Master of Science in Environmental Management

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Browsing Master of Science in Environmental Management by Subject "CIVIL ENGINEERING-Thesis"

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    item: Thesis-Abstract
    Comparative study on two different wastewater treatment processes at crepe rubber factories
    Vithanage, D; Ratnayake, N
    In Sri Lanka most commonly used treatment methods for crepe rubber factories are pond/lagoon system and activated sludge system. The objective of this study is to identify the most cost effective and commercially viable treatment system to treat the effluent generated from crepe rubber factories. Mechanically aerated lagoon/pond system at Eheliyagoda Rubber Factory and activated sludge system at Parakaduwa Rubber Factory have been selected for this study. The average flow rates during the study period for the ETP at Eheliyagoda Factory is 30m3/d and it is 60m3/d for the ETP at Parakaduwa Factory. Also it is observed that the Eheliyagoda Factory uses 19% more water and the Parakaduwa Factory uses 43% more water than the water quantity stated in the Guidelines for Natural Rubber Industry. Considerable variations of influent BOD5 & COD to the treatment plants have been observed due to the changes in weather pattern and latex tapping activities are generally affected by the weather. pH of the wastewater generated in both factories is always less than 6.0 and the BOD5& COD removal efficiencies of the anaerobic treatment unit in both plants are less than 30%. The average BOD5 & COD of the treated wastewater obtained from the ETP at Eheliyagoda Factory is 53 mg/l and 229 mg/l respectively. Also the 60% of BOD5 readings and 90% of COD readings of the treated wastewater obtained from the ETP at Eheliyagoda Factory meet CEA standards. The average BOD5 & COD of the treated wastewater obtained from the ETP at Parakaduwa Factory is 77 mg/l and 340mg/l respectively. The 22% of BOD5 readings and 78% of COD readings of the treated wastewater obtained from the ETP at Parakaduwa Factory meet CEA standards. The average TSS values of the treated wastewater obtained from the treatment plants at Eheliyagoda & Parakaduwa Factories are 315mg/l &171mg/l. Total BOD5, COD & TSS removal efficiencies of the ETP at Eheliyagoda Factory are 93.5%, 94.5% & 67.5% respectively. Such removal efficiencies for the ETP at Parakaduwa Factory are 90.5%, 91.3% and 68.3% respectively. When considering the removal efficiencies of the aerobic facultative unit of each treatment system, they are higher in the MAL than the Activated sludge tank. The initial capital cost of the activated sludge process at Parakaduwa Factory is lower than the mechanical aerated lagoon system at Eheliyagoda Factory. But when comparing the cost for operation & maintenance of the treatment systems, it is lower in the treatment plant at Eheliyagoda Factory and it is 54.5% of the cost for the treatment system at Parakaduwa Factory. For the period of 10 years of the operation of the treatment plants, the unit cost for wastewater treatment in terms of Rs/kg at Parakaduwa Factory and Eheliyagoda Factory are Rs 1.59 and Rs 1.53 respectively. Also the one kilogram of BOD load, treatment costs for Parakaduwa Factory and Eheliyagoda Factoty are Rs 46.14 and Rs 47.11 respectively. Since the low operational & maintenance cost and high treatment efficiency of MAL system, it can be concluded that the mechanical aerated lagoon system is more cost effective wastewater treatment process for natural rubber industry where the land is available. Gravity flow to each treatment unit where ever possible and daily pH correction of the raw wastewater should obtained to achieve cost effective performance in both systems. It is also recommended to maintain a correct DO &. MLSS in the aeration tank at Parakaduwa Factory and to install a sand bed as a last unit for the plant at Eheliyagoda Factory
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    item: Thesis-Abstract
    Phytoplankton as bio indicators in management of eutrophication problem of Kandy Lake
    Jayasekara, HPS; Piyasiri, S; Ratnayake, N
    Eutrophication through the process of nutrient enrichment of stagnant waters due to urbanization & agricultural practices is becoming a significant water pollution issue in Sri Lanka. The appearance of thick Microcystis aeruginosa bloom in 1999 indicates that the Kandy Lake is also becoming the victim of nutrient enrichment. Therefore an effective Lake Management and Lake monitoring programmes with integrated catchment management have to be adopted and it is a prior necessity in planning of the management practices of the catchments to get firsthand information through research on trophic status of the lake. This study is focused on the evaluation of trophic status of the lake using Phytoplankton as indicators. The objectives of the study were to find out the species composition, variation of species richness & their diversity towards the trophic nature of Kandy lake through responses of the species towards different nutrient levels of the lake, and to develop different diversity index ranges which could be used as indicator levels of Lake Eutrophication, thus making it possible to determine the status of the water body through diversity index values. To achieve these objectives, the overall physico-chemical nature of the water body, was investigated by the parameters such as water level, water transparency, dissolved oxygen, temperature, conductivity, pH, alkalinity, nitrate, orthophosphate and biological nature by the parameters such as chlorophyll - a and the phytoplankton densities and species composition were determined. The laboratory experiments also were conducted using a series of diluted lake water as culture media to monitor the effect or Nitrate & Phosphate on indicator organisms. Sampling was carried out in Kandy Lake from October 2001 to March 2002 (six months), once a month during the day time. The total number of individual species collected at 08 selected stations at each depth surface, mid and bottom were quantified and the phytoplankton density was expressed as the number of cells per cubic meter of the lake water. These data were used in calculating diversity indices. During this study an attempt was made to develop a curve to predict the number of cells in a colony according to the size of the colony of Microcystis. According to the curve there were 20 cells per unit area (1 μm2) of Microcystis colony. Low Secchi Depth value «1 m) and high chlorophyll a concentration (100-250 mg/rn ') indicates Hyper-eutrophic nature of the Lake. High nutrient loading observed through out the study period (Average values of Nutrients varied between 204.65μg/L and 512.95μ/L for Orthophosphate and 0.114 mg/L and 0.243 mg/L for Nitrate) triggers that situation and it probably maximized by the mixing nature of the lake. Only a few (06) phytoplankton species were recorded in Kandy Lake during the study period; namely Microcystis aeruginosa. Microcystis incerta, Pediastrum duplex. Merismopedia tenuissima. Melosira granulata. Diatoma elongata. Out of them Mtc...rocystis and Melosira were found in greater abundance indicating the eutrophic nature of the lake. The calculated diversity index values for water samples of entire Kandy Lake throughout the investigation period were below 10 According to previous studies diversity index 3 is clean water. Therefore values obtained for Kandy Lake indicates the eutrophicated status of the lake. Even during different seasons the values have never increased indicating permanent eutrophic status of Kandy Lake. The diversity index value of < I found for Kandy Lake could be used as a reference value to monitor the trends during restoration of the Lake. According to the physico chemical and biological observations of the present investigations, Kandy lake water is already eutrophic and therefore its bottom sediment may contain high nutrient concentrations adsorbed to the bottom sediment Therefore even if further nutrient inputs are controlled, the blooming could occur due to accumulated nutrient loads in the bottom and there is a need for quick remedial efforts if the Lake is to be saved from this bad situation. Diversity index values could be used as a monitoring tool in Management of Eutrophication in Kandy Lake even without time consuming and costly chemical analysis procedures.
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    item: Thesis-Abstract
    Waste minimization and wastewater treatment in an electroplating industry
    Jayawardana, KGS; Ratnayake, N
    Electroplating has been introduced to Sri Lanka more than a hundred years ago and there are more than 80 electroplating units in Sri Lanka, including household units. However, it has been found that the electroplating technology in Sri Lanka is lagging behind the world level and several problems of electroplating facilities with regard to plating technology and wastewater treatment had been identified. The objective of this study was to investigate the possibilities of waste minimization and optimization of wastewater treatment in the electroplating industry using readily available resources and technologies in the country, focusing on the nickel and chromium-plating process and treatment of wastewater generated in that process. Methodology of this study consisted of making observations of the existing process estimating water and energy consumption, analysis of process solutions and treated wastewater, studying process parameters used in the production process and wastewater treatment, and carrying out a designed experiment to study optimum pH for heavy metal precipitation. It was found that quality control of the product is poor and the industry lacks technical know-how to carry out the electroplating process and wastewater treatment efficiently. However, the industry has already implemented a few quality control and waste minimization activities such as quality control of intermediate product within the process, two stage rinsing, and dragout recovery. Possibilities to reduce electricity and water consumption without affecting the quality of the product through introduction of temperature control units for heaters, removal of unnecessary unit operations employed in the production process etc. and the necessity of proper stripping of rejects before recycling them into the production process in order to avoid unnecessary contaminations of bath solutions were identified. With regard to the wastewater treatment, it was found that the optimum pH for hydroxide precipitation of nickel and chromium in a mixture is pH 8.0. It is recommended to introduce drain boards, stripping for rejects, temperature feed back control system for heaters and improved process control in nickel-plating activity immediately and , to study the possibility of working longer hours a day than the normal 8hr shift, which would increase the savings on electricity used for bath heating. It is also recommended to omit unnecessary unit operations and to change over to Cr3+ chromium plating solution instead of Cr6+ solutions, while proper quality control procedures such as corrosion resistance test & Adhesion tests are carried out to increase the value of the product and reduce wastage. Measures recommended to improve the wastewater treatment system include carrying out chromium reduction at pH 3 for a minimum period of 30 minutes, strict control of Cr6+ discharge into the Heavy Metal Precipitation Tank, carrying out nickel and chromium precipitation at a pH value between 8 - 8.5 and filtering supernatant of the sedimentation tank to avoid escape of suspended material with the supernatant.