you're reading...


Making potable water safe for the seafloor

Del-Pilar-Ruso, Y., E. Martinez-Garcia, F. Gimenez-Casalduero, A. Loya-Fernandez, L.M. Ferrero-Vicente, C. Marco-Mendez, J. A. de-la-Ossa-Carrertero, J.L. Sanchez-Lizaso, (2015) Benthic community recovery from brine impact after the implementation of mitigation measures, Water Research (70) pp. 325-336 http://dx.doi.org/10.1016/j.watres.2014.11.036


Basic steps in sea water reverse osmosis processes

Figure 1: Basic steps in sea water reverse osmosis processes

Desalination through seawater reverse osmosis (SWRO) is an effective way to make potable water. The basic process of reverse osmosis desalination involves three steps (figure 1): 1) a pretreatment to remove particulates that could interfere with the reverse osmosis process, 2) a reverse osmosis processes which separates dissolved constituents (including salts) from the water, and 3) a treatment to make the ‘clean’ water meet potable standards. After the reverse osmosis step, brine concentrated in the dissolved constituents is discharged back into the ocean. The density of the discharge is greater than the surrounding seawater so it settles to the seabed. The introduction of high salinity brine may impact the benthic community. It is important to understand what the impacts are and how to control them so that the community is minimally affected by the discharge.

Diffuser in laboratory, dyed blue water represents dense brine.

Figure 2: Diffuser in laboratory, dyed blue water represents dense brine.

One solution to mitigate the disruption of brine on benthic communities near discharge sites is to install a diffuser. Diffusers enhance mixing by forcing the dense discharge up; the dense brine is diluted by ambient seawater (figure 2).

In 2008 the global production potential of SWRO desalinization processes was 24.5 million cubic meters per day, 17% of which occurred in the Mediterranean Sea. Two of the desalination plants in the Mediterranean are in southeast Spain in San Pedro; each with a production capacity of 65,000 cubic meters per day. The discharge from these two plants has a salinity of around 70, about double the salinity of ambient seawater. The brine is pipelined 5 kilometers off shore and discharged into 33 meters of water. In May of 2010 a diffuser was installed at the end of the pipeline to enhance mixing. The study reviewed here was conducted to determine the effectiveness of mitigation efforts at the pipeline discharge point.



Figure 3: Polychaetes

Station location

Figure 4: station location

Researchers used polychaetes (figure 3) as a bioindicator of the community response to salinity impacts from a SWRO desalination plant in the Mediterranean Sea.   They monitored salinity, polychaete abundance, family richness (the number of families found in a sample), and diversity at 12 stations between 29-38 meters depth (figure 4) in autumn of 2005-2012.  The first year of the study, 2005, was conducted before there was discharge. Between 2006 and 2010 there was discharge without a diffuser. In May of 2010 a diffuser at a 60-degree angle to the horizontal was installed; observations continued through 2012.

Polychaetes were chosen as the bioindicator because they are known to adapt to a range of environmental properties. Six polychaete families were focused on in the study: Magelonidae, Paraonidae, Capitellidae, Syllidae, Cirratulidae, Sabellidae.

The extent of the brine plume was monitored by a conductivity temperature depth sensor (CTD).  A CTD sensor was also used to measured bottom salinity at the stations. Polychaete communities were sampled by a grab sampler in replicates of four: three for biological analysis and one for environmental analysis.

Various statistical analyses were preformed to determine the spatial changes in the community over the study period.


Salinity increased noticeably at the three stations (B1, B2, B3) within 250 meters of the discharge location (figure 5). None of the sites further than 2 kilometers from the discharge area were impacted, suggesting that the initial brine impact on the benthic community, even without the diffuser, is constrained in area. After the diffuser was installed there was clear dilution of the plume(figure 6).

OCT salinty vs time

Figure 5: Salinity at each station over time

Oct salinity pre and post

Figure 6: Change in brine plume before (left) and after (right) diffuser installation

Total Abundance

OCT abundance at station vs time

Figure 7: Abundance change over time at each station

Eleven on the twelve stations shared similar patterns in polychaete abundance: an initial high before the discharge in 2005, then a decrease after the discharge began followed by an abundance recovery that peaked in 2008. In 2010, after the diffuser was installed the abundance was low but rebounded through the conclusion of the study in 2012.   The only site that saw a decline in the abundance throughout the discharge period was B2, the one in closest proximity to the discharge; after 2010 the abundance began to recover (figure 7).

Diversity and Richness:

In general, with the exception of station B4, the species richness and diversity decreased with the start of discharge and then began to rebound after the installation of the diffuser (figure 8)

OCT richness at stations vs. time

OCT diversity at station vs. time Figure 8: Richness (top) and diversity (bottom)  change over time at each station

Information on how different families recover from ecological disturbances is limited; further research on family specific response and recovery may be required to understand results for the specific families.


The study found that mitigation of the adverse affects of SWRO is simple, and the results come quickly.   The recovery is considered rapid, occurring in a period of months, relative to the recovery from other anthropogenic processes, like fish farming, which can take greater than 5 years to recover.   This may be related to the impacts each process has. SWRO is simple because the discharge introduces high saline low nutrient water, where as more complicated process may introduce additional pollutants into the sediment.


This study is important because it is related to satisfying anthropogenic needs while minimizing the impact on the environment. As the population continues to grow and resources change it is vital that we put our best effort into understanding how our engineering will impact the environment. Once we have that understanding, it is critical that we apply it so that unnatural impacts are minimized.





No comments yet.

Post a Comment


  • by oceanbites 2 months ago
    Happy Earth Day! Take some time today to do something for the planet and appreciate the ocean, which covers 71% of the Earth’s surface.  #EarthDay   #OceanAppreciation   #Oceanbites   #CoastalVibes   #CoastalRI 
  • by oceanbites 3 months ago
    Not all outdoor science is fieldwork. Some of the best days in the lab can be setting up experiments, especially when you get to do it outdoors. It’s an exciting mix of problem solving, precision, preparation, and teamwork. Here is
  • by oceanbites 4 months ago
    Being on a research cruise is a unique experience with the open water, 12-hour working shifts, and close quarters, but there are some familiar practices too. Here Diana is filtering seawater to gather chlorophyll for analysis, the same process on
  • by oceanbites 5 months ago
    This week for  #WriterWednesday  on  #oceanbites  we are featuring Hannah Collins  @hannahh_irene  Hannah works with marine suspension feeding bivalves and microplastics, investigating whether ingesting microplastics causes changes to the gut microbial community or gut tissues. She hopes to keep working
  • by oceanbites 5 months ago
    Leveling up - did you know that crabs have a larval phase? These are both porcelain crabs, but the one on the right is the earlier stage. It’s massive spine makes it both difficult to eat and quite conspicuous in
  • by oceanbites 5 months ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring Cierra Braga. Cierra works ultraviolet c (UVC) to discover how this light can be used to combat biofouling, or the growth of living things, on the hulls of ships. Here, you
  • by oceanbites 6 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Elena Gadoutsis  @haysailor  These photos feature her “favorite marine research so far: From surveying tropical coral reefs, photographing dolphins and whales, and growing my own algae to expose it to different
  • by oceanbites 6 months ago
    This week for  #WriterWednesday  on Oceanbites we are featuring Eliza Oldach. According to Ellie, “I study coastal communities, and try to understand the policies and decisions and interactions and adaptations that communities use to navigate an ever-changing world. Most of
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Jiwoon Park with a little photographic help from Ryan Tabata at the University of Hawaii. When asked about her research, Jiwoon wrote “Just like we need vitamins and minerals to stay
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring  @riley_henning  According to Riley, ”I am interested in studying small things that make a big impact in the ocean. Right now for my master's research at the University of San Diego,
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Gabby Stedman. Gabby is interested in interested in understanding how many species of small-bodied animals there are in the deep-sea and where they live so we can better protect them from
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Shawn Wang! Shawn is “an oceanographer that studies ocean conditions of the past. I use everything from microfossils to complex computer models to understand how climate has changed in the past
  • by oceanbites 7 months ago
    Today we are highlighting some of our awesome new authors for  #WriterWednesday  Today we have Daniel Speer! He says, “I am driven to investigate the interface of biology, chemistry, and physics, asking questions about how organisms or biological systems respond
  • by oceanbites 8 months ago
    Here at Oceanbites we love long-term datasets. So much happens in the ocean that sometimes it can be hard to tell if a trend is a part of a natural cycle or actually an anomaly, but as we gather more
  • by oceanbites 9 months ago
    Have you ever seen a lobster molt? Because lobsters have exoskeletons, every time they grow they have to climb out of their old shell, leaving them soft and vulnerable for a few days until their new shell hardens. Young, small
  • by oceanbites 9 months ago
    A lot of zooplankton are translucent, making it much easier to hide from predators. This juvenile mantis shrimp was almost impossible to spot floating in the water, but under a dissecting scope it’s features really come into view. See the
  • by oceanbites 10 months ago
    This is a clump of Dead Man’s Fingers, scientific name Codium fragile. It’s native to the Pacific Ocean and is invasive where I found it on the east coast of the US. It’s a bit velvety, and the coolest thing
  • by oceanbites 10 months ago
    You’ve probably heard of jellyfish, but have you heard of salps? These gelatinous sea creatures band together to form long chains, but they can also fall apart and will wash up onshore like tiny gemstones that squish. Have you seen
  • by oceanbites 11 months ago
    Check out what’s happening on a cool summer research cruise! On the  #neslter  summer transect cruise, we deployed a tow sled called the In Situ Icthyoplankton Imaging System. This can take pictures of gelatinous zooplankton (like jellyfish) that would be
  • by oceanbites 11 months ago
    Did you know horseshoe crabs have more than just two eyes? In these juveniles you can see another set in the middle of the shell. Check out our website to learn about some awesome horseshoe crab research.  #oceanbites   #plankton   #horseshoecrabs 
WP2Social Auto Publish Powered By : XYZScripts.com