Treatment of Wastewater Using a Constructed Wetland System (Four stages vertical flow sub-surface constructed wetland)

Abstract Constructed wetlands system is an innovative and inexpensive treatment approach that has thepotential to treat organic and inorganic compounds in wastewater. Constructed wetlands system, being simple in construction and maintenance and operation. Physical, chemical, and biological processes are combinedtogether in wetlands to remove Contaminants from wastewater. A- Four-stages of constructed wetlands system (vertical flow beds) subsurface system connected on series was investigated in this research for treating wastewater. Plastic barrels with a height of 90cm and a diameter of 45cm were placed above each others on steel stands with different elevations to achieve flow by gravity without pumping and it is received by storage barrels. In the four stages wastewater flow from the storage barrels to the first stage, then the effluent of the first stage is influent to the second stage, and the effluent of the second stage is influent to the third stage; the effluent of the third stage is also influent to the fourth stage which is the final stage in the experiment; the effluent of this stage is considered the treated wastewater. The system was replicated five times with different types of plants grown including (Corn Brooms, Barley, Alfalfa, Corn, and Sunflower). The period of the study was 6months so the plants were chosen as seasonal plants. the same media was used for all the stages in the experiment, it was three layers for total depth of 50cm. The first layer in the bottom of the bed was 13cm deep and filled with gravel size (10-15 cm). The second layer of the bed was 27cm deep filled with gravel size (1 -2cm); the third layer at the top was 10cm deep with gravel size (1-2cm) mixed with sand with percentage (3:1), (gravel: sand). The general porosity in the system was 45% which is high; thismeant more durable system, and these high voids are necessary for the aeration process of the wastewater in the system. Many tests were done during the operational period to check the efficiency of this system, tests were for BOD, COD, TSS, TDS, TKN, Cl, the removal of pollutants was high and the results are promising. The removal of BOD efficiencies for the five crops (Corn Brooms, Parley, Alfalfa, Corn, Sunflower) were (96.5, 95.4, 94, 96.3, 96.9)% respectively with HLR=72.3Kg/ha.d, the removal rates of COD were (88.2, 86, 85.9, 80.8,78.9)% for the five crops with HLR=99.3 Kg/ha.d., the removal efficiency of TSS efficiencies increased to (90.5, 95.6, 91.4, 93.5, 91.8)% for the same crops with HLR=41.1Kg/ha.d. The removal efficiencies of TKN were (68.1, 66.2, 65.1, 64.9, 65.2)%for the same crops with HLR=41.8Kg/ha.d (High removal with high loading rate).The flow in each stage was 12ml/min (HLR).This flow achieved HRT = 6 days; The experimental results for the system investigated achieved high removal efficiencies for BOD,COD and TKN the system was capable of treating 22l/day.m2 without energy (free energy). Thus, the system could be applied in Palestinian rural areas successfully. The system will provide efficient treatment of wastewater at low cost which will make it appropriate to these areas. The system allowed utilizing crops which will be planted in the constructed wetlands providing an economic return to the community when utilizing such treatment approach.