Browsing by Author "Pankkonen, Pietu"

Heterotrophic bacteria are essential for carbon cycling in water ecosystems as they bind dissolved organic carbon (DOC) to the biomass and return it to the classical food chain through microbial loop. The treated wastewater from Viikinmäki wastewater treatment plant is discharged to the Gulf of Finland where it increases the quantity of dissolved organic matter (DOM) in the water and furthermore can be an extra energy source for heterotrophic bacteria. There are not yet further studies how the heterotrophic bacteria exploit DOM in the treated wastewater or a monitoring programme for DOC concentrations in the wastewater treatment plants. DOC is the limiting factor for heterotrophic bacteria growth in the Gulf of Finland in the summer. As the bacteria exploit DOC, they consume oxygen and release carbon dioxide. DOM compounds may also diminish light penetration in water which can inhibit the growth and photosynthesis of phytoplankton and macrophytes. The aim of this thesis was to find out 1) the DOC concentrations in the treated wastewater and DOC load in the treated wastewater discharged to the the Gulf of Finland from Viikinmäki wastewater treatment plant, 2) the biodegradability of DOC and DOP in the treated wastewater and 3) how the disc filter about to be used in Viikinmäki wastewater treatment plant affects the quantity and quality of DOC and DOP in the treated wastewater. The DOC load entering the Gulf of Finland with the treated wastewater was quantified by measuring the DOC concentrations in the treated wastewater during the spring and summer 2014. The DOC concentrations correlated positively with chemical oxygen demand (COD) which is regularly measured in wastewater treatment plants. By dividing the COD with 3,66, the DOC concentrations were successfully estimated for a longer period. In order to evaluate the biological degradability of DOC and DOP in the wastewater effluent, treated wastewater was incubated (+15 °C) for two months with surface water heterotrophic bacteria from the Gulf of Finland and changes in DOC concentrations, the biological oxygen demand and nitrogen and phosphorus concentrations were measured. Furthermore the heterotrophic bacteria were incubated for one month in disc filtered wastewater effluent and also in regularly treated wastewater to find out the effect of the new filter on DOM quantity and quality. The yearly DOC load from Viikinmäki wastewater treatment plant to the Gulf of Finland was estimated to be about 1460 tons which is approximately one fifth of the annual DOC load from River Vantaanjoki. The ratio between DOC and COD concentrations calculated here can only be used to quantify the amount of DOC load from Viikinmäki wastewater treatment plant and similar ratio must be calculated individually for every point source. The biodegradability of DOC in the treated wastewater was equally low to the biodegradability of DOC in River Vantaanjoki. The quantity of DOC bound to the bacterial biomass was rather low and the amount of DOC lost via respiration was relatively high. Accordingly the DOC in Viikinmäki wastewater effluent does not become efficiently available to higher trophic levels. The disc filter has the potential to remove DOC and DOP from treated wastewater which would decrease the DOC and DOP load significantly in the Gulf of Finland. The disc filter decreased DOC concentrations 14 % in comparison to regularly treated wastewater. The disc filter didn't affect the quality of DOC, i.e. there was no difference in the biological degradability of DOC between the two wastewater treatment processes. However the disc filter was possibly able to remove the biologically available part of DOP from treated wastewater but the issue still needs further investigation.