Grey Water Treatment by Constructed Wetland

Abstract

Next to air, water is the most important requirement for human life to exist. With growing population and industrial development, demand of fresh water is increasing. Hence every community should take preventive measures to avoid careless pollution and contamination of the available water resources and reuse the waste water after treating it. For this, on-site grey water treatment with constructed wetland is the cheapest and practical option. To verify the performance of subsurface flow constructed wetland (SCW) for treatment of grey water in climatic conditions of Kerala, the present study was conducted at the instructional farm of KCAET, Tavanur. The experimental scale SCW system for discharge of 110 l/d was designed and constructed with MS sheet as per the USEPA procedure for influent BOD 5 of 85 mg/l and expected effluent BOD 5 of 5 mg/l. The SCW system was filled with crushed brick, fine river sand mixed with lime and crushed stones in the inlet, filtration and outlet section respectively. SCW system was planted with Canna macrophyte. Raw grey water from the men’s hostel of KCAET was diverted to low lying SCW system site with the use of gravitational force to avoid pumping and energy consumption for the same. The performance of SCW system for removal of TSS, BOD 5, total nitrogen, sulphates and phosphates were studied by analysing the influent and effluent grey water samples from the SCW system. On an average the influent concentrations of these parameters were 132 mg/l, 70 mg/l, 14 mg/l, 32 mg/l and 0.17 mg/l respectively while the same for effluent was 5 mg/l, 4 mg/l, 1.2 mg/l, 8 mg/l and 0.00 mg/l respectively. In all the samples the TC counts in influent water were ≥2400 MPN/100ml while it was ≤2 MPN/100ml in the effluent from the SCW system. Excellent reduction of 90 % or above in TSS, BOD 5, total nitrogen, phosphates and TC was observed and it may be due to use of fine river sand mixed with lime as filter media and Canna as a macrophite. The effect of HRT on the efficiency of removal of these parameters was studied by storing the raw grey water in SCW system for the required period of time. Statistical ANOVA calculations forHRT study show the significant effect of same on % reduction of these elements. Furthermore the extent of significance was checked with Tukey’s test and it was concluded that to have significant difference in observations the interval between successive observations should be 3 days or more. The effect of raw and treated grey water irrigation on Amaranthus and Golden Duranta plants was demonstrated by irrigating these plants in clay pots. For the Amaranthus plants irrigated with raw grey water, observed average height, number of leaves, stem thickness, canopy spread and yield were 38 cm, 51, 9 mm , 826 cm 2 and 158 gm while the same was 51 cm, 71, 12 mm, 1573 cm 2 and 296 gm respectively for the plants irrigated with effluent from the SCW. Statistical analysis with ‘student’s t’ test showed significant difference for the height, number of leaves, and yield at 1 % level of significance and for stem thickness and canopy spread at 5 % level of significance. The Golden Duranta plants irrigated with raw and treated grey water shows significant difference in height and canopy spread at 5 % level of significance. Besides this raw grey water irrigated plants show discolouration and leaf burning. Hence it was concluded that the raw grey water irrigation is not effective for these plants. From the entire study it was concluded that the SCW system is the reliable option for on-site grey water treatment. This ecological treatment system can reduce many objectionable pollutants from waste water to great extent and make it available for secondary uses. Also it has potential to reduce the health risk due to avoidance of mosquitoes and other undesirable insects.