Comparison of sapromat and oxitop-method for analysing respiration activity (AT₄)

Since 2009 at ABF-BOKU 275 respiration activity tests of samples from different stages of MBT- resp. biowaste composting processes, samples from recultivation layers, materials from landfills resp. abandoned sites and residues from anaerobic treatment were analysed parallel by Sapromat® and OxiTop®. The range of AT₄ for these 275 samples was between 0.1 and 109 mg O₂/g DM (69 of them > 20 mg O₂/g DM). Samples were ground wet to particle size < 20 mm. Water content was optimised by fist test. For Sapromat® test 30-50 g WM were put into 500 ml glass vessels; for OxiTop® test 40-65 g WM were put into 2,500 ml glass vessels. Both tests were started at same day with same well prepared sample in the same laboratory in duplicates each.

As already known there is a really good correlation between Sapromat® and OxiTop® method. First results (169 samples, R² = 0.973) already were shown at the Sardinia symposium 2011. In this former investigation high reactive samples were underrepresented (just 6 samples in the range AT₄ > 50 mg O₂/g DM). Thus additional 'high reactiveâ€� samples were analysed. Correlations were evaluated for each type of material separately as well as for all materials together. OxiTop® shows lower findings than Sapromat®. For low reactive range (AT₄ < 20 mg O₂/g DM) readings for all the different materials show very high correlations (R² between 0.983 and 0.995) and similar lower findings (mean 89 %, range from 88 to 90 %, just recultivation layers show 84 %) in OxiTop® compared to Sapromat®. The mean errors of prediction are 0.4 to 1.1 mg O₂/g DM. For full range of reactivity coefficients of determination (R²) are 0.983 to 0.996. Lower readings vary between 90 % and 97 % (mean 95 %, again low reactive recultivation layers show lowest readings 84 %). The mean errors of prediction are 0.4 to 3.1 mg O₂/g DM. The reason for increase of percentage found by OxiTop® seem to be inhibiting metabolic products of degradation, which are discharged more frequently by OxiTop® because necessity of daily opening of system for oxygen supply in case of high reactive material.

 

 

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