Determination of biological stability by oxygen uptake on municipal solid waste and derived products

A new scientific apparatus and method are proposed for determining biologic al stability by oxygen uptake (respiration index, RI), on municipal solid w aste (MSW) and derived products. For measuring the RT, a dynamic approach ( with continuous aeration) was demonstrated to be more effective than the st atic 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 perform ed on MSW and products derived from it. Carbon losses (expressed as g kg(-1 )C(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 a nd analytical data alternately for Trials 1,2,3, and 4. The comparison betw een respirometric data using continuous or no aeration showed, for the latt er, an underestimation of RI of between 70% and 90% that was more evident f or unstable biomass leading to more similar values when stabilization occur red. The scientific apparatus proposed made it possible to measure oxygen u ptake under autothermal conditions and avoid problems connected with the us e of a preset temperature, biomass temperature being a consequence of the m icrobial activity, as is also suggested by the significant linear regressio n of T versus RI (R-2 = 0.84, 0.73, 0.82, and 0.90 for the four trials, res pectively). The methods proposed could be used with advantage in the future for biological stability measurements, above all for heterogeneous materia l such as MSW and its products, thus obtaining respirometric data that bett er reflect what happens during an aerobic process.