Betydelsen av anställningsform för arbetstrivseln och sammanhållningen i en arbetsgrupp

Tillfälliga anställningar har de senaste 20 åren blivit allt vanligare på arbetsmarknaden till följd av större konkurrens och arbetsgivarens krav på flexibilitet. Tidigare studier visar att tillfälligt anställda känner ett visst utanförskap och missnöje. Huvudsyftet med studien är därför att, med stöd av Social Identity Theory och Parkers modell (2003) om psykologiskt klimat, testa om tillfälligt anställda upplever sämre arbetsgruppssammanhållning och arbetsattityder än fast anställda. Enkäter skickades ut till 796 sjuksköterskor och sedan gjordes beräkningar med t-tester för oberoende stickprov. Resultatet bekräftade tidigare teori om sambandet mellan psykologiskt klimat och arbetsattityder dvs. ju bättre arbetsgruppssammanhållning desto bättre arbetsattityder. Däremot fanns ingen signifikant skillnad mellan grupperna i upplevelse av arbetsgruppssammanhållning och i uppvisande av arbetsattityder. Framtida forskning bör ta hänsyn till heterogeniteten i gruppen tillfälligt anställda

System studies of Anaerobic Co-digestion Processes

Production of biogas through anaerobic digestion is one pathway to achieving the European Union (EU) goals of reducing greenhouse gas emissions, increasing the share of renewable energy, and improving energy efficiency. In this thesis, two different models (Anaerobic Digestion Model No. 1 and an artificial neural network) are used to simulate a full-scale co-digester in order to evaluate the feasibility of such models. This thesis also includes models of two systems to study the inclusion of microalgae in biogas plants and wastewater treatment plants. One of the studies is a life-cycle assessment in which replacement of the ley crop with microalgae is evaluated. The other study concerns the inclusion of microalgae in case studies of biological treatment in three wastewater treatment plants. Finally, the co-digestion between microalgae and sewage sludge has been simulated to evaluate the effect on biogas and methane yield. The results showed that Anaerobic Digestion Model No.1 and the artificial neural network are suitable for replicating the dynamics of a full-scale co-digestion plant. For the tested period, the artificial neural network showed a better fit for biogas and methane content than the Anaerobic Digestion Model No. 1. Simulations showed that co-digestion with microalgae tended to reduce biomethane production. However, this depended on the species and biodegradability of the microalgae. The results also showed that inclusion of microalgae could decrease carbon dioxide emissions in both types of plants and decrease the energy demand of the studied wastewater treatment plants. The extent of the decrease in the wastewater treatment plants depended on surface volume. In the biogas plant, the inclusion of microalgae led to a lower net energy ratio for the methane compared to when using ley crop silage. Both studies show that microalgae cultivation is best suited for use in summer in the northern climate

Microalgal Biomethane Production Integrated with an Existing Biogas Plant: A Case Study in Sweden

Microalgae are considered as potential sources for biodiesel production due to the higher growth rate than terrestrial plants. However, the large-scale application of algal biodiesel would be limited by the downstream cost of lipid extraction and the availability of water, CO2 and nutrients. A possible solution is to integrate algae cultivation with existing biogas plant, where algae can be cultivated using the discharges of CO2 and digestate as nutrient input, and then the attained biomass can be converted directly to biomethane by existing infrastructures. This integrated system is investigated and evaluated in this study. Algae are cultivated in a photobioreactor in a greenhouse, and two cultivation options (greenhouse with and without heating) are included. Life cycle assessment of the system was conducted, showing that algal biomethane production without greenhouse heating would have a net energy ratio of 1.54, which is slightly lower than that (1.78) of biomethane from ley crop. However, land requirement of the latter is approximately 68 times that of the former, because the area productivity of algae could reach at about 400 t/ha (dry basis) in half a year, while the annual productivity of ley crop is only about 5.8 t/ha. For the case of Växtkraft biogas plant in Västerås, Sweden, the integrated system has the potential to increase the annual biomethane output by 9.4 %. This new process is very simple, which might have potential for scale-up and commercial application of algal bioenergy.Paper ID: ICAE2012- A10560</p

Simulation of energy balance and carbon dioxide emission for microalgae introduction in wastewater treatment plants

A case study is described in which the activated sludge process is replaced with a microalgae-activated sludge process. The effects on the heat and electricity consumption and carbon dioxide emissions were evaluated in a system model, based on mass and energy balances of biological treatment and sludge handling process steps. Data for use in the model was gathered from three wastewater treatment plants in Sweden. The evaluation showed that the introduction of microalgae could reduce electricity and heat consumption as well as CO2 emissions but would require large land areas. The study concludes that a 12-fold increase in the basin surface area would result in reductions of 26–35% in electricity consumption, 7–32% in heat consumption and 22–54% in carbon dioxide emissions. This process may be suitable for wastewater treatment plants in Nordic countries, where there is a higher organic load in summer than at other times of the year. During the summer period (May to August) electricity consumption was reduced by 50–68%, heat consumption was reduced by 13–63% and carbon dioxide emissions were reduced by 43–103%

Control of waste water treatment combined with irrigation

In waste water treatment using biological treatment processes normally phosphorous, nitrous compounds as well as organic matterare removed.It is also important to remove or kill pathogens that otherwisecould cause diseases. The surplus of bio-sludge is used to produce biogas. In thepaper four different alternatives for system design and operations of systems was discussed. The alternatives integrates thewaste water treatment and irrigation offarmland using the water taken out from different positions in the waste water treatment plant

Control of waste water treatment combined with irrigation

In waste water treatment using biological treatment processes normally phosphorous, nitrous compounds as well as organic matterare removed.It is also important to remove or kill pathogens that otherwisecould cause diseases. The surplus of bio-sludge is used to produce biogas. In thepaper four different alternatives for system design and operations of systems was discussed. The alternatives integrates thewaste water treatment and irrigation offarmland using the water taken out from different positions in the waste water treatment plant

Energy Efficiency Evaluation of two Biogas Plants

Anaerobic digestion for biogas production is a promising renewable energy technology whichcan be used to achieve environmental goals set in the European Union and other regions. Thereare however many improvements that can still be made to the process. Furthermore, there arealternative energy conversion processes that compete for some of the substrates used inanaerobic digestion. Energy efficiency could therefore be a tool for measuring and comparingthe performance of biogas plants. This study suggests a method for calculating energyefficiency of the biogas plant so that it is comparable to other processes. Two examples ofexisting biogas plants in Sweden have been selected for the efficiency assessment by using themethod proposed in this paper. The results are compared between the plants to assess thefurther potential of improvement

Energy Efficiency Evaluation of two Biogas Plants

Anaerobic digestion for biogas production is a promising renewable energy technology whichcan be used to achieve environmental goals set in the European Union and other regions. Thereare however many improvements that can still be made to the process. Furthermore, there arealternative energy conversion processes that compete for some of the substrates used inanaerobic digestion. Energy efficiency could therefore be a tool for measuring and comparingthe performance of biogas plants. This study suggests a method for calculating energyefficiency of the biogas plant so that it is comparable to other processes. Two examples ofexisting biogas plants in Sweden have been selected for the efficiency assessment by using themethod proposed in this paper. The results are compared between the plants to assess thefurther potential of improvement