N-Tox^® is a patented nitrification toxicity monitoring system that provides early warning of activated sludge failure and consequent wastewater treatment works breakdown, and helps prevent ammonia pollution of the aqueous environment.

The product detects nitrous oxide (N₂O), a harmful greenhouse gas with global warming potential almost 300 times that of carbon dioxide.

The unique features of N-Tox^® include:

• critical early-warning device, used to monitor nitrification effectiveness in municipal and industrial activated sludge systems;

• real time response allowing proactive management by providing an earlier warning compared to other systems because the indicator of the failure of the treatment process, N₂O, is produced instantaneously;

• robust, non-invasive technique based on gas-phase detection which avoids sampling of activated sludge and eliminates associated probe fouling and maintenance issues;

• simple, low cost technology requires minimal operator intervention and utilises a proven, standard N₂O detector;

• innovative design comprises an integral sample pump, gas conditioning device, non-dispersive IR gas analyser, auto-calibration system and data logging unit, housed within an IP65 enclosure;

• no expensive consumables such as chemical reagents or calibration standards.

How it Works

Prior research at Cranfield University has demonstrated that nitrogen oxide (N₂O) is rapidly detected when nitrification starts to fail. The rate of N₂O production is linked to oxygen depletion, presence of toxic substances and ammonia shock loadings. Increases in levels are directly related to nitrification failure. Hence, measurement of the N₂O off-gas level allows the monitoring of nitrification performance to prevent breakthrough of ammonia in final effluent.

Using N-Tox^® to detect an increase of N₂O above the start of an activated sludge aeration lane or a trickling filter means that at least one hydraulic retention time of the final clarifier would pass before nitrification failure. The graph below demonstrates that the time lag between detection of increased N₂O and the appearance of ammonia provides typically seven hours warning of nitrification failure.

Once a failure is detected, plant operators and asset managers can implement a number of process options to restore nitrification including increasing aeration rates, bypassing influent to storage tanks, recycling final effluent to works inlet, or controlling return of high ammonia sludge liquors.

Applications

N-Tox^® can be used to monitor any activated sludge system in either municipal sewage or industrial effluent treatment systems. Many treatment works that discharge direct to the aqueous environment are consented for ammonia at < 5 mg/l as NH₃-N. These plants rely on ammonia removal through bacterial conversion to nitrate.

Inhibition by aeration failure, toxic chemicals or high ammonia concentrations can result in a wastewater treatment works not meeting its required ammonia consent. Some industrial effluents, such as landfill leachate or pharmaceutical wastewaters, have high ammonia levels. The requirement for an N-Tox^® alarm here is critical as the consequences of nitrification failure are more serious.

N-Tox^® can also be used to quantify N₂O greenhouse gas emissions from wastewater treatment plants. This is an area of increasing concern to plant operators and regulators alike, due to the particular potency of N₂O as a geeenhouse gas.

N-Tox^® Equipment Specification

: Measurement

Gas Type :		N2O (nitrous oxide, dinitrogen oxide)
Measuring Method :		Non dispersive IR absorption with CO2 luft cell
Measuring Limit :		2000 ppm N2O (4000 mg/m3)
Resolution :		1 ppm N2O (2 mg/m3)
Accuracy :		+/- 2 ppm N2O (± 4 mg/m3)
Lower Detection Limit :		2 ppm N2O (4 mg/m3)
Cross Sensitivity :		1 ppm N2O per 1000 ppm CO2
Response Time :		8 - 30 seconds (dependent gas-sample line length)
Monitoring Interval :		1 second
Operating Temperature :		0 - 50°C
Relative Humidity :		0-100% RH, non-condensing (at operating temperature)

: Features

Sampling :		Continuous single-point monitoring (multi-point available on request)
Sample Gas Conditioning :		Gas filter + semi-permeable membrane dryer
Offset & Drift Compensation :		Auto drift compensation
Calibration :		Factory set with auto adjustment for temperature drift, IR source aging and pressure changes

: Electrical & Compliance Data

Power Supply :		110 - 240 VAC, 50/60 Hz
Power Consumption :		0.015 kW
Max Current :		1 A
Certification :		Components to UL61010A-1, CSA 22.2, CE Mark

: Enclosure Details

Ingress Protection:		IP65
Material :		Glass Fibre
Dimensions :		height 647mm, width 430mm, depth 250mm

: Connections

Inlet :		Hose Barb for 4mm ID plastic pipe (max length 15m)
Purge :		Hose Barb for 4mm ID plastic pipe (max length 15m)
Exhaust :		Hose Barb for 4mm ID plastic pipe (max length 15m)

: Data Display, Inputs & Outputs

Display lights :		LCD display + Monitor On, System Fault and Alarm indicator
Keypad :		Menu navigation + Enter and Silence/Quit buttons
Data Presentation :		3 main operating screens plus function screens for data display and parameter set up
Data Storage :		Integral Datalogger – 43,000 readings, battery powered (1 year life), user settable start time and interval
Analogue Output :		4 - 20 mA current loop (utilised by Datalogger)
Alarm Signals :		3 SPDT relays for user assigned mg/l N2O alarm levels
Fault Signal :		1 SPDT relay for system fault
Computer Interface:		USB + datalogging software for launch and read out

Enquiries

For further details please contact:

N-Tox^® Product Manager
Water Innovate Limited
Cranfield Innovation Centre, University Way
Cranfield, Bedfordshire, United Kingdom
MK43 0BT

Tel. +44 (0) 1234 756014
Fax. +44 (0) 1234 752514
Email ntox@waterinnovate.co.uk