Automated Testing Apparatus for Ceramic Membrane Filtration of High-Strength Industrial Wastewater

Abstract

A common problem in laboratory-scale membrane research is that the testing methods in the laboratory are often quite different than industrial applications due to the limitations of manual experimental setups. Here, an automated membrane filtration apparatus was built in the lab to solve this problem by allowing long-term filtration, frequent backwash and clean-in-place (CIP), and high-accuracy operation. The filtration system achieves different cleaning strategies for both theoretical research and practical water and wastewater scale-up experiments. The embedded control algorithms achieve operational accuracy in terms of maintaining flux or transmembrane pressure (TMP) at their desired set points. A flux-step function enables operators to measure critical flux automatically. The filtration system handles a variety of microfiltration and ultrafiltration membranes in crossflow or dead-end mode with backwash integration, CIP capability, and aeration scouring. Synthetic and raw rendering wastewater were applied to test the apparatus in the lab and in the field, respectively. The control algorithms successfully dampened oscillations using custom calibration curves. Three backwash-CIP strategies were tested with both wastewater types. The first was time-triggered backwash and cycle number–triggered CIP, which resulted in stable and reliable operation but required close operator control and thus was not fully automated. The second strategy was time-triggered backwash with TMP-triggered CIP, which responded quickly to water quality fluctuations and achieved full automation, but the TMP target had to be carefully set to enhance the efficiency of CIP. The third strategy was target–TMP backwash with duration-triggered CIP, which can achieve the most advanced and flexible filtration system, though setting up this level of automation complexity in the field was challenging. Both backwash and CIP frequencies responded to real-time performance automatically. Ultimately, the automated lab-scale filtration apparatus operated similarly to full-scale systems, which should help fill the gap between laboratory research and scale-up of industrial applications. Laboratory membrane filtration research is usually different than industrial applications because lab workers are limited in their ability to perform all the steps that are done at full scale. An automated filtration system can solve the problem by performing continuous monitoring and control without user intervention. This paper provides detailed information about building and operating an automated filtration apparatus. The apparatus can perform experiments in the lab or the field where water quality fluctuates. All the important steps are included automatically: filtration, backwash, and CIP. This article discusses how to adjust the timing and the triggering of each step for optimal performance. Other functions, like an algorithm to easily determine critical flux, are also described. This should allow other researchers to build similar systems, thus making more laboratory work directly relevant to full-scale applications.