A Comparison of Methods to Address Anaerobic Conditions in Rainwater Harvesting Systems

Although historically used in semi-arid and arid regions, rainwater harvesting (RWH) systems have increasingly been used in non-arid and humid regions of the world to conserve potable water and mitigate stormwater runoff. Rainfall characteristics and usage patterns of stored rainwater are distinctly different in (semi-)arid and humid regions, thus presenting a unique set of challenges with respect to their utilization. Coupled with infrequent use, the addition of nitrogen and organic matter via pollen during the spring season can lead to anaerobic conditions within storage tanks, which hinders nitrogen removal, gives stored water an offensive odor, and ultimately discourages use of the water. This study evaluated three measures that can be implemented for new and existing RWH systems to prevent the development of anaerobic conditions within storage tanks: first flush diversion, simulated use, and the continuous circulation of stored water. Study findings indicate that preventing anaerobic conditions via simulated use and recirculation (1) does not necessarily remedy the issue of poor aesthetics within rainwater storage tanks, and (2) can decrease the water quality benefits provided by these systems. Rather, preventing the introduction of pollen and particulate matter to the storage tank via a first flush diverter and minimizing disturbance of settled material in the tank appear to be the most effective methods of addressing the poor aesthetics and odor problems associated with anaerobic conditions.