Daily laboratory testing is not only glamorous (not really), it’s critical (really) for process control purposes and it becomes even more important when things go wrong, which, at some point, they most certainly will. I tend to think that more testing is better than less testing but I don’t say this without having given some thought to making sure we aren’t running tests unless they generate data that is truly valuable which means that it is truly “informative.”
It’s not always easy to decide which tests to run and the frequency with which they should be run. It all comes down to how variable your wastewater is + how well your wastewater plant is running + the labor you have available to collect samples + the laboratory equipment you have to run the tests +, finally, the budget constraints you are probably dealing with all the time. So, just like everything else in life, during every minute of every day, you have to make a choice. It’s not going to be easy. You can deal with the reality of needing to do a fairly comprehensive set of testing with some regularity that can range from just once or twice a week all the way to a frequency of five or even seven days a week. But not doing enough laboratory testing is just about as bad as not doing any lab testing if the resulting data does not give details sufficient enough to form a complete picture.
You need to know how each major unit process is working. The failure of any given unit process to do its expected share in reducing the COD or TSS or O&G is going to place a much larger burden on the unit processes that follows. And in particular, when the unit process that follows is the biological reactor, the heart of the entire wastewater system, overall plant performance can be significantly compromised.
Take a look at the simplified process flow diagram in Figure 1, below. What you see is the actual testing program for an industrial wastewater treatment plant in a petrochemical facility. The biological reactor in this refinery tends to be easily overloaded. So the employees at this plant, the managers, the workers, the wastewater plant operators, all of the employees, recognize that in order to maximize the processing of crude oil, in order to maximize revenue and maintain secure employment and to be a good “neighbor” since overloaded wastewater plants tend to really stink, each employee knows that they must be aware of what the waste streams they generate in their specific part of the plant are doing to the wastewater plant.
Between the operators and laboratory personnel you can see that most days at least 34 tests are being run from the influent to the effluent of this wastewater plant. I haven’t shown additional testing done, as required by their discharge permit, on their outfall from the final pond. From a process control perspective you’ve got to have things running properly such that the secondary clarifier overflow meets all permit requirements. The two additional ponds provide a safety net for times when the plant operation is not quite as it should be.
A lot of the key testing is done by the operators and they do some of these test every four hours, seven days a week. This frequency is required to insure the wastewater plant operates within its limited capacity. The operator process control tests include TSS, COD, alkalinity, ammonia, nitrate, pH, MLSS, turbidity, phosphate, and temperature. I’m going to discuss, with varying degrees of detail, each of these tests and some of the easy ways they can be run. I’ll also discuss oxidation reduction potential (ORP) because you’ll see how quickly it can tell you what’s going on in each unit process of your plant. Unfortunately, this test is seldom run by operators at all the different plants I go to.
Figure 1: Simplified Process Flow Diagram of a Refinery Wastewater Treatment Plant