Process design of waste stabilization ponds at high altitude in Bolivia

The Altiplano, located at 15°–20°S, has an altitude of about 4000 m above sea level which determines extreme climatic conditions that may affect the performance of stabilization ponds: strong solar radiation due to a thin atmosphere of rarefied, clean, dry air; low mean temperatures of water and air; strong differences in temperature between day and night; low oxygen pressure. The oxygen pressure at 4000 m altitude is only 60% of that at sea level. However, lower water temperatures increase oxygen solubility in water compensating for the effect of altitude in the actual concentration of dissolved oxygen in water. Lack of oxygen is not a crucial limiting factor for sewage treatment at high altitudes. Anaerobic ponds are effective in the Altiplano, in spite of the low water temperatures (7–9°C). Design criteria for WSP at different altitudes in Bolivia are presented. An important conclusion with social connotations is that the communities of the Altiplano will need to construct waste stabilization ponds which are 3–5 times larger (and more expensive) than those of the “Los Llanos”.