Water Reuse Case Study: Collier County, Florida

Overview

Corkscrew Swamp Sanctuary contains a system—a “Living Machine®”—that treats wastewater generated onsite from the facility restrooms and recycles it for toilet flushing, effectively reducing demand on potable, freshwater supplies and helping to conserve groundwater. 

As visitor attendance at the sanctuary increased, the amount of wastewater generated onsite also increased to a level beyond the capacity of the old septic system. The sanctuary responded by installing an innovative treatment system, the Living Machine®, that employs plants and microorganisms instead of a traditional onsite wastewater treatment system. The Living Machine® also provides other benefits, such as educating the sanctuary’s visitors about the ability of natural wetlands to improve water quality and being aesthetically appealing.

Context

The Corkscrew Swamp Sanctuary occupies about 13,450 acres (5,440 hectares) in the Corkscrew Watershed in Collier County in southwest Florida. It was established as an Audubon Sanctuary in 1954, when the National Audubon Society purchased the land to protect the largest virgin bald cypress forest in the world (about 700 acres, or 280 hectares) from the logging industry and preserve the habitat of the largest nesting colony of federally endangered wood storks.

The sanctuary’s wetlands recharge local aquifers, rivers, and estuaries, including the Estero, Imperial, and Cocohatchee rivers. These rivers serve as an important connection from the watershed to coastal habitat, providing water to the Estero Bay Aquatic Preserve and Delnor-Wiggins State Park. The surrounding communities rely on the aquifers as a source of drinking water and for agriculture. Protecting the quality of groundwater, as well as surface water, is of critical importance for the region.

Since the mid-2000s, the sanctuary has noticed substantial changes to the water levels in the swamp. While the swamp historically held water throughout the entire (dry) winter season, the swamp is now drying out faster and water levels are remaining lower for longer periods. Efforts to monitor the water levels have shown that the downstream flood management canals—meant to drain water from low-lying communities during heavy rainfall—are now pulling water out of the wetlands. Agricultural and public water supply withdrawals also impact the drying of the swamp on the sanctuary. The changes in the water level have significant effects, including increasing wildfire risk, degradation of water supply and quality, and increases in algal blooms.

The sanctuary is a popular destination for tourists, scientists, students, and photographers. In the 1980s, the more than 100,000 visitors per year exceeded the capacity of the visitor center’s septic tank. In the early 1990’s, the sanctuary’s leadership feared that conventionally engineered options would be costly, require chemical additives, need a large amount of space, and emit noise and unpleasant odors, disrupting the tranquility of the sanctuary. As a response, the sanctuary installed an innovative sewage management system called The Living Machine® that was an alternative to the available engineered options and would adhere to Florida law. The Living Machine® addressed wastewater treatment capacity issues and provided multiple co-benefits to the facility and environment. Figure 1 shows some key attributes of the Machine, as well as a general timeline of its development.

Figure 1: Overview of the Living Machine® at Corkscrew Swamp Sanctuary. Photo source: changingflorida.org. Graphic source: World Bank based on interviews.

Solution

The Living Machine® is a wastewater treatment system constructed within a greenhouse or other indoor structure that is comprised of a series of tanks and subsurface flow treatment wetlands. It is designed to employ treatment processes that also occur in natural wetlands such as sedimentation, chemical adsorption (fixation), nitrification and denitrification, volatilization, and anaerobic and aerobic decomposition. The unique feature of the Living Machine® is that the combined treatment processes and wetlands support the growth of plants and other organisms, contributing to the system’s aesthetic benefits. The Living Machine® is also an educational tool – it is used to teach visitors about the value of natural wetlands for water quality improvement.

The Living Machine® at Corkscrew Swamp Sanctuary is used as an onsite wastewater treatment and reuse system, has a capacity of 7,500 gallons (28,400 liters) per day, and retention time of 11 days. Its main components—also shown in Figure 2—are as follows:

1. Anaerobic treatment: Wastewater from the visitor toilets is pumped to two 10,000-gallon (37,854-liter) fiberglass tanks below ground for anaerobic treatment to reduce BOD₅ (five-day biochemical oxygen demand) concentrations and total suspended solids (TSS), prior to the other treatment steps. The retention time in the anaerobic tanks is two days. The gas is released via a vent. The quantity of solids that settle within the tank are removed approximately every five years by a third party and disposed of via landfill.
2. Aerobic reactor and aeration tanks: The water from the anaerobic treatment tanks goes into one of two series of five tanks (2,500-gallon or 9,464-liter, each), arranged in parallel. Each one of these series can handle 75 percent of the maximum daily flow. The aerated tanks contain bacteria, plants (ranging from algae to trees), snails, shrimp, insects, and fish. The plants provide surface area for microbial growth, uptake nutrients, and support beneficial insects and microorganisms. The function of these reactors is to further reduce BOD and complete the nitrification processes, converting ammonia and organic nitrogen to nitrate. The nitrate is either taken up into the plants along with other macro- and micronutrients in the water or is converted into harmless nitrogen gas through denitrification in later portions of the treatment system. Periodically, the plants are harvested to prevent overgrowth and remove nutrients permanently from the system.
3. Clarification: The clarification step takes place in the next tank, a settling tank that separates any remaining suspended solids from the treated wastewater. The clear water flows onward while the settled solids are pumped back to the anaerobic tanks.
4. Constructed wetlands: The water continues to one of two constructed wetlands (30 by 30 feet, or 9 by 9 meters). These artificial marshes are lined with plastic, filled with crushed limestone, and vegetated with typical wetland species from the Corkscrew Swamp. The plants, and the microorganisms that occupy the surfaces on the granular medium, remove remaining nitrogen through uptake into plants or through denitrification, converting nitrate to harmless nitrogen gas.
5. Disinfection: A disinfection step was added to comply with Florida state permit requirements to limit potential pathogenic risks for users at the point of use. The water is disinfected with chlorine in a holding tank, then dechlorinated with sodium sulfite in a subsequent chamber to prevent the chlorine from interfering with the natural microbial processes inherent to the Living Machine® when the water is recycled.
6. Reuse for toilet flushing: Nearly 90 percent of the treated wastewater is reclaimed, pumped to storage tanks, and used in the toilets for flushing (a separate potable water supply is used for the handwashing sinks and drinking fountains). The remaining 10 percent of the treated effluent is discharged to a drainfield at the visitor parking lot as a preventative measure to reduce the buildup of minerals in the Living Machine® and to discharge excess water from the system (e.g., in periods with more visitors than usual).

The biomass from the vegetated tanks is lightly trimmed, with special attention paid to the plant roots to prevent them from damaging the tanks. These trimmings are composted onsite. The energy required for the system is supplied by the grid and powers a 0.9-horsepower (0.7-kilowatt) engine connected to a cast-iron blower motor which bubbles air into the aeration tanks.

In addition to treating the wastewater for reuse onsite, the sanctuary is responsible for treating its own potable water supply (groundwater is aerated and chlorinated). Reusing the treated wastewater effluent significantly reduces the potable water demand at the facility which may help lower groundwater depletion in the area. Use of the Living Machine® for onsite reuse also helps to raise awareness among the sanctuary’s visitors about the value of the sanctuary’s natural wetlands. This may motivate the public to prioritize supplying water to the sanctuary’s wetlands in the future.

Figure 2: Schematic showing the treatment steps of the Living Machine® at Corkscrew Swamp Sanctuary. Source: World Bank based on interviews and adapted from National Audubon Society.

Policy, Institutional, and Regulatory Environment

Florida is recognized nationally for its efforts in water reuse and has regulations for indirect potable reuse; onsite non-potable reuse; and reuse for agriculture, landscaping, and environmental restoration. According to the Florida 2021 Reuse Inventory, the state reuses 53 percent (908 million gallons, or 3.437 billion liters, per day) of its total treated wastewater for beneficial purposes. The majority of the reused treated wastewater in the state is used for irrigation of public access areas (58 percent), while the rest is used for groundwater recharge (11 percent), for industry (12 percent), for agriculture (7 percent), and for wetlands and other uses (12 percent). The original motivation for reuse in the state was to comply with state requirements that call for the consideration of water reuse instead of discharging the treated wastewater to surface waters. However, in recent years, wastewater treatment facilities in the state have come to see reclaimed water as a valuable resource.

Regulation and Standards Applicability

Use of the Living Machine® for onsite water reuse is subject to the Florida plumbing code, enforced at the local level, and several state regulations enforced by the Department of Environmental Protection (DEP) and the Department of Health (DOH).

According to DEP regulations, the Living Machine® is required to perform a similar level of treatment to that which would be achieved in a conventional wastewater treatment system by meeting secondary effluent treatment standards established in the state of Florida. For example, concentrations of biochemical oxygen demand (BOD) based on a 5-day test and total suspended solids (TSS) in the reused wastewater must not exceed 20 milligrams per liter and disinfection must be used to limit bacterial indicator concentrations to 200 fecal coliforms per 100 milliliters (single sample maximum). Additionally, because the Living Machine® discharges to a drainfield like a septic system, it must comply with the Florida DOH regulations for onsite sewage treatment and disposal systems to protect groundwater quality.

The reclaimed water that is used for toilet flushing must also be of acceptable quality to comply with Florida’s onsite non-potable water reuse regulations, which reference NSF/ANSI (National Sanitation Foundation/American National Standards Institute) Standard 350 (Florida plumbing code, 2017). This standard requires a comprehensive method of evaluation and water quality standardized at the national level through AmANSI. The NSF/ANSI 350 standards requires testing for BOD, TSS, nitrogen, turbidity and E. coli. Standards 350 and 350-1 are both based on 26 weeks of continuous testing with regularly scheduled sampling throughout, typically three days a week.

Operational Requirements

To satisfy the permit requirements and operate the sanctuary’s Living Machine® and associated reuse system, an engineer must complete and file a full report with the DEP South District every five years. In addition, DEP carries out a yearly inspection and a third-party water quality testing firm runs additional tests to ensure that the standards are maintained. Monitoring includes daily TSS and chlorine testing, as well as fecal coliform testing three times a week. Recently, DEP has instructed the sanctuary to purchase monitoring equipment to continuously test the water throughout the system. In this regard, the Living Machine® is considered like any other wastewater treatment plant and must meet standard metering requirements. For a small-scale system, like the Living Machine®, metering is a costly investment, and the requirement could be considered a barrier to implementing such treatment technologies elsewhere.

When the Living Machine® was built, state and county organizations were skeptical about its effectiveness. However, since its operation, it has effectively passed monthly Collier County Pollution Control sewage treatment plant inspections and its treated wastewater effluent has met all required water quality standards.

Financial and Contractual Agreements

The two main revenue sources at the Corkscrew Sanctuary are admission fees and philanthropy. The initial capital investment for the Living Machine® in 1995 was $395,060, which according to the sanctuary was substantially cheaper than a traditionally engineered onsite wastewater treatment solution at the time.

In 1993, the Corkscrew Swamp Sanctuary contracted a private company, Living Technologies, Inc. (Burlington, Vermont), to build the Living Machine®. Living Technologies monitored the system for a few years after the installation; maintenance and daily water quality testing is currently contracted out to Schaeffer Utility Management, which was also present at the start of construction and therefore has intimate knowledge of the system. The system currently costs about $4,000 per month to operate—primarily for contractors to keep the system functioning, equipment replacement, and disinfection chemicals (i.e., chlorine and sodium sulfite).

The Living Machine® has been in operation for nearly three decades, and will need some upgraded components to continue to meet regulatory requirements. This will require a significant capital investment. For example, new metering requirements from DEP will cost about $10,000. In addition, the constructed wetlands will need new gravel for the first time, having become saturated with organic material and sludge. Renewing the gravel will require a complete cleaning of the constructed wetlands (which will also be an opportunity to check the infrastructure and piping for any damage). The total cost of these upgrades is not fully defined at this time.

Benefits

The Living Machine® has proven to be well-suited for the Corkscrew Swamp Sanctuary. The system meets state and county requirements; uses little electricity; and has created an aesthetically pleasing environment containing plants, insects, and animals within the greenhouse – a benefit that most conventional treatment systems do not provide.

Natural aesthetic and diversity: After more than 25 years in operation, the Living Machine® contains a robust and diverse consortium of native plants and other species similar to those found within the sanctuary’s natural wetlands (Figure 3). It is also aesthetically appealing.

Education and awareness: The placement of the Living Machine® next to the visitor center and restrooms ensures visitors are aware of the facility, which has become an asset to the sanctuary rather than a hindrance. Guided with informational plaquettes, the Living Machine® is educational for adults and children alike, showing how natural systems can be used to treat water as an alternative to conventional treatment systems. This also supports visitor awareness about the value of the sanctuary’s natural wetlands and swamps.

Water reuse and offset: From a circular economy standpoint, the main benefit of the Living Machine® is that it offsets the amount of potable drinking water once treated and used for toilet flushing onsite. By using reclaimed water in the visitor center’s toilets, the sanctuary has been able to conserve fresh groundwater sources. Overuse of groundwater in the region contributes to sea water intrusion in the area.

Inspires the use of nature-based solutions in other contexts: Although the Living Machine® itself may not be considered a nature-based solution because it is disconnected from the local ecology, it can inspire the implementation of nature-based solutions in other natural parks or other areas. This is because it helps to inform visitors about the water quality benefits provided by natural systems, such as the sanctuary’s own natural swamps.

Figure 3: View of portions of the Living Machine®. Source: Corkscrew Swamp Sanctuary

Lessons Learned and Conclusions

Lessons Learned

Turning a problem into an asset: As a response to the increased wastewater flows that arose at Corkscrew Swamp Sanctuary following the increase of visitors, the Living Machine® was created, helping to inform visitors about the natural treatment processes that would also be inherent to the sanctuary’s natural swamp. The robust and diverse consortium of plants and animals that the Living Machine® supports is an educational and aesthetic attraction for the sanctuary’s visitors.

Natural treatment systems can be very effective: The Living Machine® has successfully and consistently met and exceeded water quality standards. The TSS levels measured in the treated effluent were 0.14 nephelometric turbidity units (NTU) at the last inspection, which is well below the requirement of <5 NTU for a single sample measurement.

Intentional design: The Living Machine® treats a homogenous influent from one restroom building, so it does not need the complexity of a system for a residential area. For example, residential systems need different designs to remove or filter out additional chemicals or kitchen grease in the wastewater influent, and the different wetland vegetation may be unable to thrive under these conditions.

Raising awareness is key: Along with other visitors, state and county officials often visit the Living Machine® to gain knowledge on the workings of this alternative system. They have hosted countless field trips from the DEP employees interested in learning about the Living Machine®. Natural treatment systems like this are not often implemented and successfully operated as sewage treatment solutions. Thus, public education, including educating regulators, is an important service provided by the sanctuary toward broader implementation of similar solutions.

Monitoring of small-scale reuse projects may be cost prohibitive: The Living Machine® must meet the same water quality standards as any wastewater treatment plant. However, because it is only suitable in small scale contexts, monitoring equipment and contractor support may be costly and therefore a barrier to the implementation of the Living Machine® elsewhere. Local governments may want to consider the type of monitoring and reporting requirements necessary to meet regulatory requirements in small-scale reuse projects.

Conclusions

The Living Machine® has provided many co-benefits and lessons for the sanctuary and beyond. The Living Machine® provides a solution to reuse treated wastewater effluent onsite and reduces the demand on vulnerable groundwater supplies. It shows that natural treatment systems can be very successful and even exceed regulatory requirements. Much like traditionally engineered systems, they need continuous monitoring and over time must be adapted to a changing environment. For example, a natural treatment system is subject to ongoing changes in regulations and will need upgrades to continue performing water treatment in the future.

Background Documents

• Force, J., 2018. In this Florida county, wastewater effluent goes on to become irrigation water for a variety of green spaces. TPO: Treatment Plant Operator. 
• National Audubon Society. n.d. Living Machine. 
• National Audubon Society. n.d. The Sanctuary. 
• NSF International. n.d. NSF Standard 350 for water reuse treatment systems: Questions and answers. 
• Sullivan, S. 2019. The Living Machine: Collier’s 24-year water filtration experiment is a success. Changing Florida. 
• U.S. Environmental Protection Agency. 2002. Wastewater technology fact sheet: The Living Machine. 
• Winans, K., Speas-Frost, S., Jerauld, M., Clark, M., and Toor, G. 2012. Small-scale natural wastewater treatment systems: Principles and regulatory framework. EDIS.