Temperature and Shock Load Effects

A spray irrigation system continues to purify water when temperatures are near freezing. Since the respiration of microorganisms slows down as temperature decreases, researchers believed that the impurities were being adsorbed on the surface of the vegetation and held there until the weather grew warm again. However, biological studies show that as the temperature decreases, the number of organisms increases, thus maintaining a constant level of mass activity. Figure 7.52.2 shows this phenomenon.

Spray irrigation systems have the outstanding capability of handling shock loads as well as periods of long shutdowns and immediate startups, producing excellent results in either case. In addition, variations in effluent composition, such as the results of night cleanup, produce no adverse effects. The effluent pH of a spray irrigation system stays between 6.8 and 7.0 although the waste applied at night reaches a pH of 12 for approximately 1 hour and sometimes for as long as 3 hours.

Figure 7.52.3 provides evidence of this dampening effect, showing the diurnal variations of electrical conductivity of both the wastewater and the field effluent for each season. The higher conductivity in runoff during the summer months is due to the increase in evapotranspiration and the decrease in the runoff volume.

For an overland flow system, if a single terraced slope is accidentally overloaded due to mechanical failure, the effluent treatment continues in the other terraces and waterways before the effluent reaches the receiving stream. This capability makes the spray irrigation method a safe technique.

FIG. 7.52.2 Total microbial population on control and test lots.
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