Enhancement of the submerged membrane electro-bioreactor (SMEBR) for nutrient removal and membrane fouling control

Abstract Enhancement of the submerged membrane electro-bioreactor (SMEBR) for nutrient removal and membrane fouling control Sharif Ibeid, Ph.D. Concordia University, 2011 A submerged membrane electro bioreactor (SMEBR) to enhance effluent quality and to reduce membrane fouling was patented by Elektorowicz et al (2009). In this system, activated sludge biological treatment, membrane filtration and electrokinetics are working together in one hybrid unit. The first objective of this research aimed to remove the major unwanted nutrients (Phosphorus and Nitrogen) in addition to the carbon in one single electro-bioreactor unit. The second objective was to investigate the relationship between the electrical input parameters (voltage gradient, current density and exposure mode) on sludge characteristics and therefore membrane fouling. This study consists of three phases: Phase 1 (batch tests), Phase 2 (lab-scale continuous flow) and Phase 3 (pilot-scale continuous flow). The results showed that the direct current (DC) field of medium current density (15 to 25 A/m2) has the potential to substantially improve sludge characteristics in terms of better dewaterability and high removal of soluble microbial products (SMP) and organic colloids. However, the electrical inputs should be selected based on the concentration of the mixed liquor suspended solids (MLSS). Subsequently, a high reduction of membrane fouling was obtained. The degree of membrane fouling reduction was ranging between 1 to 5 times based on the concentration of soluble microbial products (SMP) and the volatile suspended solids (VSS). This study demonstrated substantial removal efficiencies of nutrients up to more than 95% for carbon, 99% for phosphorus and 97% for nitrogen. However, the removal efficiency of nitrogen was found to be highly influenced by the temperature and the C/N ratio. High temperature (> 18º C) and high concentration of carbon in the influent wastewater led to a better removal efficiency of nitrogen. SMEBR showed outstanding results that make it a promising technology that can reduce fouling and remove all major macro nutrients at high efficiency in one single reactor

Fast multipole preconditioners for sparse matrices arising from elliptic equations

Among optimal hierarchical algorithms for the computational solution of elliptic problems, the Fast Multipole Method (FMM) stands out for its adaptability to emerging architectures, having high arithmetic intensity, tunable accuracy, and relaxable global synchronization requirements. We demonstrate that, beyond its traditional use as a solver in problems for which explicit free-space kernel representations are available, the FMM has applicability as a preconditioner in finite domain elliptic boundary value problems, by equipping it with boundary integral capability for satisfying conditions at finite boundaries and by wrapping it in a Krylov method for extensibility to more general operators. Here, we do not discuss the well developed applications of FMM to implement matrix-vector multiplications within Krylov solvers of boundary element methods. Instead, we propose using FMM for the volume-to-volume contribution of inhomogeneous Poisson-like problems, where the boundary integral is a small part of the overall computation. Our method may be used to precondition sparse matrices arising from finite difference/element discretizations, and can handle a broader range of scientific applications. It is capable of algebraic convergence rates down to the truncation error of the discretized PDE comparable to those of multigrid methods, and it offers potentially superior multicore and distributed memory scalability properties on commodity architecture supercomputers. Compared with other methods exploiting the low-rank character of off-diagonal blocks of the dense resolvent operator, FMM-preconditioned Krylov iteration may reduce the amount of communication because it is matrix-free and exploits the tree structure of FMM. We describe our tests in reproducible detail with freely available codes and outline directions for further extensibility