چكيده به لاتين
In this project, the Forward Osmosis (FO) - Reverse Osmosis (RO) hybrid system, in which wastewater treatment and desalination processes are performed simultaneously, is investigated. The role of using spacer in both FO and RO processes in the performance of this system was evaluated. One of the most important problems of this hybrid system is biofouling, which plays a significant role in reducing the process performance. Particularly, the FO membrane biofouling is very important due to the potential ability of the feed (effluent) and draw solution (very saline solution) used in this process to form biofilm on both sides of the membrane. Therefore, in order to increase the efficiency of this system, the main focus should be on the FO process. The biofilm formed on the membrane surface results from the accumulation of microorganisms, reproduction, extracellular polymeric substances (EPS) production and ultimately the death of cells. This layer acts as an obstacle to the water passing from the membrane. Consequently, understanding the processes that occur inside the biofilm is necessary to control and eliminate it. In this study, a two-dimensional model based on finite element method was developed to simulate the growth of living cells, EPS production and the death of cells in biofilm on the FO membrane surface. This model estimates the water and salt fluxes, the movement of live cells due to volume expansion and active biomass production simultaneously, considering the mass transfer of salt and nutrient. By increasing the inlet substrate concentration to the feed channel, from 0.026 to 2.6 mol/m3, the average total cell mass production rate increased by 84.11%, the average volume fraction of dead cells, EPS and live cells, 0.0032% increased and 0.029% decreased, over two hours. By examining the performance of the FO-RO hybrid system, considering the biofilm formed in both modules, it was concluded that the biofilm formed on both sides of the FO membrane greatly affects the process performance. Therefore, various strategies for hydraulic cleaning of the FO membrane biofilm were evaluated. An increase of 2 times the cross-flow velocity from the constant value of 0.086 m/s, and with the creation of the pulsed flow with a frequency of 5 and a magnitude 1.6 times the constant value of 0.086 m/s, with the lowest volume fraction of living cells and the highest erosion rate at the biofilm surface was selected as an optimal cleaning method of the biofilm on the FO membrane active layer.
Keywords: Forward Osmosis, hybrid system, simulation, biofilm, hydraulic cleaning
