Wastewater Treatment Plants and Sewage for Urban Communities

We left off on our last article after talking about the need for septic tanks in rural areas with a cliff hanger on the need for waste treatment facilities and how they operate. Most of the wastewater is collected by coming together by gravity and meeting in the sewer below the middle of the street. People’s drains from their homes flow collectively together towards a wastewater treatment facility. There will be manhole covers that run vertically into the horizontal pipe for maintenance that may need to be done if the situation arises. Sewer mains start with small pipes until they run into progressively larger ones arriving at the waste facility. Many times, these pipes will follow the trail of other water systems that flow naturally downhill to arrive at the plant. For locations where there cannot be purely gravity grinder pumps and lift stations are used to bring waste uphill.

When wastewater finally makes it to the facility it needs to go through several processes to be filtered. Plants will have between 1 and 3 stages of filtration based on their complexity. Just like a septic tank the initial treatment lets materials settle to the top, bottom, and leave water in the middle. Landfills or incinerators do the work of removing solids by burning them or disposing of them. The first part has a screen with pools that sit and allow for different density materials to fall to their correct locations. Some plants will only have this step and remove half the solids and then chlorinate the water before discharging the water. Facilities with secondary treatment allow bacteria to then eat up organic materials and nutrients that may be remaining in large aerated tanks. 90 percent of materials are generally eliminated with 2 stage facilities. The third stage can be used at certain wastewater treatment plants call the tertiary treatment that applies chemicals in the removal of nitrogen and phosphorus from the water. Chlorine as usual is applied to eliminate anything that may be left in the water after this point.

Finally, with any good wastewater treatment plant examining the effectiveness of the plant effectively is necessary. pH measures the acidity of the water that leaves a plant. pH levels should be like the water where it is being released to match the corresponding environment. BOD or bio-chemical oxygen demand is a measure of the oxygen necessary to correctly process the rest of the material in the water. BOD will hopefully be at a zero level.

Dissolved oxygen to the opposite of BOD should be as high as possible. This will be healthy for marine life it comes into contact with. Suspended solids should be at a zero amount. Nutrients remaining in the water is calculated by the measure of total phosphorus and nitrogen. Chlorine levels should be at an absolute minimum to protect the environment and should be filtered out after they have completed their use. Lastly, the coliform bacteria count is accounted for. Hopefully, this number is nothing. There may be birds that produce fecal matter that will get this amount off. “How Sewer and Septic Systems Work” by Marshall Brian has great resources on much of these plants and how they work and much more.

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