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CC Wang,1 CW Chang,1 CP Chu,1 DJ Lee,1∗ Bea-Ven Chang2 and CS Liao2. 1Chemical Engineering Department, National Taiwan University, Taipel, ...
Journal of Chemical Technology and Biotechnology

J Chem Technol Biotechnol 79:426–427 (online: 2004) DOI: 10.1002/jctb.997

Technical note Efficient production of hydrogen from wastewater sludge CC Wang,1 CW Chang,1 CP Chu,1 DJ Lee,1∗ Bea-Ven Chang2 and CS Liao2 1 Chemical

Engineering Department, National Taiwan University, Taipel, Taiwan, 10617 of Microbiology, Soochow University, Taipei, Taiwan, 111

2 Department

Abstract: Efficient production of hydrogen, approximately ten times greater than reported in the literature, could be achieved using Clostridium bifermentans isolated from waste water sludge as inoculum.  2004 Society of Chemical Industry

Keywords: hydrogen; sludge; fermentation; inoculum

INTRODUCTION Wastewater sludge collected from wastewater treatment plants contains high levels of organic matter, and thus is a potential substrate for hydrogen production. However, limited data in the literature revealed that the hydrogen yield from wastewater sludge is extremely low, c 0.08 mol-H2 kg−1 -DS using anaerobic fermentation.1 Our group utilized a pure strain of Clostridium spp purchased from a commercial company to ferment wastewater sludge. Not only was the hydrogen yield noted to be low, but also the seed bacteria needed a long time to adapt before traces of hydrogen could be produced. Cheng et al 2 observed a lag time of 66 h in their preliminary tests on sludge fermentation. We demonstrated in this work that, if the inoculum was directly derived from the collected wastewater sludge, the hydrogen production could be considerably enhanced in anaerobic fermentation.

EXPERIMENTAL Substrate and inoculum Wastewater sludge was collected and gravitationally settled to a solid content of 16.5 kg m−3 , and was the substrate for the present test. The pH value of the sludge was approximately 6.4. The chemical oxygen demand (COD) for the sludge was 24.8 kg m−3 , obtained from a direct reading spectrometer (DR/2000, Hach, USA). The COD for the filtrate of sludge sample after filtering through a 0.45-µm membrane was termed as soluble COD (SCOD), which read 0.339 kg m−3 for the original sludge. The elemental compositions of dried sample were C: 34.2%, H: 5.3%, and N:

5.4%, using oxoelemental analyzer (Perkin-Elmer 2400 CHN). The inoculum was prepared by pasteurizing waste activated sludge at 394 K and 1.2 × 105 N m−2 (Huxley Autoclave, HL-360) for 1800 s to inactivate methanogenic bacteria.3 Then 0.1 mol dm−3 of methanogenic bacterial inhibitor, sodium 2bromoethanesulfonate (BESA, from Sigma, USA), was added to the pasteurized sludge. After 86 400 s anaerobic incubation at 308 K, the dosed sludge was spread on a gel-type reinforced clostridial medium (Oxoid) and colonized for 259 200 s. Individual colonies were removed from the medium and incubated on the agar for strain purification. After three-time purifications, 10 colonies of anaerobes were picked up and incubated in liquor-reinforced clostridial medium. The bacteria strains underwent sequence analysis for 16S rDNA. The gene sequence determined by primer F8 includes: GCGGGNGNGGTNCCTAA CACATGCAAGTCGTAACANGGTATTCCACA NCAGNGNGCTGGACGGACNNGNAACAGAG GNGTGACCTGCCCTGNACACACNNGTNNC ATACCNNACGGTNTACTNGTNCNGNATNN CNTANANAAGTNCNATGGCTNTTGTATNAA AGNTNCNGCGNGNCAGGATGGACCCGGGT GTGATTAGCTNGTTGTNAAGGNANNGGCT NACCANNGCAACNATCANNATCCGNCCTG AGAGGNNNATNGNCCNCACTGNAACTGNN ACACGGNNNATACTCCTACNNNAGGCAAC NGTGNGGAATATTGCACAATGNNCGAAAG CNTGATGCAGCAACNCCGCGTGANCGANG AAAGCCTNACGGTCNTANAGCTCTGTNCT CAAGGAAGATTATGACNGNCTTGATGATG GAAGCCCNGACTAACTACGNNCCAANNNC



Correspondence to: DJ Lee, Chemical Engineering Department, National Taiwan University, Taipei, Taiwan, 10617 E-mail: [email protected] (Received 31 July 2002; revised version received 17 November 2002)

 2004 Society of Chemical Industry. J Chem Technol Biotechnol 0268–2575/2004/$30.00

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Hydrogen from wastewater sludge Table 1. Time evolution of hydrogen yield with the isolated clostridial strain

Time (s)

−1

Hydrogen yield (mol kg -CODi ) Standard deviation (mol kg−1 -CODi ) Enhancement Control

0

28 800

57 600

86 400

115 200

144 000

172 800

259 200

345 600

0 0

0.40 0.031 7.5 ND

0.62 0.057 11.6 ND

0.59 0.055 11.0 ND

0.26 0.042 4.9 ND

0.15 0.007 2.8 ND

0.055 0.036 1.0 ND

0.030 0.022 0.6 ND

0.014 0.010 0.3 ND

0

Enhancement is calculated based on the results reported in Ref 1 (0.08 mol kg−1 -dried solids). The control test was conducted with original sludge with no inoculum.

ACGGGGTAATACTTNANGGGCTANCAGNN ATNCAGANTTACTNAGCGTNAAGGGNGC GNACGTGGTTTTTTATNTCNGAAANGAAN NGCTACGGCTTATCCGGCGTAANNTNTTC AAACTACGNAACTTNAGTGCNNGAGAGGA GACCCCAACTCCTANGGTGANGGGTGATA TGCNTCTGNNTTTACGNNGNNNNCCCAN TTACGAAAGCGGGNATTCTCTNTGTCTN TNANTNGCAACTNAGGCNCTATATGNGTN GAACAGCAAACGGGGAANAGGGNCCCTTT GNNTTTGCANCNGGCCNNNNANGATTAN NAAGGGTGNNGGGNGGTTTACCCNNNTT GNTNCCCCTGGNNTAACCCACNCGNTACC CTGNNTTGNTNANTNGNTNTNGGGTNTT TNNNCTTTCAANGGATTTANNAGNGNC. These four strains are most probably members of the clostridia family, Clostridium bifermentans (100%). These four strains were mixed up and stored as the seed bacteria in the fermentation tests. Fermentation and tests A 4.5 × 10−5 m3 sample of original sludge was mixed with 5 × 10−6 m3 inoculum suspension and was anaerobically incubated at 308 K in 1.25 × 10−4 m3 serum bottles without stirring or further nutrient addition. The bottles were capped with butyl rubber stoppers and wrapped by aluminum foils to prevent possible photolysis reaction of the substrate. A GC-TCD (Shimadzu, GC-8A instrument), equipped with a stainless column packed with Porapack Q (50/80 mesh) at 343 K and a thermalconductivity detector (TCD), measured the hydrogen concentration in gas phase. The temperatures of the injector and detector of the GC were at 373 K. Nitrogen at a flow rate of 1.67 × 10−8 m3 s−1 was the carrying gas. An Integrator (HP3396 Series II) estimated the peak area of the effluent curve, and hence quantified the gaseous concentrations. Repeated measurements revealed that the hydrogen contents thus determined contain a maximum relative error of 15%.

HYDROGEN PRODUCTION Table 1 lists the time evolution of the hydrogen yield based on unit gram of CODi (mol-H2 kg−1 -CODi ), where CODi is chemical oxygen demand of the J Chem Technol Biotechnol 79:426–427 (online: 2004)

substrate before testing (that is, the inoculum + original sludge), and is thereby higher than the COD for the original sludge. As Table 1 lists, the specific hydrogen yield could reach 0.6 mol kg−1 -CODi for the original biosolids, equivalent to 0.9 mol kg−1 -dried sludge for the investigated system. This value is much higher than that reported by Huang et al(0.08 mol-H2 kg−1 -dried sludge).1 Contrary to the 237 600 s time lag reported by Cheng et al 2 for anaerobic fermentation, this study revealed a negligible time lag, which might be attributable to the fact that the inoculum used was derived directly from the substrate sludge. The hydrogen concentration in the gas phase presents an increasing–decreasing curve, with its peak occurring at around 8–24 h, indicating that a certain amount of produced hydrogen has in some way been ‘consumed’. Cheng et al 2 reported a similar ‘hydrogen consumption’ phase during anaerobic fermentation. The mechanisms corresponding to this consumption are to be explored.

CONCLUSIONS Literature results normally reported a relatively low hydrogen yield in sludge fermentation. This work demonstrated that the use of inoculum derived directly from the sludge could considerably enhance the hydrogen yield. The isolated strain was identified as Clostridium bifermentans using molecular microbiology tools. It could not only yield hydrogen to a level of 0.9 mol kg−1 -dried sludge, but also eliminate the long time lag commonly observed in similar anaerobic systems. However, the formed hydrogen had been consumed after reaching a peak value; the mechanisms of this need further exploration. REFERENCES 1 Huang CH, Lin HY, Tsai YY and Hsie YK, The preliminary studies of hydrogen production from anaerobic digestion with different substrates and cultivations, in The 25th Wastewater Tech Conference, Yunlin, Taiwan (in Chinese) (2000). 2 Cheng SS, Bai MD, Chang SM, Wu KL and Chen WC, Studies on the feasibility of hydrogen production hydrolyzed sludge by anaerobic microorganisms, in The 25th Wastewater Tech. Conference, Yunlin, Taiwan (in Chinese) (2000). 3 Lay JJ, Modeling and optimization of anaerobic digested sludge converting starch to hydrogen. Biotechnol Bioengng 68:269–278 (2000).

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