Wastewater sludge utilization

Vodokanal is a municipal water and wastewater service based in St. Petersburg that provides drinking water to 5,3 million citizens of the city and tens of thousands of companies and enterprises. Vodokanal also collects and treats wastewater to support the implementation of the Helsinki Commission’s recommendations for preservation of the Baltic Sea. St. Petersburg has, through the work of Vodokanal, become the first megalopolis in the world to solve the problem of wastewater sludge utilization, finding alternative utsages of the sledge that otherwise would be hazardious waste.

Challenge

The combination of only these two treatment stages did not ensure the quality of treated effluents stipulated in HELCOM (Convention on the Protection of the Marine Environment of the Baltic Sea) recommendations concerning nutrients total nitrogen and total phosphorus (when entering the Baltic Sea water they create a nutrient medium for bluegreen algae, that take in oxygen from water and cause the death of the water bodies living organisms).

Therefore, today, chemical and biological wastewater treatment is introduced at the Vodokanal wastewater treatment plants, which combines enhanced biological nutrients removal with the accompanying chemical phosphorus precipitation. Today, a chemical method for phosphorus removal has been introduced at all the city wastewater treatment plants, using aluminium sulphate, which is the most effective and economical chemical.

Good practices and solutions

Three sludge incineration plants operate in the city at the Central wastewater treatment plant, Northern wastewater treatment plant and South-West wastewater treatment plant. Sludge is incinerated in the fluidized-bed furnaces at the temperature of 870°C. The heat produced by sludge incineration is used for process needs, space heating and power generation for Vodokanal to save energy resources. Flue gases are treated in three stages.

Mechanical treatment is designed for wastewater clarification. This block comprises an inlet chamber, mechanized screens, grit channels and primary clarifiers. The biological treatment includes aeration tanks and secondary sedimentation tanks. The biological treatment process occurs due to vital functions of activated sludge in aeration tanks in continuous contact with atmospheric oxygen injected into the aeration tank. Activated sludge is a biocenosis inhabited by different bacteria, protozoa and multicellular microorganisms which transform contaminants in wastewater and treat them.

Outcomes & Opportunities

Vodokanal amis to provide accessible water and sanitation services to ensure high quality of life for the customers and sustainable city development, to build the culture of water use and to preserve the Baltic Sea basin. The company operates according to values of sustainability and responsibility: Responsibility before future generations; Responsibility before the customers; Responsibility before the staff; Openness to the public and responsibility before the society. It also operates with an innovative approach focused on learning from international best practices in the field.

Some examples of ongoing programmes of Vodokan to enhance its capabilities includes:

• The Neva Untreated Wastewater Discharge Closure Program: This program envisages, among other things, the completion of the extension of the Northern Tunnel Collector, and the modernization of the Northern and Central Wastewater Treatment Plants to comply with new requirements of HELCOM (The Baltic Marine Environment Protection Commission) regarding enhanced removal of nitrogen and phosphorus from wastewater.

• Improvement of sewage sludge treatment and disposal technology: Today, all the sludge produced by wastewater treatment is burnt at three sludge in-cineration plants. However, in the previous years (before the incinerators were constructed) sludge was disposed to special landfills. For instance, the area of Severny landfill in Novoselki is about 83 ha. To eliminate a negative impact of sewage sludge landfills on the environment, a landfill reclamation project was designed on the basis of Geotube technology.

Related SDG targets

• 9.4 By 2030, upgrade infrastructure and retrofit industries to make them sustainable, with increased resource-use efficiency and greater adoption of clean and environmentally sound technologies and industrial processes, with all countries taking action in accordance with their respective capabilities.
• 6.4 By 2030, upgrade infrastructure and retrofit industries to make them sustainable, with increased resource-use efficiency and greater adoption of clean and environmentally sound technologies and industrial processes, with all countries taking action in accordance with their respective capabilities.
• 6.5 By 2030, implement integrated water resources management at all levels, including through transboundary cooperation as appropriate.

 

Photo: © Justin Kauffman/Unsplash

Project: Circular Baltic 2030