Hiroshi Kubota

Bio: Hiroshi Kubota is an academic researcher from Shizuoka University. The author has contributed to research in topics: Decomposition & Coalescence (physics). The author has an hindex of 6, co-authored 7 publications receiving 161 citations.

Bubbles generated from porous plate in pure liquid and in aqueous solutions of inorganic electrolytes

Abstract: The average diameter, d, of bubbles generated from a porous plate in pure liquid and in aqueous solutions of inorganic electrolyte were measured at various gas flow rates by taking photographs of bubbles the size of which was controlled by bubble coalescence on and above the plate. For the extreme case when coalescence occurred at the maximum rate such as in water and in pure organic liquid, the empirical equations for d based on previous data and those from this experiment are proposed. The addition of inorganic electrolyte to water reduced the coalescence and thus simultaneously reduced d. The average bubble diameter in the aqueous solutions is well correlated to the experimental conditions with an empirical equation including the non-dimensional group proposed by Marrucci and also corresponding to the controlling factor of the bubble coalescence.

Moisture Relationships in Composting Processes

Abstract: Moisture is a key environmental factor that affects many aspects of the composting process. Biodegradation kinetics are affected by moisture through changes in oxygen diffusion, water potential and water activity, and microbial growth rates. These relationships are made more complex by the dynamic nature of the composting process, with changes in particle size and structure occurring over time. A deductive model of the effects of moisture on composting kinetics has defined these relationships based on fundamental physical properties and biological mechanisms. This study applies this model to experimental data from a manure and papermill sludge composting system. The results demonstrate that the optimum moisture content for biodegradation can vary widely for different compost mixtures and times in the composting process, ranging from near 50 to over 70% on a wet basis. While there is a significant reduction in biodegradation rate when operating outside the optimum range, the results also suggest opportunities to mitigate this effect through manipulation of substrate density and particle size. This framework for engineering analysis demonstrates the importance and challenges of maintaining optimum moisture content in dynamic composting systems, where biological drying, metabolic water production, and changes in compaction and porosity are all occurring over time.

A Quantitative Respirometric Method for Monitoring Compost Stability

Abstract: Compost stability was quantified using dissolved oxygen (D. O.) respirometry during composting of municipal solid waste (MSW) in a pilot-scale system. Changes in stability of samples taken at various times during the composting process were verified with chemical and physical tests. Rates of change of oxygen level in air over a compost sample incubated in a flask at 37°C were converted to a rate of O2 uptake/(g volatile solids · hour). Oxygen uptake, determined with D. O. respirometry and converted to rates of dry matter loss, was correlated with actual rates, calculated from energy balances observed in the pilot-scale system. The method can be used either as a simple quality control measure or in a more complex way to calculate rates so that efficiency within or among composting facilities can be compared.