Domestic Wastewater Treatment Mobilization Construction - AskTOP

EM 1110-3-17211 May 84CHAPTER 13DISINFECTION13-1 . General considerations . Disinfection is a process in whichpathogenic organisms are destroyed or inactivated . Several methodshave been utilized and include the following : (1) physical agents, (2)mechanical means, (3) radiation, and (4) chemical agents . Physicalagents include heat (boiling) and light . Mechanical means include theremoval of pathogens during wastewater treatment . Radiation utilizesgamma rays to sterilize wastewater . Chemical disinfection is the mostcommonly used method and will be used for mobilization work unlessother methods outlined above become expedient or feasible .13-2 . Types of chemical disinfectants . Chemical disinfectants include(1) chlorine and its compounds, (2) bromine, (3) iodine, (4) ozone, (5)alcohols, and (6) various alkalies and acids . Discussion herein islimited to disinfection of wastewater treatment plant effluents bychlorine and its compounds since it is the most universally accepteddisinfectant . Other chemicals as outlined above may be employed whenchlorine is not available .13-3 . Design basis and criteria .a . Chlorine forms . Chlorine is available as a liquid contained incylinders or in the form of chlorine compounds such as calciumhypochlorite or sodium hypochlorite . These are the most commonly usedcompounds for disinfection . Liquid chlorine is evaporated anddissolved into the wastewater as a gas . Sodium hypochlorite is,available in solution form, calcium hypochlorite is available in solidform .. b . Limitations on chlorine . Although chlorine is an effectivedisinfectant when in actual contact, the chlorine may not always comein contact with the microorganisms . Bacteria and viruses can hide (andoften do) inside particles of suspended or colloidal matter .Therefore, chlorine disinfection will not guarantee removal of allhealth hazards from wastewater . Chlorine disinfection involves a verycomplex series of events and is influenced by the kind and extent ofreactions with chlorine-reactive materials, temperature, pH, suspendedsolids concentrations, and the resiliency of some pathogenic organisms .Effective treatment will reduce the need for disinfection so properdesign and operation of the treatment plant are essential . Nitrogencompounds in the wastewater affect chlorine dosages . Sufficientchlorine must be added to overcome their neutralizing effect .c . Design parameters . For chlorination of wastewater treatmentplant effluent, a detention period of 30 minutes in the contact chamberto provide maximum disinfection is required . Table 13-1 should be usedto estimate chlorine dosage requirements .13-1