<P> Biosensors can be used to indirectly measure BOD via a fast (usually <30 min) to be determined BOD substitute and a corresponding calibration curve method (pioneered by Karube et al., 1977). Consequently, biosensors are now commercially available, but they do have several limitations such as their high maintenance costs, limited run lengths due to the need for reactivation, and the inability to respond to changing quality characteristics as would normally occur in wastewater treatment streams; e.g. diffusion processes of the biodegradable organic matter into the membrane and different responses by different microbial species which lead to problems with the reproducibility of result (Praet et al., 1995). Another important limitation is the uncertainty associated with the calibration function for translating the BOD substitute into the real BOD (Rustum et al., 2008). </P> <P> A surrogate to BOD has been developed using a resazurin derivative which reveals the extent of oxygen uptake by micro-organisms for organic matter mineralization . A cross-validation performed on 109 samples in Europe and the United - States showed a strict statistical equivalence between results from both methods . The French start - up Envolure (Montpellier, France) offers the kit ENVERDI which enables the users to perform up to 40 BOD simultaneously in 48 hours in a single 96 - wells microplate . </P> <P> Rustum et al. (2008) proposed the use of the KSOM to develop intelligent models for making rapid inferences about BOD using other easy to measure water quality parameters, which, unlike BOD, can be obtained directly and reliably using on - line hardware sensors . This will make the use of BOD for on - line process monitoring and control a more plausible proposition . In comparison to other data - driven modeling paradigms such as multi-layer perceptrons artificial neural networks (MLP ANN) and classical multi-variate regression analysis, the KSOM is not negatively affected by missing data . Moreover, time sequencing of data is not a problem when compared to classical time series analysis . </P> <P> Since the publication of a simple, accurate and direct dissolved oxygen analytical procedure by Winkler, the analysis of dissolved oxygen levels for water has been key to the determination of surface water purity and ecological wellness . The Winkler method is still one of only two analytical techniques used to calibrate oxygen electrode meters; the other procedure is based on oxygen solubility at saturation as per Henry's law . Though many researchers have refined the Winkler analysis to dissolved oxygen levels in the low PPB range, the method does not lend itself to automation . </P>

Which one of the following contributes to blackwater in municipal wastewater