Koichiro Yamakawa

Analysis of Pellet Formation of Aspergillus niger Based on Shear Stress

Abstract A theoretical discussion on pellet formation of Aspergillus niger based on shear rate or average velocity gradient (G value) was made for both cases of a reactor with paddle and a rotationally shaken flask. The average diameter of pellets (d) and the number of pellets formed per unit volume (n) are linearly related to the G value below 400 1/s on a logarithmic plot, and a regression equation, n=(1.37 × 10−5) · d−3.25, was obtained regardless of the agitation and inoculation conditions. Under non-turbulent agitation conditions, the average number of spores forming a single pellet was found to be approximately proportional to the two-thirds power of the concentration of the spore inoculated. These exponents are very close to the theoretical one. Consequently it is concluded that G value is a representative index for the evaluation of pellet formation capability, verifying the validity of the proposed theory.

Substrate permeability in pellets formed by Aspergillus niger

Experimental investigations were carried out in order to evaluate the substrate permeability of starch and its microbial metabolites, using the pellets of Aspergillus niger formed by 5-d culture. The distribution coefficients were almost constant irrespective of the initial total organic carbon (TOC) concentration, but decreased slightly with increase in the pellet diameter. This trend was negligible for substrates other than soluble starch and their average distribution coefficients were almost unity. The apparent intra-pellet diffusion coefficients of these substrates and oxygen increased with increase in the pellet diameter, and were almost identical for the same diameter of pellet regardless of the substrate. It was suggested that mass transfer flow rate of substrate appeared to be higher because of a sparser structure and a lower density with larger diameter of pellets formed by 5-d culture.

Effect of Fuzzy Control on Influent Variations in a Pilot-Scale Activated Sludge Process

Abstract A novel control system for activated sludge process using fuzzy reasoning was proposed for the effective control and maintenance. This is composed of “fuzzy instrumental control system” on the information from the instrumental measurements and “fuzzy diagnosis system” on that of the observation and judgement of operators, on-site measurements and microscopic observation. In this paper, effect of this proposed and developed system on the influent variations was examined, using a pilot-scale activated sludge treatment plant. As a result, fuzzy instrumental control and diagnosis systems were confirmed to be very effective on various influent variations and unmeasurable operational problems, respectively.

Starch Wastewater Treatment Using Pellets Formed by Fungi

Aspergillus nigerの自己造粒pelletを用いたデンプン廃水処理の可能性を検討するため, 各種の回分培養実験および連続培養実験を行った結果, 以下の知見を得た。1) pellet化したA.nigerでデンプン廃水を処理した場合, 良好なデンプン分解能およびTOC除去能を持つことを示した。2) 回分培養実験により, デンプンの2段階分解における, 各段階の至適pHを示した。3) 連続培養期間中, pelletは, 曝気等の撹拌により形状が崩れることなく, 十分な強度が確認され, その径は徐々に大きく成長した。4) 2段反応槽による連続培養から, デンプン分解率90%以上, TOC除去率75%という結果が得られた。