Cement Energy and Environment

by these industries after extraction of phycocolloids, i.e., a few thousand tonnes every year. This spent biomass forms a good and potential source for biogas (methane) production and can be a good alternative energy source for the fishermen community to meet their energy demands. Yet another source of spent biomass is the macroalgal residue generated after production of bioethanol from the saccharification and fermentation processes. Anaerobic digestibility of the residue is one of the most economic methods for biogas production and also demonstrates the mutual biorefinery approach, wherein various biofuels are produced from one biomass source. Figure 2 shows methane potential in different algae species on different days. The presence of sediment along with seaweed biomass proved to be crucial in order to achieve a good methane yield of about 380 dm3 CH4 kg-1 VSadded, a value comparable with literature data obtained through different approaches. Methane production from fresh macerated Ulva lactuca has yielded up to 271 ml CH4 g-1 VS, which is comparable to the production from livestock manure and land-based energy crops. Dried biomass has been reported to yield a 5-9 fold increase in methane production when compared to wet biomass. A high range of yield, 309±12 ml CH4 g-1 COD has been obtained during the 90-day period with the organic loading rate (OLR) of 3.5 g COD L-1 d-1 . Another research demonstrates that the methane yield obtained by anaerobic digestion of seaweed was 0.12 N I CH4 g-1 VSadded. The same amount of methane yield was obtained from seaweed leachate with maximum sustainable OLR of 20.6 g tCOD L-1 day-1 , a hydraulic retention time (HRT) of 12 h and by means of a total COD removal of about 81 per cent. However, the presence of heavy metals in the leachate and high concentrations of sulphur and sodium chloride were found to decrease methane yield. The Biochemical Methane Potential (BMP) obtained from different seaweed species with around 2.5 per cent total solids was reported in the order of 196±9, 182±23, and 154±7 L CH4 kg-1 VS from Ulva sp. , Gracilaria sp. , and Enteromorpha sp., respectively. Table 3 gives information about specific methane yields obtained from brown and red seaweeds. There are a number of rate-limiting factors which affect biomethane production. The hydrolysis of seaweed-derived polysaccharides, a b le 3: S p ecific methane yields o btain e d from brown and red se a w eeds I Seaweed BMP Count1y Y1t"ld L CH.,I kg vs Brown Seaweeds H. elongate 261 West Cork. Ireland 202 Brittany, France L. digitata 218 West Cork. Ireland 246 Sligo, Ireland F. serratus 96 West C ork. I reland S. latissirna 342 West Cork. Ireland 335 Sligo. Ireland 223 Trondheim. Norway 220 Norway 209 Brittany, France A. nodosurn 166 West Cork. Ireland U. pinnatifida 242 Brittany. France S. 255 Sligo. Ireland polyschides 216 Brittany. France S. rnuticurn 130 Brittany. France Red Seaweeds P. palrnata Brittany. France G . verrucosa Brittany. France particularly alginates, is one such rate limiting step in the AD of seaweed. This is due to the high presence of phenolic compounds particularly in the brown seaweeds. The typical seed inocula for anaerobic digesters are from municipal sewage sludge or animal manure slurry, however, the inocula containing higher proportions of bacteria, capable of fermenting marine phycocolloids has been shown to increase methane production. Therefore, the addition of bacteria from the rumen of Ronaldsay sheep, which almost entirely has seaweed for its diet, was found to increase the methane yield (0.253 L CH4 g-1 VS) and volatile solid utilization (67 per cent) from anaerobic digestion of Laminaria hyperborea. The C:N ratio is another important factor that determines the optimal ratio of digester feedstock. The biomethane potential of fresh Ulva is 183 L CH4/ kg VS. However, the Buswell equation suggests 431 L CH4/kg VS. This indicates that some more energy remains in the digested material and only about 42 per cent has been released as 49