BACKGROUND: The constructed soil filter (CSF), also known as soil biotechnology is a system for water renovation, which makes use of formulated media, culture of soil micro- and macro-organ isms, additives and plantation to purify water and wastewater. The process gives benefits in terms of applicability across very small to large scale, natural aeration, absence of moving parts, no biological sludge generation, odor free green aesthetic ambience. RESULTS: Residence time distribution (RTD) studies were carried out using laboratory scale CSF. Pulse potassium bromide tracer tests were carried out to determine RTD, and the Peclet number found to be 9-13 for a 2 m bed, and 2-3 for a 0.30 m bed with oxygen transfer of 0.08 h(-1). CONCLUSION: The two-channel dispersion model for flow behavior shows a good fit to the experimental data, indicating a reactor Peclet number 9-13 for a 2 m bed and 2-3 for a 0.3 m bed. Oxygen transfer studies carried out using various methods gave an oxygen transfer coefficient of about 0.08 h(-1). Wastewater purification studies indicate overall COD removal rate of around 50 mg L-1 h(-1), suggesting that highly aerobic conditions are prevalent in the CSF system. (C) 2009 Society of Chemical Industry