The ability of small streams to self-purification from phosphorus

Abstract

Domestic and industrial wastewater originating from small settlements enters the drainage channels and nearby streams which are capable of self – purification. The main objective of this research was to determine self-purification processes from total phosphorus in small streams and evaluate the main factors of influence. Research was carried out in the streams and drainage channels with the average discharge up to 0.2 m3/s. Water samples were taken in the dry period of the year to avoid additional attenuation and pollution with drainage water from agricultural areas. Sampling was carried out above the settlement or wastewater discharger and downstream every certain distance according to relief and peculiarity of the river flow until the nearest tributary. Data analysis showed that the change of total P concentration downstream was more intense in less watery streams compared to more watery ones. Moreover, the correlation dependence revealed that the change in total P concentration near the pollution source was little dependent on stream discharge. Increasing the distance from the pollution source the dependence on discharge also increased. It was also noticed that given low stream discharge, total P concentration changed more intensively with an increasing distance than in the case of higher discharge. Usually smaller streams are characterized by much higher relative load according to total P than more watery ones. The correlation dependence showed that total P removal was more efficient in smaller streams compared to bigger ones. Relative stream load near the pollution source had a stronger influence on total P removal efficiency than the distance from the pollution source, especially when relative load of the stream was low.