Wasserkreislaufschließung Closing the water cycle

Duration: 01.05.2023-31.07.2026

Initial situation:

The paper industry is one of the five most energy-intensive sectors in Germany. In 2021, 14.2 million tonnes of CO2 were generated by the paper industry. Although the recycling of waste paper is more sustainable than the production of paper from primary fibres, production still requires around 2.5 kWh of energy and 15 litres of water per kg of waste paper. The exact water consumption depends on the individual paper production processes of each company.

In addition, during the recycling process, large production sites produce residual materials such as deinking and fibre sludge, which are usually thermally recycled at a charge. The Confederation of the European Paper Industry aims to be the most competitive sustainable sector for a climate-neutral Europe by 2050 and to save 80% CO2. In order to achieve the reduction in CO2 emissions and to be able to sustainably cover the energy requirements of the recycled paper mill, the residual materials from the paper industry are to be used as a raw material for biogas production using an anaerobic process. In addition to biogas, biogas production also produces fermentation products rich in nutrients and water (85-92%). According to the Fertiliser Ordinance, these fermentation products are not permitted as fertiliser in agriculture (§7 (3) 19: Paper sludge must not contain waste paper and §8 (4) 9: Waste paper and plastics must not be contained in fermentation products). Environmentally friendly, resource-conserving and economical fermentation product management with fermentation product dewatering and subsequent treatment of the liquid phase is the current challenge for improving energy efficiency while at the same time conserving water as a resource.

The project:

With membrane filtration technology, it is possible to eliminate nutrients such as nitrogen, phosphorus, etc., from the water part of fermentation products from biowaste and to recover the purified water for reuse in various applications. Water treatment with membranes is a process that removes undesirable components such as nutrients, metal ions, etc. from the (waste) water. Due to a pressure difference, the components that are smaller than the membrane pores are pressed through the membrane as "permeate". The remaining components are retained as "retentate". The permeate is the treated water for reuse and the retentate is the concentrated medium. The retentate can be concentrated to a desired level for reuse, e.g. as a fertiliser.

As the composition of each fermentation product is different, it must first be determined which pre-treatment methods (solid/liquid separation) enable long-term process stability and minimise the cleaning effort for the membrane module for the respective process. Furthermore, the operating parameters of the membrane technology such as transmembrane pressure, temperature, pH value of the wastewater, pore size of the membranes, membrane efficiency, recovery rate of the membrane flux and fouling resistance are the most important parameters that must be analysed for each fermentation product with regard to an industrial application. In addition, it must be clarified whether individual or combined membranes are required for water treatment and what water quality can be achieved. The quality is decisive for the reuse of the water.

Goals:

The aim of this project is to develop, demonstrate and evaluate a wastewater treatment system for the “zero liquid discharge” concept in the recycled paper sector. The process water is to be offered in various qualities and quantities for different purposes in the recycled paper sector. Overall, the water is to be fully recycled into the manufacturing process of recycled paper, including energy recovery from the residual materials of paper recycling. The focus includes the solid/liquid separation of the waste paper fermentation products after the anaerobic fermentation of the residual materials from the recycled paper industry and the subsequent treatment of the liquid phase.

Membrane filtration processes (ultrafiltration (UF), nanofiltration (NO), reverse osmosis (UO)) are to be investigated for wastewater treatment. The water purified in this way should be of the quality required for reuse in the paper recycling process in order to reduce fresh water requirements and the associated energy and cost expenditure. The concentrate is to be analysed for possible recycling/treatment. In this way, the envisaged research idea will contribute to a significant reduction in wastewater from the recycled paper industry.