Hello Daniela, one should ...

Hello Daniela, one should look for causes:

• Rising Temperatures - Temperatures are rising as we come into the summer months and with this, the temperature of the wastewater also increases. As a result, aerobic bacteria become more active and begin digesting BOD and other nutrients at a faster rate. The warmer the water becomes, the more active they are and the more oxygen they consume. This results in low dissolved oxygen.

• Anoxic Zones - Low dissolved oxygen coupled with rising temperatures can lead to an increase in anoxic zones at the bottom of wastewater aeration basins. Anaerobic digestion releases sulphur dioxide, along with a variety of other noxious gases that are the causes of wastewater odour.

Usual Solutions (to act on causes):

Increase Oxygen Supply - Increasing oxygen supply ensures that the aerobic bacteria have the oxygen they need to aerobically digest BOD. This will help to control odours as anaerobic digestion will slow down.

Wastewater Circulation  - Ensuring dissolved oxygen is reaching the very bottom of an aeration basin is key to avoiding odour as this is where the odour-causing anaerobic digestion occurs. By circulating the wastewater effectively, you can create nearly equal dissolved oxygen throughout. This in turn will promote odour-free aerobic digestion.

Could you share the type of effluent is it and /or  some data of the activated sludge aeration? 
 

Containing and filtering the gases may be another solution. Capex and opex  depends a lot on the size of your plant. 

Best regards and feel free to contact me anytime.