Most people look at wastewater treatment and sewage treatment as being the same thing. They are, but it’s not that easy. While there are similarities, sewage treatment is a part of the wastewater treatment process. It’s handled differently. To understand the differences, it helps to understand precisely what wastewater is.
Why does it matter? The overall wastewater treatment process has to clean the water of chemicals, food particles, and grit. It also has to remove human waste, which is where sewage treatment comes in.
Wastewater Contains Black Water and Gray Water
Wastewater is made up of black water and gray water. These two types of wastewater go to the same facility for treatment, but they’re different and require different steps. Start by understanding the differences between gray water and black water.
What’s black water? Every toilet flush goes into the sewer lines or the private septic system. The water from that toilet is called black water. It’s human waste, water, and toilet paper.
There may be cleaners, too. People may have bleach tabs, toilet sanitizers, and other toilet cleaning products. While it shouldn’t contain additional items like wrappers, menstrual pads, and other trash, sometimes it does.
Gray water is the other part of wastewater. Gray water comes from dishwashers, washing machines, showers, sinks, and bathtubs also goes into those sewer lines and septic systems. It’s the water from washing things, but it also contains cleaners like soap, shampoo, and detergents. There’s also grease from washing dishes by hand or in a dishwasher.
Industrial firms may have gray water from running machines. For example, a company that extrudes plastic may run water over the materials to quickly cool or set the plastic coatings. The water will have the chemicals and small particles of plastic, so it can’t simply go back into a body of water. First, it has to be cleaned.
You also have dairy treatment plants, food processors, and breweries that add to the wastewater mix. They all release wastewater that contains high levels of biological and chemical pollutants that add additional strain on wastewater treatment plants. Municipalities need to carefully plan their wastewater treatment system to handle the wastewater that’s received.
What’s in Wastewater That Has to Be Treated?
Wastewater and sewage contain a variety of components that have to be treated. Here are the different things that are treated during wastewater and sewage treatments.
- Inorganic Materials: Inorganic materials include metals and minerals. How do they end up in wastewater? They leach from pipes that carry water, and they come from cleaning products.
- Nutrients: You also have nutrients like nitrates, nitrogen, and phosphate. If you live near a lake with algae blooms, that’s the result of too many nutrients winding up in the lake water. The nutrients cause the algae to flourish, which uses up oxygen that the aquatic life relies on.
- Organic Matter: Organic matter, like food particles, are also common. You wash dishes, and small pieces of food go down the drain. They rot and can cause harm if they end up in ponds or lakes because they use up oxygen to help the organic matter decompose.
- Organisms: There are several organisms found in wastewater. If a pet owner flushes the cat’s waste in the toilet and that waste has roundworms in it, you now have roundworms in the wastewater. Bacteria and other microorganisms are also found in it.
- Pathogens: Plants must kill bacteria, parasites, and viruses to remove them from wastewater before returning to homes, businesses, or bodies of water. These pathogens include things like cholera, E. coli, and norovirus. When COVID-19 hit, wastewater treatment plants were finding that virus in wastewater, too.
How Gray Water is Handled at a Wastewater Treatment Plant
Wastewater comes into a treatment plant through sewer lines or at a septage acceptance plant. If the wastewater is being trucked in, septic trucks drive up to the septage acceptance plant and unload the materials pumped from septic systems into the facility.
Pretreatment occurs as wastewater enters the treatment plant. Here, screens catch debris and trash from the wastewater. It goes to the grit removal, which is equally important. If sand and gritty particles get into pumps and valves, it can damage that equipment and lead to costly repairs or replacements and valves.
Wastewater treatment plants may use self-contained units that take care of the screening and grit removal at the same time. The Raptor Complete Plant is ideal for the pretreatment of septage and wastewater from the sewer lines. You can add a grease trap to it to help remove extra grease before the primary treatment begins.
From the grit chamber, wastewater goes to a clarification tank to start primary treatment. The wastewater sits for several hours to allow solids to sink to the bottom of the tank. Grease floats to the top, where it’s skimmed away. Scrapers keep moving over the bottom so that the sludge is transferred to pumps and removed from the wastewater.
The wastewater starts going through the secondary treatment process. Oxygen is added to the leftover water to help stir it up and get oxygen to begin breaking down any particles of waste or organic materials that didn’t sink to the bottom. Again, the wastewater moves to a clarification tank to allow the remaining sludge to settle, get scraped to pumps, where it goes to sewage treatment.
Tertiary treatment is the third step. Chemicals are added to remove phosphorus from the remaining wastewater. Chlorine is used to help kill bacteria that remain after the other two treatment steps. Water goes through filters and may be exposed to UV rays to remove the chlorine before the water returns to bodies of water or storage tanks.
How Black Water is Handled at a Wastewater Treatment Plant
The sludge that’s removed from clarification tanks goes through sewage treatment. Anaerobic digesters break down the sludge, and carbon dioxide and methane are removed and captured during that process. That biogas can be used to provide electricity and heat.
What happens to the fecal matter that’s left behind? It varies from one area to the next. It could be dried, ground, and turned into fertilizer. Anaerobic digestion removes bacteria, so it’s safe to use. Workers move the remaining sludge to trucks where it’s sent to a landfill to become part of the soil. It could also be incinerated. If it’s burned, the methane gas can heat the wastewater treatment plant, which is a cost-effective option for many municipalities.
Careful Planning Creates a Comprehensive Wastewater Treatment Plant
When deciding on the equipment a wastewater treatment plant requires, it’s important to know how much wastewater flows each day. Some hours will have a higher flow rate than others. When people get home from work, have dinner, do dishes, and take baths and showers, the wastewater flowing into the sewer lines increases.
You need to consider where the wastewater is coming from. If you have breweries that lack their own wastewater treatment systems, you’ll have a lot of extra wastewater coming in on brewing days. It’s essential to plan for these increases. Plant managers need to be prepared for the increases.
One of the easiest ways to do this is by hiring an expert to design your wastewater treatment system. Talk to Lakeside Equipment. With close to 100 years in the business, we can help you develop a system that treats both wastewater and sewer water. We work closely with you to help you stay on budget without cutting corners and ending up with an inefficient system.