Excess nutrient (nitrogen and phosphate) discharge into nutrient limited waters can cause toxic algal blooms that lead to hypoxic zones and fish die-offs. Nutrient pollution is also believed to make coral reefs more vulnerable to climate change causing accelerated reef erosion. For coastal communities that depend of fishing and tourism for their livelihood these effects can be devastating.  A major source of nutrient input into the aquatic environment is poorly treated wastewater from Onsite Wastewater Treatment Systems (OWTS). When properly sited, built, and maintained conventional OWTS are great for removing fats, grease, biological oxygen demand (BOD), and total suspended solids (TSS), but they are rarely designed for nutrient removal and commonly have high nutrient levels in their effluent.  This study investigates the factors that influence the performance of OWTS in the Belizean Cayes where salt water flushing is common. Using mass-balance-based models for OWTS to predict the system’s performance under various conditions, along with OWTS’ owner, maintainer, and user input, a novel community engaged system thinking approach to controlling nutrient pollution was developed. Key model performance metrics are concentrations of nitrogen species, BOD, and TSS in the effluent. To demonstrate the model’s utility, a sensitivity analysis was performed for case studies in Belize, estimating the impact on nutrient removal efficiency when changes are made to variables such as number of daily users, idle periods, tank number and volume, oxygen concentration, and recirculation.  Strategies such as aeration, biodigester tank modification, recirculation, addition of a carbon source, ion exchange media, and vegetation for nutrient uptake is predicted to decrease the effluent nitrogen concentration. Model results are shared with system manufacturers and operators to prioritize possible modifications, thereby optimizing the use of finite resources, namely time and money, for costly trial-and-error improvement efforts.

Novel community engaged system thinking approach to onsite wastewater treatment management for nutrient pollution in the Belizean Cayes

2019 Fall National Meeting

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