The European Parliament issued a directive on sewage sludge management in November 2008, known as the Waste Framework Directive. It outlined a hierarchy that established priorities for waste prevention and policies for management legislation, noting that the prevention of sewage sludge generation is impossible, because it represents an unavoidable type of waste.
The directive lists priorities for dealing with sewage sludge as:
- Prevention
- Reuse
- Recycling
- Other recovery processes
- Disposal
Prohibitions are in effect in Europe against disposal of waste in the sea, and there are limitations on landfill disposal as well, which leaves organic recycling and energy and material recycling as the two major options.
In 2013, for example 73% of France’s sewage sludge was recycled for compost and related agricultural uses. The numbers differed greatly from one nation to another, with only 7% being used by agriculture in Poland, while an almost equal amount was sent to landfills. In Germany, approximately 47% was reused or recycled for agriculture.
Costs Associated with Sludge Management
Although it is somewhat difficult to determine, based on the vast differences in operation of wastewater treatment plants in developed countries, it is estimated that the costs related to the management of sewage sludge represent between 20 and 60% of total expenditures. The higher percentages often are associated with transportation costs and the subsequent treatment of the sludge to ensure that it is suitable for reuse. Another large part of the cost relates to national or international constraints that are in effect regarding processing, treatment and reuse of the sludge.
Other Creative Uses for Sewage Sludge
Innovative uses for sewage sludge may be just around the corner, particularly in the construction industry. One traditional method of reducing the volume of sewage sludge is incineration. What is left is known as sewage sludge ash (SSA), typically only a fraction of the mass of unfired sludge; it is often transported to landfill sites for subsequent disposal.
However, a better use may be to incorporate such SSA into the manufacture of building materials such as bricks and tiles or by using it as a raw material in cement production. The European Union, as a proponent of the transition to a “Circular Economy” that promotes creative reuse of materials, envisions SSA as a viable source of aggregate materials suitable for sub-bases and embankments necessary in road construction, or as a substitute for sand or cement in stabilized bases.
It is entirely possible that cutting-edge technology will find other creative uses for sludge in the not-too-distant future.
The View Around the World
Unfortunately, the global picture is not as encouraging as wastewater control and management has become in the United States and in other developed countries. In many cases, sewer waste and fecal sludge is improperly managed, contributing to serious environmental problems and human health concerns. In some cases, it is attributable to a lack of awareness; in other situations, lacking technical expertise is at fault. And, in some instances, there is a lack of will and funding, in addition to a lack of knowledge. Whatever the root cause, the result of poor performance in the areas of sewer and septic sludge is the release of pathogens and offensive materials into the environment, material which generates odors and contributes to both surface and groundwater pollution.
