Urban waste from Lisbon and 18 neighbouring municipalities undergo treatment and recovery through an integrated system overseen by Valorsul, a company jointly owned by private and public entities.

The primary electricity-generating unit operates by incinerating unsorted urban solid waste in three incinerators, each capable of processing 28 tons of waste per hour at a temperature of 900 degrees Celsius. The heat generated from the incineration process is harnessed to produce water vapour, which, in turn, powers a turbogenerator to generate electrical energy.

For every ton of waste incinerated, approximately 587 kWh of electricity is produced, with 89 kWh utilized for operational purposes, and the surplus energy is fed into the national electricity grid. Situated in S. João da Talha, this facility processes around 1000 tons of unsorted solid waste daily, providing enough energy to meet the needs of a city housing 150 thousand inhabitants.

Additionally, each ton of incinerated waste yields approximately 200 kg of slag, which is sorted. Metallic slag is recycled to serve as raw material, while other types undergo a maturation process, resulting in an artificial aggregate utilized in civil engineering projects, particularly road construction, as a substitute for natural materials. This product holds CE mark certification.

Valorsul operates two other units that produce electrical energy by burning biogas generated through the anaerobic digestion process of biodegradable waste. These units also yield an organic compound suitable for use in gardening, green spaces, and agricultural cultivation of trees and shrubs.

Collectively, the three Valorsul units produce an average annual output of 350 GWh of electrical energy. This electricity generation is derived from the mixed domestic waste generated by 1.6 million residents within the company's operational area, constituting only 20% of the total domestic waste produced nationwide. This suggests significant untapped potential for expanding electricity production from urban waste throughout Portugal. 

https://www.valorsul.pt/pt/areas-de-negocio/tratamento-e-valorizacao-de-residuos-urbanos/valorizacao-energetica/valorizacao-energetica/
https://www.valorsul.pt/pt/areas-de-negocio/produtos/
 

DIRECT SDGs:

• SDG 7 - Affordable and clean energy: Sustainable production of clean energy from urban waste
• SDG 11- Sustainable cities and communities: Reducing the environmental impact of urban waste
• SDG 12 – Responsible consumption and production: Waste recycling for low-cost energy production

1. What is the process by which energy is generated from urban mixed solid waste?
2. What are the potential uses of slag?
3. In addition to solid waste, how else does Valorsul generate electrical energy?

Incinerating mixed municipal waste is a contentious waste disposal method, particularly concerning its environmental implications. It's crucial to acknowledge the European Union's stringent recycling targets for all member states. While there are benefits such as electricity and heat generation, as well as land conservation, we mustn't overlook the drawbacks. Before incineration or landfilling, numerous valuable secondary raw materials can be reclaimed from waste, reducing energy consumption in production and preserving primary resources. However, waste incineration produces hazardous airborne emissions, necessitating effective chimney filters and specialized storage for toxic ash.

At the S. João da Talha plant, emissions from combustion undergo treatment through a system of filters and bags and undergo constant laboratory scrutiny. Multiple public and private entities conduct regular monitoring of the plant's operations across various environmental parameters to ensure minimal adverse impacts on the surrounding environmental quality.

EDU.IN – Associação para a Educação Integral