Removal of heavy metal ions from wastewaters: A review

Extracellular polymeric substances (EPS) of microbial aggregates in biological wastewater treatment systems: a review.

Humic acid (HA) coated Fe3O4 nanciparticles (Fe3O4/HA) were developed for the removal of toxic Hg(II), Pb(II), Cd(II), and Cu(II) from water. Fe3O4/HA were prepared by a coprecipitation procedure with cheap and environmentally friendly iron salts and HA. TOC and XPS analysis showed the as-prepared Fe3O4/ HA contains similar to 11% (w/w) of HA which are fractions abundant in O and N-based functional groups. TEM images and laser particle size analysis revealed the Fe3O4/HA (with similar to 10 nm Fe3O4 cores) aggregated in aqueous suspensions to form aggregates with an average hydrodynamic size of similar to 140 nm. With a saturation magnetization of 79.6 emu/g, the Fe3O4/HA can be simply recovered from water with magnetic separations at low magnetic field gradients within a few minutes. Sorption of the heavy metals to Fe3O4/HA reached equilibrium in less than 15 min, and agreed well to the Langmuir adsorption model with maximum adsorption capacities from 46.3 to 97.7 mg/g. The Fe3O4/HA was stable in tap water, natural waters, and acidic/ basic solutions ranging from 0.1 M HCl to 2 M NaOH with low leaching of Fe (<= 3.7%) and HA (<= 5.3%). The Fe3O4/HA was able to remove over 99% of Hg(II) and Pb(II) and over 95% of COO and Cd(II) in natural and tap water at optimized pH. Leaching back of the Fe3O4/HA sorbed heavy metals in water was found to be negligible.

Coating Fe3O4 Magnetic Nanoparticles with Humic Acid for High Efficient Removal of Heavy Metals in Water

Microalgae dewatering is a major obstruction to industrial-scale processing of microalgae for biofuel prodn. The dil. nature of harvested microalgal cultures creates a huge operational cost during dewatering, thereby, rendering algae-based fuels less economically attractive. Currently there is no superior method of dewatering microalgae. A technique that may result in a greater algal biomass may have drawbacks such as a high capital cost or high energy consumption. The choice of which harvesting technique to apply will depend on the species of microalgae and the final product desired. Algal properties such as a large cell size and the capability of the microalgae to autoflocculate can simplify the dewatering process. This article reviews and addresses the various technologies currently used for dewatering microalgal cultures along with a comparative study of the performances of the different technologies.

Dewatering of microalgal cultures : a major bottleneck to algae-based fuels

A review on heavy metal pollution, toxicity and remedial measures: Current trends and future perspectives

Ultrafiltration (UF) is one of the best options for both one-stage and as part of multi-stage water and wastewater purification. This review summarises the known facts about the fouling processes and cleaning procedures and details of the most successful physical and chemical cleaning combinations. The optimum cleaning is closely linked to the nature of the fouling. Precise knowledge of both the fouling type (organic, inorganic, or biological) and the fouling mechanism (gel formation, adsorption, deposition, pore blockage, or cake formation) is the key to success in UF membrane cleaning.

Fouling and cleaning of ultrafiltration membranes: A review

http://sec.sbq.org.br/cdrom/32ra/resumos/T2421-1.pdf

Enhanced removal of heavy metal ions bound to humic acid by polyelectrolyte flocculation

The addition of water treatment chemicals has always been considered as a standard operation in water and wastewater treatment. The concentration of chemicals was usually kept to the minimum necessary to achieve a good quality of potable or otherwise treated water. A significant interruption to the status-quo occurred more than 20 years ago after a severe and highly publicized outbreak of Cryptosporidium parvum oocysts. The strategic planning after the outbreak was to shift from physical-chemical to physical treatment methods, such as membrane filtration and UV disinfection. As such, the new procedures were supposed to eliminate the threat of water contamination through a minor addition of chemicals. Such was the mistrust and disappointment with water treatment chemicals themselves. Indeed, water treatment technologies are now using novel physical treatment methods. Membranes largely replaced granular filtration, and UV is paving the way towards minimization or elimination of the use of classic disinfection chemicals, such as chlorine and its derivatives. Yet, far from the “high-tech” revolution in water treatment technologies actually reducing the use of chemicals, the latter has in fact been significantly increased. The “conventional” chemicals used for pre-treatment, disinfection, corrosion prevention, softening and algae bloom depression are all still in place. Furthermore, new groups of chemicals such as biocides, chelating agents and fouling cleaners are currently used to supplement them. These latter are the chemicals needed to protect the high-tech equipment, to optimize the treatment, and to clean the equipment between uses. The health effects of the new chemicals introduced into water are yet to be fully established. Typically, a higher treatment efficiency requires effective chemicals, yet these are not always environmentally friendly. It seems obvious that the “high-tech” revolution currently affects the sustainability of water resources, and certainly not in a completely positive way. In short, the adverse effects of the introduction of such a significant amount of treatment chemicals into our sources of water are yet to be evaluated.

Nicholas P. Hankins

Papers

Fouling and cleaning of ultrafiltration membranes: A review

Enhanced removal of heavy metal ions bound to humic acid by polyelectrolyte flocculation

Water treatment chemicals: Trends and challenges

Microbial toxicity effects of reverse transported draw solute in the forward osmosis membrane bioreactor (FO-MBR)

Removal of heavy metal ions from dilute aqueous solutions by polymer–surfactant aggregates: A novel effluent treatment process