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Newsletter and Technical Publications
Freshwater Management Series No. 1

Biosolids Management: An Environmentally Sound Approach
for Managing Sewage Treatment Plant Sludge

An Introductory Guide To Decision-Makers


Practices In Europe and North America: Waste Disposal Versus Resource Utilisation

Throughout North America and Europe, the application of biosolids to land is continuing to increase. As shown in Table 1, current biosolids applications to agricultural land in Europe and North America has become significant.

Although biosolids disposal in a landfill site is common, it should not be viewed as a long term solution. This option is considered to be environmentally beneficial only when such disposal includes methane gas recovery for application as a fuel. Modern landfills are complex and costly facilities to build and operate. They must be carefully engineered and monitored to ensure protection of both groundwater and surface water. In many locations, accessible, long-term landfill capacity is limited. Engineering and siting requirements can make the construction of new landfills prohibitively expensive. Most importantly, landfill disposal does not take advantage of the nutrient value and soil-building properties of biosolids, and takes up landfill space that can be better used for other materials. However, landfill is the unavoidable choice when municipal sludge is contaminated with industrial waste and municipal authorities are unable to monitor and control industrial discharges.

Table 1: Biosolids Management Method in European Nations and in the United States
Annual
Production

Mangagement method
(percentage of total)

 
(1,000 dry tons)
Agriculture
Landfill
Incineration
Other
Austria
320
 
13
 
56
 
31
 
0
 
Belgium
75
 
31
 
56
 
9
 
4
 
Denmark
130
 
37
 
33
 
28
 
2
 
France
700
 
50
 
50
 
0
 
0
 
Germany
2500
 
25
 
63
 
12
 
0
 
Greece
15
 
3
 
97
 
0
 
0
 
Ireland
24
 
28
 
18
 
0
 
54
 
Italy
800
 
34
 
55
 
11
 
0
 
Luxembourg
15
 
81
 
18
 
0
 
1
 
Holland
282
 
44
 
53
 
3
 
0
 
Portugal
200
 
80
 
13
 
0
 
7
 
Spain
280
 
10
 
50
 
10
 
30
 
Switzerland
50
 
30
 
20
 
0
 
50
 
UK
1075
 
51
 
16
 
5
 
28
 
US
5357
 
36
 
38
 
16
 
10
 
Total/Avg.
11988
 
38
 
43
 
10
 
9
 
Source: Chang, Page, and Asano, 1996

From an environmental point of view, incineration of biosolids is also a very limited disposal option. The ash produced in the incineration process must be treated as a hazardous waste because it contains high levels of heavy metals. Incinerators require significant capital investment and have relatively high operational costs. Because biosolids have a high percentage of water (70% - 98%), the energy costs can be significant, although some energy can be recovered by burning the organic material. Expensive and sophisticated air pollution control systems are needed to remove particulates and regulated gases from incinerator smokestacks. Like landfill disposal, incineration does not take advantage of the nutrients and soil-building qualities in biosolids. Incineration is occasionally used for biosolids disposal in urban areas where the population is large, suitable agricultural land is far away and transportation costs are prohibitively high.

Addressing Public Concerns about the Land Application of Biosolids

Opposition to land application has usually centred on local issues, such as resistance of rural communities to receiving shipments of urban biosolids. Apart from this, the most pervasive public concern about the land application of biosolids is the perception that toxic trace elements and pathogens may be released into soil and groundwater.

Biosolids often contain concentrations of trace elements greater than the concentrations found in typical soils; therefore, biosolids application may potentially increase the concentration of these elements. Most trace elements, however, are immobile and tend to concentrate in the soil only to the depth that biosolids are applied. The National Research Council in the United States has determined that where properly processed biosolids have been applied to soil according to specific guidelines and regulations, there has been no evidence of phytotoxicity or accumulation of trace elements in plants. If the agricultural use of biosolids follows appropriate regulations, including Ph requirements, no adverse effects should be expected or observed.

Communities are also concerned about the possibility of disease transmission since pathogens are present in the untreated sewage from which the biosolids are produced. In fact, pathogen populations are significantly reduced through the wastewater treatment and biosolids production processes, as well as through full compliance with regulated land application requirements. In the United States, for example, where biosolids utilisation accounts for more than half of the residual solids output, there have been no documented cases of diseases resulting from either treated wastewater reuse or agricultural use of this material. Furthermore, no adverse effects have been reported from ingestion of plants grown in biosolids-treated soils. It is essential, however, to have a fully functioning, environmentally sound biosolids management system in place to ensure public and environmental health protection.

In most communities, the land application of biosolids is usually limited to marginal or agricultural lands that are used for either animal feed or crops that are not ingested raw. For specialised commercial applications such as composting or horticultural uses, a higher degree of stabilisation is usually necessary.


A Range of Options for Biosolids Utilisation

The most successful and best-known biosolids utilisation practices are as follows:

 
• 
Agricultural cropland application, through liquid injection, or surface spreading followed by incorporation into the soil,
 
• 
Commercial sale as a fertiliser or soil conditioning material, particularly for horticultural and landscaping applications (although a higher degree of stabilisation is usually necessary),
 
• 
Rangeland and pasture application to improve available grazing,
 
• 
Remediation of contaminated areas such as mine sites,
 
• 
Soil amendment and recovery of marginal land,
 
• 
Land application in reforested areas, and
 
• 
Energy recovery.

In most cases, the option is determined by a careful cost-benefit analysis and the size and characteristics of the market for the product. Local markets usually need to be fostered through education, demonstration and training. When considering land applications of biosolids, it is important to ensure that concentrations of metals and complex organics do not exceed stringent regulatory limits. It is also essential to understand the soil properties and crop characteristics of those land areas being considered for land application of biosolids. To reduce risk, frequent, ongoing applications at the same site should be avoided.

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