Biofilm prevention in the desalination industry

Limitations of global freshwater supplies have stimulated the application of desalination technology with desalinized water coming online worldwide at a rate of 40 to 50 million m³ d⁻¹. Currently, about 50% of global desalination is based on filtration through reverse osmosis (RO) membranes requiring effective pretreatment procedures upstream to reduce fouling, maintain performance and extend membrane lifetime and to ensure the manufacturers requirements for membrane recovery yield. Transparent exopolymer particles (TEPs) are sticky, organic microgels, ranging in size from ∼0.4 to >200 μm, present in large numbers in all aquatic environments. Recently, TEPs have been implicated as an important factor in the development of aquatic biofilm and are part of the extracellular polymeric substances (EPSs) that form the matrix of microbial biofilms.
In our research we examined the direct involvement of these microgel particles in biofilm development. We showed that protobiofilm and TEPs in the feedwater contributed to fast development of biofilm and not EPSs generated by adhering, single bacteria, or bacterial aggregates. In addition, experiments comparing the initial stages of biofilm formation in filtered or in untreated seawater clearly illustrate the importance of protobiofilm and TEPs in accelerating aquatic biofilm formation.

Schematic illustration showing the involvement of organic polymers and colloids, TEP and protobiofilm in the initial stages of aquatic biofilm formation. Immediately upon exposure to seawater, organic polymers and colloids (a) and microgels such as uncolonized TEP (b) and protobiofilm (c) begin to attach to pristine surfaces. Single cells of planktonic bacteria also attach reversibly (d) or irreversibly (e) to conditioned surfaces. With time (minutes to hours) a contiguous coverage of mature biofilm (f) develops. From Bar-Zeev et al. 2013.PNAS

Desalination impacts on microbial coastal populations

The increasing importance and expansion of seawater desalination technologies and large scale coastal plants – enhances both the “visibility” and essentiality of ensuring environmental sustainability of the impacted coastlines. Our study (2015-2019) added important knowledge to the scant information that has been published either locally or globally to examine the impacts of desalination discharges on the coastal microbial communities comprising the foundation of the aquatic food webs. Our overarching goal in this project was to characterize and predict the responses of microbial and phytoplankton communities to their exposure to both enhanced salinities and chemical discharges resulting from desalination plants.

The comprehensive results of this study including the in-situ sampling, experimental manipulations, hydrodynamic simulations of plume and intake effects, and modeling brine (and temperature impacts) on the aquatic food-web all demonstrate the following. Impacts are influenced by both seasonality and site-specificity with salinity and temperature both driving biological changes. Therefore, site-specific monitoring and assessment of changes of the microbial populations is essential. Moreover, Coastal environments, exposed to long term discharge of brine, may exhibit cumulative chronic effects and affect the ecosystems more dramatically. The assessment of ecological impacts, from the rapidly expanding desalination industry, on coastal marine environments and their biota should be included as a routine monitoring tool and not be based solely on the results of short term studies such as this one.