EFFECT OF A FURTHER MATURATION PHASE ON THE LEACHING BEHAVIOUR OF MBT WASTE

Transcription

1 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

2 Introduction Resources Manufacturing Consumption Waste Landfill For reducing the organic waste disposal in landfill: Production Collection and Transport Bio stabilization treatment Bio stabilized material

3 Introduction Bio stabilization treatments: COMPOSTING USE AS FERTILIZER Source segregated MSW Bio stabilization stage Maturation stage COMPOST MECHANICAL BIOLOGICAL TREATMENT LANDFILL Residual mixed MSW Mechanical Biological Treatment MBT WASTE

4 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

5 Material Dry material removal (D>90 mm) Residual mixed Municipal Solid Wastes Metal removal Bio stabilization Dry material removal (D>30 mm) MBT waste

6 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 days MATURATION PHASE days MONITORING

7 Material and methods Chemical analysis MONITORING: Samples collected each 30 days Organic matter content Elemental composition Volatile Solids (VS) UNI TS (2006) Total Organic Carbon (TOC) UNI EN (2002) CHNS O analysis CHARACTERIZATION: Samples collected after 0, 90 and 180 days Biological stability degree Elemental composition Total metal content Metal speciation Leaching behaviour Dynamic Respiration Index (DRI) UNI TS (2016) CHNS O analysis Acid Digestion Tessier Method Batch Leaching Test (BLT) UNI EN (2004)

8 Results: Monitoring Volatile Solids (VS) and Total Carbon (TC) Volatile Solids Total Carbon Inorganic Carbon 50 Percentage % 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 %)

9 Results: Monitoring Elemental Composition Days C H N S O [%] [%] [%] [%] [%] C/N 29,43 ± 0,53 4,45 ± 0,04 1,94 ± 0,06 0,75 ± 0,15 2,51 ± 0,1 15,11 25 ± 0,38 3,51 ± 0,05 1,72 ± 0,02 0,63 ± 0,15 2,21 ± 0,03 14,48 22,11 ± 0,42 2,89 ± 0,04 1,62 ± 0,02 0,43 ± 0,28 2,13 ± 0,1 13,61 20,38 ± 1,59 2,87 ± 0,17 2,17 ± 0,07 0,56 ± 0,11 3,66 ± 0,09 9,36 21,55 ± 1,08 2,88 ± 0,13 2,14 ± 0,07 0,48 ± 0,14 3,53 ± 0,29 10,05 22,28 ± 4,23 2,66 ± 0,41 1,8 ± 0,06 0,45 ± 0,26 3,46 ± 0,21 12,31 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

10 Results: Characterization Dynamic Respiration Index (DRI) 0 days 90 days 180 days DRI mg O 2 / h*kg VS ph 8.01 ± ± ± mg O 2 /h*kg VS is the threshold value suggested for bio-stabilised organic wastes (European Commission, 2001) Dissolved Organic Carbon (DOC) DOC Residual OC g/kg days 90 days 180 days Time

11 Results: Characterization Total metal content days 90 days 180 days Total Content [mg/kg] ,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

12 Results: Characterization Metal content speciation (Tessier method) 100% 0 Days 100% 90 Days 90% 90% Total Content (mg/kg) 80% 70% 60% 50% 40% 30% 20% 10% 0% Cd Co Cu Fe Mn Ni Pb Zn Total Content (mg/kg) 80% 70% 60% 50% 40% 30% 20% 10% 0% Cd Co Cu Fe Mn Ni Pb Zn 100% 180 Days Total Content (mg/kg) 90% 80% 70% 60% 50% 40% 30% 20% 1^ Exchangable 2^ Carbonates 3^ Fe & Mn 4^ Organic 5^ Residual 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

13 Results: Characterization Leaching batch tests days 90 days 180 days 100 Concentration (mg/kg) ,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

14 Results: Characterization Metal release Release (%) C C leachate total content days 90 days 180 days Release [%] ,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

15 Results: Characterization Maturation indices and Humic substances Extraction of Humic acids (HA) and Fulvic acids (FA) by alkaline digestion (0.1 M NaOH) Humification Index Humification Ratio Percentage of Humic Acids Polimerization Rate C HA HI (%) 100 Corganic C extracted HR (%) 100 Corganic C HA Pha (%) 100 Cextracted C C HA FA 0 days 90 days 180 days Values for 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

16 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