Non-steady-state modelling of faecal coliform removal in deep tertiary lagoons

Hydro-epidemiological modelling of bacterial transport and decay in nearshore coastal waters

In recent years, society has become more aware and concerned with the environmental and human health impacts of population growth and urbanisation. In response, a number of legislative measures have been introduced within Europe (and globally), which have sparked much cross-disciplinary research aimed at predicting and quantifying these impacts, and suggesting mitigation measures. In response to such measures this paper is focused on improving current understanding of, and simulating water quality, in the form of bacterial transport and decay, in the aquatic environment and particularly in macro-tidal environments. A number of 2D and 3D hydro-epidemiological models were developed using the TELEMAC suite to predict faecal bacterial levels for a data rich pilot site, namely Swansea Bay, located in the south west of the UK, where more than 7,000 FIO samples were taken and analysed over a two year period. A comparison of 2D and 3D modelling approaches highlights the importance of accurately representing source momentum terms in hydro-epidemiological models. Improvements in 2D model bacterial concentration predictions were achieved by the application of a novel method for representing beach sources within the nearshore zone of a macro-tidal environment. In addition, the use of a depth-varying decay rate was found to enhance the prediction of Faecal Indicator Organism concentrations in 3D models. Recommendations are made for the use of these novel approaches in future modelling studies.

An inverse approach to estimate bacterial loading into an estuary by using field observations and residence time

Pathogen, whose abundance is often measured by the concentration of fecal indicator bacteria, is listed as the top cause of waterbody impairments in the US. An accurate estimation of the bacterial loading from watershed is thus fundamentally important for water quality management. Despite advances in watershed modeling, accurate estimation of bacterial load is still very challenging due to large uncertainties associated with bacterial sources, accumulation, and removal in the watershed. We introduce an inverse method using field-measured bacterial concentrations and numerical model-calculated residence time to estimate the bacterial loading from the drainage basin. In this method, an estuary is divided into multiple segments. Water and bacterial fluxes between neighboring segments are computed from a set of linear equations derived based on mass balance equation and the relationship between residence time and water fluxes. Loading to each segment can then be estimated by combining the computed water fluxes and observed bacterial concentrations. The approach accounts for seasonal and interannual variations in hydrodynamics due to tide, river discharge, and estuarine circulations. The method was applied to Nassawadox Creek, a sub-estuary of Chesapeake Bay, where Fecal Coliform concentrations at 46 stations were continuously monitored. The method is verified by the high consistency between estimated loadings and presumably known input loadings in numerical experiments with either constant or time-varying input loadings. With sparse observational data, the inversely estimated loadings agree well with the loadings from a previously calibrated watershed model, demonstrating the reliability of the method. The inverse approach can be used to cross-check the result of watershed models and assess changes in watershed condition. The method is also readily applicable to other types of materials, such as inorganic nutrients.

Design of waste stabilization pond systems: A review

A better design instruction for waste stabilization ponds is needed due to their growing application for wastewater purification, increasingly strict environmental regulations, and the fact that most of previous design manuals are outdated. To critically review model-based designs of typical pond treatment systems, this paper analyzed more than 150 articles, books, and reports from 1956 to 2016. The models developed in these publications ranged from simple rules and equations to more complex first-order and mechanistic models. From a case study on all four approaches, it appeared that rules of thumb is no longer a proper tool for pond designs due to its low design specification and very high output variability and uncertainty. On the other hand, at the beginning phase of design process or in case of low pressure over land and moderate water quality required, regression equations can be useful to form an idea for pond dimensions. More importantly, mechanistic models proved their capacity of generating more precise and comprehensive designs but still need to overcome their lack of calibration and validation, and overparameterization. In another case study, an essential but often overlooked role of uncertainty analysis in pond designs was investigated via a comparison between deterministic and uncertainty-based approaches. Unlike applying a safety factor representing all uncertainty sources, probabilistic designs quantify the uncertainty of model outputs by including prior uncertainty of inputs and parameters, which generates more scientifically reliable outcomes for decision makers. Based on these findings, we advise engineers and designers to shift from the conventional approaches to more innovative and economic tools which are suitable for dealing with large variations of natural biological systems.

Environmental considerations on solar disinfection of wastewater and the subsequent bacterial (re)growth

Solar disinfection of wastewater is under study, as a process initiated on-site and continuing in nature. The environmental factors implicating the process (light intensity, intermittence and receiving water matrix) are also under study.

The modified SWAT model for predicting fecal coliforms in the Wachusett Reservoir Watershed, USA

This study assessed fecal coliform contamination in the Wachusett Reservoir Watershed in Massachusetts, USA using Soil and Water Assessment Tool (SWAT) because bacteria are one of the major water quality parameters of concern. The bacteria subroutine in SWAT, considering in-stream bacteria die-off only, was modified in this study to include solar radiation-associated die-off and the contribution of wildlife. The result of sensitivity analysis demonstrates that solar radiation is one of the most significant fate factors of fecal coliform. A water temperature-associated function to represent the contribution of beaver activity in the watershed to fecal contamination improved prediction accuracy. The modified SWAT model provides an improved estimate of bacteria from the watershed. Our approach will be useful for simulating bacterial concentrations to provide predictive and reliable information of fecal contamination thus facilitating the implementation of effective watershed management.

Comparison of fecal coliform bacteria before and after wastewater treatment plant in the Izmir Bay (Eastern Aegean Sea)

The distribution of fecal coliforms was investigated and determined in Izmir Bay from 1996 to 2005. Izmir Bay severely was polluted from industrial and domestic discharges during decades. In early 2000, a wastewater treatment plant began to treat domestic and industrial wastes. This plant treats the wastes about 80% capacity after 2001. The sampling periods cover before and after treatment plant. Assessment method for determining the number of fecal coliform has evolved membrane filtrations. Maximum surface fecal coliform concentration was 4.9 x 10(5) cfu 100 ml(-1) in 1996-2000 period. Following the opening treatment system, fecal coliform density decreased 2.1 x 10(4) cfu 100 ml(-1) during 2001-2005. A continuous improvement can be sustained in the water quality if direct inflow of untreated wastewater is prevented.

Modelling Escherichia coli concentration in a wastewater reservoir using an operational parameter MRT%FE and first order kinetics

The operational parameter MRT%FE, representing the mean residence time of different ages fractions of effluent within a completely mixed reactor, was evaluated and integrated with first order kinetics. The parameter was used to model Escherichia coli concentrations in a municipal wastewater reservoir managed under different operating conditions (continuous and discontinuous). The study was conducted during 2004-2005 in a reservoir receiving effluents from the activated sludge treatment plant of Caltagirone (Eastern Sicily - Italy). The analytical approach is applied to the hydraulic state variables of the system (daily stored volumes, inlet and outlet flows), and the physical-chemical (pH, temperature, EC, TSS, BOD(5), COD) and bacteriological wastewater parameters (E. coli, FC, FS). In order to evaluate the reliability of the proposed approach, predicted E. coli concentrations within the reservoir were compared with measured ones by the correlation coefficient, F-test and Sperman's index. The study included the evaluation of die-off coefficient K(T) (d(-1)), light extinction coefficient K (m(-1)) and their relationships with climatic factors. Results of the study confirm that E. coli removal is related to the fractions of fresh effluent remaining each day within the reservoir with MRT%FE of about 5-8d, significantly lower than the nominal detention time (about 27d). The E. coli die-off coefficient (K(T)) was higher during system discontinuous operations and correlated with incident solar radiation and water temperature.

Hydro-epidemiology: the emergence of a research agenda

There is a growing international awareness of the health risks associated with water, and particularly in developing countries. For example: (i) a child dies in Africa every 30s due to malaria-a disease related to stagnant water, (ii) every year flooding causes many deaths world-wide, with infant mortality due to diarrhea from contaminated flood waters posing the biggest threat, and (iii) poor sanitation and its relation to hepatitis A continues to be a serious problem. A revealing measure of the extent of such global problems is that more than half of the hospital beds in the world today are occupied by people with water-related diseases. Addressing these issues mandates an interdisciplinary approach by the world's scientific and engineering community. In this spirit a workshop was held in Phoenix to provide a forum where epidemiologists, hydraulics researchers and other stakeholders of varied backgrounds (e.g., policy makers, environmental groups etc.) could all participate in a debate on a future agenda for hydro-epidemiology. The principal outcome of the workshop was a significant appreciation of the potential for interdisciplinary research and development in hydro-epidemiology and the major contribution that hydraulics professionals could offer, in partnership with the public health community, in addressing such water related disease control and prevention challenges.

The seasonality of fecal coliform bacteria pollution and its influence on closures of shellfish harvesting areas in Mississippi Sound

Runoff from agricultural lands and farm animal feedlots is one of the major sources of fecal coliforms in surface waters, and fecal coliform (FC) bacteria concentrations tend to vary with season because of seasonal variations in climatic factors. However, El Niño -Southern Oscillation (ENSO) events may affect the extent and patterns of seasonality in FC levels in coastal waters. Water quality monitoring data for shellfish management collected during El Niño (1990, 1992, 1997), and La Niña (1999, 2000) years were analyzed to evaluate the extent to which these events influenced Pearl River stage, and bacterial levels, water temperature, and salinity in the western part of Mississippi Sound. Models to predict FC levels in relation to various environmental factors were also developed. In 1990, 1992 and 1997, FC geometric mean counts peaked in late winter (January/February) reaching 120 MPN (February 1990), 165 MPN (January 1992), and 86 MPN (January 1997), and then decreased considerably during spring and summer (1.2 – 19 MPN). Thereafter, FC abundance increased slightly in fall and early winter (1.9 – 24 MPN). Fecal coliform abundance during the 2000 La Niña year was much lower (1.0 – 10.3 MPN) than in 1992 (1.2 – 165 MPN), and showed no seasonal pattern from January to August, perhaps due to the relative scarcity of rainfall in 2000. In 1995 (ENSO neutral year), peak geometric mean FC count (46 MPN) was lower than during El Niño years and occurred in early spring (March). The seasonal and between year variations in FC levels determined the number of days during which the conditionally approved shellfish growing area was opened for harvesting shellfish. For example, from January to April 1997, the area was not opened for shellfish harvesting, whereas in 2000, the number of days during which the area was opened ranged from 6 – 27 (January to April) to 24 – 26 (October to December). ENSO events thus influenced the extent and timing of the peak levels of fecal coliforms in Mississippi Sound. Models consisting of one or more of the variables: Pearl River stage, water temperature, and salinity were developed to predict FC concentrations in the Sound. The model parameter(s) explained 56 to 91% of the variations in FC counts. Management of shellfish in Mississippi Sound can be improved by utilizing information on the forecasted three to seven years occurrence of ENSO events. In addition, since Pearl River stage was the most important variable predicting FC concentration in the Sound, a study of the levels and sources of FC bacteria in the river, especially the middle and lower sections, is needed for developing a management plan for reducing FC bacteria pollution in the Sound.

Three-dimensional modeling of fecal coliform in the Tidal Basin and Washington Channel, Washington, DC

Fecal coliform are widely used as bacterial indicator in the United States and around the world. Fecal coliform impaired water is highly possible to be polluted by pathogenic bacteria. The Tidal Basin and Washington Channel in Washington, DC are on the Total Maximum Daily Load (TMDL) list due to the high fecal coliform level. To support TMDL development, a three-dimensional numerical model of fecal coliform was developed using the EFDC framework. The model calculates the transport of fecal coliform under the influences of flap gate operations and tidal elevation. The original EFDC code was modified to calculate the die-off of fecal coliform under the impact of temperature and solar radiation intensity. The watershed contribution is expressed as storm water inflow and the load carried by the runoff. Model results show that fecal coliform vary strongly in space in both the Tidal Basin and Washington Channel. The storm water only impacts a small area around the storm water outfall in the Tidal Basin and the impacts are negligible in the Washington Channel due to dilution. The water from the Potomac River may affect the fecal coliform level in the area close to the flap gate in the Tidal Basin. The fecal coliform level in the Washington Channel is mainly controlled by the fecal coliform level in the Anacostia River, which is located at the open boundary of the Washington Channel. The potential sediment layer storage of fecal coliform was analyzed and it was found that the sediment layer fecal coliform level could be much higher than the water column fecal coliform level and becomes a secondary source under high bottom shear stress condition. The developed model built solid connection of fecal coliform source and concentration in the water column and has been used to develop TMDL.

Influence of inter-annual variations in climatic factors on fecal coliform levels in Mississippi Sound

Information on the effects of inter-annual variations in climatic factors on fecal coliform levels in coastal waters is scarce. We used 11 years (1990-2001) of rainfall, water temperature, Pearl River stage and salinity data to assess the effects of the 1991-1992 and 1997-1998 El Nino events on fecal coliform levels in Mississippi Sound. El Nino-Southern Oscillation had major effects on Pearl River stage and water quality in the Sound. The geometric mean fecal coliform number differed among years (P = 0.0001), being highest during 1991-1992 El Nino years (14.22 MPN per 100 ml) and lowest during 1999-2000 La Nina years (<1.8 MPN per 100 ml). Mean salinity varied among years (P = 0.0001) from 9 ppt (1991-1992) to 21 ppt (1999-2000). Mean water temperature was lowest in 1997-1998 (14.5 degrees C) and highest in 1998-2000 (19.4 degrees C). Pearl River stage differed among years (P = 0.0001), ranging from 1.96 m (1999-2000) to 3.57 m (1997-1998). Inverse relationships were observed between fecal coliform levels and salinity (r(2) = 0.74; P = 0.001) and water temperature (r(2) = 0.69; P=0.001), whereas positive relationships were obtained with total rainfall (r(2) = 0.52; P = 0.013) and Pearl River stage (r(2) = 0.90; P = 0.0001). These relationships are useful for evaluating the potential effects of climate change on water quality and classification of shellfish growing waters in order to protect humans from consuming contaminated shellfish in shallow river-influenced estuaries.