Earth Filtration System Design

The majority of the minimum design criteria in the Ten State Standards for diatomaceous earth (DE) systems meet the SWTR (2). However, two design criteria in addition to the Ten State Standards are necessary to meet current regulations (a) The minimum amount of filter precoat should he 1 kg/m (0.2 Ih/ft ) to enhance Giardia cyst removal and (b) the minimum thickness of the precoat should be increased from 0.3 to 0.5 cm (1/8 to 1/5 in.) (found to be more important than the size graduation of the diatomaceous earth), also to enhance Giardia cyst removal. 

An additional recommendation is to use coagulant (alum or a suitable polymer) to coat the body feed to improve the removal rate for viruses, bacteria, and turbidity. Adding these chemicals to the coating does not improve Giardia removal rates. 

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Diatomaceous Earth Filtration System Design Diatomaceous Earth Filtration System Operation Diatomaceous Earth Filtration System Maintenance Types of Precoat Filters Auxiliary Parts and Equipment Bulk Filter Aid Handling... 

Conventional treatment, which includes coagulation, flocculation, clarification (sedimentation or flotation), and filtration, along with disinfection, can achieve 99.9% inactivation of Giardia cysts and 99.99% inactivation of enteric viruses when properly designed and operated. Direct filtration, slow sand filtration, and diatomaceous earth filtration systems, each combined with disinfection, have also achieved these reductions. 

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