Spatial distribution of metals in the constructed wetlands.

Investigation of the spatial distribution of metals was conducted for two constructed wetlands used as tertiary treatment in Chia Nan University of Pharmacy and Science (CNU) and Metal Processing Industries (MPI) located in Tainan, Taiwan. These two distinguished sites were selected to compare the distribution of metals for constructed wetlands treating different types of wastewater. Along the distance, samples of water, sediment, and macrophytes were analyzed for metals including Al, Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn. Additionally, measurements of water quality including temperature, pH, EC, ORP, DO, TSS, BOD, COD, and turbidity were performed. Results show that, at CNU, wastewater contained higher organic consititute (BOD 29.3 +/- 11.7 mg/, COD 46.7 +/- 33.6 mg/L) with low metals content. Wastewater at MPI contained low level of organic consititute (BOD 7.1 +/- 3.3 mg/L, and COD 66.0 +/- 56.5 mg/L) and higher metals content. Metals distribution of both sites showed similar results where metals in the sediments in the inlet zone have greater concentrations than other areas. The constructed wetlands can remove Cd, Cu, Ni, Pb, and Zn. However, there was no removal of Al, Cr, Fe, and Mn. A distance along the constructed wetlands had no effect on metal concentrations in macrophyte and water.

Plant growth and the performance of mangrove wetland microcosms for mariculture effluent depuration.

This study established wetland microcosms that were either unplanted or planted in monoculture with native mangrove species in Taiwan (Avicennia marina, Rhizophora stylosa, and Lumnitzera racemosa) for the purpose of receiving high-salinity mariculture effluents; additionally, the microcosms operated at different hydraulic retention times (HRTs). Plant growth and the performance of the microcosms with respect to pollutant removal were investigated. The results showed that seedlings of all three mangrove species survived and grew sufficiently well under continuous flooding. The presence of mangroves consistently improved SS, BOD(5), and TP removal, particularly under short HRT conditions. The mangrove microcosms removed pollutants from the mariculture effluents with efficiencies of 5.7-27.1% (SS), 4.9-36.3% (BOD(5)), 18.7-29.9% (TP), 21.2-49.8% (NH(4)-N), and 5.4-37.7% (NO(x)-N). A. marina and L. racemosa were more tolerant of continuous flooding than R. stylosa. However, no species displayed consistently superior performance in decreasing all pollutant-related parameters investigated. For all pollutants, microcosms operating at a 2-d HRT exhibited a higher removal efficiency than those operating at a 0.5-d HRT.

Constructed wetlands for water pollution management of aquaculture farms conducting earthen pond culture.

This study established farm-scale constructed wetlands integrated to shrimp ponds, using existing earthern pond areas, with a wetland-to-pond ratio of only 0.086 for shrimp culture. The constructed wetlands were used as practice for aquaculture water and wastewater treatment, to regulate the water quality of shrimp ponds and manage pollution from pond effluents. The results of water quality monitoring for influent and effluent showed that constructed wetlands significantly reduced total suspended solids (59 to 72%), turbidity (55 to 65%), chlorophyll a (58 to 72%), 5-day biochemical oxygen demand (29 to 40%), and chemical oxygen demand (13 to 24%) from pond water. The wetland treatment sufficiently regulated water quality of the recirculating shrimp pond, which was significantly (p < 0.05) better than that in a control shrimp pond, without the connection of constructed wetlands. Furthermore, the wetland-treated effluent satisfied the national effluent standards for aquaculture farms (R.O.C. Environmental Protection Administration, 2007). Accordingly, wetland treatment applications were proposed to implement the best management practices to reduce pollution from aquaculture farms in Taiwan.

Nitrate removal from groundwater using constructed wetlands under various hydraulic loading rates.

This study set up two flow-through pilot-scale constructed wetlands with the same size but various flow patterns (free water surface flow (FWS) and subsurface flow (SSF)) to receive a nitrate-contaminated groundwater. The effects of hydraulic loading rate (HLR) on nitrate removal as well as the difference in performance between the various types of wetlands were investigated. Nitrate removal rates of both wetlands increased with increasing HLR until a maximum value was reached. The maximum removal rates, occurred at HLR of 0.12 and 0.07 m d(-1), were 0.910 and 1.161 g N m(-2)d(-1) for the FWS and SSF wetland, respectively. After the maximum values were reached, further increasing HLR led to a considerable decrease in nitrate removal rate. Nitrate removal efficiencies remained high (>85%) and effluent nitrate concentrations always satisfied drinking water standard (<10mg NO3-NL(-1)) when HLR did not exceed 0.04 m d(-1) for both FWS and SSF wetlands. The first-order nitrate removal rate constant tends to decrease with increasing HLRs. The FWS wetland provided significantly higher (p<0.05) organic carbon in effluent than the SSF wetland, while the SSF wetland exhibited significantly (p<0.05) lower effluent DO than the FWS wetland. However, there was no significant difference (p>0.05) in nitrate removal performance between the two types of constructed wetlands in this study except in one trial operating at HLR of 0.06-0.07 m d(-1).

Nitrate removal and denitrification affected by soil characteristics in nitrate treatment wetlands.

Several small-scale surface flow constructed wetlands unplanted and planted (monoculture) with various macrophytes (Phragmites australis, Typha orientalis, Pennisetum purpureum, Ipomoea aquatica, and Pistia stratiotes) were established to continuously receive nitrate-contaminated groundwater. Soil characteristics and their effects on nitrate removal and soil denitrification were investigated. The results showed that planted wetland cells exhibited significantly higher (P < 0.05) nitrate removal efficiencies (70-99%) and soil denitrification rates (3.78-15.02 microg N2O-N/g dry soil/h) than an unplanted covered wetland cell (1%, 0.11 microg N2O-N/g/h). However, the unplanted uncovered wetland cell showed a nitrate removal efficiency (55%) lower than but a soil denitrification rate (9.12 microg N2O-N/g/h) comparable to the planted cells. The nitrate removal rate correlated closely and positively with the soil denitrification rate for the planted cells, indicating that soil denitrification is an important process for removing nitrate in constructed wetlands. The results of nitrogen budget revealed that around 68.9-90.7% of the overall nitrogen removal could be attributed to the total denitrification. The soil denitrification rate was found to correlate significantly (P < 0.01) with the extractable organic carbon, organic matter, and in situ-measured redox potential of wetland soil, which accordingly were concluded as suitable indicators of soil denitrification rate and nitrate removal rate in nitrate treatment wetlands.

Performance of a constructed wetland-pond system for treatment and reuse of wastewater from campus buildings.

A constructed wetland-pond system consisting of two free-water-surface-flow (FWS) wetland cells, a scenic pond, and a slag filter in series was used for reclamation of septic tank effluent from a campus building. The results show that FWS wetlands effectively removed major pollutants under a hydraulic loading rate between 2.1 and 4.2 cm/d, with average efficiencies ranging from 74 to 78% for total suspended solids, 73 to 88% for 5-day biochemical oxygen demand, 42 to 49% for total nitrogen, 34 to 70% for total phosphorous, 64 to 79% for total coliforms, and 90 to 99.9% for Escherichia coli. After passing through the scenic pond and slag filter, the reclaimed water was used for landscape irrigation. There were a variety of ornamental plants and aquatic animals established in the second FWS cell and scenic pond with good water quality, thus enhancing landscape and ecology amenity in campuses.

Performance of a constructed wetland treating intensive shrimp aquaculture wastewater under high hydraulic loading rate.

A water treatment unit, mainly consisting of free water surface (FWS) and subsurface flow (SF) constructed wetland cells, was integrated into a commercial-scale recirculating aquaculture system for intensive shrimp culture. This study investigated performance of the treatment wetlands for controlling water quality. The results showed that the FWS-SF cells effectively removed total suspended solids (55-66%), 5-day biochemical oxygen demand (37-54%), total ammonia (64-66%) and nitrite (83-94%) from the recirculating water under high hydraulic loading rates (1.57-1.95 m/day). This led to a water quality that was suitable for shrimp culture and effluent that always satisfied the discharge standards. The area ratios of wetlands to culture tank being demonstrated (0.43) and calculated (0.096) in this study were both significantly lower than the reported values. Accordingly, a constructed wetland was technically and economically feasible for managing water quality of an intensive aquaculture system.

Seasonal effect on ammonia nitrogen removal by constructed wetlands treating polluted river water in southern Taiwan.

A pilot-scale constructed wetland (CW) system, combining a free water surface wetland and a subsurface wetland in series, was used to purify highly polluted river water. The concentrations of constituents varied seasonally. The effects of season-dependent parameters, such as temperature, mass loading rate and inflow salinity, on the removal of ammonia nitrogen (AN) in the wetland system were examined at a constant hydraulic loading rate, based on data from June 1998 to February 2000. AN removal of the CW varied cyclically with the seasons. The removal efficiency and the first-order volumetric removal rate constant (k(V)) increased exponentially with water temperature, yielding a high temperature coefficient (theta). However, the mass removal rate decreased exponentially as temperature increased. These contradictory results made the actual effect of temperature uncertain. The inhibition of high water salinity on AN removal was also unclear because k(V) (as well as k(V20)) and mass removal rate were inversely proportional to salinity. However, mass loading rate (MLR) predominantly affected both the removal efficiency and the mass removal rate of AN, both of which were factors that explicitly determined seasonality. A power equation, k(V20)' alpha MLR(-n), was proposed to correct the variation of the mass loading rate in estimating k(V) and thus in designing a constructed wetland.

The potential use of constructed wetlands in a recirculating aquaculture system for shrimp culture.

A pilot-scale constructed wetland unit, consisting of free water surface (FWS) and subsurface flow (SF) constructed wetlands arranged in series, was integrated into an outdoor recirculating aquaculture system (RAS) for culturing Pacific white shrimp (Litopenaeus vannamei). This study evaluated the performance of the wetland unit in treating the recirculating wastewater and examined the effect of improvement in water quality of the culture tank on the growth and survival of shrimp postlarvae. During an 80-day culture period, the wetland unit operated at a mean hydraulic loading rate of 0.3 m/day and effectively reduced the influent concentrations of 5-day biochemical oxygen demand (BOD5, 24%), suspended solids (SS, 71%), chlorophyll a (chl-a, 88%), total ammonium (TAN, 57%), nitrite nitrogen (NO2-N, 90%) and nitrate nitrogen (NO3-N, 68%). Phosphate (PO4-P) reduction was the least efficient (5.4%). The concentrations of SS, Chl-a, turbidity and NO3-N in the culture tank water in RAS were significantly (P

Effects of macrophytes and external carbon sources on nitrate removal from groundwater in constructed wetlands.

Several microcosm wetlands unplanted and planted with five macrophytes (Phragmites australis, Commelina communis, Penniserum purpureum, Ipomoea aquatica, and Pistia stratiotes) were employed to remove nitrate from groundwater at a concentration of 21-47 mg NO3-N/l. In the absence of external carbon, nitrate removal rates ranged from 0.63 to 1.26 g NO3-N/m2/day for planted wetlands. Planted wetlands exhibited significantly greater nitrate removal than unplanted wetlands (P<0.01), indicating that macrophytes are essential to efficient nitrate removal. Additionally, a wetland planted with Penniserum showed consistently higher nitrate removal than those planted with the other four macrophytes, suggesting that macrophytes present species-specific nitrate removal efficiency possibly depending on their ability to produce carbon for denitrification. Although adding external carbon to the influent improved nitrate removal, a significant fraction of the added carbon was lost via microbial oxidation in the wetlands. Planting a wetland with macrophytes with high productivity may be an economic way for removing nitrate from groundwater. According to the harvest result, 4-11% of nitrogen removed by the planted wetland was due to vegetation uptake, and 89-96% was due to denitrification.

Removal of solids and oxygen demand from aquaculture wastewater with a constructed wetland system in the start-up phase.

A pilot-scale, constructed wetland system consisting of a free water surface (FWS) and a subsurface flow (SF) wetland operated in series was set up for treating aquaculture farm wastewater. This study examined the system start-up phenomena and evaluated its performance in removing suspended solids, algae, and chemical oxygen demand (COD) under various hydraulic loading rates (1.8 to 13.5 cm/d). The SF wetland achieved stable effluent qualities without an adaptation period, while the FWS wetland required approximately 5 months to reach consistent removal levels for suspended solids and algae. Macrophyte density was a critical factor affecting the reduction of suspended solids and chlorophyll for the FWS wetland, but not for the SF wetland. Suspended solids removals in both of the wetlands and the combined system (47 to 86%) decreased significantly as the hydraulic loading rate increased, strongly following the first-order mass-decrease equation. Phytoplankton solids (biomass and detritus) were a primary source of suspended solids in the aquaculture wastewater. Both chlorophyll reduction (76 to 95%) and COD removal (25 to 55%) in the constructed wetland system were apparently not affected by hydraulic loading. While algae died out because of limited sunlight in both wetlands, algae detritus probably still contributed fine particles that were difficult to remove from the water by either filtering or settling out. Removed suspended solids did not result in the increase of COD and nutrients, indicating that further solids stabilization occurred in the wetland system.

Microcosm wetlands for wastewater treatment with different hydraulic loading rates and macrophytes.

Constructed wetlands (CW) usually require large land areas for treating wastewater. This study evaluated the feasibility of applying CW with less land requirement by operating a group of microcosm wetlands at a hydraulic retention time (HRT) of less than 4 d in southern Taiwan. An artificial wastewater, simulating municipal wastewater containing 200 mg L(-1) of chemical oxygen demand (COD), 20 mg L(-1) of NH4+-N (AN), and 20 mg L(-1) of PO4(3-)-P (OP), was the inflow source. Three emergent plants [reed, Phragmites australis (Cav.) Trin. ex Steud.; water primrose, Ludwigia octovalvis (Jacq.) P.H. Raven; and dayflower, Commelina communis L.] and two floating plants [water spinach, Ipomoea aquatica Forssk.; and water lettuce, Pistia stratiotes L.] plants were tested. The planted systems showed more nutrient removal than unplanted systems; however, the type of macrophytes in CW did not make a major difference in treatment. At the HRTs of 2 to 4 d, the planted system maintained greater than 72,80, and 46% removal for COD, AN, and OP, respectively. For AN and OP removal, the highest efficiencies occurred at the HRT of 3 d, whereas maximum removal rates for AN and OP occurred at the HRT of 2 d. Both removal rates and efficiencies were reduced drastically at the HRT of 1 d. Removals of COD, OP, and AN followed first-order reactions within the HRTs of 1 to 4 d. The efficient removals of these constituents obtained with HRT between 2 and 4 d indicated the possibility of using a CW system for wastewater treatment with less land requirement.