Chemical Dosing Monitoring and Safety

OdourPro on 20 December 2017

Two of the common questions chemical dosing customers ask are:

  • How do I know that I am not using more chemicals than I need to?
  • How do I handle dosing chemicals safely?

The increase in environmental pressure on waste water management, along with the economic constraints of business are causing many companies to assess their chemical dosing strategies and to optimise their odour control systems. There can be no compromise on environmental performance and no increase in smell complaints received. Yet, there can also be no wastage of dosing chemicals to keep costs under control.

Waste water management companies are also concerned about the safety of their employees. They focus on safe work practices, the correct use of PPE and training of staff about the hazards of the chemicals they are using.

Monitoring and Optimisation

Monitoring systems help companies to measure the effectiveness of their chemical dosing systems. There are different parameters to monitor, each of which gives insight into dosing performance and risk areas:

H2S Gas Measurement

H2S is the primary odour culprit. Once H2S is present in the gas leaving a sewer system, complaints are sure to follow. H2S gas measurement in critical rising mains and other sewer network locations gives a clear indication of where chemical dosing is insufficient.

Dissolved Sulphides

Dissolved sulphides in the sewer is an indicator of where there is potential for H2S gas to form. Bacteria in sewerage target sulphates to release oxygen. This process produces sulphides, which combine with Hydrogen to form H2S gas and odours.

Chemical dosing either prevents the bacteria from targeting sulphates, or reacts with sulphides to prevent them from releasing hydrogen sulphide gas. Either way, a presence of a high number of free sulphides indicates a problem with the chemical dosing system.


Magnesium Hydroxide dosing raises the pH of waste water to 8.5 or above. At this level, bacterial reduction of sulphates is inhibited and any dissolved sulphides present remain in solution rather than releasing as hydrogen sulphide gas.

Monitoring the pH of waste water reveals whether the chemical dosing is optimal. A pH below 8.5 indicates that there is not enough chemical dosing into the waste water. But, a pH of close to 9 indicates that too much chemical is being used. There is no advantage to keeping the pH above 8.5 as the extra chemical used to achieve this has no effect.

Residual Iron or Residual Nitrate

Ferrous Chloride react with sulphides in waste water streams to form a precipitate. Too little iron dosage leaves sulphides present, which could form H2S and odours. Too much iron results in residual iron left over, once all the sulphide has reacted. Measuring residual iron indicates whether too much Ferrous Chloride is being used.

Calcium Nitrate provides an alternative source of oxygen for bacteria to sulphates. If too little nitrate dosing occurs, the bacteria will still target some sulphates leading to odours. If too much nitrate dosing occurs, there will be residual nitrate left in the waste water. Measuring residual nitrate indicates whether too much Calcium Nitrate is being used.

Automated Monitoring Systems

OdourPro offers odour monitoring and telemetry solutions to assist waste water companies to manage their chemical dosing systems. Monitoring stations are set up at optimal measuring points and data from multiple stations can be monitored simultaneously.

Central Coast Council (NSW) and Muswellbrook Council (NSW), both use ferrous chloride in their wastewater networks and a monitoring system from us.

Safety Practices for Chemical Dosing

Chemical dosing systems come with integrated safety systems.

  • A bund protects the environment from a chemical spill
  • Safety showers and eye wash basins are provided
  • Chemical dosing system suppliers specify PPE such as eye protection, gloves and safety shoes.

Ferrous Chloride is a hazardous substance and therefore has additional safety precautions. Acid resistant overalls and a face shield are mandatory when handling this material. All personnel should be properly trained in the hazards of the chemicals they are using as well as the safety precautions.

Find out more about chemical dosing monitoring and safety or call our expert team on 1800 510 704 today to arrange a consultation to help you design and implement a chemical dosing monitoring system for your business.