Adsorption desalination: Advances in porous adsorbents

With the continuous growth of the world population, the demand for fresh water is ever increasing. Water desalination is a means of producing fresh water from saline water, and one of the proposed solutions in the scientific community for solving the current global freshwater shortage. Adsorption is foreseen as a promising technology for desalination due to its relatively low energy requirements, low environmental impact, low cost and high salt removal efficiency. More importantly, chemicals are not required in adsorption processes. Active carbons, zeolites, carbon nanostructures, graphene and coordination framework materials are amongst the most investigated adsorbents for adsorption desalination, which show different performances regarding adsorption rate, adsorption capacity, stability and recyclability. In this review, the latest adsorbent materials with their features are assessed (using metrics) and commented critically, and the current trend for their development is discussed. The adsorption mode is also reviewed, which can provide guidance for the design of adsorbents from the engineering application point of view.     

Membrane-distillation desalination: Status and potential

This paper presents an assessment of membrane distillation (MD) based on the available state of the art and on ourpreliminary analysis. The process has many desirable properties such as low energy consumption, ability to use low temperature heat, compactness, and perceivably more immunity to fouling than other membrane processes. Within the tested range, the operating parameters of conventional MD configurations have the following effects:(1) the permeate fluxes can significantly be improved by increasing the hot feed temperature (increasing the temperature from 50 to 70°C increases the flux by more than three-fold), and by reducing the vapor/air gap (reducing the vapor air gap thickness from 5 to 1 mm increase the flux 2.3-fold); (2) the mass flow rate of the feed solution has a smaller effect: increasing it three-fold increases the flux by about 1.3-fold; (3) the concentration of the solute has slight effect: increasing the concentration by more than five-fold decreases the flux by just 1.15-fold; (4) the cold side conditions have a lower effect (about half) on the flux than the hot side; (5) the coolant mass flow rate has a negligible effect; (6) the coolant temperature has a lower effect than the mass flow rate of the hot solution. Fouling effects, membranes used, energy consumption, system applications and configurations, and very approximate cost estimates are presented. The permeate fluxes obtained by the different researchers seem to disagree by an order of magnitude, and better experimental work is needed.     

In-plant microfouling in desalination

Microfouling of solid surfaces exposed to sea water by primary film forming bacteria is a phenomenon reasonably well known. Microfouling is believed to serve as a percursor to marine macrofouling and corrosion, significantly reduce the efficiency of condenser-heat exchangers, and cause a reduction in efficiency of performance of reverse osmosis membranes. The complex poorly understood microfouling-corrosion process has caused a huge and continuing cost to the desalination industry.Microfouling in desalination is a process in which the rate of increase of the mass of surface film is dependent in large part on the specific character of the environment, most particularly the physical, chemical and biological condition of the intake sea water. The microfouling process occurs in four stages: (1) Chemical Conditioning, (2) Attachment and Colonization by bacteria, (5) Colonization by other microorganisms, and (4) Accumulation. The attachment of bacteria to surfaces is mediated by a glycoprotein polymer. This adhesion-inducing polymeric material has been recovered from filtered sea water, marine bacteria, and algal cultures. The glycoprotein is active in exceedingly low concentration and has been shown to adhere very effectively to solid surfaces.While microfouling is a known phenomenon in reverse osmosis, its role in accelerating corrosion as well as causing a decrease in the overall heat transfer coefficient in distillation has still not been fully studied. Sucessful control of microbial fouling will follow when a complete understanding of the process has been achieved.     

染整前处理绿色助剂及新型前处理工艺

在纺织品的染色前处理、染色、后处理阶段,由于必须使用大量的助剂和洗涤工序,产生大量的废水。在新世纪,人们越来越关心环境保护,因此,有关纺织品的各个处理阶段的环保型助剂研发和采用环保型新工艺成为纺织印染行业的重要任务。同时,还就染色前处理的绿色助剂和绿色工艺进行讨论。     

RO systems: the importance of pre-treatment

The ability or reverse osmosis (RO) to produce a continuous and dependable water product has seen its use within the water treatment industry grow. However, incorrectly designed pre-treatments to this technology can reduce the expected benefits. Simon Gare, Ecolochem International Inc, UK, explores both physical and chemical pre-treatment methods routinely used with RO systems, and discusses some of the factors that are important when choosing the right pre-treatment.