Guidelines on Implementation of Wastewater Management Program

Controlling activated sludge process requires understanding on the fundamental principles related to the basic operation of the system so that one can fine-tune and conduct performance monitoring to ensure each component is working properly and optimally as per design. Basically there are 4 different approaches or control methods that can be included as part of the wastewater management program so that these can be used as a tool and guidelines for plant operators, technicians and engineers to refer to. Each of the listed approaches here demands that certain tests are to be performed to obtain relevant information for further adjustments.

1. Constant Solid Method
Maintaining performance of activated sludge process using this method will need information on the MLVSS to be made available so that this will indicate and tell the plant operators that the current value is the best working condition for your wastewater treatment system. Without these it will be rather impossible maintaining a constant and manageable plant process parameters range and this information is usually concluded based on trial and error by conducting a performance study.

Once an ideal range has been obtained, it will be the duty and role of every person involved managing the system to strive and work towards maintaining the ideal range by performing sludge wasting on a daily basis. The only disadvantages of using this approach is that control can be made complicated if let’s say the plant is encountering fluctuation on the influent loading rate.

effective wastewater treatment program2. Food to Microorganisms (F/M) Ratio
F/M generally represents the amount of foods available to the number of microorganisms present in the aeration system. Usually an ideal ratio is needed and maintained at a certain range in order to avoid settling problems in the clarifier section. Similarly like constant solid method mentioned earlier, F/M ratio also requires that MLVSS test to be carried out. Apart from that oxygen demand of the influent wastewater expressed in terms of BOD or COD is also needed to determine the quantity of foods present.

For calculation purposes, either one of these parameters can be chosen but once you have decided which one to refer to, it should remain the same for comparative purposes. COD (Chemical Oxygen Demand) test can usually give fast results in under 4 hours while BOD will take longer time up to 5 days, thus COD is always the preferred choice for ease of determining the F/M ratio. Refer to the table below for examples to help you calculate the value based on the formula given here.

F/M = [(COD, mg/L) x (Q, m3/day)] / [(MLVSS, mg/L) x (Aeration Volume, m3)]

Take an example, if
COD = 5700 mg/L
Q = 144 m3/day to the aeration tank
MLVSS = 3500 mg/L
Aeration Tank Capacity = 1000 m3

F/M = (5700 x 144) / (3500 x 1000) = 0.2345

Typical performance of conventional activated sludge process to be incorporated into the wastewater management control program should be:
0.15 to 0.70 if COD is used as calculation
0.10 to 0.50 if BOD is used as calculation

3. Sludge Age Determination
Sludge Age can roughly tell you what is the length of time the microorganisms has already remain and grow in the wastewater treatment system. Usually it can be calculated based on the tank MLVSS divided by the amount of wasted sludge plus the effluent VSS load. Normally, in order to obtain consistent discharge quality meeting regulatory standards, the typical sludge age should be adjusted to around 5 to 15 days based on conventional systems operating conditions.

Both the sludge age and F/M ratio mentioned earlier are interrelated meaning that a change in one will affect the other. For instance if sludge age is increasing, that usually translate to higher MLVSS resulting in lower F/M ratio. Vice versa if the sludge age in getting lower and lower, the F/M ratio will now move in the opposite direction. Usually observations based on the appearance of water in the aeration tank and by conducting some simple tests can tell you that whether your sludge is too young or the F/M ratio is just too high. These are the signs to watch out.
  • Sludge appears light brown in color and it will settle slowly in the clarifier
  • Thick foam is building up as the wastewater undergoes aeration
  • Dissolved oxygen drops below 2ppm level

4. SVI and SOUR
Finally, SVI and SOUR are the other plant parameters which you can use as part of your wastewater management schedule to monitor the performance of your activated sludge process. I won’t go into details covering this topic over here as you can refer to this article posted earlier about SOUR measurement and SVI test.

Recommended Engineering Books