Wastewater - What is it?
Wastewater is water that has been used and must be treated before it can be released into another body. This process will ensure that it doesn't pollute other water sources, as there are many sources of wastewater. All the water you flush down your drain or down your toilet is an example of wastewater.
Along with other pollutants, rainwater and runoff that goes down the street gutters, eventually ending up at a tertiary wastewater treatment plant. You can also get wastewater from industrial and agricultural sources. There are a few tertiary wastewater treatment processes that are more difficult than others. For example, industrial wastewater can prove very difficult to treat.
However, domestic wastewater is much easier to put through the tertiary wastewater treatment process due to the increased amount of pharmaceuticals and personal hygiene products found in domestic wastewater.
Who is Responsible for Ensuring that Tertiary Wastewater Treatment is Done Properly?
The federal government has delegated tertiary wastewater treatment responsibility to the individual cities and states themselves, much like drinking water provisions. Many state level governments have laws regarding tertiary wastewater treatment standards. Operators of wastewater treatment plants must apply for permits or licenses from said governments.
These permits can also be required to limit or add treatments to effluent discharges. Municipalities are generally assisted by the local governments to fund infrastructure construction and maintenance.
The tertiary wastewater treatment process is overseen by municipal governments, who can also pass additional bylaws, and because of this, have created programs to eliminate harmful substances from the tertiary wastewater treatment process. This requires all commercial, industrial, and institutional facilities to limit the number of pollutants allowed to enter the sewers.
What Can Cities Do to Discharge Wastewater Safely?
There are three levels of wastewater treatment: primary, secondary, and tertiary wastewater treatment. Many municipal wastewater treatment facilities employ primary and secondary levels of treatment. Some also use tertiary wastewater treatment.
Screens and settling tanks are used to remove most solids. This is a crucial step because solids account for approximately 35% of all pollutants that must be eliminated. Screens usually have very small openings, which is effective in collecting sticks, garbage, and other large items from the wastewater. This material is removed from the wastewater and disposed of at the landfill.
The wastewater is then placed in clarifiers or settling tanks. It sits there for several hours to allow the sludge and scum to settle. The scum is then removed from the top and the remaining wastewater is sent to the secondary treatment stage. Primary wastewater treatment typically removes approximately 50 percent of the biological oxygen demand.
These are substances that take up oxygen in water. It also removes around 90 to 95 percent of suspended solids and as much as 55 percent of fecal matter. Although primary treatment can remove a lot of hazardous substances from wastewater, it does not guarantee that all pollutants are gone.
Secondary treatment of wastewater involves bacteria to break down the remaining pollutants. This is done by forcing the wastewater to be mixed with bacteria and oxygen. The oxygen aids the bacteria in digesting the pollutants more quickly. The water is then transferred to settling tanks, where the sludge settles again. This leaves the water free from pollutants in the range of 90 to 95 percent.
To remove more pollutants, some treatment plants add a sand filter. The water is then treated with chlorine, ozone, or ultraviolet light and finally discharged. The wastewater is treated separately from the sludge and scum from the settling tanks.
Anaerobic bacteria, which does not require oxygen, feeds off the sludge for between 10 and 20 days at 38 degrees Celsius. This reduces the odor of the sludge and the organic matter. It also creates highly combustible gases of methane, carbon dioxide, that can be used to heat the plant.
The centrifuge is a spinning machine that causes the liquid and solid to separate. The liquid can be combined with the wastewater to make the liquid, and the solid can be used as fertilizer for the fields.
Tertiary wastewater treatment (or advanced wastewater treatment) removes dissolved substances such as color, metals, and organic chemicals, and nutrients like nitrogen and phosphorus. Tertiary wastewater treatment can be performed using a variety of biological, chemical, and physical treatment methods.
Treatment plants treat wastewater by first undergoing the primary and secondary treatment. The bioreactors are used for the tertiary wastewater treatment and uses bacteria to break down contaminants in water in different environments in multiple tanks. Each tank has its own unique environment, and each one contains different levels of oxygen.
The water passes through the tanks and the phosphorus and ammonia are removed. Other bacterial processes cannot do this. The water is left in the bioreactors for approximately nine hours before it enters the secondary clarifier. This is where bacteria-laden sludge settles at the bottom of the tank.
How Do Small Communities Manage Wastewater to Make it Safe for Consumption?
Small communities may have one or more wastewater treatment systems. These systems can be simple collection systems that discharge the effluent directly to the surface waters, or municipal holding tanks that are emptied every year.
These facilities typically treat and disperse waste as close to the source as possible, minimizing maintenance costs and operational costs. This makes it less likely that the waste will contaminate drinking waters sources. Some communities keep the waste in ground-based storage areas while others discharge the waste directly into the water supply.
The ground-based storage areas then hold the waste until it is released to soil or water. These holding tanks are shallow, which allows the solid waste to settle to its bottom for primary treatment. It takes between 6 and 20 days. However, the holding tanks cannot remove all the contaminants that can cause problems for ground or surface water.
Small communities often empty their holding tanks roughly once a year. Many rural communities use the land around them to dispose of their wastewater. If the soil is sufficient and there are no nearby water sources, bacteria in soil can remove or break down contaminants in wastewater.
This can be an effective way to treat wastewater because of the availability land in many rural areas. There are however other communities that dump waste in a manner that could threaten the water source, such as a river, lakes, or groundwater sources. Combining inefficient drinking water treatment with inadequate tertiary wastewater treatment can lead to serious contamination issues for many rural communities.
It is often difficult for rural communities to set up and maintain wastewater treatment facilities. While many communities still have insufficient methods for treating wastewater, some communities are pioneering innovative treatment methods and water conservation measures.
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