Abstract
Ninety‐nine communities in the northern plains area use artificial ponds as the sole method of sewage treatment. Five ponds, selected for variability in design and loading, were studied intensively during each season for one year.A typical biota principally composed of algae and bacteria becomes established and participates in the treatment process. Reduction in coliform density (most probable number) was 99% more than half the time and always 95% or greater. Oxygen demand (B.O.D.) was typically reduced by 70–90%. Total suspended matter was reduced 80% or more in winter, but sometimes was increased up to 258% in summer as result of algal production.Various factors affect the treatment process. Depth of the euphotic zone ranged from 0.1–0.7 meter. Bottle tests gave oxygen production rates between zero and 3.6 g/m2/hr at different times of day, and total respiration rates from 0.1–2.4 g/m2/hr. Oxygen demand from contributed sewage was only 6–7% of total respiratory demand. Vertical gradients, diurnal variations, ice cover, and other factors prevent simple projection of bottle test data to the ponds.
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