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A tourism company that offers fly-in safaris is faced with the challenge to route and schedule its fleet of airplanes in an optimal way. Over the course of a given time horizon several groups of tourists have to be picked up at airports and flown to their destinations within a certain time-window. Furthermore the number of available seats, the consumption of fuel, the maximal takeoff weight, and restrictions on the detour of the individual groups have to be taken into account. The task of optimally scheduling the airplanes and tour groups belongs to the class of vehicle routing problems with pickup and delivery and time-windows. A flow-over-flow formulation on the time expanded graph of the airports was used in the literature in order to model this problem as a mixed integer linear program. Most of the benchmark problems however could not be solved within a time limit of three hours, which was overcome by formulating the problem for a simplified (time-free) graph and the use of an incumbent callback to check for feasibility in the original graph. While this approach led to very good results for instances, where few time-free solutions were infeasible for the original problem, some instances remained unsolved. In order to overcome this problem we derive two new exact formulations that include time as variables. Although these formulations by themselves are not better than the approach from the literature, they allow for an effective construction of graphs which can be interpreted as intermediate graphs between the graph of airports and the expanded graph with vertices for each visit. Using similar relaxation techniques to the time-free approach and constructing these graphs based on solutions of the relaxations guarantees that only critical airports are expanded. A computational study was performed in order to compare the new formulations to the methods from the literature. Within a time limit of 3 hours the new approach was able to find proven optimal solutions for all previously unsolved benchmark instances. Furthermore the average computation time of all benchmark instances was reduced by 90 percent.
Rapid urbanisation in Ghana has resulted in individuals expanding the cities for abodes without considerations of the negative externalities these may have on the environment. One of the major challenges with rapid urbanisation is the formation of urban slums associated with lack of basic sanitation facilities. This has led to recurrent outbreak of cholera and typhoid fever. The use of a single-stage solar-supported hyper-thermophilic anaerobic biogas digester for the treatment of black water has not been investigated, hence this study. The performance of three seeding sludge under three different hyper-thermophilic temperatures (60°C, 65°C and 70°C) were tested in batch tests. The three seeding sludge were sewage sludge, sludge from maize silage and cow manure. The results from the batch tests showed cow manure at 65°C as the preferred seeding sludge and optimal hyper-thermophilic temperature.
A 50 L single-stage laboratory-scale hyper-thermophilic continuous stirred tank reactor (HT-CSTR) was operated to treat only black water for 10 weeks using cow manure at 65°C as the seeding sludge and optimal hyper-thermophilic temperature. Afterwards, co-digestion of blended kitchen food waste and black water was also practised for 12 weeks. With a mean hydraulic retention time (HRT) of 23.3 days, a mean total COD removal of 86.3 % was achieved. The reactor had an average COD volumetric loading rate of 6.22 kgCOD/(m3.d) and remained uninhibited. It also had organic loading rate of 0.3 kgVS/(m3.d) and a degradation performance (R) of 5.43 kgCOD/(m3.d). Treatment of only black water produced biogas with less methane content of 34.9 % even though a stable pH of 6.9 was recorded both in the reactor and in the effluent. Co-digestion with kitchen food waste increased the percentage content of methane in the biogas by 77 % from 34.9 % to 61.8 %.
The effectiveness of the HT-CSTR to hygienise the effluent for agricultural purpose was assessed by spiking the reactor with 200 ml each of 2 x 109 CFU/ml Salmonella senftenbergensis and 8 x 108 CFU/ml Escherichia coli. The HT-CSTR was able to hygienise all bacteria of Salmonella senftenbergensis and E. coli. A simulation test confirmed that between 30 minutes and 1 hour, all the cells of Salmonella senftenbergensis and E. coli in the treatment system were killed at 65 °C. Eubacteria, Methanosarcina spp., Methanomicrobium spp. and Methanococcus spp. were identified in the seeding sludge at the hyper-thermophilic temperature of 65°C. The design, construction and performance of a pilot-scale reactor in Terterkessim slum in Elmina, Ghana was based on results from the laboratory-scale HT-CSTR. It achieved 97 % removal of influent total COD and could produce about 2.52 Nm³CH₄/(kgCOD.d) which could be burned for
at least 8 hours. The effluent cannot be used for cultivation of leafy vegetables such as cabbage since it had some concentrations of pathogens like Salmonella spp. and E. coli but can be used for cotton crop.
This dissertation examines how migration and development narratives are (re)produced in transnational digital migrant media using an example of Kenyan migration to Europe. It also raises questions about existing gaps in the literature on the role of the media specifically, transnational digital migrant media in constructing influential discourses. It achieves this quest by submitting to an objective to examine the contribution of migrant media discourses to development in migration-sending countries (De Haas, 2007). Using postcolonial-discourse theoretic approach, the thesis analyses the criteria for selection of texts on migration and development, and how the texts inform the discourse. The theoretical concepts of development in this thesis follow Arturo Escobar’s (1995) deconstruction of conventional development theory. It includes an appreciation of multi-faceted theoretic dynamics, especially historical effects on development and creation of hegemonic disparities causing migration of Kenyans to Europe. The dissertation explores the relation of liberal development narratives to Postcolonial perspectives of Edward Said (1977), Gayatri Chakravorty Spivak (1986) and Homi Bhabha (1983), whose writings expose stereotypes like those found in development constructs. The study highlights similar aspects of representations of migration and development in the media. It does not only expose migrant’s contribution to development but accentuates the discourse forming function of migrant media in the production of heterogeneous narratives on migration and development. This reflection is an attempt to look at possibilities of alternative development trajectories in migrant media and Postcolonial texts, that resist neo-colonial economic narratives forced on people of African descent. The findings for this thesis show that migrant media provides hegemonic ideas on development, as well as alternative counter-hegemonic views. Even though poverty and political instability of Africa characterize narratives in the mainstream media, migrant media utilizes new media platforms for “subalterns” to be heard. Migrants’ inputs on development (re)produced in migrant media, inform a discourse that champions initiatives aimed at improving livelihoods in migration-sending countries. To answer the main sociological question on (re)production of narratives this dissertation learns from Norman Fairclough’s (1995, 2012) guidelines to discourse analysis, as informed from Michel Foucault’s (1980) theoretic approach. As a qualitative research strategy, the dissertation explores Texts from transnational digital migrant media for Kenyans in Europe (Germany and UK) and expert interviews with Kenyan media producers in Germany and in Britain. On this basis, the thesis argues that not only are media expert’s contributors to development but also important creators of a discourse that qualifies migration as a reality in Kenya’s development.