By Ryan Hennessy
Wastewater process control is becoming increasingly complex as permit limits become more stringent and BNR (biological nutrient removal) configurations are incorporated into new designs and plant upgrades. Also, there are many facilities that are operating above design loading conditions with aging equipment and infrastructure. In many smaller municipalities and industrial wastewater treatment systems, funding for plant upgrades can often be problematic.
Every wastewater treatment facility has its own unique set of challenges, but the basic principles of phase contrast microscopy do not change. A trained professional is capable of finding out what is going on in a system within several minutes, using techniques from the 3rd Edition Manual on the Causes and Control of Activated Sludge Bulking, Foaming, and Other Solids Separation Problems (Jenkins, 2004).
Sludge quality problems
In wastewater operations, the goal is to produce a good quality sludge that settles and compacts well and leaves behind a clear supernatant. Regardless of the process flow schematic, there is an area where biological treatment occurs and an area where solids (bacteria) are separated from the treated water. Also, growth pressures within the system will dictate the type of micro-organisms that will compete.
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To grow the desired types of organism, a “bug friendly” environment is needed. This involves the type of food present (such as limiting fats, oils, grease, septicity and sources of toxicity) in the influent; maintaining the desired values for pH, alkalinity, dissolved oxygen and nutrients; and, having a general control over the biological growth rates (sludge age, food to micro-organism ratio).
Ultimately, sludge quality problems are a result of the conditions present within the plant. Common problems include dispersed growth (results in turbid effluent), sludge bulking (poor settling), poor floc quality (pin floc, diffuse floc structure, etc.) and foaming in the aeration basin. The microscope can be used to diagnose problems. Then, based on this diagnosis, short-term and long-term control strategies can be determined, on an individual basis, with respect to plant design and configuration, severity of problems, and financial implications.
Microscope essentials and tips
To effectively use the microscope in wastewater, a research-grade, phase contrast microscope with 10x and 100x (oil immersion) phase contrast objectives that yield magnifications of approximately100x and 1000x, respectively, is needed (Jenkins, 2004). For photography, a microscope with a trinocular head and a digital camera is needed. It is beneficial to include photos of floc structure and individual micro-organisms within a report to add to its credibility and professionalism.
Becoming proficient at using the microscope and identifying filamentous bacteria is a learned skill that is developed over an extended period of time from hours of experience. For this reason, plant personnel often prefer to send samples out periodically to specialists that have experience with a wide variety of operations and routinely perform microscopic evaluations.
The preferred frequency of microscopic evaluations is dependent upon the changes and stability of the plant and also the influent loading characteristics. Typically, every few sludge cycles is sufficient, but more frequent evaluations may be needed for specific plants. For plants that chlorinate the return activated sludge (RAS) line to control filamentous bacteria growth, it is important to determine the health of filamentous bacteria on a daily basis. Once 70-80% of filaments show damaged cells or empty sheaths, it is recommended that chlorination be decreased or stopped (Richard, 2003).
It is useful to know what “normal” is for a facility. Previous reports can also serve as beneficial troubleshooting guides to determine which direction certain characteristics may be heading. For example, if it is normal for a plant to have a common abundance of a certain filamentous organism and this organism has now reached “very common” abundance, a process change may be desired to help detect a problem before it develops.