With a background in innovation and improvement, Kinergetics is a company familiar with many areas of development, and we recently found ourselves with the chance to expand to a new field: Wastewater reclamation and repurposing. As water scarcities become more frequent and cities tighten treatment requirements, fines increase for polluted water. In residential settings, this isn’t always an issue, but for industrial settings the process becomes a lot more complicated. Industrial wastewater is often high in organics, salts, and other pollutants that require multi-step treatment systems.
In this case, we were asked to treat textile wastewater for process reuse. The reclaimed water needed all color and textile dyes removed, and to meet city water standards for pH and mineral content. To start the project, raw wastewater quality testing provided some basic information: high levels of TSS, BOD, and heavy metals/hardness. Visibly, the water was dense, dark brown and oily, with an odor that hit you in the face from across the room. In essence, the opposite of potable water.
While larger companies have the funds and equipment to select filtration systems by thoroughly characterizing raw wastewater quality, we’re not a big company. So, we had to get creative.
With the goal of running batch tests to confirm that these quality results could be met through filtration, we had to choose the most appropriate membrane separation steps. Nanofiltration was selected as the final filtration step as it would filter out about 20% of the monovalent ions and essentially not affect pH. However, due to the Total Suspended Solids (TSS) and Biological Oxygen Demand (BOD) of the raw wastewater, pretreatment using a microfilter would be necessary to protect the nanofilter.
The percent reduction of the tested contaminates is shown in the table below. For reference, polluted water usually has a BOD ~5, and TSS involves any suspended solid above 2um. Since the two are intertwined, finding a filtration system that would reduce TSS would likely bring down the BOD as well.
The microfilter adequately pre-treated the water for the nanofilter by removing a significant percentage of the TSS. The nanofilter was able to remove all dyes, and also kept minerals in the permeate, stabilizing the pH at ~7.9.
| TSS | BOD | Hardness | |
| Post-Microfilter | ⬇99% | ⬇7.5% | N/A |
| Post-Nanofilter | No Detection | ⬇84% | ⬇88% |
However, BOD wasn’t completely removed from the nanofilter permeate. Aside from the BOD, the potable water standards were met by the membrane system. Depending on the intended use of the repurposed wastewater, an elevated BOD may or may not be a problem. The next steps will be to perform continuous testing to assess the quality and performance of the membranes over time.
