Construction of a new Magnesium Ammonium Phosphate (MAP) Precipitation Plant

Cause

The Steinhof wastewater treatment plant was overloaded in 2019 and the discharge limits for the parameters nitrogen and phosphorus could not be safely met. In order to optimise sludge treatment, a fundamental process conversion was carried out, the integration of thermal pressure hydrolysis and nutrient recovery from the sludge dewatering process water. The nutrients nitrogen and phosphorus are converted into agriculturally usable fertilisers. In this context, Bremer pro aqua designed a facility for MAP precipitation for phosphorus removal.

Process

The task of the MAP precipitation plant is to remove the freely dissolved ortho-phosphate from the process water as far as possible with the side effect of reducing the alkalisation requirement of the subsequent ammonium stripping. In principle, MAP precipitation reduces the risk of deposits forming in the ammonium stripping process. Nevertheless, care had to be taken when designing and controlling the plant to ensure that insufficient CO2 stripping combined with an overdosage of precipitation chemicals did not cause operating problems in the ammonium stripping process.

The PO4-P is precipitated in the system by adding Mg as magnesium ammonium phosphate. If necessary, the pH value of the process water must be raised. This is done by stripping out CO2. The plant was installed in a newly constructed sludge treatment building.