Modeling and control of non-ideally mixed bioreactors

Mixing plays a substantial role in determining the overall performance of a bioreactor. Well mixing in bioreactor, especially for ethanolic fermentation process is important for the homogenization of miscible and immiscible liquids, gas dispersion and suspension of solid particles. Improper mixing will eventually affect the biological and kinetics reactions occurring in the bioreactor and subsequently deteriorate the bioreactor performance. Currently, most modeling and control applications of bioreactors have been devoted to ideally mixed assumption, for simplicity. This is not realistic in practical applications. Furthermore, the strength and accuracy of the bioreactor models reflect their performance and subsequently its control strategy. Therefore, it is vital to consider the imperfect mixing for the control of bioreactor.In this study, a batch, micro-aerobic bioreactor for ethanolic fermentation process will be considered for modeling. Up to date, not much study has been conducted in exploiting the mixing mechanism for controlling this type of bioreactor. Traditionally, only the bioreactor conditions such as temperature and pH are controlled for such a batch bioreactor. Other parameters, such as aeration rate and stirrer speed are not used to control the bioreactor. Thus, it is difficult to improve the bioreactor performance as the bioreactor performance is less sensitive to both temperature and pH than to the mixing mechanism. However, the mixing behaviour of the bioreactor needs to be captured if we are to employ both aeration rate and stirrer speed for the control of such a batch bioreactor.It is known that aeration rate and stirrer speed could significantly affect the biological and kinetics reactions. Therefore, both aeration rate and stirrer speed are suggested in this work as manipulated variables in the modeling of batch bioreactor. Thus, with this approach the ideally mixed assumption will be relaxed.The models proposed will be implemented for control studies. New control strategies will be established for continuous bioreactor, whereby dilution rate and substrate concentration are considered as disturbance variables and both aeration rate and stirrer speed are suggested as manipulated variables. With this approach, the practicability of the proposed models could be investigated.The aims of this research have therefore been as follows: 1. To experimentally study the impact of aeration rate and stirrer speed on the bioreactor performances, i.e. yield and productivity. 2. To develop an integrated bioreactor model to allow us to employ the aeration rate and stirrer speed as manipulated variables for control design. 3. To establish new control strategies for bioreactor without the ideally mixed assumption.A systematic approach has been proposed to develop the non-ideally mixed bioreactor model and to design the control strategy of the lab-scale fermentation process. Three modeling approaches are employed, i.e. data-based, kinetics hybrid and kinetics multi-scale models for the analysis of the impacts of both aeration rate and stirrer speed on the performance of bioreactor. Using the three models, the aeration rate and stirrer speed are also used to analyze the mixing mechanism in the bioreactor.Furthermore, new control strategies are then proposed for the bioreactor. By using the proposed control strategies, the effect of both aeration rate and stirrer speed on the overall performance could be analyzed in the face of disturbances on other process parameters. Furthermore, the stability and achievable performance of the control strategies could be compared for different models. Hence, the proposed control strategies would lead to a better operation of the bioreactor.The study highlighted the following main findings: 1. It is identified that both aeration rate and stirrer speed could affect significantly the overall performance of the bioreactor. Therefore, both aeration rate and stirrer speed rather than temperature and pH could be used as manipulated variables for controlling the bioreactor. The ideally mixed assumption is relaxed where the mixing mechanism of the bioreactor is included in the proposed model.2. The main issue in modeling is the complexity of the microbial reactions and kinetics of the bioreactor performance for the non-ideally mixed behaviour of the bioreactor. Thus, it is important to identify the main reactions and kinetics which actually affect the bioreactor performance. In this study, Monod’s kinetics has been employed with the implementation of both aeration rate and stirrer speed. It is shown that the kinetics multi-scale model demonstrated good predictions of the mixing mechanism of bioreactor. Different conditions of aeration rate and stirrer speed influence the mixing mechanism and thus, contribute to the dynamics and kinetics within the bioreactor. These show that both aeration rate and stirrer speed play important role in studying the non-ideally mixed mechanism of the bioreactor.3. Optimization results, however, suggest that the kinetics hybrid model gives the most comparable values of maximum yield and productivity. Thus, this model is suggested for the determination of the optimum conditions of the bioreactor operation due to its simplicity in model construction, as compared to the kinetics multi-scale model.4. The control strategy of bioreactor using the data-based model does not always produce good performance, especially in the face of large disturbances. This implies that the use of models with ideally mixed assumptions would not always give good overall performance. Therefore, the controllability of the bioreactor performance is further improved with the implementation of the proposed non-ideally mixed bioreactor model. It is observed that both databased and kinetics hybrid models are able to keep the controlled variables in their set-point values by manipulating both aeration rate and stirrer speed for low disturbance changes.Hence, this research contributes on the understanding of mixing phenomena in micro-aerobic fermentation process from which a set of optimal operational conditions and control strategies to enhance its performance are developed

We Come. We Work. We Relate. The Migrant Labourers in Penang

The PhD-project looks at the everyday work and lives of labour migrants in Penang. They are women and men from Indonesia, Vietnam, Nepal, Myanmar, Bangladesh, and The Philippines. The research employed a mixture of qualitative and quantitative methods. However, the data collection relied mainly on the ethnographic research method, which enriched and enhanced the understanding of¬ workers’ daily activities. This thesis departs from the diagnosis that how migration is studied in Asia and for Malaysia, follows the old scientific divide – either they focus more on structural issues constraining migrants (perspective from ‘above’) or the agency of the migrants themselves (from ‘below’). In consequence, the thesis aims to reconcile the strengths of both scientific camps by taking their respective perspectives on life realities of labour migrants as point of departure for an empirically based synthesis. To capture the experiences and activities of labour migrants in and outside their workplace as detailed as possible, the conceptual framework takes everyday practices as guiding lens. The principal argument deriving from the findings is that, despite the exploitative labour regime, migrant workers seek to translate their aspirations to ‘live a normal life’ and integrate in the receiving society through relational practices that connect them to people, places and certain ideas. My approach to a reconciliation of ‘from-above’ and ‘from-below’ approaches allows me to make sense of how migrants negotiate both aspects of their lives – the exploitative practices in the workplace, and the social activities they pursue in their free time after work. To attempt a synthesis by looking at migrants’ activities is the overarching point of this study. It should not only enable new empirical insights about how labour migration as a process is being experienced from the perspective of the migrants themselves, but also contribute to develop more appropriate analytical tools on a theoretical-scientific level to understand labour migration in its different dimensions and its ramifications better. The concept of relational practices which the thesis employs as analytical lens allows to focus on mundane aspects of the migrants’ life-worlds and to portray them as ordinary denizens with multiple aspirations concerning their life in Penang (and not ‘back home’), plus efforts for self-realisation and achieving satisfaction in everyday life. As a result, the migrant labourers appear neither one-dimensionally to be victims of an exploitative regime, nor permanent activists who seek close network ties with members of their own communal (ethnic) background in order to cope abroad. Moreover, the empirical insights the thesis derived at, allow portraying labour migrants as ordinary inhabitants of Penang, whose everyday life does not substantially differ from that of citizens. In this sense, the thesis also contributes to draw a more realistic picture of the everyday life experiences of migrant workers than scholars have done so far. It was revealed how workers are de facto integrated in local society and self-determined members of urban mainstream society of Penang – sharing similar ambitions and concerns in everyday life

Three new species of the Phaonia acerba group (Diptera: Muscidae) from Palaearctic and Oriental Regions

Three new species of the Phaonia acerba group fromthe Palaearctic and Oriental Regions are described: P. gaoligongshanensis Xue & Yu, sp. n., P. zhangxianggi Xue & Yu, sp. n. and P. hongkuii Xue & Yu, sp. n. An identification key to the males of 8 species of the Phaonia acerba group from the Palaearctic and Oriental Regions is provided

Understanding Inclusive Education in the “Front of the Class” Movie in Chinese Perspective

To explore the beliefs of Inclusive Education in the film " Front of the class ", this study uses the method of content analysis to interpret and analyze this film from the perspective of the concept of inclusive education, inclusive family, inclusive school, and inclusive society. It found that the film contains rich beliefs and concepts of inclusive education, which helps to pursue the quality of education examine educational equity and social equity, provide intellectual support for the construction of inclusive society, responding the UN's sustainable development goal 4 (SDG 4) focuses on ensuring inclusive and equitable, quality education and lifelong learning opportunities for all

Analysis of a Single Species Model with Dissymmetric Bidirectional Impulsive Diffusion and Dispersal Delay

In most models of population dynamics, diffusion between two patches is assumed to be either continuous or discrete, but in the real natural ecosystem, impulsive diffusion provides a more suitable manner to model the actual dispersal (or migration) behavior for many ecological species. In addition, the species not only requires some time to disperse or migrate among the patches but also has some possibility of loss during dispersal. In view of these facts, a single species model with dissymmetric bidirectional impulsive diffusion and dispersal delay is formulated. Criteria on the permanence and extinction of species are established. Furthermore, the realistic conditions for the existence, uniqueness, and the global stability of the positive periodic solution are obtained. Finally, numerical simulations and discussion are presented to illustrate our theoretical results

Comparison of N uptake and internal use efficiency in two tobacco varieties

AbstractTo explain the observation in field experiments that tobacco variety CB-1 was more nitrogen (N)-efficient than K326, the influence of two N levels on growth, N uptake and N flow within plants of the two tobacco varieties was studied. Xylem sap from the upper and lower leaves of both tobacco varieties cultured in quartz sand was collected by application of pressure to the root system. CB-1 took up more N with smaller roots at both high (HN, 10mmolL−1) and low (LN, 1mmolL−1) N levels, and built up more new tissues in upper leaves especially at LN level, than K326. Both varieties showed luxury N uptake, and CB-1 accumulated significantly less NO3− in new tissues than K326, when grown at the HN level. At both N levels, the amount of xylem-transported N and phloem-cycled N from shoot to root in K326 was greater than those in CB-1, indicating higher N use efficiency in CB-1 shoots than in K326 shoots. The major nitrogenous compound in the xylem sap was NO3− irrespective of N level and variety. Low N supply did not cause more NO3− reduction in the root. The results indicated that the N-efficient tobacco variety CB-1 was more efficient in both N uptake by smaller roots and N utilization in shoots, especially when grown at the LN level

Finding Answers to Definition Questions Using Web Knowledge Bases

PACLIC 23 / City University of Hong Kong / 3-5 December 200

At the limits of ‘Capability’: The sexual and reproductive health of women migrant workers in Malaysia

Despite the centrality of sexual and reproductive health (SRH) to UN Sustainable Development Goals (SDGs), women migrant workers in Malaysia face an environment inimical to their SRH needs. Drawing on qualitative case study material, we present the first empirical application of the Capability Approach (CA) to explore the reproductive health needs of women migrant workers in a developing country, offering an original analysis of the capability for SRH of these women. Specifically, we explore the resources available to them; their opportunities and freedoms (‘capabilities’); and factors which mediate transformation of resources into capability sets (‘conversion factors’). While SRH information and healthcare is notionally available, women migrant workers face multiple challenges in converting resources into functionings, constraining the achievement of capability for SRH. Challenges include language barriers, personal beliefs, power relations between workers and employers and the consequences of current migration policy. We consider the scale of the challenges facing these women in securing SRH rights, the difficulties of operationalising the CA within such a setting, and the implications of our findings for the adequacy of the CA in supporting marginalised populations