Cement Energy and Environment

collected between August and January in the widely adopted method is through anaerobic coastal region of Tamil Nadu. digestion (AD) to biogas of which - 60 per cent is A standing crop of 16,000 tonnes of Sargassum and Turbinaria has been reported from Indian waters per year. The total production of seaweeds in India in the year 2000 was approximately 600,000 tonnes (wet weight). India produces 110-132 tonnes of dry agar annually, utilizing about 880-1100 tonnes of dry agarophytes. Annual algin production is :360 to 540 tonnes from 3,600 to 5,400 tonnes of dry alginophytes. The southern coast of India is rich in seaweed biodiversity, especially in the Gulf of Mannar region along a 10 km stretch of the Palk Bay towards Mandapam (Ramanathapuram district) in Tamil Nadu, with technical support from Marine Algal Research Station (CSMCRI), which has been found suitable for cultivation of seaweeds due to available nutrients and favourable nature of the sea for growth of seaweeds (Picture 1). There are many cultivation aspects already in process but only commercial seaweeds (Kappaphycus sp.) are cultivated on a large scale. Hundred hectares of contract seaweed farming systems grown in individual plots of 0.25 ha (40 m x 60 m) were used for cultivation. Each harvest cycle from planting to harvesting takes about 45 days with an annual yield of 100 tonnes (wet weight) per hectare, which translates into 10 tonnes of dry seaweed . Seaweeds have significant quantity of polysaccharides (phycocolloids), which are mostly five carbons in structure when hydrolysed. This property makes seaweeds a potential source of feedstock/ substrate for methanogens to convert phycocolloids to biogas. Biogas, particularly biomethane, is the potential alternative fuel that could possibly meet the demand of liquefied methane. The methane produced can be used for various purposes such as heating, electricity generation or compressed for use as a transport fuel. Research conducted in the 1980s still provides benchmark for biogas yields from a number of macroalgal species. However, since then there have been developments in AD technology and also an enormous increase in its use. Figure 1 shows overview of biogas production from seaweeds. Agar, carrageenan, and alginate are the three commercially extractable phycocolloids available in the market. These phycocolloids are mostly used in the food and pharmaceutical industries. A huge amount of spent biomass waste is being generated Seaweeds (dry, drifted, spent) 1 Wash with tap water, dry under sun and cut into small pieces 1 Co-digestion with different substrates (cow dung, sewage sludge, etc.) l Incubation in anaerobic digester/ reactor under controlled conditions 1 Biogas collection and testing for methane proportion 1 Applications: Heating, cooking, power generation, transport fuel Figure 1: Overview of biogas production petroleum gas (LPG) in the near r---- - --------------- -----, future. These available phycocolloids can be converted to U> biogas through anaerobic ~~ ... digestion by methanogens. ,, ::~:· Biogas from Seaweeds: The Process Seaweeds are characterized as having no lignin, low cellulose, and lipid content. Seaweed biomass can be converted to ~ biofuels by various processes, - 90 days - 60 days - 30 days including thermal treatment and fermentation; however, the most A Figure 2: Methane potential in different algae species o n different days 48