Demo case: Pulp & paper industry
FELIX SCHOELLER
Main challenges of the demo case: At the Weißenborn site, approximately 2 million cubic meters (m³) of surface water are withdrawn annually from the river for paper production and functionalization processes, as well as for the on-site power plant (primarily for steam generation). After use, the water undergoes treatment in the company’s wastewater treatment plant before being returned to the pre-flooder. An additional 350,000 m³ of contaminated process water is generated after surface treatment. These effluents pose challenges due to their diverse contaminants, including pulp fibers, inorganic compounds (especially fillers), organic components (such as dyes, pigments, and binders), and chemical regulators. Waste heat recovery from the low-temperature and “dirty” waste stream is also a challenging aspect. The main solutions to face these challenges include recovering valuable solutes for reuse in the production process, reusing water in papermaking or as feed for the power plant (depending on quality), and reducing the load of specific inorganic compounds (fillers) and organic substances (COD) to enhance overall water reclamation in a closed loop.
Approach to overcome the challenges: The proposed treatment process for effluent streams, designed at a 1 m³/h scale, combines several steps. First, a multi-step membrane filtration process recovers suspended solids (fibers and mainly inorganic particulate matter) using microfiltration (MF) and ultrafiltration (UF), as well as colloids (pigments, binders, etc.) through UF. Additionally, dissolved organics (such as chemical regulators, dyes, and optical brighteners) are recovered using nanofiltration (NF). Next, a membrane distillation (MD) step is employed to recover dissolved inorganic salts. This process utilizes both the intrinsic heat of process water (up to 45°C) and readily available waste heat from the production site (e.g., cooling cycles of the paper machine). Heat recovery will be implemented only at the FELIX site, as its heat is low-grade compared to other sites with high-temperature streams, necessitating the use of heat pumps.
