sludge composting

Increasing stringent statutory restrictions are resulting in new rules on treatment and discharge being imposed on sludge producers with the following objectives:

• reducing amounts;
• long-term storage;
• sanitisation;
• changes in texture;
• biological stabilisation;
• improving the agronomic quality of sludge;
• changing the image of sludge and improving its acceptability.

Sludge composting is used to satisfy these objectives in so far as the processes used are thoroughly controlled. Composting sewage waste sludge results in the production of a humus-like, sanitised and saleable organic soil improver (authorisation system or implementation of a standard such as, in France, the NFU 44 095) for use in market gardens, floral horticulture, nurseries, viticulture, forestry, restructuring eroded soils or spreading over major crops when the sludge’s heavy metal content is acceptable. If absolutely necessary, the compost can be routed to landfill sites that only take high dry solids content products (revegetation).

Given platform investment and running costs, sludge composting remains relatively undeveloped.

Marketing the end product requires a thorough preliminary market analysis together with a cheap, plentiful and local supply of carbonaceous support.