Supervisor: Timo Kikas, PhD.
Opponent: prof Bo Mattiasson, PhD (Lundi Ülikool, Rootsi)
Pollution load of wastewaters is determined on the basis of their biochemical oxygen demand (BOD) which measures the oxygen required for the biochemical degradation of organic material. Although the BOD test is not specific to any pollutant, it continues to be one of the important general indicators of the substance potential to be an environmental pollutant for surface waters. However, it takes 5 or 7 days to gain results and management of wastewater treatment facilities can be very difficult using this kind of tests. To address this limitation, simple and reliable semi-specific BOD biosensors were constructed which enabled us to gain results within less than 30 minutes. In addition, these biosensors can measure BOD derived from refractory compounds to which they are semi-specific. Therefore, better estimation of BOD is gained. On the other hand, universal biosensor and biosensors not semi-specific to that certain refractory compound cannot detect it and thus, underestimate the BOD7 of the sample to the extent made up by this compound, 10-25%. Although biosensors underestimated the BOD7 of most real industrial wastewater samples, the semi-specific biosensors still produced better correlation of sensor-BOD and BOD7 in real samples than universal biosensor which underestimated the BOD7 of samples to a greater extent. Therefore, semi-specific biosensors are more appropriate for measuring BOD in specific industrial wastewaters than universal biosensor. However, it is vital to have a prior knowledge about samples composition and origin to select the suitable sensor. This problem was overcome by using different biosensors as an array - bioelectronic tongue - and application of multivariate data analysis. Qualitative information was extracted by using PCA, which enabled us to distinguish different samples by their composition and BOD7 values. In addition, PLS was used for quantitative analysis which resulted in good correlation of sensor-BOD and BOD7 in all samples.