Effluent Plume Research Articles

Influence of Solar Radiation on Microbiological Degradation of Sewage Submarine Outfalls and the Safety of Bathing Areas

The ocean disposal of wastewater is an efficient alternative in the sewage system of coastal areas since the urban density of such regions is a barrier to the settlement of conventional sewage treatment plants. In addition, the associated costs of this alternative are significantly lower than the convention in the long term. The degradation of microbiological contaminants strongly depends on solar radiation and the factors that regulate its intensity, such as the depth of the effluent plume, seasons, and cloud cover. The submarine disposal of domestic sewage constitutes a low-sanitation-risk alternative regarding the contamination of bathing areas. The results based on computational modeling corroborate this alternative, showing that the coastal zone is not affected by marine sewage discharges.

The Efficiency of Phosphate Removal via Shallow Wastewater Injection into a Saline Carbonate Aquifer.

Wastewater-derived phosphate contributes to eutrophication if the phosphate is not efficiently removed before it is discharged to surface waters. In the Florida Keys (USA), shallow injection of treated wastewater into saline limestone aquifers is a common mode of wastewater disposal. We assessed the possibility of efficient and permanent phosphate removal following injection at a wastewater treatment facility in Marathon, Florida. The concentrations of nutrients, dissolved ions, and anthropogenic compounds in groundwater and nearshore waters were monitored over two years, as was the progression of a patch of fluorescent dye emplaced by the wastewater injection well. The density contrast between the wastewater effluent and saline groundwater caused the effluent plume to buoy to the shallow subsurface near the injection well. Soluble reactive phosphorus (SRP) and sucralose were both detected in nearshore waters, indicating incomplete removal of contaminants. However, ∼75% of the SRP is removed from the plume in the first 10 days of transit by adsorption followed by a slower removal mechanism, bringing the P removal efficiency above 90%. A positive relationship between excess calcium and phosphate removal efficiency, together with high levels of calcium phosphate mineral supersaturation, supports calcite dissolution followed by calcium phosphate mineralization as this slower removal process.

A tracer model nowcast/forecast study of the Tampa Bay, Piney Point effluent plume: Rapid response to an environmental hazard

An emergency discharge of nutrient-rich effluent from the defunct Piney Point fertilizer stack into Tampa Bay at Port Manatee occurred from 30 March–8 April 2021. This resulted in a pollutant plume that evolved over time and space across the entire bay, including its environmentally sensitive marine preserves, and out onto the adjacent continental shelf. As a rapid response to environmental concerns, the plume evolution was simulated using the high resolution, unstructured grid, Tampa Bay Coastal Ocean Model (TBCOM) nowcast/forecast system, with an embedded tracer module that included realistic point discharge rates. Normalized tracer distributions were automatically updated each day, providing 1-day hindcasts and 3.5-day forecasts. Due to mixing and advection, tracer concentration was quickly reduced by two or more orders of magnitude as the plume spread out. Highest tracer concentrations hugged the southeastern Tampa Bay shoreline during the first week. Lower tracer concentrations were gradually advected to the western side of Tampa Bay, and the tracer was slowly flushed out of the bay to be transported primarily northward along the coast. The modeled plume evolution served as principal guidance for coordinating environmental monitoring by state, local and academic personnel. The model results also provide a basis for future multidisciplinary studies.

Wastewater plumes can act as non-physical barriers for migrating silver eel.

Non-physical barriers for migrating fish, such as effluent plumes discharged by sewage treatment plants (WWTPs), are hardly considered, and field studies on this topic are very scarce. The encounter with these plumes however may evoke behavioural responses in fish and could delay or (partially) block the migration. In this study, the behavioural responses of 40 acoustically-tagged silver eel (Anguilla anguilla) were monitored in situ, when confronting a WWTP effluent plume during their downstream migration in the canal Eems, the Netherlands. Their behavioural responses and the potential blocking effect of the plume were assessed using a 2D and 3D telemetry design displayed in the waterway, and matched to a modelled and calibrated WWTP effluent plume. When confronted with the WWTP effluent plume during their downstream migration, 22 of the silver eels (59%) showed an avoidance response, varying from lateral diverting to multiple turning in the vicinity of the effluent plume. Nineteen out of these 22 (86%) eventually passed the study site. No silver eel showed attraction to the plume. Delays in migration were from several hours up to several days. Due to the strong variation in discharged volumes and flow velocity of the receiving canal, the WWTP plume did not always flow over the full width of the canal. As a result, numerous migratory windows, where silver eels could pass the WWTP while avoiding direct contact with the plume, remained available in time. When discharge points cannot be avoided, reduced or restricted to areas that are not preferred as fish migration routes, discharge points should be designed such, that the chance is limited that a waterway is (temporarily) impacted over its full width.

The Effect of a Step Increase in Depth and Decay upon Dispersion of Coastal Effluent Discharges

Coastal wastewater-discharged effluents contain a mixture of pollutants with decay rates that vary with water depth. Analytical models using a two-dimensional advection-diffusion equation are presented to study the effects of a cross-stream sudden depth change and decay on mixing and dispersing steady discharge of effluents through a sea outfall. The solutions are illustrated graphically by plotting contours of concentration, resembling snapshots of discharged effluent plumes in the far-field. Different shapes of effluent plumes are observed due to the variability of length of the step seabed, and the concentration at the step seabed is formulated to measure how much has discharged effluents dispersed into or out of the shallow coastal waters.

Influence of wastewater effluents on the bioaccumulation of volatile methylsiloxanes in the St. Lawrence River

The bioaccumulation of cyclic volatile methylsiloxanes (D3 to D6) as well as linear siloxanes (L3 to L5) was studied in a food web in the St. Lawrence River downstream of the effluent of the municipal wastewater treatment plant in Montreal, Canada. For most species, differences in δ15N in fish and prey showed a clear separation of individual fish feeding in food webs influenced by the wastewater plume from those feeding outside the plume. Cyclic siloxanes were detected in all biotic samples from the individuals identified as feeding in the effluent plume. Siloxane D5 accounted for more than 80% of the total siloxanes. Linear siloxane L5 was also abundant in walleye and gull eggs. Total siloxane concentrations in suspended sediments were 17.3 times higher than in surface sediments in the region of the river in the effluent plume. Caged freshwater mussels (Elliptio sp.), placed in the effluent plume, bioaccumulated 43 times more total siloxanes than PBDEs in 30 days, demonstrating how readily siloxanes are taken up in biota and what a significant component of the contaminant body burden they can account for. The sediment-biota accumulation factors (BSAF) for total siloxanes (∑ D3 to D6 and L3 to L5) showed values of 65.4, 27.8, 9.9 and 6.4 for walleye, northern pike, yellow perch and round goby respectively.

Detecting the Surface Signature of Riverine and Effluent Plumes along the Bulgarian Black Sea Coast Using Satellite Data

The clear and reliable detection of effluent plumes using satellite data is especially challenging. The surface signature of such events is of a small scale; it shows a complex interaction with the local environment and depends greatly on the effluent and marine water constitution. In the context of remote sensing techniques for detecting treated wastewater discharges, we study the surface signature of small river plumes, as they share specific characteristics, such as higher turbidity levels and increased nutrient concentration, and are fresh compared to the salty marine water. The Bulgarian Black Sea zone proves to be a challenging study area, with its optically complex waters and positive freshwater balance. Additionally, the Bulgarian Black Sea coast is a known tourist destination with an increased seasonal load; thus, the problem of the identification of wastewater discharges is a topical issue. In this study, we analyze the absorption components of the Inherent Optical Properties (IOPs) for 84 study points that are located at outfall discharging areas, river estuaries and at different distances from the shoreline, reaching the open sea area at a bottom depth of more than 2000 m. The calculations of IOPs take into account all available Sentinel 2 cloudless acquisitions for three years from 2017 until 2019 and are performed using the Case-2 Regional CoastColour (C2RCC) processor, implemented in the Sentinel Application Platform (SNAP). The predominant absorber for each study area and its temporal variation is determined, deriving the specific characteristics of the different areas and tracking their seasonal and annual course. Optical data from the Galata AERONET-OC site are used for validating the absorption coefficient of phytoplankton pigment. A conclusion regarding the possibility of distinguishing riverine, marine and coastal water is derived. The study provides a sound basis for estimating the advantages and drawbacks of optical satellite data for tracking the extent of effluent and fluvial plumes with unknown concentrations of optically significant seawater constituents.

The Fucales Index: A new tool for monitoring subtidal rocky habitats, and its application to an Atlantic bay subjected to nuclear power plant's effluents

Ecological indices are useful tools for environmental managers to monitor and detect changes caused by natural or anthropogenic disturbances. Despite the fact that descriptors of Fucales species are often included in indices for evaluating changes in coastal marine habitats, there is no index based solely on Fucales abundance. This study proposes the Fucales Index (FI), based on four classes of abundance of a selected Fucales species. The ability of FI to detect changes in the abundance of Sargassum sp. was tested in a Brazilian bay that is subjected to the effluent plume from a nuclear power plant. FI was significantly different when comparing areas inside and outside of the plume area, and it increased with increasing distance from the source of the disturbance. These findings suggest that FI is a suitable tool for assessing the effect of an effluent plume and potentially of other disturbances on rocky shores hosting Fucales.

Spatial and Temporal Vertical Distribution of Chlorophyll in Relation to Submarine Wastewater Effluent Discharges

The vertical distribution of chlorophyll in coastal waters is influenced by a combination of the hydrodynamic environment and different biotic and abiotic processes. The spatial and temporal occurrences of chlorophyll profiles provide a good representation of the changes in the marine environment. The majority of studies in the Adriatic Sea have so far been conducted in areas unaffected by anthropogenic pressure. Our study site is located near two marine outfalls, which are part of the public sewage system. This study aims to characterize the chlorophyll vertical distribution and describe its variability based on the stratification conditions and the presence of a wastewater effluent plume. Based on these conditions, we identified three characteristic scenarios/types of chlorophyll profiles. The first one occurs when the vertical mixing of the water column creates the upwelling of chlorophyll and nutrients to the upper part of the water column. The second and third scenarios occur during stratified conditions and differ by the extent of the effluent plume intrusion. Using modern fluorescence techniques, we identified and described three different vertical chlorophyll profiles, characterizing them according to their physical and biological parameters and processes. For cases with a visible effluent intrusion, we confirmed the importance of the pycnocline formation in keeping the effluent below and maintaining the higher water quality status at the top of the water column.

Sedimentary processes at the mouth of a tidally‐influenced delta: New insights from submarine observatory measurements, Fraser Delta, Canada

AbstractThis paper examines particle settling dynamics in a tidally‐influenced delta, including observations of convective settling, strongly modulated by seasonal discharge and tidal cycles. Long time series of Acoustic Doppler Current Profiler backscatter, a proxy for suspended sediment concentration in the water column, current and sediment accumulation measurements from the slope of the Fraser River delta show variability of sedimentary processes over timescales from semi‐diurnal to annual. Acoustic Doppler Current Profiler backscatter shows a lagged response to river discharge and strong diurnal/semi‐diurnal variability. Most of the tidal cycle is characterized by a buoyant effluent plume. During the ebbing phase of diurnal major tides, discrete settling events are observed extending through the entire water column. The pulse‐like nature of these events is the result of downward plunging fingers characteristic of convective settling, similar to those observed in laboratory flume experiments, and appear to be initiated at the interface between the surface buoyant plume and the underlying ambient water. Currents show strong variability in a three‐layer water column. The surface plume shows offshore and southward directed transport of sediments. The remaining water column is influenced by tidal flows, but near surface and intermediate water‐depth currents are out of phase by several hours, indicating a stratification of the basin water and decoupled propagation of surface and internal tides. This phase lag is unlikely to cause discernible facies changes, but may have implications for basin‐fill patterns in restricted basins with strong tidal range. The results of this work will help to better understand river mouth sedimentation processes and dispersal patterns in other modern deltas and in the geological record.

The comparative toxicity of rainfall overflows and a municipal effluent plume in Elliptio complanata using a novel qPCR array approach

Municipal effluents have the potential to disrupt the endocrine system involved in reproduction in aquatic organisms. The purpose of this study was to develop a novel a quantitative polymerase chain reaction (qPCR) array for the freshwater mussel Elliptio complanata to compare the toxic properties of municipal effluents and rainfall overflows. Mussels were caged for 3 months at upstream and downstream sites of a municipal effluent discharge point and 2 rainfall overflow sites in the Saint-Lawrence River. The data revealed that exposure to municipal effluents and overflow sites lead to increased expression of vitellogenin (VTG) in male mussels, altered sexual differentiation in females, gene expression involved in oxidative stress (superoxide dismutase, glutathione S-transferase) and DNA damage (chromosome mismatch and repair of covalently-bound DNA adducts). Mussels at the downstream site accumulated also large amounts of heterotrophic bacteria but not at the overflow sites. However, mussels at the overflow sites had decreased expression in ABC transporter gene expression. Scaling analysis revealed that the following gene expression were related to effects at higher level of biological organization such as total RNA levels, gonad mass and gonad somatic index: DNA repair of covalent DNA adducts, mistmach chromosomal recombination during meiosis and undifferentiated cells in gonads. In conclusion, exposure to rainfall overflow sites have similar effects to municipal effluents based on VTG and oxidative stress responses at the transcriptomic levels only but the effects at the DNA integrity and sexual differentiation were involved in adverse outcome pathways of urban pollution in Elliptio complanata mussels.

The effect of a step change in seabed depth on spreading discharged brine effluents from a two-outfall system

Discharged brine effluents from coastal desalination plants through marine outfall systems contain some reactive chemicals that may be derived from corrosion product, toxic antifoulants, antiscalants and other chemicals used in desalinating seawater. These effluents are subject to significant loss due to temporal decay that varies with water depth as the results of consumption by bacteria or radioactive decay, heat loss or evaporation through the surface, and break up or dissolution by turbulence. A far-field model using a two-dimensional decay-advection-diffusion equation with two point sources in a simple step seabed profile is presented to study the variability of decay with water depth. Analytical solutions are illustrated graphically by plotting contours of concentration to simulate the spreading of discharged brine effluent plumes from two outfalls in coastal waters. The maximum value of the compounded concentration at the shoreline is formulated and used as a measure for assessing the quality standards of coastal waters. It is found that, for coastal effluent discharges, the modern engineering practice which installs a two-port diffuser at the end of the outfall pipeline does produce low potential environmental impact.

Colored Dissolved Organic Matter (CDOM) as a tracer of effluent plumes in the coastal ocean

Mapping wastewater effluent plumes is typically conducted using ammonia as a tracer, but this provides low spatial resolution since it is collected as discrete bottle samples. Here we evaluate the use of colored dissolved organic matter fluorescence (CDOM) collected continuously with a CTD+ water column profiler as potential plume tracer alternative. We developed an algorithm for plume detection based on the image segmentation approach in 3D space and validated it against interpolated ammonia values collected during fourteen years of water quality monitoring (2004–2017) around three southern California ocean outfalls. There was 78%–81% agreement between plume site identification by CDOM and ammonia methods at the three outfalls, with an almost equal fraction of the differences attributable to apparent error from each tracer. The biggest shortcoming of using ammonia concentration was its rapid transformation in seawater via nitrification or biological uptake, which is most problematic at stations at the plume perimeter. Shortcomings of the CDOM method include calibration problems, inappropriate excitation/emission characteristics of standard WETStar fluorometers and non-effluent (confounding) sources of CDOM in seawater around the outfalls, but these are largely correctable and are outweighed by the greater spatial and temporal resolution this method offers.

FVCOM-plume - A three-dimensional Lagrangian outfall plume dilution and transport model for dynamic tidal environments: Model development.

Although numerous steady-state effluent plume dilution models are in use, their application in tidal environments remains a challenge. Three-dimensional dynamic circulation models are also inadequate, often due to the lack of required resolution and simplifying assumptions. To overcome these limitations, we present FVCOM-plume-an outfall plume dilution and transport model that operates within the Finite Volume Coastal Ocean Model (FVCOM) framework. It provides simultaneous inclusion of near-field dilution and far-field plume transport processes. The near-field is based on UM3 model using Lagrangian Control Volume approach to compute buoyant plume trajectory and dilution from multiport diffusers. The far-field uses neutrally buoyant particles with point masses and the random walk method to solve unsteady advection-diffusion processes. A density kernel approach is used to compute concentrations at point locations and analyze far-field plume characteristics. The results demonstrate the ability of FVCOM-plume to simultaneously capture near-field and far-field effluent plume dynamics in tidal environments.

Water Table Impacts on Wastewater Storage around Onsite Drainfield Trenches: Evaluation by Model Simulation

Core Ideas Water storage volume is important for loading rates of on‐site wastewater systems. HYDRUS (2D/3D) was used to model the slope of the effluent surface away from a trench. Modeled slopes confirm field observations across conductivity classes and soils. Arkansas uses a unique system for determining effluent loading rates for onsite wastewater systems based on wastewater storage in unsaturated soil above a seasonal water table. Evaluation of the soil volume available for storage relies on estimates of the slope of the effluent plume away from the trench, which has rarely been evaluated in the field. The objectives of this study were (i) to evaluate the simulated effluent slope for select soils in different hydraulic conductivity classes and with different seasonal water table depths, and (ii) to illustrate the utility of using model simulations to evaluate regulatory parameters established with limited measured data. The geometry of the effluent surface was evaluated by simulation of wastewater input and effluent movement with the HYDRUS (2D/3D) two‐dimensional model. Nine soils mapped in Arkansas and in varying hydraulic conductivity classes were used. For each soil, initial seasonal water tables were established at target depths of ∼40, 60, and 100 cm. Limited lateral spread of effluent resulted in effluent slopes that increased proportionately to water‐table depth. Averaged across water‐table depths, the mean slope of the effluent surface was 16, 15, and 29% for soils in the high, moderate, and low hydraulic conductivity classes, respectively. Model‐simulated slopes for soils in moderate and low conductivity classes were lower than those currently assumed for calculation of effluent storage volume. The differences were small, however, and regulatory storage volumes result in appropriately conservative loading rates that minimize the risk of failure due to effluent surfacing in the drainfield area.

Estimation of the dilution field near a marine outfall by using effluent turbidity as an environmental tracer and comparison with dye tracer data.

The alternative use of effluent turbidity to determine the dilution field of a domestic marine outfall located off the city of Rio de Janeiro was evaluated through field work comprising fluorescent dye tracer injection and tracking with simultaneous monitoring of sea water turbidity. A preliminary laboratory assessment was carried out with a sample of the outfall effluent whose turbidity was measured by the nephelometric method before and during a serial dilution process. During the field campaign, the dye tracer was monitored with field fluorometers and the turbidity was observed with an optical backscattering sensor interfaced to an OEM data acquisition system. About 4,000 samples were gathered, covering an area of 3 km × 3 km near the outfall diffusers. At the far field - where a drift towards the coastline was observed - the effluent plume was adequately labeled by the dye tracer. The turbidity plume was biased due to the high and variable background turbidity of sea water. After processing the turbidity dataset with a baseline detrending method, the plume presented high correlation with the dye tracer plume drawn on the near dilution field. However, dye tracer remains more robust than effluent turbidity.

Bioconcentration of polycyclic musks in fathead minnows caged in a wastewater effluent plume

The synthetic polycyclic musks HHCB (Galaxolide®) and AHTN (Tonalide®) were monitored in fathead minnows (FHMs) caged for a month at various locations in the North Saskatchewan River (NSR), upstream and downstream of the Gold Bar wastewater treatment plant that serves the city of Edmonton, AB, Canada. In addition, the distribution of these musk compounds in the river was predicted using the fugacity-based Quantitative Water Air Sediment Interface (QWASI) model. In FHMs caged 0.15 km downstream of the wastewater outfall, mean concentrations of HHCB and AHTN were 7.4 and 0.4 μg g−1 wet weight, respectively. These are among the highest reported concentrations of these musk compounds in fish exposed to treated wastewater. The musk concentrations in FHMs were significantly lower further downstream of the outfall. High bioconcentration factors (BCFs) in FHMs that exceeded 104 higher than estimated concentrations in water indicated that there were low rates of biotransformation of the musks in the fish. In the FHMs caged at the site closest to the wastewater outfall, HHCB concentrations in FHMs were comparable to the body burdens that have been reported to moderate expression of vitellogenin in female rainbow trout, indicating that fish in the NSR downstream of the wastewater outfall may be at risk of anti-estrogenic effects. The QWASI model applied to six individual river sections of the NSR predicted that the largest fluxes of HHCB and AHTN would be for downstream transport in water, which explains why FHMs accumulated elevated concentrations of the musks at the furthest downstream site, 9.9 km from the wastewater discharge.

Microplastic abundance and distribution in the open water and sediment of the Ottawa River, Canada, and its tributaries

Microplastic pollution is prevalent in the Ottawa River, with all open water samples ( n = 62) and sediment samples ( n = 10) containing microplastics. The median microplastic concentration of nearshore 100 L water samples was 0.1 fragments per L (ranged between 0.05 and 0.24 fragments per L). The larger volume Manta trawls samples taken in the middle of the Ottawa River had an overall mean concentration of plastics of 1.35 fragments per m3. Plastic concentrations were significantly higher downstream of the wastewater treatment plant (1.99 fragments per m3) compared with upstream of the effluent output (0.71 fragments per m3), suggesting that the effluent plume is a pathway for plastic pollution to the Ottawa River. The mean concentration of microplastic fragments recovered in the sediment samples was 0.22 fragments per g dry weight. The abundance of microplastics in the sediment was not significantly related to the mean particle size or the organic content of the sediment. The most common form of plastic particles found was microfibers. These made up between 70% and 100% of all plastic particles observed, although plastic microbeads and secondary plastic fragments were also recovered.

Unusually low234Th in a hydrothermal effluent plume over the Southwest Indian Ridge

Particle dynamics in hydrothermal plumes are crucial to understanding the cycling of carbon and trace elements in the global oceans, but this subject area has been poorly studied. We investigated radioactive 234Th in a hydrothermal plume of a recently discovered vent over the Southwest Indian Ridge (SWIR). Above the plume, total 234Th was in equilibrium with 238U, showing the typical characteristic of general deep water. However, there was a 234Th deficit within the plume, with 234Th/238U ratios in the 0.77–0.91 range. Particulate 234Th accounted for ∼10% of the total 234Th, contrasting with 4% in the overlying water. On average, the scavenging and removal rates of 234Th were 17.5 ± 2.5 dpm m−3 d−1 and 11.8 ± 2.5 dpm m−3 d−1. The residence time of dissolved 234Th (avg. 108 ± 8 d) was much higher than particulate 234Th (avg. 19 ± 1 d), indicating that scavenging of 234Th from dissolved to particulate phase dominated its residence time scale. Particulate organic carbon (POC) increased 15% within the plume, compared with the overlying water. Combining the removal of 234Th and the ratio of POC to particulate 234Th, the POC removal flux was 9.3 ± 0.6 mmol m−2 d−1. Similarly, 2.2 ± 0.6 mmol m−2 of particulate nitrogen (PN) was removed per day from the plume. The magnitude of POC and PN removal implied an important role of the hydrothermal plume in delivering organic matter to the seafloor. This study thus reveals the different particle dynamic characteristics within the hydrothermal plume over the SWIR compared to the ordinary deep oceans.

Glider and remote sensing observations of the upper ocean response to an extended shallow coastal diversion of wastewater effluent

The Orange County Sanitation District (OCSD) diverted wastewater discharge (5.3 × 108 l d−1) from its primary deep (56 m) outfall 8 km offshore, to a secondary shallower (16 m) outfall 1.6 km offshore for a period of three weeks. It was anticipated that the low salinity and density of the effluent would cause it to rise to the surface with limited dilution, elevating nutrient concentrations in near-surface waters and stimulating phytoplankton blooms in the region. Three Teledyne Webb Slocum gliders and a Liquid Robotics surface wave glider were deployed on transects near the outfalls to acquire high spatial and temporal coverage of physical and chemical parameters before, during, and after the wastewater diversion. Combined autonomous underwater vehicle (AUV) and MODIS-Aqua satellite ocean color data indicated that phytoplankton biomass increased in the upper water column in response to the diversion, but that the magnitude of the response was spatially patchy and significantly less than expected. Little evidence of the plume or its effects was detectable 72 h following the diversion. The effluent plume exhibited high rates of dilution and mixed throughout the upper 20 m and occasionally throughout the upper 40 m during the diversion. Rapid plume advection and dilution appeared to contribute to the muted impact of the nutrient-rich effluent on the phytoplankton community in this coastal ecosystem.