Biological processes of wastewater treatmnent have found wide applications due to their lower costs and higher efficiency. Membrane bioreactors (MBR’ s) form one group of such processes in which membrane fouling is of great importance. Efficiency of critical flux (CF) has been proved to be a parameter effective in fouling control (CF). CF is itself influenced by three main groups of variables that include sludge parameters، operating conditions، and membrane types. In this stidy، the effects of such factors as trans-membrane pressure، protein and carbohydrate concentrations in extracellular polymeric substances (EPS)، and soluble microbial products (SMP) on CF were investigated in a submerged MBR. Moreover، the effects of such operating conditions as periodic and continuous suctions at two sludge concentrations were studied. It was found that increasing flux led to enhanced membrane fouling rates. Extracellular polymeric substances (EPS) were found to have no relations with critical flux (CF)، probably because EPS are mostly found as bigger flocks. Finally، a reverse relationship was established between CF and carbohydrate concentration of the SMP. Membrane fouling control was observed to be positively affected by the rest modes during periodic suctions.

Membrane bioreactor (MBR) systems are considered a suitable approach for this purpose. However, the main challenge of these systems is membrane fouling. This study investigated the filtration performance of a ceramic membrane in two operating modes: side-stream and submerged. The impact of physical and chemical cleaning on fouling removal and filtration performance was evaluated. The results showed that total fouling in submerged and side-stream MBRs reached 93.6% and 82.3%, respectively. Reversible fouling rates were 50.9% and 56.2%, and irreversible fouling rates were 42.7% and 26.3%, respectively. Additionally, the levels of extracellular polymeric substances (EPS) formed on the membrane decreased from about 255 mg/gVSS to about 120 in the submerged MBR and 65 in the side-stream MBR. The Chemical Oxygen Demand (COD) removal efficiency was 88% for the side-stream MBR and 82% for the submerged MBR. Fourier-transform infrared spectroscopy (FTIR) tests identified the components and compounds present in the activated sludge. FTIR and EPS analyses indicated that acidic compounds such as humic acid, and amine and hydroxyl-containing compounds such as polysaccharides, halides, and alkyl halides were present on the membrane cake layer, causing pore blockage and cake formation.

Nowadays, due to strict laws to prevent environmental pollution as well as the importance of recycling and reuse of effluent, the use of processes that can treat wastewater with high efficiency has received special attention. One of the biological and widely used mechanism of domestic and industrial sewage treatment is activated sludge which microorganisms break down organic matter in the sewage while consuming oxygen. The advantages of this method are simple design, simple guidance, optimal efficiency in organic matter removal and less sensitivity to seasonal variations in temperature. After demonstrating the proper performance of the activated sludge in the treatment of variety of sewages, various adjustments and changes were made to adapt this process to different requirements. The disadvantages of conventional activated sludge method are the need to relatively high electrical and mechanical equipment, operational problems, the need for relatively high space for the construction of the wastewater treatment plant and low efficiency in the separation of all suspended organic matter. Membrane bioreactor (MBR) is a method to solve the problems of activated sludge especially reducing the steps of the purification process (removal of sedimentation and disinfection) and increasing the efficiency of reducing organic pollutants. Despite the use of an active sludge reactor, the separation of sludge from water is done by a membrane microfiltration system. This system has been highly efficient for domestic and industrial wastewater treatment and has received special attention in recent years.