What You Need to know About Nitrification /Denitrification that Compliance Monitoring and Grab Samples Can’T tell you

Effluent monitoring is a way of life for operators at any wastewater treatment plant with a National Pollutant Discharge Elimination Permit (NPDES). Effluent sampling for most parameters requires composite samples. This gives regulating agencies a measure of how well a treatment plant is operating and also provides a record of what is being discharged into the receiving waters. For the treatment plant operator it provides more of a pass/fail benchmark on how well the job is performed. When the laboratory results indicate all parameters are within the permitted limits, life is good. When those results indicate noncompliance, the operator is left with the task of performing a “post mortem” on the treatment plant to determine what went wrong. The task usually begins with an analysis of the Monthly Operating Report that contains all of the data that is submitted for NPDES compliance reporting.Composite samples maybe good for determining compliance, but they are terrible for troubleshooting operational problems when things have gone wrong. This is especially true for smaller systems that may not have sophisticated laboratories and large staff. Besides having results up to a week or more after the fact, composite sampling, even flow paced sampling, tends to hide the daily peaks and valleys of influent loadings. In effect, it muddies the peaks and valleys to yield one number for each parameter for each day. For troubleshooting operational issues, treatment plant staff usually must rely on process control grab samples to see how the inputs and outputs of the treatment units vary. This can be a time consuming process, especially for small systems whose operators wear many hats.The Ohio EPA Compliance Assistance Unit (CAU) has for years used multiple grab samples and datalogging equipment to troubleshoot out-of-compliance WWTPs. The CAU uses field wet chemistry for ammonia, nitrate and orthophosphate analysis, and datasondes for oxidation-reduction potential (ORP), dissolved oxygen (DO), conductivity and pH measurements. The CAU prefers the wet chemistry because it provides a direct measurement of the biological activity that takes place in treatment units. Datasonde information provides secondary measurements that can be used to gain insights into potential causes of noncompliance. In 2013, the CAU purchased the YSI/Xylem IQ SensorNet system with a VARiON instrument containing ammonium and nitrate electrodes. This instrument gives the CAU the ability to easily measure in real time the ammonium and nitrate concentrations in treatment units and to datalog that information for further analysis. The CAU now has a tool that provides a complete picture of nitrification and denitrification measuring the primary parameters of concern. The system is portable enough to move from tank to tank or from WWTP to WWTP as necessary. It is also easy enough to install, calibrate, and program. The VARiON has become a valued tool in the CAU troubleshooting toolbox.