How can technology help to eliminate coagulant overdosing, ensure water safety and save money?

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Julian Edwards of ABB Measurement & Analytics explains the importance of taking a holistic approach to coagulation control in order to accurately calculate dosing levels.

  JEJulian Edwards
  Continuous Water Analysis
  Sales Product Manager
Most natural water sources will contain dissolved and suspended particles, which get into water through land erosion, minerals dissolving, the decay of vegetation and from discharged organic and artificial waste. Failure to remove these contaminants can result in the spread of bacteria, algae and viruses.
 
Cryptosporidium is a particularly nasty parasite that can cause severe diarrhoea illness and can even be fatal. It is resistant to chlorine and many other filtering techniques.
 
Removal of these dissolved particles is achieved by coagulation and flocculation. The coagulation process typically uses either aluminium or iron-based salts (coagulant) to help bind together small particles in water known as “colloids” that will not settle or float, and which cannot be removed by conventional filtering.

Shepherding the flocs

Most particles suspended in water have a negative charge, thereby repelling each other, and making them more difficult to remove. Chemical reaction between coagulant and colloids causes the destabilised particles to overcome their negative charge and bind together to form larger particles. The water then flows into a flocculation tank, where it is gently agitated to bring these large particles together to form even larger particles known as “flocs”. These can then be more easily filtered from the raw water.

When adding coagulant, operators will often overestimate the amount needed, to make plenty sure that no dangerous Natural Organic Matter (NOM) enters the water supply. Over-dosing can lead to high residuals of coagulant in treated water, elevated colour (when dosing a ferric based coagulant) and post-treatment precipitation of particles can cause turbidity, deposition and coating of pipes in the distribution system. Coagulant is also expensive.



 

Maximise coagulation process efficiency

Whilst the ability to measure variables such as pH, Turbidity, colour UV analysis of dissolved organics are not new, upgraded measurement tools and techniques can provide more accurate data than previously possible and provide context. Measurements should be made at key points throughout the water treatment process in order to review and advise on treatment efficiency.

 
Suggested locations include:
 
 
  • Raw Water – UV Dissolved Organics / Colour, turbidity, pH;
  • Dosed Water – pH; 
  • Clarified Water – UV Dissolved Organics / Colour, turbidity, residual Fe/Al, pH;
  •  Filtered/Final Water – UV Dissolved Organics / Colour, turbidity and residual Fe/Al, pH 
RVG200 paperless recorder feeds measurements through configurable algorithm to optimise coagulant use

The real leap forward in efficiency for water treatment are the tools available to analyse all the data collected. ABB’s RVG200 paperless recorder feeds measurements through a fully configurable algorithm. This enables adjustments to be made to for potential variations caused by seasonal fluctuations or a change in the coagulant used. It also offers the ability for remote monitoring, enabling operators to view live and historic data and make necessary changes, all of which are logged by an audit trail to protect against unauthorised tampering.

ABB is one of a number of companies that can provide end-to-end solutions for coagulation processes, combining accurate measurement with enterprise software to make sense of the vast amounts data. This helps to provide real improvements to process efficiency, without compromising safety. For more information, call 0870 600 6122 or email enquiries.mp.uk@gb.abb.com ref’ coagulant dosing’.
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