Wastewater treatment has come a long way. Modern wastewater treatment is extremely effective at turning human waste into clean water, and in doing so, wastewater treatment has become a highly sophisticated and precise process. Three major innovations currently reshaping wastewater treatment are Ultraviolet Disinfection, Biological Nutrient Removal, and Biogas Production.
Disinfecting Water
Water, particularly wastewater, has the potential to host dangerous diseases. Bacteria, viruses, protozoan cysts, and parasites are all common in untreated waste. If improperly disposed of, wastewater can cause outbreaks of nasty diseases like typhoid, cholera, and dysentery. Fortunately, such diseases are uncommon in the United States thanks to disinfection methods. Disinfection allows people to swim, paddle, and play in rivers without fear of becoming sick.
Chlorine Disinfection
The most common method of disinfection is chlorination. After wastewater goes through the normal treatment process to remove debris, solids, and organic material, chlorine is added to the water to kill or deactivate pathogenic organisms. Chlorine has many advantages as a disinfectant:
- Chlorination is reliable and effective against a wide range of pathogenic organisms.
- Residual chlorine that remains in wastewater can prolong disinfection after initial treatment.
- Doses are flexible and can be easily controlled.
Unfortunately, chlorination for disinfection has many disadvantages as well:
- Chlorine is extremely toxic to aquatic life, even at low levels. Therefore, a dechlorination step is required in the wastewater treatment process to remove residual chlorine, adding to cost and complexity.
- Chlorine is hazardous to humans and highly corrosive, making the transport and storage very dangerous.
- Chlorine can react with various compounds in wastewater to create new hazardous chemicals.
Ultraviolet Disinfection
As an alternative, ultraviolet light is becoming a more common means of disinfecting wastewater. Several treatment facilities within the DuPage River watershed are already using these systems instead of chlorination. Ultraviolet, or UV light, is a high energy form of light that is invisible to people, but is able to destroy an organism’s genetic material. This renders the bacteria and viruses inert and unable to reproduce and spread disease.
There are many advantages to using a UV disinfection system over a chlorination system:
- UV disinfection is highly effective.
- UV disinfection does not require the handling, storage, and transportation of hazardous materials.
- There are no residual chemicals that are harmful to humans or aquatic life.
- Disinfection is much quicker, taking only 20-30 seconds.
- UV disinfection systems use less equipment and save space in cramped facilities.
While UV is often a better option than chlorination, there are some drawbacks to consider:
- Preventive maintenance is required on the UV lamps in contact with wastewater. Frequent cleaning is required to mitigate fouling.
- High turbidity and Total Suspended Solids can interfere with disinfection and reduce effectiveness.
- Capital upgrades to UV disinfection systems can be expensive to build although operating costs are competitive with chlorination.
- Organisms can sometimes repair or reverse genetic damage from UV light through a process called “photoreactivation.” This is very uncommon and unlikely to occur in enough organisms to cause an outbreak of disease.
There are many other facility specific considerations when deciding to switch from chlorination to UV disinfection, but UV has the potential to be safer and more effective. As the technology improves and costs come down, UV will likely become the dominant method of wastewater disinfection.
Addressing Nutrient Pollution: Biological Nutrient Removal
Excessive nutrients in our waterways, namely nitrogen and phosphorus, cause problems like algal blooms that have a cascade of effects. A large source of these nutrients in our waterways is from wastewater. Wastewater treatment plants must meet nutrient requirements in their effluent and treat for the removal of nutrients and organic material.
The most widespread treatment for phosphorus is currently chemical polishing. Essentially, chemical compounds are added to wastewater that cause the phosphorus dissolved in the water to precipitate, clump together, and fall to the bottom of the tank where it can be removed.
Another method of phosphorus removal is called Biological Phosphorus Removal (BPR) and involves using a controlled growth of bacteria in the water tanks to digest and remove the phosphorus. Enhanced Biological Phosphorus Removal (EBPR), also called Biological Nutrient Removal (BNR), uses different types of bacteria in multiple tanks to remove nitrogen and phosphorus.
Advantages of using a BNR system over chemical polishing include:
- BNR systems can achieve much greater reductions of nutrients than chemical polishing can achieve.
- BNR systems are less expensive to operate.
- BNR systems use little to no chemical additives.
There are of course disadvantages that must be considered as well:
- BNR systems are very technical and difficult to operate. They require a lot of monitoring and hands on adjustment of systems to ensure that the biological process is operating effectively.
- BNR systems must maintain a healthy ecosystem for the bacteria that do the treatment. A seasonal change or error that kills off the bacteria will take a long time to recover, with the plant unable to effectively treat waste in the interim.
- BNR systems require a lot of space and may not be feasible in a plant that has little room to expand.
As nutrient regulations become stricter in order to protect aquatic life and human health, chemical polishing will likely become cost prohibitive as more and more chemicals are needed to reach low limits. Due to the variability inherent in a biological system, many plants are finding a balance by using BNR as the primary means of nutrient removal with a chemical polishing as a backup system.
Biogas Production: Turning Waste into Energy
Wastewater treatment produces two things: clean water and sludge. While treated water is discharged into rivers after treatment, sludge, the solid material collected during the treatment process, needs a different kind of disposal. Sludge is high in nutrients and organic material, so after being treated and dewatered, it is usually applied to farm fields as fertilizer.
However, sludge also produces the potent greenhouse gas methane, which must be managed by the treatment plant. Some treatment plants, rather than essentially throwing this material away, are able to instead digest the sludge in anaerobic digesters and convert it into renewable natural gas (RNG). RNG can be collected and burned as a source of energy.
For instance, Downers Grove Sanitary District on the East Branch DuPage River uses biogas derived from their sludge and community food waste to power their facility. Treatment plants use a lot of energy to run their systems. As technologies develop that require more power, such as UV disinfection, generating power onsite from waste materials can help keep operating costs down.
Society has come a long way in how it manages its wastewater. UV disinfection, Biological Nutrient Removal, and Biogas production are just some of the new and exciting technologies that are improving wastewater management. It will be interesting to see how these innovations continue to develop to keep our rivers clean and protect public health.
