When a wastewater plant is making plans on receiving a new influent stream or removing an existing stream, it is good test for potential impact upon biological treatment units. If the change is minor, I have used rapid acute toxicity tests including a rapid heterotrophic organism respiration inhbition and Ammonia Oxidizing Bacteria (Nitrifer) screen - both of these tests take less than 4 hours to complete. But if the changes are greater or new compounds are of high concern, we can use a bench scale activated sluge unit to test specific waste streams, dilutions, treatment protocols, and best evaluate best operating practices. All the testing reduces likelihood of major problems in the actual wastewater treatment plant.
Key points for a bench scale reactor test
The lab scale activated sludge can be as complex as you want. The most common type is often called an Eckenfelder Reactor which dates back to the 1960s. It uses gravity separation in a clarifier section with recycle via a port at the bottom of the clarifier. More complex systems include a separate clarifier with pump recycle to control RAS and MCRT with greater accuracy. In our lab, we select the reactor type to match closely the system being studied. We also adjust the test to meet the study objectives and information required.
Below is an example study done at Aster Bio for determining the impact of a various waste streams on AOB (Nitrosomonas) and NOB (Nitrospira) populations. The testing found that one of the streams was responsible for problems with nitrification and required adjustments to pre-treatment. So why run the more complex, multiple day test? Earlier screening with acute toxicity nitrifier concentrate (Tox-N) did not detect the suspected chronic toxicity - which is best detected using qPCR molecular testing.
Key points for a bench scale reactor test
- Keep it simple - lab reactors are not your actual system but a close approximation. Don't ask a bench test to determine to many variables at one time
- Be ready to test various pre-treatment or dilutions
- Adding 16s MCA - total microbial census - helps to understand the changes inside the biomass that would take longer to manifest as visible problems and is more sensitive than turbidity and COD tests that are normally run on the effluent
- There is a learning curve to operating a lab scale activated sludge unit. It is good to do a few practice runs before doing even a simple evaluation.
The lab scale activated sludge can be as complex as you want. The most common type is often called an Eckenfelder Reactor which dates back to the 1960s. It uses gravity separation in a clarifier section with recycle via a port at the bottom of the clarifier. More complex systems include a separate clarifier with pump recycle to control RAS and MCRT with greater accuracy. In our lab, we select the reactor type to match closely the system being studied. We also adjust the test to meet the study objectives and information required.
Below is an example study done at Aster Bio for determining the impact of a various waste streams on AOB (Nitrosomonas) and NOB (Nitrospira) populations. The testing found that one of the streams was responsible for problems with nitrification and required adjustments to pre-treatment. So why run the more complex, multiple day test? Earlier screening with acute toxicity nitrifier concentrate (Tox-N) did not detect the suspected chronic toxicity - which is best detected using qPCR molecular testing.
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