Independent thesis Advanced level (degree of Master (One Year)), 10 credits / 15 HE credits
Tjörn is a cluster of islands, located in Västra Götaland’s county, on the west coast of Sweden. A fishing industry called Kädesholmen Seafood AB is located at Kädesholmen, one of the larger islands of Tjörn. The industry produces different types of fish preserves. The resulting waste water is polluted with mostly nutrients and organic matter in high concentrations. In lack of other treatment alternatives, the waste water is collected and transported to Trollhättan for biological degradation. Sweco, a consulting company, has been working together with Klädesholmen Seafood AB to establish a local treatment alternative for the fishing industry’s waste water. The ambition is to find a pretreatment option that enables treatment of the waste water in the municipal waste water treatment plant at Tjörn. Currently a pretreatment system consisting of a flocculation step followed by a flotation step is investigated as a possibility. The system would reduce especially organic matter and nutrient content of the waste water, but also other contaminations to some extent.
The subject of my master’s thesis was to perform a small scale investigation of the pretreatment alternative mentioned above. Waste water effluent collected from the industry was tested in combinations with three different flocculation chemicals; ferric chloride, Ekoflock 71 and Ekoflock 90, at different dosages and pH- levels. The aim was to obtain as high separation of contaminations from the water as possible. The flocculation results of each series were evaluated visually, according to a five grade scale. The test series with the most successful separation of sludge- and clear water phase were sampled for analysis. A limited physical and chemical characterization was performed at Halmstad University. The parameters analyzed were pH, conductivity and nutrients. The results were used for determining the success of the flocculation experiment. The flocculation experiment resulted in a discovery of a successful span for flocculation to occur, regarding both chemical dosage and pH- level. Ferric chloride proved to be more successful in separating the two phases (water- and sludge phase) from each other than the other two flocculation chemicals. The addition of chemicals caused a decrease in pH and therefore the addition of NaOH was needed to increase pH to a level beneficial for the reaction to occur. The analysis showed a decline of nutrients in the water, but not as much as anticipated. Little or no difference of conductivity was obtained and pH was low after flocculation, even with addition pH elevating substances during the flocculation.
The conclusion; flocculation is a possible treatment option for the waste water. However, large amounts of flocculation chemicals are required and the reduction of pollutants is poor. A modification of the flocculation process or another form of treatment alternative is preferable.
2011. , 31 p.