The biofilm emerges by forming a conditioning film on a membrane surface that comprises a range of organic compounds, followed by the attachment of microbial cells or clusters cemented by extracellular polymeric substances (EPS). Among different fouling types, biofouling is one of the most severe and pervasive fouling 12, 13, 14. Membrane fouling causes permeate flux decline, high energy consumption, pore wetting, and poor permeate quality 10, 11. Membrane fouling is an intricate phenomenon described as the accumulation, adsorption, or precipitation of the feed water constituents on the membrane surface or within its pores 8, 9 that substantially obstructs the performance of MD systems. Given these advantages, the MD process could contribute to global water sustainability as an affordable desalination technology by using low-grade energy sources, especially in arid and semi-arid coastal areas that experience water draughts and lack of inland freshwater basins. The MD advantages include compactness, lower operating temperatures, ambient operating pressures, utilization of renewable and low-grade energy sources, lower pretreatment requirements, high ions rejection, and little reliance on feed salinity 6, 7. At the same time, capillary forces prevent hydrophilic liquids from entering membrane pores 5. In MD, the heated saline stream is brought in contact with a hydrophobic microporous membrane, and water vapor evaporates at the membrane surface interface through the dry membrane pores and condenses on the permeate side 4. However, due to continuous increases in oil and gas prices and their potential depletion, conventional desalination, like multi-stage flash and multi-effect distillation, is becoming costly, necessitating the development of alternative desalination technologies that could overcome the limitations of existing seawater desalination plants. Even though the history of MD includes several decades, it has been shadowed by conventional desalination mainly due to low oil and gas costs making them more affordable options.

Membrane distillation (MD), a thermally driven separation technology, has been actively explored in an array of water treatment applications, ranging from seawater desalination to wastewater reclamation and brine management 1, 2, 3. The post-cleaning permeate conductivities were low suggesting that employed cleaning protocols did not cause pore wetting of hydrophobic polytetrafluoroethylene microporous (0.22 μm) membrane, and membrane rejection properties remained stable. Membrane cleanings substantially reduced the thickness of the residual biofilm layer and decreased its bacterial concentration and resistance to vapor pressure. The results showed that permeate flux recovery increased in the order of hydraulic cleaning <3%w w −1 citric acid <0.3%w w −1 NaOCl ≈0.3%w w −1 EDTA. Hydraulic cleaning and chemical cleanings with 0.3%w w −1 ethylenediaminetetraacetic acid (EDTA), 0.3%w w −1 NaOCl, and 3%w w −1 citric acid were tested. This study explores the efficiency of different cleaning strategies in biofilm removal during seawater MD. However, MD is susceptible to biofouling. Washington, DC: Island Press.Membrane distillation (MD) is an emerging process with a proven ability to recover freshwater from streams with a wide range of salinities. Ecosystems and human well-being: Current state and trends. Developing these indicators at the national scale represents a significant scientific and research challenge. Indicators for other ecological processes, such as respiration, nutrient cycling, or decomposition have been developed for ecosystems at watershed scales, but have not been developed at the national scale. Repeated measures over a season might provide an indicator of net primary production. The Normalized Difference Vegetation Index has been estimated at a national scale using remote sensing. For example, remote sensing imagery has been used to obtain 'snapshots' of indicators of ecosystem conditions over time, and to infer ecological processes such as terrestrial net primary production. This is difficult to achieve for many ecosystems at a local scale and even more difficult at the national scale. Only one indicator that meets the ROE criteria, Carbon Storage in Forests, is available to address this question because ecological processes are difficult to measure directly, particularly at a national scale.Įcological processes such as primary production, respiration, energy, carbon and nutrient flow through food webs, reproduction, and decomposition are represented as rates of change, which requires repeated measurement over time.

Physical and chemical processes