FUEL GAS PRODUCTION BY MARICULTURE ON LAND
After, in the previous project ESE-R-020-D (B), the feasibility of the whole cycle of methane production by MCL has been demonstrated (consisting of algae production, harvesting, fermentation to biogas, and mineral nutrient recycling into the algae ponds in the form of the fermentation sludge), the aim of this project was upscaling and testing of the system at pilot size. For this purpose the total pond area at Lamezia was enlarged to 560 m**2. The construction was the same as already described earlier. Some experimentation was done with the technical realization of the low energy mixing procedure using the mixing board. This needs still further improvement. According to the MCL concept, the principal carbon source for the algae cultures is fresh seawater which, for this purpose, has to be exchanged in the ponds by about 30-40% per day. In order to avoid loss of added nutrients during this exchange, the nutrient regime in the ponds has to be managed in such a way that at the time of water (culture medium) release the levels of added nutrients are virtually zero. As could be shown during this project, this is possible without any significant loss of productivity. The harvested cell concentrate of Tetraselmis (2.5-3.0% dry weight) was directly given into a 1 m**3 fermenter provided by the group of Profs. Nyns and Naveau of the Catholic University of Louvain. The volumetric feed rate varied from 0.5-1.5 kg volatile solids per m**3 per day, the retention time between 20 and 50 days. The methane yield was between 0.2 and 0.35 m**3/kg volatile organic matter. More details of this process are found in the Louvain report. According to the results obtained at Louvain, it looks likely that the efficiency of the fermenter can be higher, and that the optimal operation parameters could not be realized under the conditions given at Lamezia. Finally, the collected results were used to make up the energy budget of the methane production process by MCL. At a productivity of 25 g/m**2/day, the output of methane is about 8.8 l/m**2/day, or 0.09 kWh-thermic/m**2/day. The total energy input (for agitation, seawater pumping, harvest handling, and the energy equivalent of the used mineral nutrients) is 0.038 kWh/m**2/day (after all items have been converted into thermal units to make them comparable). This means a net energy output of 0.052 kWh/m**2/day, or 2.2 W thermic energy/m**2 of pond area. This is 57% of the gross production in the forms of methane output. As far as the costs are concerned, only an estimate is possible. Using a basis of 1 hectare, the total investment is about $ 50,000. Assuming an amortization time of seven years and 10% interest on investment p.a., the total operational costs are $ 117/ha/month which means about $ 2/GJ. Capital costs count for 38 % of this. For larger units it can be expected that the wages (presently 28 %) may go down.
Bibliographic Reference: EUR 10109 EN (1986) MF, 21 P., BFR 150, BLOW-UP COPY BFR 200, EUROFFICE, LUXEMBOURG, POB 1003
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Record Number: 1989125015100 / Last updated on: 1987-02-01
Available languages: en