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|Title:||ECOLOGICAL MODELLING OF OXIDATION POND|
|Authors:||Devkota, Sushil Chandra|
|Keywords:||WATER RESOURCES DEVELOPMENT AND MANAGEMENT;ECOLOGICAL MODELLING;OXIDATION POND;BOD|
|Abstract:||In general, communities across the world are facing water supply challenges due to tremendously increased societal demands, drought, depletion and contamination of existing water resources. Water reclamation, recycling and reuse address these challenges by resolving water resource issue to certain extent by increased public acceptance and improved understanding on public health risks. There is no doubt that urban wastewater effluents represent a valuable source of water in many parts of world and are reused for irrigational, navigational and industrial purposes either with or without treatment. However, recent outbreaks of waterborne diseases have raised public concerns regarding the safety of the water supply and in specific, water reuse. Thus, the raw wastewater should be treated properly before discharging into the surface waters or reuse for different purposes. In many parts of the world, wherever, suitable land is available at reasonable cost and solar energy is an abundant energy resource, oxidation ponds are an efficient mean of wastewater treatment. In addition, oxidation ponds are not very sensitive to organic or fecal coliforms shock loads, because of their large hydraulic retention time. Because of the lack of sound basic design criteria for the design of oxidation ponds, designers apply equations derived from different environmental conditions, resulting in the poor performance of oxidation ponds. Such models are unlikely to work effectively as the decay of fecal bacteria and organic pollutants involves complex interactions among factors peculiar to the environment and season. In spite of extensive research worldwide, factors affecting the decay of coliforms have not been adequately modeled. Therefore, the present study mainly emphasizes on the development of models for the decay of BOD and indicator organisms, in order to precisely design and simulate the oxidation ponds at northern India and southern plain of Nepal. The observations revealed that the decay of BOD and both indicator organisms i.e. total coliforms (TC) and fecal coliforms (FC) are greatly influenced by variations in temperature. The BOD and coliforms decay rate was observed significantly less in nighttime due to the low temperature, dissolved oxygen (DO) concentration and pH as well as no algal activity due to the absence of sun light. iii No direct relationship could be established between the solar radiations and the decay of indicator organisms. However, the enhanced decay during daytime shows the influence of solar radiation as it increases the temperature of pond water. The solar radiations also stimulate the photosynthetic activity of algae, which release 02 and use free CO2 thus leading to increasing both DO and pH. The effect of settling was observed insignificant in case of coliforms decay; however, it affects BOD decay significantly. The decay of BOD was found to depend upon the temperature and settling velocity. The BOD decay coefficients at 20°C was K20 = 0.0685-per day, for temperature correction factor, 0 =1.043 and settling velocity, VS 0.3315 m/day. The coliforms decay was observed to dependent on temperature, pH and DO concentration. In a multifactor developed model the fecal coliforms decay rate coefficient at 20°C was K20 = 0.7664 per day, for temperature correction factor, 0 =1.048, for pH, KPH= 0.0115 per day and for DO, KDO = 0.0509 Lmg'.day'. The coefficients for total coliforms was K20 = 0.6971 per day, 0 =1.07, KPH= 0.0183 per day and KDO = 0.0287 Lmg l.day 1. The model was successfully verified for the observed data of full- scale pond systems at Rishikesh, Muzaffamagar and Agra cities of Northern India. The RZ values during model verification for BOD model, FC model and TC model were 0.95, 0.83 and 0.90 respectively suggesting the robustness of the model.|
|Research Supervisor/ Guide:||Kazmi, Absar A.|
|Appears in Collections:||MASTERS' DISSERTATIONS (WRDM)|
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