UNEP-IETC: Sludge Avoidance and Treatment Seek Technological Solutions


About UNEP	UNEP offices	News centre	Publications	Calendar	Awards	Milestones	UNEP Store

United Nations Environment Programme
Division of Technology, Industry and Economics

INSIGHT, Spring '95 Edition

Sludge Avoidance and Treatment Seek Technological Solutions

Municipalities worldwide are expanding their sewage treatment facilities, resulting in a higher incurrence of sludge which is often difficult and expensive to dispose of. Because of the increasing number of sewage treatment plants with a tertiary treatment stage, the quantity of municipal sewage sludge will continue rising.

Further, because of its contamination with heavy metals and organic pollutants, the quantity of dredged sludge (derived from waterways, harbors and dam sites) requiring treatment will also increase. The remainder of this sludge will continue to be dumped into tributaries, or sludge ponds established specifically for this purpose. The situation in developing countries is not yet as acute as in industrialised nations, but it is gaining in gravity as the number of sewage treatment plants rises. Municipalities are therefore particularly interested in economically feasible schemes for the treatment and disposal of sewage sludge.

Plant manufacturers and sludge treatment/utilisation companies must adapt themselves quickly and flexibly to the vast spectrum of needs of municipalities and industrial undertakings, and in cooperation with them develop appropriate strategies for the sustainable and economically feasible solution of sludge problems. The most common technologies in wastewater treatment and in avoiding sludge are summarised in the overview below, showing a tendency to combined technologies.

- Summary of Trends - Processes in Wastewater Treatment/Sludge Avoidance

Intensive Biology
A technology incurring only low levels of secondary substances, suitable for production processes characterized by high levels of organic pollutants.

Anærobic Methods
The trend is away from ærobic and towards anærobic methods, especially when the incurrence of sludge is high (e.g. in the paper industry); these methods allow utilisation of energy in the form of biogas and low incurrence of sludge (the disposal of which is becoming more and more expensive).

Physical Methods
The trend is away from chemical and towards physical (mechanical or thermal) methods with the goal of reducing the incurrence of sludge by not using additives (neutralising agents, stabilisers, etc.), culminating in the achievement of residue-free methods.

Membrane Methods
Residue-free (no incurrence of extra sludge attributable to additives) and - in comparison with thermal methods - lower energy consumption; also allows us of recycling technology.

Oxidative Methods, UV-initiated Oxidative Processes
Residue-free (CO2, H2O) methods with the elimination of pollutants.

Combination of Biological and Membrane Methods/Oxidative Methods
Exploitation of the advantages of biological treatment (relatively affordable treatment of large quantities of organic, biodegradable pollutants) as a basic method, of membrane methods (very high purification performance), and of oxidative methods for post-treatment and for the removal of residual, difficult-to- decompose pollutants; offers optimal combination for minimizing overall extent of task.

Recycling Technologies
Separation/recovery of valuable materials from the wastewater for internal or external utilisation (membrane technologies, electrolysis, crystallisation, vaporization, etc.)

Brochure

International Year of Forests

World Environment Day

UNEP Campaign