Upgrade of the sludge treatment facilities of the Petrodvorets wastewater treatment plant

Summary

The results of upgrading the Petrodvorets wastewater treatment plant, and the sludge treatment facilities, in particular, are presented. The upgrade provided for the following effluent parameters, mg/l: suspended solids < 5.2; BOD5 3.7; total nitrogen 5.5; total phosphorus < 0.5. The process flow scheme includes separate sludge thickening, dewatering in centrifuges, and transportation by spiral conveyor to special storage hopper with unloading devices. The system of pumping sludge out of primary settling tanks was left unchanged with the use of NN-50/25 pumps. Separately thickened raw primary sludge and excess activated sludge from secondary settling tanks are conveyed to the mixing chamber. Separately thickened sludges enter the sludge tank of the sludge treatment system. From pilot experiments Flottweg Z4E-4/454 centrifuges were selected for sludge dewatering. Improving cake dryness is provided by special design of the Z4E-4/454 centrifuge bowl and by maintaining high torque generated by the scroll. Dewatered sludge is transported to the storage tank by spiral conveyors. An outfeed assembly includes two storage hoppers equipped with outfeed bottom plates that have outfeed openings with overlapping devices installed on them, and horizontal scrolls with drives for transporting dewatered sludge into the outfeed openings. It was found that the upgrade of the sludge treatment facilities provided
for 72.5–75.2% sludge moisture at 99.7% dry solids capture rate. High level of dewatering process automation allows minimizing manual labor, cake loading into trucks for transportation to wastewater sludge incineration facilities of St. Petersburg for utilization.

Key words

wastewater , pumping station , aeration tank , sewerage treatment facilities , sludge , thickener , screw conveyor , scroll , storage hopper , outfeed device