PROBLEMS OF WASTEWATER TREATMENT OF ULAANBAATAR (MONGOLIA)

Abstract

The problem of wastewater treatment in the city of Ulaanbaatar and ways to solve it are described. The influence of insufficient treated urban wastewater on the condition of reservoirs in the Selenga River basin is indicated.  

The subject of the study. Two municipal wastewater treatment complexes are being considered: a functioning one, built in 1964, and one under construction, which is scheduled to be commissioned at the end of 2025. The design parameters of the wastewater used in the design of the new sewage treatment plant complex, as well as the average actual values of the indicators for 2023, are given.  The possibilities of functioning wastewater treatment plants operating using outdated technology, which provides for a reduction in two indicators in the wastewater: suspended solids and total BOD, are evaluated. The complex under construction with a capacity of 250 thousand m³ per day is designed to purify wastewater flowing in two streams: stream "A" (household fecal effluents), stream "B" (a mixture of household fecal and industrial effluents). According to the project, mechanical purification, complete biological purification with nitrification and denitrification, post-treatment and disinfection on granular filters are used for household and fecal effluents, and for industrial ones, physico-chemical purification is provided, followed by biological purification and post-treatment of effluents. 

Research methods. For both facilities (functioning and under construction), design estimates were studied, the technical condition was examined in detail, data from laboratory and production control of the functioning facility were analyzed, and a verification calculation of the complex under construction for the actual values of pollution was performed.  It has been established that the technology of the complex under construction is designed to receive household fecal effluents along the "A" stream and chromium-containing effluents along the "B" stream.  The survey showed that wastewater containing industrial effluents will flow through both streams for treatment. In both streams, the chromium content is so low that it cannot affect the operation of the biological purification unit. However, the active reaction (pH) of both streams is at the level of 9-12.

Results. Studies have been conducted to adjust the technology of wastewater treatment of the complex under construction. Reagents have been selected to neutralize effluents before they are fed to the biological treatment unit. The best option is to use a complex represented by an acidic reagent (aluminum oxychloride) and sulfuric acid. 

Conclusions. In the future, it is desirable to move the industrial complex, including tanneries, dyeing and wool washing factories, outside the city, providing for them local sewage treatment plants in two or even three stages, which will exclude accidental or intentional discharges of industrial effluents to urban structures.