Citation:

King, D., M. Jahne, AND S. Pfaller. Using HVAC Condensate as a Reuse Option for Water Conservation (8th ASM Conference). 8th ASM Conference on Biofilms, Washington, DC, October 07 - 11, 2018.

Impact/Purpose:

In this study, the microbiological quality of untreated HVAC condensate was evaluated to determine its safety for reuse purposes. Heterotrophs are not necessarily pathogenic but concentrations in were on average, higher than the <500 CFU/ml recommended for potable water. While species-specific pathogen detection by qPCR (MA, MI/C, Lp SG1) was rare and concentrations were low, clinically relevant species were isolated by the general Mycobacterium culture method. Disinfection could provide sufficient bacterial log reduction to enable HVAC condensate water safe for many potable and non-potable uses. This research may inform states on concentrations of opportunistic bacterial pathogens and non-pathogens in untreated HVAC condensate and aid in recommending fit-for-purpose treatment options for this type of reclaimed water.

Description:

HVAC (heating, ventilation, and air conditioning) condensate can be a beneficial source of water that is currently going down the drain. As warm air is cooled by an air conditioning system, humidity in the air forms condensation that is essentially distilled water. Typically, this high-quality water is drained into wastewater systems, but it can alternatively be collected to support water conservation and sustainable water use. In hot, humid weather, an air conditioner may produce three to ten gallons of water per day per 1000 square feet of air-conditioned space. The goal of this study was to assess if HVAC condensate water was safe for various reuse purposes by testing bulk water samples and surface biofilms for opportunistic bacterial pathogens. The bulk condensate water from four air handling units in two buildings in North Carolina was monitored biweekly from May through October, 2017. Additionally, 36 biofilm samples were collected a single time from condensate surfaces (100 cm2 swabbed), collection pans (25 cm2 swabbed), and drain pipes (variable sized areas swabbed) of each handler using sterile swabs. Microbial analyses included heterotrophic plate counts (HPC), culture and qPCR for nontuberculous mycobacteria (NTM), and qPCR for Legionella pneumophila serogroup 1 (Lp SG1). The average HPC counts for the bulk condensate water were 6.05 x 103 CFU/ml. The average HPC counts for biofilm drain pipe samples were 1.83 x 106 CFU/ml, 4.15 x 103 CFU/cm2 for collection pans, and 6.24 x 103 CFU/cm2 for condensation surfaces. No biofilm samples and 2.5% (1/40) of condensate samples were positive for Mycobacterium avium (MA) by qPCR. Six percent (2/36) of biofilm samples and 7.5 % (3/40) of condensate samples were positive for M. intracellulare/chimaera (MI/C). Lp SG1 was detected by qPCR in one biofilm sample and one condensate sample, both quantities below the assay's limit of quantification. Nearly 50 putative mycobacteria were isolated from condensate water samples and two biofilm samples. In this study, the microbiological quality of untreated HVAC condensate was evaluated to determine its safety for reuse purposes. Heterotrophic bacteria are not necessarily pathogenic but concentrations were higher than the <500 CFU/mL recommended for potable water. While species-specific pathogen detection by qPCR (MA, MI/C, Lp SG1) was rare and concentrations were low, clinically relevant species were also isolated by the general Mycobacterium culture method. Disinfection could provide sufficient bacterial log reduction to utilize HVAC condensate water safely for many non-potable uses including irrigation, toilet flushing, and cooling tower makeup water. This research will inform States on concentrations of opportunistic bacterial pathogens and non-pathogens in untreated HVAC condensate and aid in recommending fit-for-purpose treatment options for this type of reclaimed water.

Record Details: