| In recent years, the several changes in regulations have resulted in development and constant improvement of knowledge in the field of drinking water. Tighter requirements have contributed to increased interest and competitiveness for microfiltration (MF) and ultrafiltration (UF) as alternatives to conventional processes. However, although these technologies are very efficient at removing particulate matter and most colloidal, they have a limited capacity to remove dissolved contaminants such as dissolved organic matter (DOM) and ammonia.;The specific objectives of these pilot tests were to verify the system's performance concerning DOM and ammonia removal, and the viability of the process from an operational standpoint (flux, permeability, cleaning).;An industrial pilot of the CREDEAU was used for these tests. The pilot was made of two membrane bioreactors (patent name OpalineBRTM) supplied in parallel with clarified-ozonized water. The hollow fiber modules Puron, made of polyethersulfone, (specific surface area of 10m2 and pore diameter of 0,05 mum) were installed in a submerged configuration and aerated to maintain the PAC in suspension and minimize membrane clogging. Both bioreactors were operating continuously for a period of 100 days with a concentration of 20 g/L of PAC PicahydroLP39 (25 mum) and various filtration fluxes of 15, 30 and 45 L/m2/h. During the monitoring period, the water temperature ranged from 10 to 25°C. The bioreactors were operated for different solids retention time periods (46 vs. 100 days), via the addition of fresh PAC. Operational parameters (pressure, flux, temperature, pH) were recorded non-stop on a SCADA system, whilst water quality data were measured in the laboratory (DOC, BDOC, AOC, ammonia, UV254, THM, HAA) and continuously via online analysers (TOC, temperature, turbidity).;The study's results show that the bioreactors act as a very effective filtering barrier for removing turbidity (<0,04 NTU). During the initial period of operation, adsorption plays a main role and allows maximum mean removal of DOC (55%), UV254 absorbance (55%) and COR (45%). The gradual depletion of the PAC adsorption capacity (0 to 30 days) is compensated by the increasing acclimation of biomass within the bioreactors. In dominant biological removal conditions, results have shown a mean lower limit for removal of DOC (20%), UV254 absorbance (18%) and non-biodegradable organic carbon (12%) as well as a mean upper limit for removal of BDOC (74%) and AOC (73%). Full nitrification was observed after 30 days of operation in warm water. Furthermore, results show that the bioreactors were effective at reducing the risk of bacterial increase in the distribution system. Otherwise, the control of particle age had no significant effect on the process performances regarding water quality.;In response to this limitation, the combined use of membrane filtration MF/UF and powdered activated carbon (PAC) appears to be a promising solution. The main advancement of this hybrid method is based on three fundamental mechanisms: adsorption by the PAC, biodegradation by the microorganisms attached to PAC particles and physical removal by the membranes. To date, several researchers have published conclusive results about the adsorption capacities of PAC. The present study aims to evaluate full scale performances of the process operated in biological mode, i.e. promoting the growth of biomass on the carbon particles.;From an operational standpoint, there is an optimal operational flux (probably between 15 and 30 L/m²/h), but the study has not identified this precisely. Fresh PAC particles have no impact on membrane clogging in the short term, but colonized PAC forms aggregates which cause significant physical clogging of the membranes. It appears that using a PAC concentration below 20 g/L, finding a way of reducing the physical clogging (eg: improvement of the agitation within the modules) or operating with a lower solid age, could prevent the formation of PAC aggregates on the membranes, as was observed in biological mode. Finally, the good recovery of the membranes' initial properties (permeability) after physical cleaning (> 80%) indicates that membrane clogging is mainly reversible. The PAC aggregation phenomenon inside the bundles of membranes appears to be the main cause of the clogging and also the reason why chemical cleanings were not effective and could not be properly assessed.;In conclusion, the hybrid systems PAC/membranes offer an attractive treatment alternative to conventional treatment mainly because of their flexibility to operate in a dominant mode of adsorption or biodegradation. Combined with the membrane's excellent potential for removing particulate organic matter, the process operated under biological mode appears to be a very interesting strategy to eliminate dissolved pollutants such as dissolved organic matter (DOC, BDOC) and ammonia. |
