Drinking water denitrification in membrane bioreactor/ membrane contactor systems

The results of an experimental study, developed on a membrane bioreactor/membrane contactor pilot plant, aimed at drinking water denitrification are presented and discussed. In the adopted configuration the water, contaminated by nitrates, flows inside the fibres of a membrane unit. Due to the existing concentration gradient, nitrates migrate through the membrane and are reduced to nitrogen gas by the autotrophic biomass attached on the exterior of the fibres, and fed with an external source of organic carbon. Data obtained varying influent flow values and nitrate influent concentrations, confirm the potentiality of the system and show the possibility of full-scale applications. A new mathematical model, useful for both simulation and design of the system is also presented. The model is based on simple mass balances in the flow direction, and through the membrane. Each fibre is considered a plug-flow reactor, and nitrate concentration outside the fibres is assumed to be always zero. To obtain an explicit expression useful for simulation and design of membrane bioreactors/membrane contactors, steady-state conditions are supposed. Experimental data are in good agreement with the model’s results, and confirm its applicability.

The principal results of the presented research study can be summarized as follows: • MBR/MC systems are potentially an interesting alternative for drinking water denitrification, as they reduce the risk of induced contamination and do not require high operational costs: denitrification rate values obtained in the optimal working conditions of the pilot plant confirmed the potentiality of the system; • membrane choice is critical to reduce diffusive resistances and water losses caused by the trans-membrane pressure; water pre-treatments experimental data (g•m-3) Biological compartment discharge Start up -3 simulated data (g•m ) Fig. 10. Effluent nitrate concentration: comparison between simulated data and experimental ones.