Rules of Thumb (ROT)

Actual vs. Wahlberg-Predicted RAS TSS

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July 16, 2020

This post contains two sections with Section 1 covering Wastewater Solids production and Section 2 describing Influent Wastewater Characteristics.

Section 1: Wastewater Solids

It can be helpful to quickly estimate solids production in wastewater. Certainly, each wastewater treatment plant and its collection system, with variable ratios...

July 16, 2020

A comment was made to me recently that water does not weigh 8.34 pounds per gallon (3.78 kilograms per gallon) and that the unit of 8.34 was the result of a completely unrelated (to the weight of water) derivation. Actually, I think I understood the confusion so I thought I would go to an excellent source and simply quote (almost verb...

May 25, 2020


Hydrogen peroxide can be used to increase the dissolved oxygen (DO) concentration in an aerobic bioreactor, often referred to as “DO supplementation.” Using peroxide is rarely a first choice because chemically increasing DO is more expensive than using a mechanical method (diffused aeration, mechanical mixing, etc.). But i...

May 10, 2020

The organic strength of wastewater is measured in three ways: 1) as 5-day biochemical oxygen demand (BOD5), 2) chemical oxygen demand (COD), and/or 3) total organic carbon. Typically, municipal wastewater treatment plants will use BOD5 as a measure of the organic concentration into, and through, the wastewater plant. Industrial wastew...

May 10, 2020

Some Simple Guides

This page provides some tips and insights I've come across. A search on Google for “Rule of Thumb” leads to the following definition:

“A broadly accurate guide or principle, based on experience or practice rather than theory.”

Best Wastewater Treatment Option Based on Organic Concentration

Here is a favorite, very handy...

October 2, 2019


Many wastewater plants suffer capacity loss due to inflow and infiltration. For the majority of municipal treatment plants there is likely to be a seasonal impact resulting from rain events, snowmelt, spring thaw, etc. But there are also wastewater plants located next to or near the ocean that suffer from infiltration ever...

September 29, 2019

GSA, MCRT, SRT, and Sludge Age Defined

I think there is confusion, sometimes, in how operators (which includes me) define the terms mean cell residence time (MCRT), solids retention time (SRT), sludge age, and, though seldom used these days (was it ever used?), Gould sludge age (GSA). In this post I want to have a detailed discuss...

September 10, 2019


In this post I'm going to discuss how you can estimate the solids concentration in the return activated sludge (RAS) using the treatment plant influent flow rate, the RAS flow rate, and the mixed liquor suspended solids (MLSS) concentration. This approach is new for me, having read about it in a great, new textbook from Er...

Bits and Pieces of Information

When I come across information related to water and wastewater topics, information that I'm not yet prepared to comment on in detail, I post it here. Some of this information I post because I know I will need to come back to it when I'm at a wastewater plant doing work. My hope is that the...

July 30, 2019

Recommended Wastewater Treatment Textbooks

I get asked now and then what the best books are for learning more about wastewater treatment. There are many, many excellent technical references available but here I want to highlight just those that I find myself coming back to most often. My work brings me into both industrial and municipa...

February 11, 2019

The following is quoted from W. Wesley Eckenfelder, Jr. in his excellent textbook “Industrial Water Pollution Control”, Third Edition, 2000.

Waste Characteristics—Estimating the Organic Content

Although the interpretation of most of the waste characteristics is straightforward and definitive, special consideration must be given to the o...

January 15, 2019

The Math You Need, When You Need It

Mean Cell Residence Time (MCRT)

The MCRT is also referred to as sludge age or solids retention time (SRT).

This is the "complete" or full version of the MCRT equation that includes the mass of solids in the secondary clarifiers.

This form of the MCRT equation does not include the mass of solids in the s...

January 12, 2019

A lot of my work is with high-strength industrial wastewater. Issues that arise with any given industrial waste stream may consist of, but are not limited to, the following:

1. High chemical oxygen demand (COD) that exceeds the treatment capacity of the onsite wastewater treatment system (activated sludge or biological treatment unit).


January 2, 2019

Detailed Review of Bioaugmentation

Bioaugmentation is the addition of a specially prepared bacterial culture to a bioreactor (aeration tank, oxidation ditch, etc.). The goal of bioaugmentation includes objectives such as: 1) increasing the density of more desirable bacteria, 2) achieving a specific operational goal such as degrading co...

November 18, 2017

With links to (valuable and informative!?!) portable document format (PDF) files scattered all over this website I thought it might be helpful to consolidate those documents in one place. Therefore, what you will find here will be links to the documents referenced in the blog pages. You won't find all of the d...

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