Odour control demonstration

Method

The sewerage pump station is a known contributor to hydrogen sulphide odours within the sewer network.

This site has been identified as one culprit for emitting H₂S gas, and has been fitted with a calcium nitrate dosing system in the past.

ACTI-Mag is a mildly alkaline mineral based substance which is non-toxic and non-hazardous to humans and the environment. Calcium nitrate on the other hand is a toxic, corrosive liquid which can be hazardous to handle.

A very simple chemical dosing system was installed at the sewerage pump station, which consisted of a 300 litre conical tank, a peristaltic pump mounted on a dosing skid and a PLC controller. Chemical addition was designed to immediately occur after the pump had stopped and the level within the wet well was very low. Adding the correct amount of ACTI-Mag at this stage would allow the product to be mixed in as the well refilled over time.

A simple peristaltic pump running through a one inch hose was used to add the ACTI-Mag into the pump station.

Thanks to the non-toxic and non-hazardous nature of ACTI Mag, complex bunding and containment is not required, unlike most other chemicals used for this application.

Figure 2: ACTI-Mag dosing unit at the sewerage pump station

THE RESULTS

The data for hydrogen sulphide monitoring can be seen in figure 3, which shows three non-consecutive periods that were monitored for the demonstration.

The first period corresponds to a business-as-usual case, with the current odour control strategy using calcium nitrate.

The second period used no odour control product to set the baseline, and the final period used ACTI-Mag for odour control.

ACTI-Mag outperformed the baseline data and the current dosing regimen of calcium nitrate.

As can be seen from the graph, the baseline order emissions of hydrogen sulphide spiked up to 350 parts per million regularly without treatment.

Under the current operation with the addition of calcium nitrate dosing, hydrogen sulphide levels were reduced, however regular excursions between 50 and 100 parts per million were not unusual.

In contrast throughout the period of ACTI-Mag demonstration the hydrogen sulphide level remained well below 20 parts per million for the vast majority of the time with regular excursions up to 25 parts per million.

These results conclude that ACTI-Mag is four times more effective at controlling excursions than the current odour control system, and 14 times more effective than the baseline.

It is expected at this level of hydrogen sulphide emissions that there would be no odour complaints at the discharge point and corrosion within the network would have significantly reduced.

The demonstration took place over a three week period, in order to build a strong baseline for ACTI-Mag comparison.

Week 1
Business as usual: Dosing calcium nitrate for odour control into the sewerage pump station.

Week 2
Switch off calcium nitrate to measure the extent of the underlying H₂S problem.

Week 3
Inject ACTI-Mag and perform demonstration.

Figure 3: Odour monitoring during the trial

RECOMMENDATION

The results could not be more clear when it comes to efficacy of odour control. Throughout the demonstration period ACTI-Mag was able to effectively eliminate far more hydrogen sulphide emissions compared to no dosing or using calcium nitrate.

The next step in assessing ACTI-Mag within the regional NSW council network would involve the scale up of the demonstration to a larger pump station that has odour control issues. This would allow us to accurately optimise the injection rate of ACTI-Mag at a larger scale.

Figure 4: Second sewerage pump station

Another sewerage pump station has been suggested as a good candidate, as it currently has no odour control measures, and has been identified as a primary contributor to hydrogen sulphide emissions.

This second site runs directly into a dedicated manhole just inside the gate of the depot. This would allow for monitoring without any interference from other pump stations going into the same line.

Figure 5: Receiving manhole at a regional NSW council depot