Application of the flexible fiber filter module (3FM) filter to sea water filtration.

The new 3FM filter (Flexible Fiber Filter Module), implementing very fine nylon fibers as filtration media was tested at pilot scale for the first time on sea water. The objective was to improve the quality of raw sea water to produce water for injection into offshore wells for extraction purposes on oil-bearing fields. Particles larger than 5 microm must be removed from the water of injection to avoid clogging at the point of injection into the porous rock. The purpose of the tests carried out over several months at Palavas Les Flots (France) was to specify the optimal operating conditions of the 3FM filter. Various coagulants and combinations of reagents were tested at velocities ranging between 50 and 200 m(3)/m(2)/h (ground filtration velocity). On raw sea water of about 1 NTU turbidity and at velocities of 100 m(3)/m(2)/h, the filtered water contained about 300 particles per mL larger than 1 microm, and less than 15 particles larger than 5 microm per mL. The filter runs range from one hour to few hours, variable according to the raw water turbidity, the reagent dosing rate and the filtration velocity. Backwashes, a succession of air scours at high air flow rates combined with water phases, the total duration of which did not exceed 1 minute, were shown to be efficient during the three months testing period. 3FM filter performance was promising for many other possible applications.

Particulate products and new polymers for a more efficient removal of dissolved organic matter in drinking water resources.

More restricting legislation on dissolved organic carbon (DOC), especially when applied to waters with high DOC contents and low turbidity, urges the drinking water industry to improve the removal of dissolved organic matter (DOM). Jar tests were carried out on sand-filtered water (SFW) and raw water (RW), with respectively 50 different particulate compounds and different cationic polymers. Analytical measurements of DOC and UV absorbance at 254 nm, as well as a characterisation by size exclusion chromatography (SEC), were performed in order to determine the efficiency of the process. Experiments on SFW showed that activated carbon was the only compound able to remove efficiently the residual DOC remaining after conventional treatments (up to 40% of reduction). Other trials on RW using mixes of ferric chloride (FeCl3) and cationic polymers (polyamines and polyDADMAC) pointed out that the molecular mass and the reticulation ratios have a significant influence on the efficiency of the treatment. Finally, the addition of activated carbons to the previous reagents significantly improved the observed removal efficiencies by similar amounts.

Resistance of Legionella to disinfection in hot water distribution systems.

The efficiency of various disinfection treatments against Legionella was tested on a hot water distribution system (HWDS) pilot unit. The results demonstrated clearly that most Legionella in the networks were fixed in the biofilm at the surface of the pipe (more than 98% for each loop). Chemical treatments (continuous chlorination, hyperchlorination, hydrogen peroxide and peracetic acid mixing) commonly used for the eradication of Legionella in hot water distribution networks appeared to be inadequate for eradicating the bacteria in the biofilm. Unfortunately, the biofilm contained most of the pathogens in an HWDS whereas legislation is only restricted to the Legionella concentration in the water phase. Thermal treatment appeared to be efficient to disinfect most of the biofilm but seemed to promote the biofilm re-growth as well. It was then concluded that the best solution to prevent Legionella contamination in hot water distribution systems would be to have perfect control of the temperature in the networks (temperature > 55 degrees C at all points). Nevertheless, in many cases it is difficult to have such control, so during the time necessary to modify networks, the best solution to control Legionella proliferation appears to be to apply a treatment shock (thermal or chlorination as a function of pipe characteristics). These treatments must be followed by a continuous chlorination that is totally controlled and equipped with alarm systems. This study demonstrates that biofilm sampling devices must be installed in hot water distribution systems to anticipate Legionella contamination and correctly determine the efficiency of the treatments.

Applications of advanced oxidation processes: present and future.

The use of advanced oxidation processes (AOPs) to remove pollutants in various water treatment applications has been the subject of study for around 30 years. Most of the available processes (Fenton reagent, O3 under basic conditions, O3/H2O2, O3/UV, O3/solid catalyst, H2O2/M(n+), H2O2/UV, photo-assisted Fenton, H2O2/solid catalyst, H2O2/NaClO, TiO2/UV etc.) have been investigated in depth and a considerable body of knowledge has been built up about the reactivity of many pollutants. Various industrial applications have been developed, including ones for ground remediation (TCE, PCE), the removal of pesticides from drinking water, the removal of formaldehyde and phenol from industrial waste water and a reduction in COD from industrial waste water. The development of such AOP applications has been stimulated by increasingly stringent regulations, the pollution of water resources through agricultural and industrial activities and the requirement that industry meet effluent discharge standards. Nevertheless, it is difficult to obtain an accurate picture of the use of AOPs and its exact position in the range of water treatment processes has not been determined to date. The purpose of this overview is to discuss those processes and provide an indication of future trends.