Nitrate Monitoring for Decentralized Wastewater Treatment Systems
The use of decentralized wastewater treatment systems (DWTS) is increasing worldwide due to a several reasons:
- Cost effective than sewer systems
- Scalability
- Water reuse
When designing decentralized systems, there are several operational challenges that need to be addressed:
- These systems typically do not have dedicated operators unlike central wastewater plants
- Nitrogen levels in the influent are highly variable
Nitrate sensors can help address these challenges and make it easier to leverage the benefits decentralized systems can offer. These sensors can monitor the variation in influent quality and automatically control aeration and carbon additions to meet the low nitrogen requirements in the effluent. As much as a 25- to 50-percent reduction in the use of carbon and frequency of sludge hauling can be achieved. In turn, this leads to a lower cost of ownership for end users.
The existing line of technologies that are used for nitrate monitoring have several crucial limitations. For example, Ion Specific Electrodes (ISE) have limited life, require frequent calibration and therefore, are not suited for real-time monitoring. While UV lamp sensors are suitable for real-time monitoring, they can be cost-prohibitive for DWTSs.
An alternative solution is UVC LED-based sensors. By using UVC LEDs, the optical sensor design can be simplified because the UVC light is emitted in a near monochromatic spectrum, and very high light intensities can be produced at the desired wavelengths. UVC LED-based sensors can be turned on instantly when a measurement needs to be taken. Moreover, UVC LEDs have a relatively long life. Taken together, these factors make it possible for calibration intervals to be relatively long and allow for remote operation.
Nitrate sensors using UVC LED light sources exhibit excellent accuracy in measuring nitrate levels across concentration ranges in treated wastewater (see Figure below). The availability of durable, affordable nitrate sensors can enable decentralized systems to optimize their operation to match the waste characteristics of the influent.
