Intensification of activated sludge sedimentation processes by means of vacuuming

Abstract

Introduction. The mixed liquor of nitrogen removal wastewater treatment plants is characterized by a high concentration of nitrates and dissolved oxygen at the inlet to the secondary settling tank. In the sludge layer of secondary sedimentation tanks, conditions of decreased oxygen content and uncontrolled denitrification processes take place. This leads to the floating up and removal of sludge with the effluent and secondary pollution of treated water. The purpose of this article is to study the parameters of activated sludge sedimentation in municipal wastewater treatment plants and their intensification by means of vacuuming.
 
 Materials and methods. The studies were carried out under laboratory conditions. Activated sludge vacuuming and sedimentation processes were simulated. Diagrams of the “sludge-water” phase reduction (Kinsh curves) were drawn. Mathematical and graphic processing of the results was carried out.
 
 Results. Biological treatment of municipal wastewater (aerotank — secondary settling tank) and methods of its intensification by influencing the activated sludge were considered in this article. Trends of activated sludge (at different concentrations of mixed liquor suspended solids) sedimentation were experimentally obtained for municipal wastewater treatment plants. The process of sludge vacuuming was researched, the process efficiency was determined as a function of the treatment time.
 
 Conclusions. Vacuuming allows removing gases from the fluid, which accelerates the process of sludge separation from the treated water and prevents it from floating to the surface. The treated sample is characterized by better sedimentation characteristics, density, coarseness and integrity of flakes. The optimal duration of mixed liquor vacuuming before sedimentation is 0.5 minutes; this accelerates the processes of subsequent sedimentation and reduces the removal of sludge with treated water. The results of laboratory tests can be applied to the design of the mixed liquor vacuuming unit before the secondary sedimentation tanks and its sludge separation.