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Report from the Ecological Engineering Breakout Session

At the conference "Ecological Engineering for Integrated Water Management", Harvard, USA, Oct. 30-Nov. 2, 2003

By Erica Gaddis
Vermont, USA

Contact: 

This session focused on various aspects of new applications and developments in ecologically engineered wastewater treatment technologies. Erica Gaddis focused on a specific project using Restorer Technology in Southeast China to clean up a sewage-laden canal. David Austin presented a new generation of wetland treatment designs that use mechanical inputs and scientific insights into internal treatment mechanisms to improve the effectiveness of constructed wetland technologies. David Del Porto discussed ways to work with certification programs to integrate ecologically engineered systems into green design.

Remediation of a Sewage-laden Canal in an Urban Area of Southeast, China

Presented by Erica Gaddis for Ocean Arks International (http://www.oceanarks.org)

**This project is summarized in more detail in the next issue of Ocean Arks International's periodical, Annals of Earth.

Erica Gaddis worked with Ocean Arks International last summer to remediate a sewage-laden canal in Southeast China. Waterborne diseases claim the lives of 40,000 people every day in developing nations. Many urban areas, especially in Asia, are particularly plagued by wastewater flowing through open canals in dense population centers. Fuzhou is a large city on the coast of southeast China with 80 kilometers of open canals that transport roughly 130,000 m³ wastewater per day through the city, out to the Min River, and eventually to the Min Estuary, an important fishery for the Fujian province. City officials found that sewering the city and pumping wastewater to conventional treatment plants would be prohibitively expensive. They were looking for a mechanism to treat the water in the canals themselves. Given the constraints and unknowns of the project Ocean Arks International installed a linear Restorer. Restorer Technology was originally designed for restoration of polluted ponds on Cape Cod and was transformed in 2000 to upgrade a storage lagoon at a chicken processing plant in Maryland to a secondary treatment system. Restorer Technology is comprised of a floating platform to support planted ecosystems, an aeration system to maintain an aerobic aquatic ecosystem, a walkway for operator access, and a bioaugmentation system provided by Bacta-Pur®. The technology is flexible, attractive, and most appropriate to meet the onsite treatment challenge posed by the canals.  Partially mixed aerated lagoon kinetics are used to determine the aeration design.

The 500-meter Baima Canal receives 2,800 m³ wastewater and stormwater daily (three times the ratio of wastewater volume to canal length of other canals in the city) from a neighbourhood of approximately 12,000 people. The appearance of the Restorer is dominated by more than 13,000 native Chinese plants, many of which are now over two meters tall. The Baima Restorer also includes fabric media as attached growth surface area, recycle to an anoxic zone, a fine bubble aeration system, and automatic dosing of beneficial bacteria. The Restorer has successfully reduced odours, eliminated floating solids, and improved the clarity of the water and aesthetics of the neighbourhood. Water has reached secondary effluent standards for several parameters throughout the canal. Our Chinese partners have taken to planting new local plants on the Restorer and along its banks.  It appears that at the least, the quality of life in the neighbourhood has improved and a new ecology is taking hold in the middle of a dense urban area. Very little data is available concerning the reduction of pathogens in the canal.

The project has not been without challenges. The system has experienced a major fire in the floating blower building. The canal was entirely drained once due to a dam failure at the end of the canal. The system has also endured several torrential rains and tropical storms. Yet still, the biology appears to be thriving and treating water.

Questions:

A question was raised regarding the possible aerosolization of pathogens from the canal as a result of the aeration system. David Austin noted that the fine bubble aeration technology used in this project would not lead to aerosolization for very far above the water surface. Erica Gaddis said she would look into this concern but assured the questioner that the public is not usually allowed on the canal itself (there is a 5 foot drop from the canal wall to the water surface) and that in the future plants could be used to cover the entire canal to alleviate this concern.

Evolution of Fourth-Generation Wetland Treatment Technologies for Advanced Tertiary Treatment and Water Reuse

Presented by David Austin, PE, Director of Research and Development, Living Machines Inc. (http://www.livingmachines.com)

This work will be published in the conference proceedings and other venues in 2004.

David Austin presented the evolution of constructed wetland design and a new generation of technologies, which use mechanical assistance to achieve advanced tertiary treatment. Austin began by summarizing the first three generations of constructed wetland design. Wetland technologies arose in the mid to late nineteenth century and included passive systems such as slow sand filters for drinking water treatment and gravel flood and drain systems. By the early twentieth century, unmonitored sewage discharge to wetlands had become more common practice and also utilized trickling filter technology, planted sand and gravel beds, and pressurization of surface bed on fill. From these technologies emerged the passive design philosophy and a great emphasis on plant specific treatment. This generation of wetland designers viewed blowers and pumps as unnatural and created an ideological constraint against using mechanical equipment to improve treatment. This philosophy held true through the second and third generations of wetland design as well.

Austin described the second and third generation of wetland design to have branched from the first generation. Where as second generation designs used an empirical approach based on basic engineering hydraulic design criteria to avoid clogging, the third generation developed empirical equations used to achieve predetermined treatment levels for BOD and TSS. These two schools of thought are currently in competition with one another and neither has proven to be a better design approach in all circumstances. Strengths of these approaches include widespread application, pH stabilization, metal sequestration, and treatment of xenobiotic compounds. Weaknesses include a lack of nitrification, naïve hydraulic design, a record of design failures, and weak mathematical design models.

In the last decade a fourth generation of wetland design philosophy has emerged as the result of work done by many workers. Living Machines Inc. and North American Wetland Engineering Inc. have contributed to this emerging area of wetland technology. This approach aims to understand the internal mechanisms of the 'black box' including hydraulics, the role of plants in treatment, microbiology and biogeochemistry, and, if necessary, appropriate use of mechanical assistance to achieve tertiary treatment standards.

The results of this new generation of technologies appears to be promising for many wastewater applications. Adding aeration to constructed wetlands can reduce the footprint required to achieve treatment by 75% or more. Whereas second and third generation constructed wetlands generally reach BOD and TSS effluent concentrations of 30 mg/l, fourth generation designs can achieve 5 mg/l. Perhaps most important, fourth generation wetlands can achieve better nutrient reduction by encouraging the nitrification and denitrification processes at specific zones within the wetland. Effluent from fourth generation wetlands can be used in parks, landscaping, groundwater recharge, or surface reuse.

LEED and CHPs Points for Ecological Water Features

Presented by David Del Porto, Senior Designer, Ecological Engineering Group
(www.ecological-engineering.com )

David Del Porto encouraged an integrated water management approach that couples ecological engineering with two existing certification processes, LEED (Leadership in Energy and Environmental Design) and CHPS (Collaborative for High Performance Schools). He also addressed the question of how to encourage developers and municipalities to include such certifications in their permitting process. For example, in Newton, Massachusetts, Del Porto's hometown, the city now requires that all engineers and architects be LEED certified.

There are several steps for water reuse including reduce, separate, pre-treat, reuse, store, and recycle. There are many forms of water that can be harvested for use in buildings including rain, stormwater, treated wastewater, and fog. LEED is a national, performance-based rating system for "green buildings" that provides several mechanisms by which appropriate water management can be integrated into building design including:

• Water efficient landscaping (with plants that need little water)
• Innovative wastewater technologies
• Water use reduction
• Stormwater management such as treatment to minimize evaporative loss through the system and replace constructed surfaces with biological surfaces.

The Collaborative for High Performance Schools process is a program, based in California, that aims to facilitate the design of schools that are not only energy efficient, but also healthy, comfortable, well lit, and contain the amenities needed for a good education. There are many opportunities for integration of ecological engineering into this program. This program focuses on Low Impact Development (LID) and rethinks the issue of stormwater management. Strategies employed in LID include porous pavement, Ecoroofs, parking lot swales, large canopy trees, and rainwater collection and storage.

For integrated water management, Del Porto recommends the following strategies:

• Manage the demand by conserving water;
• Focus on irrigation management;
• Employ stormwater best management practices for reuse;
• Employ ecologically engineered systems for wastewater treatments, including constructed wetlands, wastewater gardens, and solar aquatic systems;
• Use composting toilets when possible and manage and treat graywater.
• Employ phytoremediation to clean-up contaminated sites.

Questions:

During the question period there was discussion about the iterative process of LEED standards. They are refined and revisited frequently.

There was also discussion regarding graywater. Del Porto said that in many ways graywater is more dangerous than blackwater, since it contains both pathogens and many chemicals. There was also discussion about the need to consider all environmental consequences when proposing new products and technologies. For example, the fleece made from recycled plastics is excellent as a clothing material but micro-fibers from the fabric can clog leachfields if appropriate lint filters are not installed on washing machines.