Places of corrosive gas generation in the sewerage network

Summary

The factors that affect the generation of corrosive gases in the wastewater disposal system, saturation of the gas air environment with corrosive gases in sewers are considered. A number of structural components as well as hydraulic patterns of wastewater flow, its physical properties that enhance the gas generation processes are considered and described. The evaluation and prediction of the places of corrosive gas generation and emission provide for forecasting the measures focused on the reduction of the negative impact of emissions or their complete elimination. The operating services carry out regular sewer network monitoring with the purpose of detecting the places of emission generation. The future work of the services is limited to the isolation of corrosive gases by redistribution in the network, disposal into the atmosphere, neutralization or purification. The results of introducing the design of a pipe drop with a dead blanking in the lower part of the sewer shaft, ejector and pipe air vent are presented.

Key words

sewer , sewerage network , shaft , gas emission , corrosive gases , gas generation

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

The experience of operating sewer tunnels in St. Petersburg

Summary

A short description of the sewer tunnels in St. Petersburg, their building conditions, operation and maintenance, safety arrangements during inspection is presented. A portable, mobile diagnostic unit for the inspection of the underwater space of the tunnel has been designed. The measuring part of the unit comprises ultrasonic sensors for underwater space scanning, TV camera with zooming and rotation in different direction, and recorders of the wastewater chemical composition. Scanning the underwater part of the tunnel provides for the information on defects and damages of the tunnel trough and lining, level of silting. Basing on the inspection results the causes of the tunnel and in-line structures failures are determined. In parallel with the tunnel inspections the experts of the St. Petersburg University of Architecture and Civil Engineering carried out an analysis of the hydraulic control of the inspected sections of the tunnels. The results of the inspection and hydraulic control analysis provided the basis for the development of priorities, tunnel repair and rehabilitation activities; allowed improving the integrity of the municipal wastewater disposal system. A short description of the solution of the problem of cleaning the polluted emissions from the sewer and tunnels alongside with the references of the gas cleaning system are presented.

Key words

wastewater , sewer tunnel , shaft , bore hole , air-gas corrosion , tunnel inspection