The Four Pillers of Activated Sludge

 

The goal of this article is:

  1. To Introduce the reader to the basic framework of activated sludge troubleshooting and process control.  
  2. To provide basic guidance in using this basic framework in optimizing and troubleshooting the activated sludge

Learn Theory! Learn Theory! Learn Theory! If you know theory you can use it! If you don’t know theory you can’t use it!

Thinking in terms of complex systems is difficult. Many people, even after studying for years, do not understand basic principles. Systems thinking is often counterintuitive at many points. It takes many years to gain any degree of skill, and it still often eludes us. (Extraordinary Leadership: Thinking Systems, Making a Difference, 2009, Reberta M. Gilbert, M.D, pg 5)

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 The Georgia Rural Water Association is always available to assist any municipality that serve a population of <10,000 with process control, troubleshooting, training, lift station maintenance, smoke testing, leak detection, standard operating procedure development, asset management development, or any other compliance and operational issues that may crop up. To request their assistance, please contact them at Contact Us - Georgia Rural Water Association (grwa.org).

The next few posts will focus on Activated Sludge Concepts. After that, I will focus on some water related topics of interest.

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My career from April 2002 till June 2023 involved many hours per week of windshield time and many lonely nights in hotels. Interspersed in this time were numerous calls for assistance in troubleshooting issues with activated sludge facilities. Early on, to get a handle on the issues at the facility, I would either go to the plant to review the data, or have the staff email me the data if it was in a suitable format.  Being a ‘road warrior’ offered me plenty of time for contemplation and meditation. The following Four Piller Framework came to me one day during one of those contemplation sessions between plant visits. I was mulling over how I could more effectively troubleshoot plant compliance issues without having to visit the plant or request information to be emailed to me when I realized wastewater could be boiled down to four basic themes: Food, Population, Time and Environment.

Think of the Activated Sludge Process as a Table, and the four themes as the four legs.
 

 

 
These four foundational principles can be further broken down into subcomponents that require additional questions. But the answer to each question quickly narrows down the potential suspects.

FOOD can be subdivided into: Quality (proteins, carbohydrates, fats, ammonia, phosphorous, nutrients); Quantity (Too much, too little, just right?); Form (soluble, insoluble, etc) and Inert (sand, silt, grit, wood chips, sawdust, etc).

POPULATION can be subdivided into: Quality (floc size and shape, clarity of water between floc, settleabilty [SVC, SVI], filamentous organisms present, etc); Quantity (MLSS, MLVSS, settleabilty [SVC, SVI], relative population of Indicator Organisms, relative population of filamentous organisms); also of importance is knowing the relative growth rates of various organisms (growth rates can vary from a few minutes to +40 days) 

TIME can be subdivided into: Hydraulic Detention Time (capacity issues [Flows too high/low affecting treatment, settled solids taking up volume in reactors], Recycle/Recirculation [Flows too high/low affecting retention time or settling]); Solids Retention time (F/M Ratio, MCRT, SRT)

ENVIRONMENT can be subdivided into: Dissolved Oxygen levels, Adequate Mixing, Alkalinity, pH, Temperature, Oxidation/Reduction Principle (ORP), Toxicity, Surfactants, presence of nitrates or oxygen in “anaerobic” zones (Q - When is an anaerobic zone really an anoxic zone? A - When nitrates are present), presence of oxygen in an anoxic zone.

The beauty of reducing activated sludge down to four basic principles is the ability to ask pointed questions and quickly drill down towards a solution. These principles enabled me to take a phone call and troubleshoot a WWTP compliance issue within a relatively short time just by asking a few specific questions. The ability to troubleshoot WWTP issues on the phone was critical when traveling 40+ weeks out of the year.

But don't let the simplicity of the above overview fool you. Many of these subdivisions can be placed in two or more categories. For example, organism growth rates can be placed under the heading of population and time. F/M ratio can be placed under food, population and time. This just adds to the complexity, which is all the more reason for trying to simplify process control in the first place. 

Someone might ask, ‘What about mechanical issues? Won’t they have an impact on treatment? You don’t even address these!’.

To the above question my answer would be this. I cannot tell you how often ‘operation’ issues can be traced to mechanical issues. If one is experiencing a dissolved oxygen (DO) issue, one should inspect the mechanical equipment (Blowers: inspect the intake/outlet to see if there are obstructions, the vanes to make sure they clearances are correct, the piping to make sure there are no leaks, the motor, couplings and belts to make sure there are no issues there. Brush Aerators: inspect the motor, couplings and belts, inspect the water submergence. Impellor devises: Inspect the impellors for wear, the shear pins, belts couplings, etc). Check the recycle/recirculation pumps to make sure they are pumping the rated capacity. Etc.    

Having the ability to rapidly troubleshoot issues at your plant will enable you to focus more on the other times that take up your time: personal, maintenance, regulatory issues, etc.

The next post will begin to introduce the subcomponents of the framework introduced above and provide more information on how to use them in process control and troubleshooting. 

Feel free to contact me should you serve a population >10,000 or have any questions or issues that the GRWA is unable to assist you with. Also, if you would like to contribute an article feel free to email me at the address below. I am always looking for contributors that have an interesting perspective, topic or has an interesting case that they would like to share – especially if the solution is a direct result of applying the principles from this forum.

Dennis Brown, Wastewater Specialist and Trainer, Retired

dbrown.grwa@gmail.com

678.750.3996


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