The different problems are explained more in detail in this section (European Environment Agency (2014)):

Air emissions: If the waste of a city is not managed in a sustainable way, much of it will be disposed in landfills or burned in waste treatment facilities. The results of those waste treatment methods are enormously affecting the air. A lot of modern waste incineration plants are minimizing the toxic fumes or hazardous particles that are emitted. Still, there are less advanced facilities where the toxic fumes are emitted in the atmosphere which threatens health of flora and fauna. The disposal of waste in landfills brings another problem with it. The degradation of organic waste causes the emission of gases like methane and carbon dioxide which are main drivers for the climate change. Additionally, the vehicles to remove the waste are emitting Co2.

Soil and groundwater contamination: The contamination of soil and (ground-)water that for example results from the disposal of waste in landfills is a big problem for humans, animals and plants. Hazardous substances that are extracted in the soil can directly and indirectly (food chain) harm flora and fauna. 

Endangerment of ecosystems: Especially coastal areas and the marine environment as ecosystems are affected by a poor waste management. Illegal dumping or littering that is not prevented by the city administration leads to the pollution of the sea. Toxic particles and a bad water quality are destroying the habitat of marine life. 

There are some possibilities how the generated waste can be treated in an environmentally friendly way. The objectives of a smart city administration, when it comes to waste management, should be, to either make use of the waste within the most sustainable way or to influence the inhabitants to generate less waste. Figure 1 shows the different possibilities, how solid waste can be treated from the most sustainable way down to the least sustainable way. 

The objective of the smart city should be to eliminate the endangerment of the environment caused by the wrong treatment and the loss of resources; thus the waste should not be brought to a landfill or a facility where the material (waste) is lost without an added value.