SIMULATION OF WASTEWATER TREATMENT SYSTEMS WITH MEMBRANE SEPARATION

Proceedings of ECOpole Vol. 2, No. 1 2008 Marta KORNILUK 1, Agnieszka MONTUSIEWICZ 1, Adam PIOTROWICZ 1 and Grzegorz ŁAGÓD 1 SIMULATION OF WASTEWATER TREATMENT SYSTEMS WITH MEMBRANE SEPARATION SYMULACJA SYSTEMÓW OCZYSZCZANIA ŚCIEKÓW Z MEMBRANOWĄ SEPARACJĄ BIOMASY Summary: The application of membrane separation to the biological treatment processes by activated sludge eliminates the secondary clarifier. The solution introduces significant differences in clarification process, as the retention of biomass separated on membranes does not depend on sludge sedimentation properties. Thus, in membrane bioreactors a high biomass concentration and a high flow rate can be achieved. Such specific conditions impose the growth of characteristic activated sludge population which differs from conventional process with respect to biotic community composition and its performing. Therefore, by employing membrane separation it is possible to influence the wastewater effluent parameters, that is the efficiency of biological treatment. Computer modeling has become a helpful tool in analysis of performance and effectiveness of wastewater treatment systems. The simulation presented in the text was carried out in GPS-X program which makes it possible to create the model of wastewater treatment plant, run the simulation and subsequently interpret the results and draw appropriate conclusions. Assuming parameters at the entry point of treatment process, the performance of membrane separation system in comparison with conventional activated sludge system was examined. Keywords: WWTP simulation, wastewater treatment, activated sludge, MBR, membrane bioreactor Sewage is the major source of contamination of both surface and groundwaters. Conventional activated sludge process with its limitations is often insufficient in removing some contaminants which results in certain amounts of biogenic substances and suspended solids discharged into receiver. Therefore, further development and research on advanced biological wastewater treatment processes is necessary. One of the examples of a new approach to the problem is the membrane biological reactors (MBR) technology [1]. Membrane bioreactor is the combination of biological treatment using activated sludge and membrane filtration. In this solution membrane is used to separate solids from the effluent and thereby effectively replace conventional secondary clarifier [2]. The technology implicates significant differences in clarification process due to biomass retention in the membrane bioreactor which is independent of sedimentation properties. In such a case, a high concentration of biomass and a high flow rate can be achieved. The conditions characterizing MBR cause the growth of characteristic activated sludge population [3]. There are two basic configurations of MBR systems. In the first one the membrane module is located inside the aeration tank while in the other a separate external membrane tank is used [4]. MBR technology is an attractive option for densely built-up urban areas or the areas where a high effluent quality is required [5]. Computer simulation has become a helpful tool in analysis of performance and effectiveness of wastewater treatment systems. Using advanced program it is possible to create a model of wastewater treatment plant, run a simulation and subsequently interpret results and draw conclusions [6]. 1 Faculty of Environmental Engineering, Lublin University of Technology, Nadbystrzycka 40B, 20-618 Lublin, tel. +48 81 538 41 39, email: M.Korniluk@fenix.pol.lublin.pl

42 Marta Korniluk, Agnieszka Montusiewicz, Adam Piotrowicz and Grzegorz Łagód The aim of presented study was to examine the performance of membrane bioreactor based upon the results obtained in computer simulation. Additionally, for the assumed influent parameters an efficiency comparison was made between the MBR and the conventional bioreactor utilizing MUCT process. The simulations were carried out in the GPS-X program (version 5.02). Methods In order to conduct simulation two separate models of wastewater treatment systems were created. Figure 1 presents schematic diagram of both analyzed systems in one layout. Fig. 1. Schematic diagram of analyzed systems: the MUCT process with secondary clarifier and the MBR Quantity and composition of the raw wastewater plays an important role in modeling procedure. As an input data the same, arbitrarily chosen values of influent parameters were used for both systems. The average daily flow rate was set equal to 10000 m 3 /d. The values of the main wastewater indicators were as follows: BOD 5-420 g/m 3, COD - 800 g/m 3, TSS - 400 g/m 3, total nitrogen - 62 g/m 3, NH nitrogen - 49 g/m 3, + 4 NO x nitrogen - 1 g/m 3, total phosphorus - 13 g/m 3, orthophosphate phosphorus - 10 g/m 3. The alkalinity was equal 350 g CaCO 3 /m 3. The above characterization was made using the codfractions model as the influent model in GPS-X. To achieve the influent consistent with the assumed values of parameters some changes were made in the default settings of influent stoichiometric coefficients: volatile/total suspended solids ratio (VSS/TSS) was changed from 0.60 to 0.69, particulate COD/volatile suspended solids ratio (XCOD/VSS) - from 2.20 to 1.88, BOD 5 /BOD ultimate ratio - from 0.66 to 0.68, inert fraction of soluble COD - from 0.35 to 0.29, substrate fraction of particulate COD - from 0.75 to 0.77, heterotrophic and autotrophic biomass fraction of particulate COD - from 0 to 0.02 and 0.01, respectively.

Simulation of wastewater treatment systems with membrane separation 43 Fig. 2. Schematic comparison of analyzed systems: MUCT and MBR The MUCT system consists of 10 tanks with total capacity of 11000 m 3 and the circular secondary clarifier with capacity of 2925 m 3 (Fig. 2). External recirculation returns the settled activated sludge from the clarifier to the predenitrification chamber while the two internal recirculation streams return mixed liquor from aerobic to anoxic zone and from anoxic to anaerobic zone, respectively. The overall amount of internal recirculation equals 500% of the daily flow rate. The MBR system also consists of 10 tanks with the solids separation filter placed in the final one. Total capacity is smaller comparing to the MUCT process and equals 4225 m 3. In this solution there are two internal recirculation streams in the total amount of 400% of the daily flow rate. The idea of separating recycle streams was to improve phosphorus removal as well as facilitate even distribution of concentrated mixed liquor. In both cases the ASM2d biological model with default values was used. The dissolved oxygen concentration in the aerobic zones was maintained at the level of 2 mg/dm 3. All the parameters concerning physical and operational properties were chosen experimentally to maximize the effectiveness of the modeled systems. Results and discussion In this paper only the steady-state simulation results are presented. The MBR was operated in simple mode in which all the parameters concerning physical aspects of the filtration process (eg transmembrane pressure, filter resistance) are neglected. Figure 3 depicts the profiles of four selected parameters through individual tanks, which were obtained during the simulation of MBR system. On the above-mentioned graphs an effect of internal recycle streams can be clearly seen. The values of characteristic output data for the systems compared (MUCT and MBR) are presented in Figure 4. In both cases the results concerning removal efficiency are satisfactory.

44 Marta Korniluk, Agnieszka Montusiewicz, Adam Piotrowicz and Grzegorz Łagód Fig. 3. Concentration profiles of selected parameters in individual tanks The elimination of contaminants is in most cases higher with regard to membrane bioreactor. The most noticeable difference relates to suspended solids, for which the removal level exceeds 99.8%. However, there are no meaningful differences in the elimination of the soluble substances. Fig. 4. Comparison of effluent parameters of the modeled systems: MUCT (left) and MBR (right) Conclusions Conducted simulations allow coming to the following conclusions: 1. The application of membrane separation technology in activated sludge systems significantly influences the course of the occurring processes. 2. In membrane bioreactors a high efficiency of contaminant removal can be achieved using relatively small volumes and internal recycle streams together with the lack of external recirculation.

Simulation of wastewater treatment systems with membrane separation 45 3. Computer simulation of wastewater treatment process with membrane separation using GPS-X program greatly facilitates selecting optimal parameters for the design and operation purposes and allows predicting the removal efficiency with regard to any wastewater pollution indicator. References [1] Bodzek M., Bohdziewicz J. and Konieczny K.: Techniki membranowe w ochronie środowiska. Wydawnictwo Politechniki Śląskiej, Gliwice 1997. [2] Stephenson T., Judd S., Jefferson B. and Brindle K.: Membrane Bioreactors for Wastewater Treatment. IWA Publishing, London, UK 2000. [3] Bodzek M., Debkowska Z., Lobos E. and Konieczny K.: Biomembrane wastewater treatment by activated sludge method. Desalination, 1996, 107, 83-95. [4] Larsson E. and Persson J.: Viability of Membrane Bioreactor Technology as an Advanced Pre-Treatment for Onsite Wastewater Technology. Master of Science Programme, Luleå University of Technology, 2004. [5] Yang W., Cicek N. and Ilg J.: State-of-the-art of membrane bioreactors: Worldwide research and commercial applications in North America. J. Membrane Sci., 2006, 270, 201-211. [6] GPS-X Technical Reference. SYMULACJA SYSTEMÓW OCZYSZCZANIA ŚCIEKÓW Z MEMBRANOWĄ SEPARACJĄ BIOMASY Streszczenie: Wykorzystując separację membranową w procesach biologicznego oczyszczania ścieków metodą osadu czynnego, eliminuje się z układu osadnik wtórny. Taka zmiana układu technologicznego jest moŝliwa, poniewaŝ efektywność zatrzymania biomasy w wyniku separacji membranowej nie zaleŝy od właściwości sedymentacyjnych osadu. W reaktorach membranowych mogą być osiągane wysokie stęŝenia biomasy i duŝe natęŝenia przepływu ścieków przez układ. Specyficzne warunki w bioreaktorze powodują wykształcenie charakterystycznej populacji osadu czynnego, która róŝni się pod względem składu biocenozy i funkcjonowania od osadu w układzie konwencjonalnym. Zastosowanie separacji membranowej wpływa więc na parametry ścieków w odpływie z oczyszczalni, czyli na skuteczność biologicznego oczyszczania. W pracy przedstawiono analizę działania oraz ocenę efektywności usuwania zanieczyszczeń w systemie z bioreaktorem membranowym (MBR). Jako narzędzie wykorzystano symulację komputerową z zastosowaniem programu GPS-X. Jako układ odniesienia, słuŝący do oceny efektywności MBR, przyjęto model oczyszczalni konwencjonalnej z bioreaktorem przepływowym osadu czynnego oraz osadnikiem wtórnym w systemie MUCT (Modified University of Cape Town). W celu porównania układów analizę przeprowadzono przy identycznej charakterystyce ilościowej i jakościowej ścieków dopływających do badanych systemów. Słowa kluczowe: symulacja systemów oczyszczania ścieków, osad czynny, MBR, bioreaktor membranowy