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Articles by Hideki Aoyagi
Total Records ( 3 ) for Hideki Aoyagi
  Charles Ogugua Nwuche , Hideki Aoyagi and James Chukwuma Ogbonna
  Palm Oil Mill Effluent (POME) cause serious pollutions of soil, water and environment but could be exploited as substrate for microbial citric acid production because of its rich mineral and high carbohydrate contents. Therefore in this study, Aspergillus niger ATCC 9642 was grown in the different concentrations (25, 50, 75 and 100%) of cellulase-digested POME for 7 days. Result showed that citric acid was highest (0.78±0.02 g L-1) in the 75% POME but lower (0.32±0.04 g L-1) in the undiluted POME. When supplemented with methanol (3%), citric acid production increased (1.02±0.03 g L-1) only in the 100% POME. Citric acid was not detected in the 25% and the non-digested POME. Biomass measurement showed that the 100% POME gave the highest (10.2±0.6 g L-1) mycelial weight among the digested treatments. As the dilution increased, the biomass concentration decreased proportionally. Biosolids from the non-digested POME supplemented with glucose (1%) weighed 13.4±0.15 g L-1. The Chemical Oxygen Demand (COD) of the digested POME (100%) dropped by 47.4% but the presence of methanol did not significantly affect the COD kinetics. However, at higher POME dilutions, COD reduction rate was greater than 63% but in the non-digested batches, COD reduction was negligible. The sugar utilization patterns showed that glucose was completely used up in the different POME dilutions except the undigested and glucose (1%) supplemented batches which had 75 and 40% sugar uptake, respectively. The use of POME hydrolysates as substrate could lower the present cost of citric acid as well as save treatment costs and help solve environmental problems.
  Charles U. Ugwu and Hideki Aoyagi
  Mixing is of paramount importance to microalgal cultures. There are various methods of inducing mixing in microalgal cultures; however, the type of mixing to be adopted would depend on various factors such as, the type of microalgal strain, type of culture system (i.e., open ponds or photobioreactors), scale of culture systems (i.e., small or large-scale cultures), as well as, on the environment where the culture is operated (i.e., indoor or outdoor type). In any case, mixing is mainly done to improve the mass transfer efficiency in the culture broth and to maintain efficient distribution of gases (air, oxygen, carbon dioxide, etc.) and nutrients. Furthermore, efficient mixing would improve the light utilization by the microalgal cells and thus, enhance biomass productivities. It is therefore, important to implement efficient mixing to maximize the potentials of microalgae during cultivation. This paper reviews some strategies to achieve mixing in microalgal culture systems, with more emphasis on photobioreactor designs, operation and applications.
  Charles O. Nwuche , Hideki Aoyagi and James C. Ogbonna
  An integrated treatment and valorization of Palm Oil Mill Effluent (POME) by Aspergillus terreus IMI 282743 immobilized on Luffa sponge was investigated. Effects of POME concentrations and nitrogen supplementation on Chemical Oxygen Demand (COD) reduction, microbial lipase and biomass production were evaluated in batch cultures. A 50% POME promoted the highest lipolytic activities in both immobilized and free cell cultures. In the former, the maximum lipase activity was 5.14 U mL-1 but in the non-immobilized batch, it was only 2.10 U mL-1. Lipase activities were low in the 25 and 100% POME due to overdilution and presence of inhibitory compounds, respectively. The pH was unchanged in the 100% POME but in other cultures, there were significant increase in the pH values. The pH of the 75% POME increased after a 48 h lag but in the 25 and 50% POME, the pH rose from 4-6.43 within a period of 96 h. COD did not change in the 100% POME but in the 75% POME, a 60.7% reduction was achieved. The COD of both the 50 and 25% POME decreased by 45% respectively. The immobilized biomass concentration was highest in the 75% POME (0.83 g L-1) but in the 25 and 100% POME, it was 0.27 and 0.63 g L-1, respectively. Supplementation of the 50% POME with a mixture of ammonium sulphate and yeast extract increased lipase production to10.6 U mL-1, biomass concentration to 3.7 g L-1 while the COD decreased by 80%. Lipase production from POME could be economically competitive to present industrial processes and provides additional incentive of treatment that is cheap and sustainable.
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