The disinfection of wastewater is not something that is currently in use at any wastewater treatmentplant in Sweden. The government has however stated some requirements for some wastewatertreatment plants to have a plan to implement disinfection in their treatment process, if asked.Therefore the goal of the project is to research if disinfection with sodium hypochlorite can beimplemented at Slottshagen wastewater treatment plant. There are several factors that will affect the efficacy of the disinfection of the wastewater. Firstly, thedisinfection process is dependent on the pH of the water solution. This is because the weakhypochlorous acid has better disinfection than the hypochlorite ion, and hypochlorous acid is presentthe most in the solution at pH 3-6. Another factor that is important to consider is the amounts ofnutrients present in the solution, since the chlorine oxidizes the nutrients rather than reacting with theorganisms in the solution. Some of the products from the oxidation of the nutrients are bad for bothhuman health and the environment. Also the temperature of the water and the concentration of thechlorine will affect the disinfection. Lastly, depending on which organism that is sought out to bedisinfected, the chlorine will have more or less effect on that particular organism. To research the chlorination effect, different additions of sodium hypochlorite were added to samplesolutions from the treatment plant and got to react in the solution for 5 minutes. Following thesamples were neutralized with ascorbic acid, and the amount of E. coli , coliform bacteria andintestinal enterococci were analyzed. The disinfection of the water during 1,5 minutes and at a shortertemperature were also analyzed. The results showed that the temperature, the contact time with thesolution and the concentration all are important factors to reach a proper disinfection, but the resultsalso showed that the amount of bacteria in the solution also is an aspect to take into considerationwhen treating wastewater. Finally, the considerations of disinfection of the wastewater with sodium hypochlorite is discussed.The point of addition of the chlorine was concluded to best be directly after the last chemicaltreatment step. When analysing if the disinfection would be possible, the disinfection was from theresults possible, but it was noticed that the results fluctuated a lot. The most probable reason why isbecause of the water quality. The water quality in general fluctuates regularly throughout the day, aswell as in between days of the week. Therefore throughout the disinfection process, the additions ofchlorine would need to be depending on several parameters, making the disinfection difficult toimplement. One solution to this could be to add a lot of chlorine to the bulk water at all times, but itwould cost too much if treating the water for a longer time, as well as it would be a higher risk to theenvironment. A solution to this problem could be to possibly neutralize the water before it is releasedas well, however when analyzing the cost of the ascorbic acid that was used as neutralization in thisproject, the cost to neutralize the water completely would be too high. Lastly it was discussed that theonly time disinfection of the wastewater would give any desirable results, is if the specific organismsthat are being sought out to be treated are bacteria or some viruses. If the particular organism that iswished to be treated is parasites, the disinfection with chlorine would not work.
| Identifer | oai:union.ndltd.org:UPSALLA1/oai:DiVA.org:liu-175172 |
| Date | January 2021 |
| Creators | Johansson, Emmy |
| Publisher | Linköpings universitet, Institutionen för fysik, kemi och biologi |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Student thesis, info:eu-repo/semantics/bachelorThesis, text |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess |
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