tolerate sudden changes in environmental conditions. Aerobic systems are less likely to cause nuisance conditions such as objectionable odours.

If the composting mass is producing foul odours, then this could be an indication that there is not enough oxygen present in the pile. A slow temperature rise during the active stage of the composting process or an unexpected drop in temperature in later stages is another indication that the pile needs better mixing to provide additional oxygen to the pile. Other signs include the slowing in the breakdown of the organic matter and the absence of expected physical changes in the composting mass.

In practice the rate of aeration should be determined by experimenting with the waste to be composted. If aeration is achieved by turning then how often the turning occurs becomes the important consideration in trying to supply enough oxygen. With composting systems which used forced aeration the rate and volume of throughput air is the primary factor to be considered.

While it is possible to accelerate composting by adding pure oxygen to the input air stream it is unlikely that the benefits would out-weigh the cost of such an approach.

4.5 Nutritional Requirements

The organisms which create the compost, like all living things, need moisture, air and a source of nutrients. The most important nutrients to supply the microbes in a compost mass are carbon and nitrogen. Other nutrients including cobalt, manganese, magnesium and copper should also be present but in smaller amounts. Calcium can also be important to ensure that the pile can resist changes in acidity (pH). Nitrogen is probably the only nutrient which needs to be added to ensure that a suitable carbon/nitrogen ratio is achieved.

The nutrients must be present in a form that the microbes can use or digest. Some substances will be very resistant to breakdown by the composting process even under ideal conditions. These can include wood, straw and paper as well as feathers and shellfish.

Experience has shown that, with the exception of carbon and nitrogen, most organic wastes contain nutrients in the amounts and ratios required for composting. The ideal carbon/nitrogen ratio is 25 to 30 parts carbon to one part nitrogen. The composting process becomes increasingly slower as the ratio rises beyond this range. The carbon/nitrogen ratios for a number of organic materials are shown in table 1.

 

Table 1. Carbon/Nitrogen Ratio of Compostable Materials

Compostable Material Carbon/Nitrogen Ratio
Chicken manure 10
Chicken manure with manue 13-18
Cattle manure 20
Horse manure 25
Manure with straw 25-30
Green Plants 7
Grass clippings 12-25
Hay 15
Leaves 45
Straw 100
Peat 30-50
Wood shavings 100-150
Sawdust 100-500
Paper/cardboard 200-500
Garden Waste 20-60
Kitchen scaps 12-20
Domestic waste 30-40
Sewage sludge 11

Source: Jacques Petit, Compost: Théorie et pratiques, Éditions de l'oiseau moqueur

 

4.6 Particle Size

In theory, the smaller the particle size, the more rapid the rate of decomposition. However, below a minimum size this does not hold true as the air space provided by the particles supplies oxygen for the composting process. For material which is rigid, such as wood chips, the optimum size is from 5 to 7.5 centimetres. The maximum size for green plant material such as food wastes, fruit and lawn clippings should be no less than 5 centimetres and the maximum size can be as large as 15 centimetres.

4.7 Mixing Requirements

To ensure decomposition occurs uniformly throughout the composting mass, it is important to ensure proper mixing takes place. Mixing ensures that all compost material is exposed to conditions which will destroy pathogens. For aerobic composting, it renews the oxygen supply in the spaces between particles necessary for composting to occur. Mixing also helps reduce excess moisture from the composting mass.

4.8 Acidity (pH)

Usually the pH level drops to about 5 as soon as composting conditions have been established. This initial drop is soon followed by a gradual rise that continues until a level of approximately 8.5 is reached. It is unnecessary, therefore, to add lime to the process. The one possible exception may be in the composting of fruit waste in which case the initial drop may be slightly lower. Adding lime can, however, improve the physical condition of the composting mass by improving the porosity and texture of the pile

 

 

5.0 Site Selection Guidelines

5.1 Separation distances are necessary in order to minimize potential environmental conflicts between non-compatible land uses, to minimize odour related problems and to ensure the integrity of groundwater systems.

 

Table 2. Separation Distances for Composting Facilities

  Separation Distance
Neighbouring Properties:  
dwelling 400m
commercial building 300m
industrial building 300m
farm 100m
   
Roadways:  
right of way of a local road and arterial or collector highways 50m
   
Watercourses:  
rivers/streams 150m
private well 150m
lakes 300m
   
Buffer Zones:  
minimal buffer strip between composting facility
boundary and adjacent property
30m

Table 2 indicates the recommended separation distances. However, these may be modified, if deemed necessary by the environmental inspector, to make a project environmentally acceptable. Modifications will be based on the type of material to be composted, the composting site, operational procedures, etc.

5.2 The comporting facility shall not be located in areas subject to flooding and where seasonal high groundwater table is less than 1 meter from the ground water table or where the minimal depth to bedrock is less than 1.5 meter.
5.3 The composting facility shall not be located within a protected watershed as defined by the Clean Water Act
5.4 The composting facility shall be located on a surface with a slope of between 1% and 6%.
5.5 The Department must obtain a letter from the development officer of a municipality or a District Planning Commission stating the proposed project is in conformity with local planning regulations relative to land use provisions adopted for the area under the Community Planning Act.
5.6 The proponent shall notify the owner(s) whose property is located within 1/2 kilometer from the proposed composting facility prior to issuing an Approval.
 

6.0 Operational Requirements


The requirements of these Guidelines apply to all composting operations and facilities with the exception of backyard composting. An Approval must be obtained prior to the construction of a new composting facility or expansion of an existing facility and prior to any facility beginning operation.

An Approval must still be obtained by presently operating composting facilities after a site evaluation by an environmental inspector.

In addition to the Department of Environment's approval, all buildings and structures related to the composting facility shall meet the conditions of all Municipal, Provincial and Federal regulatory agencies responsible for adequacy of design, health, sanitary, safety and water quality requirements. Should composting operations cease, efforts must be made to ensure that no environmental damage will occur.

6.1 The operation of the composting facility shall be properly maintained to the satisfaction of the environmental inspector.
6.2 The composting operation shall have adequate security to prevent illegal dumping and vandalism
6.3 If the composting operation involves mixing, it shall be carried out in a location, approved by the environmental inspector, allowing for the collection of leachate, and recycling it back into the compost pile.
6.4 Should the final composted product be considered inadequate for usage, it should be hauled to a designated disposal site.
 

7.0 The Approval


An Approval will be issued for composting facilities whose premises and practices are consistent with the conditions and recommendations of these Guidelines.

All composting projects are subject to inspection and review by the Department of Environment. The issuance of an Approval will be determined by a site inspection and the information given on a completed application form which is based on the following information (see Appendix A: Approval Application Form):

  • Name and address of proponent.
  • Written description of composting methods, equipment employed and management of site.
  • Type and volume of waste to be composted, source of raw materials, bulking agents and leachate control methods.
  • Proponent's knowledge and experience on composting and the marketing strategy for the final product.
  • Location of the proposed composting operation indicated on a 1 :12,500 scale map or equivalent sketch indicating separation distances to the following:
    - farms
    - private wells
    - industrial areas
    - residential areas
    - right of way of local roads
    - right of way of arterial or collector highways
    - watercourses
    - commercial areas
    - property boundaries
    - watershed boundary
  • The slope of the land surrounding the proposed composting location.
 

8.0 Conclusion


The basic principles and technologies described earlier may be applied to municipal, commercial/industrial and agricultural composting operations. The characteristics of each waste type will dictate the best approach that should be taken for that material. There is no question that organic material, if properly processed can be composted. If composting is to be successful, however, siting and operating conditions must be closely followed.