Assessing relative risks of municipal wastewater disposal options for Southeast Florida.

A comparative assessment of the risks of the three current wastewater effluent disposal options and three other potential options was conducted for Southeast Florida communities. The question was how the risk to humans from the use of potable reuse compares to the other five available wastewater disposal alternatives. The need for this type of risk assessment is due to the potential to use potable reuse as a water supply and the potential resistance from the public as a result of such a proposal. Water quality data relevant to disposal of wastewater treatment plant effluent from South Florida utilities along with water quality data on the receiving waters and drinking water standards were obtained for the project. The comparison of the public health risks associated with these disposal alternatives indicated that health risks associated with deep wells and direct potable reuse were generally lower than those of the other alternatives.

Demonstrating the Benefits of Predictive Bayesian Dose-Response Relationships Using Six Exposure Studies of Cryptosporidium parvum.

A conventional dose-response function can be refitted as additional data become available. A predictive dose-response function in contrast does not require a curve-fitting step, only additional data and presents the unconditional probabilities of illness, reflecting the level of information it contains. In contrast, the predictive Bayesian dose-response function becomes progressively less conservative as more information is included. This investigation evaluated the potential for using predictive Bayesian methods to develop a dose-response for human infection that improves on existing models, to show how predictive Bayesian statistical methods can utilize additional data, and expand the Bayesian methods for a broad audience including those concerned about an oversimplification of dose-response curve use in quantitative microbial risk assessment (QMRA). This study used a dose-response relationship incorporating six separate data sets for Cryptosporidium parvum. A Pareto II distribution with known priors was applied to one of the six data sets to calibrate the model, while the others were used for subsequent updating. While epidemiological principles indicate that local variations, host susceptibility, and organism strain virulence may vary, the six data sets all appear to be well characterized using the Bayesian approach. The adaptable model was applied to an existing data set for Campylobacter jejuni for model validation purposes, which yielded results that demonstrate the ability to analyze a dose-response function with limited data using and update those relationships with new data. An analysis of the goodness of fit compared to the beta-Poisson methods also demonstrated correlation between the predictive Bayesian model and the data.

The use of multiple tracers to evaluate the impact of sewered and non-sewered development on coastal water quality in a rural area of Florida.

When onsite wastewater treatment and disposal systems (OSTDS) are not sited appropriately or installed properly, wastewater constituents can be a source of adverse environmental impacts to soil and groundwater, which can lead to potential public health risks. A paired monitoring design developed to compare water quality in sewered and non-sewered areas is presented here. It is suggested as a possible monitoring scheme for assessing the impact of sewer installation projects. As such, two sets of single-family, rural residential Florida neighborhoods were evaluated over a two-year period to gain insight into the effects of small-community use of OSTDS on coastal water quality. One set of two neighborhoods were connected to the sanitary sewer network and the other set of two were served exclusively by OSTDS. Water quality sampling was conducted at the paired sites during seasonal high water table (SHWT) and seasonal low water table (SLWT) events. Measured surface water quality during the SHWT showed indications of environmental impacts from OSTDS in terms of nutrients, microbial pathogen indicators, and other water quality measures, such as turbidity and conductivity. However, during the SLWT events, no obvious impacts attributable to OSTDS were detected. The water quality results indicate that OSTDS impacts may be measureable in rural areas. Other factors, such as microbial indicator survival and regrowth potential, may confound the understanding of water quality impacts of sewer projects. For example, the microbial indicators Escherichia coli and enterococci were found to persist over time and therefore did not always represent true comparisons of OSTDS and sewered areas between seasons. The timeframe for evaluating the effects of sewer projects may be longer than anticipated because of this survival and regrowth phenomenon.

Application of photochemical technologies for treatment of landfill leachate.

Because of widely varying practices in solid waste management, an all-inclusive solution to long-term management of landfill leachate is currently not available. There is a major technological need for sustainable, economical options for safe discharge of leachate to the environment. Two potential on-site pretreatment technologies, photochemical iron-mediated aeration (PIMA) and TiO(2) photocatalysis were compared for treatment of landfill leachate at laboratory scale. Results of bench scale testing of real landfill leachate with PIMA and TiO(2) photocatalysis showed up to 86% conversion of refractory COD to complete mineralization, up to 91% removal of lead, up to 71% removal of ammonia without pH adjustment, and up to 90% effective color removal with detention times between 4 and 6h, in field samples. The estimated contact times for 90% removal of COD, ammonia, lead, and color were found to be on the order of 10-200 h for PIMA and 3-37 h for TiO(2) photocatalysis. Testing with actual leachate samples showed 85% TiO(2) photocatalyst recovery efficiency with no loss in performance after multiple (n>4 uses). Pre-filtration was not found to be necessary for effective treatment using either process.

Farfield tracing of a point source discharge plume in the coastal ocean using sulfur hexafluoride.

Pathways and dilution of a point source ocean discharge in the farfield (approximately to 10-66 km) were measured using the deliberate tracer sulfur hexafluoride (SF6). The injection of SF6 was performed by bubbling the gas over a period of 6 days into an ocean outfall pipe discharging into the southeast Florida coastal ocean. The surface SF6 concentrations show that the discharged water flowed northward parallel to the coast with a broadening of the width of the plume to about 3 km at the farthest point sampled, 66 km from the outfall. The discharge was fully mixed throughout the water column within 13 km of the outfall terminus. In the first 20 km from the outfall, SF6 surface concentrations were highly variable, while beyond this the SF6 concentrations decreased monotonically going northward. The currents were measured during the study with a bottom-mounted acoustic Doppler current profiler (ADCP) located 5.5 km from the outfall. Velocities were variable in magnitude and direction but showed a net northward flow during the 6-day study. Maximum concentrations decreased by about 200-fold per kilometer from the outfall to the northern end of the study area. The study shows that SF6 is an effective method to trace point source releases far from their origin.

Comparative assessment of municipal wastewater disposal methods in southeast Florida.

A comparative assessment of the risks of three effluent disposal alternatives currently available to wastewater utilities in Southeast Florida is presented in this paper. The alternatives are: deep well injection and ocean outfalls following secondary treatment, and surface water (canal) discharges following secondary wastewater treatment, filtration and nutrient removal. Water quality data, relative to disposal of wastewater treatment plant effluent were gathered, along with water quality data on the receiving waters, from utilities. Comparisons and conclusions regarding potential health concerns associated with the three disposal alternatives are presented. The results indicated that health risks associated with deep wells were generally lower than those of the other two alternatives. The proximity of injection wells to aquifer storage and recovery wells was a determining factor relative to injection well risk. Urban ecological risks were also indicated to be lower, though impacts of urban water use/reuse to the Everglades were not studied. Additional data collection and analysis were recommended to understand the effects of wastewater management on the cycling of water, nutrients and other constituents on southeast Florida. In particular, it was recommended that monitoring of effluents for nitrosamines and pharmaceutically active substances be implemented on a broad scale.