Effluent Plume Research Articles

Wastewater injection, aquifer biogeochemical reactions, and resultant groundwater N fluxes to coastal waters: Kā'anapali, Maui, Hawai'i

We utilize N and C species concentration data along with δ15N values of NO3− and δ13C values of dissolved inorganic C to evaluate the stoichiometry of biogeochemical reactions (mineralization, nitrification, anammox, and denitrification) occurring within a subsurface wastewater plume that originates as treated wastewater injection and enters the coastal waters of Maui as submarine groundwater discharge. Additionally, we compare wastewater effluent time-series data, injection rates, and treatment history with submarine spring discharge time-series data. We find that heterotrophic denitrification is the primary mechanism of N loss within the groundwater plume and that chlorination for pathogen disinfection suppresses microbial activity in the aquifer responsible for N loss, resulting in increased coastal ocean N loading. Replacement of chlorination with UV disinfection may restore biogeochemical reactions responsible for N loss within the aquifer and return N-attenuating conditions in the effluent plume, reducing N loading to coastal waters.

Assessment of wastewater impact on dissolved oxygen around southern California’s submerged ocean outfalls

Ocean wastewater dischargers in southern California maintain extensive water quality monitoring programs to assess their effects on coastal receiving waters, but there is no shared protocol to analyze these measurements for compliance with California Ocean Plan standards. Here we present an assessment methodology that we apply regionally to determine discharge effects on dissolved oxygen (DO). The methodology was developed using an optimization algorithm to determine the following: (1) the most appropriate number of reference sites to capture natural variability among sites without moving so far from the potentially affected site to confound the comparison with natural latitudinal and offshore gradients; (2) the thickness of depth slices for comparing profiles between reference and potentially affected sites that minimizes false positives from natural vertical variability while not being so large as to average out plume-caused deviations; and (3) an allowable difference from the reference mean associated with variability among reference profiles. The algorithm was based on maximizing the chance of detecting DO outranges in the effluent plume, while simultaneously minimizing the chance to falsely identify outranges at reference sites outside of the plume zone. The assessment methodology also differentiates DO outranges resulting from physical upward entrainment of deep, low-oxygen water by rising of lower density plume water, as opposed to outranges resulting from low-oxygen and oxygen demanding properties of the effluent, using temperature-oxygen relationships as a tracer of water masses. When the algorithm was applied to a ten year monitoring record from four discharge monitoring programs along the southern California coast, 11% of effluent sites were found to contain DO outranges, with about half of them resulting from deep water entrainment.

Impacts of a tertiary treated municipal wastewater effluent on the carbon and nitrogen stable isotope signatures of two darter species (Etheostoma blennioides and E. caeruleum) in a small receiving environment

This study contrasted the influence of tertiary treated municipal wastewater effluent (MWWE) exposure on the abundance, food selection (stomach contents), and carbon (δ13C) and nitrogen (δ15N) stable isotope signatures of Rainbow Darter (Etheostoma caeruleum) and Greenside Darter (Etheostoma blennioides) in a small receiving stream in southern Ontario, Canada. Despite tertiary treatment resulting in relatively high effluent quality, there is continued concern for environmental degradation downstream of the effluent outfall because of the relatively small size of the receiving environment and recent studies that have indicated changes occurring in relative fish abundance and stable isotope signatures. In July and August of 2009 fish and benthic invertebrate communities were examined along with analysis of δ13C and δ15N of the most common species to determine the effects of effluent exposure on the food web. Rainbow Darter increased in abundance and their δ15N values were enriched immediately downstream of the effluent outfall throughout the summer (July and August). In contrast, while δ15N of Greenside Darter followed a similar pattern in July, they were not enriched in August. The benthic community was changed immediately downstream of the outfall and the δ15N of invertebrates was enriched, similar to that observed in Rainbow Darter. Stomach contents of the two darter species diverged the most in the summer possibly explaining some of the changes in δ13C and δ15N among sites. It is possible that Greenside Darter fed on less enriched food downstream of the outfall, or fed outside of the effluent plume during the summer. Rainbow Darter may be able to exploit the changes in habitat and prey composition, resulting in differences in relative abundance of darters immediately downstream of the effluent outfall.

The fine-scale vertical variability of a wastewater plume in shallow, stratified coastal waters

We observed the fine-scale vertical variability of a wastewater plume discharged into shallow, stratified coastal waters with a set of wave-powered profiling moorings and bottom-mounted Acoustic Doppler Current Profilers. These in situ observations demonstrated that the effluent plume occupied a variable portion of the water column, but was typically at or above the pycnocline. The plume was characterized by small vertical scales away from the surface, while complicated patterns of vertical temperature and salinity compensation were found in the plume above the pycnocline. The particular design of the diffuser led to an effluent plume that was roughly split between depth-trapped and trapped at the surface. Estimates of dilution from temperature/salinity diagrams indicated that the plume dilution ranged between 60 and 120, and that the environmental mixing end-members ranged from waters well below the pycnocline to the waters at or near the surface. Far from the outfall, oceanographic variability at frequencies equal to and higher than the diurnal frequency dominated the vertical shear in local currents and thus the vertical and temporal distribution of the plume. Mixing driven by the high frequency non-linear internal waves and bore-like manifestations of the cross-shore baroclinic tide, as suggested by elevated inverse Richardson number within the leading and trailing edge of the bores, was likely the primary source of mixing between the plume and ambient waters far from the outfall. Complicated patterns in plume water characteristics demonstrated the complexity of the plume dilution even in a surfacing plume. The co-occurrence of elevated chlorophyll fluorescence and plume waters was evident in the later part of the diversion period, but the overall response of the phytoplankton to the effluent diversion was limited. Implications for outfall wastewater monitoring and diffuser design are briefly considered.

Subsurface seeding of surface harmful algal blooms observed through the integration of autonomous gliders, moored environmental sample processors, and satellite remote sensing in southern California

AbstractAn observational study was performed in the central Southern California Bight in Spring 2010 to understand the relationship between seasonal spring phytoplankton blooms and coastal processes that included nutrient input from upwelling, wastewater effluent plumes, and other processes. Multi‐month Webb Slocum glider deployments combined with MBARI environmental sample processors (ESPs), weekly pier sampling, and ocean color data provided a multidimensional characterization of the development and evolution of harmful algal blooms (HABs). Results from the glider and ESP observations demonstrated that blooms of toxic Pseudo‐nitzschia sp. can develop offshore and subsurface prior to their manifestation in the surface layer and/or near the coast. A significant outbreak and surface manifestation of the blooms coincided with periods of upwelling, or other processes that caused shallowing of the pycnocline and subsurface chlorophyll maximum. Our results indicate that subsurface populations can be an important source for “seeding” surface Pseudo‐nitzschia HAB events in southern California.

Toxicity of two pyrethroid-based anti-sea lice pesticides, AlphaMax® and Excis®, to a marine amphipod in aqueous and sediment exposures

Abstract Pyrethroid pesticides used to control ectoparasitic sea lice in salmon aquaculture are released in effluent plumes from cage sites and have the potential to adversely affect non-target organisms. Pyrethroids have been shown to be highly toxic to crustaceans, but the toxicity of the pyrethroid-based anti-sea lice pesticides AlphaMax® (active ingredient (a.i.) deltamethrin) and Excis® (a.i. cypermethrin) has not been thoroughly studied for non-target, marine benthic crustaceans such as amphipods. The amphipod Echinogammarus finmarchicus, which is ubiquitous in near-shore environments in the northern Atlantic Ocean, was collected from the field for use in laboratory toxicity tests. Amphipods were exposed to the two pesticides in 1- and 24-h water-only, single-pulsed exposures and 10-day spiked sediment tests. In water-only tests, immobility occurred within 1- or 24-h of exposure to the highest test concentrations and delayed mortality and immobility were observed following exposure to lower concentrations as well. Effect thresholds ranged from 6.7–70 ng/L for deltamethrin and 20–220 ng/L for cypermethrin. Organisms exposed to sediment were affected within 2–4 days; resulting 10-d LC50s were 16 and 80 ng/g (dry weight) for deltamethrin and cypermethrin, respectively. Results suggest that amphipods in an effluent plume may be exposed to aqueous concentrations of pyrethroids sufficient to cause adverse effects, including delayed toxicity. In contrast, the 10-day sediment LC50s were much higher than (limited) reported environmental concentrations in sediment. Overall, these results suggest a low potential for risk from sediment exposures for a northern Atlantic species of amphipod that inhabits the near-shore environment where cage aquaculture sites are located.

Modelling of Far-Field Mixing of Industrial Effluent Plume in Ambient Receiving Water: The Ikpoba River Hub Example

A study was initiated with a view to understanding the mathematical physics of industrial effluent plume dispersion in Ikpoba River which has resulted in the development of a sacrificial stretch along the river course and which made water body from that stretch unfit for various uses on account of resulting water quality parameters that are above threshold values. This study sought to describe the dynamics of advective and dispersive transport of the effluent plume in the river and also ascertain the extent of its effect from discharge location to downstream far-field region. A homogenous differential equation was used as analytics to describe the physical process that describes the wave of dispersion in water as a Doppler shift run. The model developed provides a geometric illustration of the dispersion process which gives a graphic detail of wavefronts distribution of effluent matter. Another important result of this study is that in the initially 3-D mixing process, the drop-off of the maximum mass concentration is relatively fast but thereafter the concentration gradually loses intensity downstream and at 1800m the concentration variations become below the water quality threshold criteria. In effect, industrial effluent loading is continuous and concentrated thereby causing a stretch of 1.8km sacrificial region to develop along the river course. http://dx.doi.org/10.4314/njt.v33i2.10

Effluent Discharges from Two Outfalls on a Sloping Beach

A marine outfall is a long pipeline that continuously discharges large amounts of effluent streams into the sea. As the number of marine outfalls along the coastal areas is growing, a far field mathematical model with two point sources on a sloping beach is used to assess the coastal water quality following discharges from two outfalls. Asymptotic approximation will be made to the concentration at the beach to measure how well the effluent plumes are mixed and diluted in the coastal waters. The result found agrees with the engineering practice of installing a two-port diffuser at the end of a single outfall to minimize its potential environment impacts.

Wastewater Effluent Impacts Ammonia-Oxidizing Prokaryotes of the Grand River, Canada

The Grand River (Ontario, Canada) is impacted by wastewater treatment plants (WWTPs) that release ammonia (NH3 and NH4+) into the river. In-river microbial communities help transform this ammonia into more oxidized compounds (e.g., NO3- or N2), although the spatial distribution and relative abundance of freshwater autotrophic ammonia-oxidizing prokaryotes (AOP) are not well characterized. This study investigated freshwater N cycling within the Grand River, focusing on sediment and water columns, both inside and outside a WWTP effluent plume. The diversity, relative abundance, and nitrification activity of AOP were investigated by denaturing gradient gel electrophoresis (DGGE), quantitative real-time PCR (qPCR), and reverse transcriptase qPCR (RT-qPCR), targeting both 16S rRNA and functional genes, together with activity assays. The analysis of bacterial 16S rRNA gene fingerprints showed that the WWTP effluent strongly affected autochthonous bacterial patterns in the water column but not those associated with sediment nucleic acids. Molecular and activity data demonstrated that ammonia-oxidizing archaea (AOA) were numerically and metabolically dominant in samples taken from outside the WWTP plume, whereas ammonia-oxidizing bacteria (AOB) dominated numerically within the WWTP effluent plume. Potential nitrification rate measurements supported the dominance of AOB activity in downstream sediment. Anaerobic ammonia-oxidizing (anammox) bacteria were detected primarily in sediment nucleic acids. In-river AOA patterns were completely distinct from effluent AOA patterns. This study demonstrates the importance of combined molecular and activity-based studies for disentangling molecular signatures of wastewater effluent from autochthonous prokaryotic communities.

Micropollutant Dynamics in Vidy Bay—A Coupled Hydrodynamic-Photolysis Model to Assess the Spatial Extent of Ecotoxicological Risk

The direct discharge of effluent wastewater into Vidy Bay (Lake Geneva) results in the formation of an effluent plume with locally high concentrations of wastewater-derived micropollutants. The micropollutant hotspots above the wastewater outfall present a potential ecotoxicological risk, yet the spatial extent of the plume and the associated ecotoxicological risk zone remain unclear. This work combines the two main processes affecting the spreading of the plume, namely dilution of micropollutants due to mixing and degradation by photolysis, into a coupled hydrodynamic-photolysis model, with which we estimated the spatial extent of the risk zone in Vidy Bay. The concentration of micropollutants around the wastewater outfall was simulated for typical wind scenarios and seasons relevant to Vidy Bay, and the resulting ecotoxicological risk was evaluated. Specifically, we determined the direct and indirect photolysis rate constants for 24 wastewater-derived micropollutants and implemented these in a hydrodynamic particle tracking model, which tracked the movement of water parcels from the wastewater outfall. Simulations showed that owing to thermal stratification, the zone of ecotoxicological risk is largest in summer and extends horizontally over 300 m from the outfall. Photolysis processes contribute to reducing the plume extent mainly under unstratified conditions when the plume surfaces. Moreover, it was shown that only a few compounds, mainly antibiotics, dominate the total ecotoxicological risk.

Effects of a surfacing effluent plume on a coastal phytoplankton community

Urban runoff and effluent discharge from heavily populated coastal areas can negatively impact water quality, beneficial uses, and coastal ecosystems. The planned release of treated wastewater (i.e. effluent) from the City of Los Angeles Hyperion Wastewater Treatment Plant, located in Playa del Rey, California, provided an opportunity to study the effects of an effluent discharge plume from its initial release until it could no longer be detected in the coastal ocean. Non-metric multi-dimensional scaling analysis of phytoplankton community structure revealed distinct community groups based on salinity, temperature, and CDOM concentration. Three dinoflagellates (Lingulodinium polyedrum, Cochlodinium sp., Akashiwo sanguinea) were dominant (together >50% abundance) prior to the diversion. Cochlodinium sp. became dominant (65–90% abundance) within newly surfaced wastewater, and A. sanguinea became dominant or co-dominant as the effluent plume aged and mixed with ambient coastal water. Localized blooms of Cochlodinium sp. and A. sanguinea (chlorophyll a up to 100mgm−3 and densities between 100 and 2000cellsmL−1) occurred 4–7 days after the diversion within the effluent plume. Although both Cochlodinium sp. and A. sanguinea have been occasionally reported from California waters, blooms of these species have only recently been observed along the California coast. Our work supports the hypothesis that effluent and urban runoff discharge can stimulate certain dinoflagellate blooms. All three dinoflagellates have similar ecophysiological characteristics; however, small differences in morphology, nutrient preferences, and environmental requirements may explain the shift in dinoflagellate composition.

Characterizing the effluence near Waikiki, Hawaii with a coupled biophysical model

Aperiodic discharge from the Ala Wai Canal near Waikiki, Hawaii is often contaminated with naturally occurring harmful bacteria that may affect nearby beaches. Using a coupled hydrodynamic and biological model, we examine how tides, wind, surface waves, and light affect the fate of this effluent plume. The nearshore circulation and tidal flows constrain the freshwater plume to the surface. Winds can overcome both the stratification and ambient tidal advection to keep the plume to the west (away from major beaches) and mix the plume deeper into the water column. Surface waves due to swell act to mix the plume deep and keep the plume onshore. We find that the plume does not extend offshore in the presence of winds or waves. Using Enterococcus spp. as the bacterial agent, we find that residency is increased when mixed deeper away from the light. Comparing predicted Enterococcus spp. with in-situ samples for five distinct plume events, we find that the model accurately represents the observed bacterial concentrations when the Ala Wai is the primary source of Enterococcus spp. discharge. The results show that predictive models may be an invaluable complement to water quality sampling programs for regions of high human activity.

Geostatistical Prediction of Ocean Outfall Plume Characteristics Based on an Autonomous Underwater Vehicle

Geostatistics has been successfully used to analyse and characterize the spatial variability of environmental properties. Besides providing estimated values at unsampled locations, geostatistics measures the accuracy of the estimate, which is a significant advantage over traditional methods used to assess pollution. This work uses universal block kriging to model and map the spatial distribution of salinity measurements gathered by an Autonomous Underwater Vehicle in a sea outfall monitoring campaign. The aim is to distinguish the effluent plume from the receiving waters, characterizing its spatial variability in the vicinity of the discharge and estimating dilution. The results demonstrate that geostatistical methodology can provide good estimates of the dispersion of effluents, which are valuable in assessing the environmental impact and managing sea outfalls. Moreover, since accurate measurements of the plume's dilution are rare, these studies may be very helpful in the future to validate dispersion models.

Effects of ocean thermal energy conversion systems on near and far field seawater properties—A case study for Hawaii

In light of renewed interest and efforts in the development of ocean thermal energy conversion (OTEC) systems with a vision to provide mankind with a long-lasting energy resource, the potential environmental impacts of this technology should be considered from the perspective of sustainability. As an important step toward such a goal, we examine effects of OTEC effluent discharge on the physical aspects of the ocean environment near a Hawaiian Island in the North Pacific Ocean. We use modeling tools comprised of a mixing model that predicts the near field dilution of effluent plumes and a high-resolution ocean circulation model that simulates the dispersion of effluent in the far field. Numerical experiments are conducted to explore factors that influence effluent dispersal. We find that OTEC thermal resource is favorable and stable at the chosen location for the time period experimented. For a given OTEC design, the effluent discharge settles at a depth sufficiently far from the depths of discharge or intakes, and becomes dispersed quickly away from the site by highly variable ocean currents. Changes in ocean stratification and flow field are negligible for one OTEC device but are notable when multiple OTEC devices are present. These changes do not persist beyond 2 weeks after switching off OTEC activity.

Using radium isotopes to estimate the residence time and the contribution of submarine groundwater discharge (SGD) in the Changjiang effluent plume, East China Sea

This paper reports the initial result of the flux of submarine groundwater discharge (SGD) into the Changjiang effluent plume (CEP). A radium mass balance model and a 224Ra/223Ra activity ratio (AR) apparent age model were applied to estimate the residence time of water above the pycnocline in the CEP. These two approaches gave similar results, yielding residence times of 5.4d and 7.0d, respectively, in the inner and outer plume zones. The nonconservative inventory of 226Ra was established in the CEP, and converted to a 226Ra flux by dividing by the water residence time and assuming steady state conditions. After subtracting the desorption of 226Ra from suspended sediment and the diffusion from the bottom sediment, the 226Ra flux from SGD was converted to a total SGD flux by dividing by the measured activity of 226Ra in local groundwater. The SGD flux in the CEP is estimated to be 0.2–1.0×109m3d−1, which is equivalent to 6–30% of the Changjiang water discharge during flood season. This large flux indicates that SGD may be another important nutrient source to the East China Sea.

Algal δ15N values detect a wastewater effluent plume in nearshore and offshore surface waters and three-dimensionally model the plume across a coral reef on Maui, Hawai‘i, USA

The coral reef at Kahekili, Maui is located ∼300m south of the Lahaina Wastewater Reclamation Facility which uses four Class V injection wells to dispose of 3–5million gallons of wastewater effluent daily. Prior research documented that the wastewater effluent percolates into the nearshore region of Kahekili. To determine if the wastewater effluent was detectable in the surface waters offshore, we used algal bioassays from the nearshore region to 100m offshore and throughout the water column from the surface to the benthos. These algal bioassays documented that significantly more wastewater effluent was detected in the surface rather than the benthic waters and allowed us to generate a three-dimensional model of the wastewater plume in the Kahekili coastal region. Samples located over freshwater seeps had the highest δ15N values (∼30–35‰) and the effluent was detected in surface samples 500m south and 100m offshore of the freshwater seeps (∼8–11‰).

Merging Effluent Discharge Plumes from Multiport Diffusers on a Sloping Beach

Multiport diffusers are the effective engineering devices installed at the marine outfall systems for the steady discharge of effluent streams from the modern coastal plants, such as municipal sewage treatment, power generation and seawater desalination. A far field mathematical model using a two-dimensional advection-diffusion equation is presented for continuous discharges of effluent streams from multiple outfalls on a uniformly sloping beach with a current parallel to the shoreline. The analytical solutions are illustrated graphically to replicate and capture the merging process of effluent plumes in shallow coastal waters, and then asymptotic approximation will be made to the maximum shoreline’s concentration to formulate effluent discharge plume dilution from a multiport diffuser.

Influence of density stratification on effluent plume dynamics

In this study we modelled sea temperature (T), salinity (S) and density field dynamics using a 3D numerical model applied to Rijeka Bay (Croatia) in order to explore their effect on effluent plume dynamics in the vicinity of four submarine sewage outfalls when the bora wind (NE direction) is blowing. The vertical density stratification in the area studied is strongly related to the bora wind, which contributes significantly to the lowering of the pycnocline depth through enhanced mixing in the vertical, giving rise to changes in the neutral buoyancy level. The features of near-field plume dynamics were calculated with the use of a separate near-field numerical model, using information on the vertical density distribution previously calculated using a 3D numerical model.The results of the numerical simulations and statistical analysis of the wind data indicate a very low probability of complete water column homogenization and consequent effluent plume rise to the sea surface under the influence of the bora wind during the peak tourist season (May–September).

Immunotoxicity of Municipal Effluents to Freshwater Mussels

The release of treated municipal wastewaters to the aquatic environment raises concern about the health impacts on local resident invertebrates such as mussels. The purpose of this study was to examine the immunotoxicity of two types of treated municipal effluents—physico-chemical treated and physico-chemical with additional ozonation—to freshwater mussels. Immunocompetence was followed by tracking changes in hemocyte viability, adherence, phagocytosis, vitellogenin (Vtg)-like proteins and the pro-inflammatory precursors nitric oxide (NOx) production and arachidonate cyclo-oxygenase (COX) activity. The study results revealed that following a two-week continuous-flow exposure to the effluents, a reduction in hemocyte viability, adherence, NOx and COX activities was observed. Vtg like proteins were also increased, highlighting the estrogenic nature of the effluents. A significant correlation was found between Vtg-like proteins and the phagocytic efficiency index (r=0.34; p<0.001), which suggests that estrogenic compounds may have been involved in the immunocompetence of mussels exposed to municipal effluents. In conclusion, short-term exposures to treated municipal effluents have the potential to impede the immunocompetence of mussels occurring in the vicinity of an effluent dispersion plume.

Evidence of feminization in wild Elliptio complanata mussels in the receiving waters downstream of a municipal effluent outfall

The endocrine-disrupting activity of municipal effluents has the potential to alter the reproductive system and induce feminization to aquatic organisms. The purpose of this study was to examine the sex ratio, vitellogenin (Vtg)-like proteins, serotonin, arachidonate cyclooxygenase (COX) activity and dopamine status in wild mussels living at sites upstream and downstream of two municipal effluent outfalls in the Mille-Îles River (Quebec, Canada). Gonad integrity was also studied by monitoring the gonado-somatic index (GSI), the activity of the rate-limiting enzyme aspartate transcarbamoylase (ATC) for purine synthesis, and changes in lipid peroxidation (LPO). The results showed that the proportion of females was dramatically increased from 30% at the upstream sites to 80% at the downstream sites. The levels of Vtg-like proteins were significantly elevated in the male mussels only. Male mussels downstream of the municipal effluent plumes expressed female-specific protein bands (Vtg-like), as determined by high-resolution gel electrophoresis and silver staining. The serotonin/dopamine ratio was significantly decreased in the downstream mussels, indicating that the gonad was in a state of early vitellogenesis. However, this change was not accompanied by changes in ATC, suggesting no significant egg production was underway; this was confirmed by the observation that the downstream mussels displayed significantly low GSIs. GSIs were rather dependent on the serotonin/dopamine ratio (r = 0.44; p < 0.001), while Vtg-like proteins were dependent on dopamine levels (r = 0.50; p < 0.001). The increase in COX activity at the downstream sites and its close relationship with increased serotonin levels suggest a concomitant serotonergic signalling in addition to VTG production. The production of Vtg-like proteins combined with the serotonergic effects of the municipal effluents was associated with oxidative damage (LPO) in the gonad. This study provides the first evidence of feminization in wild mussel populations and the disruption in gonad physiology by exposure to municipal effluents.