Treatment for Pathogen Reduction
Pathogen reduction is often a top priority requirement for a decentralized wastewater treatment system, particularly if water reuse is planned. Pathogen destruction can be achieved using disinfection technologies that are designed to destroy pathogenic mi
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14-1. Scope Pathogen reduction is often a priority requirement for a decentralized wastewater treatment system, particularly if water reuse is planned. Pathogen reduction can be achieved using disinfection technologies that are designed to destroy pathogenic microorganisms in highly treated wastewaters and reduce the risk of infectious disease transmission that could result from exposure during discharge and reuse applications. Disinfection can also be achieved using removal processes in secondary and tertiary treatment unit operations. This section describes the process principles and design of disinfection methods for pathogen reduction in decentralized applications.
14-2. Key Concepts ■
Pathogenic microorganisms in wastewaters can include bacteria, viruses, protozoa and helminthes. • These microorganisms can cause infectious disease in humans through direct (e.g., ingestion of drinking water or body contact through bathing) or indirect exposures (e.g., consumption of shellfish raised in polluted waters). • Disinfection refers to the process of removing or destroying pathogenic microorganisms in a media like water so that the risk of infectious disease transmission through human contact with (directly or indirectly) that media is reduced. • The relative ease of achieving disinfection varies for different microorganisms. For example, protozoa are generally more resistant than viruses, which are relatively more resistant than bacteria.
© Springer International Publishing AG 2017 R.L. Siegrist, Decentralized Water Reclamation Engineering, DOI 10.1007/978-3-319-40472-1_14
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Treatment for Pathogen Reduction
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Analyzing for specific pathogens is difficult and costly which inspired the concept of using indicator microorganisms. Indicator microorganisms are non-pathogenic and have been used to assess the likely presence or absence of human fecal contamination of water. The presence of an indicator suggests the possible presence of fecal pathogens and vice versa. Fecal coliform bacteria have been used as indicator microorganisms but their relevance to assess the need for and efficiency of disinfection to enable discharge and reuse options continues to be debated. Other microorganisms have been proposed that are believed to be better indicators of the occurrence and fate of infectious bacteria, viruses and protozoa.
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Disinfection agent technologies are technologies that have the primary function of destroying pathogens. Common disinfection agent technologies that have been used in decentralized systems include chlorination, ultraviolet light irradiation, and ozonation. • Destruction mechanisms include: oxidation of cellular materials, destruction of cell walls, nucleic acids and C:N bonds, and disruption of replication or death. • A number of factors can potentially affect the effectiveness of disinfection agent technologies used for different types of wastewaters ○ Initial mixing is critical to the effectiveness of chemical disinfection methods. ○ Contact time is needed for a minimum period of exposure t
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