Environmental Engineering Research

Korean Society of Environmental Engineers (대한환경공학회)
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Hydraulic Evaluation and Performance of On-Site Sanitation Systems in Central Thailand

  • Koottatep, Thammarat (Environmental Engineering and Management, School of Environment Resources and Development, Asian Institute of Technology) ;
  • Eamrat, Rawintra (Environmental Engineering and Management, School of Environment Resources and Development, Asian Institute of Technology) ;
  • Pussayanavin, Tatchai (Environmental Engineering and Management, School of Environment Resources and Development, Asian Institute of Technology) ;
  • Polprasert, Chongrak (Department of Civil Engineering, Faculty of Engineering, Thammasat University)
  • Received : 2014.05.27
  • Accepted : 2014.08.26
  • Published : 2014.09.30
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Abstract

On-site sanitation systems are typically installed to treat grey and toilet wastewaters in areas without sewer and centralized treatment systems. It is well known that, due to inappropriate design and operation, treatment performance of these systems in developing countries is not satisfactory in the removal of pathogens and organic matters. This research aimed to investigate the hydraulic conditions occurring in some on-site sanitation systems and the effects of hydraulic retention times (HRTs) on the system performance. The experiments were conducted with a laboratory-scale septic tank (40L in size) and an actual septic tank (600L in size), to test the hydraulic conditions by using tracer study with HRTs varying at 12, 24 and 48 hr. The experimental results showed the dispersion numbers to be in the range of 0.017-0.320 and the short-circuit ratios in the range of 0.014-0.031, indicating the reactors having a high level of sort-circuiting and approaching complete-mix conditions. The removal efficiency of $BOD_5$ was found to be 67% and the $k_{30}$ values for $BOD_5$ was $2.04day^{-1}$. A modified complete-mix model based on the relationship between $BOD_5$ removal efficiencies and HRTs was developed and validated with actual-scale septic tank data having a correlation coefficient ($R^2$) of 0.90. Therefore, to better protect our environment and minimizing health risks, new generation toilets should be developed that could minimize short-circuiting and improving treatment performance.

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References

  1. World Health Organization (WHO). Lacking sanitation [Internet], Carlton: World Health Organization; c2013 [cited 2013 July 24]. Available from: http://www.who.int/ceh/risks /cehwater/en.
  2. Brandes M. Characteristics of effluents from separate septic tanks treating grey water and black water from the same house. USA: Toronto. Ontario; 1977.
  3. Polprasert C. Septic tank and septic systems. Asian Institute of technology, Thailand: P.S. Service center; 1982.
  4. Levenspiel O. Chemical reaction engineering. 3rd ed. New York: John Wiley and Sons; 1999.
  5. Metcalf and Eddy. Wastewater engineering treatment and reuse. 4th ed. New York: McGraw-Hill; 2003.
  6. Eaton AD, Clesceri LS, Rice EW, Greenberg AR. Standard methods for the examination of water and wastewater. 21th edition. Washington: American Public Health Association; 2005.
  7. Edward L, Thackston F, Douglas S, Paul R. Residence time distributions of shallow basins. Environ. Eng 1987;113:1319-1332. https://doi.org/10.1061/(ASCE)0733-9372(1987)113:6(1319)
  8. Pollution control department. Housing estate standards [Internet]. Carlton: Pollution Control Department; c2014 [cited 2014 March 3]. Available from: http://www.pcd.go.th.
  9. Ittiusupornrat S, Sienglum C, Wongsila K, Poonnotok A, Sunthornwatthanophong V, Yaithavorn P, Milintawisamai M. Environmental Research and Training Centre (ERTC). Project on efficiency verification testing of wastewater treatment tank. Carlton ERTC; c2014 [cited 2014 March 12]. Available from: http://www.ertc.deqp.go.th/ertc/images/stories/user/water/water.pdf.
  10. Crites R, Tchobanoglous G. Small and decentralized wastewater management systems. San Francisco: WCB/McGraw Hill; 1998.
  11. Wanasen S. Upgrading conventional septic tanks by integrating in-tank baffles [Thesis]. Bangkok: Asian Institute of Technology; 2003.
  12. Nguyen AV, Pham NT, Nguyen TH, Morel A, Tonderski K. Improved septic tank with constructed wetland, a promising decentralized wastewater treatment alternative in Vietnam. International Conference of the National Onsite Wastewater Recycling Association (NOWRA) and International Water Association; 2007; IWA, Maryland, USA.