Sewage Treatment Plant

How Your Sewage System Works

Infrastructure, Tutorials and Tips

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After outlining the Storm Water system’s configuration and function, it is time to explain the pipes that are often adjacent to storm water lines.  Sewage refers to waste water and excrement, any water that has been flushed from showers, sinks, toilets, laundry and commercial waste.  Commercial waste is generated by industrial businesses and is often referred to as trade waste.  Trade waste often contains more contaminates than residential waste, like chemicals, metals, fats and detergents.  These additional contaminants force businesses to obtain permits for their sewage production, so cities can monitor and plan treatment processes.

It is estimated that when we take into account industrial uses, the United States create 375 gallons of waste per person per day.  This is a lot of water to be managed!  The water enters a network of pipes underground, located beneath roads and lawns.  There are access points along the way through manhole covers for the purpose of inspection, inspections performed by various Deep Trekker remotely operated vehicles.  It is even more important that these pipes are maintained because of the nature of the water.  If sewage were to leak from these pipes, it would most likely seep into the water table, contaminating drinking water sources far more severely than storm water leaks would.

These pipes then distribute the waste water to larger pipes and tunnels, often referred to as trunk sewers.  These are managed by the treatment facility.  The tunnels are on a slight downward slope in most cases to allow gravity to pull the water toward the facilities.  Often along the way are pumping stations, that move water at thousands of gallons a minute toward treatment facilities on the surface or through more pipes to another pumping station.

Once at the treatment facility, there are a series of stages the sewage goes through before it is recycled back into the water network.  There are 3 Stages of Treatment:  Primary, Secondary and Tertiary.  Within these stages are a few steps before the sewage moves on to the next.  The goals of treatment is to remove the following impurities:

Suspended Solids

These are physical particles that can clog rivers or channels as they settle.  The accumulation of these does the most damage because they limit pipe capacity, causing flooding of waste water and pipe back up (the inability to flush your water into the system).

Biodegradable Organics

Otherwise referred to as BOD, these serve as food for microorganisms in the receiving body.  The microorganisms combine with oxygen in the water and then multiply.  If these microorganisms multiply too quickly, they consume too much oxygen and leave the water body with no oxygen for fish.  These are referred to as “dead zones.”

Pathogenic Bacteria

This is disease causing organisms that is most important to remove if the recycled water will be in close contact with humans or is intended for drinking purposes.

Nutrients

This refers to compounds such as nitrates and phosphates that feed organisms such as algae.  Algae in large quantities causes the same issues as BOD, by consuming too much oxygen.  The problems with BOD like algae are not just during the incoming process, if the water treatment does not remove the BOD and the nutrients that come with them, the recycled water would then also damage the outbound’s water system as well.

Here are the ways that treatment facilities remove these impurities:

Stage 1:  Primary Treatment

The goal of this stage is to remove gross, suspended and floating solids from raw sewage.  This is often referred to as mechanical treatment, although chemicals are often used to speed the sedimentation process.  The raw sewage is screened to trap solid objects and is aerated, using gravity and motion to “push” the solids to the bottom.  The force creates oxygen and allows for the sedimentation process to occur.

Before and during the process, the lagoons that contain the sewage are covered and suppress the odor.  Along with suppression of the odors, the methane gas is collected.  This methane gas is used to power the plant’s aerators.

Stage 2:  Secondary Treatment

This is also referred to as biological treatment.  The goal of this level of treatment is to remove the dissolved organic matter that was not removed by aeration or screening.  Microbes that are intentionally “farmed” for the treatment plant consume the targeted organic matter as food and convert it to carbon dioxide, water and energy.

Secondary Sedimentation also takes place at this stage with additional settling tanks that collect up to 85% of the suspended solids and BOD.

Stage 3:  Tertiary Treatment

This is the final stage of treatment, with a goal of removing over 99% of all impurities from sewage.  This stage only exists in well developed countries where there is the money for the technology, the technical expertise and a steady source of energy.  There is a combination of ultraviolet radiation treatment, chlorine disinfection and more microbe infusion that are focused on removing remaining nutrients and bacteria.

The most important factor of a water treatment facility is consistency; if water is not being treated properly and is discharged back into our environment, there are dire consequences for our health and the environment.

The first step to consistency is maintaining the structures that contain the water to ensure no seepage or break in the system.  

Routine inspection is the most cost effective way to maintain a structure and using Deep Trekker ROVs to inspect these systems is the most affordable solution for routine inspection.  

Contact us for more information about how we can help maintain your water treatment facilities.

 

 

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