previousWorking safety Referencesnext
Controlling of process of a wastewater treatment plant

Figure 15 shows the activated sludge process for wastewater treatment. In the figure, some monitoring units, and sampling points of the process are given.

Some parameters for controlling the process of the activated sludge system are pH, dissolved oxygen concentration (DO) and acid capacity with electrodes. The pH value and acid capacity are often used for dosage of liquids to stabilise the activated sludge process. The concentration of dissolved oxygen is used to control the activity of the aeration system. If the aeration system produce more oxygen than the process needs, the operation costs increase.

Figure 15: Flow chart of the activated sludge process

To get informations of the efficiency of the wastewater purification, taking samples at every stages of the process (influent, effluent, aeration tank, etc.) should be necessary. Parameters e.g. like ammonium, nitrate, nitrite, biochemical oxygen demand (BODt), chemical oxygen demand (COD), suspended solids (SS), the mixed liquor suspended solids (MLSS) and the sludge volume index (SVI) should be analysed regularly. (For further information:

Control measurement, monitoring and your own work

Support and control of the technical units as well as care and attention of human work are prerequiresite for the good working process. By creating a monitoring list of the maintenance of measurements could be helpful to organise the support and control e.g. of pH, oxygen and automatically working sampling units. A journal for sampling and the results of analyses will complete the monitoring.

Taking samples with human error and technical failure

The sampling points 1, 2, 4, 5 and 6 as shown in figure 15 can be piped with a bypass (by closing closed the valve) to take grab samples or can be connected with an automatically working sample taking system to take composite samples. At sampling points 3 a grab sample will be taken directly out of the aeration tank to determine the concentration of the mixed liquor suspended solids (MLSS) and the sludge volume index (SVI).

In the following you will find some hints for taking samples:

  • Use a clean glass or plastic bottle for samples

  • Label a bottle (e.g. point and kind of sampling, date and time, name of sample collector, parameters of analyses)

  • Do not touch the inner of the bottle with your fingers (contamination)

  • Through the first flush out of a pipe away and than take your sample

  • Stir the sample before you fill it into the flask

  • Fill the bottle up to the top. Oxygen in the flask let continue a biological process and the concentration of ammonium will decrease and the concentration of nitrate will increase

  • Take care that the volume of the samples will be big enough for analyses

  • Carry the sample as soon as possible to the laboratory or analyse it onsite (biological degradation still takes place!)

  • Cool the sample, do not leave it in the sun

  • Sample should be stirred, homogenised or filtrated before you start the analyse (depends on the kind of parameter for analyses)

  • Check and clean automatically working sampling units frequently

  • Control the cooling system (wrong temperature will change the ingredients

  • Take care that the whole volume of the connected samples will not be bigger than the volume of the flask

previousWorking safety Referencesnext