Biofiltración de compuestos orgánicos volátiles utilizando diferentes tipos de lecho basados en mezclas de compost de RSU-poda: monitorización mediante diversas técnicas

Abstract

Composting is one of the most successful biological processes for the treatment of the residues enriched in putrescible materials. The optimization of parameters which have an influence on the stability of the products is necessary in order to maximize recycling and recovery of waste components. The influence of the composting process parameters (aeration, moisture, C/N ratio, and time) on the stability parameters (organic matter, N-losses, chemical oxygen demand, nitrate, biodegradability coefficient) of the compost was studied. The composting experience was carried out using Municipal Solid Waste (MSW) and Legume Trimming Residues (LTR) in 200 L isolated acrylic barrels following a Box-Behnken central composite experimental design. Second-order polynomial models were found for each of the studied compost stability parameter, which accurately described the relationship between the parameters. The differences among the experimental values and those estimated by using the equations never exceeded 10% of the former. Results of the modelling showed that excluding the time, the C/N ratio is the strongest variable influencing almost all the stability parameters studied in this case, with the exception of N-losses which is strongly dependent on moisture. Moreover, an optimized ratio MSW/LTR of 1/1 (w/w), moisture content in the range of 40-55% and moderate to low aeration rate (0.05-0.175 Lair kg-1 min-1) is recommended to maximise degradation and to obtain a stable product during co-composting of MSW and LTR. On the other hand, the concentration of volatile organic compounds (VOCs) during the composting of kitchen waste and pruning residues in a pilot plant, and the abatement of VOCs by different compost biofilters was studied. VOCs removal efficiencies greater than 90% were obtained using composts of municipal solid waste (MSW) or MSW-pruning residue as biofilter material. An electronic nose identified qualitative differences among the biofilter output gases at very low concentrations of VOCs. These differences were related to compost constituents, compost particle size (2-7 or 7-20 mm), and a combination of both factors. The total concentration of VOCs determined by a photoionization analyser and inferred from electronic nose data sets were correlated over an ample range of concentrations of VOCs, showing that these techniques could be specially adapted for the monitoring of these processes. Finally, a biofiltration system was designed using mature composts of municipal solid waste (MSW) or MSW mixed with pruning residues (MSW-P) as packing materials to treat vapours of ¿-pinene (a dominant volatile organic compounds (VOC) emitted during the MSW- P co-composting) and Methyl ethyl ketone (MEK). Monitoring the efficiency of the biofiltration system was carried out using a photoionization analyser, a commercial electronic nose (e-nose) and gas chromatography ¿ mass spectrometry (GC/MS). Results indicated that removal efficiencies for both kinds of biofilters were greater than 90% at different stages of the experiment. The acclimatization periods were 10 and 25 days for the MSW biofilter and MSW-P biofilter, respectively in the experiment with ¿-pinene and 14 days for both biofilters when the MEK was the contaminant present in the air stream to treat. Removal efficiency of the system was strongly dependent upon the moisture content of the packing materials, but the nature of the contaminant (hydrophilic or hydrophobic) plays an important role in the degradation. As moisture content in the biofilters fell to below 66% (dw) for the MSW and 51% (dw) for MSW-P, the removal efficiency decreased to less than 90% when the contaminant was an hydrophobic volatile organic compound (¿-pinene). In the case of MEK, the optimal range of moisture content for the packing materials used in this experiment was between 21.5 and 67.5 % (d.w) in the case of the MSW biofilter and between 25.7 and 91.8 % (d.w) for MSW-P biofilter. E-nose and GC/MS data indicate a complete degradation of the ¿-pinene and MEK by biofiltration, although the e-nose did detect background emissions, characteristic of each type of biofilter. Also, was possible to obtain information about the performance of the biofiltration system in different stages of the experiment. Results suggest that e-nose¿s will become a more powerful tool for monitoring VOC compounds in biofiltration and composting processes in the future.