Jan Vymazal

Constructed Wetlands for Wastewater Treatment: Five Decades of Experience†

The first experiments on the use of wetland plants to treat wastewaters were carried out in the early 1950s by Dr. Käthe Seidel in Germany and the first full-scale systems were put into operation during the late 1960s. Since then, the subsurface systems have been commonly used in Europe while free water surface systems have been more popular in North America and Australia. During the 1970s and 1980s, the information on constructed wetland technology spread slowly. But since the 1990 s the technology has become international, facilitated by exchange among scientists and researchers around the world. Because of the need for more effective removal of ammonia and total nitrogen, during the 1990 s and 2000s vertical and horizontal flow constructed wetlands were combined to complement each other to achieve higher treatment efficiency. Today, constructed wetlands are recognized as a reliable wastewater treatment technology and they represent a suitable solution for the treatment of many types of wastewater.

The use of sub-surface constructed wetlands for wastewater treatment in the Czech Republic: 10 years experience

Wetlands have been intensively studied in the Czech Republic for more than 30 years, but the first full-scale constructed wetland (CW) for wastewater treatment was built in the Czech Republic in 1989. By the end of 1999, about 100 CWs were put in operation. The majority of the systems are horizontal subsurface flow (HSF) CWs and are designed for the secondary treatment of domestic or municipal wastewater. The size of CWs ranges between 18 and 4500 m2 and between 4 and 1100 population equivalent (PE). Most frequently used filtration media are gravel and crushed rock with size fractions of 4/8 and 8/16 mm and Phragmites australis is the most commonly used plant. The treatment efficiency is high in terms of BOD5 (88.0% for vegetated beds) and suspended solids (84.3% for vegetated beds). The removal of nutrients is lower for vegetated beds, and averages 51 and 41.6% for total phosphorus and total nitrogen, respectively.

Wastewater treatment in constructed wetlands with horizontal sub-surface flow

The Authors.- Preface.- Introduction.- Transformation Mechanisms Of Major Nutrients And Metals In Wetlands.- Wetland Plants.- Types Of Constructed Wetlands For Wastewater Treatment.- Horizontal Flow Constructed Wetlands. Types Of Wastewater Treated In HF Constructed Wetlands.- The Use Of HF Constructed Wetlands In The World.- References.-Suggested Reading.- Subject Index.

Plants used in constructed wetlands with horizontal subsurface flow: a review

The presence of macrophytes is one of the most conspicuous features of wetlands and their presence distinguishes constructed wetlands from unplanted soil filters or lagoons. The macrophytes growing in constructed wetlands have several properties in relation to the treatment process that make them an essential component of the design. However, only several roles of macrophytes apply to constructed wetlands with horizontal subsurface flow (HF CWs). The plants used in HF CWs designed for wastewater treatment should therefore: (1) be tolerant of high organic and nutrient loadings, (2) have rich belowground organs (i.e. roots and rhizomes) in order to provide substrate for attached bacteria and oxygenation (even very limited) of areas adjacent to roots and rhizomes and (3) have high aboveground biomass for winter insulation in cold and temperate regions and for nutrient removal via harvesting. The comparison of treatment efficiency of vegetated HF CWs and unplanted filters is not unanimous but most studies have shown that systems with plants achieve higher treatment efficiency. The vegetation has mostly a positive effect, i.e. supports higher treatment efficiency, for organics and nutrients like nitrogen and phosphorus. By far the most frequently used plant around the globe is Phragmites australis (Common reed). Species of the genera Typha (latifolia, angustifolia, domingensis, orientalis and glauca) and Scirpus (e.g. lacustris, validus, californicus and acutus) spp. are other commonly used species. In many countries, and especially in the tropics and subtropics, local plants including ornamental species are used for HF CWs.

The use of hybrid constructed wetlands for wastewater treatment with special attention to nitrogen removal: A review of a recent development

The hybrid systems were developed in the 1960s but their use increased only during the late 1990 s and in the 2000s mostly because of more stringent discharge limits for nitrogen and also more complex wastewaters treated in constructed wetlands (CWs). The early hybrid CWs consisted of several stages of vertical flow (VF) followed by several stages of horizontal flow (HF) beds. During the 1990 s, HF-VF and VF-HF hybrid systems were introduced. However, to achieve higher removal of total nitrogen or to treat more complex industrial and agricultural wastewaters other types of hybrid constructed wetlands including free water surface (FWS) CWs and multistage CWs have recently been used as well. The survey of 60 hybrid constructed wetlands from 24 countries reported after 2003 revealed that hybrid constructed wetlands are primarily used on Europe and in Asia while in other continents their use is limited. The most commonly used hybrid system is a VF-HF constructed wetland which has been used for treatment of both sewage and industrial wastewaters. On the other hand, the use of a HF-VF system has been reported only for treatment of municipal sewage. Out of 60 surveyed hybrid systems, 38 have been designed to treat municipal sewage while 22 hybrid systems were designed to treat various industrial and agricultural wastewaters. The more detailed analysis revealed that VF-HF hybrid constructed wetlands are slightly more efficient in ammonia removal than hybrid systems with FWS CWs, HF-VF systems or multistage VF and HF hybrid CWs. All types of hybrid CWs are comparable with single VF CWs in terms of NH4-N removal rates. On the other hand, CWs with FWS units remove substantially more total nitrogen as compared to other types of hybrid constructed wetlands. However, all types of hybrid constructed wetlands are more efficient in total nitrogen removal than single HF or VF constructed wetlands.

Development of constructed wetlands in performance intensifications for wastewater treatment: a nitrogen and organic matter targeted review.

The knowledge on the performance enhancement of nitrogen and organic matter in the expanded constructed wetlands (CWs) with various new designs, configurations, and technology combinations are still not sufficiently summarized. A comprehensive review is accordingly necessary for better understanding of this state-of-the-art-technology for optimum design and new ideas. Considering that the prevailing redox conditions in CWs have a strong effect on removal mechanisms and highly depend on wetland designs and operations, this paper reviews different operation strategies (recirculation, aeration, tidal operation, flow direction reciprocation, and earthworm integration), innovative designs, and configurations (circular-flow corridor wetlands, towery hybrid CWs, baffled subsurface CWs) for the intensifications of the performance. Some new combinations of CWs with technologies in other field for wastewater treatment, such as microbial fuel cell, are also discussed. To improve biofilm development, the selection and utilization of some specific substrates are summarized. Finally, we review the advances in electron donor supply to enhance low C/N wastewater treatment and in thermal insulation against low temperature to maintain CWs running in the cold areas. This paper aims to provide and inspire some new ideas in the development of intensified CWs mainly for the removal of nitrogen and organic matter. The stability and sustainability of these technologies should be further qualified.

Removal of organics in constructed wetlands with horizontal sub-surface flow: A review of the field experience

Constructed wetlands with horizontal sub-surface flow (HF CWs) have successfully been used for treatment various types of wastewater for more than four decades. Most systems have been designed to treat municipal sewage but the use for wastewaters from agriculture, industry and landfill leachate in HF CWs is getting more attention nowadays. The paper summarizes the results from more than 400 HF CWs from 36 countries around the world. The survey revealed that the highest removal efficiencies for BOD(5) and COD were achieved in systems treating municipal wastewater while the lowest efficiency was recorded for landfill leachate. The survey also revealed that HF CWs are successfully used for both secondary and tertiary treatment. The highest average inflow concentrations of BOD(5) (652 mg l(-1)) and COD (1865 mg l(-1)) were recorded for industrial wastewaters followed by wastewaters from agriculture for BOD(5) (464 mg l(-1)) and landfill leachate for COD (933 mg l(-1)). Hydraulic loading data reveal that the highest loaded systems are those treating wastewaters from agriculture and tertiary municipal wastewaters (average hydraulic loading rate 24.3 cm d(-1)). On the other hand, landfill leachate systems in the survey were loaded with average only 2.7 cm d(-1). For both BOD(5) and COD, the highest average loadings were recorded for agricultural wastewaters (541 and 1239 kg ha(-1) d(-1), respectively) followed by industrial wastewaters (365 and 1212 kg ha(-1) d(-1), respectively). The regression equations for BOD(5) and COD inflow/outflow concentrations yielded very loose relationships. Much stronger relationships were found for inflow/outflow loadings and especially for COD. The influence of vegetation on removal of organics in HF CWs is not unanimously agreed but most studies indicated the positive effect of macrophytes.

RESPONSE OF EVERGLADES PLANT COMMUNITIES TO NITROGEN AND PHOSPHORUS ADDITIONS

Nitrogen(N) and phosphorus(P) were applied to sawgrass (Cladium jamaicense), mixed sawgrass-cattail (Typha domingensis), and slough (shallow water communities dominated byUtricularia spp.,Eleocharis spp., andPanicum spp.) communities in the Everglades for two years to test for N or P limitations and to investigate the plant community response. Nitrogen (as NH4+) and P (as PO43−) were applied singly and in combination at rates of 0.6, 1.2, and 4.8 g P · m−2·yr−1 and 5.6 and 22.4 g N·m−2·yr−1. Plant response was quantified by measuring aboveground standing crop biomass and tissue N and P concentrations each year. Everglades plant communities are P limited. Phosphorus additions at the highest rate (4.8 g·m2-yr−1) resulted in increased P uptake and biomass production by emergent vegetation. Tissue P concentrations of sawgrass and cattail were significantly higher in response to the high P (329–684 μg·g−1) and high N+P (371–594 μg·g−1) treatments (control=94–256 μg·g−1) in both years after the initiation of nutrient additions. Aboveground biomass also increased in response to the highest rat of P at the sawgrass (2618–3284 g/m2; control=1158 g/m2) and mixed (1387–1407 g/m2; control=502 g/m2) communities, but only after two years. At the slough site, the high P and high N+P treatments resulted in a significant decline of theUtricularia periphyton mat after only one year of nutrient additions (16–74 g·m2−; control=364 g·m−2). During the second year, the macroalga,Chara, expanded in these plots and replaced the floating mat as the major nonemergent component of the plant community. In all three communities, P additions at the highest rate resulted in a significant increase in bicarbonate-extractable and total soil P (0–5 cm depth). There was no effect of N additions on biomass production, nutrient uptake, or N enrichment of the peat during the two-year study. We observed no significant change in macrophyte species diversity or expansion of cattail in plots receiving nutrient additions during the two year study. However, the decline of theUtricularia-periphyton mat (and the subsequent increase inChara) in slough plots receiving 4.8 g P·m−2·yr−1 may serve as an early indicator of P enrichment in the Everglades.

The use of constructed wetlands for removal of pesticides from agricultural runoff and drainage: A review

Pesticides are used in modern agriculture to increase crop yields, but they may pose a serious threat to aquatic ecosystems. Pesticides may enter water bodies through diffuse and point sources, but diffuse sources are probably the most important. Among diffuse pollution, surface runoff and erosion, leaching and drainage represent the major pathways. The most commonly used mitigation techniques to prevent pesticide input into water bodies include edge-of-field and riparian buffer strips, vegetated ditches and constructed wetlands. The first attempts to use wetland macrophytes for pesticide removal were carried out as early as the 1970s, but only in the last decade have constructed wetlands for pesticide mitigation become widespread. The paper summarizes 47 studies in which removal of 87 pesticides was monitored. The survey revealed that constructed wetlands with free water surface are the most commonly used type. Also, it has been identified that removal of pesticides is highly variable. The results of the survey revealed that the highest pesticide removal was achieved for pesticides of the organochlorine, strobilurin/strobin, organosphosphate and pyrethroid groups while the lowest removals were observed for pesticides of the triazinone, aryloxyalkanoic acid and urea groups. The removal of pesticides generally increases with increasing value of KOC but the relationship is not strong.

Removal of trace elements in three horizontal sub-surface flow constructed wetlands in the Czech Republic.

Between March 2006 and June 2008 removal of 34 trace elements was measured on a monthly basis at three horizontal-flow constructed wetlands in the Czech Republic designed to treat municipal wastewater. In general, the results indicated a very wide range of removal efficiencies among studied elements. The highest degree of removal (average of 90%) was found for aluminum. High average removal was also recorded for zinc (78%). Elements removed in the range of 50-75% were uranium, antimony, copper, lead, molybdenum, chromium, barium, iron and gallium. Removal of cadmium, tin, mercury, silver, selenium and nickel varied between 25 and 50%. Low retention (0-25%) was observed for vanadium, lithium, boron, cobalt and strontium. There were two elements (manganese and arsenic) for which average outflow concentrations were higher compared to inflow concentrations. Reduced manganese compounds are very soluble and therefore they are washed out under anaerobic conditions.