IFM was recently asked by a long-time consumer products manufacturing client for help in reducing the Biological Oxygen Demand (BOD) from a waste stream at one of their facilities. The facility discharges to a Public Operated Treatment Works (POTW) with a BOD limit of 250 mg/L. On average, the facility’s waste stream had a BOD concentration between 750-1,250 mg/L. The current treatment consisted of plate and frame filtration for sludge removal.
There are several methods for reducing BOD in waste streams. Feed water characteristics determine which method is most suitable and yield the best results. Some methods include biological, advanced oxidation, chemical precipitation followed by Dissolved Air Flotation, or Reverse Osmosis (RO). Each method has specific pros and cons that need to be weighed prior to deciding which is the correct application. The client and IFM selected Reverse Osmosis as the treatment method for the trial. Reverse Osmosis has several advantages which make it an attractive option for BOD removal. Typically, an RO system requires little operator interaction when compared to other methods, while still delivering consistent results. In many cases, the permeate stream produced by the RO system can be reused in other processes such as cooling tower makeup water.
The goal for this project was to achieve the highest possible recovery, while also meeting the required discharge limitations for BOD. The trial conducted by IFM involved an EQ tank, Process feed tank, 600 PSI RO system, and RO Permeate tank. Raw wastewater was pumped from the EQ tank to the Process tank to maintain a set volume. Water was then pumped to the RO system where it was repressurized to feed the membranes. After flowing though the membranes, the concentrate stream was recycled back to the process tank, while the permeate stream was collected in a separate tank. Operating in this fashion allowed the system to achieve the desired recovery over time without compromising the proper operating parameters of the RO system.
The study included two samples taken per run from raw, permeate and concentrated stream water and then analyzed for TSS, COD and pH levels at IFM McClure’s in-house lab. Each trial performed showed successful results for all three parameters, exceeded the set goals. The trial also consistently achieved water recoveries up to 95% while maintaining BOD concentrations below the 250 mg/L requirement. Based on these results, it was determined that with proper operating parameters and cleaning procedures, RO is a viable option for long-term BOD reduction for this facility.