Process Design of Stabilization Ponds

Juanico M., H Weinberg and N Soto (2000). Process design of waste stabilization ponds at high altitude in Bolivia. Wat. Sci. Tech. 42(10-11):307-313.

ABSTRACT

The Altiplano, located at 15o-20o 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 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 oC). 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”.

Figure 1. Schematic West-East profile of Bolivia across the Andes.

Table 1. Climatic constrains and their effect on the WSP design parameters herein recommended for the conditions of Bolivia.

	Parameter	units	Altiplano	Valles	Llanos
	Altitude	m	4000	2500	400
	Mean water temp. (1)	^oC	9	20	24
	D. Oxygen saturation	mg/l	7.3	7.0	8.4
	Solar radiation	cal/cm²/day	550	300	200
Recommended design parameters (see discussion below).
Anaerobic	Max. organic loading	g BOD/m³/d	100	200	400
Ponds	Minimum retention time	days	2.5	2	1.5
	Minimum depth	m	5	4	4
Facultative	Max. organic loading	kg BOD/ha/d	100	200	250
Ponds	Minimum retention time	days	15	13	11
	Minimum depth	m	2	1.5	1.7
Maturation	Minimum retention time	days	5 each one	5 each one	5 each one
Ponds	Minimum depth	m	1.2	1.2	1.2

1) Mean water temperature measured in WSP.