**2.4 The quantification of anaerobic degradation**

The COD of methane produced in the anaerobic degradation of organic substrate corresponds with the COD of the removed organic mass (Lettinga & Hulshoff Pol, 1990). The amount of organic matter removed during the anaerobic treatment, the degree of degradation, was determined by measuring the total amount of methane produced during the period (T), which was converted to COD, taking into account that 1 Ndm3 methane is equivalent to 2.86 g CH4-COD. Based on this, the degree of degradation of the organic material was defined by the formula below:

$$\mathrm{D\_{\Gamma}\%} = \big(\mathrm{\underline{\chi}}\mathrm{CH\_{4}}\mathrm{COD\_{\Gamma}} \mid \text{sludge}\,\mathrm{COD}\right) \times 100\tag{1}$$

We fitted a logistic function-relation (DT% = Dmax / (1 + e-k(t-t0))) to the measuring results with SPSS 14.0 software. We used sludge as seeding material and the substrate for the tests after storing at 5°C, therefore we had to calculate with the lag phase in the beginning by choosing the logistic function-relation. The logistic curves take into consideration the startup phase, pursuant to the Monod and the Briggs-Haldane model.

We determined the value of maximum degradation (Dmax) in case of biowaste and sludge for the fitting as 65% and 50% respectively, which values were based on our former own measuring results (Rózsané et al, 2011) and on technical literature data (Haug, 1980). We determined the *k* invariant of reaction speed and the *t0* time defining the inflexion point in a way that the function-relation would have the best fit (R2) of the measuring results.

In the case of methane production projected to the volume of reactor, we did not deduce the methane production of the seeding material, but we used the results for the whole volume of the mixture of waste and seeding sludge. In case of the measuring results used for the volume of the reactor, we fitted the function-relation in a way identical with the previous, where the maximal degree of methane production (CH4max) was determined with the account of substrate to seeding material mixing rates and the maximal degradability. To characterize the speed of the degradation process, in the case of both measuring results, we determined the values of the starting v10d and v30d degradation speed as the direction tangent to the fitted curves.
