The wastewater industry will have to tweak septic system design and operation to deal with inevitable changes caused by climate change, experts say.
According to two experts in the decentralized wastewater industry, there is no point in arguing about climate change. It’s here. And they say it’s high time the industry prepares for a future demanding different solutions for wastewater treatment.
George Loomis is a research and extension soil scientist at the University of Rhode Island and director of the New England Onsite Wastewater Training Center. Jose Amador is a professor at the university and oversees its Laboratory of Soil Ecology and Microbiology. They have been working on what climate change will do to the onsite industry, and with Jennifer Cooper, who worked with them as a graduate student, have published scientific papers that make a start at answering these questions.
Broadly speaking, climate change means more water or less water depending on what area of the country you’re talking about, Amador says. Rising sea levels will mean less dry soil available for treatment in coastal areas because groundwater will be closer to the surface. There will be more water from above as large storms that were once infrequent become more common. Other parts of the country will be drier, making water conservation more important and making wastewater more concentrated.
There’s also temperature, he says. All microbes and biological systems react to temperature, and the warmer temperatures of climate change will affect a number of biological processes that treatment depends on.
STORM CLOUDS LOOMING
Climate scientists say you cannot tie any single event to climate change because through history we have seen extreme weather, Loomis says. For example, the storm that caused extreme flooding in Louisiana in August 2016 — with some instruments recording more than 2 feet of rain in 48 hours — may or may not have been the result of climate change. What the science says is that storms like this will become more frequent, according to Loomis.
“It’s real. It’s happening now. It has been happening for a while,” he says.
The National Weather Service reported that a storm like the one in Louisiana has a probability of 0.1 percent in any given year. To put it another way, one storm like it will occur once every 1,000 years.
“It’s going to mean the industry has to become more adaptable. They have to first realize this is an issue that needs to be on the agenda,” Loomis says. “Other industries are already doing this. Our industry is always comparing itself to the big-pipe industry, and the reality in this situation is they are already responding with plans and actions to help reduce the impact of climate change.”
Loomis says people in the onsite industry may believe what they wish about climate change, but the reality is that other people are using climate change as a competitive advantage. For example, if a community is trying to make a decision between centralized and decentralized wastewater systems and wants it to be climate-change-ready, then the onsite industry must be able to show it is also ready.
And onsite industry people need to consider whether their business can be successfully passed to children or younger relatives.
“So you want an industry that is as robust as possible because that means more people will be interested in buying your business, because they see it has a future,” Loomis says.
Research is only beginning to figure out what will happen to onsite systems as climate change progresses. For example, a scientific paper published in the journal PLOS ONE by Cooper, Loomis and Amador looked at nitrogen removal in three drainfield types: a pipe-and-stone system, a low-pressure pipe, and a shallow, narrow drainfield with geotextile fabric, which received advanced-treated effluent.
Compared to advanced drainfield systems, the traditional pipe-and-stone system removed more nitrogen under conditions simulating climate change. That’s probably because there is less oxygen lower in the soil and more carbon in septic tank effluent, and the microbes were using the carbon quickly to process nitrogen, Amador says. Because it’s cleaner, effluent from advanced systems contains less carbon to begin with, so there would be less carbon available for microbes. On the other hand, there was less phosphorus removal in all three drainfield types under climate change.
But that’s not the whole story, Loomis says. Advanced systems are likely to be more effective overall at removing nitrogen because they can target different substances in various components of the treatment train. In the soil you have to accept whatever happens. In other words, nitrogen or other substances will be treated within components of the treatment train before water reaches the soil, Amador says.
This means the industry has a great opportunity to work on new technologies that target specific contaminants, Loomis says. Those that are a problem now — nitrogen, phosphorus and bacteria — are likely to remain problems in the future.
LOOKING AT WETLANDS
Some of those technologies will involve what installers already know: pumps and switches. Others will not.
There are alternative systems that use engineered wetlands to treat effluent, Amador says. This is already common in Europe but is not widely accepted in the U.S. Yet, when the choice is between a $30,000 advanced system of pumps and switches, and a gravity-powered, nonelectrical biological system costing much less, acceptance may change — but not necessarily in all places, because wetlands do not work efficiently during winter in cold climates.
The drawback to wetlands is the area of land they require, Loomis says. Where land is at a premium, wetlands will not be the chosen solution. It’s the system with the smallest footprint that will win, he says.
“Areas that are dry now will become drier with climate change, and water will become even more valuable than it is now. Reclamation and source separation will be important there. You won’t try to get rid of the gallons. You’ll do everything possible to reuse those gallons,” Loomis says.
Areas that are wetter — because of sea level rise or increased rainfall — can expect more movement of disease-causing bacteria and viruses, Amador says. This will happen because saturated soil moves water so quickly that there is less time for pathogens to stick to soil particles. And warmer and wetter soil may allow bacteria to grow more. Viruses need living cells to reproduce, so there won’t be more of them, but they will still move faster through saturated soils.
ON THE HORIZON
If there is one topic researchers should look at next, it is what happens in soil, Amador says. Soil is the end recipient of effluent, and the quality of onsite wastewater treatment depends on what happens there. But the standard descriptions don’t work. For example, in addition to denitrification by denitrifying bacteria, in nitrogen removal there is also denitrification by nitrifying organisms, nitrous oxide produced by those nitrifying organisms, nitrogen gas produced by anaerobic ammonia oxidation, and more, he says.
“I would have to go with Jose’s response,” Loomis says. “We think we know what’s going on in the soil, but we’re not really sure. For instance, we have textbooks that say this is what takes place in the nitrification process, and there are these two microorganisms involved. But this knowledge is 30 years old, and it’s based on the only two microbes that we could grow in a laboratory culture dish. That was all we could do back then.”
“But now we have the technology. We can look at the genes. We can look at the DNA for the whole soil microbial community and say, wait, there is one gene for this and another for that, yet we have not gotten away from those obsolete explanations,” Amador says.
If we don’t do the research, we will not understand the system, Amador says. That means we cannot tweak a system to favor one outcome over another. It also means we cannot redesign or re-engineer systems to favor the microbial communities that can adapt to the stresses of climate change, Loomis says.
“It would be good if our industry at least remains open to discussion and new ideas because some of this research is showing us that nature is more dynamic than we thought,” Loomis says.