James D. Englehardt sees no reason why southeastern Florida needs to draw a half billion gallons of water from the Everglades every day and then discharge treated wastewater into the ocean and saltwater aquifers. That water could easily be reused, he says, because wastewater coming out of south Florida treatment plants already meets 87 of the 93 numeric federal standards for drinking water. As a professor of environmental engineering at the University of Miami, Englehardt was in a position to make his thought a reality. With support from the National Science Foundation and the cooperation of the university and regulators, he led a project to create a net-zero dormitory — a building that does not import or export a significant amount of water.

Pumper: How did the project start?

Englehardt: Originally, we proposed retrofitting a 20-bed residence hall unit to create a net-zero-water building. The project was approved, but the estimate for equipment installation by the university was more than $1 million, so we negotiated to retrofit a four-bedroom residence hall apartment, which in any case better represents a typical single-family dwelling.

Before writing the proposal, I presented the plan to the regulators who would have to approve it. I explained that in order to study the complex chemistry and microbiology of the recycled water, this basic research had to be conducted at an occupied apartment, though the students would be supplied with city water for drinking. I was expecting resistance, but instead found a high level of support.

Pumper: How much did the project cost?

Englehardt: Even after downsizing, the cost of installation was still about $500,000 because we had to open walls and floors to install additional piping, and we excavated to put treatment equipment in the courtyard. Research expenses, including treatment equipment, study of psychological aspects and initial development of real-time water-quality monitoring technology, totaled $2 million.

Pumper: What equipment did you use, and how does the system operate?

Englehardt: Wastewater flowed first to a septic tank that settled solids and provided primary treatment. Liquid then flowed to a membrane bioreactor from Bio-Microbics. Next in the process was a metal-mediated aeration reactor that we developed and constructed. It used a small electrical current to push aluminum into the water from electrodes in the presence of aeration. This precipitated several minerals, including phosphate and coagulated impurities. The water was flocculated and passed through an ultrafiltration membrane operating at less than 5 psi vacuum. We then injected hydrogen peroxide and passed the water through a UV light reactor to mineralize residual organics and kill remaining pathogens. Spartan Environmental Technologies provided that equipment. Finally, we introduced a small amount of chlorine to protect water quality in the storage tank. The system treated an average of 260 gpd over a two-year period.

Pumper: How is the water quality coming out of the system?

Englehardt: The effluent complied with all 115 Florida drinking water standards. In collaboration with Florida International University, we also scanned for 1,006 chemicals. All but five were either not detected or were removed more than 90 percent. Even though it was beyond the scope of the project, we also sent water samples to the (U.S.) Environmental Protection Agency to be analyzed for viruses, and no viable pathogens were found in the treated water in those initial tests.

The total dissolved solids in the treated water were approximately 500 mg/L after 1 1/2 years of operation. That’s a secondary standard for drinking water, but a low value for a mineral water. As an indication of the quality of the water, when I lived there for a couple of weeks one summer, I was able to detect only a faint residual mineral film in the sink. In order to maintain this level of minerals, the system disposed of 10 to 15 percent of the treated drinking water and replaced it with 10 to 15 percent rainwater.

Pumper: Where can systems like these be used?

Englehardt: Our economic analysis found that total costs for systems serving 100 to 10,000 households are approximately the same as conventional water and wastewater treatment technologies. The systems would be significantly more expensive for a single home.

Another advantage of small systems is thermal energy conservation. Conventional technology discharges treated wastewater to the environment along with all the thermal energy added by household water heaters. Our system conserves that heat so we don’t have to reheat the water much for use as hot water. In fact, a small portion may need to be cooled for drinking because in our system the temperature ran about 30 C (86 F).

Moreover, the energy saved by this system is projected to be several times the amount needed to run the treatment system. To our knowledge this is the first energy-positive water management system to be designed.

Pumper: Can these systems recycle 100 percent of water?

Englehardt: No known system can exceed 90 percent. There will always be some water loss, at least to prevent minerals from building up. In reverse osmosis systems perhaps 25 percent of the water that goes in comes out as a concentrate with minerals and other substances, and that has to be disposed of. In addition, the treated water is so devoid of minerals that it is corrosive and so must be chemically conditioned or blended with another water stream. Those systems typically recycle about 20 percent of the wastewater stream.

Pumper: How long would it take to put systems like these in place?

Englehardt: I think five to 10 years is a fair estimate for this country. Other countries may likely leapfrog us because they aren’t as heavily invested in centralized infrastructure, and their regulatory environments are less restrictive. In fact, a project like ours has just been proposed in India. What we need here in this country is more small demonstration projects to collect the data that regulators need to write rules.

Pumper: Where do you take this idea next?

Englehardt: I would like to apply for funding to restart our project. Right now there are only three net-zero water recycling systems in existence. One is ours. One is a composting toilet-based system at the Bullitt Center in Seattle. The third is on the International Space Station. Our system is the first to offer the prospect of energy-positive, net-zero-water municipal water management. Part of our continuing research is the development of a net-zero-water system that can be dropped into a remote area to provide running water at an Ebola treatment unit. A net-zero system can greatly reduce the need for imported water at an emergency site anywhere.

With systems like ours, Miami would withdraw those half billion gallons of water once instead of every day. Reductions in pumping (water from wells) would alleviate the intrusion of salt water from the ocean to groundwater aquifers, which is already happening, and the need for energy-intensive desalination. We are nearing the point now where the challenges to net-zero water use are more psychological than technological.