Wastewater BOD Monitoring


Biochemical oxygen demand (BOD) is one of the most important measurements in wastewater treatment. Regulatory requirements normally determine the permissible threshold for treated waters discharged back into the environment using a lengthy test such as BOD5 to control. Recent advances in online measurement systems now make it possible to measure BOD, COD and other parameters in real-time and with improved accuracy.

Wastewater BOD

BOD is a measurement of the amount of oxygen consumed by bacteria and other microorganisms to break down organic matter found in wastewater. In order to safely be discharged back into the environment, treated waters must have sufficiently low BOD to avoid depleting ecosystems of their dissolved oxygen (DO) supply.
Raw wastewater typically has a DO concentration of less than 20% or 1-2 mg/L, while a healthy river ecosystem should be near 100% saturation (8-10 mg/L).
Discharge of insufficiently treated wastewater may cause bacteria to consume oxygen faster than aquatic plants, algae and natural aeration can replenish it.
Resulting low DO levels can stress an ecosystem and have detrimental effects on aquatic life such as fish kills and species loss.
BOD5 is the most common control test to determine quality of discharge waters, but it is very slow (5 days) and provides only limited accuracy.
When waters are found to be over the compliance thresholds, it is too late to take corrective measures because they have already been discharged.
Municipalities with combined sewer systems that also collect rainwater are subject to Combined Sewer Overflows (CSOs) which may release high-BOD waters.

Typical Wastewater BOD Monitoring System

Recent advances in sensing technology now make it possible to accurately sample wastewater for BOD at any stage of the treatment process - a dramatic improvement over traditional methods such as BOD5. By combining the Proteus multiparameter water quality sonde with NexSens telemetry systems, accurate BOD measurements can be delivered in near real-time.

The Proteus was developed in the UK via collaboration between RS Hydro and the University of Birmingham. In addition to BOD, it supports calibrations for other parameters relevant to water and wastewater treatment including chemical oxygen demand (COD), dissolved organic carbon (DOC), and total organic carbon (TOC). The probes also accommodate other sensors for basic and advanced measurements like pH, DO, turbidity, CDOM and tryptophan, all in a single instrument package.

Combining the Proteus with the NexSens X3 environmental data logger allows for online data collection from nearly any location. The X3 runs from a fixed AC power supply or SP-Series solar power pack. Data is transmitted wirelessly to the WQData LIVE web datacenter, which includes a rich feature set for viewing, manipulating, reporting and exporting of data. Configuration of alarm notifications is also possible to inform personnel when critical thresholds are surpassed.

Besides the Proteus, systems can easily be expanded with a wide range of industry-standard sensor types such as water level sensors and velocity/flow meters. The multiple sensor ports on the X3 data logger facilitate multi-sensor deployments from the same unit. Buoy-based measurements are also possible, for example, to measure DO at locations where effluent is discharged back into surface waters.

Contact a NexSens Applications Engineer today to discuss your wastewater BOD monitoring application.

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