Characterisation of the physical and rheological properties of evaporation products in a thermally integrated treatment of pharmaceutical wastewaters

• Vacuum evaporation and integrated waste heat (∼60 °C) achieve 90 % volume reduction. • Distillates are near-water properties with up to 98 % COD removal. • Concentrate viscosity rise at ∼85 % volume reduction, defining operational limits. • Electrocoagulation and lime precipitation increased sulphate removal to 75 %. Pharmaceutical wastewater streams contain elevated concentrations of sulphates, nitrogen species and organic impurities, making them challenging to treat with conventional methods. The present study evaluates an integrated treatment strategy of vacuum evaporation, electrocoagulation and lime precipitation, with the emphasis on thermal performance and compatibility with low-grade industrial waste heat. A pilot-scale vacuum evaporation trial was conducted at pressures ranging from 50 to 150 mbar. It was ascertained that an optimum pressure of 50 mbar was conducive to effective coupling with on-site waste-heat sources, with temperatures around 60 °C. In the given conditions, the following outcomes were achieved: stable boiling behaviour, effective heat transfer and a volume reduction of up to 90 %. However, these outcomes were followed by a sharp increase in viscosity. The distillates demonstrated close to water-like physical properties and a maximum chemical oxygen demand reduction of 98.0 %, while the concentrates exhibited significant boiling-point elevation and rheological transitions at elevated levels of solids‘ content. Electrocoagulation has been demonstrated to remove up to 67.9 % of sulphates, and the addition of lime has been shown to increase the total removal to 75.0 %. The findings indicate that a thermally integrated, multi-stage approach can lead to substantial reductions in pollutant loads, the recovery of high-quality water and a decrease in waste volumes. This provides a promising basis for scaling to multi-effect systems, and for implementing energy-efficient, circular wastewater management in pharmaceutical production.