6 th International Conference on Sustainable Solid Waste Management EFFECT OF A FURTHER MATURATION PHASE ON THE LEACHING BEHAVIOUR OF MBT WASTE Daniela Zingaretti, Alessio Lieto, Francesco Lombardi, Renato Gavasci DEPARTMENT OF CIVIL ENGINEERING AND COMPUTER SCIENCE ENGINEERING University of Rome “Tor Vergata”
Introduction Resources Manufacturing Waste Landfill Consumption For reducing the organic waste disposal in landfill: Collection and Bio ‐ stabilization Bio ‐ stabilized Production Transport treatment material D. Zingaretti - Effect of a further maturation phase on the leaching behaviour of mbt waste
Introduction Bio ‐ stabilization treatments: COMPOSTING USE AS FERTILIZER COMPOST Maturation Source ‐ segregated Bio ‐ stabilization MSW stage stage MECHANICAL BIOLOGICAL TREATMENT LANDFILL MBT WASTE Residual mixed Mechanical ‐ Biological MSW Treatment D. Zingaretti - Effect of a further maturation phase on the leaching behaviour of mbt waste
Introduction A stabilization step is adopted in both Composting and Mechanical Biological Treatment However a further 6 months maturation phase to enhance the chemical properties of the material is applied only in the composting plants Aim of the study: Evaluation of the effects of a secondary maturation stage on the main chemical properties and environmental behaviour of a MBT waste Experimental activities: Simulation of a maturation stage; • Monitoring of organic matter, elemental composition and carbon content; • Characterization of samples collected at 0, 90 and 180 days • D. Zingaretti - Effect of a further maturation phase on the leaching behaviour of mbt waste
Material Dry material removal (D>90 mm) Residual mixed Municipal Solid Wastes Metal removal Bio ‐ stabilization Dry material removal (D>30 mm) MBT waste D. Zingaretti - Effect of a further maturation phase on the leaching behaviour of mbt waste
Material and methods Simulation of a Maturation stage • a 300 kg ‐ sample of MBT waste was collected at the end of its treatment and stored indoor for 180 days • Each 10 days the sample was manually overturned and humidified simulating the typical maturation phase of a compost • Samples were collected at specific time intervals CHARACTERIZATION 90 0 180 days MATURATION PHASE 90 120 150 0 30 60 180 days MONITORING D. Zingaretti - Effect of a further maturation phase on the leaching behaviour of mbt waste
Material and methods Chemical analysis MONITORING: Samples collected each 30 days Organic matter content Volatile Solids (VS) ‐ UNI TS 11184 (2006) • Total Organic Carbon (TOC) ‐ UNI EN 13137 (2002) Elemental composition CHNS ‐ O analysis • CHARACTERIZATION: Samples collected after 0, 90 and 180 days Biological stability degree Dynamic Respiration Index (DRI) ‐ UNI TS 11184 (2016) • Elemental composition CHNS ‐ O analysis • Total metal content Acid Digestion • Metal speciation Tessier Method • Leaching behaviour Batch Leaching Test (BLT) ‐ UNI EN 12457 (2004) • D. Zingaretti - Effect of a further maturation phase on the leaching behaviour of mbt waste
Results: Monitoring Volatile Solids (VS) and Total Carbon (TC) 70 Volatile Solids 60 Total Carbon Inorganic Carbon 50 Percentage 40 % 30 20 10 0 0 30 60 90 120 150 180 Time (d) The concentration of VS decreases from 59% to 40% in the first 60 days and then • remained almost constant The Total carbon content passes from 31 to 20 % in the first 60 days • The inorganic carbon content showed a 60% increase (from 1.25 to 2 %) • D. Zingaretti - Effect of a further maturation phase on the leaching behaviour of mbt waste
Results: Monitoring Elemental Composition C H N S O Days C/N [%] [%] [%] [%] [%] 0 29,43 ± 0,53 4,45 ± 0,04 1,94 ± 0,06 0,75 ± 0,15 2,51 ± 0,1 15,11 30 25 ± 0,38 3,51 ± 0,05 1,72 ± 0,02 0,63 ± 0,15 2,21 ± 0,03 14,48 60 22,11 ± 0,42 2,89 ± 0,04 1,62 ± 0,02 0,43 ± 0,28 2,13 ± 0,1 13,61 90 20,38 ± 1,59 2,87 ± 0,17 2,17 ± 0,07 0,56 ± 0,11 3,66 ± 0,09 9,36 120 21,55 ± 1,08 2,88 ± 0,13 2,14 ± 0,07 0,48 ± 0,14 3,53 ± 0,29 10,05 150 22,28 ± 4,23 2,66 ± 0,41 1,8 ± 0,06 0,45 ± 0,26 3,46 ± 0,21 12,31 180 21,67 ± 1,86 2,98 ± 0,26 2,27 ± 0,11 0,45 ± 0,05 3,24 ± 0,13 9,54 Decrease in the carbon content and increase in the nitrogen content due to the • degradation of organic matter Decrease in the C/N ratio • D. Zingaretti - Effect of a further maturation phase on the leaching behaviour of mbt waste
Results: Characterization Dynamic Respiration Index (DRI) 0 days 90 days 180 days DRI mg O 2 / h*Kg VS 1503 369 267 pH ‐ 8.01 ± 0.04 8.13 ± 0.03 8.07 ± 0.03 1000 mg O 2 /h*kg VS is the threshold value suggested for bio-stabilised organic wastes (European Commission, 2001) Dissolved Organic Carbon (DOC) 350 DOC Residual OC 300 250 200 150 g/kg 100 50 0 0 days 90 days 180 days Time D. Zingaretti - Effect of a further maturation phase on the leaching behaviour of mbt waste
Results: Characterization Total metal content 100000 0 days 90 days 180 days 10000 Total Content [mg/kg] 1000 100 10 1 0,1 Al Ba Cd Co Cr Cu Fe Li Mn Mo Ni Pb Zn High concentrations of Al and Fe (>10000 mg/kg) and Ba, Cu, Mn, Pb and Zn (>100 mg/kg) • The weight loss due to organic matter degradation entails an increase in the heavy metals • concentration D. Zingaretti - Effect of a further maturation phase on the leaching behaviour of mbt waste
Results: Characterization Metal content speciation (Tessier method) 90 Days 0 Days 100% 100% 90% 90% 80% 80% Total Content (mg/kg) 70% 70% Total Content (mg/kg) 60% 60% 50% 50% 40% 40% 30% 30% 20% 20% 10% 10% 0% 0% Cd Co Cu Fe Mn Ni Pb Zn Cd Co Cu Fe Mn Ni Pb Zn 180 Days 100% 90% 1^ Exchangable 80% Total Content (mg/kg) 2^ Carbonates 70% 60% 3^ Fe & Mn 50% 4^ Organic 40% 30% 5^ Residual 20% 10% 0% Cd Co Cu Fe Mn Ni Pb Zn The metals are mainly related to Carbonates and organic matter • Only the exchangable metals are influenced by the applied further maturation step • D. Zingaretti - Effect of a further maturation phase on the leaching behaviour of mbt waste
Results: Characterization Leaching batch tests 10000 0 days 90 days 180 days 1000 100 Concentration (mg/kg) 10 1 0,1 0,01 0,001 Al Ba Cd Co Cr Cu Fe Li Mn Mo Ni Pb Zn The concentration of metals in the eluate from the leaching tests decreases for • increasing maturation times D. Zingaretti - Effect of a further maturation phase on the leaching behaviour of mbt waste
Results: Characterization Metal release C leachate Release (%) C totalcontent 100 0 days 90 days 180 days 10 Release [%] 1 0,1 Al Ba Cd Co Cr Cu Fe Li Mn Mo Ni Pb Zn The metal release proved to generally decrease for increasing maturation times • D. Zingaretti - Effect of a further maturation phase on the leaching behaviour of mbt waste
Results: Characterization Maturation indices and Humic substances Extraction of Humic acids (HA) and Fulvic acids (FA) by alkaline digestion (0.1 M NaOH) Humification Humification Polimerization Percentage of Index Ratio Rate Humic Acids C C C C HA HA extracted HA HI (%) 100 HR (%) 100 Pha (%) 100 C C C C organic organic extracted FA Values for 0 days 90 days 180 days Mature compost* C/N 15,11 9,36 9,54 < 12 C water soluble (C w ) g/kg 33,30 5,99 4,42 < 5 C W /C organic % 11,28 3,06 2,39 <1.7 HI % 2,8 7,4 5,8 > 3.5 HR % 10,7 14,3 11,2 > 7 P HA % 25,8 52,1 51,5 > 50 C HA /C FA g/g 0,35 1,09 1,06 > 1 * Bustamante et al., 2012; Garcia ‐ Gomez et al., 2005; Bernal et al., 1998 D. Zingaretti - Effect of a further maturation phase on the leaching behaviour of mbt waste
Conclusions The high heavy metal content and limited biological stability hindered the reuse of MBT waste so far. This study showed that the environmental characteristics of the MBT waste could be improved adopting a further maturation phase similar to the one used for the compost The further maturation phase proved to enhance the chemical properties of the MBT waste by: Increasing the biological stability; • Lowering the organic carbon content; • Decreasing the release of carbon and metals . • The effects exerted on the characteristics of the material are mainly observed in the first 90 days of the treatments while afterward the properties remained almost constant D. Zingaretti - Effect of a further maturation phase on the leaching behaviour of mbt waste
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