FERMENTATIVE HYDROGEN PRODUCTION USING GRANULATED SEWAGE SLUDGE MICROFLORA

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1 J. Environ. Eng. Manage., 17(1), (27) FERMENTATIVE HYDROGEN PRODUCTION USING GRANULATED SEWAGE SLUDGE MICROFLORA Feng-Yuan Chang and Chiu-Yue Lin* Biohydrogen Laboratory, Department of Hydraulic Engineering Feng Chia University Taichung 4724, Taiwan Key Words: Fermenter design, granule, hydrogen production, UASB, up-flow velocity ABSTRACT Sewage sludge microflora was anaerobically granulated in an up-flow anaerobic sludge blanket (UASB) system to investigate its hydrogen production efficiency. The UASB reactor with a height/diameter (H/D) ratio of 7.4 was operated and its hydrogenic characteristics were compared with a report on a lower H/D ratio of 3.8. The substrate, sucrose (2 g COD L -1 ), was fed in a continuous mode. The reactor was operated at a temperature of 35 ± 1 C, ph of 6.7 and operating hydraulic retention times (HRT) of 24-6 h. Granulated sewage sludge microflora were demonstrated to efficiently produce hydrogen. A proper reactor H/D ratio enhances the efficiency and reactor operation stability. The highest hydrogen production was obtained at 8 h HRT. Each mol of sucrose yielded 2.9 mol of hydrogen with each g of microflora-solids producing.1 mol H 2 d -1. This high H/D ratio reactor, as compared with the reported low H/D ratio reactor, had a small biomass concentration variation, constant volatile suspended solids to total suspended solids concentration ratio, constant alkalinity value and high hydrogen production rate. INTRODUCTION Hydrogen is a promising energy alternative because it is clean, renewable and generates no toxic byproducts during combustion. Hydrogen can be produced microbially using fermentative bacteria, pohotophilic microorganisms or algae. Anaerobic hydrogen-producing enrichment culture applications producing hydrogen from organics have received considerable attention [1-2]. Fermentative hydrogen production has been shown to have great potential as practical biohydrogen systems and an improvement in the hydrogen yield is one of the problems that must be solved [3]. Anaerobic sewage sludge contains a variety of mixed microflora for efficient hydrogen production from organic wastes in completely stirred tank reactor (CSTR) fermenters [4-6]. Little has been reported on using granulated sewage sludge microflora for anaerobic hydrogen production. An up-flow anaerobic sludge blanket (UASB) process is an extensively applied anaerobic treatment system with high efficiency and a short hydraulic retention time (HRT). This process can maintain high concentrations of large biogranules with high bioactivity for efficient reactor operation. Our laboratory has successfully operated a hydrogen-producing UASB system seeded with sewage sludge microflora [7]. This reactor used a height/diameter (H/D) ratio of 3.8 and resulted in a low specific hydrogen production rate value (the hydrogen production ability of the biogranules in the bed zone, mmol H 2 g -1 VSS d -1, SHPR) with the same level of hydrogen yield (the ability of converting sucrose into hydrogen, mol H 2 mol -1 sucrose, HY) compared to other UASB reactors that used other seed sources [7]. Converting organic wastes into valuable products is sustainable. A UASB system seeded with sewage sludge microflora is a process with potential for organic waste-originated hydrogenic fermentation. The H/D ratio is an important design factor for an UASB reactor. Many methanogenic UASB reactors employed in laboratories and industrial practices use H/D ratio values of about 5-6 [8-9]. However, values up to 11-3 in laboratory experiments have also been reported [1-11]. In a UASB reactor, a high H/D ratio results in high upflow velocity and then enhances biosolids-granulation. In light of the above developments, this research was aimed at investigating the UASB process to reevaluate the hydrogen-producing activity of the granulated sewage sludge microflora. A H/D ratio value of 7.4 was used in these experiments. The H/D ratio- * Corresponding author cylin@fcu.edu.tw

2 58 J. Environ. Eng. Manage., 17(1), (27) affective biosloid-granulation, reactor performance stability and hydrogen production efficiency were studied. MATERIALS AND METHODS The seed sludge was collected from a final sedimentation tank (Li-Min Municipal Sewage Treatment Plant, Taichung, Taiwan; an activated sludge process) and then screened with sieve No. 8 (2.35 mm) to eliminate large particulate materials. The ph, volatile suspended solids (VSS) and total solids (TS) concentrations of the screened sludge were 7.4, 2964 and 4835 mg L -1, respectively. Before seeded into the reactor, the seed sludge was heat-treated at 1 C for 45 min to inhibit the methane-producing bacteria activity. The substrate sucrose (2 g COD L -1 ) was fed in a continuous mode. This substrate contained sufficient inorganics for bacterial growth (mg L -1 ): NH 4 HCO 3, 524; K 2 HPO 4, 125; MgCl 2 6H 2 O, 15; FeSO 4 7H 2 O, 25; CuSO 4 5H 2 O, 5; CoCl 2 5H 2 O,.125; NaHCO 3, 672. Figure 1 schematically describes the lab-scale UASB reactor system. The sampling ports were along 1 cm height intervals from the bottom. The reactor had a H/D ratio of 7.4 with a working volume of 2 L, interior diameter of 7 cm and height of 52 cm. Some hydrogen production data used for comparison were obtained from a lower H/D ratio fermenter (H/D ratio 3.8) with a working volume of 3 L, interior diameter of 1 cm and height of 38 cm [7]. These reactors were operated at a temperature of 35 ± 1 C and a ph of 6.7 ±.2 by adding 1 N NaOH or 1 N HCl. The operating HRTs were 24, 2, 16, 12, 1, 8 and 6 h, starting from 24 h. For each HRT, the reactor was operated for three weeks to allow steady-state condition development. Steady-state conditions were established when the variation in the product concentrations was small (gas production, ± 5%; effluent COD concentration, ± 1%) during two weeks of operation. After the parameter data were obtained, the retention time was then shortened. Temp controller Gas/liquor/solid separator Thermal insulating layer Blanket zone Bed zone H Sampling ports Pump Gas meter Substrate tank Fig. 1. Schematic of the UASB reactor for continuous biohydrogen production. The reactor effluent was monitored twice a week for alkalinity, volatile fatty acid (VFA), sucrose, total suspended solids (TSS) and VSS concentrations. Gas composition and volume were monitored every day. The analytical procedures of Standard Methods were used to determine the above parameters of liquid content [12]. VFA and gas composition were analyzed with a gas chromatograph having a flame ionization detector (glass column, 145 C; injection temperature, 175 C; carrier gas, N 2 ; packing, FON 1%) and a thermal conductivity detector (column, 55 C; injection temperature, 9 C; carrier gas, Ar; packing, Porapak Q, mesh 8/1), respectively. The gas volumes were corrected to a standard temperature ( C) and pressure (76 mm Hg). For determining the size distribution, the biogranule sample was taken from the port of 1 cm height. The collected biogranule was separated into six fractions with various openings (.2,.6, 1., 2., 4. mm) and was measured with an Image Analyzer System (Image-Pro Plus, Media cybernetics Co., USA). 1. Start-up Period RESULTS AND DISCUSSION Before reaching stable reactor performance, fluctuations were observed in the total gas production, hydrogen gas production and H 2 gas content. This resulted from the increase in the organic load rates when the HRT was shortened. An increase in the organic load rate resulted in a new environment in the reactor. The microorganisms must then adapt to the new conditions. The hydrogen content in the produced gas ranged from % and was markedly higher than the results (9-12%) from Nakamura et al. [13] who operated a CSTR system for hydrogen production at short HRTs of 1 to 2 h. During these start-up periods the total gas production volume from the high H/D ratio reactor was larger than that from the low H/D ratio reactor [6]. 2. Steady-state Condition Period Based on a five month stable hydrogen production period and high sucrose degradation efficiency, the reactor was considered to operate successfully. The reactor efficiency was evaluated based on the monitoring parameter values during the steady-state condition. Seventy days were required for the reactor to reach the steady-state condition of 24 h HRT. For the other HRTs, a 3-4 week operating period was necessary to reach steady-state conditions. Table 1 summarizes the data under the steady-state conditions at each HRT. The sewage microflora-biomass concentrations were HRT and H/D ratio-dependent. Concentration variations in the high H/D ratio reactor ( g L -1 ) were smaller than that in the low H/D ratio reac-

3 Chang and Lin: Hydrogen Fermentation from Sewage Sludge 59 Table 1. Data under steady-state conditions at each HRT HRT (h) Loading (mmol sucrose L -1 d -1 ) V a (m h -1 ) Sucrose degradation b VSS (mg L -1 ) VSS/TSS Alkalinity (mg L -1 as CaCO 3 ) TVFA (mg L -1 as COD) H/D ratio of ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± 628 H/D ration of ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± 338 a V, up-flow velocity = influent liquid/surface area of the UASB reactor b n, 3~8 tor ( g L -1 ). The VSS/TSS ratio in the reactor denotes the organic biogranule component because the influent was a synthetic substrate solution with no granular inorganic materials such as grit or clay contributing to decreased VSS/TSS ratio values. A H/D ratio-dependent variation trend in the VSS/TSS ratio values was observed. This high H/D ratio reactor had constant values of The reported low H/D ratio reactor values fluctuated between Reported values for various UASB reactors treating sewage were.6-.8 [13]. A high H/D ratio resulted in a stable biomass composition. The sucrose degradation in the reactors reached 87-96% with the high H/D ratio reactor having lower values (87-9%). The alkalinity concentrations decreased with decreasing HRT in the low H/D ratio reactor, from 74 mg L -1 (at 24 h HRT) to 276 mg L -1 as CaCO 3 (at 6 h HRT). For the high H/D ratio reactor, a constant alkalinity value ( mg L -1 as CaCO 3 ) was achieved. The average total VFA (TVFA) concentrations were higher in the high H/D ratio reactor than in the low H/D ratio reactor. The hydrogen production was accompanied with VFAs or solvent formation during the anaerobic organic degradation. For hydrogen gas production, this high H/D ratio reactor produced high amounts of hydrogen gas (53.2 vs L d -1 ) and high hydrogen gas content (52.4 vs. 42.4%). Based on the relationships between the H/D ratio, HRT, VSS/TSS ratio, alkalinity and hydrogen production, we can conclude that a high H/D ratio favors hydrogen production in a UASB system with stable reactor performance. High hydrogen production with lower substrate degradation in this high H/D ratio reactor is related to the biomass activity (discussed later). 3. Biosloids Granulation Granule formation is an indicator of successful UASB reactor operation. When the reactors reached steady-state conditions, the granule size distributions were HRT-dependent (Fig. 2). Figure 2 shows that shortening the HRT markedly improved the biosolids granulation. For the high H/D ratio reactor, at HRT 8 h, the granules were 1.4 mm in average diameter, 1.1 g ml -1 in density and 8.6 m h -1 in setting velocity. The granule diameter in the high H/D ratio reactor was 3.26 times larger than that in the low ratio reactor. This H/D ratio-dependent granulation tendency was similar to some reports. Van Langerak et al. [14] reported that the average granule diameter was 1.1 mm in an UASB reactor with a H/D ratio of 5.5. Yan and Upflow Upflow velocity velocity (m h-1) (m/h) Upflow velocity of the low H/D ratio Upflow velocity of the high H/D ratio Diameter of the low H/D ratio Diameter of the high H/D ratio HRT (h) Fig. 2. The relationships between up-flow velocity, hydraulic retention time (HRT) and the granule diameter (low H/D ratio reactor data were from [7]) Diameter (mm)

4 6 J. Environ. Eng. Manage., 17(1), (27) Tay [1] experimented with a high H/D ratio (= 12) reactor resulting in a granule diameter of 2.2 mm. Upflow velocity is an important factor affecting the granulation of UASB reactor biosolids and relates directly to the reactor height, length and width/diameter values [15]. The up-flow velocity was m h -1 and m h -1 for the low and high H/D ratio reactors, respectively. A high H/D ratio resulted in higher up-flow velocity and enhanced anaerobic sewage microflora biosolids granulation in the reactor. These up-flow velocity values were in the same magnitude as that for methanogenic reactors (.1 m h -1, Campos and Anderson [16];.26 m h -1, Yan and Tay [1];.6 m h -1, van Langerak et al. [14]). 4. Granulated-microflora Activity and Hydrogen Production Figure 3 illustrates the relationships between hydrogen yield (HY), hydrogen production rate (HPR, mmol H 2 L -1 d -1 ), SHPR and HRT. The HY in the high H/D ratio reactor increased with an increase in HRT. However, after reaching a peak value, it then decreased from 1.8 mol H 2 mol -1 sucrose at HRT 24 h to 2.9 mol H 2 mol -1 -sucrose at HRT 8 h, and to 1.1 mol H 2 mol -1 sucrose at HRT 6 h. The HY of the high H/D ratio reactor was higher than that for the low H/D ratio reactor. The highest hydrogen production efficiency obtained for the high H/D ratio reactor was at HRT 8 h. In this reactor, the HPR increased with decreasing HRT from 16 mmol H 2 L -1 d -1 at HRT 24 h to 512 mmol H 2 L -1 d -1 at HRT 8 h (up-flow velocity,.33 m h -1 ). This HPR value was higher (more than 15% increment) than the reported values for other re-actor systems. A bell-type hydrogen production-hrt curve was found for the high H/D ratio reactor at HRT HY HY (mol H 2 2 / mol -1 sucrose) SHPR (mmol (mmol-h H 2 g -1 2 /g VSS VSS-d) d -1 ) HPR (mmol (mmol-h H 2 L -1 2 /L-d) d -1 ) HP of the low H/Dratio HP HP of the of the low high H/Dration ratio HP HAc/HBu of the high of H/D the low ratio H/D ratio HAc/HBu of the of the low high H/D H/D ratio ratio HAc/HBu of the high H/D ratio SHPR of the low H/D ratio SHPR of the high H/D ratio HPR of the low H/D ratio HPR of the high H/D ratio HRT (h) Fig. 3. The relationships between HAc/HBu ratio, hydrogen yield (HY), hydrogen production rate (HPR), specific hydrogen production rate (SHPR) and HRT (low H/D ratio data were from [6]) HAc/HBu 8 h (Fig. 3). This indicates that hydrogen production efficiency is both HRT and H/D ratio-dependent. At the highest hydrogen production yield 2.9 mol H 2 mol -1 sucrose by 8 h HRT (HY). Each gram of granulated sewage sludge microflora produced.1 mol H 2 d -1 (SHPR). These HY and SHPR values were higher than those from a high-rate anaerobic sequencing batch reactor and a fixed-bed reactor packed with activated carbon [17,18]. Table 2 summarizes the relative ΔV, ΔHY, ΔHPR and ΔSHPR value increments (shown in Fig. 3) for the high H/D ratio reactor compared to that for the low H/D ratio reactor. The HRT dependent increments in these parameters were obtained with 24 h exhibiting the most marked values. This 24 h result might arise from the fact that at this HRT, the low H/D ratio reactor had too low hydrogen production efficiency. Moreover, parameter-dependent increments were also observed with HY having the most marked values. All of these facts indicate enhancement of the high H/D ratio. Specifically, except for HRT 24 h, at HRT 8 h (with the highest hydrogen production), the relative increments for these parameters peaked with ΔHY 418%, ΔHPR 89% and ΔSHPR 133%. 5. Proposed Strategies for Optimal Hydrogen Production The hydrogen gas content obtained from the high H/D ratio reactor was higher than that from the low H/D ratio reactor, both at start-up and steady-state periods. The smallest biomass concentration variation, constant VSS/TSS ratio, constant alkalinity value and highest hydrogen production rate were obtained in the high H/D ratio reactor. These results show the enhancement of the high H/D ratio on hydrogen production in a UASB system. Another notable fact is that the high H/D ratio reactor had both lower sucrose degradation values (87-9%) and biomass concentrations (especially at HRTs 16-6 h). It also had higher hydrogen production. This implies that the granulated Table 2. Relative changes of ΔV, ΔHY, ΔHPR and ΔSHPR values of high H/D ratio reactor to that of low H/D ratio reactor. HRT (h) ΔV a ΔHY ΔHPR SHPR a Δ 1*(V High H/D V LowH / D ) V= V LowH / D

5 Chang and Lin: Hydrogen Fermentation from Sewage Sludge 61 sewage sludge microflora in the high H/D ratio reactor possessed high bioactivity for hydrogen production. Moreover, the characteristic hydrogen production efficiency is both HRT and H/D ratio-dependent (Fig. 3). This indicates the importance of selecting a proper reactor configuration to coincide with the operating HRT for efficient hydrogen production. In light of the above observations, designing a proper H/D ratio reactor is preferable to using a UASB system for efficient hydrogen production. Other methods, such as selecting a proper nutrient level, cultivating dominant organisms from mixed microflora, controlling the influent carbon/nitrogen ratio, or using gas stripping to reduce high hydrogen partial pressure inhibition or CO 2 levels might increase the hydrogen yield [19]. CONCLUSIONS The experimental results showed that anaerobic sewage sludge microflora could granulate in a UASB system to convert sucrose into hydrogen. The hydrogen production in the UASB system was HRTdependent and peaked at 8 h HRT. This study also demonstrated that proper reactor H/D ratio enhances hydrogen production efficiency and reactor operation stability in a UASB system. According to our results, in a UASB reactor with a H/D ratio of 7.4 and a HRT of 8 h, each mol of sucrose yielded 2.9 mol of H 2 and each g of granulated sewage sludge microflora produced.1 mol H 2 d -1. ACKNOWLEDGMENTS The authors would like to thank the National Science Council of the Republic of China for financially supporting this research under Contract No. NSC E REFERENCES 1. Hansel, A. and P. Lindblad, Towards optimization of cyanobacteria as biotechnologically relevant producers of molecular hydrogen, a clean and renewable energy source. Appl. Microbiol. Biot., 5(2), (1998). 2. Yokoi, H., Y. Maeda, S. Hayashi and Y. Takasaki, H 2 production by immobilized cells of Clostridium butyricum on porous glass beads. Biotechnol. Technol., 11(6), (1997). 3. Levin, D.B., L. Pitt and M. Love, Biohydrogen production: Prospect and limitations to practical application. Int. J. Hydrogen Energ., 29(2), (24). 4. Aoyama, K., I. Uemura, J. Miyake and Y. Asada, Fermentative metabolism to produce hydrogen gas and organic compounds in a cyanobacterium, Spirulina platensis. J. Ferment. Bioeng., 83(1), 17-2 (1997). 5. Lin, C.Y. and R.C. Chang, Hydrogen production by anaerobic acidogenesis process. J. Chem. Technol. Biot., 74(6), (1999). 6. Chen, C.C., C.Y. Lin and J.S. Chang, Kinetics of hydrogen production with continuous anaerobic cultures utilizing sucrose as the limiting substrate. Appl. Microbiol. Biot., 57(1-2), (21). 7. Chang, F.Y. and C.Y. Lin, Biohydrogen production using an up-flow anaerobic sludge blanket reactor. Int. J. Hydrogen Energ., 29(1), (24). 8. Liu, H. and H.H.P. Fang, Hydrogen production from wastewater by acidogenic granular sludge. Water Sci. Technol., 47(1), (23). 9. Yu, H.G., H.H.P. Fang and G.W. Gu, Comparative performance of mesophilic and thermophilic acidogenic upflow reactors. Process Biochem., 38(3), (22). 1. Yan, Y.G. and J.H. Tay, Characterisation of the granulation process during UASB start-up. Water Res., 31(7), (1997). 11. Annachhatre, A.P. and P.L. Amatya, UASB treatment of tapioca starch wastewater. J. Environ. Eng.-ASCE, 126 (12), (2). 12. Nakamura, M., H. Kambe and J. Matsumoto, Fundamental studies on hydrogen production in the acid-forming phase and its bacteria in anaerobic treatment processes. Water Sci. Technol., 28(7), (1993). 13. APHA-AWA-WPCF, Standard Methods for the Examination of Water and Wastewater, 19th Ed. American Public Health Association, New York (1995). 14. Van Langerak, E.P.A., G. Gonzalez-Gel, A. Van Aelst, J. B. Van Lier, H.V.M. Hamelers and G. Lettinga, Effects of high calcium concentrations on the development of methanogenic sludge in upflow anaerobic sludge bed (UASB) reactors. Water Res., 32(4), (1998). 15. Van Haandel, A.C. and G. Lettinga, Anaerobic Sewage Treatment, John Wiley and Sons, Inc., London UK (1994). 16. Campos, C.M.M. and G.K. Anderson, The effect of the liquid upflow velocity and substrate concentration on the start-up and steady-state periods of lab-scale UASB reactors. Water Sci. Technol., 25(7), 41-5 (1992). 17. Chang, J.S., K.S. Lee, and P.J. Lin, Biohydrogen production with fixed-bed bioreactors. Int. J. Hydrogen Energ., 27(11-12), (22). 18. Lin, C.Y. and C.H. Jo, Hydrogen production from

6 62 J. Environ. Eng. Manage., 17(1), (27) sucrose using an anaerobic sequencing batch reactor process. J. Chem. Technol. Biot., 78(6), (23). 19. Lin, C.Y. and C.H. Lay, Carbon/nitrogen-ratio effect on fermentative hydrogen production by mixed microflora. Int. J. Hydrogen Energ., 29(1), (24). Discussions of this paper may appear in the discussion section of a future issue. All discussions should be submitted to the Editor-in-Chief within six months of publication. Manuscript Received: August 15, 25 Revision Received: December 2, 25 and Accepted: December 27, 25