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The aims of the research project were to observe the operation of stabilization ponds with a view to investigating the value of various existing approaches used in the design of both facultative and maturation wastewater stabilization ponds and, if possible, to produce a realistic and reliable method for pond design. This latter aim was to be carried out either through the modification of existing equations or by the development of a new approach. In addition it was also intended to investigate the phenomena of dissolved oxygen and thermal stratification within stabilization ponds. The required data for this work was obtained as a result of detailed observation of the four-pond wastewater treatment installation in the Cayman Islands, British West Indies. Details of flows, flow strengths, removal of BOD and faecal coliform organisms were collected and numerous profiles of the pond contents were carried out to investigate dissolved oxygen and thermal stratification. Information concerning temperatures, solar radiation, hours of sunshine, relative humidity, rainfall, evaporation and wind speed and direction were also recorded over the three year investigational period. The most common design methods, the first-order complete-mix approach of Marais and Shaw and the modified empirical approach of McGarry and Pescod as modified by Mara and Arthur, were studied in detail using the results collected. These two design approaches were those used for the initial design of the Cayman ponds. Suggestions were then made for modifications to the first-order, complete-mix equation with regard to the values of the reaction coefficients employed for the removal of organic matter and of faecal coliform bacteria. Modifications of the equations to obtain K (the first-order reaction coefficient for either BOD or faecal coliform removal) were suggested. Following that a new empirical design approach was developed using the data collected from the operational ponds together with the climatological information. The models were developed in three steps. Firstly, matrices of correlation coefficients were produced to discover the existance of any strong correlations between any of the dependent and independent variables considered. Secondly, the Stepwise Backward Selection procedure for multiple regression (SBS) was applied to select the most relevant preliminary variables for multiple regression models. Then finially, the relevant variables were grouped in ordinary least-squares multiple regression models using a Hierarquical Multiple Regression procedure (HMR) to construct the models. As a result of this work groups of semi-empirical and empirical models were produced_ Two semi-empirical design models were developed to express K as a function of loading and climatic factors. These two equations were for the removal of BOO and faecal coliforms in facultative ponds. Two other groups of empirical design equations with a total of fourteen possible design models relating pond efficiency to factors such as loading, retention time and climatic conditions were also produced for the design of facultative and maturation ponds in the Caribbean region treating weak and saline wastewater. Also carried out were extensive field investigations into the temporal and spatial distributions of dissolved oxygen and water temperature in the ponds and as to how these varied with climatic conditions.

Pilot-scale constructed wetlands (CW), with electric arc furnace steel slag phosphorus removing filters were built and implemented for treating dairy wastewater on the Paul Miller Dairy Farm at the University of Vermont. Two distinct CW types were used in the study, hybrid and integrated. Hybrid CWs consist of more than one CW in-series, and in this research three hybrid CW systems were tested. Two hybrid CWs used a vertical saturated flow (VF) CW followed in-series by a horizontal saturated flow (HF) CW. One hybrid CW used a HF CW followed in series by a second HF CW. In this study, three integrated CW systems were implemented which consisted of a CW followed by a phosphorus removing slag filter. Two integrated CW systems consisted of a VF CW followed in-series by a saturated horizontal flow slag filter. One integrated CW system consisted of a HF CW followed by a horizontal saturated flow slag filter. All individual CWs and slag filters had the same dimensions; a length, width, and height of 1.7m, 1.1 m, and 0.5 m, respectively. CWs were filled with 2 cm diameter gravel, topped with 3 cm of compost, and planted with river bulrush (Schoenoplectus fluviatilis). Slag filters were filled with 2-5 cm diameter slag, having a porosity of 0.42. From August to December of 2007 the six CW systems were fed with a pulse flow of dairy wastewater with a hydraulic loading rate of 1.9 cm/day. This gave a nominal retention time of ~10 days for each CW system. From May to September of 2008 the flow was changed to a continuous inflow, and resulted in a hydraulic loading rate of 3.9 cm/day. A nominal retention time of ~5 days for each CW system was calculated. Weekly monitoring was carried out for five-day biochemical oxygen demand (BOD5), total suspended solids (TSS), ammonium (NH4+), dissolved reactive phosphorus (DRP), and pH. Integrated CWs and hybrid CWs were monitored for their ability to treat dairy wastewater. The analyses focused on determining if there were important differences in pollutant treatment efficiencies between the two distinct systems. Time series temporal semivariogram analysis of the measured water parameters illustrated that different treatment efficiencies existed in the beginning of the 2008 summer (early summer) compared to the end of the 2008 summer (late summer). Furthermore, the CWs were found to have significantly different (p-value < 0.0001) treatment performances, in terms of TSS and BOD5 removal, from early to late summer 2008. Integrated CWs remove significantly more DRP than hybrid CWs (p-value < 0.05). During the late summer of 2008, the integrated CWs removed significantly more ammonium (p-value < 0.05) then all other CW systems. Hybrid and integrated CWs were both efficient in removing organics, but the hybrid systems were significantly (p-value < 0.05) more efficient during the period of highest macrophyte biomass. Mechanisms of pollutant removal in these CW systems were further analyzed. Ultimate BOD laboratory experiments were used to determine the maximum amount of biologically available organic matter and the corresponding rate constants for the removal kinetics of organic matter in the dairy wastewater. Geochemical modeling of the minerals that form on steel slag show that hydroxyapatite controls the activities of phosphate and calcium ions. The geochemical modeling results show a similar finding to field results, because as the wastewater:slag ratio decreases the pH increases (pH > 11) and phosphorus is removed.

"Characterizing the effects of subsurface wastewater effluent discharges remains as a significant challenge impacting both ground-water and surface water resources. Important aspects of this challenge relate to the quantification of the main processes affecting oxygen consumption within a wastewater plume and to the ability of representing these conditions over a range of scales. The goal of this research is to improve our understanding of the relevant processes affecting oxygen consumption and thus, controlling natural attenuation in wastewater contaminated aquifers, and also to characterize and quantify these processes through modeling approaches considering different scales. The analysis included consideration of restoration processes associated with a former sewage disposal discharge in Falmouth, MA. The discharge was removed in 1995, and the site has been experiencing natural restoration since removal. A small-scale natural gradient tracer test, completed 6 years after cessation of sewage disposal, was used in previous research to develop parameters to characterize aerobic respiration and nitrification processes, key oxygen consuming processes for this site. In addition, field monitoring by the United States Geological Survey has provided a series of concentration profiles at different locations along the flowpath associated with the contaminant source. For this research, predictions obtained with the existing model were used in conjunction with these concentration profiles to assess the sensitivity and applicability in the parameters from this small-scale test, as well as their pertinence to the larger scale restoration process. By evaluating the applicability of this model to different scales and the associated variability of key model parameters, the approach provided an improved characterization of the primary processes affecting oxygen consumption."