Evaluation of two water reuse applications : cooling tower makeup water and residential HVAC condensate reuse

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2016-12-02

Authors

Reuter, Samantha Jean

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Abstract

This study evaluated the potential impacts of two water reuse applications – urban cooling towers and residential homes. Large water demands make cooling towers an attractive target for water reuse applications. However, poorly operated cooling towers have historically been linked to diseases such as Legionnaire’s Disease, and there is limited understanding on how transitioning from potable to alternative water sources will impact the microbial communities within cooling tower basins. Therefore, the microbial communities of three well-maintained and disinfected urban cooling towers were studied to assess the impact of source water on microbial populations, diversity, and the presence of potentially pathogenic organisms. Illumina sequencing results indicate that different makeup water sources do yield microbial basin communities that differ substantially in composition and diversity. Also, total bacterial loads in each basin decreased with increasing fraction of potable water used in the makeup water. Legionella spp. levels above 6 logGC/L were observed in a cooling tower basin that used reclaimed and potable water as makeup water sources. However, none of the basin or makeup water sources had quantifiable levels of L. pneumophila, indicating the Legionella present in the cooling towers was mostly non-pneumophila Legionella. Residential HVAC condensate was evaluated because it is a largely untapped water source that may be suitable for recovery and reuse. The two main challenges for HVAC condensate collection is estimating the condensate production volume and understanding the water chemistry of the condensate. Both production rate and water chemistry are crucial to understanding which reuse options are available for HVAC condensate. Thus, this study tested a method for estimating condensate production volumes and analyzed the water chemistry of condensate samples from three separate HVAC units at different residences. Measured condensate production volumes were within 12 to 25 percent of predicted values, and the water chemistry results identified the presence of both metals and organic species. Both studies indicate the importance of considering water quality for water reuse applications.

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