Tuomas Stoor
University of Oulu
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Publication
Featured researches published by Tuomas Stoor.
Measurement Science and Technology | 2005
Markus Honkanen; Pentti Saarenrinne; Tuomas Stoor; Jouko Niinimäki
This study describes a robust bubble image recognition algorithm that detects the in-focus, ellipse-like bubble images from experimental images with heavily overlapping bubbles. The principle of the overlapping object recognition (OOR) algorithm is that it calculates the overall perimeter of a segment, finds the points at the perimeter that represent the connecting points of overlapping objects, clusters the perimeter arcs that belong to the same object and fits ellipses on the clustered arcs of the perimeter. The accuracy of the algorithm is studied with simulated images of overlapping ellipses, providing an RMS error of 0.9 pixels in size measurement. The algorithm is utilized in measurements of bubble size distributions with a direct imaging (DI) technique in which a digital camera and a pulsed back light are used to detect bubble outlines. The measurement system is calibrated with stagnant bubbles in a gel in order to define the bubble size dependent effective thickness of the measurement volume and the grey scale gradient threshold as a focus criterion. The described concept with a novel bubble recognition algorithm enables DI measurements in denser bubbly flows with increased reliability and accuracy of the measurement results. The measurement technique is applied to the study of the turbulent bubbly flow in a papermaking machine, in the outlet pipe of a centrifugal pump.
Environmental Technology | 2013
Elisa Koivuranta; Jukka Keskitalo; Antti Haapala; Tuomas Stoor; M. Sarén; Jouko Niinimäki
This study introduces a novel optical monitoring method to image and characterize activated sludge flocs and to study the dependency of sludge settling properties on the floc structure. The novel method can easily analyse thousands of particles in a short timeframe using the developed image analysis program. The main advantage of this method is its applicability for in situ use because the only required pre-treatment is sample dilution. This study tested real process samples from activated sludge plants treating wastewater from a pulp mill. The sludge samples were collected in bulking and non-bulking situations, and the image analysis results were compared to the settling speed of the samples. The structure of the activated sludge flocs was clearly different in bulking sludge situations as characterized by more fragile and elongated flocs. Additionally, excessive amounts of filamentous bacteria hold the flocs apart, hindering sludge settling. These results show that this method is suitable for studying and optimizing activated sludge processes.
Environmental Technology | 2014
Elisa Koivuranta; Jukka Keskitalo; Tuomas Stoor; J. Hattuniemi; M. Sarén; Jouko Niinimäki
A charge-coupled device camera was used for the optical monitoring of activated sludge flocs and filaments, and the image analysis results were compared with the effluent clarity at a full-scale activated sludge plant during a three-month period. The study included a maintenance stoppage at the wastewater treatment plant, which was followed by a settling problem. Thus, the study presents the development of floc morphology from poor flocculation to good flocculation. In this case, the evolution of flocs was a slow process, and the optimum floc morphology was achieved before the purification results improved. To diagnose the cause of the settling problems using optical monitoring, four major factors were found to be relevant: the mean area of the flocs, the amount of small particles, the amount of filament and the shape parameters of the flocs. In this case, the settling problem was caused by dispersed growth based on the image analysis results. In conclusion, the method used has the potential for usefulness in the development of monitoring applications to predict plant performance and also to diagnose the causes of the settling problems.
Waste Management & Research | 2009
Matti Kuokkanen; Toivo Kuokkanen; Tuomas Stoor; Jouko Niinimäki; Veli Pohjonen
Up to 20 million tons of waste wood biomass per year is left unused in Finland, mainly in the forests during forestry operations, because supply and demand does not meet. As a consequence of high heat energy prices, the looming threat of climate change, the greenhouse effect, and due to global as well as national demands to considerably increase the proportion of renewable energy, there is currently tremendous enthusiasm in Finland to substantially increase pellet production. As part of this European objective to increase the eco- and cost-efficient utilization of bio-energy from the European forest belt, the aim of our research group is — by means of multidisciplinary research, especially through chemical methods — to promote the development of Nordic wood-based pellet production in both the qualitative and the quantitative sense. Wood-based pellets are classified as an emission-neutral fuel, which means that they are free from emission trading in the European Union. The main fields of pellet research and the chemical toolbox that has been developed for these studies, which includes a new specific staining and optical microscope method designed to determine the cross-linking of pellets in the presence of various binding compounds, are described in this paper. As model examples illustrating the benefits of this toolbox, experimental data is presented concerning Finnish wood pellets and corresponding wood-based pellets that include the use of starch-containing waste potato peel residue and commercial lignosulfonate as binding materials. The initial results concerning the use of the developed and optimized specific staining and microscopic method using starch-containing potato peel residue as binding material are presented.
Particulate Science and Technology | 2015
Elisa Koivuranta; Terhi Suopajärvi; Tuomas Stoor; J. Hattuniemi; Jouko Niinimäki
Optical monitoring with a charge-coupled device camera was used to assess the breakage of activated sludge flocs obtained from three different activated sludge plants: two municipal and one industrial. In this method, the samples were processed through the imaging unit and recycled back to a beaker using a centrifugal pump which causes the breakage of flocs together with hydrodynamics forces. Based on the image analysis results, the breakage models of the activated sludge flocs vary between the plants. The major breakage model in the two municipal plants was surface erosion whereas it was large-scale fragmentation in the industrial plant. A larger amount of filaments in the industrial plant most likely caused the large-scale fragmentation. Furthermore, the effect of the addition of a cationic polymer on the strength of activated sludge floc was studied in one sample. When the cationic polymer was used, the flocs started to grow at the start of the breakage process. However, they broke up at the end of the process and remained small, as found in flocs not exposed to any chemical treatment. Based on the results, the optical monitoring seems to be suitable for analyzing the breakage of flocs.
International Journal of Sustainable Economy | 2015
Antti Haapala; Janne Harkonen; Pekka Leviäkangas; Pekka Kess; Hely Häggman; Jouko Arvola; Tuomas Stoor; Ari Ämmälä; Katja Karppinen; Mari Leppilampi; Jouko Niinimäki
The paper contributes towards improving the understanding over the potential of bioeconomy by focusing on a regional context. The study is realised by applying a combination of PESTEL analysis, resource analysis and analysing true and potential cases with high bioeconomy relevance and potential for substantial commercial volume. Hence, this article combines approaches of strategy development and analyses cases in bioeconomy context with a specific regional perspective. The results provide an overview on the potential of bioeconomy, particularly that of Northern Finland, but also the entire country. The article brings forward sustainability considerations aside from demonstrating the complexity inherent to the topic. Opportunities and potential are demonstrated by presenting case examples. The findings can benefit both the academia and those involved in planning and implementing relevant actions towards bioeconomy - both in general and in the selected setting.
Environmental Technology | 2017
Elisa Koivuranta; Terhi Suopajärvi; Joni Hattuniemi; Tuomas Stoor; Mirja Illikainen
ABSTRACT The effect of seasonal variations on floc formation in the activated sludge process (ASP) was studied in a municipal wastewater treatment plant in Finland nearly 16 months. Floc formation was measured with an online optical monitoring device, and results were correlated with the temperature of the upcoming wastewater and the treatment efficiency of the ASP. Results showed that floc formation has a clear, seasonal pattern, with flocs in summer being larger and rounder and having fewer filaments and small particles. In addition, treatment efficiency increased in summer. The study correlated the results of image analysis with the composition (chemical oxygen demand and suspended solids content) and temperature of the wastewater before and after the ASP. Results showed that the composition of upcoming wastewater has no clear correlation with floc morphological parameters. However, the wastewater temperature clearly correlated with floc formation. Results indicated that cold winter conditions enhanced the growth of filamentous bacteria in wastewater, decreasing treatment efficiency. Furthermore, these results confirmed that floc formation has seasonal variations.
Bioresources | 2011
Matti Kuokkanen; Teemu Vilppo; Toivo Kuokkanen; Tuomas Stoor; Jouko Niinimäki
Journal of water process engineering | 2015
Elisa Koivuranta; Tuomas Stoor; J. Hattuniemi; Jouko Niinimäki
Bioresources | 2011
Ossi Laitinen; Kalle Kemppainen; Tuomas Stoor; Jouko Niinimäki