A duckweed, Wolffia arrhiza, was examined for its potential use as a feedstock for ethanol production. The starch contents of its turions, the plant’s dormant form, were 43%, whereas that of vegetative frond as the growth form was 13%. The ethanol yield from turions was 0.28 g－ethanol·g－biomass^－1 in the simultaneous saccharification and fermentation mode (SSF) using a commercially available cellulase for enzymatic hydrolysis after alkaline / oxidative pretreatment. Ethanol was produced efficiently from starch-rich turions of W. arrhiza, in SSF using the amylase mixture with a comparable yield of 0.25 g－ethanol·g－biomass^－1. Ethanol was produced from the vegetative fronds at the yield of 0.16 g－ethanol·g－biomass^－1 in the SSF mode using cellulase, although that with the amylase mixture was only 0.07 g－ethanol/g－biomass. These results suggest that W. arrhiza, especially its turions, presents considerably high potential for use as an ethanol production feedstock.

View full abstract

It is expected that the hybrid water treatment system, which is combined with pre-coagulation/sedimentation and biological oxidation, can save energy and give some good effects because much particulate organic matter is removed by pre-coagulation/sedimentation. Remained organic matter is treated by aerobic biological filtration. During over 2 years operation of hybrid system of Jet Mixed Separator and Aerobic Moving Bed Biofilter （MBB） which was a kind of down-flow packed bed aerobic biofilter, it was found that MBB could remove organic matter from wastewater within only one hour and had been operated continuously without clogging of filter bed. In this paper, by investigating oxygen consumption of organic matter in water and oxygen uptake rate of biofilm, it was demonstrated that very rapid clarification of water was due to transfer of organic matter from water to biofilm. It was suggested that the balanced fluctuation of organic matter upon/within biofilm could cause stable and continuous treatment of MBB.

View full abstract

Aging of night soil treatment facilities and variation of accepted amounts of night soil are considered to be the factors that affect deterioration of treatment efficiency, but the actual states have not yet been made clear. If their states are surveyed and the effects on utilities are analyzed, it will become possible to operate and maintain such facilities in an efficient and planned manner. In this paper, factors affecting the deterioration of treatment efficiency have been examined from the viewpoint of facility aging and variation of accepted amounts of night soil, based on our previous survey results on the maintenance of night soil treatment facilities employing the biological denitrification method. For consumption of electricity, this study confirmed a trend that unit consumption rate increases with age of a facility, reduction in the accepted amount of night soil, and/or reduction in the accepted contamination load, from which we were able to obtain an indicator for efficiency deterioration. For consumption of fuel, this study confirmed a trend that unit consumption rate increases with reduction in the accepted amount of night soil and/or reduction in the accepted contamination load. For consumption of chemicals, the effect varies with the kind of chemicals; the results suggest the possibility that unit cost of chemicals may be reduced with age.

View full abstract