Wastewater sludge processing and utilization at the wastewater treatment facilities of Saint-Petersburg: best practices and prospects

Summary

Best practices of processing and utilization of wastewater sludge at the wastewater treatment facilities of Saint-Petersburg is presented. Centrifuging is used as the main dewatering technology. The dewatering equipment for 40 years has been continuously upgraded; at present decanters – latest generation equipment are used that provide for 72–75% dewatered sludge moisture content and sludge incineration without any fuel addition. All sludge generated at the municipal treatment facilities in the city is incinerated at three incineration plants. Sludge is incinerated in fluidized bed furnaces at 800–850 °С. Ash after sludge incineration is classified as hazard class IV. The amount of sludge is reduced 12-fold. As a result storing dewatered sludge at special landfills was abandoned; consequently the need of constructing new ones was no longer valid. Flue gas cleaning is carried out by wet scrubbing (incineration plants at the Central Wastewater Treatment Facilities and South-Western Wastewater Treatment Facilities) and dry scrubbing. At present the project of upgrading the incineration plant at the Central Wastewater Treatment Facilities has been designed.

Key words

treatment facilities , wastewater sludges , ash , centrifuges , sludge incineration plant , dewatered sludge

Reconstruction of the sludge incineration plant at the Central wastewater treatment facilities in St. Petersburg

Summary

The need for the reconstruction of the wastewater sludge incineration plant at the Central wastewater treatment facilities of St. Petersburg is substantiated. A short description of the technological processes of sludge incineration, flue gas purification and treatment of wash water generated in the process of gas purification is given. The advanced technologies of sludge pretreatment before incineration, flue gas purification, heat utilization, electric energy generation are presented. The results of the biochemical, toxicity, chemical and radiological studies carried out in SUE «Vodokanal of St. Petersburg» showed the possibility of using wastewater sludge incineration ash in the production of constructional materials. Cementing properties of ash that improve the structure and quality of constructional materials were determined. The use of ash in the production of concrete and bitumen concrete in amount of 10–12% of the concrete weight is also promising. The use of ash will improve the concrete strength by increasing the imporosity of the poured concrete, bitumen concrete. Solving the task of ash beneficial use will become a concluding stage in the package of measures on wastewater sludge utilization and will provide for zero waste process of wastewater treatment.

Key words

sludge , wash water , scrubber , sludge drying , incinerator , flue gases , ash , dry matter