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53-685: A series of oxidation ponds, treatment wetlands and enhancement marshes are used to filter sewage waste. The marshes also serve as a wildlife refuge , and are on the Pacific Flyway . The Arcata Marsh is a popular destination for birders. The marsh has been awarded the Innovations in Government award from the Ford Foundation / Harvard Kennedy School . Numerous holding pools in the marsh, called "lakes," are named after donors and citizens who helped start

106-406: A biofilter and/or can remove a range of pollutants (such as organic matter, nutrients , pathogens , heavy metals ) from the water. Constructed wetlands are designed to remove water pollutants such as suspended solids, organic matter and nutrients (nitrogen and phosphorus). All types of pathogens (i.e., bacteria, viruses, protozoans and helminths ) are expected to be removed to some extent in

159-529: A habitat for native and migratory wildlife , although that is not their main purpose. Subsurface flow constructed wetlands are designed to have either horizontal flow or vertical flow of water through the gravel and sand bed. Vertical flow systems have a smaller space requirement than horizontal flow systems. Many terms are used to denote constructed wetlands, such as reed beds , soil infiltration beds, treatment wetlands, engineered wetlands, man-made or artificial wetlands. A biofilter has some similarities with

212-437: A septic tank for primary treatment (or other types of systems) in order to separate the solids from the liquid effluent. Some constructed wetland designs however do not use upfront primary treatment. In subsurface flow constructed wetlands the flow of wastewater occurs between the roots of the plants and there is no water surfacing (it is kept below gravel). As a result, the system is more efficient, does not attract mosquitoes,

265-896: A wheat field. Detritus from decomposing wetlands vegetation forms the base of a food chain for aquatic organisms, birds and mammals . Individuals who value wetland environments may not realize the effluent characteristics necessary for release of treated wastewater to Humboldt Bay. Although there is no evidence of harm to wildlife, some regulators suggest potential risk to wildlife using treatment wetlands because of an absence of significant research on wildlife exposure to partially treated effluent and to potential accumulation of chemicals being removed from effluent in wetland treatment processes. Ongoing research at Cal Poly Humboldt minimizes potential risk to Humboldt Bay wetlands and wildlife. The City of Arcata generates an average volume of 2.3 million US gallons (8,700 m) of sewage per day. Winter rainfall onto treatment ponds and marshes increases

318-523: A constructed wetland used for water treatment. Constructed wetlands are of two basic types: subsurface flow and surface flow wetlands. Constructed wetlands are one example of nature-based solutions and of phytoremediation . Constructed wetland systems are highly controlled environments that intend to mimic the occurrences of soil, flora, and microorganisms in natural wetlands to aid in treating wastewater. They are constructed with flow regimes, micro-biotic composition, and suitable plants in order to produce

371-541: A constructed wetland, but is usually without plants. The term of constructed wetlands can also be used to describe restored and recultivated land that was destroyed in the past through draining and converting into farmland, or mining. A constructed wetland is an engineered sequence of water bodies designed to treat wastewater or storm water runoff . Vegetation in a wetland provides a substrate (roots, stems, and leaves) upon which microorganisms can grow as they break down organic materials. This community of microorganisms

424-399: A constructed wetland. Subsurface wetlands provide greater pathogen removal than surface wetlands. There are two main types of constructed wetlands: subsurface flow and surface flow. The planted vegetation plays an important role in contaminant removal. The filter bed, consisting usually of sand and gravel , has an equally important role to play. Some constructed wetlands may also serve as

477-471: A constructed wetland; however, greater pathogen removal is expected to occur in a subsurface wetland. In a free water surface flow wetland one can expect 1 to 2 log10 reduction of pathogens; however, bacteria and virus removal may be less than 1 log10 reduction in systems that are heavily planted with vegetation. This is because constructed wetlands typically include vegetation which assists in removing other pollutants such as nitrogen and phosphorus. Therefore,

530-402: A loss of treatment capacity through too much suspended solids, sludge or fats. Subsurface flow wetlands require the following maintenance tasks: regular checking of the pretreatment process, of pumps when they are used, of influent loads and distribution on the filter bed. Subsurface wetlands are less hospitable to mosquitoes compared to surface flow wetlands, as there is no water exposed to

583-493: A similar ways as in sewage treatment plants, except that no external, energy-intensive addition of air (oxygen) is needed. It is a two-step process, consisting of nitrification followed by denitrification . The nitrogen cycle is completed as follows: ammonia in the wastewater is converted to ammonium ions; the aerobic bacterium Nitrosomonas sp. oxidizes ammonium to nitrite; the bacterium Nitrobacter sp. then converts nitrite to nitrate. Under anaerobic conditions, nitrate

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636-492: A thick mat of roots and rhizomes upon which biofilms form. In most cases, the bottom is lined with either a polymer geomembrane , concrete or clay (when there is appropriate clay type) in order to protect the water table and surrounding grounds. The substrate can be either gravel —generally limestone or pumice/volcanic rock, depending on local availability, sand or a mixture of various sizes of media (for vertical flow constructed wetlands). Constructed wetlands can be used after

689-402: A variety of different wastewaters, such as household wastewater, agricultural, paper mill wastewater, mining runoff , tannery or meat processing wastes, storm water . The quality of the effluent is determined by the design and should be customized for the intended reuse application (like irrigation or toilet flushing) or the disposal method. Depending on the type of constructed wetlands,

742-406: A vertical flow constructed wetland is preferable to a horizontal because of an unsaturated upper layer and a shorter retention time, although vertical flow systems are more dependent on an external energy source. Evapotranspiration (as is rainfall) is taken into account in designing a horizontal flow system. The effluent can have a yellowish or brownish colour if domestic wastewater or blackwater

795-461: A vertical or a horizontal flow regime are also common and can be integrated into urban areas as they require relatively little space. The main three broad types of constructed wetlands include: The former types are placed in a basin with a substrate to provide a surface area upon which large amounts of waste degrading biofilms form, while the latter relies on a flooded treatment basin upon which aquatic plants are held in flotation till they develop

848-419: Is an artificial wetland to treat sewage , greywater , stormwater runoff or industrial wastewater . It may also be designed for land reclamation after mining , or as a mitigation step for natural areas lost to land development . Constructed wetlands are engineered systems that use the natural functions of vegetation , soil , and organisms to provide secondary treatment to wastewater . The design of

901-563: Is fundamental not only to designing wetland systems but to understanding the fate of chemicals once they enter the wetland. Theoretically, wastewater treatment within a constructed wetland occurs as it passes through the wetland medium and the plant rhizosphere . A thin film around each root hair is aerobic due to the leakage of oxygen from the rhizomes , roots , and rootlets. Aerobic and anaerobic micro-organisms facilitate decomposition of organic matter. Microbial nitrification and subsequent denitrification releases nitrogen as gas to

954-409: Is known as the periphyton . The periphyton and natural chemical processes are responsible for approximately 90 percent of pollutant removal and waste breakdown. The plants remove about seven to ten percent of pollutants, and act as a carbon source for the microbes when they decay. Different species of aquatic plants have different rates of heavy metal uptake, a consideration for plant selection in

1007-430: Is less odorous and less sensitive to winter conditions. Also, less area is needed to purify water. A downside to the system are the intakes, which can clog or bioclog easily, although some larger sized gravel will often solve this problem. Subsurface flow wetlands can be further classified as horizontal flow or vertical flow constructed wetlands. In the vertical flow constructed wetland, the effluent moves vertically from

1060-419: Is reduced to relatively harmless nitrogen gas that enters the atmosphere. Nitrification is the biological conversion of organic and inorganic nitrogenous compounds from a reduced state to a more oxidized state, based on the action of two different bacteria types. Nitrification is strictly an aerobic process in which the end product is nitrate ( NO 3 ). The process of nitrification oxidizes ammonium (from

1113-409: Is the biological filtration through a biofilm of aerobic or facultative bacteria . Coarse sand in the filter bed provides a surfaces for microbial growth and supports the adsorption and filtration processes. For those microorganisms the oxygen supply needs to be sufficient. Especially in warm and dry climates the effects of evapotranspiration and precipitation are significant. In cases of water loss,

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1166-422: Is their operational robustness which is particularly important in developing countries. The fact that constructed wetlands do not produce secondary sludge ( sewage sludge ) is another advantage as there is no need for sewage sludge treatment . However, primary sludge from primary settling tanks does get produced and needs to be removed and treated. The costs of subsurface flow constructed wetlands mainly depend on

1219-522: Is thought to cause methemoglobinemia in infants, which decreases the blood's oxygen transport ability. Moreover, excess input of N from point and non-point sources to surface water promotes eutrophication in rivers, lakes, estuaries, and coastal oceans which causes several problems in aquatic ecosystems e.g. toxic algal blooms, oxygen depletion in water, fish mortality, loss of aquatic biodiversity. Ammonia removal occurs in constructed wetlands – if they are designed to achieve biological nutrient removal – in

1272-727: Is treated. Treated greywater usually does not tend to have a colour. Concerning pathogen levels, treated greywater meets the standards of pathogen levels for safe discharge to surface water. Treated domestic wastewater might need a tertiary treatment, depending on the intended reuse application. Plantings of reedbeds are popular in European constructed subsurface flow wetlands, although at least twenty other plant species are usable. Many fast growing timer plants can be used, as well for example as Musa spp., Juncus spp., cattails ( Typha spp.) and sedges . Overloading peaks should not cause performance problems while continuous overloading lead to

1325-466: Is typically the major limiting nutrient. Under undisturbed natural conditions, phosphorus is in short supply. The natural scarcity of phosphorus is demonstrated by the explosive growth of algae in water receiving heavy discharges of phosphorus-rich wastes. Because phosphorus does not have an atmospheric component, unlike nitrogen, the phosphorus cycle can be characterized as closed. The removal and storage of phosphorus from wastewater can only occur within

1378-582: The Pacific Flyway . Over 327 species of birds have been recorded at the sanctuary. Numerous plant, mammal , fish , insect , reptile and amphibian species inhabit the marsh. These include river otters , gray foxes , red-legged frog , tidewater goby , bobcat , striped skunk , praying mantis and red-sided garter snake . The Friends of the Arcata Marsh (FOAM) operate the Arcata Marsh Interpretive Center that contains exhibits about

1431-403: The atmosphere . Phosphorus is coprecipitated with iron , aluminium , and calcium compounds located in the root-bed medium. Suspended solids filter out as they settle in the water column in surface flow wetlands or are physically filtered out by the medium within subsurface flow wetlands. Harmful bacteria , fungi , and viruses are reduced by filtration and adsorption by biofilms on

1484-608: The city of Arcata is treated and released to Humboldt Bay via complex flow routing through a number of contiguous ponds, wetlands, and marshes. Resemblance of treatment features to natural bay environments may cause potential ambiguity about where wastewater ceases to be considered partially treated sewage and meets enhancement objectives of the California Bays and Estuaries Policy . The wastewater treatment system includes both treatment wetlands and enhancement marshes . Treatment wetlands improve oxidation pond effluent quality to meet

1537-477: The common way of reporting removal efficiencies as percentages: 1 log10 removal is equivalent to a removal efficiency of 90%; 2 log10 = 99%; 3 log10 = 99.9%; 4 log10 = 99.99% and so on. Constructed wetland systems can be surface flow systems with only free-floating macrophytes , floating-leaved macrophytes, or submerged macrophytes; however, typical free water surface systems are usually constructed with emergent macrophytes. Subsurface flow-constructed wetlands with

1590-434: The constructed wetland has to be adjusted according to the type of wastewater to be treated. Constructed wetlands have been used in both centralized and decentralized wastewater systems . Primary treatment is recommended when there is a large amount of suspended solids or soluble organic matter (measured as biochemical oxygen demand and chemical oxygen demand ). Similar to natural wetlands, constructed wetlands also act as

1643-431: The constructed wetland itself. Phosphorus may be sequestered within a wetland system by: Aquatic vegetation may play an important role in phosphorus removal and, if harvested, extend the life of a system by postponing phosphorus saturation of the sediments. Plants create a unique environment at the biofilm's attachment surface. Certain plants transport oxygen which is released at the biofilm/root interface, adding oxygen to

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1696-406: The costs of sand with which the bed has to be filled. Another factor is the cost of land. Surface flow wetlands, also known as free water surface constructed wetlands, can be used for tertiary treatment or polishing of effluent from wastewater treatment plants. They are also suitable to treat stormwater drainage. Surface flow constructed wetlands always have horizontal flow of wastewater across

1749-432: The effluent needs to first pass a primary treatment which effectively removes solids. Such a primary treatment can consist of sand and grit removal, grease trap, compost filter, septic tank , Imhoff tank , anaerobic baffled reactor or upflow anaerobic sludge blanket (UASB) reactor. The following treatment is based on different biological and physical processes like filtration, adsorption or nitrification. Most important

1802-453: The federal definition of secondary treatment . Disinfection and dechlorination is the final step of the wastewater treatment process. Disinfected wastewater may be discharged either to Humboldt Bay or to enhancement marshes. Enhancement marshes purify the wastewater and provide wetland habitat. Enhancement marsh effluent is disinfected to improve coliform index changes from birds using tertiary treatment enhancement marsh habitat. After leaving

1855-439: The gravel or sand media in subsurface flow and vertical flow systems. The dominant forms of nitrogen in wetlands that are of importance to wastewater treatment include organic nitrogen , ammonia , ammonium , nitrate and nitrite . Total nitrogen refers to all nitrogen species . Wastewater nitrogen removal is important because of ammonia's toxicity to fish if discharged into watercourses. Excessive nitrates in drinking water

1908-595: The importance of sunlight exposure in removing viruses and bacteria is minimized in these systems. Removal in a properly designed and operated free water surface flow wetland is reported to be less than 1 to 2 log10 for bacteria, less than 1 to 2 log10 for viruses, 1 to 2 log10 for protozoa, and 1 to 2 log10 for helminths. In subsurface flow wetlands, the expected removal of pathogens is reported to be 1 to 3 log10 for bacteria, 1 to 2 log10 for viruses, 2 log10 for protozoa, and 2 log10 for helminths. The log10 removal efficiencies reported here can also be understood in terms of

1961-439: The increased efficiency a vertical flow subsurface constructed wetland requires only about 3 square metres (32 sq ft) of space per person equivalent , down to 1.5 square metres in hot climates. The "French System" combines primary and secondary treatment of raw wastewater. The effluent passes various filter beds whose grain size is getting progressively smaller (from gravel to sand). Subsurface flow wetlands can treat

2014-648: The intermediary by product, N 2 O , are gases that re-enter the atmosphere. Constructed wetlands have been used to remove ammonia and other nitrogenous compounds from contaminated mine water , including cyanide and nitrate. Phosphorus occurs naturally in both organic and inorganic forms. The analytical measure of biologically available orthophosphates is referred to as soluble reactive phosphorus (SR-P). Dissolved organic phosphorus and insoluble forms of organic and inorganic phosphorus are generally not biologically available until transformed into soluble inorganic forms. In freshwater aquatic ecosystems phosphorus

2067-530: The marsh project, including Cal Poly Humboldt professors George Allen and Robert A. Gearheart who were instrumental in the creation of the Arcata Marsh. In 1969 Allen also started an aquaculture project at the marsh to raise salmonids in mixtures of sea water and partially treated wastewater. Despite being effectively a sewer, the series of open-air lakes do not have an odor, and are a popular destination for birdwatching , cycling and jogging . The sewage treatment process takes place in stages: Sewage from

2120-663: The most efficient treatment process. Constructed wetlands can be used to treat raw sewage, storm water, agricultural and industrial effluent . Constructed wetlands mimic the functions of natural wetlands to capture stormwater, reduce nutrient loads, and create diverse wildlife habitat. Constructed wetlands are used for wastewater treatment or for greywater treatment. Many regulatory agencies list treatment wetlands as one of their recommended " best management practices " for controlling urban runoff . Physical, chemical, and biological processes combine in wetlands to remove contaminants from wastewater. An understanding of these processes

2173-434: The operations of the treatment plant, the importance of the marsh, and about the plants and animals that live there. Volunteer docents give tours of the marsh. Education programs are offered for school, scout and other groups, as well as summer camp programs. 40°51′30″N 124°05′27″W  /  40.858341°N 124.090728°W  / 40.858341; -124.090728 Treatment wetland A constructed wetland

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2226-602: The planted layer down through the substrate and out (requiring air pumps to aerate the bed). In the horizontal flow constructed wetland the effluent moves horizontally via gravity, parallel to the surface, with no surface water thus avoiding mosquito breeding. Vertical flow constructed wetlands are considered to be more efficient with less area required compared to horizontal flow constructed wetlands. However, they need to be interval-loaded and their design requires more know-how while horizontal flow constructed wetlands can receive wastewater continuously and are easier to build. Due to

2279-498: The quantities measured in untreated sewage from the City of Arcata. Unfortunately, when measuring concentrations leaving treatment wetlands, neither of these analytical methods can distinguish between unremoved conventional pollutants originally arriving in sewage, or detritus of decomposing wetland vegetation; so the limitations may apply to the sum of both. The Arcata Marsh and Wildlife Sanctuary encompasses 307 acres of land situated along

2332-729: The removal of dissolved metals and metalloids . Although these contaminants are prevalent in mine drainage, they are also found in stormwater , landfill leachate and other sources (e.g., leachate or FDG washwater at coal-fired power plants ), for which treatment wetlands have been constructed for mines. Constructed wetlands can also be used for treatment of acid mine drainage from coal mines. Constructed wetlands are not designed for pathogen removal, but have been designed to remove other water quality constituents such as suspended solids, organic matter (biochemical oxygen demand and chemical oxygen demand) and nutrients (nitrogen and phosphorus). All types of pathogens are expected to be removed in

2385-517: The roots of the plants, rather than vertical flow. They require a relatively large area to purify water compared to subsurface flow constructed wetlands and may have increased smell and lower performance in winter. Surface flow wetlands have a similar appearance to ponds for wastewater treatment (such as " waste stabilization ponds ") but are in the technical literature not classified as ponds. Pathogens are destroyed by natural decay, predation from higher organisms, sedimentation and UV irradiation since

2438-484: The same route every year, at almost the same time. Ornithologists and birdwatchers can often predict to the day when a particular species will show up in their area. Along the Pacific Flyway, there are many key rest stops where birds of many species gather, sometimes in the millions, to feed and regain their strength before continuing. Some species may remain in these rest stops for the entire season, but most stay

2491-709: The surface. Mosquitos can be a problem in surface flow constructed wetlands. Subsurface flow systems have the advantage of requiring less land area for water treatment than surface flow. However, surface flow wetlands can be more suitable for wildlife habitat. For urban applications the area requirement of a subsurface flow constructed wetland might be a limiting factor compared to conventional municipal wastewater treatment plants . High rate aerobic treatment processes like activated sludge plants, trickling filters, rotating discs, submerged aerated filters or membrane bioreactor plants require less space. The advantage of subsurface flow constructed wetlands compared to those technologies

2544-401: The treatment wetlands the effluent is mixed with water returning from the enhancement marshes. Wild bird feces contain coliform bacteria similar to those found in human sewage. Recreational access is limited to areas where effluent has received secondary treatment and disinfection. Wetland plants use the energy of sunlight to produce five to ten times as much carbohydrate biomass per acre as

2597-404: The volume of effluent discharged from the wetland treatment system to as much as 16.5 million US gallons (62,000 m) per day. National Pollutant Discharge Elimination System regulations require monthly average effluent concentrations of biochemical oxygen demand and of total suspended solids to be no greater than 30 mg/L, with an additional requirement for removal of 85 percent of

2650-500: The wastewater passes through a gravel and more rarely sand medium on which plants are rooted. A gravel medium (generally limestone or volcanic rock lavastone ) can be used as well (the use of lavastone will allow for a surface reduction of about 20% over limestone) is mainly deployed in horizontal flow systems though it does not work as efficiently as sand (but sand will clog more readily). Constructed subsurface flow wetlands are meant as secondary treatment systems which means that

2703-413: The wastewater) to nitrite ( NO 2 ), and then nitrite is oxidized to nitrate ( NO 3 ). Denitrification is the biochemical reduction of oxidized nitrogen anions, nitrate and nitrite to produce the gaseous products nitric oxide (NO), nitrous oxide ( N 2 O ) and nitrogen gas ( N 2 ), with concomitant oxidation of organic matter. The end product, N 2 , and to a lesser extent

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2756-637: The water is exposed to direct sunlight. The soil layer below the water is anaerobic but the roots of the plants release oxygen around them, this allows complex biological and chemical reactions. Pacific Flyway The Pacific Flyway is a major north-south flyway for migratory birds in the Americas, extending from Alaska to Patagonia . Every year, migratory birds travel some or all of this distance both in spring and in fall, following food sources, heading to breeding grounds, or travelling to overwintering sites. Any given bird species travels roughly

2809-451: The wetland system. Plants also increase soil or other root-bed medium hydraulic conductivity. As roots and rhizomes grow they are thought to disturb and loosen the medium, increasing its porosity, which may allow more effective fluid movement in the rhizosphere. When roots decay they leave behind ports and channels known as macropores which are effective in channeling water through the soil. Constructed wetlands have been used extensively for

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