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A Novel Community Engaged System Thinking Approach to Controlling Nutrient Pollution in the Belize Cayes Nutrient pollution (anthropogenic discharge of nitrogen and phosphate) is a major concern in many parts of the world. Excess nutrient discharge into nutrient limited waters can cause toxic algal blooms that lead to hypoxic zones, fish die-offs, and overgrowth on reefs. This can lead to coral reefs being more vulnerable to global warming and ocean acidification. For coastal communities that depend of fishing and tourism for their livelihood, and for reefs to protect coastlines, 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, the Caribbean region’s most common type of treatment technology, in the Belizean Cayes where salt water flushing is common. Using mass-balance-based models for existing and proposed 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 will be 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. For the systems considered here, strategies such as aeration, increased biodigester tank size, addition of aerobic and anoxic biodigesters, recirculation, addition of a carbon source, ion exchange media is predicted to decrease the effluent nitrogen concentration, and integration of vegetation for nutrient uptake both on land and in the nearshore environment. In a previous case, the addition of an aerator was predicted to decrease the effluent ammonium concentration by 13%, whereas increasing the biodigester tank size would only decrease the effluent ammonium concentration by ~7%. 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. 

A hybrid algal photosynthesis and ion exchange (HAPIX) process was developed that uses natural zeolite (chabazite) and wild type algae to treat high ammonium strength wastewater. In the HAPIX process, ammonium ions are temporarily adsorbed from the liquid, which reduces the free ammonia concentration below the inhibitory level for algal growth. The slow release of adsorbed NH4+ subsequently supports the continuous growth of algae. In this study, a HAPIX reactor reduced NH4+-N concentrations in centrate from an anaerobic digester from 1,180 mg/L to below 10 mg/L without dilution. Chabazite doses of 60 g/L produced more biomass, with higher protein and starch contents, than doses of 150 g/L and 250 g/L. Approximately 67-70% of fatty acids in the biomass harvested from HAPIX reactors were unsaturated. A mathematical framework that couples a homogeneous surface diffusion model with a co-limitation algal kinetic growth model reasonably predicted the biomass production and NH4+-N concentrations in the HAPIX reactors. The HAPIX process has the potential to serve a two-fold purpose of high NH4+-N strength wastewater treatment and agricultural or commercial biopolymer production. 

Twenty-five United Nations member states in the wider Caribbean region ratified the Cartagena Convention, which covers the marine environment of the Gulf of Mexico, the Caribbean Sea and some parts of the Atlantic Ocean. The Land-Based Sources and Activities protocol (LBS Protocol) of that convention addresses nutrient pollution from sewage discharges, agricultural runoff and other sources. Unfortunately, most Caribbean people use conventional onsite wastewater treatment systems (OWTs), especially septic systems. These systems fail to remove nitrogen effectively, posing a challenge for near shore environments. Passive biological nitrogen removal (BNR) processes have been developed for OWTs that rely on simple packed bed bioreactors, with little energy or chemical inputs and low operations and maintenance (O&M) requirements. This paper provides a case study from Florida on the partnerships and pathways for research to develop an innovative technology, Hybrid Adsorption and Biological Treatment System (HABiTS), for nitrogen reduction in OWTs. HABiTS combine ion exchange materials and BNR to remove nitrogen from septic tank effluent and buffer transient loadings. HABiTS, employs natural zeolite material (e.g. clinoptilolite) and expanded clay in the first stage to achieve both ammonium ion exchange and nitrification. The second stage of HABiTS utilizes tire chips, elemental sulphur pellets and oyster shells for adsorption of nitrate as well as sulphur oxidizing denitrification. Under transient load applications, the nitrogen in excess of the biodegradation capacity during high loading events was partially retained within the ion exchange and adsorption materials and readily available later for the microorganisms during lower loading events. Results from a bench scale bioreactor study with marine wastewater, which is relevant to where seawater is used for toilet flushing, are also presented. Pilot scale tests on the OWT of an engaged stakeholder dependent on the marine environment, would contribute to broader discussions for paradigm shifts for nutrient removal from wastewater.