(31f) Assessing the Use of Ceramic Membrane Bioreactor for Anaerobic Treatment of High-Load Food Wastewater at Bench Scale and Pilot Scale

Abstract: A novel type of ceramic membrane was tested in two anaerobic membrane bioreactors (AnMBR): a bench scale reactor (12 L) and a semi-industrial pilot plant (2.5 m³). A highly loaded industrial wastewater from corn-processing was successfully treated, reaching COD reductions close to 95%, while up to 99% removal was achieved for a simulated wastewater. The performance of both AnMBRs is still being optimized for the industrial effluent; the digesters show a similar behaviour and the semi-industrial filtration module seems to have an improved permeability. This study confirms many of the benefits attributed to the AnMBR technology, combining the advantages of the anaerobic digestion with the efficiency and robustness of the ceramic filtration.

Keywords: Membrane bioreactor; ceramic membranes; anaerobic digestion; corn-processing wastewater

INTRODUCTION

The Anaerobic Membrane Bioreactor (AnMBR) combines the anaerobic digestion process with a membrane filtration to provide complete solid-liquid separation. AnMBR system makes possible to work with high biomass concentration to treat industrial complex wastewaters heavily loaded with solids, oil and grease, and/or toxic compounds (Futselaar, 2013; Skouteris, 2012). Anaerobic digestion offers several widely known advantages over conventional aerobic processes, since no oxygen is required and the biogas production reduces the associated energy cost of wastewater treatment and it compensates for high-energy requirements related to cross-flow filtration, which is a common drawback of membrane filtration-based technologies. Nevertheless, it presents some limitations that have limited its wide-spread use (lower purification efficiency, poor effluent quality and process instability). The AnMBR technology allows overcoming these limitations as it combines the advantages of the anaerobic process and MBR technology in a robust and compact solution, characterized by the higher biogas production and the excellent effluent quality due to the small pore size of the membranes and the total retention of the suspended solids. As a result, AnMBRs technology has gained popularity in recent years, and more attention has been focussed on the further development of this process for the treatment of high-concentrated wastewater, mainly food and beverage industry wastewaters (Fuchs, 2003) although they have not yet been employed widely at industrial scale (Grant et al., 2008, Christian et al, 2011). However, recent technical advances in membrane and system design are promising great reductions in operation costs, and thus, broader application of AnMBRs (Scott, 2008). As membrane fouling is a limiting issue for implementing AnMBRs, ceramic membranes may have a good opportunity, since the inorganic membrane materials are reported to present less fouling and to possess higher chemical and thermal resistance (Futselaar, 2013; Skouteris, 2012; Sutton, 2006; Wolff, 2013; Kroll, 2010).

In the present work two ceramic AnMBRs have been studied, a bench scale AnMBR fed with both synthetic wastewater and industrial corn-processing wastewater, and a semi-industrial plant fed with industrial corn-processing wastewater. The objective is to evaluate the maximum digestion capacity of the anaerobic reactor, to study the behaviour of the membrane and to optimize the filtration process to get the maximum permeate flow with an optimal transmembrane pressure (TMP).

MATERIAL AND METHODS

The AnMBRs consist on a CSRT digester coupled to an external ceramic membrane filtration module equipped with backwash and CIP devices. Both, bench and semi-industrial, reactors are operated in mesophilic conditions (35ºC) and with average MLSS of 20 g/L. The start-up was carried out with seed sludge from a municipal anaerobic digester.

Bench scale AnMBR

The bench scale AnMBR is a 12 L reactor, mounted with a single tubular ceramic membrane of 0.02 m². Cross-flow velocities of 2 and 3 m/s and different backwash sequences have been tested. The bioreactor was initially fed with a simulated wastewater with high starch content, increasing the organic load (OLR) gradually from 0.7 to 7 kgCOD·m^-3·day^-1. Then the substrate was replaced with the industrial effluent at an initial OLR of 6 kgCOD·m^-3·day^-1. 

Semi-industrial pilot plant

The semi-industrial pilot plant with the capacity of 2.5 m³ is equipped with a ceramic ultrafiltration system made up of 4 modules consisting of 7 ceramic membranes with 19 tubular channels (1.7 m² of filtration area per module). The MBR is operated at a CFV of 2 m/s and the reactor is fed with a highly loaded wastewater from the corn cooking process (COD ≈ 35 g/L). The OLR has been increased from 0.25, in the start-up, to 3.5 kgCOD·m^-3·day^-1.

RESULTS AND CONCLUSIONS

In the bench scale AnMBR, a 95-99% of both COD and TOC was removed from the simulated effluent at a gradually increasing OLR from 0.7 to 7.0 kgCOD·m^-3·d^{-1. A high quality permeate with an output COD of 60-300 mg/L and TOC of 20-80 mg/L was achieved, whereby the average specific methane production was 0.34 m3}CH₄·kgCOD_removed^-1.

The treatment of industrial corn-processing wastewater obtained about 90-95% of COD and TOC reduction at an OLR of 6.0 kgCOD·m^-3·d^-1, yielding an average specific methane production of 0.30 m³CH₄·kgCOD_removed^-1 and permeate of 300-400 mg/L in COD and 70-150 mg/L in TOC, respectively.

A permeate flux up to 50 LMH could be reached in the bench scale single channel filtration module, according to both the flux-step tests and the long-term studies.

Meanwhile, in the semi-industrial pilot plant the OLR was increased from 0.25 to 3.5 kgCOD·m^-3·d^-1 with COD reduction up to 95%, similar to the laboratory studies. The biogas production also increased with the OLR obtaining an average specific methane production of 0.32 m³CH₄·kgCOD_removed^-1, close to bench scale results. Ceramic filtration worked satisfactorily, having a permeability over 120 L·h^-1·m^-2·bar^-1 with permeate flux up to 45 LMH and average TMP of 0.25 bar.

Many of the AnMBR technology advantages were confirmed. The solids retention by membranes results in a high quality effluent, free of suspended solids, bacteria and reduced COD, which allows to reduce or, even, eliminate a post-treatment. Highly hydrophilic ceramic membranes maximized the performance.

REFERENCES

Fuchs, W., Binder, H., Mavrias, G. and Braun, R. (2003). Anaerobic treatment of wastewater with high organic content using a stirred tank reactor coupled with a membrane filtration unit. Water Research, 37, 902-908. 

Futselaar. H., Rosink, R., Smith, G., Koens, L. (2013). The anaerobic MBR for sustainable industrial wastewater management. Desalination and Water Treatment, 51(4-6), 1070-1078.

Grant, S., Page, I., Moro, M., Yamamoto, T. 2008 Full-Scale Applications of the Anaerobic Membrane Bioreactor Process for Treatment of Stillage from Alcohol Production in Japan. Proceedings of the Water Environment Federation. WEFTEC 2008: Session 101 through Session 115: 7556–7570.

Kroll, S., Treccani, L., Rezwan, K., Grathwohl, G. 2010 Development and characterisation of functionalised ceramic microtubes for bacteria filtration. Journal of Membrane Science 365(1-2), 447-455.

Scott, C., Grant, S., McCarthy, P., Wilson, D., Mills, D. (2011). The First Two Years of Full-Scale Anaerobic Membrane Bioreactor (AnMBR) Operation Treating High-Strength Industrial Wastewater. Water Practice & Technology, 6 (2). doi:10.2166/wpt.2011.032.

Skouteris, G., Hermosilla, D., Lopez, P., Negro, C., Blanco, A. (2012). Anaerobic membrane bioreactors for wastewater treatment: A review. Chemical Engineering Journal, 198, 138-148.

Sutton, P. M. (2006), Membrane bioreactors for industrial wastewater treatment: applicability and selection of optimal system configuration, Proceedings WEFTEC 2006.

Wolff, C., Beutel, S., Scheper, T. (2013). Tubular membrane bioreactors for biotechnological processes. Applied Microbiology and Biotechnology, 97(3), 929-937.