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The seasonal availability of Ulva spp. (U) poses a problem for the continuous operation of thalassic (TH) biogas digesters. Hence, rice straw (RS) was tested as an alternative substrate because of its abundance in Asian countries. The anaerobic monodigestion (AMD) of RS was performed under freshwater (FW) and TH conditions to investigate the TH biogas production performance using terrestrial biomass. Biological hydrolysis (BH-P) and 3% NaOH (NaOH-P) pretreatments were employed to minimize the limitation of biomass hydrolysis in the methane fermentation process. The BH-P [FW = 62.2 ± 30.9 mLCH4 g-1VS (volatile solids); TH = 75.8 ± 5.7 mLCH4 g-1VS] of RS led to higher actual methane yield (AMY) than NaOH-P (FW = 15.8 ± 22.8 mLCH4 g-1VS; TH = 21.4 ± 4.2 mLCH4 g-1VS) under both conditions (P = 0.008), while AMY of FW BH-P was comparable (P = 0.182) to TH BH-P. Thus, TH and BH-P was applied to the anaerobic co-digestion (ACD) of U and RS of varying mixture ratios. All ACD set-ups resulted in higher AMY (25U:75RS = 107.6 ± 7.9 mLCH4 g-1VS, 50U:50RS = 130.3 ± 10.3 mLCH4 g-1VS, 75U:25RS = 121.7 ± 2.7 mLCH4 g-1VS) compared with 100% RS (75.8 ± 5.7 mLCH4 g-1VS) or 100% U (94.8 ± 6.8 mLCH4 g-1VS) alone. While the AMY of 50U:50RS was comparable to 75U:25RS (P = 0.181), it is significantly higher (P = 0.003) than its estimated methane yield (EMY; 85.3 mLCH4 g-1VS), suggesting a synergistic effect on ACD of U and RS under 50:50 ratio. The results show that RS can be used as an alternative mono-feedstock for TH biogas production, and a high AMY can be obtained when RS is used as co-feedstock with U.

RESUMEN

Sea wrack (dislodged sea grasses and seaweeds) was used in biogas production. Fresh water scarcity in island communities where sea wrack could accumulate led to seawater utilization as liquid substrate. Three microbial seeds cow manure (CM), marine sediment (MS), and sea wrack-associated microflora (SWA) were explored for biogas production. The average biogas produced were 2172±156 mL (MS), 1223±308 mL (SWA) and 551±126 mL (CM). Though methane potential (396.9 mL(CH4) g(-1) volatile solid) computed from sea wrack proximate values was comparable to other feedstocks, highest methane yield was low (MS=94.33 mL(CH4) g(-1) VS). Among the microbial seeds, MS proved the best microbial source in utilizing sea wrack biomass and seawater. However, salinity (MS=42‰) observed exceeded average seawater salinity (34‰). Hence, methanogenic activity could have been inhibited. This is the first report on sea wrack biomass utilization for thalassic biogas production.

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The status of the cell-wall polysaccharide of the red seaweed, Gracilaria eucheumatoides upon postharvest storage was assessed in this study. The yield, chemical composition, physical and textural properties of alkali-treated agar extract was determined at different time intervals within 31 months of storage at dried state after harvest. Minimal fluctuation in agar yield was observed, ranging from 22.9% to 29.0%. The gel strength of agar extracts averaged 318gcm(-2) until the third month of storage but decreased considerably thereafter. The relative viscosity and molecular weight of the extracts varied inversely with storage time. Results indicated that both physical and textural parameters of agar generally decreased with storage time, likely due to depolymerization as indicated by decrease in molecular weight. Agar extracted from seaweeds up to 3 months of storage could be considered to exhibit gel quality suitable for food applications. Prolonged storage of the seaweed harvest is not recommended.

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Intensive fish farming is an emerging coastal activity that can potentially enhance sedimentation and promote eutrophication in fringing coral reefs. Here, we investigate the effect of fish farm effluent on the juvenile survivorship of the reef-building coral Seriatopora caliendrum. One-month old juvenile corals (on terracotta tiles) were deployed in fish farm and reference (reef) sites in Bolinao, the Philippines at a depth of 2m. After forty days, no survivor was recovered in the fish farm, while survivorship was low (11%) in the reference site, with the survivors' growth rate at 3.3polypsmo(-1) or 1.3mm(2)mo(-1). The fish farm deployed tiles were covered with muddy sediment and were colonized by barnacles, whereas those in the reference site were overgrown by a short stand of filamentous macroalgae. Environmental monitoring revealed higher nutrient levels (ammonia and phosphate), sedimentation rate, and organic matter flux, as well as diminished water transparency and dissolved oxygen levels in the fish farm compared to the reference site. Hence, intensive fish farming offers a suite of physical, chemical and biological modifications of the coastal marine environment which have a detrimental effect on the survivorship of coral juveniles.

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The action of k-carrageenan gel to sequester paralytic shellfish poison (PSP) was tested and characterized. When an extract from a Philippine strain of Pyrodinium bahamense var. compressum was used as PSP solution, the PSP-sequestering property of kappa-carrageenan gel was found to be dependent on gel surface area, interaction time, and polysaccharide concentration. The interaction was also found to be affected by high concentrations of monovalent cations. The characteristics of kappa-carrageenan as a PSP-sequestering agent all point to cation exchange as its mechanism of action. It is also proposed that the polysaccharide gel can be utilized as an agent to alleviate PSP intoxication.