Home Humidifiers as a Potential Source of Exposure to Microbial Pathogens,Endotoxins, and Allergens

The propensity of various types of home humidifiers to support and disseminate microbial contaminants into indoor air was tested. Reservoir water and air discharged from humidifiers seeded in the laboratory or naturally contaminated in the home were analyzed by standard microbiological methods. Clinically insignificant as well as overt or potentially pathogenic microorganisms were found to colonize the reservoirs of all types of humidifiers, but only cool mist and ultrasonic units readily aerosolized bacteria and endotoxin. Only cool mist units emitted hydrophobic fungal spores. Cool mist units discharged the greatest number of water particles in the inhalabk size range (4–16 μm) while ultrasonic units were more likely to emit respirable-sized water particles (< 0.2–4 μm). Overt pathogens isolated from humidifiers in homes included Legionella and a pathogenic Acanthamoeba. Aerosolizing humidifiers should thus be avoided if frequent, thorough cleaning of the units is not practical.     

Perchlorate and nitrate treatment by ion exchange integrated with biological brine treatment

Groundwater contaminated with perchlorate and nitrate was treated in a pilot plant using a commercially available ion exchange (IX) resin. Regenerant brine concentrate from the IX process, containing high perchlorate and nitrate, was treated biologically and the treated brine was reused in IX resin regeneration. The nitrate concentration of the feed water determined the exhaustion lifetime (i.e., regeneration frequency) of the resin; and the regeneration condition was determined by the perchlorate elution profile from the exhausted resin. The biological brine treatment system, using a salt-tolerant perchlorate- and nitrate-reducing culture, was housed in a sequencing batch reactor (SBR). The biological process consistently reduced perchlorate and nitrate concentrations in the spent brine to below the treatment goals of 500 microg ClO4(-)/L and 0.5mg NO3(-)-N/L determined by equilibrium multicomponent IX modeling. During 20 cycles of regeneration, the system consistently treated the drinking water to below the MCL of nitrate (10 mgNO3(-)-N/L) and the California Department of Health Services (CDHS) notification level of perchlorate (i.e., 6 microg/L). A conceptual cost analysis of the IX process estimated that perchlorate and nitrate treatment using the IX process with biological brine treatment to be approximately 20% less expensive than using the conventional IX with brine disposal.