Process Control Testing

Wastewater operators know they must sample for the parameters (CBOD5, TSS, pH, DP, etc) listed on the KPDES permit at the frequency indicated on the permit. The operators know the limits these analyses must meet. The big question is how operators assure their wastewater treatment plant continues to meet these criteria. The easiest way to keep the effluent from wastewater in compliance is through process control testing.

Process control testing can be any test to help the operator understand what is happening in the plant during normal or upset conditions.  Process control testing is used to track plant performance on a day-to-day basis, allowing the operator to see how changes in flow, organic loading and/or pH can affect the plant’s performance. 

The tools for process control consist of a portable pH meter, portable DO meter, settleometer and, if one is available, a microscope. The pH and DO should be monitored throughout the wastewater treatment process, not only in times of upset, but when the plant is functioning normally. Then there is a history of the pH and DO levels that can be expected during normal operations. The settleometer test gives operators of wastewater treatment plants the ability to observe and measure the rate and characteristics of the separation of solids. This is essential for the operational control of the biological treatment process in which sludge is produced. The settling rate is also an indication of sludge age, which will allow the operator to control the wasting of sludge to keep the plant in control. A microscope allows an operator to visually monitor the protozoa and metazoa in the sludge.  A healthy system usually contains about the same number of free swimming ciliates, stalked ciliates and rotifers. A higher number of free swimmers and amoebae are found in a system with young sludge, while a system with older sludge will have a higher concentration of stalked ciliates, rotifers and invertebrates, such as nematodes. In either case, the operator should decrease sludge-wasting (young sludge) or increase sludge-wasting (older sludge) to optimize the treatment process.

Even with no instrumentation an operator can perform process control testing. The simplest process control tests involve the operator’s senses. An operator at the wastewater treatment plant should observe the appearance, color and odor of the aeration tanks, clarifiers, influent and effluent streams, correlating these properties with pH and DO levels in the system at the time. Changes in color, odor or appearance can serve as a warning that the plant has been affected by a spill from a local industry, high organic loading from waste haulers or a toxic stream from industry or another source. If there is a change in color, odor or appearance, an operator should use other process control tests, such as pH, DO or COD to determine the cause of the change.  A high organic load may cause a decrease in DO levels and an increase in COD levels in the system. A high or low pH can be an indication of an industrial spill entering the system. Any change from the norm will require the operator to change how the system is being operated to handle the situation at hand.

In closing, process control testing is a necessary part of controlling one’s wastewater treatment process.  An operator must use all tools available at the site, and use all five senses as effective process control tools.

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