Shellfish Breeding and Hatchery Management (2+1)

25.2.2.1 Physical Methods of Disinfection

i) Cleaning

The cleaning removes sessile organisms. It is mainly used for equipment disinfection. The tanks and other equipments are scrubbed with brushes or scrub pads of various designs. This can be enhanced by using standard detergent powders to inactivate the organism even if they cannot be removed. Use of detergents will also help in the removal of nutrient base that will encourage the growth of microbes.

ii) Heating

This is very common method of disinfection that will help in reducing the microbial load in any system or component. The basic idea is that the temperature above certain level would kill the microbes by dehydration of the cells. Heat exchangers of some hatchery systems raise the water temperature to a level that is intolerable to some microbial pathogens. Heating of water is suitable only for smaller systems.

iii) Filtration

This is the physical removal of debris and other solid material that is present in suspension and is mainly used to remove solids from supply water. This solid removal also helps in the reduction of microbial load associated with those solids in suspension. This filtration is effected by designed filters and filter materials that are non-toxic and non-corrosive. There are physical filters and biological filters with the application of biological principles such as Nitrification for removal of Ammonia in the rearing water. It can be said that a perfectly designed biological filter will keep the water free from ammonia and mortality due to ammonia.

iv) Dehydration

Dehydration or drying and reducing water contact of equipment or entire system provides a degree of disinfection. Drying easily destroys fragile stages of many parasites and dry surface have greater exposure to the effects of ultra violet light.

v) Radiation

Disinfection by radiation is especially used in hatcheries. The ultraviolet light of approximately 2500-2650 Ǻ wave length effectively destroys vegetative stages of many pathogens such as virus, bacteria and fungi. During water disinfection by radiation, pretreatment such as sedimentation and filtration make the water suitable for UV radiation treatment, by removing the hurdles for penetration of UV light. The ultraviolet rays are used to disinfect the organisms in limited dose. The dosage depends on intensity of light, duration of UV-light on organisms.