Leveraging green infrastructure for efficient treatment of reclaimed water

Monitoring iohexol and its transformation products as evidence of reclaimed water irrigation input to contiguous waterbodies

Irrigation with reclaimed water alleviates water supply shortages, but excess application often results in impairment of contiguous waterbodies. This project investigated the potential use of iohexol, an iodinated contrast media used in medical imaging, together with its bio- and phototransformation products as unique reconnaissance markers of reclaimed water irrigation intrusion at three golf courses within the state of Florida. Inter-facility iohexol concentrations measured in reclaimed waters ranged over ~2 orders of magnitude while observed intra-facility seasonal differences were ≤1 order of magnitude. A ~50 % reduction in iohexol was observed post-disinfection for reclaimed water facilities utilizing UV light while none was observed with use of chlorine. Iohexol biotransformation products were observed to decline or shift to lower molecular weight compounds when exposed to UV light but not during disinfection using chlorine. Iohexol biotransformation products were observed in most of the samples but were more prevalent in samples collected during the dry season. Much fewer iohexol phototransformation products were observed in chlorinated reclaimed water, and they were only observed in UV light irradiated reclaimed water when the pre-disinfectant iohexol concentration was ≥5000 ng/L or from solar exposure of reclaimed water spiked with 10 μM of iohexol. For the Hillsborough golf course overlaying an aquifer, the groundwater did not contain iohexol or phototransformation products but did contain biotransformation products. It is not known if these biotransformation products are from active or historical intrusion. The additional presence of sucralose in the aquifer suggests that intrusion has occurred within the past 3 years. This study demonstrates three crucial points in attempting to utilize iohexol to denote reclaimed water intrusion from irrigation overapplication: (1) interpretable results are obtained when iohexol concentrations in the reclaimed water employed for irrigation are ≥1000 ng/L, with higher concentrations in the range of ≥5000 ng/L better able to meet analytical sensitivity requirements after further dilution or degradation in the environment; (2) it is beneficial to assess iohexol transformation products in tandem with iohexol monitoring to account for environmental transformations of iohexol during storage and transport to the receiving water of concern; and (3) inclusion of monitoring for sucralose, an artificial sweetener ubiquitous in wastewater sources that is comparatively stable in the environment, can aid in interpretating whether reclaimed water intrusion based on identification of iohexol and transformation products in the receiving water is attributable to historic or ongoing irrigation overapplications.

Do all algae grow faster in environments replenished by reclaimed water? Examples of two effluents produced in Beijing

Reclaimed water with nitrogen, phosphorus, and other contaminants may trigger algal blooms during its ecological utilization in replenishing rivers or lakes. However, the effect of reclaimed water on algal growth rates is not well understood. In this study, the growth potentials of algae in terms of Cyanophyta, Chlorophyta, and Bacillariophyta, as well as mixed algae in both regular culture medium and reclaimed water produced from treatment plants in Beijing with similar N and P concentrations, were compared to evaluate whether reclaimed water could facilitate algal growth. In addition, reclaimed water was also sterilized to verify the impact of bacteria's presence on algal growth. The results indicated that most algae grew faster in reclaimed water, among which the growth rate of Microcystis aeruginosa even increased by 5.5 fold. The growth of mixed algae in reclaimed water was not enhanced due to the strong adaptive ability of the community structure. Residual bacteria in the reclaimed water were found to be important contributors to algal growth. This work provided theoretical support for the safe and efficient utilization of reclaimed water.