Determination of Biological Stability by Oxygen Uptake on Municipal Solid Waste and Derived Products

Abstract

A new scientific apparatus and method are proposed for determining biological stability by oxygen uptake (respiration index, RI), on municipal solid waste (MSW) and derived products. For measuring the RI, a dynamic approach (with continuous aeration) was demonstrated to be more effective than the static approach (without aeration). The validity of the method was tested by comparing carbon losses calculated using both respirometric (carbon losses_resp) and analytical data (carbon losses_anal) during four trials performed on MSW and products derived from it. Carbon losses (expressed as g kg⁻¹C_i, in which C_i represents initial carbon content) were: 219.0 and 248.0, 67.9 and 57.1, 39.6 and 36.4, and 250.7 and 280.3, using respirometric and analytical data alternately for Trials 1,2,3, and 4. The comparison between respirometric data using continuous or no aeration showed, for the latter, an underestimation of RI of between 70% and 90% that was more evident for unstable biomass leading to more similar values when stabilization occurred. The scientific apparatus proposed made it possible to measure oxygen uptake under autothermal conditions and avoid problems connected with the use of a preset temperature, biomass temperature being a consequence of the microbial activity, as is also suggested by the significant linear regression of T versus RI (R² = 0.84, 0.73, 0.82, and 0.90 for the four trials, respectively). The methods proposed could be used with advantage in the future for biological stability measurements, above all for heterogeneous material such as MSW and its products, thus obtaining respirometric data that better reflect what happens during an aerobic process.