Self-purification ability of natural waters in the arid zones

The paper presents the analysis of literature data and research results on self-purification and self-purification ability of natural waters at arid zones (on example of closed Lake Balkhash). The self-purification processes are a combination of all natural (hydrodynamic, chemical, microbiological and hydrobiological) processes in contaminated natural waters. A large number of pollutants and specific (physical and geographical) conditions of reservoirs causes the complexity and variety of cleaning processes of natural waters. Large amounts of pollutants discharged into water reservoirs and drains impede the self-purification processes. It has been established that the sediments and clay of Lake Balkhash absorb the metal ions. Thus, the process of absorption of Mn2+ ions by clay minerals mainly occurs within the first three hours of contact, whereas sorption by slits continues until 10-15 days. The sediments are good absorbents for cadmium (90%), zinc (86%) and copper (78%). The sorption properties in the dynamic mode decreases in the row of zeolite (SEC = 1.02·10-3), then Fe (OH)3 (SEC = 0.28·10-3) and Al (OH)3 (SEC = 0.10·10-3 mmol-eq/g) with respect to Mn+2 ion with concentrations from 5.0 to 100 μg/L.