Hirokazu Takanashi

Back extraction of lactic acid with microporous hollow fiber membrane

In this work, back extraction was considered a promising alternative to regenerate carboxylic acids of low-volatility into appropriate aqueous solution from organic phase. Identification of an efficient back extraction system for lactic acid recovery was focused on. Screening of back extraction reagents was first carried out by employing a wide variety of inorganic compounds. From the viewpoints of high stripping power, low cost and capability of simultaneously regenerating the extractant, aqueous sodium chloride solution was selected as the most suitable one for recovery of lactic acid from lactate–TOMAC (tri-n-octylmethylammonium chloride) complex. However, TOMAC and oleyl alcohol are likely to pose the troubling emulsion problem in conventional mixer–settler system. Therefore, non-dispersive back extraction of lactic acid from organic phase was attempted in a microporous hollow fiber (MHF) membrane device by aqueous NaCl solution. A satisfactory recovery was accomplished, signifying the great potential of integrating membrane back extraction with extractive fermentation process for lactic acid production.

Method for measuring mutagen formation potential (MFP) on chlorination as a new water quality index

A novel water quality index, the mutagen formation potential (MFP) is proposed for use in evaluation of the quality of drinking water which may contain pollutants capable of forming mutagens when chlorinated under the conditions used in water purification processes. A method for measuring MFP was established as follows. The water sample to be tested is diluted until the TOC reaches 3-4 mg l-1, the pH is adjusted to 7.0 +/- 0.2, sodium hypochlorite is added to obtain conditions where Cl/TOC = 3-4 mg Cl (mg C)-1, and the water sample is left standing for 24 +/- 2 h at room temperature. Thereafter, 21 of the chlorinated water sample at pH 2.0 +/- 0.1 is passed through a Sep-Pak Plus CSP-800 cartridge to adsorb any mutagens formed, and DMSO is applied to the cartridge to desorb the mutagens. Then, a 2 ml sample of the eluate is collected after the DMSO had begun to flow out of the cartridge and evaluated by the Ames Salmonella mutagenicity assay (preincubation method).

Statistical procedures for estimating the detection limit and determination limit of the Ames Salmonella mutagenicity assay

Novel and flexible procedures for estimating the detection limit as well as the determination limit of the Ames mutagenicity assay were proposed to evaluate the genetoxicity of a water sample. The accumulated data under the test conditions of TA 100-S9 by our group were taken as examples and analyzed to estimate the detection limit and the determination limit. The detection limit was estimated at 1.7 as the MR value when duplicate plates were used in the negative control test. However, it decreased to 1.4 as the MR level when quadruple plates were used in the negative control test. Therefore it was found that the sensitivity of the Ames mutagenicity assay was improved very easily by increasing the number of plates for the negative control test from two to four. The application of the conventional twofold rule to the data obtained with the strain TA100 was considered too conservative. The determination limit was regarded at 2.2 as the MR value under the following conditions: (a) quadruple plates were used in the negative control test; (b) three dose-steps including negative control step were designed at regular intervals; and (c) duplicate plates were used for each dose-step. It was proved by comparing data of two students that the detection limit and the determination limit estimated in this study were considered acceptable to any well trained students.

Analysis of acclimation behavior against nitrification inhibitors in activated sludge processes

The acclimation behavior of activated sludge against nitrification inhibitors was explored by continuously adding thiourea and/or aniline to unacclimated sludge. Thiourea, which is difficult to biodegrade, severely inhibited the ammonia oxidation step, whereas aniline inhibited both the ammonia and nitrite oxidation steps and its biodegradation by nitrifying sludge was possible after a short acclimation period. Since thiourea-acclimated sludge showed higher tolerance than unacclimated sludge, the recovery of complete nitrification after being in contact with thiourea over a long period was attributed not only to the acquisition of biodegrading ability but also to the tolerance acquired by the sludge. Once both biodegrading ability and tolerance were acquired, they remained even after stopping the addition of thiourea for several weeks. In contrast, aniline-acclimated sludge was suspected to acquire only biodegrading ability.

KINETICS OF LACTIC ACID EXTRACTION WITH QUATERNARY AMMONIUM SALT

Extraction and stripping kinetics of lactic acid in extractive fermentation were studied using tri-n-octylmethylammonium chloride, a quaternary ammonium salt, as an extractant and oleyl alcohol as a diluent. The kinetic analysis was performed through simulated time course studies of lactate concentration in both the extraction and stripping phases. Dependences of extraction rate on initial lactate and extractant concentrations and those of stripping rate on initial chloride and extractant-lactate complex concentrations were examined. Because diffusion through the organic film was a rate-controlling step, the experimental results of both extraction and stripping could be explained well by a simple equation.