The U.S. Environmental Protection Agency’s (EPA) Water Infrastructure Resiliency and Finance Center, in collaboration with the...
A unique ammonia/phosphate analyzer designed to take readings directly in the wastewater, in other words, precisely where the nutrient concentration needs to be measured, also delivers real-time, online information about nutrient concentration in the process.
Designed especially for the water and wastewater industry, the EVITA INSITU 4100 analytical nutrient analyzer now is available from Danfoss Water & Wastewater, N.A. Division. It was developed to provide a system that saves money, improves efficiency and measurement accuracy, and reduces maintenance.
Monitoring and controlling nutrients with a real-time, online system can provide these important benefits to a wastewater treatment plant:
How does INSITU 4100 work? It utilizes a unique antibacterial, ion-permeable membrane to stop bacteria and sludge from entering the analyzer. This membrane allows the analyzer to operate using a clean carrier solution, instead of wastewater as used in a traditional analyzer. This helps eliminate any measurement errors caused by a fluctuation in sludge density or color, thereby increasing measurement accuracy and reducing maintenance frequency. The insitu analyzer measures continuously — performing a new measurement of the ion concentration every second.
The output signal is only delayed slightly from the real-time value, making it useful for advanced process control.
The insitu analyzer "sees" the wastewater's nutrient concentration by allowing only ions to transfer through its ion-permeable membrane; wastewater does not flow into the analyzer.
A carrier solution (de-ionized water) is pumped through a channel behind the membrane. Ions in the wastewater migrate through the membrane, into the carrier solution, until the concentration of ions in the carrier solution is equal to the concentration of ions in the wastewater.
Reagents are mixed into the carrier solution, resulting in a color change. The color intensity, which depends on the ammonia or phosphate concentration, is measured by a photometer (colorimetric technology) and an electronic signal is sent to the converter for display and control.
After the measurement is complete, the waste solution is pumped to a sealed retention bag for storage within the transmitter.
The cost of installing a traditional nutrient monitoring system often can exceed the cost of the system itself. Traditional analyzers require the installation of a pump to draw a sample from the wastewater basin, heated piping to bring the sample to the analyzer, a filter to "clean" the sample, and a protective housing or building to ensure a stable measurement environment. These external environmental requirements add to the installation cost, impede real-time measurement, and create the potential for inaccurate measurement results.
The traditional system pumps a sample from the wastewater to the analyzer, where it is measured. Using wastewater as the carrier solution results in a measurement error when the sludge density or color fluctuates. In order to reduce the effect of this problem, these systems depend on filters to clean the sludge and bacteria from the wastewater sample before it enters the analyzer.
The problem with using a filter is that they tend to clog. If the system has a clogged filter, it will adversely effect the response time, causing a delay of up to 100 minutes before the sample reaches the analyzer. Finally, filters can also distort the measurement because the bacteria trapped in the filter is still active. Consequently, the concentration of nutrients from the sampling point is altered before the sample ever reaches the analyzer. Once the sample reaches the analyzer, a periodic measurement is taken only once every 20 to 30 minutes. This long delay, between taking the sample and measuring it, makes reliable automatic process control very difficult to achieve.
The development of the insitu system was driven by a desire to provide a system that saves money, improves efficiency and measurement accuracy, and reduces maintenance. As shown in the photo, the analyzer is easily mounted directly into the wastewater, significantly reducing the cost of installation (no pumps, piping, filter, or protective housing). Its unique design allows the analyzer to float up or down with the surface of the wastewater, making it ideal for applications with frequent fluctuations in level.
The INSITU 4100 analyzer comes with a replaceable, ion-permeable membrane cartridge. All of the reagents necessary for reliable calibration and measurement are supplied in an easily replaced, sealed container. This container consistently ensures the correct quantity and concentration of chemicals and eliminates the need for handling of potentially dangerous chemicals by the operator.
The insitu analyzer requires only about 15 minutes of maintenance five to six times per year. Traditional analyzers must be disassembled for internal cleaning once a week and require cleaning of the filter, using a strong acid, at least once a week or more (depending on process conditions). They also have tubes and lamps that must be checked and/or replaced every two months, and the filter material must be replaced at least once a year.
The insitu analyzer also features an optional cellular communication package, which enables the transmission of alarm/error messages in text format for up to four mobile phones. Using this information a problem can be diagnosed and corrected from a remote location, further reducing labor costs.