No doubt you’ve heard the phrase treatment train – an industry term for the wastewater collection, treatment, and dispersal process. Well, meet the reuse ladder. The reuse ladder describes how much cleaning will need to be done to wastewater before it can be reused. And it all starts with how.
“How will it be used?” asks Garry-Lee Espinosa, senior systems engineer at Orenco Systems. “The need to treat wastewater you plan on reusing depends on what its reuse will be and its risk of human contact.”
Each rung of the reuse ladder represents a different treatment level, with the lowest rungs requiring the least treatment because of their limited exposure to humans. “The higher you climb, the more treatment you’ll need,” Espinosa says.
The Bottom Rung
On the bottom rung, there’s treated domestic-strength wastewater that’s used for another purpose before it goes back into the water cycle. “A good example of this is groundwater recharge by way of drainfields,” Espinosa says.
Drainfields are extremely common in areas where municipal sewer systems aren’t available. They’re the most widely used subsurface wastewater disposal components in conventional septic systems.
“It’s the typical septic tank to a drainfield setup where the septic tank retains the solids for anaerobic digestion,” he says. “The effluent is conveyed either by gravity or pump to a drainfield. Because this waste is contained from where it exits the dwelling to the drainfield, there’s little to no potential for human contact, except for possibly a maintenance situation.”
Subsurface irrigation is a similar reuse setup, Espinosa says.
“Its purpose is specifically for irrigation, but the potential for human contact is pretty much low to none,” he says. “It is still contained and discharged underground, so this would be one of those applications on the lower rung of that ladder. You would want to remove some of that particulate matter before it goes to drip irrigation and causes operational issues.”
Moving Up the Ladder
The next rung up the ladder is non-potable reuse, he says. Non-potable water is reclaimed water that isn’t suitable for drinking but can be used in a variety of other non-drinking-water applications, like cooling towers, dust control, and irrigation.
“Many golf courses use non-potable reclaimed water for their irrigation,” Espinosa says.
Surface irrigation and dust control have more potential for human contact, so their use requires more treatment than buried drip lines do.
“That increased risk can be mitigated by adding highly understood, proven stages of treatment to prevent adverse health implications,” Espinosa says. “Redundancy may need to be added to the critical processes along with increased monitoring and system performance compared to the lower rungs.”
Then there’s stormwater, he adds, “the surface runoff resulting from rainfall or snowmelt. People are looking to find ways to recapture rainwater and reuse it, but there are states where it is illegal to harvest rainwater.”
Because of the low occurrence of human contact, these types of repurposed water require relatively simple technology to clean, Espinosa says.
“Reuse options on the lower rungs probably won’t require complex technologies like disinfection because the potential for human contact is low,” he says. “Whereas as you go higher up the ladder, human contact is increased. Then you have the need for some advanced treatment, coupled with disinfection and increased monitoring.”
The Higher Rungs
We start reaching the higher rungs when we talk about using recycled water to flush toilets. In this scenario, rather than flush with fresh water, toilets flush with treated effluent. The practice is highly regulated (before doing anything with effluent, check your local laws and ordinances), but it’s gaining interest – particularly in drought-stricken areas, Espinosa says.
“This is starting to become a more popular idea, especially in areas where water scarcity is an issue,” he says. “Energy can really be saved because you’re applying recycled water close to its point of generation.”
The higher up the reuse ladder, the more advanced the treatment will need to be – and that brings with it an increased cost per gallon.
“Reusing wastewater is always going to require advanced treatments, some disinfection, and maybe some additional complex processes,” he says. “When you look at that, we’re adding to the overall treatment process, and with that comes a higher cost per treated gallon.”
The highest rung of all, of course, is reused water that’s clean enough to wash with, cook with, and drink. “Using recycled water for potable water is the crown jewel of water reuse,” Espinosa says.
The technology is there, Espinosa says, and it’s been around for decades. “When you think about it, the astronauts have to drink their recycled urine on the space station.”
But the general public isn’t quite ready for it.
“Until the public can overcome the thought that they’re drinking recycled wastewater, it will be a tough battle to overcome,” Espinosa says. “People still object to the idea of using treated wastewater despite the fact that all water is ultimately recycled on a large scale in the natural environment.”
Hopefully, that stigma will dissipate, because clean water is a finite resource.
“As water continues to become the world’s most precious resource, we’re going to overcome some of those barriers that prevent us from framing water reuse on a much larger scale,” he says. “Human ingenuity and determination motivated by increasing stress on the water supply and water quality will prevail over these challenges.”
Learn more about wastewater reuse by listening to the full podcast “Resource Conservation: Reusing Wastewater” on Make It Clear at Orenco.com/resources/podcasts or on your favorite podcast platform.