biogas production from anaerobic digestion of spirulina maxima algal biomass
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Biogm Production from Anaerobic Digestion of Spiralina maxima Afgd Biomass
The photosynthetic spectrum of solar energy could be exploited for the production of chemical energy of methane through the combined algal-bacterial process. In this process, the algae are mass produced from light and from carbon in the first step. The algal biomass is then used as a nutrient for feeding the anaerobic digester, in the second step, for the production of methane by anaerobic bacteria. The carbon source for the production of algal biomass could be either organic carbon from wastewaters (for eucaryotic algae), or carbon dioxide from the atmosphere or from the combustion exhaust gases (for both prokaryotic and eukaryotic algae).
The technical feasibility data on the anaerobic digestion of algal biomass have been reported for many species of algae including the macroscopic algae such as the giant brown kelp, Macrocystis pyrzzera, 1,2 the red marine alga, Gracilario ~ e a e , ~ and the green marine alga, Ulva l a ~ t u c a . ~ Among the microscopic algae, the following cultures have been successfully used for the production of methane: the mixed culture of Scenedesmus spp. and Chlorella ~ p p . , ~ the mixed culture of Scenedesmus spp., Chlorella spp., Euglena spp., Oscillatoria spp., and Synechocystir sp.,' the culture of Scenedesmus sp. alone, and together with either Spirulina sp., Euglena sp., Micractinium sp., Melosira sp., or Oscillatoria S P . , ~ the mixed culture of Hydro- dictyon reticulaturn, and Clodophora glomerata. '
Research being conducted in our laboratory consists of using the semimicroscopic blue-green alga Spirulina marima as the sole substrate for this combined algal-bacterial process. This species of alga is very attractive for the process because of its capability of using the atmospheric carbon dioxide as carbon source and its simple harvesting methods. Furthermore, it appeared that the fermentability of S. marima is significantly higher than other microscopic
This communication presents the results on the anaerobic inoculum development by the adap- tation technique. This inoculum was then used for the semicontinuous anaerobic digestion of S. marima algal biomass. The evolutions of biogas production and composition, biogas yield, total volatile fatty acids, alkalinity, ammonia nitrogen, pH, and electrode potential were followed.
MATERIAIS AND METHODS
The semimicroscopic blue-green alga S. maxima was maintained and cultivated in synthetic medium as reported else~here.~'" The algal biomass grown in either 16-L carboys or 64-L laboratory-built photobioreactors was concentrated to a slurry containing 30% total solid with the De Lava1 model Gyrotest continuous centrifugal. This algal slurry was kept frozen at -30C until use. The frozen algal slurry was thawed to mom temperature and then diluted to a desired volatile solids (VS) concentration prior to feeding the anaerobic digester. A mixed culture of anaerobes used as culture starter in this work was the fresh sludge coming from the anaerobic digester of the Valcartier sewage treatment plant (Quebec, Canada).
The sludge adaptation experiment was conducted in the New Brunswick Scientific model MA-105 Magnaferm fermenter containing 12 L of culture medium. The experiment was oper- ated at 35"C, under anaerobic condition and with continuous agitation (100 rpm) during the first two months, then occasional agitation afterward (five months).
The adapted sludge was then used as inoculum for starting up one experiment on the semicon- tinuous anaerobic digestion of S. marima algal biomass. This experiment was conducted in the New Brunswick Scientific model MA-105 Magnaferm fermenter containing 10 L of medium for 14 weeks. It was operated under the following conditions: temperature 35"C, occasional mixing, daily feeding, loading rate of 0.97 kg VS m-3 day,-' and retention time of 33 days.
Biotechnology and Bioengineering, Vol. XXIV, 4. 1919-1924 (1982) 0 1982 John Wiley & Sons, Inc. CCC 0006-3592/82/081919-06$01.60
1920 BIOTECHNOLOGY AND BIOENGINEERING VOL. XXIV (1982)
Routine chemical analyses were carried out on the mixed digester content and the algal biomass fed to the digester. The following analyses were carried out at regular intervals. Total volatile fatty acids were determined by the extraction procedure'* and expressed as milligrams of CH,COOH per liter. Alkalinity was determined by titrating to pH 3.1 an aliquot of the super- natant liquor with 0.01N H2S0,.I2 Ammonia nitrogen was determined with the Orion model 95-10 ammonia e l e~ t rode . '~ . ' ~ Particulate carbon, nitrogen, and hydrogen were determined on lyophilized samples using the Hewlett-Packard model 185 CHN analyzer. The total and volatile solids were determined according to Standard Methods.'2 The electrode potential (EP) was measured using a platinum electrode, together with a calomel half-cell connected to a Fisher model Accumet 425 pH/ion meter. Gas samples were analyzed on a Fisher model 1200 gas par- titioner. All gas measurements are expressed at 0C and 1 atm pressure.
RESULTS AND DISCUSSION
The sludge adaptation experiment was started with 9 L of fresh sludge mixed together with 3 L of S. marima slurry containing 5% VS. The results of this experiment were reported as cycle A in Table I. The biogas productivity [v/(v day)] was very high at the beginning and decreased as the fermentation progressed. In contrast, the ratio CH4/C02 was very low at the beginning and
TABLE I Biogas Production From Spirulina marima Biomass Substrate With Fresh Sludgea
Total biogas Fermentation time Biogas productivityb produced' EP'
Cycles (day) [v/(v day)] (L) CH4/C0zb pH (mV)
A d 1 4 5 6 7 8
1 2 3 4 5 6 7 8
10 12 13
0.48 0.46 0.39 0.32 0.39 0.40 0.30 0.10
0.39 0.25 0.31 0.28 0.26 0.24
0.23 0.13 0.14 0.13
7.0 22.8 1.95 - 21.5 2.80 - 31.3 3.02 1.3 36.5 3.10 - 40.8 3.10 1.2 51.0 3.23 1.4 58.2 3.50 1.4
- - 4.7 7.7 1.03 1.3
11.4 1.36 - 14.8 1.80 - 17.9 2.18 1.3 20.8 2.43 - 23.7 2.66 1.4 26.4 2.84 - 28.0 3.12 - 31.3 - 7.6 34.5 3.31 1.6
- - 382 -
-320 - 320 -325
- -340 -
- 320 -
- 320 -310
aExperiment started on August 29, 1980. bMean value from at least two separate measurements per 'Estimated from the biogas productivity data. dFed with 3 L of algal slurry containing 5% VS. eFed with 1 L of algal slurry containing 5% VS. 'Electrode potential.