Solutions for the treatment of silt deposits of water utilities

The growing sewage sludge is one of the critical problems of modern urban development, which has a negative impact on the environment.

At the same time, the sediment is a promising raw material for obtaining various useful products – biogas, fertilizers, etc.

This study conducted by SBS Consulting is devoted to the analysis of current solutions and technologies for the treatment of water treatment plants' sludge. It examines various methods, their advantages and disadvantages, as well as the economic feasibility of their application in Russia. Particular attention is paid to comparison with European practices and evaluation of prospects for the introduction of innovative technologies.

Current situation and dynamics of water consumption

Urban water consumption:

• Water consumption of the urban population in Russia has been declining over the last 5 years at an average annual rate of 1%.
• The average annual rate of decline in sewage sludge generation was 2% in 2016-2020.

Sewage sludge volume:

• In 2020, the volume of sewage sludge generation was about 67 mln m³/year.

Methods of sludge treatment

European practices:

• The EU countries predominantly rely on composting and agricultural use of sludge.
• In 2018 in the EU, 20% of sludge was used in agriculture, 17% was composted, 27% was incinerated, 14% was deposited in landfills, and 23% was used in other ways.

Russian practices:

• In Russia, a large share of sludge is stored in sludge drying beds.
• In 2020 about 5-7% of sludge was used as fertiliser.
• About 6% of the sludge was incinerated (mainly at 3 plants in St. Petersburg).

Sludge treatment and utilisation technologies

Technologies under development:

1. Electroosmotic dewatering:

• An additional stage of sludge dewatering.
• The technology is under development in Russia and abroad.

Technologies used on a small scale:

1. Composting/Vermicomposting:

• Obtaining fertiliser from sludge.
• Used on a small scale in Russia.

2. Sludge dewatering in geotextile containers:

• Intermediate dewatering stage between mechanical dewatering and sludge drying beds.
• Used on a small scale in Russia.

3. Incineration:

• Used in St. Petersburg.

4. Anaerobic digestion:

• Biogas production
• Used on a small scale in Russia.

Technologies used on a small scale abroad:

1. Pyrolysis:

• Synthesis gas production.
• Used in related industries in Russia.

2. Production of liquid fuel from sludge:

• Production of oil-like substance.
• Not used in Russia.

3. Supercritical water oxidation:

• Significant sludge reduction without the use of incineration.
• Not used in Russia.

4. Sludge biodrying:

• High intensity composting to produce dried biofuel.
• Used at 2 sites in the Netherlands.

Экономические аспекты технологий

Сравнение затрат на обработку и утилизацию осадков:

• Incineration:

—CAPEX: RUB 83,200/tonne of sewage sludge

—Cost price: RUB 8,800/tonne of sewage sludge

• Composting:

—CAPEX: RUB 32,700/tonne of sewage sludge

—Cost price: RUB 5,600/tonne of sewage sludge

• Anaerobic digestion:

—CAPEX: RUB 7,700/tonne of sewage sludge

—Cost price: RUB 10,600/tonne of sewage sludge

• Pyrolysis:

—CAPEX: RUB 31,300/tonne of sewage sludge

—Cost price: RUB 9,900/tonne of sewage sludge

• Sludge vitrification:

—CAPEX: RUB 32,900/tonne of sewage sludge

—Cost price: RUB 5,400/ tonne of sewage sludge

Conclusion

The study shows that many water treatment plants in Russia continue to accumulate sludge in sludge drying beds due to a lack of funding for the implementation of modern technologies. Technologies that are under development or already in use on a small scale have great potential for being commercialised in Russia. The study shows that many water treatment plants in Russia continue to accumulate sludge in sludge drying beds due to a lack of funding for the implementation of modern technologies. Technologies that are under development or already in use on a small scale have great potential for being commercialised in Russia.