Temperature Variation Effect in Nutrient Removal by Constructed Wetland.

Abstract

Most of the water bodies nearby the cities are getting polluted due to untreated wastewater disposal. This problem is expected to increase in future due to rapid urbanization if suitable measures are not taken. In the developed countries, centralized wastewater treatment system is in practice but in the countries like Nepal such system are uneconomical and unsustainable. Constructed wetland is natural, low cost, environmentally friendly biological wastewater treatment system which resembles with natural wetland ecosystem. Main objective of the study was to know the effect of change in ambient temperature on removal efficiency of constructed wetland. Study was carried out in the existing wetland of IOE. During the study, different parameters like NH4-N, NO3-N, NO2-N, PO4-P and BOD were analyzed. Removal efficiency of NH4-N, NO3-N, NO2-N, PO4-P and BOD during winter season, when average ambient temperature was 12.75oC, was found to be 20.13, 11.51, 29.46, 27.03 and 48.57 percent respectively. Similarly, removal efficiency of NH4-N, NO3-N, NO2-N, PO4-P and BOD during summer season, when ambient temperature was 25.5oC, was found to be 90.24, 40.36, 54.95, 53.22 and 68.42 percent respectively. In addition, reaction rate constant KT20 was found to be 0.166, 0.0646, 0.6793, 0.2586 d-1 and θ was found to be 0.83, 0.87, 0.93, and 0.94 for NH4-N, NO3-N, PO4-P and BOD respectively. Nitrogen and phosphorus are primary micronutrients for plant growth. During winter season, various biological activities like growth of plant and rhizome, microbial activity is very low, as a result of which removal of nitrogen and phosphorus was found to be low. As temperature rises, all the biological activities and number of new plants increase which results in increase in removal of nutrients.