Ultrafiltration for the post-treatment of biowater from process water treatment

Since 2020, Progroup Paper PM3 has been producing corrugated base paper at its Sandersdorf-Brehna site in a closed water circuit with an internal recirculating water treatment system - ProAquaPlus - and uses BAT to keep the overall process as stable as possible. In fact, Progroup fully implements the BAT and does more than it recommends - e.g. complete extraction of the stripping tanks. At the ProAquaPlus, the highly contaminated process water is cleaned anaerobically and then decalcified and freed of solids by means of short-term aeration and flotation. The efficiency of the recirculating water treatment plant is approx. 75%.

With a view to further technological optimisation of process water treatment, an ultrafiltration technology established in open water circuits was tested for biowater treatment. The main objective of the project was to reduce the organic and inorganic load of the recycled biowater using a test plant and to determine the capacity of this technology. The constituents and the fibre content of the water to be filtered are decisive for the success, in order to be able to assess the effect, a filtrate containing fibres was temporarily added to the biowater.

The test showed that ultrafiltration technology can also be used for biowater. The system coped well with the water. The membranes had to be rinsed alkaline and acidic twice a week. In the open circuits, once a week is usual. The filterable substances in the permeate could be reduced by approx. 75%. The COD content and the content of organic acids could be reduced by 20-30%. The experiment was less successful in the area of inorganic pollution, the conductivity (sum parameter for the salts) remained unchanged, only the sulphate concentration could be reduced by 5-10%. The yield from the inlet was > 70 %, with a capacity of approx. 80-100 litres/h/m² membrane.

From a technological point of view, ultrafiltration is suitable for the post-treatment of the biowater in a partial flow. The point in the process at which the purified permeate can be used must be considered on an individual commercial basis.