simulation of wastewater treatment systems with membrane separation

Proceedings of ECOpole
Vol. 2, No. 1
2008
Marta KORNILUK1, Agnieszka MONTUSIEWICZ1, Adam PIOTROWICZ1
and Grzegorz ŁAGÓD1
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,
20-618 Lublin, tel. +48 81 538 41 39, email: [email protected]
Nadbystrzycka
40B,
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 m3/d. The values
of the main wastewater indicators were as follows: BOD5 - 420 g/m3, COD - 800 g/m3, TSS
- 400 g/m3, total nitrogen - 62 g/m3, NH +4 nitrogen - 49 g/m3, NO −x nitrogen - 1 g/m3, total
phosphorus - 13 g/m3, orthophosphate phosphorus - 10 g/m3. The alkalinity was equal
350 g CaCO3/m3. 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,
BOD5/BODultimate 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 m3 and the
circular secondary clarifier with capacity of 2925 m3 (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 m3. 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/dm3. 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
1.
2.
Conducted simulations allow coming to the following conclusions:
The application of membrane separation technology in activated sludge systems
significantly influences the course of the occurring processes.
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
3.
45
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]
[2]
[3]
[4]
[5]
[6]
Bodzek M., Bohdziewicz J. and Konieczny K.: Techniki membranowe w ochronie środowiska.
Wydawnictwo Politechniki Śląskiej, Gliwice 1997.
Stephenson T., Judd S., Jefferson B. and Brindle K.: Membrane Bioreactors for Wastewater Treatment. IWA
Publishing, London, UK 2000.
Bodzek M., Debkowska Z., Lobos E. and Konieczny K.: Biomembrane wastewater treatment by activated
sludge method. Desalination, 1996, 107, 83-95.
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.
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.
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