THE INFLUENCE OF THE WAY OF SEWAGE SLUDGE TREATMENT ON AMMONIUM NITROGEN CONTENT IN THE RETURN WASTEWATER FLOW

Abstract

Wastewater treatment facility receives, in addition to the influent, the return flow after sewage sludge treatment. Thus, the organic load on the facility increases as well as the nitrogen and phosphorus content load. There was studied the effect of different stages of sewage sludge treatment (sludge thickening, mechanical dewatering, storage on the grit bays and in the gathering ponds) on ammonium nitrogen content in the incoming flow. It is established that the most concentrated water by ammonium nitrogen is the return water from the gathering ponds, but the less concentrated is the supernatant water from sludge lagoons. Taking into account volume of the return flow the secondary ammonium nitrogen load from the every stage of sewage sludge treatment is calculated. It is revealed the seasonal and climatic impact on the gathering ponds return flow composition; it is shown that the biggest fluctuations occur in spring-summer period. The dependence of ammonium nitrogen content in the return flow on sludge thickening process time in the sludge lagoons is determined. The load contribution on the treatment facility by ammonium nitrogen in the return flow was 3% in the relation to this in the influent. The conclusion was made that with the existing technology of sewage sludge treatment the isolated scheme of return water treatment is not required. The comparative analysis on the effect of thermophilic and mesophilic conditions of anaerobic sewage sludge treatment on ammonium nitrogen content in the liquor was carried out. It was found that the higher ammonium nitrogen secondary load is created by the liquor of thermophilically treated sewage sludge: it is 16,4% versus 11,8% of mesophilically treated. Hence, the including of anaerobic sewage sludge treatment in the scheme significantly increases the load on treatment facility by ammonium nitrogen. In the conditions of cascade denitrification the distribution of incoming in the denitrification zones water flow is of great importance for providing required content of readily available organic substances. The change of ammonium nitrogen content in this flow will require the adjustment of its volume.