Articles - Ryan Hennessy Wastewater Microbiology

Understanding F:M Ratio

February 8, 2024

Ryan Hennessy

Wastewater Microbiologist

F:M ratio as a theory is one of the most important aspects in wastewater treatment but also one of the most poorly understood concepts. Occasionally textbook numbers are good guides, however there are many instances in which understanding the complexity of F:M ratio may help to provide further insight. As a consultant it is very […]

Thoughts on Career Development and Workplace Relationships

October 8, 2023

Ryan Hennessy

Wastewater Microbiologist

In this blog, we are going to deviate from the more technical aspects and more into what I hope are useful tools for career development and success. I have been “around the block” enough that I feel some of these thoughts may be useful to the up-and-coming generation of new wastewater professionals. This article will […]

Toxicity and Inhibition

July 13, 2023

Ryan Hennessy

Wastewater Microbiologist

Toxicity and Inhibition are two important but distinctly different concepts in biological wastewater treatment processes. While both are viewed as negative, it is important to recognize the differences in these terms. The following will start with an explanation on toxicity and go on to explain the areas of overlap as well as the distinct differences […]

Why I Dislike the Diluted Settleability Test

June 15, 2023

Ryan Hennessy

Wastewater Microbiologist

I have been to treatment plants that have had settleability issues and seen tables full of settleability tests with various dilutions of MLSS. I believe the intended objective of the diluted settleability test is to see if less biomass would correlate with improved settling; the general idea that if less biomass settles better, then wasting […]

What are the Basics that Wastewater Operators Should be Aware of Regarding Organic Acids?

June 15, 2023

Ryan Hennessy

Wastewater Microbiologist

A brief look at a table demonstrating the various bulking filamentous bacteria types commonly observed in wastewater treatment process will show that a high % of filamentous bacteria (and other bacteria that may potentially be undesirable at certain amounts) are recognized to “proliferate at elevated concentrations of low molecular weight organic acids”. This produces a […]

strong flocs with filamentous briding cropped from 1000x-phase contrast scaled

RAS Chlorination for Filamentous Bacteria Control (Essentials)

May 29, 2023

Ryan Hennessy

Wastewater Microbiologist

There are no general 1 size fits all solutions for troubleshooting biological wastewater treatment systemissues and while it is always preferred to address the root source of a problem, there are simply times inwhich this may not be feasible, or logistically practical. A common instance of these scenarios includestroubleshooting challenges with filamentous bacteria bulking. Filamentous […]

Nostocoida limicola III Organic Acid Filament Type measurement

Low DO vs. Septicity: Separate Scenarios/ Growth Causes for (often) Undesirable Microbe Types.

May 4, 2023

Ryan Hennessy

Wastewater Microbiologist

There is an interesting and very important correlation with notable differences between the common terms “Low DO” (dissolved oxygen) and septicity. Due to this relatively complex relationship, there is often confusion regarding these terms. The goal of this blog is to briefly explain these differences and how each term should be thought of. What is […]

Why the MLSS Concentration is Not Always Representative

April 6, 2023

Ryan Hennessy

Wastewater Microbiologist

It is highly common and often successful to operate activated sludge treatment systems based on maintaining a targeted MLSS (mixed liquor suspended solids) concentration, however as with just about everything in wastewater, there are notable exceptions to the rule. What makes up the MLSS? As can be seen from the chart above there are several […]

A view of a higher life form under a microscope

Should I Waste based on Higher Life Form Organisms?

April 6, 2023

Ryan Hennessy

Wastewater Microbiologist

Higher life form organisms such as stalked ciliates and rotifers may be easily viewed under brightfield microscopes. They are fascinating, motile, and easy to recognize however process control changes should not be based strictly upon higher life form organisms and their abundance. The best analogy to use is that “you are what you eat” and […]

Sludge Bulking: Microthrix

March 28, 2023

Ryan Hennessy

Wastewater Microbiologist

One of the most challenging problems commonly encountered in biological wastewater treatment processes is sludge bulking due to overabundance of Microthrix filament types. What is Microthrix? Microthrix filament types are recognized due to their Gram-positive staining characteristics and are generally 0.8 µm diameter with no visible septa (cell walls). Microthrix are recognized to grow on […]

Wastewater Microbiology Articles