Hiroaki I. Ogawa

Degradation of volatile fatty acids in highly efficient anaerobic digestion

To improve the efficiency of anaerobic digestion, we examined the effects of C2–C6 volatile fatty acids (VFAs) on methane fermentation, as well as the behavior of VFAs in anaerobic digestion. The VFA concentrations and methane production in anaerobic digestion were increased by pretreatment of waste activated sludge (WAS), such as ultrasonic disintegration, thermal and freezing treatments. The major intermediate products of anaerobic digestion for untreated and pretreated WAS, such as acetate, propionate, isobutyrate, butyrate, isovalerate, valerate, isocaproate and caproate, were used as substrates and the anaerobic degradation of these was carried out under the same conditions. It was found that decomposition rates of the VFAs (C2–C6) with a straight chain (normal form) were greater than those of their respective isomers with a branched chain (iso form). It was shown that the decomposition rates of the iso and normal forms of butyrate were greater than those of valerate and caproate. This was caused by the isomerization between butyrate and isobutyrate which occurred during the digestion process. Anaerobic bacteria in digested sludge converted butyrate to isobutyrate and vice versa by migration of the carboxyl group to the adjacent carbon atom. In addition, inhibition of degradation of the VFAs by acetate in a digester was also examined.

Upgrading of anaerobic digestion of waste activated sludge by ultrasonic pretreatment

To enhance the efficiency of anaerobic digestion, we examined the effects of ultrasonic pretreatment on the solubilization of waste activated sludge (WAS) and on methane generation. Organic substances in WAS were solubilized by ultrasonic pretreatment. In the digestion with WAS pretreated by ultrasonic pretreatment for 30 min, the total quantity of generated methane increased by 64%, as compared with experimental control (non-treatment). In addition, the relationships between methane generation and concentrations of soluble protein, carbohydrate and volatile fatty acid (VFA) were also examined.

Purification and characterization of a lipase from Pseudomonas aeruginosa KKA-5 and its role in castor oil hydrolysis

An extracellular lipase (triacylglycerol acylhydrolase, EC 3.1.1.3) from Pseudomonas aeruginosa KKA-5 hydrolyzed castor oil by 90%. Purification of this castor oil-hydrolyzing lipase included ammonium sulfate precipitation and successive hydroxylapatite column chromatography. The enzyme was purified 518-fold. It was homogeneous electrophoretically and its molecular weight was estimated to be 30 kDa. The enzyme was stable up to 45°C and retained its activity in the alkaline pH range. Lipase was highly stable in the presence of aqueous organic solvents like methanol and ethanol. It was weakly inhibited in the presence of acetone. The anionic surfactant, sodium dodecyl sulfate, was inhibitory while the cationic surfactants, Triton X-100 and Tween-80 appreciably enhanced activity. Lipase was stabilized significantly by Ca2+. Inactivation of the enzyme by EDTA was overcome by sequential CaCl2 treatment. This finding suggests the existence of a calcium-binding site in Pseudomonas aeruginosa KKA-5 lipase.

Isolation, identification of sludge-lysing strain and its utilization in thermophilic aerobic digestion for waste activated sludge

A strain of sludge-lysing bacteria was isolated from waste activated sludge (WAS) in this study. The result of 16S rRNA gene analysis demonstrated that it was a species of new genus Brevibacillus (named Brevibacillus sp. KH3). The strain could release the protease with molecule weight of about 40 kDa which could enhance the efficiency of sludge thermophilic aerobic digestion. During the sterilized sludge digestion experiment inoculated with Brevibacillus sp. KH3, the maximum protease activity was 0.41 U/ml at pH 8 and 50 degrees C, and maximum TSS removal ratio achieved 32.8% after 120 h digestion at pH 8 and 50 degrees C. In the case of un-sterilized sludge digestion inoculated with Brevibacillus sp. KH3, TSS removal ratio in inoculated-group was 54.8%, increasing at 11.86% compared with un-inoculation (46.2%). The result demonstrated that inoculation of Brevibacillus sp. KH3 could help to degrade the EPS and promote the collapse of cells and inhibit the growth of certain kinds of microorganisms. It indicated that Brevibacillus sp. KH3 strain had a high potential to enhance WAS-degradation efficiency in thermophilic aerobic digestion.

Delivery of Doxorubicin from Biodegradable PEG Hydrogels Having Schiff Base Linkages

In our quest to develop new drug delivery systems, we designed and synthesized PEG-conjugates and PEG-hydrogels with a degradable linkage to the drug. Specifically, methoxyPEG-doxorubicin (MPEG-CH=N-Doxo) and doxorubicin-PEG aldehyde (OHC-PEG-CH=N-Doxo) conjugates, plus poly (vinyl amine)-PEG-doxorubicin (PVAm-PEG-Doxo) hydrogels were prepared. The hydrogels were crosslinked by PEG-Schiff base linkages, and the Doxo was conjugated to the gel by pendant Schiff base bonds (PVAm-N=CH-PEG-CH=N-Doxo). The release profile of Doxo from the hydrogels was dependent on pH and on the ratio of PVAm to the PEG-dialdehyde crosslinker. These degradable PEG hydrogels could be good candidates for slow release of Doxo from subcutaneous or IM implants.

Suppression of growth of putrefactive and food poisoning bacteria by lactic acid fermentation of kitchen waste

Abstract In order to produce lactic acid, from kitchen waste, which is a raw material for biodegradable plastic production, it is necessary to store waste for some days in the system of kitchen waste collection and transportation through disposers and pipes. The changes of counts of viable cells in kitchen waste during storage were observed. In spite of seasonal variations, lactic acid bacteria (LAB) became preferential bacteria after the kitchen waste had been stored for 24 h. In contrast, coliforms and Clostridium spp . which are the indices of putrefaction and contamination decreased. Coliforms were not detected after 72 or 96 h storage. None of food poisoning bacteria, such as Staphylococcus aurens and Bacillus cereus , were detected after 24 h storage. The results of adding S. aureus to waste indicated that LAB also easily became preferential even if food poisoning bacteria gained predominance at the beginning of storage. This study clearly indicated that lactic acid fermentation during the storage process inhibits the growth of putrefactive bacteria and food poisoning bacteria, which as a result, enables the preservation and deodorization of the kitchen waste to be realized with ease.

Effects of anaerobic/aerobic incubation and storage temperature on preservation and deodorization of kitchen garbage

To develop a garbage recycling system for the purpose of the production of lactic acid (LA) to use as raw material for producing biodegradable plastics, the preservation and deodorization of garbage during storage are very important. Anaerobic incubation (i.e., storage) was prove to be more suitable than aerobic incubation during the garbage storage in terms of concentration of LA and soluble sugar, pH value, viable bacteria counts and offensive odour substances. This difference is due to a fact that the growth of putrefactive bacteria such as coliforms and Clostridium spp. appeared to be inhibited by anaerobic fermentation during the storage, because the fermentation caused a drop of garbage pH and generated inhibitory substances, i.e., bacteriocins. Under anaerobic condition, LA concentration in the stored garbage was found to be higher in the order: 37 > 25 > 50 > 5 degrees C, and the concentration of sugar accumulated during the 50 degrees C-storage was the highest. Among the conditions employed, the optimum condition for the storage of kitchen garbage was anaerobic at 5 degrees C.

Enhanced production of lactic acid with reducing excess sludge by lactate fermentation

The development of a facile technology for utilizing effectively and/or reducing excess sludge is one of the urgent problems since a large quantity of sewage sludge is formed by activated sludge processes. Excess sludge containing 50mM sucrose was fermented at 50 degrees C using endogenous bacteria in excess sludge, resulting in a high lactic acid production (8.45 g/L) and in an increased sludge reduction (38.2%). Conversion rate to lactic acid was up to 106.0% by standard fermentation at 50 degrees C compared to 43.8% at 30 degrees C and this phenomenon that conversion rate was higher was observed only at 50 degrees C as the fermentation at less or more than 50 degrees C had lower conversion rate than that at 50 degrees C. Lactic acid bacteria increased at 50 degrees C during 1-d fermentation whereas the number of total viable bacteria only increased slightly, indicating that lactic acid bacteria in sludge at 50 degrees C were preferentially able to utilize the sucrose for producing lactic acid. Finally, pH-vibration fermentation at 50 degrees C enabled to completely consume residual sucrose in the normal fermentation, resulting in the maximum production of lactic acid. Lactate fermentation by a purely cultured lactic acid bacterium TS1 with autoclaved excess sludge containing 50mM sucrose had more than 100% of conversion rate to lactic acid, indicating that a part of sludge was converted into lactic acid during the fermentation. Our technique is useful as a facile engineering for reducing excess sludge concomitantly with producing lactic acid by lactate fermentation.

RELATIONSHIP BETWEEN MUTAGENICITY AND REACTIVITY OR BIODEGRADABILITY FOR NITROAROMATIC COMPOUNDS

Although many studies have reported that nitroaromatics such as 2,4,6-trinitrotoluene (TNT) have strong mutagenicity, the mechanism of mutagenic activity in these compounds has not yet been reported. We examined the mutagenicity versus reactivity and biodegradation by bacteria using TNT and its analogs (1,3,5-trinitrobenzene [TNB], 2,4,6-trinitroaniline [TNA], 2,4,6-trinitro-phenol [TNP], N,2,4,6-tetranitro-N-methyl-aniline [tetryl], 2,4-dinitrotoluene [24DNT], and 2,6-dinitrotoluene [26DNT]). Aromatic compounds harboring three nitro groups (except TNP) have high mutagenicity, judging from the results of the umu test using luminescent bacteria (Salmonella typhimurium strain TA1535/pTL210). Single-electron reduction potentials for these chemicals were -530, -555, -565, -575, -640, -674, and -764 mV for TNA, tetyl, TNT, TNB, 24DNT, 26DNT, and TNP, respectively, indicating that trinitro-aromatics (except TNP) were more reducible than other compounds. Pseudomonas sp. strain TM15, which was isolated from TNT-contaminated soils in the Yamada Green Zone, Kitakyushu City, Japan, could efficiently biotransform TNT, TNB, TNA, and tetryl; 24DNT, 26DNT, and TNP were less biodegradable. This strain converted all TNT analogs into reduction products; nitro groups were reduced to amino groups. We revealed that the mutagenicity of nitroaromatics correlate with reactivity and biodegradability. This finding may contribute to the elucidation of mutagenic expression of nitroaromatic compounds in organisms.

Upflow biological filtration with floating filter media

An aerobic biological filter with floating filter media was tested using domestic wastewater to determine the optimum operating and backwashing parameters in this study. This system was designed for a small-scale joint treatment plant and 4 mm diameter polystyrene foam pellets were used as the filter media. As the backwash is the most important point for using a floating biofilter, “air shot” system, a turbulent-flow backwashing utilising the air reverse syphon and the buoyancy of the filter media, was developed for this purpose. Through the test, the optimum position of the diffuser tube and the structure of the backwashing device were determined. It was confirmed that the system could achieve effluent biological oxygen demand (BOD) of under 10 mg/l, and a nitrification rate of over 86% at a BOD loading of 0.7 kg/m3 per day and “total-nitrogen (T-N) loading” of 0.16 kg/m3 per day. The backwashing frequency should be as many times as possible per cycle to remove the sloughed sludge thoroughly in order to maintain good effluent quality after backwashing.