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Optimization of wastewater treatment through Bio-Geo filter for hotels surrounding Bolgoda Lake
By Admin | March 19, 2009
Wetland systems are playing a key role of keeping rich bio-diversity in favors of mainly aquatic lives of in and around inland waters. Bolgoda wetland is an important wetland system in Sri Lanka, which keeps number of endemic species and a bird sanctuary, compiled with striking natural beauty. This unique feature ultimately helps to increase the number of hotels, restaurants and residences in the vicinity. As a result improper waste disposal become a significant threat to the wetland system, causing nutrient enrichment followed by massive growth of water hyacinths at the lake.
Controlling measures of nutrient enrichment of Bolgoda Lake is an utmost need, and therefore a study was aimed to identify present wastewater disposal practices in order to develop an economical wastewater treatment system that can be adopted by hotels and dwelling units. Hence, a questionnaire survey was carried out among hoteliers to identify the significant malfunctions of present wastewater disposal practices. The results showed that only 7% of hotels use proper wastewater treatment units and 20% use combined units of septic tanks and soakage pits, while 46% use only septic tanks. It has also revealed that septic tank effluents are directly discharged into the lake through subsurface soil and even available soakage pits are malfunctioning due to high ground water table. Hence this research was then focused to design a low-cost wastewater treatment unit to optimize nutrient removal efficiency.
The BGF is a subsurface flow constructed wetland cell, consisted with two key components of bio and geo materials which interrelate with each other offering a combined physical and biological treatment process, in removing pollutants from wastewater. Considering the nitrogen, phosphorous, BOD and suspended solids concentrations in wastewater and the level of treatment required, Bio-Geo filters were designed for three categories such as: a hotel with 10 rooms/ 05 rooms and for a dwelling unit, having wastewater flows of 14 m3/d, 9 m3/d and 1 m3/d respectively. The filter ditch was designed with a bottom layer of laterite (Kabook) of 0.6m deep and top layer of sand and coir dust mixture of 1:1 proportion of 0.2m deep. Washed laterite of effective diameter of 40mm was used as the main geo material, as it enhances phosphorous removal while marigold, colias and some aquatic plant were selected as bio materials concerning their performance within the system. The analysis revealed that average retention time requirement of any BGF is about 20 hrs and their treating capacity is about 80-85% removal of BOD, 78% removal of suspended solids, 59% removal of nitrogen and 65% removal of phosphorous.
The cost of BGF unit is estimated as approximately Rs 75,000-100,000 for 1m3/d wastewater flow, which is considerably low compared to the common wastewater treatment systems. Possible drawbacks of the system, such as clogging or flooding are also called-upon with suitable alterations.
Chandima Jayasekara, Bandunee Liyanage
Department of Civil Engineering, The Open University of Sri Lanka
Topics: Pollution control, Resource Management, Water Resources, symposium2008 | No Comments »