N. Zealand. M. NZ,
“Intermittent biological sand filters for wastewater treatment”, vol. CDP 906/A. New Zealand, Ministry of Works and Development, Wellington, New Zealand, p. 11 p. : 4 fig., 1982.
V. S. Rajput and Polprasert, C.,
Septic tank and septic systems, vol. no. 7/8. Bangkok, Thailand: Environmental Sanitation Information Center, ENSIC, 1982, p. 110 p.