Determination of the effects of nanoparticles on anaerobic digestion of municipal waste activated sludge

In this thesis, 5, 50, 150, 250 and 500 mg NP/gTS concentrations of Ag, Al2O3, Fe2O3, CuO and CeO2 nanoparticles (NP) were added to waste activated sludge to evaluate the long term effects of NP?s on waste activated sludge anaerobic digestion by means of biochemical methane potential (BMP) test. In order to determine the acute affects of nanoparticles on waste activated sludge anaerobic digestion, ISO 13641-1 inhibition test was performed. During the inhibition test, 750 and 1000 mgNP/gTS concentrations were used in addition to the same NP concentrations which were used in the BMP test. The fluorescence in situ hybridization (FISH) technique was applied to observe the effects of nanoparticles on anaerobic archaea after BMP and inhibition tests. According to the results of 48 days long BMP test, the cumulative increase of BMP values of 250 mgAg/gTS Ag NP concentration has been determined as 7.9% relatively to the control group, while 500 mgAg/gTS concentration display maximum 12.1% decrease. No inhibition effect has been observed for Al2O3 NP, on the contrary 14.8% of positive effect on biogas production was detected. As a result of the BMP test for Fe2O3 NP, increasing dosage has indicated a negative effect on methane production with a maximum inhibition of 28,9% for 500 mgNP/gTS concentration. Among all BMP tests, CuO NP was determined as the most toxic nano particle under anaerobic conditions. Hereunder 150 mgCuO/gTS concentration caused a 23.4% inhibition on gas production, while 250 and 500 mgCuO/gTS concentrations output a lower methane production than inoculum. Similar to Al2O3 NP, no inhibition has been observed for CeO2 NP, and 25.5% increase was indicated. Within the 72 hours long ISO 13641-1 inhibition analysis, inhibition has been determined through total gas pressure measurement unlike the methane production measurement in BMP tests. According to the results of ISO 13641-1 test, Ag NP did not cause a significant inhibition effect on the biogas production from municipal waste activated sludge anaerobic digestion. Similar results were observed for Al2O3 NP. Conversely to BMP test results, Fe2O3 nanoparticles displayed no inhibition effect on biogas production, yet it caused an increase of 8.7% on gas production. Parallel to the BMP test results, CuO NP was detected as the most toxic nanoparticle on biogas production. After only 50 mgCuO/gTS dosage, 84.2% of inhibition effect of biogas production has been observed compared to the control group. CeO2 NP was determined as not effective on gas production during 72 hours long test. According to the results of the FISH analysis imaging, archaea, Methanosaeta spp., Methanococcus spp. and Methanosarcinales were all affected differently by the contact with nanoparticles. Archaea and Methanosaeta spp. populations were reduced due to the Ag, Fe2O3 and CuO NP existance in the test environment while Methanococcus spp. population was not affected and kept similar properties as the population of the control group. On the other hand Methanosarcinales was effected mildly negative in the existance of CuO NP.