What are Managed Aquatic Plant Systems (MAPS)? Managed Aquatic Plant Systems or MAPS refers to a category of water treatment technologies that employ aquatic plants to remove pollutants, and are optimized through the routine recovery of plant biomass. HydroMentia’s proprietary MAPS include the Algal Turf Scrubber® (ATS™) and Water Hyacinth Scrubber (WHS™). The two technologies are similar in that they capitalize on nature’s restorative abilities to remove pollutant nutrients (phosphorus and nitrogen) from water resources using cultivated plants. The Algal Turf Scrubber® (ATS™) capitalizes on the rapid growth of attached algal assemblages, while the Water Hyacinth Scrubber (WHS™) utilizes the floating macrophyte, water hyacinth to perform treatment. Both systems use natural processes in controlled, engineered systems in order to maximize their capacity for nutrient pollutant removal. The Algal Turf Scrubber® provides the industry’s highest nitrogen and phosphorus removal rates. Capable of operating within a broad range of temperatures, the Algal Turf Scrubber® offers superior level nitrogen and phosphorus recovery when applied to stormwater runoff, impaired surface waters and agricultural and domestic wastewater. For tropical and subtropical applications with high nutrient and organic loads, the Water Hyacinth Scrubber provides a cost-effective alternative to the Algal Turf Scrubber®.
How does an ATS™ work? Algal Turf Scrubbers® are engineered systems in which attached algae (periphyton) are cultured and biomass is routinely harvested to facilitate recovery of pollutants from impaired waters. Primary structural components of the ATS™ system include an inclined floway over which pollutant laden water is discharged in a pulsed, laminar flow. The floway is constructed with an impervious lined surface and attachment grid for enhanced algal growth. Water is introduced to the floway through a distribution header in surges to enhance the growth of algae assemblages. Treated water is collected in an effluent flume which runs the entire width of the ATS™ floway The algae assemblages, better known as “algal turf” or periphyton consist of attached algae, diatoms, beneficial bacteria and macro-invertebrates which utilize nutrients for growth. Nutrients are removed from source water through biological uptake and chemical and physical processes such as precipitation and filtration. The algal turf is maintained in an accelerated growth phase through routine harvesting. Biomass is detached from the grid using specialized harvest equipment, and transferred to the effluent flume where it is recovered for further processing. Harvested biomass is generally converted to high-quality compost, but may also be used as livestock feed and as feedstock for biofuel production. Because pollutants are recovered and removed from the system, high level treatment performance is sustained.
How are nitrogen and phosphorus removed from water treated by the ATS™? Nutrients (such as nitrogen and phosphorus) are assimilated into the algal biomass. Phosphorus and nitrogen are incorporated into plant tissue during cellular production. In addition, precipitated pollutants and filtered particles are recovered within the algal turf, while ammonia may be volatilized and lost to the atmosphere. A major advantage of the ATS™ is that pollutants are removed from the system on a regular basis through harvesting or recovery of biomass. Treatment performance is maintained since there is no build-up of pollutants within the system to reduce its effectiveness.
How is the biomass recovered? Biomass from the ATS™ is recovered using HydroMentia’s proprietary harvesting method and specialized harvesting equipment. Algal turf is detached from the growing matrix and transported within the flow of the system. It is removed from the effluent at a centralized recovery facility using a bar screen with an automatic self cleaning rake. Recovered biomass is then transported to an on-site biomass processing facility.
What is the end-use of the recovered biomass? Recovered biomass is typically converted to a high-quality compost soil amendment. However, opportunities exist for further development of the material. As an example, over one million pounds of biomass produced at a Florida treatment facility has been fed to livestock as a high protein feed ingredient. As demand for alternative fuel sources grows, processing the recovered algae into a biofuel product may prove valuable and economical.
How are operations of the ATS™ facility conducted? HydroMentia’s team of biologists and operation managers have developed an adaptable O&M schedule that maximizes the performance of the ATS™ for pollutant removal, while minimizing the need for on-site personnel. The majority of routine tasks can be handled with a few pieces of equipment specifically designed for the ATS™. HydroMentia’s proprietary biomass harvesting methods make maintenance fast and efficient. Once-weekly visits to MAPS facilities requires one to two laborers and includes biomass harvesting, recovery and processing; water quality sample collection; site maintenance; and pump, valve and level checks . Pumps may be monitored remotely to allow timely repairs. Algal harvesting equipment is specially designed to quickly detach the algae from the growing matrix, and a skid steer loader is used for transporting the harvested biomass to the compost pad, as well as for maintenance of the compost windrows. For most facilities, HydroMentia’s mobile operations staff will conduct ATS™ maintenance for the client. This approach is the most cost effective, as HydroMentia owns and maintains all equipment necessary for facility operation. Where independent operation is required, staff training and O&M procedures are provided by HydroMentia, Inc. to ensure continual success of the treatment technology investment. Our staff is always available for consultation and support throughout the life of the facility.
How do ATS™ treatment costs compare with other treatment technologies such as treatment wetlands and chemical treatment? Several studies in Florida have established that when treatment goals are equal, MAPS systems are more cost effective than treatment wetlands. When considering operational costs for chemical treatment which include electricity, alum supply and disposal of residual sludge, HydroMentia’s MAPS technologies offer a lower cost solution for phosphorus control.
What is the primary difference between the ATS™ and treatment wetland systems? Treatment facility size: The most notable difference between MAPS and treatment wetland systems is their relative areal removal rate capabilities. ATS™ systems typically remove 10 to 40 times more pollutant per unit area than treatment wetlands, thus requiring less land for equal treatment performance. Areal removal rates for both systems vary according to influent water quality; however phosphorus removal rates typically range from 200 to 1000 lbs/ac/yr for ATS™ systems and from 5 to 30 lbs/ac/yr for treatment wetlands. Nitrogen removal rates for the ATS™ range from 500 to 8,000 lbs/ac/yr and for treatment wetlands from about 30 to 300 lbs/ac/yr. Pollutant Storage: Another important difference in the systems is the method and frequency by which pollutants are removed or stored. In treatment wetlands, phosphorus is stored as plant biomass and accrued sediments. Dependent on the treatment wetland design and loading, management plans to maintain system performance may include herbicide control of undesirable species, burning, drawdown and ultimately sediment removal. In contrast, ATS™ systems operate like advanced wastewater treatment facilities where biomass is recovered on a routine basis. This maintains the algal community in an optimal growth phase; facilitating higher areal removal rates, and assuring sustainable performance. System Design: ATS™ systems and treatment wetlands also vary in their design. ATS™ systems are engineered to maximize pollutant recovery by providing optimal conditions for (i) algal biomass production, (ii) pollutant precipitation and (iii) particle filtration within a system designed for the efficient and cost-effective recovery and management of algal biomass. The ATS™ is a lined system which maintains a pulsed, shallow, laminar flow along a sloped floway. Attachment grid serves as a matrix for the algal turf. In contrast, treatment wetlands are expansive systems in which pollutants are removed from source water through natural biological processes, and accumulated as sediment. To maintain treatment performance over extended periods of time, typically some form of sediment management must be implemented.
Are toxic chemicals used in ATS™ systems? No. An advantage of the Algal Turf Scrubber® technology is that it is based on biological and physical processes that use naturally occurring algae species for nutrient removal, and herbicide and pesticide use is not necessary.
What is the minimum concentration the ATS™ can achieve for nitrogen and phosphorus? ATS™ systems can be designed to (i) restore surface waters to “natural background” levels, (ii) treat wastewater to below AWT standards, or (iii) maximize pollutant load reduction. The minimum concentration of nitrogen and phosphorus achievable by the ATS™ is dependant upon source water quality and specific facility design. HydroMentia’s team of engineers and scientists work with each client to determine treatment objectives, which may focus on pollutant load reductions or effluent concentration requirements. HydroMentia offers an ATS™ mobile pilot unit (MPU) that provides a low cost method for investigating on-site conditions to verify treatment performance under a broad range of system configurations.
Can ATS™ systems remove organic nitrogen and phosphorus? Yes. ATS™ systems have been shown to effectively recover both nitrogen and phosphorus in organic forms.
Where can ATS™ systems be used? The Algal Turf Scrubber can be implemented anywhere photosynthesis takes place. The majority of research and commercial scale projects have been conducted in warm climates including Florida, Texas and California. In cooler climates, where most productivity occurs during the summer months, specific design considerations would include sizing the system to handle a large percentage of the treatment during those months, or provisions to maintain flow to the system during freezing weather. However, since the ATS™ utilizes natural populations of algae for treatment, cultivated assemblages will proliferate even in cooler climates, as long as flow can be maintained.
What are minimum and maximum facility sizes for ATS™ systems? For typical applications, individual ATS™ modules can be designed to treat from 1 MGD to 25 MGD. For large, regional applications, standard 25 MGD modules can be placed in parallel, providing treatment capacities over 100 MGD. This module approach further reduces land area requirements while significantly enhancing operational efficiency.
How does the ATS™ affect pH? As in natural aquatic systems, pH is elevated in the outflow from an ATS™ during daylight hours when photosynthesis occurs. The reason pH is elevated is that during photosynthesis, carbon dioxide in the water is consumed by the plant and stored for energy. When carbon dioxide is dissolved into water, the result is a slightly acidic solution of carbonic acid, hydrogen and hydroxide ions in addition to the H2O molecules. When carbon dioxide is removed from the water, the pH increases. The amount of change is determined by the ATS™ system design and the amount of available carbon within the water. Diurnal monitoring of ATS™ systems shows that the occurrence of pH at or above 9 is only found during the hours of highest sunlight intensity when photosynthesis is at its maximum, and alkalinity in the source water is relatively low. During much of the 24-hour day, pH of discharged water is likely to be closer to neutral, around 6.5-8.5.
How does the ATS™ affect dissolved oxygen levels? A benefit of the ATS™ system is that dissolved oxygen levels are increased to above saturation during the daylight hours. Due to thin, laminar flow along the ATS™, near saturation levels are maintained at night. In polluted systems where low dissolved oxygen levels impact aquatic health, this increased oxygen provides an additional benefit.
Are mosquitoes a problem with ATS™ systems? No. Mosquitoes prefer stagnant water, which the ATS™ does not provide. ATS™ systems maintain relatively high flow rates and are shallow in design, which makes them inhospitable to mosquitoes.
What is typical water depth on an ATS™? Water flowing over an ATS™ system is generally less than one inch in depth. This pulsed; laminar flow pattern has been shown to enhance growth and nutrient uptake on the ATS™.
What is the hydraulic retention time on the ATS™? Retention time on the ATS™ is dependent upon the length of the ATS™ floway and can range from under 7 minutes to more than 12 minutes. These relatively short retention times allows the ATS™ to accommodate large flows within a small footprint.
Can ATS™ systems be used to recover carbon dioxide (CO2) and produce feedstocks for biofuels? ATS™ systems designed to recover nitrogen and phosphorus offer the added benefit of CO2 recovery and biomass production. While researchers to date have focused primarily on phytoplankton-based algae systems for these applications, the Algal Turf Scrubber® may offer a better solution. A critical measurement of an algae systems ability to recover CO2 is the systems algal production rate. Interestingly, algal production rates in Algal Turf Scrubber® system have exceeded those levels achieved at the Department of Energy’sNational Renewable Energy Laboratory Outdoor Test Facility (OTF) in Roswell, New Mexico by 50 to 230 percent. These production levels have been achieved not in laboratory scale systems, but in large outdoor water treatment facilities. Additionally, Algal Turf Scrubber® systems address one of the primary challenges of phytoplankton based systems by offering proven, low energy, cost effective biomass recovery. In the future, large scale Algal Turf Scrubber® systems designed to recover nitrogen and phosphorus from major river systems and estuaries may also provide direct recovery of CO2 emissions from power generating facilities, while producing biofuel feedstocks for energy production.