Introduction of membrane technologies at the wastewater treatment facilities of Molodezhnoe settlement

Summary

The experience of introducing membrane wastewater treatment technology at the wastewater treatment facilities in Molodezhnoe settlement (St. Petersburg) is presented. The treatment facilities include: a main pumping station, a combined mechanical wastewater treatment plant, a wastewater regulator, a bioreactor (aeration tank operating using nitri-denitrification technology) for enhanced nitrogen removal, a membrane bioreactor, an ultraviolet effluent disinfection unit, a screw press for excess activated sludge dewatering, aluminum sulfate dosing unit for the chemical removal of phosphorus compounds (phosphates). The effluent after disinfection is discharged through a deep-water outlet into the Gulf of Finland. Membrane filtration provides for the enhanced tertiary treatment to remove fine suspended solids and colloidal particles. To achieve a stable quality of the effluent during the operation of membrane modules, the following requirements shall be strictly met: the high efficiency of screenings removal; prevention of the ingress of foreign particles into the bioreactor after mechanical treatment; high concentration of sludge in the aeration tank and membrane unit; timely chemical washing of the membranes. During the trial operation of the treatment facilities in Molodezhnoe, the irregular hydraulic and pollution loading was noted. During the operation period the operating modes of the facilities were adjusted with account of the irregular characteristics of the incoming flow while achieving the design parameters of the process line of wastewater treatment.

Key words

wastewater , advanced biological treatment , transmembrane pressure , membrane module , membrane technology , hydraulic loading

Upgrade of horizontal sedimentation tanks with the use of dissolved-air flotation

Summary

The analysis of the efficiency of low turbidity colored water of the Vychegda River purification at the water treatment facilities of Syktyvkar in horizontal sedimentation tanks operating in the mode of coagulation at 2–3 times lowered hydraulic loading is presented. The necessity of upgrading the sedimentation tanks by redesigning their exit sections into flotation chambers is substantiated. The enhancement of the sedimentation tank operation by equipping with a flotation chamber provides for meeting the regulatory requirements to the drinking water quality under the conditions of significant seasonal fluctuations of the raw water quality indicators and temperature. Enhanced clarification of the water being coagulated is ensured before the filtration stage; at that the flow rate of backwash water decreases 3 times, the number of filter washes per day decreases to 0.5 times and less (filter run increases to 2 days and more). Backwash water purification together with raw water provides for streamlining the process flow scheme and chemical facilities (the number of chemical injection and dosing points decreases); facilitating the operation of the facilities, 8% operational expenses saving and plant demand decreasing to 3%. The upgrade of horizontal sedimentation tanks with the use of dissolved air flotation is more economically and environmentally feasible than the reconstruction of the two-stage filtration facilities. It provides for doubling the sedimentation facilities output, decreasing the amount of wash water and combined with raw water handling.

Key words

wash water , horizontal settling tank , filtration , pressure flotation , low turbidity colored water , hydraulic loading , water treatment plant

Dissolved-air flotation in water treatment (a review of foreign literature)

Summary

A review of foreign literature on one of the perspective water treatment technologies, i. e. dissolved-air flotation, is presented. The process of dissolved-air flotation provides for decreasing water turbidity, eliminating algae, Giardia cysts and Cryptosporidium oocysts; whereby, the treatment efficiency is higher compared to sedimentation. The technology ensures efficient removal of low turbidity levels. Overseas, beyond controversy, the tendency of using dissolved-air flotation units for purification of water and wastewater of different origin is increasing.

Key words

water treatment , efficiency of treatment , pressure flotation , hydraulic loading