Study On The Effects Of Sludge Properties On Self-forming Dynamic Membrane (SFDM) Formation And Fouling

Recently, a low-cost membrane bioreactor (MBR), termed self-forming dynamic membrane bioreactor (SFDMBR), has emerged as an innovative and cost-effective wastewater treatment system. The basic idea is to utilize the filtration modules made of cheap coarse-pore materials such as non-woven fabric, nylon mesh, and industrial filter-cloth instead of microfiltration (MF)/ultrafiltration (UF) membranes to reduce capital cost, and take advantage of the self-forming dynamic membranes (SFDMs) (i.e. initial "desired" sludge layers developed on the coarse-pore materials) to achieve required solid-liquid separation efficiency. Since the development of SFDM is essentially a result of sludge deposition/adsorption on coarse-pore materials, the characteristics of SFDM including formation and fouling are reasonably expected to be significantly affected by sludge properties.This study investigated the impacts of sludge properties on the formation time (Tf), filtration resistance (Rsm) and fouling propensity (KR) of SFDM. Sludge properties includes the extracellular polymeric substances (EPS) content which is considered as the sum of polysaccharides (EPSc) and protein (EPSp), soluble microbial products (SMP) content, particle size distribution (PSD), relative hydrophobicity (RH), zeta potential, specific oxygen uptake rate (SOUR), dynamic viscosity, capillary suction time(CST) and sludge volume index (SVI). Statistical analyses were conducted to determine the effects of sludge properties on each SFDM characteristic. The results showed EPS content presents positive/negative correlations with SOUR, Zeta potential, viscosity and SVI with rp=-0.751,-0.520,0.560,0.736, respectively. Especially, EPSc content was the major factor affecting SOUR and viscosity of the sludge (rp=-0.709; 0.684) while EPSp content affecting Zeta potential and SVI (rp=-0.767; 0.672). As a result, the EPS content and other sludge properties except these four should be considered as independent factors to conduct this study.In the sequent study, it is found that PSD was the major factor affecting both SFDM formation rate and filtration resistance with rp=-0.808; -0.690, P=0.000; 0.001, respectively, while RH displayed as a sub-factor affecting SFDM formation time (rp=-0.578; P=0.052). The EPS content contributed to SFDM fouling propensity (rp=0.723, P=0.000). In particular, increasing EPSc concentration (rp=0.760, P=0.000) could result in serious SFDM fouling while no correlation was found between EPSP and SFDM fouling propensity. The SFDM formation and fouling mechanisms was proposed based on these analyses. In addition, dynamic viscosity demonstrated a considerably positive correlation with SFDM fouling propensity (rp=0.801, P=0.004) while SOUR appeared a relatively lower negative correlation (rp=-0.642, P=0.032). Consequently, dynamic viscosity could be chosen as an indicator for examining SFDM fouling.