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Case Study- Evaluating Inhibition in a Refinery

A petrochemical refinery in Alabama wanted to determine if its activated sludge wastewater treatment system was being affected by a new waste stream (X) that was recently added to the system. This new waste stream was only being added to one of two parallel activated sludge reactors; this reactor began experiencing a loss of treatment efficiency soon after addition of X began.

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EBS designed a series of experiments using Surcis BM-Advance Respirometers to simulate the wastewater treatment system in question. Surcis BM Respirometers are open, batch type systems that measure dissolved oxygen and pH in the reaction chamber while the test solution is being thoroughly aerated and mixed to simulate an activated sludge reactor. Because the Surcis is open, the user can remove or add material while the test is running without interrupting data collection as would occur in a typical closed system. This can allow the user to test many other parameters mid-test.

In these experiments we varied the concentration of the waste stream in question, X, by adding it to a sample of the WWTP influent as it was added to return activated sludge (RAS) at a ratio simulating that which is normally found in the system. RAS from the second activated sludge reactor was used because it was acclimated to influent from the wastewater system in question but had not been receiving the X waste stream. This was very important as it allowed us to see the acute effects of the X waste stream from the beginning and to analyze its accumulation in the biomass.

sour-top2The acute inhibition caused by this waste stream can be seen easily in the SOUR graph above that shows a decrease in oxygen consumption as the concentration of X increases. This is a classic sign of inhibition. Experiments on chronic inhibition were also conducted by simulating the release of effluent and addition of influent to the Surcis Respirometer daily. This data, shown on the graph to the left, reveals that the biomass had a much slower response to influent addition as well as decreased respiration in general. These chronic tests also allowed us to sample biomass for advanced chemical analysis by GC/MS and HPLC that showed an increase in inhibitory chemicals in the biomass. The ability of the Surcis Respirometer to simulate an activated sludge treatment system is a key tool that allows EBS to study and optimize many parameters of a wastewater treatment system in order to help our clients manage risks and increase efficiency.