Biofilters
Biofilters associated with closed or semi-closed production systems are an important control point for disease. Biofilters are designed to maintain a colony of beneficial bacteria used to enhance water quality. The conditions that support these bacteria may also enhance survival of some pathogenic agents should they be present. It is normally not possible to disinfect biofilters without also destroying beneficial bacteria. Therefore potential water quality issues should be taken into account when planning strategies for disinfection of biofilters.
When disinfecting biofilters and their substrates, the system should be drained, organic residues removed and surfaces cleaned. Disinfection of biofilter systems can be undertaken by modifying water pH levels (using either acid or alkaline solutions). Where this is undertaken, the pH levels must be sufficient to inactivate the pathogenic agent, but should not be corrosive to pumps and equipment within the biofilter system. Alternatively, the biofilter can be completely dismantled, including removal of biofilter substrate, and the components cleaned and disinfectants applied separately. In the case of emergency disease response, the latter procedure is recommended. The biofilter substrate should be replaced if it cannot be effectively disinfected. Biofilter systems should be thoroughly rinsed before re-stocking.