Friday, February 17, 2012

Pretreatment of water for RO Plants

Algal blooms not created equal

Since the first commercial seawater RO plant was installed in 1974, pretreatment has been the single biggest variable in determining an installation’s success. More than 3,200 SWRO plants are now producing almost 24 million m3/d (6.3 billion GPD) of fresh water, and of all the pretreatment issues, the ability to effectively deal with harmful algal blooms (HABs) remains the most challenging.

Last week, at an expert workshop entitled Red Tides and Harmful Algal Blooms (HAB): Impact on Desalination Plants, public and private sector organizations met in Muscat, Oman to share information and work towards developing a better understanding of HABs. The event was jointly organized by the Middle East Desalination Research Center (MEDRC), Australia’s National Centre of Excellence in Desalination (NCED) and King Abdullah University of Science and Technology (KAUST). The event was held under the patronage of HE Mohammed Al Mahrouqi, Chairman of Oman’s Public Authority for Electricity & Water.

HABs refer to fast-growing algal blooms that make toxic chemical byproducts that can concentrate in the tissues of fish or shellfish. Animals and humans who eat the shellfish may become sick or suffer severe respiratory problems including paralytic shellfish poisoning (PSP).

Certain phytoplankton species contain reddish pigments; when they bloom, the water often appears to be colored red, hence the term ‘red tide’. However, scientists prefer referring to the blooms as HABs and consider the term ‘red tide’ to be a misnomer because the events are not associated with tides and because the phytoplankton species that are harmful may never reach the densities required to discolor the water.

Don Anderson, a senior scientist at Woods Hole Oceanographic Institution, told the workshop attendees that HABs are an expanding threat to public and ecosystem health and coastal aesthetics worldwide. “HABs are diverse phenomena, caused by many different species, producing different toxins and other compounds, in different hydrographic environments. Methods that might mitigate the impacts of one type of HAB may not work for others. The threat from HABs to desalination plants is real, and deserves attention through targeted research,” said Dr Anderson.

HABs have caused several well-publicized desal plant shutdowns in Oman since 2008. Dr Hamed Al Gheilani, with Oman’s Marine Science and Fisheries Center, and Dr. Hamad Al Hasni, with Oman PAEW, outlined the impacts of those events and described the monitoring program initiated to help predict future events and mitigate their impacts on desalination plants.

The workshop concluded with the attendees dividing into three groups to prepare recommended research topics.

According to MEDRC deputy director Shannon McCarthy, “The workshop resulted in some very specific recommendations for research projects that will help identify the onset of HAB events and to develop methods to mitigate their impact on desalination plant performance and water quality. Over the next few weeks, MEDRC, NCED and KAUST will consolidate those recommendations and determine how selected projects might be funded. We have also already begun planning a follow-up event to build on what has been learned at last week’s workshop.”

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