Topic: Sub-surface flow constructed wetland to treat domestic wastewater Supervisor: Professor Nguyen Thi Loan Group members: Nguyen Tuan Anh Le Nam Thanh Content  Introduction  Study methodology  Study result  Discussion and Conclusion I Introduction: Constructed wetland  Wetlands: those areas that are inundated or saturated by surface or ground water at a frequency and duration sufficient to maintain saturated conditions  Constructed wetland: wetland specifically constructed for the purpose of pollution control and waste management, at a location other than existing natural wetlands I Introduction: Constructed wetland The interest in aquatic wastewater treatment systems can be attributed to three basic factors: Recognition of the natural treatment functions of aquatic plant systems and wetlands, particularly as nutrient sinks and buffering zones In the case of wetlands, emerging or renewed application of aesthetic, wildlife, and other incidental environmental benefits associated with the preservation and enhancement of wetlands Rapidly escalating costs of construction and operation associated with conventional treatment facilities I Introduction: Cost effectiveness The major cost of implementing a discharge system is for pumping treatment plant effluent to the site Once there, further wastewater treatment occurs by the application of natural processes In some cases, the wetland alternative can be the least cost advanced wastewater treatment and disposal alternative In locations where poorly drained land that is unsuitable for land application is available, wetlands can often be constructed inexpensively with minimal diking I Introduction: Two types of CWS I Introduction: Sub-surface flow wetlands The SSF type of wetland is thought to have several advantages over the FWS type Little risk of odors, exposure, or insect vectors Offer greater thermal protection in cold climates than the FWS type Greater available surface area for treatment than the FWS concept so the treatment responses may be faster for the SF type, which therefore can be smaller in area than a FWS system designed for the same wastewater conditions I Introduction: Horizontal sub-surface flow wetland The design typically consisted of a rectangular bed planted with the common reed (P australis) and lined with an impermeable membrane Mechanically pre-treated wastewater is fed in at the inlet and passes slowly through the filtration medium under the surface of the bed in a more or less horizontal path until it reached the outlet zone where it is collected before discharge via level control arrangement at the outlet During the passage of wastewater through the reed bed the wastewater makes contact with a network of aerobic, anoxic and anaerobic zones I Introduction: Horizontal sub-surface flow wetland II Study methodology  We collected data from scientific monographs  We based on Vietnam technical standard  We used some mathematical model III Study results: Outlet structures  Outlet structures in use at operational SF wetland systems include subsurface manifolds, and weir boxes or similar gated structures The perforated subsurface manifold is the most commonly used device  The use of an adjustable outlet is recommended to maintain an adequate hydraulic gradient in the bed This device can also have significant operational and maintenance benefits The surface of the bed can be flooded to encourage, development of newly planted vegetation and to suppress undesirable weeds, and the water level can be lowered in anticipation of major storm events and to provide additional thermal protection against freezing during winter operations in cold climates III Study results: Vegetation selection III Study results: Vegetation selection The Phragmites used in many European systems offer several advantages for a low maintenance treatment system They will grow and spread faster than bulrush; their roots should go deeper than cattails; and they are not a food source for muskrats and nutria which have been a problem for cattail and bulrush wetlands III Study results: BOD5 removal  The major oxygen source for the subsurface components (soil, gravel, rock) is the oxygen transmitted by the vegetation to the root zone  Organic compounds are degraded by bacteria attached to plants underground organs (root, rhizomes) and media surface III Study results: HSF design III Study results: Information  Aspect ratio = 3:1  Media=Fine gravel (Effective size=16 mm)  Root penetration = 0.6 m  Subsurface inlet  Adjustable outlet  Normal reed (Phragmites Australis) to plant III Study results: Calculation  A residential area of 1000 people Assume that person consume 150 l water/day and wastewater amount is 80% of water supply The amount of waste water is 120,000l/day III Study results: Calculation Take influent = 200 mg/l and effluent = 30 mg/l for drinking water III Study results: Calculation Use formula: Ah = Qd ( lnCo – lnCt)/KBOD5 Where: Ah = Surface flow of bed Qd = Average flow = 120 m3/d Co = Influent BOD5 = 200 mg/l Ct = Effluent BOD5 = 30 mg/l KBOD5 = Rate constant = 0.01m/d => We have Ah = 22765 m2 = 2.3 III Study results: Calculation Therefore, based on aspect ratio, if we suppose to build a rectangular wetland =>  Length = 262 m  Width = 87 m  Root penetration = 0.6 cm IV Discussion  It has a great attraction due to low cost of installation and maintenance  However, 2.3 is a large area in Vietnam situation, so we may need to consider it carefully  Also, opportunity cost is really large IV Conclusion IV Conclusion  Aspect ratio = 3:1  Media=Fine gravel (Effective size=16 mm)  Root penetration = 0.6 m  Subsurface inlet  Adjustable outlet  Normal reed (Phragmites Australis) to plant  Area needed = 2.3 ha, l = 263m, w = 87m Reference  Reddy, K.R., and W.F DeBusk Nutrient Removal Potential of Selected Aquatic Macrophytes J.Environ Qual 14:459-462, 1985  Zirschky, J.O., and S.C Reed The Use of Duckweed for Wastewater Treatment JWPCF 60:1253-1258, 1988  Hayes, T.D., H.R Isaacson, K.R Reddy, D.P Chynoweth, and R Biljetina Water Hyacinth Systems for Water Treatment In: Reddy, pp 121-139, 1987  Reed, S.C., and R.K Bastian Aquaculture Systems for Wastewater Treatment: An Engineering Assessmenf U.S EPA Office of Water Program Operations, EPA 430/9-80-007, 1980  Leslie M 1983 Water Hyacinth Wastewater 11 Treatment Systems: Opportunifies and Constraints in Cooler Climates U.S Environmental Protection Agency, EPA/600/2-83-095, Washington D.C  QCVN 14:2008/BTNMT Thank you for attention [...]... and subsurface installations In one case the subsurface- manifold utilized two to three valved outlets in the cell A surface manifold developed by TVA uses multiple, adjustable outlet ports This allows the operator to make adjustments for differential settlement of the pipe and to maintain uniform distribution of the wastewater The proponents of subsurface inlet manifolds claim they are necessary to. .. design of SF wetland systems, since the maximum potential hydraulic gradient is related to the available depth of the bed divided by the length of the flow path  The bottom of the bed could be flat or with a very slight slope to ensure drainage, when required However, because of the hydraulic gradient requirements, the aspect ratio will have to be relatively low (in the range of 0.4:1 to 3:I ) to provide... conditions should be closer to laminar When turbulent flow occurs in the coarser media listed in Table 5, the “effective” hydraulic conductivity will be less than the values listed in the table III Study results: Media It is, however, necessary to provide a large safety factor against these contingencies and adoption of an approach similar to that used in the design of land treatment systems (30) is... for Water Treatment In: Reddy, pp 121-139, 1987  Reed, S.C., and R.K Bastian Aquaculture Systems for Wastewater Treatment: An Engineering Assessmenf U.S EPA Office of Water Program Operations, EPA 430/9-80-007, 1980  Leslie M 1983 Water Hyacinth Wastewater 11 Treatment Systems: Opportunifies and Constraints in Cooler Climates U.S Environmental Protection Agency, EPA/600/2-83-095, Washington D.C ... toward the use of larger sizes of rock is believed due to the impression created by the surface flow conditions on many of the early systems  However, the use of smaller rock sizes has a number of advantages in that there is more surface area available on the media for treatment, and the smaller void spaces are more compatible with development of the roots and rhizomes of the vegetation, and the flow. .. rock surfaces and resulting clogging adjacent to a surface manifold III Study results: Outlet structures  Outlet structures in use at operational SF wetland systems include subsurface manifolds, and weir boxes or similar gated structures The perforated subsurface manifold is the most commonly used device  The use of an adjustable outlet is recommended to maintain an adequate hydraulic gradient in... discharge should ensure a more than adequate safety factor in the hydraulic design of the system These two limits will also have the practical effect of limiting the aspect ratio of the bed to  Length = 262 m  Width = 87 m  Root penetration = 0.6 cm IV Discussion  It has a great attraction due to low cost of installation and maintenance  However, 2.3 ha is a large area in Vietnam situation, so we may need to consider it carefully  Also, opportunity cost is really large IV Conclusion... size=16 mm)  Root penetration = 0.6 m  Subsurface inlet  Adjustable outlet  Normal reed (Phragmites Australis) to plant  Area needed = 2.3 ha, l = 263m, w = 87m Reference  Reddy, K.R., and W.F DeBusk Nutrient Removal Potential of Selected Aquatic Macrophytes J.Environ Qual 14:459-462, 1985  Zirschky, J.O., and S.C Reed The Use of Duckweed for Wastewater Treatment JWPCF 60:1253-1258, 1988  Hayes,