THE USE OF MUNICIPAL WASTE COMPOST IN THE RENATURALIZATION OF A CONTROLLED LANDFILL

Transcription

1 Dipartimento di Scienze grarie e mbientali Università di Perugia THE USE OF MUNICIPL WSTE COMPOST IN THE RENTURLIZTION OF CONTROLLED LNDFILL Coordinator: Prof. M. Businelli Collaborators : G. Gigliotti, M. Pagliai, R. Calandra, D. Businelli, F. G. Erriquens, D. Said-Pullicino,. Leccese

2 The objective of the present work was to study the consequences of using a mechanically separated municipal waste compost (MWC) as covering layer in a controlled landfill. The surface landfill soil was obtained by mixing an excavation soil with MWC in varying proportions through over time. The experiment was performed at the Pietramelina controlled landfill in the Municipality of Perugia (Italy), which is managed by Gesenu S.p.. The disposal of waste by burial in the landfill was done in horizontal layers starting from the downhill side, and raising the level bit by bit up to the maximum level planned. Each layer has an external front which constitutes a portion of the capping surface, corresponding to the depositions from the years 1993 to 1. ISW Conference Perugia 6 2

3 LEGEND Composting plant Leachate basin Leachate treatment plant PIETRMELIN landfill ISW Conference Perugia 6 3

4 Materials Some chemical properties of the substrates used through a 1-year period. Substrate ph CaCO 3 * (%) CEC* (meq/1g) TOC* (%) Texture EC (ms/cm) Low permeability clay Clayloam 2.5 Excavation soil Siltyloam.8 Municipal waste compost = 29.6 = 4.5 *Data are expressed on a dry basis (15 C). The proportion between excavation soil and MWC was variable during the 1 years with the maximum in the first year (1993). ISW Conference Perugia 6 4

5 Methods Soil sampling was carried out in 3 in the external fronts of 1993, 1994, 1997 and 1 depositions, which represent soils of 1, 9, 6 and 2 years of age, respectively. visual pedological examination of the profiles obtained allowed the identification of three horizons: excavation soil mixed with MWC excavation soil alone low permability clay 9 soil samples were collected from each horizon for a total of 27 samples for each deposition year and 18 samples for the four depositions chosen. ISW Conference Perugia 6 5

6 Results: PEDOLOGICL CHRCTERISTICS : 1 cm : 1 cm : - 3 cm : 3 9 cm : 9 cm : 9 13 cm Year 1 Year 1993 The pedological inspection of the profile allowed to verify that only the upper horizon has gained some characteritics that allow to classify it as a pedogenetic horizon. ISW Conference Perugia 6 6

7 RESULTS Hydrologic parameters of the horizon. percentage Field capacity % Wilting point % vailable water % years With the increase of the soil age the horizon improve its hydrological characteristics. ISW Conference Perugia 6 7

8 Table 3. Variation in soil macroporosity over the 1-year time series after amen dment with compost. Time elapsed from Horizons compost addition C 1 years % % 2 7. a 4.5 a a 4.7 a b 6.1 a c 6.7 a Values, expressed as a percentage of the total area occupied by pores larger than 5 µm per thin section, represent the mean (n = 9); Within each column varying letters indicate a significant difference (P =.5) Results: Physical Characteristics horizon Macroporosity (%) years 6 years 9 years 1 years Elongated Irregular Irregular Regular horizon Regular >1 Size Classes (? m) Figure 1. Macropore size distribution according to equivalent pore diameter for regular and irregular pores and width for elongated pores, in the horizon ( 1 cm) after 2, 6, 9 and 1 years from compost amendment. Macroporosity (%) years years years 1 years Elongated Irregular Irregular >1 Size Classes (? m) Figure 2. Macropore size distribution according to equivalent pore diameter for regular and irregular pores and width for elongated pores, in the C 1 horizon after 2, 6, 9 and 1 years from compost amendment. ISW Conference Perugia 6 8 Regular

9 Results: Physical Characteristics horizon horizon 2 years 6 years 2 years 6 years 9 years 1 years 9 years 1 years Figure 3. Macrophotographs of vertically oriented thin sections of the horizon ( 1 cm) after 2, 6, 9 and 1 years from compost amendment, showing the transformation from a compact massive structure (after 2 years) to a more open subangular blocky structure (after 9 and 1 years). Plain polarised light; pores appear white; frame length 3 cm. Figure 4. Macrophotographs of vertically oriented thin sections of the horizon after 2, 6, 9 and 1 years from compost amendment showing an increase of elongated and continuous pores along the time series (from 2 to 1 years). Plain polarised light; pores appear white; frame length 3 cm. ISW Conference Perugia 6 9

10 Results: Chemical Characteristics Horizon Elapsed time from compost addition (years) TOC (% soil) DOC (mg kg -1 soil) TEC (% TOC) F (% TEC) H (% TEC) NH (%TEC) a a 16.2 b 24.6 a 59.2 c 6 3. a a 15.1 b 3.1 a 54.8 c 9 3,52 a a 11.3 a 47.9 b.8 b b b 8.3 a 57.9 c 33.8 a 2 1,61 b a 13.9 a 37,1 c 49. b 6.44 a b 55.8 b 7. a 37.1 a 9.94 ab a 15.9 a 27.7 b 56.4 c 1 1.3ab a 16. a 36.7 c 47.3 b 2.49 a a 13.5 a 27. a 59.4 b 6.94 b ab 14.2 a 42.8 b 42.8 a b a 13.3 a. a 53.3 ab 1.52 a 83 31,5 b 8.3 a 33.3 ab 62.5 b The only significant differences among the parameters taken into consideration in the same horizon during the ten-year period are found in the horizon. ISW Conference Perugia 6 1

11 Results: Chemical Characteristics Horizon Elapsed time from compost addition (years) TOC (% soil) DOC (mg kg -1 soil) TEC (% TOC) F (% TEC) H (% TEC) NH (%TEC) a 134 a 27.6 a 16.2 b 24.6 a 59.2 c 6 3. a 124 a 27. a 15.1 b 3.1 a 54.8 c 9 3,52 a 83 a 25.3 a 11.3 a 47.9 b.8 b b 468 b 31.9 b 8.3 a 57.9 c 33.8 a The total and dissolved organic carbon content increased with elapsed time instead of the expected decrease due to degradation. The increase in H and decrease in F and NH are indeces of a positive evolution of organic matter. This positive trend is confirmed by the variation in the humification parameters after ten years. ISW Conference Perugia 6 11

12 Results: Biochemical characteristics mg/kg Biomass C DOC mg/kg years years Soil microbial biomass on horizons, C 1 and C 2 of the landfill covering soils. DOC on horizons, C 1 and C 2 of the landfill covering soils. ISW Conference Perugia 6 12

13 Results: Total metals mg/kg Copper mg/kg Zinc mg/kg Lead 2 6 years years years 9 1 mg/kg 8 6 Nickel 2 6 years 9 1 mg/kg Chromium 2 6 years 9 1 mg/kg 3, 2,5 2, 1,5 1,,5, Cadmium years ISW Conference Perugia 6 13

14 Chemical speciation of metals was obtained by a sequential extraction: 1M Mg(NO 3 ) 2 at ph 7 1M CH 3 COONa at ph 5.4M NH 2 OH.HCl in CH 3 COOH 25% H 2 O 2 at ph 2 HCl + HNO 3 (conc) exchangeable carbonates-bound Fe+Mn oxides-bound organic matter-bound insoluble residual fraction ISW Conference Perugia 6 14

15 Results: Metals speciation Exchangeable Oxides-bounded CaCO3-bounded OM-bounded Insoluble salts Cu 1 8 Zn 1 8 Pb 1 8 percentage 6 percentage 6 percentage Ni 1 8 Cr 1 8 Cd 1 8 percentage 6 percentage 6 percentage ISW Conference Perugia 6 15

16 CONCLUSIONS The research shows that over a ten year period the addition of MWC to excavation soil has promoted its evolution, evidenced by pedological, physical, chemical and biochemical modifications. The concentration of heavy metals added through the application of MWC increased only in the horizon because, as demonstrated by the speciation experiment, the main chemical forms found are those in which metals are bound to organic matter and precipitated as insoluble inorganic compounds. In these forms no leaching of metals is expected. ISW Conference Perugia 6 16

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