Claire Gerente

Antibacterial Effects of Chitosan Powder: Mechanisms of Action

Chitosan, the deacetylated derivative of chitin, is a natural D-glucosamine polymer that can be extracted from the shells of seafood such as prawns crabs and lobsters. It can be used as a flocculent, plant disease resistant promoter, anti-cancer agent, wound healing promotion agent and antimicrobial agent. The aim of this paper is the study of the interaction between chitosan powder and various kinds of pathogen microorganisms potentially present in water. First of all, physico-chemical characterisations of chitin and chitosan powder were performed. The deacetylation yields were 35 %, 60 % and 80 ± 10 %. The experimental studies focused on the measurements of the mortality constant rate for various bacterial strains, Escherichia coli, Pseudomonas aeruginosa, Enterococcus faecalis and Staphylococcus saprophyticus. An explanation of the antibacterial mechanisms is proposed involving the cell wall disruption due to free amino groups present in chitosan.

Uranium Removal Onto Chitosan: Competition with Organic Substances

Organic materials and especially humic substances are often present in natural waters. The influence of organic compounds on uranium removal onto chitosan is studied. The pH of the media is fixed at 6. In operating conditions, uranium major species present in solution are: (UO2)3(OH)5 +. and (UO2)4(OH)7 +. Capacity of fixation is found to be 450 mg g−1, considering precipitation phenomena. Experimental results show that chitosan offers a selective adsorption depending on the different organics used: the adsorption capacity is maximum with benzaldehyde, average with humic acids, limited with phenol and insignificant with benzoic acid. Phenol does not affect the fixation capacity of uranium significantly whereas benzoic acid and benzaldehyde have an average effect upon it and humic acids decrease it to 200 mg g−1 and less as the concentration of the acid increases.

Removal of Rare Earth Elements and Precious Metal Species by Biosorption

In Rare Earth Elements (REE) or Precious Metal Species (PMS) removal many types of biological phenomena can take place, such as biosorption, bioaccumulation, resistance/detoxification mechanisms, and direct or indirect utilization in the microbial metabolism. The high demand for the REE or PMS implies demand on increased production of ores containing REE or PMS (i.e. mining) and recycling of solutions to recover the elements contained in waste. But the use of REE and PMS in many anthropogenic applications and devices has led to an increased of public and environment exposure. The aim of this chapter is to compare under different operating conditions, the biosorption capacities of various microbial species and natural by-products for rare earth elements, to investigate the involved sorption mechanisms and to evaluate the potential industrial use of this process to metal ion removal.

Membrane process treatment for greywater recycling: investigations on direct tubular nanofiltration.

On-site greywater recycling and reuse is one of the main ways to reduce potable water requirement in urban areas. Direct membrane filtration is a promising technology to recycle greywater on-site. This study aimed at selecting a tubular nanofiltration (NF) membrane and its operating conditions in order to treat and reuse greywater in buildings. To do so, a synthetic greywater (SGW) was reconstituted in order to conduct experiments on a reproducible effluent. Then, three PCI NF membranes (AFC30, AFC40 and AFC80) having distinct molecular weight cut-offs were tested to recycle this SGW with a constant concentration at 25°C at two different transmembrane pressures (20 and 35 bar). The best results were obtained with AFC80 at 35 bar: the flux was close to 50 L m⁻²  h⁻¹, retentions of 95% for chemical oxygen demand and anionic surfactants were observed, and no Enterococcus were detected in the permeate. The performances of AFC80 were also evaluated on a real greywater: fluxes and retentions were similar to those observed on SGW. These results demonstrate the effectiveness of direct nanofiltration to recycle and reuse greywater.