Organic radicals and paramagnetic metal complexes in municipal solid waste composts. An EPR and chemical study

Otemosphere,Vol. 39. No. 2, pp. 253-268,1999

Pergamon

© 1999ElsevierScienceLtd.All rightsreserved 0045-6535/99/$ - see front matter

PII: S0045-6535(99)00107-1

ORGANIC RADICALS AND PARAMAGNETIC METAL COMPLEXES IN MUNICIPAL SOLID WASTE COMPOSTS. AN EPR AND CHEMICAL STUDY

Mafia Jerzykiewicz ,1, Jerzy Drozd2 , Adam Jezierski I

1Faculty of Chemistry, Wroelaw University, Wroclaw, Poland, 2 Institute of Soil Science and Agricultural Environmental Protection, Agricultural University, Wroclaw, Poland

ABSTRACT The physicochemieal properties of composted municipal solid wastes (MSW) were investigated

by chemical and spectroscopic methods (EPtL NMIL IR, UV-Vis, ICP).

Transformations of the eomposted organic matter during 150 days were observed. The water content was controlled in the composts; in some cases the composted MSW were nitrogen enriched by urea addition. The maturation of the composts was observed using standard methods. Quantitative EPR measurements were made on isolated humic and fulvic acids; the concentration of semiquinone free radicals and g parameters were determined. The maximum radical concentration (1.2' 1017 spins/gram) in isolated humic acids was observed in about the 6th week of the composting process in good quality composts. Moreover, distinct linear changes in g parameters of isolated humic acids (HA) from 2.0031 to 2.0037 were observed during the composting process. These changes were correlated to increasing E,dE6 ratio characterizing the intensity of the oxidation processes and formation of oxygen-rich functional groups. The heavy metal (Cu, Fe, Mn, Pb) concentrations were examined in the composts and humic (HA) and fulvic acid (FA) fractions. The increase of copper binding by HA extracted from composts enriched in nitrogen was observed;

the coordination sites of the ligand were

characterized on the basis of EPR spectra. The various Fe(III) and Mn(II) complexes in the HA and FA fractions detected by EPR were used as additional indicators of oxidation-reduction processes in the composts. ©1999Elsevier ScienceLtd. All rightsreserved INTRODUCTION During the composting process of municipal solid wastes (MSW) mineralization and humification of the organic matter oceurrs [1-3]. The intensity of these changes depends on the 253

254 methods which are used to accumulate wastes and on conditions of the composting process [4, 5]. The conditions of the composting process affect the chemical and physicochemical properties of humic and fulvic acids isolated from the MSW composts [5-8]. These properties corresponding to different levels of the compost's maturity were shown using spectroscopic methods: EPR, UV-Vis, FTIR, ICP. These measurements

have demonstrated changes in humic substances' structure

depending on composting time and composting conditions. Inhibiting or stimulating effect of these substances on plant growth was also investigated [9]. The humic substances formed during composting stabilize organic (mainly semiquinone) radicals in their macromolecular matrix. These radicals are sensitive to pH, ionic strength, redox properties and interactions with metal ions [6, 7, 10]. The radicals play an important role in the polymerization and depolymerization processes in the soil and composts. The aim of this work was to establish the influence of different moisture levels (50% and 60%) and differential N manuring (as urea) on composting processes of municipal solid wastes. The application of the EPR spectroscopy to studies on the humification process and compost maturity is also presented. MATERIALS

AND METHODS

The studies were conducted on municipal solid wastes from industrial Upper Silesia region (Poland). The initial material used for the experiment was produced by a composting factory according to Dano technology. The material is put into the sealed fermentation chamber (which is also a drum grinding machine) and the temperature is increased to 50°C.

After 36h the raw

product, which is the initial material for our experiments, is received. After leaving the technology line, this material contains a high amount of organic matter. The municipal solid wastes after the initial transformation were composted in a pile and in plastic containers (1 m 3 capacity) for 150 days. The following experiments were carried out: 0 - composting process in the pile, without any additions (about 50% w.w. moisture), I-

in plastic containers, at 50% w.w. moisture,

II - in plastic containers, at 60% w.w. moisture, III - in plastic containers, at 50% w.w. moisture with the addition of 2.5 g nitrogen/kg as urea, IV - in plastic containers, at 50% w.w. moisture with the addition of 5 nitrogen/kg as urea. The temperature was measured in the pile and in the containers each day. Every 10-14 days the compost was turned over and 20 samples were taken out from different places of each kind of compost (0-IV). After these procedures, collected samples were appended to mean (averaged) samples of the proper kind of compost. The samples were air dried, and sieved with a 1 mm sieve.

255 ttumic (HA) and fulvic (FA) acid components were isolated by conventional procedures described by Stevenson [11] and Hayes [12] by shaking the compost samples in a solution of NaOH and Na4P2OT, centrifugation, acidification to pH 1.0 with HCI. The fulvic acids were purified using XAD-8 polymeric resin. The dried composts and the prepared samples of humic and fulvic acids were the subject of the physicochemical studies. Elemental analysis was performed for C, H, N with a Perkin-Elmer 2000 instrument. Electron paramagnetic resonance (EPR) spectra were obtained with Radiopan SE and Bruker ESP300E spectrometers operating at X-band frequencies at room temperature for solid state smnples packed in quartz tubes. The Brnker spectrometer has a 100 kHz magnetic field modulation and is equipped with Brnker NMR gaussmeter (ER 035M) and Hewlett-Packard microwave

frequency counter

(HP

5350B). A Li/LiF sample was used for g parameter

calibration; 4-hydroxy-TEMPO and Reckitt's ultramarine were used as spin concentration standards. The quantitative EPR technique (QEPR) was applied (microwave power 2 mW, modulation amplitude 1 G, 30.0 mg samples, standard quartz tubes of the same diameter, etc.) for measurement of free radical concentration. The samples containing about 20% water were EPR examined; after the EPR measurements the water content was determined for each sample, and the spin concentration was calculated for dry mass. Infrared spectra OR) were recorded with a Bruker FTIR l13v spectrometer, from KBr pellets (1 mg sample and 400 mg KBr). I~C NMR measurements were taken from solution of 50 mg HA substance dissolved in a 0.5M solution of NaOH in D20. All spectra were recorded on a Brnker AMX 300 at the frequency of 75.4 ~

in a 5 mm multinuclear high resolution probe head in the deuterium lock mode.

NMR measurments were performed using conditions and parameters described by Thorn et al. [13]. E4/E6 ratios were calculated on the basis of the spectra determinated in 0.5N NaHCO3 solutions of HA's using absorbances at 465 and 650 nm on Specord M40 UV-Vis spectrophotometer. Total metal concentration (Fe, Cu, Mn) for humic and fulvic acids was measured using ICP AES (ARL 3410 instrument). Moisture was determined by heating samples at 105 °C for 24 hours. In the Figures 1, 7, 9 - 12 mean values are presented; the experimental error as standard deviation (SD) was marked, the number of replicates was in most cases 5.

256 RESULTS AND DISCUSSION Standard methods of investigations of municipal solid waste composts. Monitoring of the humification process. Atomic ratios (C/N, CFL~/CFA)of humic acids (HA) and fulvic acids (FA)

extracted fromthe compost samples show significant fluctuations during the composting period. C/N atomic ratios for extracted humic and fulvic acids are presented in Figure 1. 16 14~ ~. 2-1 ".

I

16

IV

'

. . . . FA ==4-- HA

I

fl

'

I

20

'

I

40

'

I

60

80

,6o

, ,o

60

80

'

I

•

100

I

•

120

t

'

140

14~-~'.Ill

~',~,

.

12

, ,o

.-,

. 4o

.-,,oo ~,

.

.

.

7 . ,,o

"

o-,

.

14~16~", 12

,

,

I 20

.

,

,

40

100

120

.

140

'.

o

'~,.,.,.,.~,

16

-0.-

14_]±..

20

40

60

80

. . ., . .

,

"~,

100

120

140

0

10

s

6

-~ ......... .~.....~..:i;.-.~.._ , 0

.

i 20

,

i 40

,

i 60

,

i 80

__ ==,

, ' 100 Composting time [days]

i 120

140

Figure 1. C/N atomic ratio vs composting time for humic (HA) and fulvic acids (FA) isolated from MSW composts.

The C/N ratio is used as a index of compost maturity [8]. High C/N ratio (above 30) usually characterizes an immature compost [14]. In our experiments, the C/N ratio determined for the starting material is about 16 (in the case of FA) and 11 (in the case of HA). Until about 6 weeks the C/N ratios decrease significantly during composting; after this time, transformation rate measurexl by the ratio is distinctly slower. The humification ratio CHA/CFAincreases in our experiments from about 1.0 to 1.3 + 0.2.

257 The EPR specmun of humic and fulvic acids isolated from municipal solid wastes consists of a broad signal due to the presence of Fe(III) bound to organic and inorganic substances and a narrow-line signal at g = 2.0035 (average value for humic acids), g = 2.0043 (average value for fulvic acids). A typical spectrum is shown in Figure 2.

begi-nlnof~thecomlmpr stinoce~ g e FA0

~

/

t

I 500

i

f

I 1000

i

r

I 1500

,

I 2000

e

i

t 2500

i [G]

radical

I 3000

i

I 3500

,

I 4000

,

I 4500

,

i 5000

Figure 2. EPR spectrum at room temperature of solid fulvic acid FA(O); the broad-lines due to Fe(HI) compounds, weak hyperfme 55Mn sextet of Mn(II), and narrow-line free radical signal are observed.

The observed free radical signals are attributed to semiquinone free radicals [6, 7]. For

some samples of humic and fulvic acids extracted from MSW compost after 10-20th weeks the 55Mn hyperfme sextet, due to presence of Mn(II) species, and weaker bands of Fe(]II) were observed. This is interpreted as .the result of reducing conditions present in that stage of the composting process (Figure 3). In some cases (HA fractions) anisotropic Cu(]I) spectra were detected (Figure 4). (see Part lI and Part 1TIof this work).

258

FA IV 36 days of composting process

Jr-

m

the SSMn hyperfine sextet /

,

I

i

500

I

i

1000

I

i

I

1500

J

I

2000

~

2500

I

[G]

i

3000

free radical

I

i

3500

I

i

4000

I

,

4500

Figure 3. EPR spectrum at room temperature of solid fulvic acid FA (IV); weak signal at - 1600 G due to Fe0II), sharp hyperfme 55Mn sextet of Mn(II) and narrow flee radical signal are observed. (c~) I-IA0 126 days of the composting procesa free radical

i

I

500

,

I

1000

,

I

1500

,

I

2000

,

I

i

2500

I

3000

L

I

5500

,

I

4000

i

I

4500

i

I

5000

[Gl Figure 4.

I

5000

EPR spectrum at room temperature of solid humic acid HA(O), the weak line at 1600 G due to Fe(III), the anisotropic signal of immobilized Cu(II) -HA complex and free radical signal are observed.

259 The IR spectra are characteristic of humic materials in all cases (Figure 5). The common features are: a broad band at 3400 to 3000 cm q (H-bonded OH group), a slight shoulder at 3085 (aromatic C-H stretch), sharp peaks at 2920-2851 cm q (aliphatie C-H stretch), a shoulder at 1712 cmq (C=O of COOH ,C=O ketonic carbonyl), a peak at 1650 cm q (aromatic C=C, COO, hydrogen bonded C=O), sharp peaks at 1510 cm q (C=C of aromatic rings), 1460 cm q (aliphatic C-H), 1420 cm "1 (aromatic ring stretch; COO'), a broad peak at the 1290 to 1200 cm q region (-C-O- stretch of OH-detbrmation of COOH), a sharp peak at 1150 cm "l (symmetric bonding of aliphatic CH2, OH, or C-O stretch of various groups), and a peak around 1100 to 1020 cm q (C-O stretch of polysaccharides) [4].

FA III 54 day.

FA III 22 days

HA 0 65 days

~./ , 4000

•

,

•

3500

, 5000

.

,

HA 0

beginning of the comp~ting pr oceslt

.

,

2500

2000

•

, 1500

.

, 1000

.

. 500

[cm-1] Figure 5.

Selected IR spectra (transmittance

vs

wavenumbers) of humic and

fulvic acids isolated from MSW compost (different time of the composting process).

The IR spectra suggest that the COOH groups (1710 and 1220 cm "l) dissociate to COOgroups (1650 cm q) during the composfing process [7]. Loss of aliphatic structure (a smaller signal

260 at 2960 cm "1) is also observed. The decrease in the intensity of the band at the 1100 to 1020 cm "1 region indicates less -OCH3 and -OH polysaccharide groups in humic materials isolated from MSW at the end of the studied process. The 13C NMR spectra for the three humic acids are given in Figure 6. The presence of unsubstituted aliphatic carbon is indicated by signals in the 0-to 50 ppm region of the spectrum, carbon in C-O of methoxyl groups between 50-60 ppm, carbon in all other C-O groups between 60-95 ppm, anomeric carbon between 95-110 ppm, and aromatic carbon between 110-160 ppm, while those near 155 ppm arise from phenolic C and others (142-160 ppm), and carbonyl carbon in C=O ketonic groups in the 190-to 230 ppm) [15].

HA IV

HA 0

end of the composting process

end of the composdng process

HA 0 beginning of the composdng process

II !

200

150

100

50

0

[ppm]

Figure 6. n3C NMR spectra ofhumic acids isolated from MSW composts.

Regardless of the intense aromatic carbon peaks in all humic acid spectra in this study, the humic acids are all considerably more aliphatic than aromatic in composition. The aromaticity (calculated with the total carbonyl carbon region from 160-230 ppm excluded from the total spectral area) for humic acids extracted from municipal wastes at the beginning of the composting process averaged about 14%, whereas after five months the aromaticity averaged about 25-28%.

261 This means that during the composting process aromacity increased with time. The humic acids at the beginning of the process may contain six aliphatic carbons for every one aromatic carbon, whereas after five months may contain five aliphatic carbons for every two aromatic carbons. The E4/E6 ratio for HA fractions slightly increases during the composting process (Figure 7). The increase of the parametar is caused mainly by oxidation processes and oxygen functional groups formation in smaller molecules [2,3, 5]. HA

10 ~[

y--A+B*x

2 -~

T

"r"

K=0.66

-/-

! 0

6

•

Ill ~

,~

-[-

t 20

'

~

0

~

'

40

60

80

100

t 120

60

80

100

120

I

'

|

•

t

'

•

I

'

140

-I'-

20

40

'tT

140

tI

"

0

!

'

20

I 40

''

I

'

! 60

'

!

•

I

'

80

I

'

100

I

""

t I

'

0

1

•

20

60

40

I

•

80

I

'

120

'

100

I

.... I

120

'

160

'

,, I

'

140

t t 4,

,' , o

,

20

'

,

4o

'

,

6o

'

r

so

",

,

,oo

.

,

12o

~~r=°': I

l~o

,

Composting time [days]

Figure 7. E4/E6 parameter vs composting time for humic acids isolated from MSW

composts; A, B and R parameters describethe liney= A+Bx.

The above mentioned changes are characteristic of a strongly exothetraic process in a compost, as seen by the temperature evolution during the composting of organic municipal solid [16]. The temperature distinctly increas~ in the first three weeks of transformation [Figure 8]. The next measurements showed a gradual decrease of the temperature until about 15 weeks. After this time the temperature of composting material depends only on the surrounding conditions.

262

4--

0

•

1

60 ~

III IV

i~

50 ,

40-

30-

20-

10-

'

0

2'0

,'0

.

. 8~d . 60 . Composting time ays]

Figure 8. Changes of the temperature

vs.

100.

.

120

140

composting time for different

types of MSW composts.

Complexation of iron and copper by HA and FA fractions of MSW composts. The iron and copper content in HA and FA fractions was analyzed in all experiments during the eomposting process. The results are given in Figure 9 and Figure 10. Our goal was to characterize the formed copper(II) complexes in humic and fulvic acids fractions extracted from composts and compare the results with investigations made for contaminated soils. The complexing ability of humie and fulvic acids results mainly from their content of oxygen functional groups (phenolic -OH and carboxylic -COOH) and nitrogen coordinating groups in amino acids. The Maillard reaction is probably responsible for the formation of melanoidin polymers trapping free radicals. This reaction between amines and carbonyl compounds may play a significant role in the humification process in nature. It seems to be possible that the reaction is also responsible for the various composting processes. The effectiveness of the Maillard reaction depends on the water content of the reaction mixture (the most effective conditions are rather low concentrations of water) and the presence of alkaline nitrogen compounds [17]). The investigated composts contain about 0.015% Cu. The extraction procedure makes possible the knowledge of copper distribution in HA and FA fractions. In Fig. 10 the effect is very distinct: the copper binding by humie substances gradually increases during the eomposting process, especially the first 10 weeks, but in case of compost III and IV (urea added) the effectiveness of the copper

263

binding is especially high

(theaverage concentrations

of Cu in HA is 0.038% and 0.053%,

respectively, in comparison with 0.032% for the compost R). In the FA fraction the average copper concentrations are about 0.01% in all cases and remain nearly constant during the composting process.

10 0.5

t

- - -la-- "HA o FA

IV

J 0 1.0 ~ 1

20

40

60

80

100

120

140

III

os~

I

I ...........

•

i

•

0

I"=-

•

20

l

,

1

40

•

60

i

.

80

i

,7, ,

~ ,

i ~ '

100

120

140

~.oI " ....'"~"-X... ...! 0.51 X' ":X---x ....

0.0

i4

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,""

0 1.0 t

20

'

i

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40

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,

'--i

80

I

" ......'"

•

100

i

120

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•

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l

o.51 :g

~ ..... :g"x---X

o.o "7 : - , . , , / 0

1.o -~

20

40

o

/ . .......

. 0

,": ,-.",. i.

60

80

100

120

140

120

140

I

o5-~ o

.....x.

o 20

40

x.

1

~

60 80 100 Composdng time [days]

,

Figure 9. Fe concentrationvs compostingtime for humic (HA) and fulvic (FA) acids isolated fromMSW composts. The EPR parameters observed for the Cu(ID-HA complex are Az=145'104 cm"l, gz=2.290 (Figure 4). The lowered hyperfine parameter (in comparison with soil Cu(H)-HA complexes) may be explained by one nitrogen and three oxygen atoms coordination of Cu(II) in this [18].

264 + H A

"-'~'" F A

0.10 "1

0061 0.041 0.02 -t ~

~ ~...~.--~ . . ~ ~

^ ^ ^ .i ~ . . . . . ~ , . . . ~ . . . . . ~ .

u.uu

i

0.10

0

.

i

--'-~

~

....

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i

20

.

~

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..u_ i

40

-

.

.

,

60

.

.

.

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=--= ,

80

.u.

i

'

100

i

""~ .

i

120

•

140

0.08 1

o.o61

ill

c,' 3 r 0.~0

_

~

~'" ~''''~"

I

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-_4 0 , 0 0

I

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~-I

20

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•

.... '

i

.

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,

40

~

I

'

too

. . . . I

'

~20

I

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,40

_~..t ==

..... .i..,

20

0.08 1

I

~

0.021 ~ . . . . - ~ .

0

~-

80

=-

o.o4-~ ~ 0.00

'

60

o.o6-1

0.10

I

40

.-.m.. - : ~ " I

.

60

i

"" " t y - . . . ~ . •

80

i

I

100

120

..... •

i

•

140

I

0.06 ~

?-. :-=:-.-y ::---.y 0.10

0

0.08 I 0.06

20

40

60

0

°.°41

I

0

100

-

'

I

20

120

140

~

~

.~-

-

0.02 -t = ~ k - ^ ^~ 1 ~ " 3 K ~ O .Lit..'

80 -

'

I

40

" J L "'''~-'''-~ '

I

60 Composting

'

.-n-....~....-n.-'"" . . . . :~....:u_ I

80

'

I

100

'

I

'

l

'

120

time [days}

Figure 10. Cu concentration vs composting time for humic (HA) and fulvic (FA) acids isolated from MSW composts.

The concentrations of iron (see Figure 9) are the lowest for of HA and FA isolated from the HI and IV composts, while the concentrations for FA isolated from I and II are relatively high. The oxygen coordination is rather characteristic for iron(IID; thus, the oxygen coordination dominates in this case. The various forms of iron(III) (see Figure 2), and probably iron(ID are characteristic for the FA fractions. The composts contain 1.0% Fe; the average concentration in HA is 0.1% Fe, in FA 0.1-0.6%. Spin concentrations and g parameters of the free-radical species in MSW composts and HA and FA fractions. The polyphenolic matrix of humic/fulvic substances and possibility of melanoidin matrix formation is responsible for stabilization of the free radicals in HA and FA substances. During the processes of humification, maturation of composts, formation of organicclay complexes, coalification and carbonization, the organic matter is known to undergo a variety

265

of free-radical reactions. Termination of the free-radical reactions in soil yields relatively stable, mainly semiquinone radicals in the HA and FA matrices [6, 7]. EPR spectra of the non-fractionated dried composts show the broad Fe0ID lines and dominating intense free-radical lines at g=2.0027-2.0029;

the average spin concentrations are

relatively high: 5.48'1017 spins/g (for compost 0), 5.24 (in the same units, for I), 5.31 (for ID, 4.91 (for HI) and 4.52 (for IV). No distinct changes of g values or spin concentrations in the case of the non-fractionated composts are observed during the composting process. The EPR signals of free 2.0 -~

--.o--- FA

oo1 1.0

..'"-.

0.5

2.0

0

1.5 ~1.0

"~2 0

20

III

0

" 40

"~

20

60

0

80

100

120

140

80

100

120

140

=x=

40

60

~o.o-~----~..~_--::~, ~ 2.0

"-.

~

~-.-,

#.÷.

,.

20

40

60

80

100

120

140

20

40

60

80

100

120

140

100

120

140

1.5 1.0 0.5

0.0 2.0

0

o

1.5

~"I

I

1.0 0.5

0.0 0

20

40

60

80

Composdng6me [days]

Figure 11. Spin concentration

vs

composting time for humic (HA) and fulvic

(FA) acids isolated from MSW composts.

radicals in humic and fulvic fractions (at higher g values) in the non-fractionated composts are completely covered by strong radical signals due to the humins (g = 2.002722.0029). The average values of g parameters observed for our HA fraction and FA fraction are 2.0035 and 2.0043, respectively; moreover, the spin concentrations in these fractions change during the composting

266

process (Figure 11); the g pmameters calculated for HA fractions change distinctly during the composting process (Figure 12). The HA isolated from compost I (controlled water mount 50%), and from the composts III and IV (nitrogen added as urea) show maximum of free radical concentration about the 40 day of the composting process (Figure 11); in case of the compost 0 (pile; probably the best contact with air) the maximum of free radical concentration is observed for FA fraction. In the case of the compost III (60% water) no maximum of spin concentration was observed;

the reduction

processes are intense in this case (see other parameters described in the text). Thus, good quality composts [J. Drozd and Y. Cben, personal communication] exhibit a maximum of free radical concentration in the HA (or FA) fractious. This conclusion is in good agreement with previous observations of microbiological activity, temperature and free radical concentrations in the HA fraction [ 16]. HA

T -i- T T Y=^~Y=A+B*x

2.0040 ]

IV

2.0037 ~ 2.0034 -.]

-r 7 -t'- ..~t,.-----~r"~

2oo,,-1T " •

0 2.0040"]

~

"

I

i

i

i

i

i

I

20

40

60

80

100

,20

' 40

T

111

2°°'71

' 0

T

±

2.oo,41~ 2.003' 1 i

t ..L -1- ..L A---2.00 B =4.03E-6

J_ ,

20

,

,

,

40

T

~ ,

,

00

~-~oo ~.,~,

?

. . . .

,0

,00

R=0;7, ,20

T

~2.0o4o-~

,40

T

"IT

~

°'"

~ 2.0034 2.0031

A=2.00 B =4.07E. 6 -[-.

i

i

i

i

i

I

I

0

,

20

40

60

80

100

120

140

0

20

40

60

80

100

120

'40

2.0040

2.0037

0

"T"

2°°"~_ti~ 0

20

,

40

1-

.

,

60

.

,

80

.

,

100

.

,

120

."I

.~'.

140

Composting time [days]

Figure 12. g- parameter

vs

eomposting time for humic (HA) acids isolated

from MSW composts.

267 CONCLUSIONS The changes of the g parameter of free radicals in natural organic substances may be used as an indicator of aromatization, oxidation, coalification and carbonization processes [19]. Our observations made on the g parameter of HA fractions isolated from municipal solid wastes demonstrate

usefulness of this parameter for investigations of maturation of the compost,

especially oxidation processes in the composts. The g parameters change from 2.0031 to 2.0037 during the eomposting process; the dependence on time has a linear character (Figure 12). The increased g parameters remain in good correlation with E4/E6 parameters (Figure 7). We suppose that oxidation processes leading to formation of oxygen-rich groups (e.g. semiqninone or similar oxygen-rich radicals) in the HA molecules increase both g parameters for HA and the E4/E6 ratio.

Thus, we postulate that the g parameter for an isolated HA fraction from MSW

composts may be used as measure of oxidation processes and maturity of the compost. The maximum free radical concentration can give additional information about intensity of eomposting processes. ACKNOWLEDGMENT The authors express thanks to Professor Nicola Senesi from Bad University (Italy) for valued suggestions and helpful discussion. This work was financially supported by KBN, grant 3 T09A 004 13. REFERENCES

[1]

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