Constructed Wetlands By Dave Lomeli Why use

Constructed Wetlands By Dave Lomeli

Why use a Constructed Wetland • Constructed wetlands can treat wastewater from a variety of sources. One of the more common uses is to provide additional or advanced treatment of wastewater from homes, businesses and even communities. Wetlands treat wastewater that has already had most of the solid materials removed from it through some type of primary or secondary treatment. • Homes, businesses, farms, schools, highways and other individual • wastewater sources in rural areas sometimes can add a constructed wetland to a septic system or other onsite system to replace or assist a soil absorption field. Some onsite systems can be specifically designed from the start to use a constructed wetland in addition to a soil absorption field on properties with site constraints, such as tight or saturated soils. • Wetlands are good at handling intermittent periods of both light and heavy wastewater flows. Therefore, they often work well with wastewater treatment systems that serve hotels, campsites, resorts and recreational areas.

Types • Constructed wetlands – built to mimic natural wetlands, not part of natural systems • Surface-flow • Subsurface-flow • Vertical Flow Systems • New design systems used to overcome oxygen depletion problems in wetlands

Wet Land Design factors Basic questions: - Geographic - Economic - Vegetation - Substrate/soils - Chemical input/output - Compartments/cells - Maintenance - Unexpected events - Outlet considerations

Design Factors One of the most important factors affecting treatment is temperature. • Biological treatment processes tend to speed up in warm weather and slow down in cold weather. In cold climates, systems must be large enough to accommodate the longer hydraulic residence times needed for treatment. • Plants help treatment processes in several ways. The wetland plants filter wastes, regulate flow and provide surface area for bacterial and treatment. • Floating plants, such as water lilies and emergent plants, such as cattails, shade the water surface and control algae growth. • Even in winter when plants are dormant, they often are contributing to treatment Plants also contribute to treatment by taking up nutrients, metals, and other substances and retaining them. Many of these substances can accumulate again in the wetland when the plants die and decompose. Therefore harvesting vegetation is a good idea.

Design types

Surface Flow • Surface-Flow Treatment Wetlands • As soon as wastewater enters a surface flow wetland cell, natural processes immediately begin to break down and remove the waste materials in the water. Before the wastewater has moved very far in the wetland small suspended waste materials are physically strained out be submerged plants, plant stems, and plant litter in the wetland. The roots, stems, leaves, and litter of wetland plants also provide a multitude of small surfaces where wastes can become trapped and waste-consuming bacterial can attach themselves.

Operation & Maintenance Surface Flow Wetland • Surface flow wetlands have few operation and maintenance requirements, but maintenance must be performed properly to ensure system performance. • Operation may entail alternating cells or adjusting water levels and harvesting vegetation. • Some systems may have banks and berms that need to be maintained, and inlet and outlet structures that should b cleaned periodically. • Mosquitoes and burrowing animals present problems in some systems. Different control methods are available, including natural solutions, such as trapping and relocating animals, introducing fish that eat insect larvae, and building bat houses.

Subsurface Flow In SSF wetlands the polluted substrate is transported through material (depends on what they want to use) where bacteria in the substrate and on the plants come in contact with the contaminated water and effectively degrade or bind the pollutant. Four basic parameters are considered when finalizing the layout and design of SSF wetlands: (1) Inlet distribution system, (2) Basin configuration, (3) Bed media, and (4) Outlet control system (Kadlec et al, 1996).

Operation & Maintenance Subsurface Flow Wetland • Surface flow wetlands have few operation and maintenance requirements, but maintenance must be performed properly to ensure system performance. • Operation may entail alternating cells or adjusting water levels and harvesting vegetation. Some systems may have banks and berms that need to be maintained, and inlet and outlet structures that should be cleaned periodically

Advantages • Constructed wetlands are typically inexpensive • • • to build and maintain. They require little or no energy to operate. They can provide effective tertiary treatment. They can provide additional wildlife habitat. They can be aesthetically pleasing additions to homes and neighborhoods. They are viewed as an environmentally friendly technology and are generally well received by the public.

Disadvantages • Constructed wetlands require more land area • • than many other treatment options. Surface flow wetlands can attract mosquitoes and other pests. Wetlands are not appropriate for treating some wastewater with high concentrations of certain pollutants. The performance of wetlands may vary based on usage and climatic conditions. There may be a prolonged initial start-up period before vegetation is adequately established.

Examples of Constructed Wetlands • Mai Po Marshes, Honk Kong • Putrajaya Lake and constructed wetlands, Malaysia

In : (1) Mai Po Marshes, Honk Kong

Mia Po Marshes • 1976 - the Mia Po Marshes were recognized as a protected area • 1983 - They were Declared a nature conservation area • The WWF then took over managing and developing the area for conservation and education. • 1995 – Mia Po Marshes and Inner Deep Bay area were named wet lands of International importance under the Ramsar convention

Mai Po Marshes • The Ponds are 10 ha and 1 -1. 5 m deep • Largest area of vegetation in Mai Po is in the mangroves, reedbeds, & sedges (F: cyperaceae) • Mangrove forests along w/those of the Deep Bay Mia Po marshes cover an area of 400 ha • 45 -46 ha of marshes are composed of reedbeds

Importance • An estimated 2 -3 million water birds migrate from their breeding grounds in northern China, Mongolia and Siberia, to their wintering grounds in southeast Asia and Australasia • In winter, up to 68, 000 birds winter in these wetlands before flying back north in spring to their breeding grounds. During the spring and autumn migration periods, the site is used by an estimated 20, 000 - 30, 000 shorebirds.

Importance • Other mammals recorded from Mai Po and Inner Deep Bay include the Eurasian Otter (Lutra lutra chinensis), Pangolin Manis pentadactyla, Chinese Leopard Cat Felis bengalensis, Crab-eating Mongoose Herpestes urva, Seven-banded Civet Viverricula indica and various Muridae, e. g. Bandicoot Rat Bandicota indica, Soricidae, e. g. House Shrew Crocidura murinus and bats such as the Pipistrellus abramus. • Although the Chinese White Dolphin Sousa chinensis has previously been recorded up the Shenzhen River as far as Lok Ma Chau, its presence in Shenzhen Bay is now doubtful due to heavy boat traffic and pollution.

Importance • Important for biodiversity • Important for agriculture • Important Education and Economic reasons

In (2): Putrajaya Lake and constructed wetlands, Malaysia

Putrajaya Wetlands • Created in 1998 by flooding 2 Valleys: Sungai Chau & Sungai Bisa and creating a Dam • The Dam was constructed (across Sungai Chau) in 1998 and the valley was able to be fully flooded in 1999 • Objectives of the project: make sure it’s environmentally sustainable, water quality sustainable for recreation, and education and research. Largest Fresh Water wetlands in tropics Consists of 335 ha

Putrajaya • Putrajaya was founded on October 19, 1995 and is located in the middle of the Multimedia Super Corridor (MSC). Population: 1) Current residential population: 30, 000 2010 target: 350, 000 2). Current working population: 34, 000 2010 target: 200, 000 Development Phases: i. Phase 1: 1996 - 2000 (Completed) ii. Phase 2: 2000 - 2010/2020 Land Use : 1). Core Area comprising Government Mixed Development, Civic & Cultural, Commercial and Sports & Recreation Precincts, 2) The Periphery comprising residential areas and Diplomatic Enclave. 3) Utilities, facilities, amenities • It is set to be a model garden city with sophisticated information network base on multimedia technologies. • Putrajaya is a planned city and a Federal Territory that acts as a federal government administration centre of Malaysia and it was moved here because of the overcrowding and congestion in Kuala Lumpur.

Cells • Wetland consists of 24 cells seperated by weirs • Each cell has miniature wetland function that differ between cells • Cells have surface and subsurface flows

Habitat • More than 70 species of wetland plants totaling 12. 3 million plants were planted and 24 species of indigenous fish were introduced in the wetland. • The wetland performs an ecological role, as a home to a unique and rare species of birds, insects, plants, amphibians, reptiles, small mammals and other invertebrates including water snails.

The Putrajaya Lake • The lake is at the southern part of the wetland. • About 60% of the lake water flow is from the wetland the remaining 40% is the direct discharge from bordering promenade. The 20 m width promenade is the buffer feature along the lake shorelines. • The water surface area of the whole lake is about 400 hectares. The total volume of the whole lake water is about 23. 5 million cubic meters and the water depth is in the range of 3 to 14 meters. • The lake has been planned to cater for multi-functional uses, including recreation, fishing, water sports and water transport. The lake and its foreshores also form Putrajaya's most popular resource for informal recreation as a waterfront city.

Conclusion • Constructed Wetlands provide a number of benefits for animals and humans • Provide a great resource for natural filtering system and flood control system • Cheap alternative to conventional methods

Questions?