Preconditions:
The objective of the purifying plant in Göttingen is the removal and reclaiming of ammonium from filtrate water according to the latest scientific techniques. Otherwise, the municipality would not be able to fulfill the minimum legal requirements. Especially the high component of nitrogen in Göttingen's drainage water was an unusual difficulty here for a purely biological cleaning procedure. But after successful pre-trials, it was decided to find a process that should not only be economically attractive, but which could also be meaningfully integrated in the existing plant technology. The final objective was, in addition, the manufacture of a still-to-be-marketed product that resulted from the eliminated nitrogen.

Concept:
The method of air stripping followed by an "acid scrubber" was determined to be an economically cost-effective process for the special boundary conditions for the purifying plant at Göttingen. Of particular advantage here is the lime conditioning of the sludge that is carried out before drainage, which results in an increase in the pH-value in the filtrate. In addition, the heat emitted was usefully integrated in the heat circuit of the purifying plant. Another important factor in the process of awarding the contract was that a guaranteed take-up of the ammonium sulfate over a period of 10 years was required and offered. This gave Göttingen's city water treatment facility the highest possible cost safety in addition to maximum operational guarantee. Therefore, particularly when calling for tenders, attention was paid to the construction and the subsequent running of operations as mentioned above.

Technology:
The process and plant engineering is distinguished by the following points:

• The chamber filter press generates the filtrate water in single-shift operation. 
  At a rated volume flow of 17-20 m³/h, the filtrate water is stored temporarily in steel-enameled tanks.

• After the withdrawal of the medium from the storage tanks, the pH-value can be increased with caustic soda if required, By using internal sources such as the waste heat from the return water, the temperature of the filtrate water increases.

• In a stripping column, the ammonia present in the filtrate water is then driven out with circulating air.

• The concentration of ammonium is now reduced in one process step to below 
  100 mg/l. The stripping efficiency in trial runs after removal of pure water and the residual heat was more than 95 %.

• The purified air is returned back to the stripping column. A closed air circuit is thus guaranteed.

• The tower packing piling, in this case, in the stripping column and absorption column facilitate a large phase contact surface area, which favors the material exchange. Rauschert Hiflow-Rings are used as the tower packings. Their open grid structure makes them resistant to dirt. Other advantages are low weight, high loading capacity and mechanical strength. The low pressure loss saves on blower power.

Result:
The ammonium sulfate solution that results can be used as a type-approved fluid manure in agriculture or horticulture. Alternatively, the process product can be used in the leather industry, the wood-processing industry and for the smothering of furnaces and cement works. 

Owing to the reclaiming of ammonium, the primary requirement of the Kreislaufwirtschafts- und Abfallgesetz (German pollution law) is fulfilled: no waste is generated at all.