Sewage sludge utilisation

Sewage sludge is the term used for digested sludge from waste water treatment plants. In the initial state it has a low viscosity and is dark in colour. It is rich in nutrients and humus matter, as during the biological phase, the bacteria use the substances in the waste water for the formation of biomass. Included therein are nitrogen, phosphate, potassium, calcium and magnesium. Sewage sludge is used agriculturally as a natural fertiliser.

The sewage sludge is used in two forms:

Irrigation using clear water with sewage sludge: In accordance with the regulations concerning waste sewage sludge and fertiliser, the clear water used for irrigation purposes is mixed with digested sewage sludge for the period in which the plants are able to absorb nutrients. Half of the sewage sludge accrued at the treatment plant during the waste water purification process can be thereby used as fertiliser.

Distribution of the dehydrated sewage sludge: The sewage sludge which is not used for irrigation is dehydrated at the treatment plant and is used on agricultural surfaces outside of the Association’s area, also serving in this form as fertiliser.

The high quality of the utilised sewage sludge and the responsible handling thereof are reflected in the fact that in 2006, the Abwasserverband Braunschweig was the first-ever body in Germany to receive the certificate „a quality assurance system for the agricultural utilisation of sewage sludge“ (QLA)  in the categories input material, end product and utilisation concept from the VDLUFA-QLA GmbH.

Due to the more stringent requirements of the fertilizer ordinance at federal and state level in recent years and the associated severe restrictions on organic fertilization in agriculture, it is unfortunately no longer possible to use all of the sewage sludge for agricultural purposes.

In order to guarantee the security of disposal, we decided in good time to tender partial quantities of the sewage sludge incurred for thermal recycling and thereby secured long-term quotas.