Defra

1. Specification for UV treatment of river water to control Ralstonia solanacearum.

 

i Use high output low pressure or Amalgam UV lamps to give a dose of at least 300J per m2 at a wavelength of 254 nm throughout the useful working life of the lamps and at the maximum operating flow rate and assuming a UV transmission through 10 mm depth (T10) of only 50%.  Water must not be allowed to pass through to the irrigators until the UV lamps have reached the minimum safe UV output level.

ii The UV unit must be initially sized to take account of the T10 UV transmission level (% transmission through 1cm depth) of the water and the maximum flow rate to be treated by the system.  The UV transmission level of the water should be pre-tested at every site where UV treatment is proposed to establish the lowest water quality to be treated during the course of an irrigation season.  The UV unit used should be specifically designed for treating turbid liquids.  Water with a T10 reading of less than 50% is not considered suitable for UV treatment.

iii All UV units should be fitted with a real time UV intensity monitor with 'low UV' alarm set point/cut out.  The cut out should be set at 60% transmission to avoid treating water near to the critical quality limit.

iv An automatic cut-out system should ensure that the flow of water from the UV unit is immediately stopped if the UV intensity falls below the minimum design level (60%), e.g. due to lamp ageing, lamp failure, deposits on the lamp, or poor quality water passing through the UV unit.

v A pre-filter (100 micron or finer) should ensure that particulate matter in the water does not interfere with effective water flow or UV transmission.

vi UV units should be fitted with an efficient, preferably fully automatic, wiping system to prevent build up of deposits and maximise UV transmission.

2. Specification for chlorine dioxide treatment of river water to control Ralstonia solanacearum.

 

Water should be dosed with chlorine dioxide to achieve a residual chlorine dioxide concentration of at least 0.1 mg per litre (parts per million), measurable over a minimum period of 2 minutes.  Thorough mixing of the chlorine dioxide in the water should take place during the minimum 2 minute reaction time.  The residual level of chlorine dioxide should be checked before each irrigation to account for changes in chlorine demand due to variation in water quality.  For each new source of river water to be treated, the chlorine dioxide demand of the water should first be determined over the expected range of water quality to ensure that the chlorine dioxide dose will be consistently sufficient to generate the required minimum residual level (0.1 mg per litre) at all times.

3. Specification for peroxygen product treatment of river water to control Ralstonia solanacearum.

 

Water should be dosed with peroxygen products to achieve a minimum residual level of peracetic acid of at least 4 mg per litre (parts per million), measurable over a minimum period of 2 minutes.  Thorough mixing of the peroxygen product in the water should take place during the minimum 2 minute reaction time.   The residual level of hydrogen peroxide should be checked before each irrigation to account for changes in peroxygen demand due to variation in water quality.