ISSN: 1579-4377
EFFECT OF WOOD WASTE DISPOSAL ON DYNAMICS OF SOIL
CHEMISTRY
AND WOOD BIOPOLYMERS IN A FOREST AREA SITUATED ON
BISTRITA AND BICAZ VALLEY, NEAMT COUNTY, ROMANIA
Carmen – Alice Teaca1, Ruxanda Bodirlau1, Iuliana-Gabriela Breaban2
1
“Petru Poni” Institute of Macromolecular Chemistry, 41 A Gr. Ghica-Voda Alley, Iasi, RO-700487, Romania
2“Al. I. Cuza” University, Department of Geography, 1Carol I Blv., Iasi, RO-700503, Romania
ABSTRACT
Wood waste represents a significant proportion of the waste stream. Forestry/saw mills and the pulping industries produce wood waste, as well as the construction and demolition activities. Wood waste, principally a relatively inert, but organic material becomes a priority material, considering the rapidly evolving field of processing and end markets of this waste material. Wood wastes (sawdust, wood chips, etc.) present disposal problems for industries that generate such wastes. In our country, there are many districts that have significant sawmilling and timber harvesting industries. One of them-Neamt district- generates a large quantity of wood residue (especially, sawdust composed from 80 % softwood and 20 % hardwood) that is now being landfilled as waste. Experimental data on wood biopolymers for sawdust specimens assayed from wood waste dumpsites, located in different areas on the Bistrita and Bicaz Valley, Neamt County, Romania, are presented here. Besides chemical analysis, IR and DTG investigations were also performed in order to evidence the wood biodegradation process. The study of soil dynamics from the wood waste disposal sites included humus, mineral elements (N, P, K), pH, and total soluble salts content values (CTSS) determination
KEYWORDS
INTRODUCTION
Biodegradable natural materials are permanently exposed to degradation processes of an environmental, chemical or microbial nature. The extent of the deterioration depends on the environment in which these materials are usually found. Among biodegradable materials, wood is considered to be a durable material that withstands weathering well without lossing much of its structural properties (except for microbial attack). However, a number of environmental (non-biological) parameters contribute significantly to the degradation of wood, including humidity, temperature, solar light irradiation time, atmospheric ozone content, and pollution. Another important aspect that may significantly affect the degradation rate of wood is the kind of wood, i.e. softwood or hardwood. Hardwood and softwood differ in several aspects, like fiber dimensions, chemical component composition and lignin and cellulose content. The hardwood presents a vessel element and lignin with both guaiacyl and syringyl units. Softwood does not contain vessel element, the lignin being composed mostly of essentially only guaiacyl units [1]. In the present paper, data on a chemical investigation of the softwood specimens (sawdust) assayed from wood waste disposal sites (situated on Bistrita and Bicaz Valley, Neamt County, Romania), as different profiles, are presented having mainly in view the biodegradation process. A dynamic evolution of nutrients in the soil bed, including nitrogen, phosphorus, potassium contents, as well as the humus, the extractives salts total content and pH values, was also approached.
MATERIALS AND METHODS
Study site
The wood waste disposal sites considered here are located in the Neamt County, north-eastern Romania, in a mountain region (Bistrita and Bicaz Valley), being surrounded by mixed coniferous and decidous forests. The soils are typical brown earths, with a structure of siliceous sandstones and stones. The forests are mainly composed by coniferous tree species, such as fir (Abies alba L.) and spruce (Picea abies L.), being also present some decidous tree species, namely beech (Fagus sylvatica) and birch (Betula alba). The wood wastes landfilled as dumps in this region are generated through forestry and sawmilling activities.
Soil dynamics analysis
Chemical investigation on the wood waste from disposal sites
In Table 1 are presented the wood sawdust specimens analyzed, the height of the wood wastedumps ranging in the 1.5 – 2.0 m domain.
Table 1. Wood waste dump profile sections used for the sawdust specimens’assay
Geographical location (Neamt district)
Wood waste dump profile section
Bicaz (P1) 0-12 cm (P209) 0-18 cm (P206)
Tasca (P2) 0-4 cm (P200) 4-8 cm (P200a, P200b)
Borca (P3) 0-20 cm (P213) 20-60 cm (P214) 60-80 cm (P215)
The wood sawdust specimens were preliminary washed and sieved for removing soil, and further let air-dry thoroughly. The experimental methodology included the specific techniques used by the wood chemistry [2]. To determine the wood biopolymers and extractives content by the standard procedures, the fraction passed through the sieve having 0.40 mm mesh size has been used [3-7]. All the results are relative to the dry matter content (%DM).
The wood sawdust specimens and their major chemical components (cellulose and lignin) were further investigated through IR spectroscopy method and thermogravimetry (DTG) in order to evaluate the biodegradation process. IR spectra were obtained by using a SPECORD M-80 Carl Zeiss Jena spectrophotometer model, on samples in KBr pellets. A MOM derivatograph (Paulik-Erdey type, Budapest, Hungary) was used in order to perform the thermal analysis for wood sawdust specimens and cellulose component (sample weight 50 mg, under a dynamic air flow, at a constant heating rate of 12 0C/min up to the maximum heating temperature of 600 0C). The device recorded simultaneously the following curves: T – temperature curve for each moment, TG – weight of sample at each moment, and DTG – rate of weight loss. The kinetic parameters for the main thermal decomposition reaction were determined by the Coats-Redfern method [8].
RESULTS AND DISCUSSION
Soil analysis
The study of soil dynamics at wood waste disposal sites has evidenced some differences for soil parameters, as it is shown in Table 2.
Soil horizon pH humus, % CTSS N, % P, ppm K, ppm
Thus, it can be mentioned that the wood waste disposal influences significantly the soil chemistry through increasing the pH value up to 7.8 – 8 (a typical brown soil has a pH value of 4.8-5). A decrease for humus content is noticed, while the mineral elements content variation is different: N and P decrease, K increases (for P1 –Bicaz and P2- Tasca). The disposable P and K are present in a small quantity, a higher value of 24 ppm for P being determined in the soil horizon A0 (8-31 cm) at P2 disposal site (Tasca). The determined
values for N, P, K are different as a function of wood waste disposal site.
Chemical investigation and thermogravimetry on wood sawdust specimens
The experimental data obtained on the wood sawdust chemical components are presented in Table 3.
Table 3. Chemical analysis of wood sawdust specimens assayed from the wood waste disposal sites
Sawdust
The wood sawdust specimens were also investigated by thermogravimetry analysis [9, 10], exhibiting both a degradation process for different biopolymers, and a cleavage of various bonds present in the lignocellulosic matrix. The literature data [11] evidenced that 1, 6-anhydro-glucopyranose represents the major component of solid waste resulted after thermal decomposition of lignocellulosics and cellulose.
A slowly biodegradation process for the wood samples under study is evidenced from the experimental data resulted from DTG analysis. In general, until 200 0C, the combustion proceeds without significant differences, first occurring the dehydration of reaction products. It follows a concurrence domain (200 – 300 0C) when the combustion process for cellulose and lignin are quite different.
The carbohydrates exhibit significant weight losses of about 55 – 65 % at 350 0C. Only lignin exhibits a different combustion process, a weight loss of 50 % being recorded at 450 – 500 0C. For carbohydrates, it can be observed a spontaneous cleavage of their catenes through radicalic reactions in the temperature range of 300 – 400 0C, evidenced through the considerable slope of the curves. Table 4 presents the parameters from thermogravimetry data obtained for the wood sawdust specimens.
Table 4. Thermogravimetry data on wood sawdust specimens thermal decomposition (DTG curves)
Wood sawdust specimens
P1 (Bicaz) P2 (Tasca) P3 (Borca)
Characteristic (0-18 cm) (0-4) cm (4-8) cm (0-20) cm (20-60) cm (60-80) cm
T50, ºC 360 358 350 365 363 367
Ti, ºC 218 230 217 213 204 210
Tmax, ºC 350 340 345 336 345 343
WTmax, % 36.3 32.7 36.0 34 33.5 33.3
Tf, ºC 387 380 380 375 383 380
WTf, % 49.3 47.6 49.5 50.5 47.5 46.8
Ea, Kj/mol 111.06 113.9 108.9 102.26 99.57 92.28
n 1.1 1.2 1.1 1.1 0.9 0.8
where: Ti – initial temperature; Tmax – maximum temperature; WTmax – weight loss at Tmax; Tf - final
temperature; WTf – final weight loss; T50 – temperature corresponding to a weight loss of 50 %; Ea – activation
energy; n – reaction order.
The activation energy calculated by using the Coats-Redfern method [8, 12] presents lower values for the main thermal decomposition process of wood and cellulose, showing differences as a function of structural changes extent for the analyzed wood sawdust specimens. The activation energy values increase as the temperature increases.
In Table 5 are presented the values for endothermic peaks for cellulose thermal decomposition process, for all wood waste dumps profiles.
Cellulose
Characteristic P1 (Bicaz) P2 (Tasca) P3 (Borca)
(0-18 cm) (0-4) cm (4-8) cm (0-20) cm (20-60) cm (60-80) cm bottom of wood waste dump. For cellulose, weight loss WTmax presents values of 63-69 %.
The activation energy values for wood sawdust specimens vary in the 92.28-113.9 Kj/mol range, while the reaction order values of 0.8-1.2 are noticed. For cellulose, significant differences as a function of location and profile sections are observed.
The weight losses for wood and its biopolymers as main constituents (cellulose and lignin) are presented in Fig. 1-3.
T, 0C
T, 0C
Fig.2. Weight loss for cellulose isolated from wood sawdust specimens
T , 0C
Fig.3. Weight loss for lignin isolated from wood sawdust specimens
As it can be observed, the wood residues exhibit an intermediary evolution, giving a mean weight loss situated between those for cellulose and lignin. The latter ones have a different behavior depending on their specific thermal stability. Thus, the weight loss for cellulose shows a significant decrease, more pregnant in the temperature range of 300-350
0
C, after that reaction occurring considerable slowly. Lignin is the most stable vegetal component to the thermal destruction and shows significant weight loss in the temperature range of 350-550 0C.
In Fig. 4-6 are presented the IR spectra for wood sawdust specimens and constitutive biopolymers – cellulose and lignin. Depending on the chemical structure investigated, the specific frequency bands cover a well-established domain in the IR spectra.
where the IR band intensities decrease in the 1460-1730 cm –1 range, comparatively with those for the other profiles.
Fig.4. IR spectra for wood sawdust specimens 1) P200; 2) P200a; 3) P200b; 4) P209; 5) P206; 6) P213; 7) P214; 8) P215
IR spectra for celluloses isolated from wood waste specimens are represented in Fig. 5. The frequency shift to the left, at 1660 cm –1 band evidences possible interactions between the chemical groups. In the 2900-3400 cm –1 frequency domain, a different vibration is observed between the profile sections. For specimens from P3 location (60-80 cm profile), a decreasing of frequency band from 2940 cm –1 (νCH2) is noticed. Some differences also
Fig.5. IR spectra for cellulose isolated from wood sawdust specimens 1) P200; 2) P200a; 3) P200b; 4) P209; 5) P206; 6) P213; 7) P214; 8) P215
The IR lignin spectra (Fig. 6) present the following specific bands: 3450 cm-1 (νOH),
2950 cm-1 (νCH3, νCH), 1730 cm-1 (νC=O), 1600-1650 cm -1
(for aromatic chains), and 900 cm
-1
(νC − O − C). Besides other specific bands for lignin (at 1600, 1550, 1430, 1220, 1110, and
1040 cm-1), significant vibrations at 840 cm-1 and 1720 cm-1 (νC=O) are evidenced. Lignin
presents a reduced stiffness for this type of bonds.
The typical absorbance ratios giving some indication of relative differences in aliphatic to aromatic units ratio and the condensation level, calculated from IR spectra for lignin, are presented in Table 6 [13].
Table 6. Absorbance ratios from IR lignin spectra
Absorbance ratio A2936/A1510
aliphatic / aromatic Quantitative analysis of the IR spectra may evidence the structural peculiarities for wood biopolymers during their isolation from wood sawdust waste, especially for the carbonyl groups.
CONCLUSIONS
Soil dynamics presents differences as a function of wood waste disposal site. A slowly increase for the soil pH values is noticed for all dumpsites.
Different extent of the wood biodegradation process is evidenced for wood waste dumps considered here, the process being more intense at the bottom of these.
Extractives content decreases as a function of profile section from wood waste dumps due to the rain water percolation.
Cellulose content exhibits an opposite evolution comparatively with the lignin content, showing a significant decrease, fact evidenced for the oldest wood waste dump. It is possible that the lignin biodegradation products are quickly involved in the humus formation process.
The wood sawdust specimens were subjected to the thermal destruction exhibiting both a degradation process for the biopolymers (cellulose and lignin), and a cleavage of various bonds present in the lignocellulosic matrix.
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