Membranbioreaktoren zur industriellen Abwasserreinigung

• Membrane bioreactors for industrial wastewater treatment

Baumgarten, Sven; Dohmann, Max (Thesis advisor)

Aachen : Publikationsserver der RWTH Aachen University (2007, 2008)
Dissertation / PhD Thesis

Aachen, Techn. Hochsch., Diss., 2007

Abstract

Membrane bioreactor (MBR) technology for treatment of organically contaminated wastewater is one of the notable developments in recent years. MBR technology is based on the ongoing development of biological water treatment with suspended biomass, where membranes are used to separate the biologically treated water from the biomass. Major benefits of MBR compared to existing technologies are the improved effluent quality and lower footprint. Both characteristics are of special interest in industrial applications, because in addition to environmental issues, the possibility exists for the direct/ indirect reuse of the treated water within the industrial process. However, applicability of MBRs relies on their technical feasibility and cost-effectiveness. Both criteria are primarily dependent on the filtration performance of the membrane unit, which determines membrane surface area required and operating costs, as well as on the cleaning efficiency or the treated effluent quality. In the municipal sector, there is substantial experience with MBR filtration and cleaning performance, due to the number of operating installations and similarity of the wastewater to be treated. In general, municipal MBR performance varies little between applications. In contrast, significant variations exist between industrial wastewater sectors, due to the highly application-dependent characteristics of industrial wastewaters. To date, most of the plants reflect specific applications and there is little detailed or transferable knowledge available to account for these differences in performance. In addition, much of the existing knowledge remains primarily with the technology providers and operators of MBR systems. In order to develop a basis for the optimal introduction of MBR technology within the industrial sector, a more accurate and comprehensive investigation of the differences in performance is required. Consequently, the primary goals of this work were to identify the key factors of MBR performance, to develop suitable methods for the characterization, quantification and - where feasible - prediction of MBR performance. Based on the gathered knowledge, advanced approaches for the improvement of MBR performance have been developed. Investigations of MBR performance were carried out by treating different water sources in MBR systems. Wastewaters were derived from the chemical, pharmaceutical, textile and paper industry as well as heavily loaded process wastewaters from solids disposal and biotreatment and sludge handling. The wastewaters used represent a wide range with respect to the types and concentrations of contaminants to be eliminated and their biodegradability. Consequently, a wide variety of filtration and cleaning performance was achieved during MBR treatment. For some of the treated wastewaters, a lack of performance indicated that MBR technology was not technically or economically viable. The biodegradability of soluble or low molecular weight organic compounds is a key factor in achieving the desired cleaning performance. A detailed assessment can be undertaken in analytical laboratory testing. In comparison, the molecular weight cut off of the applied micro- or ultrafiltration membranes is of minor importance. Desired filtration performance and especially variances from municipal applications are primarily determined by the fouling factors "colloidal fouling" and "scaling". Suitable methods have been developed to evaluate or forecast the fouling and scaling potential of mixed liquors and raw wastewaters. Further investigations indicated a high potential for optimizing performance. As an alternative to advanced treatment downstream the MBR, improvements in cleaning performance can be achieved by simultaneous addition of powdered activated carbon. Improvements of filtration performance through reduction of fouling and scaling potential were also successfully tested by upstream or simultaneous removal of related compounds. All approaches for optimization were critically evaluated to identify if and under which conditions a sustainable and economical increase in performance could be achieved. It is anticipated that the knowledge gathered in this work will help to solve operational problems of existing MBRs, improve MBR cost-effectiveness and further expand the applicability of MBRs to previously problematic industrial wastewater applications.