Aerial view of the Warren, Maine lagoon system. Photo courtesy of Woodard and Curran.

Lagoon Systems In Maine 

Systems In Maine

An Informational Resource for
Operators of Lagoon Systems

Mars Hill Wastewater Lagoon System - Mars Hill  Maine. Photo Courtesy of Wright-Pierce Engineers.
 Mission  |  Search  |  Acknowledgements  | Discussion Group |  Contact Us  | Links

Design & Operation
Lagoon Aeration
Tech Papers
Operation Articles
Lagoons In Maine
The Laboratory
Maine Lagoon News
Lagoon Biology

2003 Maine Wastewater Salary Survey as conducted by the Maine Wastewater Control Association

2003 Maine Wastewater Rate Survey conducted by the Maine Rural Water Association

Maine DEP Monthly
O & M Newsletter

Maine and WEF's
Operation Forum

Penobscot Watershed and Development of a TMDL 

EPA Binational Toxics

Maine Rural Water

Maine Wastewater
Operator Certification

Maine Is Technology

Maine Wastewater Control Association

Maine WasteWater Control Association

Wastewater Engineering



Tim Loftus

A number of lab-prepared solutions in the wastewater laboratory are measured in molarity (M). It is one of the ways to measure the concentration of an element, ion, or compound in solution. The potassium chloride solution used to calibrate a conductivity meter and the standard sodium chloride solution for chloride analysis are typically measured in molarity.

This unit of concentration is based on the chemical concept of a mole (abbreviated to “mol” in most references). A mol is the gram-atomic (or molecular) mass of an element (or molecule) and is a measure of the number of atoms (or molecules). For example, from the periodic chart, the gram-atomic mass of hydrogen is 1.0. One gram of hydrogen is one mol and contains 6.0 x 1023 hydrogen atoms. The gram-atomic mass of oxygen is 16. Sixteen grams of oxygen is one mol and also contains 6.0 x 1023 oxygen atoms. Even though the masses are different, one mol of each element contains the same number of atoms.

This same concept is also used to determine the mol of a compound. The gram-molecular mass of water, H2O, is 18 (two hydrogen atoms at 1 and one oxygen at 16 = 18). Eighteen grams of water is one mol and contains 6.0 x 1023 water molecules.

Using the mol as a measurement tool is especially helpful when determining how much of one compound or element reacts with another.

When the mol unit of measurement is used with compounds in solution, it is called molarity. It is defined as the gram-molecular mass of a compound per liter of solution. Take potassium chloride (KCl) for example. One mol of KCl is equal to 74.6 grams (from the periodic chart, the gram-atomic mass of potassium is 39.0 and that of chlorine is 35.5. Add together for the gram-molecular mass of 74.6). If you took 74.6 grams of KCl and diluted this to one liter with water, you would have a 1.00 M KCl solution. Double the grams to 149 and dilute to one liter and you would have a 2.00 M KCl solution.

To determine how many grams of a compound you will need for a specific molarity, use the following formula:

Grams of the compound needed = (M)(gram-molecular weight)(liters)

An example: The test method for conductivity requires that I standardize the meter with a 0.010 M KCl solution. I don’t want to make a whole liter; 250 ml would be enough. How many grams of KCl do I need to dilute to 250 mL to obtain a 0.010 M KCl solution?

Grams of the compound needed = (0.010 M)(74.6)(0.250 liters) = 0.187 grams KCl.

While you will find some of the chemical solutions in your laboratory measured in molarity (M), most of the solutions will be measured in normality (N). These will typically be your acids and bases. The concept of normality is similar to molarity, and will be covered in the next article.

Please note that this article specifically covers what is typically found in a wastewater treatment laboratory. There are exceptions to how the concentrations of solutions are measured, and this depends on the scope and application of a particular test method.

If you have any questions, suggestions, or comments, contact NEWEA Lab Practices Committee Chair Tim Loftus at (508) 949-3865 For more information on the NEWEA Laboratory Practices Committee, please contact Tim Loftus or Elizabeth Cutone, NEWEA Executive Director, 100 Tower Office Park, Woburn, MA 01801, (781) 939-0908,

All past articles are posted on our website. Go to and follow the link to the Committee Pages then to the Laboratory Practices page.





Top of Maine Wastewater Lagoon systems

  Copyright 2003 |  Home | Site Map                                          

Search  |  Contact Us  | Links