Masao Ukita

A model for membrane bioreactor process based on the concept of formation and degradation of soluble microbial products.

A mathematical model of soluble microbial products (SMPs) formation-degradation was established based on the activated sludge model no. 1 and was applied to the membrane bioreactor process with high concentration of activated sludge under intermittent aerobic operational condition. The simulation results were in good agreement with the experimental data which indicated that the coefficients used in the model could successfully describe the treatment performance. The most advantage of this modified model over the conventional one was that the significant importance of SMP existence was demonstrated and the model provided an reasonable comprehension for SMP concept. The present study demonstrated that SMPs contributed most to the organic matter in the effluent, and the results coincided well with the observations of many other researchers.

Start-up performances of dry anaerobic mesophilic and thermophilic digestions of organic solid wastes

Two dry anaerobic digestions of organic solid wastes were conducted for 6 weeks in a lab-scale batch experiment for investigating the start-up performances under mesophilic and thermophilic conditions. The enzymatic activities, i.e., beta-glucosidase, N-alpha-benzoyl-L-argininamide (BAA)-hydrolysing protease, urease and phosphatase activities were analysed. The BAA-hydrolysing protease activity during the first 2-3 weeks was low with low pH, but was enhanced later with the pH increase. beta-Glucosidase activity showed the lowest values in weeks 1-2, and recovered with the increase of BAA-hydrolysing protease activity. Acetic acid dominated most of the total VFAs in thermophilic digestion, while propionate and butyrate dominated in mesophilic digestion. Thermophilic digestion was confirmed more feasible for achieving better performance against misbalance, especially during the start-up period in a dry anaerobic digestion process.

Simulation of eutrophication and associated occurrence of hypoxic and anoxic condition in a coastal bay in Japan

A probabilistic method of calculating the occurrence of oxygen-depleted water within a combined hydrothermal and water quality model was presented in this paper to investigate the environmental impact of eutrophication on the living resources. The method was applied to an eutrophicated shallow coastal bay in western Japan, where the occurrence of red tides at the water surface and the onset of bottom hypoxic waters are observed every summer. Both meteorology and freshwater inflow contribute to the development of stratification of the bay, thus limiting the dissolved oxygen supply to bottom waters. The resulting hydrodynamics enhances the development of oxygen-depleted bottom waters by transporting organic matter produced by algal blooms to the inner bay, where it decomposes and exerts high SOD. During August, about 60% of the inner bay is hypoxic for prolonged durations and as a result most of the benthic biota and fish die. The method used here is a very useful and informative way to evaluate the spatial and temporal damage and severity caused by hypoxia on living resources. Moreover, the model results agreed very well with the observed hydrodynamics, thermal structure and water quality data of the stratified bay. The model can be used for other lakes and bays where knowledge of temperature and density stratification is important for assessing water quality.

A shallow-sea ecological model using an object-oriented programming language

Abstract The purpose of this study is to construct a model that can predict the impact on fisheries caused by coastal development activities. To accomplish this, many species of fish must be incorporated in the model, because each type of fish has a different value as a fishery resource and a different behavior for the same impact. In addition the effect of fish swimming must be considered because even when the total resource amount of fish does not change, fish may still disappear from the object area. These factors make the model structure complicated. Meanwhile, a new concept called ‘object oriented programming’ (OOP) is attracting the attention of modellers. In this paper, we have constructed a model called the ‘hallow-sea ecological model’ (SSEM), by using Smalltalk, which is representative of the OOP language. This showed that the fishing ground environment are expressed very flexibly and plainly by Smalltalk. Furthermore, we incorporated the effect of fish swimming by preference using a multicriteria analysis. The result of numerical experiments suggested that the effect of fish swimming by preference may be the essential factor for shallow-sea ecological modelling.

Effect of Enforced Aeration on In-Vessel Food Waste Composting

A laboratory composting was conducted to determine the effect of the continuously enforced aeration on the composting performance. The mixture of dog food, excess sludge, and woodchip was used as raw composting materials. The temperature changes in the decomposition process, and pH, weight loss, ash, and extract composition from the final product after 17 days composting were investigated. The results demonstrated that flow rate of enforced aeration indeed influenced the composting performance. Composting under 0.05-0.1 l min−1 condition seemed better than that under 0.2-0.4 l min−1 condition. Higher flow rate of air not only cooled the composting mixture significantly, further adversely affected temperature rise, but also evaporated moisture mostly. Thermophilic composting can occur under 0.05-–0.1 l min−1 air flow rate condition, while composting in cases of 0.2-0.4 l min−1 air flow rate mainly resulted in a mesophilic process. Microbial activity was considered to be significantly inhibited at 0.4 l min−1 air flow rate condition based on the analyses of total organic carbon and volatile fatty acids from water extraction of composting products.

A model of fish distribution in rivers according to their preference for environmental factors

Abstract We present a model of fish distribution according to the fish preference for environmental factors such as water temperature, cover, current velocity, turbidity, food amount, etc. This model can be used to estimate the influence of nearshore construction activity on fish. Our model has the good feature that the parameter values for the environmental preference and the weight values of the environmental factors can be determined separately. New environmental factors can be introduced without calibrating the preference parameters again. In our first experiment, two separate tanks with different environmental conditions are connected by a narrow junction. Fish can swim to the tank they prefer and their distribution is recorded by a video camera every minute for 50 min. The parameters are calibrated according to these observations. The second experiment uses a single tank where several environmental conditions are tested simultaneously. The observed fish distribution in the second experiment and the distribution calculated with the model show a good agreement. Finally, this model is included in the Shallow Sea Ecological Model (SSEM), and fish behavior in a virtual river is simulated to replicate fish distribution during a flood.

A model of fish preference and mortality under hypoxic water in the coastal environment.

Eutrophication and associated occurrence of hypoxic condition could cause significant damage to marine ecosystems, resulting in considerable economic losses to fisheries and aquaculture and is a major source of stress that fish often have to contend with in order to survive. This problem is likely to be exacerbated in the coming years, since the wastewater treatment facilities is unlikely to catch up with increasing human activities. Moreover, large-scale reclamation projects in coastal areas have recently been increased, and these activities certainly have adverse impacts on water quality and fisheries resources. Coastal construction has a significant role in the development of hypoxic water by changing the current and mixing pattern of water. Changes in species composition and decreases in species richness and diversity have been well documented in hypoxic systems. Hypoxia could cause endocrine disruption in fish and eliminate populations of sensitive species. Shallow coastal areas are of great importance for the special nursery of fish and shellfish and land reclamation in these areas cause strong damage to fisheries. Although the tolerance of aquatic life to hypoxia is known, there is no information about the mortality of fish caused by hypoxia because fish can swim around it and no modeling study has yet been carried out. Criteria that influence the movement of fish are: amounts of food, water temperature and depth, dissolved oxygen concentration and nature of seabed. However, among these, water temperature and dissolved oxygen are the most crucial parameters that affect survival, movement and growth of fish. In this paper, a model of fish preference and mortality for environmental conditions was developed and applied to the Hakata Bay where hypoxic water occurs every summer. For the purpose of this study, a field survey of fish behavior under hypoxic water was conducted by releasing marbled sale (Pleuronectes yokohamae) in the inner bay. Moreover, a series of preference tests for DO, salinity and temperature in the laboratory were conducted in order to decide preference parameters of fish. Using the results of both field and laboratory studies, a sub-module of fish preference and mortality was coded within an integrated hydrothermal and eutrophication model (CHEM) to predict the behavior and mortality of marbled sale when hypoxia would occur in the bay. The model could reasonably simulate the behavior of the fish under hypoxia. An assessment of the impact of the ongoing land reclamation project of about 401 ha in the Wajiro tidal flat zones at the head of the bay on the fisheries resources was also conducted using the model. The results showed that the artificial land lowered the mortality rate of fish under hypoxic condition in the bay during the summer period.

Simulation of fish behavior and mortality in hypoxic water in an enclosed bay

A model of fish preference for environmental conditions (dissolved oxygen (DO) and water temperature) and mortality was developed and coded within a combined hydrothermal and eutrophication model. The model was applied to an enclosed bay located in the western part of Japan, where eutrophication and associated onset of hypoxia at the bottom waters would occur in every summer. A field survey of fish behavior under hypoxic and non-hypoxic waters was conducted by releasing marbled sale in the bay and tracked its movement. At the same time, vertical profiles of DO, salinity and water temperature were measured at every 0.5m vertical interval at several locations along the tracking path of fish. Moreover, a series of preference tests for DO, salinity and temperature in the laboratory were conducted in order to decide preference parameters of fish. The model could simulate reasonably the observed behavior and movement of the fish under both hypoxic and non-hypoxic waters in the bay; thereby, validated its applicability. Using the model, an assessment of the impact of the ongoing land reclamation project of about 400 ha in the bay on the fisheries resources was also conducted. The results showed that a substantial mortality of the fisheries resources would take place when hypoxic condition occurs in every summer and the construction of the artificial land will lower the mortality rate of fish during the summer period in the bay. Strong offshore winds cause the upwelling of bottom hypoxic waters in summer and the initial mortality of the fisheries resources increase under northerly offshore wind of 5 m/s or more.

Compost Stability Assessment Using a Secondary Metabolite: Geosmin

Composting is a process involved not only in transformation of organic matter (OM), but also for transition of the microbial community. Microorganisms can directly provide important information on the stages and characteristics of composting. This paper was aimed at characterizing compost stability by a microbial secondary metabolite, geosmin, which is a volatile compound presenting an earthy smell. Since secondary metabolite production is dependent on the nutrient state of microorganisms, its production in association with physical and chemical parameters was monitored in the laboratory-scale and plant-scale composting processes. The results showed that the peaked geosmin liberation was consistent with stable state of composting indicated by the ambient temperature achieved, a slightly alkaline product and steady states of dissolved organic carbon (DOC), N and P contents and OM degradation in the laboratory-scale experiment. It was also in accordance with the stability identified by the facilities and CO2 respiration rate in the plant-scale composting. In addition, the production of geosmin was correlated with the C/N ratio for the solid sample. These results demonstrated that geosmin levels could be used as an index for the compost stability assessment in different composting processes with various organic solid wastes.

Study on the modelling of the behavior of phosphorus released from sediments

Abstract In order to realize long-term assessments of eutrophic water quality, the interaction between water and bottom sediments, and the ecological structures must be taken into consideration. The release of phosphate from sediments is markedly controlled by the oxidation-reduction potential (ORP) condition. Resulting from this complicated mechanism, satisfying models for phosphate regeneration have not yet been proposed. In this study, focusing on the exchange of nutrients between water and sediments, together with primary production of phytoplankton, the modelling for assessments of eutrophic water and sediment quality was investigated. This model was applied to a simplified core system, and consists of two layers of water and two layers of sediments. The fundamental elements are phosphorus, nitrogen, oxygen and iron. Sulfide is regarded as a debt of dissolved oxygen (DO) and ferric oxide as a store of DO, respectively. An oxidized zone (ferric oxide), which has a certain capacity of phosphate adsorption, is formed with the reaction between active iron in the upper layer of sediments and DO in the lower layer of water. While the oxidized zone is reduced by the sulfide in the upper layer of sediments, the adsorbed phosphates are released equivalently. The supply of phosphorus and nitrogen to the sediments depends upon the sink of phytoplankton from water. They are then decomposed to inorganic nutrients, and a part of them is adsorbed to the clay surface or to the oxidized zone. The released nutrients diffuse upward to the water or downward to the lower layer of sediments. The former are assimilated by phytoplankton which sink onto sediments and recycle in the same manner. The main parameters are changed seasonally as function of temperature. Using this model, the characteristic patterns of seasonal variation of phosphate discharge from sediments, DO concentration in water and also the rise and fall of the oxidized zone were satisfactorily simulated. The method proposed here will be useful as the significant sub-model for prevailing water quality assessments.