Quality evaluation and improvement of mechanically–biologically treated municipal solid waste in view of a possible recovery

Abstract

This study aimed to identify possibilities to improve the quality of the stabilized biowaste coming from the mechanical-biological treatment of municipal solid waste produced in Rome for possible recovery rather than landfilling. The waste sampled before and after the first and the fourth week of aerobic biodegradation as well as different particle size classes composing the biostabilized materials were characterized in order to investigate the content and distribution of contaminants. Results showed, firstly, that the stabilized biowaste was not biologically stable after 4 weeks of biostabilization process, presenting dynamic respiration index [1,000 mg O 2 kg VS -1 h -1 . Heavy metal (Cd, Cr, Cu, Ni, Pb, Zn) content fulfilled the requirements for utilization, but by contrast, their release in water phase was quite high and not complying with Italian regulatory limits for waste recovery. In order to raise the quality, the biological process management should be improved by increasing the water amount to add to the rotting waste since the output material had moisture (19.7 % WM) lower than the recommended content for an optimized aerobic biodegradation ([40 %). Furthermore, fractions having particle size higher than 10 mm, composed of high content of impurities and heavy metals, should be separated by obtaining a reduction in chemical-physical contamination. Finer waste flow (\10 mm) can be recovered in environmental remediation activities, whereas coarser fractions ([10 mm) can be used in waste-to-energy plants, given the great content of high calorific value materials and the compliance with characteristics defined for solid recovered fuels.

Microbiota Dynamics of Mechanically Separated Organic Fraction of Municipal Solid Waste during Composting

“…The values of pH, electrical conductivity (EC), water content, organic matter (OM), total organic carbon (C), NH 4 + and NO 3 − content, germination index (GI), total Kjeldahl nitrogen (N), and C/N were measured and calculated as described previously [17]. The water-soluble compounds, pH, EC, and GI were determined from a suspension of the sample (10 g) in 300 mL distilled water [18].…”

“…The total organic carbon (%) was estimated as OM:1.8 [20]. The soluble NH 4 + and NO 3 − were determined on a Hach Lange DR 5000 spectrophotometer (Hach, Düsseldorf, Germany) according to the manufacturer's manual: NH 4 + was measured with Nessler's reagent, and NO 3 − was measured by the method based on cadmium reduction. The Kjeldahl total nitrogen (N, %) in the dry matter was determined by sample mineralization in a DKL 6 automatic digester (Velp Scientifica, Usmate, Italy) under conditions of heating up to 420 • C with concentrated sulfuric acid in the presence of hydrogen peroxide, and a mixed catalyst with subsequent distillation of ammonium into a boric acid solu-tion using an UDK 139 semiautomatic distillation system (Velp Scientifica, Usmate, Italy) and titration with hydrochloric acid on an Easy Plus titrator, model Easy pH (METTLER TOLEDO, Greifensee, Switzerland).…”

“…MSW is subjected to mechanical-biological treatment (MBT) [ 2 ], including (i) recovery of recyclable fractions and separation of materials with a high calorific value for the production of fuel from waste [ 3 ]; (ii) mechanical separation of a fraction ≤70 mm containing >50% of the biodegradable organic fraction (OFMSW); and (iii) aerobic high-temperature microbiological stabilization (composting) of mechanically separated OFMSW (ms-OFMSW) [ 4 , 5 ]. As a result, biostabilized residual waste (BSRW) is obtained [ 6 ], which is further subjected to disposal at landfills [ 7 ].…”

Analysis of the role of the sanitary landfill in waste management strategies based upon a review of lab leaching tests and new tools to evaluate leachate production

“…The study thus suggests the need to extend and optimize the biological treatment applied in MBT facilities, in view of possibly recovering the output instead of landfilling it. The second study (Di Lonardo et al, 2015b) confirmed that stabilized bio-waste did not prove to be biologically stable after 4 weeks of the stabilization process, presenting a dynamic respiration index well above 1,000 mg O2 kg VS -1 h -1 . The metal content (Cd, Cr, Cu, Ni, Pb, Zn) fulfilled the requirements for utilization, but instead the leaching of these elements was quite high and not compliant with Italian regulatory limits for waste recovery.…”

Scenarios of Bioenergy Recovery from Organic Fraction of Residual Municipal Waste in the Marche Region (Italy)

“…The OFMW, representing a level of about 35.4% in the composition of the generated MW (as the Italian average estimate in the multiyear period 2009-2019), is mainly diverted as a separately collected stream (sc-OFMW), accounting in Italy for 39.5% of the total amount of sc-MW in 2019 [1]. However, a non-negligible amount of organic fraction still remains in the residual municipal waste (RMW) stream [2], that accounted in Italy for about 11.6 million ton in 2019 [1]. The direct disposal of organic waste in landfills can generate potential environmental impacts on the air, soil, and water through the uncontrolled release of biogas and leachate [3].…”