DESIGN OF A STEAM STRIPPER / DISTILLATION PROCESS TO TREAT PHARMACEUTICAL WASTEWATER

This paper deals with the design of an innovative pharmaceutical wastewater treatment facility (WWTF), including a steam stripper / distillation process to treat pharmaceutical wastewater for removal of organic compounds prior to discharge to a Publicly Owned Treatment Works (POTW). This wastewater treatment process was constructed to meet the Pharmaceutical Effluent Guidelines for indirect dischargers as defined under 40 CFR Part 439 — Pharmaceutical Manufacturing Point Source Category.The wastestreams at this facility are generated by liquid-liquid extraction and organic synthesis operations that utilize various organic solvents and other organic compounds. EPA set effluent limits on some of these compounds that are not readily biodegradable and that may pass through the POTW. Bench scale treatability studies showed that steam stripping of these wastestreams is a feasible option for treatment since many of the regulated compounds form low boiling point azeotropes and have relatively high vapor pressures allowing them to be stripped from the wastewater to low concentrations by using the steam stripping / distillation process.Wastewater characterization, bench scale testing and modeling work showed that a 4,400 Kg/hr steam stripper column sized to handle an average COD loading of 2,100 Kg/d would be best suited for this application. The wastewater organic loading consists primarily of methanol, ethanol and four regulated compounds; acetone, methylene chloride, MIBK and toluene. The selected column is a tray-type column with thirty valve trays operating at an average L:V ratio of 4:1 and a reflux ratio of 12:1. The column is 610mm in diameter with fifteen equilibrium stages. The overall height is 18m. Twenty trays are located in the stripping section below the feed point and ten trays are located in the rectification section above the feed point. Overheads are condensed in shell and tube condensers, collected in a reflux tank and refluxed back to the rectification section of the column. Concentrated solvent product is pumped from the reflux tank to a product tank for storage and periodic transfer to a tanker-truck for off-site incineration for energy recovery. The bottoms are passed through a heat exchanger for heat recovery and then conveyed to a storage tank for final monitoring prior to discharge. The system performance is continuously monitored using an on-line gas chromatograph.The final design utilizes a number of other unit processes consisting of; flow and load equalization, pH neutralization, chemical metering, solids filtration, heat recovery, cooling water and steam systems and air emission controls. The complete system is constructed within a compact 8.5m × 24.4m reinforced concrete containment structure with metal-sided superstructure that accommodates the space limitations and aesthetic considerations of the site.