Study of the quality of supernatant separated in the process of sludge thickening at the water treatment plant in Rostov-on-Don

Summary

The results of studying the qualitative and quantitative composition of supernatant separated from the sludge after sedimentation tanks washing at the water treatment plant in Rostov-on-Don. The chemical water analysis carried out in accordance with Standard Methods showed that the given effluent type does not meet the requirements set to the discharge into the municipal sewer and poses a threat to the environment. In connection with this the technology of wash water reuse was chosen as the most efficient under the given conditions. It provides for the effluent returning into the mainstream of the water to be treated or using it for the water plant needs. At that the effluent organoleptic properties shall be considered: at 5 hours sedimentation of sludge with 5–40 g/dm3 concentration it can be classified as low-turbid, medium or high colored (depending on the season of sludge generation in the sedimentation tanks). Increasing the time of supernatant retention above the sludge (up to 120 hours) insignificantly improves the clarification and decoloration efficiency that is indicative of the presence of highly dispersive and dissolved substances highly resistive to sedimentation in supernatant. Improving significantly the supernatant quality is possible by sludge pre-conditioning with lime or cationic polyacrylamides.

Key words

sedimentation tank , filter washings reuse , slime water , sludge thickening , supernatant

The experience of constructing the extension of the main sewer in the northern part of St. Petersburg

Summary

The experience of constructing the extension of the main sewer in the northern part of Saint-Petersburg is presented. The works were carried out in a complex hydrological environment with the use of advanced tunneling machinery. Pressure-gravity drain siphon was chosen from the options considered. During the shaft construction both traditional methods (drilling freezing columns, shaft freezing with formation of glacial soil massive, boring in glacial soil shield with installation of immediate support of reinforced concrete tubing, construction of reinforced concrete jacket and technological shaft equipping), and new ones (shaft shielding with piled walls followed by drilling and constructing reinforced concrete jacket, shaft boring with shaft sinking machine and installing immediate support of segment blocks and sinking the whole support structure with shaft sinking) were used. In the process of constructing the main siphon tunnels boring with mechanized complexes with simultaneous assembling the immediate support of the tunnel with reinforced concrete tubing was used. At wash-out site in the process of boring the second line of the siphon an advanced tunnel-boring complex with hydroweight and hydrohaulage with constructing immediate support of the tunnel of segment blocks was used. To provide for the nonsilting flow rate in the sewer under the conditions of wastewater flow decrease a flow regulation facility was built in the lowest sewer point. The use of the advanced tunneling complex provided for shortening the timeline to completion of the sewer construction, ensuring leaktightness of the constructions and operations safety eliminating workers access to the tunnel face. Commissioning the extension of the sewer in the northern part of Saint-Petersburg provided for increasing wastewater treatment to 98.4%.

Key words

wastewater , monitoring , sewer , gas corrosion , shaft , tunneling complex , microtunnel