Industrial wastewater contains number of impurities but the heavy metal present in it is harmful for surface water, ground water and soil. Constructed Wetland are considered as natural system with greater efficiency to treat industrial wastewater. Tidal flow constructed wetlands as a type of 4th generation wetland systems for biological wastewater treatment. This study reports the removal of copper from synthetic wastewater using tidal flow constructed wetland. This study was carried out on laboratory scale tidal flow constructed wetland system of dimension 35cm x 35cm x 120cm.
A constructed wetland system, consisting of pair of cells operated in tidal flow for detention period of 7 days. The bed of cell arranged in layers with different media size, typha species was used for vegetation. Copper removal was observed to be 89% in soil layer, 80% in course aggregate layer respectively for detention period of 7 days.
Industrialization has become an important factor to the development of a country’s economy, through the establishment of plants and factories.
The waste or by-products discharged from them are severely disastrous to the environment consists various kind of contaminant which contaminate the surface water, ground water and soil. The contaminant from the discharge is directly related to the nature of the industry. For example, in textile industry, the discharge is usually high chemical oxygen demand (COD), biochemical oxygen demand (BOD) and color paint, tannery industry is on the other hand, produces discharges which have high concentration of metal. There is a technology, which has been recognized and accepted as a creative, cost-effective and environmentally friendly system when compared to the expensive conventional treatment systems (Xinxi Fu, et.
al.,2008). Wetlands are considered today as natural systems with great ecological significance which provide habitat for numerous species and support their life. It was gradually realized that natural wetlands had always been capable of providing water purification and improving water quality, at least up until the point where industrial contamination had become so intensive (Alexandros I. Stefanakis,2015).
Constructed wetlands are engineered systems that have been designed and constructed to utilise the natural processes involving wetland vegetation, soils, and the associated microbial assemblages to assist in treating wastewaters. They are designed to take advantage of many of the same processes that occur in natural wetlands, but do so within a more controlled environment (Jan Vymazal et.al; 2006).Constructed wetlands are artificial wastewater treatment systems consisting of shallow (usually less than 1 m deep) ponds or channels which have been planted with aquatic plants, and which rely upon natural microbial, biological, physical and chemical processes to treat wastewater. They typically have impervious clay or synthetic liners, and engineered structures to control the flow direction, liquid detention time and water level. Depending on the type of system, they may or may not contain an inert porous media such as rock, gravel or sand (EPA, 2000). The constructed wetlands have evolved into a reliable wastewater treatment technology for various types of wastewater. The classification of constructed wetlands is based on: the vegetation type (emergent, submerged, floating leaved, free-floating); hydrology (free water surface and subsurface flow); and subsurface flow wetlands can be further classified according to the flow direction (vertical or horizontal). In order to achieve better treatment performance, namely for nitrogen, various types of constructed wetlands could be combined into hybrid systems.
Ina Weinheimer (2015) explain Tidal flow artificial wetlands (TFAW) as a type of 4th generation (or intensified) wetland systems for biological wastewater treatment that are designed to copy the processes of natural tidal wetlands. The Tidal Flow Wetland Living Machine incorporates a series of wetland cells, or basins, filled with special gravel that promotes the development of micro-ecosystems. Tidal flow systems employ two or more flood and drain cycles per day within the wetland bed. These highly flexible cells may be integrated into exterior landscaping or built into a building or greenhouse. As water moves through the system, the cells are alternately flooded and drained to create multiple tidal cycles each day, much like natural wetlands, resulting in high quality reusable water. The micro-ecosystems within the cells efficiently remove nutrients and solids from the wastewater, resulting in high quality effluent. The final polishing stage, which involves filtration and disinfection, leaves water crystal clear and ready for reuse.
A TFAW operates by continually filling and draining the wetland cell with wastewater. This cycle of filling and draining introduces additional oxygen to the wetland cell. With this engineered CW vastly improved aeration and hence outstanding total nitrogen removal compared to traditional wetland systems is possible. Early research of tidal flow wetlands was done in the late 1990s and TFAWs were defined by having a fill and drain cycle of less than a day. A tidal flow wetland was created with different stages of wetland cells which were operated in series. The water that filled the first stage was drained to the next stage and so on.
Tidal flow wetland system was fabricated; the constructed wetland units made up of acrylic having dimensions 35cm x 35cm x 120cm. The model was set up with overall capacity of 200 L. The system comprises of two wetland units having different layer of aggregates, coarse sand, fine sand and soil with typha. The inlet and outlet arrangements were provided at bottom of units at both ends, detail of the setup is shown in fig 3. The fill and drain cycle in bed for various detention periods were achieved by programming, electrically operated solenoid valve and moisture sensors. Each wetland cell is 1.2 m in depth, different layer of filter media are provided within cell. Bottom layer consists of coarse gravel having depth of 7.5cm; above this layer fine aggregate is placed having depth 7.5 cm. After placing the fine aggregate the depth of 10cm of fine sand is provided. The top layer consists of soil up-to a depth of 70cm, typha is placed in unit which is collected from local stream.
Industrial wastewater sample was collected from the Nagpur (Butibori) MIDC based on the results of wastewater characteristic, the synthetic wastewater was prepared with known concentration of copper, to find the concentration of copper in treated wastewater calibration curve was prepared for the range of 1 mg/l to 10 mg/l. The prepared wastewater filled in storage tank. The flow is regulated by gravity and electrically operated solenoid valve. In step first the influent from storage tank is allow to pass through the wetland cell 1 with constant rate maintain by using regulating valve. As the level of wastewater reaches to the root zone the moisture sensor detect the level. Then the inflow in cell 1 stop and the wastewater is detained for detention time required. After that the solenoid valve between the cells is open and the wastewater from cell 1 is drain out to cell
Similarly water level is detected by moisture sensor, then the inflow in cell 2 is stop and the wastewater is detained for detention time required. After that the last solenoid valve is open and treated effluent is collected at the end of cell.
Wastewater was detained for the period of 7 days in the wetland. The characteristic of the wastewater in the inlet and the characteristic of treated wastewater at the outlet were studied for the detention period 7 day for cell 1 during study, it was found that the percentage removal of copper in soil layer was in the range of 87%, percentage removal of copper in fine sand layer was in the range of 86%. Fine Aggregate layer was in the range of 82% and shows the percentage removal of copper in coarse Aggregate layer was in the range of 79%. Figure 5 shows the % removal of copper in different layers for cell 1.
For cell 2 during study, it was found that the percentage removal of copper in soil layer was in the range of 89%, percentage removal of copper in fine sand layer was in the range of 88%. Fine Aggregate layer was in the range of 85% and shows the percentage removal of copper in coarse Aggregate layer was in the range of 81%. Figure 6 shows the % removal of copper in different layers for cell 2. Removal of Copper in wastewater wetlands occur by typha uptake, soil adsorption, and precipitation. The copper that pass by the root structure tend to accumulate on the structure of the root rather than being absorbed by the typha. Wetland soils are also sources into which can trap metals.
The results of this study have shown that the tidal flow constructed wetlands are suitable alternatives for removal of copper in wastewater. The maximum percentage removal efficiency for copper was found to be in the range of 89 % in soli layer and minimum percentage removal efficiency was found to be in the range of 80 % in course aggregate layer. Metals like copper that are required for plant and animal growth but these are in small amounts. Removal of metals in wastewater wetlands occur by plant uptake, soil adsorption, and precipitation. There are some types of plants which are capable of storing large amounts of metals in plant biomass and in its roots.