Tatsuki Toda

Maximum organic loading rate for the single-stage wet anaerobic digestion of food waste.

Anaerobic digestion of food waste was conducted at high OLR from 3.7 to 12.9 kg-VS m(-3) day(-1) for 225 days. Periods without organic loading were arranged between the each loading period. Stable operation at an OLR of 9.2 kg-VS (15.0 kg-COD) m(-3) day(-1) was achieved with a high VS reduction (91.8%) and high methane yield (455 mL g-VS-1). The cell density increased in the periods without organic loading, and reached to 10.9×10(10) cells mL(-1) on day 187, which was around 15 times higher than that of the seed sludge. There was a significant correlation between OLR and saturated TSS in the sludge (y=17.3e(0.1679×), r(2)=0.996, P<0.05). A theoretical maximum OLR of 10.5 kg-VS (17.0 kg-COD) m(-3) day(-1) was obtained for mesophilic single-stage wet anaerobic digestion that is able to maintain a stable operation with high methane yield and VS reduction.

Effect of temperature on VFA’s and biogas production in anaerobic solubilization of food waste

The effectiveness of methane fermentation treatment used in food waste processing is currently limited by solubilization and acidogenesis. In efforts to improve the treatment process, this study examined the effects of temperature on solubilization and acidogenesis. The solubilization rate of food waste, which was based on suspended solid removal, was 47.5%, 62.2%, 70.0%, 72.7%, 56.1% and 45.9% at 15 degrees C, 25 degrees C, 35 degrees C, 45 degrees C, 55 degrees C and 65 degrees C, respectively. Solubilization rate was accelerated from the middle to late experimental periods under mesophilic (35 degrees C and 45 degrees C) conditions. In contrast, overall solubilization rate was significantly lower under thermophilic (55 degrees C and 65 degrees C) conditions than under mesophilic conditions, although solubilization occurred rapidly in the early experimental period. The production of biogas was high under mesophilic conditions of 35 degrees C and 45 degrees C, at 64.7 and 62.7mL/g-VS, respectively, while it was scarce under thermophilic conditions. Solubilization of food waste was accelerated under both mesophilic and thermophilic conditions; however, solubilization rate was observed to be particularly high under mesophilic conditions, and a shortening of the hydraulic retention time is expected under thermophilic conditions.

The effect of the labile organic fraction in food waste and the substrate/inoculum ratio on anaerobic digestion for a reliable methane yield.

Influence of the labile organic fraction (LOF) on anaerobic digestion of food waste was investigated in different S/I ratio of 0.33, 0.5, 1.0, 2.0 and 4.0g-VSsubstrate/g-VSinoculum. Two types of substrate, standard food waste (Substrate 1) and standard food waste with the supernatant (containing LOF) removed (Substrate 2) were used. Highest methane yield of 435ml-CH4g-VS(-1) in Substrate 1 was observed in the lowest S/I ratio, while the methane yield of the other S/I ratios were 38-73% lower than the highest yield due to acidification. The methane yields in Substrate 2 were relatively stable in all S/I conditions, although the maximum methane yield was low compared with Substrate 1. These results showed that LOF in food waste causes acidification, but also contributes to high methane yields, suggesting that low S/I ratio (<0.33) is required to obtain a reliable methane yield from food waste compared to other organic substrates.

High Ash Content in Net-Plankton Samples from Shallow Coastal Water: Possible Source of Error in Dry Weight Measurement of Zooplankton Biomass

Annual examination of net-plankton biomass in dry weight, ash-free dry weight, organic carbon, and nitrogen weight at the Manazuru harbor, central Japan revealed that net-plankton samples from shallow coastal water contained considerable amount of ash (53±13% of dry weight) which would be caused by contamination of inorganic materials from re-suspendion of sediments, terrestrial runoff and chain-forming diatoms. Therefore, in coastal water, dry weight is inadequate fro determination of zooplankton biomass in volving the possibility of over-estimation. Practical estimation of net-plankton biomass in shallow coastal waters, ash-free dry weight, organic carbon, and/or nitrogen are more adequate.

Variability in the Relative Penetration of Ultraviolet Radiation to Photosynthetically Available Radiation in Temperate Coastal Waters, Japan

UVR and PAR wavelengths are attenuated to different extents within the water column, causing variations in spectral composition with depth. The present investigation (a) describes the variability of UVR and PAR penetration at a station in the temperate coastal waters of Sagami Bay and determines (b) the characteristics of relative UVR penetration to the euphotic zone. Examination of the seasonal irradiance profile measurements indicated eight measurements displaying two distinct attenuation coefficients (Kd) for specific UVR wavelengths and PAR. The two attenuation coefficients observed from specific wavelengths in the water column may be caused not only by chlorophyll pigments, but also by dissolved organic material in the upper layer. The 1% depth of surface UVR at 305, 320, 340, and 380 nm averaged 10.8 ± 5.7, 14.9 ± 9.5, 19.8 ± 12.1, and 30.4 ± 17.6 m, respectively. The depth of euphotic layer displayed less variability averaging 62 ± 15 m throughout the entire study. Relative UVR penetration within the euphotic zone averaged 17.8 ± 8.1, 22.9 ± 10, 30.5 ± 13.8, and 46 ± 46.9% for 305, 320, 340, and 380 nm, respectively. A large variation of the relative transmission of UVR within the euphotic zone was found although the spectral composition was relatively stable in the air throughout the study.

Variability of Bio-optical Factors Influencing the Seasonal Attenuation of Ultraviolet Radiation in Temperate Coastal Waters of Japan¶

Abstract The study identifies the relative contribution of various bio-optical factors to the total attenuation of ultraviolet radiation (UVR) wavelengths and photosynthetically active radiation (PAR) in temperate coastal waters of Japan by surveying the physical properties of the water column, UVR and PAR penetration, and the absorption characteristics of dissolved and particulate material. Spectral absorbance properties of pigment (aph), detritus (ad) and chromophoric dissolved organic material (aCDOM) displayed both seasonal and wavelength specific variability. On an annual basis, absorbance by aCDOM was the highest absorbing fraction (47–59%) for the UVR wavelengths measured (305, 320, 340 and 380 nm) but decreased (32%) at 450 nm. Contribution of pigments to total absorbance was highest (40–60%) during a spring bloom for both UVR and PAR. A large variability (C.V. > 42%) for annual average attenuation coefficients (Kd[λ]) at respective wavelengths observed suggests that the spectral composition of the water column changes throughout the year in this region. A significant relationship was observed between Kd(λ) and aCDOM at 305, 320, 340 and 380 nm only (P < 0.01) but not for 450 nm (PAR) indicating the role of CDOM in regulating variations in Kd(λ), particularly in the UVR range. The slope S, obtained from a natural-log plot of the absorption coefficient of CDOM against wavelength, ranged between 0.014 and 0.036 nm−1 annually (average = 0.020±0.007, C.V. = 35%) and suggests seasonal changes in the origin of CDOM between terrestrial (low S) and biogenous (high S) CDOM.

Seasonal variation in chemical properties and degradability by anaerobic digestion of landfill leachate at Benowo in Surabaya, Indonesia.

Seasonal variations in the physical and chemical characteristics of leachate taken from Benowo landfill in Indonesia, including factors likely to inhibit anaerobic digestion, were investigated to determine the impacts on the stability of anaerobic treatment. To evaluate the biodegradability of the leachate, a continuous experiment was conducted by changing the organic loading rate (OLR). Chemical oxygen demand (COD) ranged between 2621 and 16,832 mg L(-1), and COD in the dry season was twice the level in the rainy season owing to reduced rainwater input and significant evaporation. COD, pH, and the concentrations of ammonium ion, and metals in the leachate were within acceptable ranges for decomposition by anaerobic digestion. However, the Na(+) and Cl(-) in the leachate are high enough to inhibit anaerobic digestion. From chemical investigation of leachate at six monitoring wells in Benowo, food waste accumulation and seawater intrusion might cause high salinity in the leachate. In the continuous experiment, COD removal efficiency was maintained at 40% regardless of OLR, suggesting that at least 40% of the leachate contained biodegradable substances. Based on these results, issues surrounding the biological treatment of saline and refractory substances in landfill leachate were discussed. It is suggested that high salinity and refractory substances in the leachate are common issues during the leachate treatment by anaerobic digestion as the implications for similar landfills in other countries around the world.

Estimation of optimum specific light intensity per cell on a high-cell-density continuous culture of Chlorella zofingiensis not limited by nutrients or CO2

To determine the optimum light intensity per cell required for rapid growth regardless of cell density, continuous cultures of the microalga Chlorella zofingiensis were grown with a sufficient supply of nutrients and CO2 and were subjected to different light intensities in the range of 75-1000 μE m(-2) s(-1). The cell density of culture increased over time for all light conditions except for the early stage of the high light condition of 1000 μE m(-2) s(-1). The light intensity per cell required for the high specific growth rate of 0.5 day(-1) was determined to be 28-45 μE g-ds(-1) s(-1). The specific growth rate was significantly correlated to light intensity (y=0.721×x/(66.98+x), r(2)=0.85, p<0.05). A high specific growth rate was maintained over a range of light intensities (250-1000 μE m(-2) s(-1)). This range of light intensities suggested that effective production of C. zofingiensis can be maintained outdoors under strong light by using the optimum specific light intensity.

Direct observations of a dense occurrence of Bolinopsis infundibulum (Ctenophora) near the seafloor under the Oyashio and notes on their feeding behavior

A dense occurrence of the ctenophore Bolinopsis infundibulum was observed at depths of approx. 1250 m from the manned submersible SHINKAI 2000 from 1998 to 2000 near the seafloor off Kushiro, Hokkaido, Japan. Body length ranged from 6.5 to 16.5 cm for seven specimens sampled from the submersible. Horizontal transects by the submersible showed that B. infundibulum were scarce shallower than 1000 m, but were abundant within 30 m of the bottom, ca. 0.8 ctenophore m � 3 , then decreasing gradually to 80 m above the seafloor. The ctenophores forage with extended oral lobes and hanging quiescently in the water column. Ninety ctenophores among 112 observed at 1200–1270-m depth were in the foraging posture. One individual captured at depth had a female C5 stage of Neocalanus cristatus and fragments of calanoids (? Aetideidae) in its gut. Carbon and nitrogen stable isotope ratio data indicated that the B. infundibulum relied on surface photosynthetic products for food and their position in the trophic pyramid is relatively low. B. infundibulum feeds mainly on copepods, at least some part of which consist of carbon-rich copepods such as Neocalanus spp. and Eucalanus bungii, which grow in surface layers but sink to depth when diapausing as C5 or adult stages. Carbon-based estimations showed that one Neocalanus cristatus C5 or 4–6 N. plumchrus+flemingeri C5+female are sufficient for daily maintenance of a medium-sized (B10 cm) B. infundibulum. Considering the abundance of B. infundibulum, we conclude that this deep ctenophore population may contribute substantially to the mortality of these epipelagic copepods during diapause. r 2003 Elsevier Science Ltd. All rights reserved.

Changes in Bacterial Communities Accompanied by Aggregation in a Fed-Batch Composting Reactor

The contents of fed-batch composting (FBC) reactors often aggregate after prolonged operation. This process leads to irreversible breakdown of the decomposition reaction and possible alteration of the bacterial communities. We compared the structures of bacterial communities in reactors under aggregate and optimal conditions. The results of 16S rRNA gene clone analysis showed that populations of the family Bacillaceae (such as Bacillus spp., Cerasibacillus spp., Gracilibacillus spp.), which dominate (98%) under optimal condition, were significantly decreased under aggregate condition. In contrast, populations of the family Staphylococcaceae considerably increased after aggregation and accounted for 53% of the total. Phylogenetic analysis also showed that anaerobes or facultative anaerobes related to Tetragenococcus halophilus, Atopostipes suicloacalis, Jeotgalicoccus pinnipedialis, and Staphylococcus spp. were dominant in the aggregates. These results suggested that aerobic Gram-positive bacteria mainly contributed to organic degradation and that aggregation created some anaerobic environment, which promoted the growth of bacterial communities usually not found in well-functioning FBC reactors.