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

Calculation of membrane surface in membrane bioreactors

Summary

On the basis of the foreign publications analysis membrane bioreactors and membranes used in them are considered. In pressure units with a remote membrane assembly the specific flow through the membrane (at 20°C) is 80–200 l/(h∙m²) at 20–500 kPa transmembrane pressure; whereas in the units with submerged membranes – 8–30 l/(h∙m²) at 10–60 kPa vacuum. The specific power consumption in bioreactors with pressure membranes is within the limits of 1.5–4 kW·h/m³; with submerged membranes – 0.5–0.7 kW·h/m³. The results of analyzing the equipment market showed that submerged membrane elements and modules have been used in 97–99% biomembrane units. The comparison of submerged membranes shows that modules made of hollow fiber membranes have higher specific surface (300–600 m²/m³) compared to flat ones (50–150 m²/m³). Hollow fiber membranes are characterized by lower cost, higher resistance to fouling and backwashing. Flat membranes have higher mechanical toughness and can be more easily replaced. The operation of membrane batch bioreactors, the use of osmotic membrane bioreactor and nanofiltration processes in biomembrane technology are described. The technique of calculating submerged hollow fiber membrane surface with account of various allowed specific flows depending upon the durability of the design flows, time lost for backwashing and «relaxation», reflux from membrane backwashing is presented. At determining the number of the operating in parallel process lines one should take into account possible shutdown of one membrane tank for chemical washing or repair.

Key words

wastewater , biological treatment , transmembrane pressure , power consumption , membrane bioreactor , specific flow

Comparative Evaluation of Ultrafiltration Plant at Treatment of Water of Lake Ladozhskoye and Aftertreatment of the Neva’s City Water.

Summary

The comparative evaluation of operation of two industrial ultrafiltration plants with the same design and output and intended for treatment of water from one source is made. The practical experience of operation shows that the restoration of operational characteristics of membrane operating in water containing a bulk of polluting substances (taken from Lake Ladozhskoye directly) takes place according to standard methodology with the use of alkali solution of sodium hypochlorite and hydrochloric acid. The use of these reagents for restoration of operational characteristics of membranes aftertreating Lake Ladozhskoye water after their preliminary treatment at city water supply facilities of St. Petersburg (the Neva’s city water) was inefficient. Results of the study aimed at determination of reasons for rapid pollution of ultrafiltration membranes operating at aftertreatment of the Neva’s city water as well as methods developed for restoration of their operational characteristics are presented.

Key words:

ultrafiltration membrane , back and chemical wa¬shings , restoration of operational characteristics , transmembrane pressure