Anaerobic Digestion of Ulva sp. 3. Liquefaction Juices Extraction by Pressing and a Technico-Economic Budget

Abstract

In many countries, the algae of "green tides" are harvested in the fight against pollution. Ulva often represents the main component of the tide, and intensive research has been conducted on the possibility to use the algae as a methanisation substrate. However, methanisation is hampered by various practical obstacles, which requires a compromise between productivity and biological yield.The process described here calls upon a pre-digestion phase of Ulva which, besides the economy of time and volume of the digestion, makes it possible to obtain a biogas of good quality. The methanisation substrate is the hydrolysis juice collected by draining, followed by pressing. The cake resulting from the pressing process can be used as organic enriching or fertilizing agent in agriculture. Various presses were tested. The screw press was found the most suitable to recover a great quantity of sufficiently loaded pressing juice after only a short hydrolysis time. For a 3 month hydrolysis period, the different fractions amounted to 158 L of hydrolysis juice, 192 L of pressing juice, and 0.075 m 3 of cake per m 3 of initial algae.The bi-phasic anaerobic digestion with forced recuperation of juices offers interesting pollution abatement perspectives, with total and soluble chemical oxygen demand cleaning rates of respectively 79 and 95% during the methanogenic phase, for a volume productivity of 1.5 m 3 CH 4 m −3 digester day −1 . The quality of the Ulva juice also makes it suitable for use as substrate for industrial processes or co-substrate of methanisation in pre-existing reactors, so that subsequent investment could be avoided.

Ulvan: A Versatile Platform of Biomaterials from Renewable Resources

“…To this aim algae could represent a potentially advantageous biomass to be explored since they are very abundant and cheap and very often involved in uncontrolled proliferation processes detrimental for marine and aquatic environments (Barghini et al, 2010, Chiellini et al, 2008, Fletcher, 1996. Today most of the naturally produced and harvested algal biomass is an unused resource and often is left to decompose on the shore creating waste problems (Morand et al, 2006). The current use of this huge underexploited biomass is mainly limited to food consumption and as bio-fertilizer, but its potentiality as renewable and sustainable feedstock for energy and material production is gaining more and more attention (Demirbas A.…”

Solar-to-fuel conversion in algae and cyanobacteria

“…The latter is a green macroalga that is harvested from natural populations or cultivated in aquaculture land-based systems (Morand et al 2006). The biomass yield of Ulva lactuca has been estimated to be 45 t dry weight ha −1 year −1 , offering remarkable potential for bioenergy production (Bruhn et al 2011).…”

“…Macroalgal biomass represents a natural resource for the generation of biofuels, in particular, macroalgae can be cultivated in aquaculture land-based systems or harvested from natural populations. Naturally produced biomass is often unused, mainly dumped or left stranded to decompose on the shore (Morand et al 2006). Use of this biomass would offer combined benefits in bioenergy production and in mitigation of the environmental impact of excessive growth of seaweeds observed in coastal ecosystems closed to agricultural, urbanized and industrial zones.…”

Biogas from Marine Macroalgae: a New Environmental Technology — Life Cycle Inventory for a Further LCA

“…280 [29] 94-177 lCH4/kgVS [30] 77-560 [26] 275 l/kgVS [18] 125 [29] 83-430 [26] 540 [30] V. ALGAE GROWING: CONSIDERATION AND RESULTS OF…”