Control measures

in drinking-water treatment

Defining measures for the elimination of cyanotoxins in drinking water treatment requires basic investment decisions on the treatment systems to use, e.g. whether to use pre-oxidation to enhance flocculation and precipitation of algae and cyanobacteria, to install ozonation and granular activated carbon filtration. In case these techniques are already in place due to e.g. high DOC or other water quality problems related to eutrophication, they should also be optimized for the removal of cyanobacteria and cyanotoxins.

All measures require adequate planning and design and need to be embedded in the treatment train. It should be ensured by operational controls that the overall treatment process is functioning as intended at all times – e.g. even when challenged by a massive cyanobacterial bloom.

Expertise in drinking water treatment, esp. in the elimination of algae, cyanobacteria and dissolved substances is necessary for the successful planning and implementation of measures.

Examples of measures in drinking water treatment and their operational monitoring can be found here.

Process Step	Examples ofmeasures	Examples of (operational) monitoring
Planning	Planning of treatment steps in relation to cyanobacterial occurrence and magnitude, e.g. to optimise removal of cells and dissolved cyanotoxins.	Review of the suitability of the treatment steps planned in relation to available information on cyanobacteria and cyanotoxin occurrence in the source water.
Planning	Planning of situation-specific periodic dosing of powdered activated carbon (PAC) in relation to requirements of your specific setting; determination of an operational parameter triggering dosing.	Review choice of carbon, amounts to be stored for use during bloom situations; conditions that trigger application.
Design, construction and maintenance	Design, construction and operation of filters so that backwashing effectively removes cells and cellular debris before release of cyanotoxins.	Review of records of backwashing frequency in relation to cyanobacterial abundance in raw water.
	Construction and maintenance of facilities for dosing of oxidants so that dose and contact time can be maintained as targeted.	Inspection of the structures and documented records of maintenance works.
	Construction and maintenance of activated carbon filters with sufficient retention capacity for removal of cyanotoxins (including selection of a suitable type of activated carbon)	Inspection of the structures and documented records of maintenance works and of selection of the activated carbon.
Operation	Pre-oxidation with sufficient dosing of oxidant to ensure oxidation of released cyanotoxins or to ensure that subsequent treatment steps will remove them (see below).	Monitoring of oxidant dosing in relation to pre-determined minimal amount required for cyanotoxin oxidation, or monitor the subsequent treatment steps that should remove dissolved cyanotoxins (see below).
	Operation of filters to ensure they retain cyanobacterial cells efficiently.	Monitoring of on-line parameter(s) that would indicate break-through of cells, e.g. turbidity or fluorescence.
	Operation of filters to avoid cell lysis and release of dissolved cyanotoxins e.g. by adapting backwashing frequency to the amount of cellular material accumulated on the filters.	Monitoring of filter resistance in relation to pre-determined threshold that would indicate elevated risk of break-through.
	Post-oxidation to remove dissolved cyanotoxins should be operated as specified to meet this target.	Monitoring of dosing of oxidant in relation to pre-determined dose and contact time needed to ascertain sufficient oxidation.
	Granular activated carbon filtration (GAC) or PAC dosing for removal of dissolved cyanotoxins should be operated as specified to meet this target.	Monitoring of filtration or dosing of GAC or PAC in relation to pre-determined dose and contact time needed to ascertain sufficient binding of dissolved cyanotoxins.

This list of examples is neither comprehensive nor should all measures listed necessarily be implemented. Rather, the nature of control measures and their monitoring should be demonstrated and provide the basis to develop your own control measures adequate for your setting.