THE INFLUENCE OF FILTER DEPTHS IN CAPTURING NUTRIENT CONTAMINANTS FOR NON- VEGETATED BIORETENTION COLUMN: A PRELIMINARY STUDY

摘要

Engineered soil media plays significant role in enhancing bioretention performance in terms of water quantity and quality aspects. There was limited research on hydraulic response in establishing design parameters such as soil depths. This paper presents a preliminary study on the evolution of hydraulic conductivity over time and examine the stormwater treatment efficiency for engineered soil media consisted of various depths. This study focused on three small-scale column namely C1,C2 and C3 with 74mm in diameter and 700 mm in height. Column C1,C2 and C3 comprise 500 mm, 400 mm, 300 mm deep engineered soil media, respectively. Soil composition of engineered soil media consists of 50% medium sand, 30% topsoil, and 20% organic leaf compost. Daily hydraulic conductivity was monitored over 10 weeks to observe the declination of this parameter over the time. Then, approximately 3.3 L collected 'dry' stormwater sample (no rain was observed during November-January 2013) were poured into each column. Both influent and effluent were collected and tested. Results found that C3 has the greater K_(sat) (280.2±63.4mm/hr) due to having narrow depth of filter media. However, C1 (88.2±36.7mm/hr) and C2 (74.6±15.1mm/hr) has lower hydraulic conductivity due to having deeper depth of filter media. Preliminary results illustrates that a declination in hydraulic conductivity very quick in the first two weeks progression in all cells then it tends slowly decreased at remain at one value. Besides, C1 has highest retention time was capable to remove total nitrogen (TN) pollutants with 52.2±8.5%. TN removal for C2 and C3 were slight lower than C1 which were 35.8±3.4% and 24.2±9.8%, respectively. Total phosphorus (TP) was treated well in all columns with C1 and C2 with 71.8±14.4% and 81.6±6.1%, respectively. C3 was ineffectively removing nutrient pollutants with less percentage of pollutant removal. It was probably C3 has narrow depth of engineered filter media which provide lesser treatment on stormwater pollutants due to insufficient retention time to soil microbes react with the contaminants. It was suggested that a minimum depth of 400 mm of engineered filter media capable to remove nutrient contaminant due to having longer retention time which giving more natural treatment processes to occur.