The influence of artificial destratification on chemical processes in upper layang reservoir

Abstract

Upper Layang Reservoir located 40 km from Johor Bahru is an impounded reservoir for water supply. The reservoir suffered serious water quality problems in 1995 due to algal bloom which dramatically impacted the water treatment process. An extensive study of the reservoir was conducted in order to understand the behavior of a tropical reservoir. This study comprises of three major components which focused on physical and chemical water quality properties of Upper Layang Reservoir. The first component involves investigation of long term processes affecting water quality in the reservoir. The second component addresses a trial study of an artificial destratification system designed to improve the water quality at the reservoir. The third component involves reservoir modeling with HEC-5Q in terms of temperature and dissolved oxygen simulations. In the first component, weekly observation was conducted for the duration of fourteen months at four selected sites at the Upper Layang Reservoir. The observation includes in-situ and water quality parameters measurements for nutrients and metals. In-situ parameters include temperature, dissolved oxygen, redox and pH. Nutrient analysis involves nitrate, nitrite, ammonia, total Kjeldahl nitrogen, dissolved phosphorus and total phosphorus whereas metal analysis involves dissolved iron, total iron, dissolved manganese and total manganese. The data obtained showed that Upper Layang Reservoir underwent thermal stratification for the majority of the year. Brief periods of natural mixing were also observed due to heavy downpour in the monsoon season. In the second component, a destratification process was effected using bubble plume perforated line diffuser at the reservoir. During destratification, the number of sampling sites was increased to twenty seven sampling sites. Intensive study was conducted for a period of two months on a daily basis for the first three weeks and three days a week until aeration completed. The result obtained showed that thermal stratification was successfully eliminated after seven days of continuous aeration. Dissolved oxygen concentration at the bottom of the reservoir was also increased to more than 4.50 mg/L which facilitates the reduction of iron and manganese concentrations at the bottom waters and also reduced the concentration of ammonia and phosphorus.