The WWTP (200.000 PE) was suffering from a high sludge volume index for years, which led to a high costs for precipitating agents. One main reason for that was the high percentage of industrial waste water in the influent.
A further aim was to reduce energy consumption and therefore the energy costs of the biological stage.
Step 1: Changing the aeration strategy
The sludge volume index could be reduced significantly and long term by changing the aeration strategy in the activated sludge tanks.
Step 2: Optimization of precipitants
In a second step different precipitants have been tested, based on a Europe-wide tendering procedure. Furthermore the location of the precipitant addition, of the control strategy and of the costs of the precipitant itself have been optimized
As a result the costs for the precipitants reduced notably and the sludge volume index could be stabilized under 100 ml/g. Furthermore the nitrogen removal could also be improved.
Step 3: Dynamic simulation in order to optimize the energy consumption
H2Office developed a simulation model for the secondary treatment which was calibrated with measurements on the WWTP. A simulation carried out for time period of 1.5 years showed the effects on the effluent and the energy consumption for the optimized aeration and operation strategy in comparison to the former applied strategy.