Why does your neighborhood stink?

WhatsThatSmellNow that we are talking about mystery smells around Pensacola, I feel that it would be useful to talk about one of the biggest offenders on a national scale and that is sewage.

In most cases, they are already in the ground when we buy our houses so we aren’t always aware of where all of the functioning parts are located. For the most part they work extremely well, a true wonder of modern living, but they are not perfect.

One of the problems in modern sewage is the tendency of sewage to generate gas bubbles in the pipes while it is on its way to be processed. Sewage is full of living organisms that create all sorts of smelly products including mercaptan and hydrogen sulfide.


Typical manhole

As the sewage flows through the pipes, these and other gasses accumulate in the high spots of the sewage systems and over time can form large bubbles. These bubbles have to be vented from the system or they can cause serious damage including pipe ruptures.

In order to properly vent the gas, utilities install Air Relief Valves (ARVs) at regular intervals on the pipe. In fact, most of the man holes that you see in neighborhoods contain these valves to protect the pipe system.

 ARV-OPEN ARV has vented all gas
 ARV-Bubles Gas generated by the decomposition of sewage begins to fill ARV chamber with sewer gas.
 ARV-RELEASE  When the ARV chamber is full of sewer gas, the weight of the float pulls a tiger valve at the top of the chamber that vents the sewer gas to the neighborhood.

The ARVs do not continuously vent gas. They are designed to accumulate gas and then vent the accumulated gas all at once in much the same way that a toilet flushes waste. This has a lot to do with the unpredictable nature of sewer odors. Since the accumulation rates vary with time and temperature, you never really know when the valve is going to go off.

Most ARVs are equipped with something similar to an activated charcoal filter that does a pretty good job of reducing odors depending upon the volume of gas released and the concentration of smelly components.

While the utility companies like ECUA would have us believe that these systems are perfect, they are far from it. Poor maintenance, rapid production of some of the smellier gasses or just plain damaged valves can all affect the performance of the valves and the filter medium.

Nationwide, these valves often windup being the culprit when mystery odors are detected. So the next time you are wondering, where is that smell coming from, the answer may be as close as you nearest man hole.

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