Challenge
In December 2009, a non-hazardous liquid waste treatment facility in Wisconsin was exceeding their permitted level of 0.165 ppm tin in their final wastewater effluent discharge to the Publicly Owned Treatment Works (POTW). Additionally, effluent levels for lead and copper also approached permit limits and were a concern to this customer. After failing to obtain a variance from the municipality to allow higher discharge limits and exploring different treatment technologies, the firm contacted Evoqua to evaluate their treatment process and provide recommendations.
The customer's existing treatment process consisted of conventional chemical batch treatment of non-hazardous wastewaters from metal stamping fluids. Steps in the process were skimming of free oils, coagulant addition, pH adjustment, flocculant addition and dewatering of the resultant metal sludge. After processing the liquid wastewater through their chemical precipitation system, the tin levels still averaged 0.2 – 0.3 ppm and required further reduction to allow discharge compliance.
Solution
After consultation and process review with Evoqua's technical staff, the facility sent a representative sample of the pre-treated wastewater to Evoqua's Roseville laboratory for a complete analytical characterization and treatability study. Bench-scale testing indicated that Evoqua's new, SCU™ heavy metal selective adsorptive media successfully lowered the tin concentrations to 0.008 ppm. Additionally, the lead and copper levels were also lowered to meet the customer's secondary goal of overall reduction prior to discharge.
The Evoqua full-scale treatment solution features a 20 micron cartridge filter, (1) 14" x 50" activated carbon and (2) 14" x 50" SCU media vessels aligned in a serial configuration. The cartridge filter removes fine particulates prior to the media exchange system. Due to the high organic background in the metal stamping fluid, an activated carbon vessel was specified to reduce TOC levels. Finally, the SCU adsorptive media vessels act in a worker/polisher configuration to remove the target metals – tin, copper, and lead.
When the media capacity is exhausted, Evoqua's local service technicians remove spent media/vessels from the site and replace them with fresh tanks containing new media. The vessels are transported to our company-owned RCRA permitted and licensed TDSF treatment facility for compliant treatment and recovery of metals. The system's modular design allows for easy exchange and service with minimal disruption to daily operation.
Results
Evoqua's service-based solution provided a rapid treatment response without requiring the customer to invest additional capital or time to achieve their discharge goals.
The use of Evoqua's SCU heavy metal selective adsorptive media as a final step following the site's existing treatment process, the customer was able to conserve valuable financial resources, eliminate the need for onsite handling/storage of hazardous treatment chemicals, save valuable plant space (due to the system's minimal footprint), and meet all regulatory goals established by their sewer district.