Tom Stephenson
University of Sheffield
How can nitrous oxide emissions at wastewater plants be monitored in real time?
The challenge
Industrial effluents, such as landfill leachate or pharmaceutical wastewater, have high ammonia levels. Many wastewater treatment works are consented by the Environment Agency (EA) at < 5 mg/l NH3-N in treated effluent, and the consequences of nitrification failure can be serious. As one example, Severn Trent Water experienced nitrification issues at its Strongford Wastewater Treatment plant due to a customer illegally discharging toxic industrial effluent into the sewerage network. This ultimately resulted in fish being killed, and an investigation by the EA.
With typical fines imposed by the courts for prosecutions brought by the EA increasing, both in number and value, there is a critical need for effective alarm systems.
The solution
N-TOX® was developed by scientists at Cranfield University specifically for the monitoring of nitrous oxide (N2O) emissions from wastewater treatment facilities. The N-TOX® unit is capable of measuring nitrous oxide off-gases from a variety of wastewater treatment processes including activated sludge, sequencing batch reactors, industrial continuously stirred bioreactors and trickling filters. Nitrous oxide is a very powerful greenhouse gas – almost 300 times more damaging than the equivalent amount of carbon dioxide (CO2), and the data generated can be used both for toxicity monitoring and quantifying greenhouse gas emissions from wastewater treatment processes.
N-TOX® was commercialized by spin-out company Water Innovate (now a subsidiary of Bluewater Bio) which worked with Cranfield University and Severn Trent Water to identify ways to minimise both indirect and direct emissions from wastewater treatment processes. Greenhouse gas emissions from activated sludge processes were evaluated using N-TOX® to quantify emissions of nitrous oxide, whilst implementing novel control of their activated sludge plants. This enabled Severn Trent’s plants to be optimised not just in terms of performance, but also power consumption and greenhouse gas emissions.
Resulting benefits
The non-invasive nature of the N-TOX® detection system combined with remote access to data, makes installation and use relatively simple. Its low cost technology requires minimal operator intervention, utilises a proven N2O detector, and requires no expensive consumables such as chemical reagents or calibration standards.
The system provides an earlier warning compared to other systems because the indicator of the failure of the treatment process, N2O, is produced instantaneously.
Future directions
Water Innovate’s product portfolio also includes GHG-TOXTM, a development of N-TOX® that incorporates measurement of other important greenhouse gases that includes carbon dioxide (CO2), methane (CH4) and nitric oxide (NO), and MC-RTM, a zero waste advanced oxidation process for recalcitrant wastes. The company has a pipeline Memorandum of Understanding (MoU) on technology transfer with Cranfield University.
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