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