| Abstract | Prema aktualnom Planu gospodarenja otpadom Republike Hrvatske (RH) za razdoblje 2023. -
2028. godine (NN 84/2023), u RH su u pogonu tri od ukupno jedanaest predviđenih centara za
gospodarenje miješanim krutim komunalnim i ostalim otpadom kojeg nije moguće izravno
reciklirati (CGO). Od postojećih centara, CGO Kaštijun i CGO Marišćina primjenjuju tehnologiju
biološko-mehaničke obrade (BMO) dok se u sklopu CGO Bikarac primjenjuje tehnologija
mehaničko-biološke obrade (MBO) otpada. Obje primijenjene tehnologije kombiniraju i
mehaničke i biološke postupke obrade komunalnog otpada. Tijekom BMO komunalni otpad se
podvrgava procesu biosušenja pri čemu je jedan od produkata obrade dijelom bio-stabilizirana
sitnozrnata frakcija, tzv. „metanogena frakcija“, pogodna za odlaganje na bioreaktorsko odlagalište
(BO) u sklopu CGO. U BO se uvođenjem tekućine (najčešće odlagališnog filtrata - eluata) u tijelo
odlagališta potiču procesi biološke razgradnje odloženog otpada. Mikrobiološki procesi razgradnje,
potaknuti vlaženjem, odvijaju se u anaerobnim uvjetima. Produkt anaerobne razgradnje je
odlagališni plin - metan, koji se koristi za energetske potrebe tj. za proizvodnju električne energije.
Optimalno funkcioniranje BO podrazumijeva upravljanje procesom sakupljanja, ekstrakcije i
recirkulacije filtrata u tijelu BO. Recirkulacijom se ubrzava biološka razgradnja organske
komponente otpada i povećava proizvodnja odlagališnog plina. Nužan preduvjet recirkulacije,
odnosno stalni kontinuitet u tekućoj fazi, realizira se na način da su donji dijelovi BO trajno
zasićeni filtratom.
Vodopropusnost je hidrauličko svojstvo koje uvjetuje mogućnost kontinuiranog kretanja fluida
unutar poroznog medija, odnosno u kontekstu BO, omogućuje nesmetan protok filtrata unutar tijela
odlagališta. Cilj istraživanja provedenog u sklopu ove doktorske disertacije je utvrđivanje
hidrauličkih svojstava BMO otpada u zasićenom stanju kroz utvrđivanje koeficijenta
vodopropusnosti navedenog materijala. Provedeno istraživanje može se podijeliti u tri faze,
detaljnije opisane u nastavku.
Prva faza istraživanja uključuje preliminarnu karakterizaciju BMO otpada određivanjem njegovih
osnovnih fizikalnih i geotehničkih parametara. U tu su svrhu provedena laboratorijska ispitivanja
za određivanje: udjela vlage, udjela organske tvari, sastava po komponentama, sastava prema
obliku čestica, granulometrijskog sastava i gustoće čvrstih čestica. Provedenim ispitivanjima je
utvrđeno da je BMO otpad dobro graduirani materijal sa širokim rasponom veličina zrna te je u
tom pogledu usporediv s krupnozrnatim tlom. Visoka utvrđena vrijednost udjela organske tvari od
38,39 % kao i niska inicijalna vrijednost udjela vlage koji iznosi 13,93 % (u odnosu na suhu masu),
potvrđuje prikladnost ispitanog BMO otpada za ugradnju u BO te proizvodnju metana.
U drugoj fazi istraživanja provedena je modernizacija nestandardnog hidrauličkog edometra
Laboratorija za inženjerstvo okoliša na Geotehničkom fakultetu. Riječ je o edometru velikih
dimenzija s ćelijom promjera 500 mm i visine 200 mm. Uređaj je konstruiran za potrebe ispitivanja
krupnozrnatih materijala poput obrađenog komunalnog otpada. Osim nestandardnih dimenzija,
specifičnost tzv. „velikog edometra“ je i njegov sustav za opterećivanje koji se sastoji od
hidrauličkog agregata s tlačnim cilindrom te torusne gumene membrane ispunjene vodom.
Modernizacija velikog edometra uključivala je implementaciju dvaju značajnih poboljšanja, a to
su ugradnja potpuno novog sustava za opterećivanje i mjerenje vertikalnih pomaka te ugradnja
potopnog mjerila sile.
Novi sustav opterećivanja bazira se na električnom aktuatoru sile GDSFA, proizvođača GDS
Instruments Ltd. Sustav je pomoću novoizrađene noseće konstrukcije montiran na gornju ploču
velikog edometra. Izvedenom nadogradnjom omogućeno je potpuno automatizirano provođenje
ispitivanja te znatno preciznije mjerenje parametara ispitivanja: vertikalnih opterećenja i
vertikalnih pomaka, uz maksimalni iznos naprezanja na uzorak koji iznosi 254,78 kPa.
Potopno mjerilo sile Omega LSHD-50K-60FT koje je kablom povezano s digitalnim mjeračem
Omega DP41-S-230, ugrađeno je na dno edometarske ćelije s ciljem mjerenja sile trenja koja se
javlja između oboda uzorka i unutarnje stjenke ćelije. Utjecaj trenja na rezultate ispitivanja
analiziran je uzimajući u obzir otklon osi djelovanja glavnih naprezanja od horizontalne ravnine.
U trećoj fazi istraživanja provedena su laboratorijska ispitivanja za utvrđivanje koeficijenta
vodopropusnosti BMO otpada u zasićenom stanju. Ispitivanja uključuju: izravno određivanje
koeficijenta vodopropusnosti u standardnom hidrauličkom edometru tipa Rowe & Barden, zatim
neizravno određivanje koeficijenta vodopropusnosti na temelju rezultata troosnih ispitivanja te
neizravno određivanje koeficijenta vodopropusnosti na temelju rezultata ispitivanja provedenih u
velikom edometru.
U standardnom hidrauličkom edometru su ispitana 3 uzroka svježeg BMO otpada i 3 uzorka
razgrađenog BMO otpada. Predmetni materijal je prosijan kroz sito od 3 mm te ugrađen u uzorke
promjera 63,69 mm i visine 19,11 mm s početnom vrijednosti suhe gustoće od 380,23 kg/m3.
Koeficijenti vodopropusnosti određeni su izravnim mjerenjem vertikalnog protoka vode kroz
uzorak, induciranog nametnutim gradijentom pritiska, pri vrijednostima konsolidacijskog pritiska
od 50, 100, 200 i 400 kPa, te pri rasterećenju na vrijednost od 200 kPa.
Troosna ispitivanju su provedena na svježim uzorcima BMO otpada s početnom srednjom
vrijednosti suhe gustoće od 378,65 kg/m3 te 487,64 kg/m3. Srednje vrijednosti promjera i visine
manje zbijenih uzoraka iznose 100,26 mm odnosno 100,00 mm dok srednje vrijednosti promjera i
visine zbijenijih uzoraka iznose 100,51 mm odnosno 100,00 mm. Ispitano je 8 manje zbijenih i 7
zbijenijih uzoraka koji su bili podvrgnuti konsolidacijskim pritiscima od 45 do 304 kPa odnosno
od 18 do 203 kPa. Koeficijenti vodopropusnosti određeni su neizravno, na temelju rezultata
ispitivanja provedenih u uvjetima izotropne konsolidacije.
Ispitivanja u moderniziranom velikom edometru provedena su na 3 svježa uzorka BMO otpada
promjera 500 mm i visine 95 mm te početne vrijednosti suhe gustoće od 379,75 kg/m3. Uzorci su
ispitani pri inkrementima naprezanja u rasponu od 4,74 do 124,74 kPa te dekrementima naprezanja
od 64,76 i 4,74 kPa. Koeficijenti vodopropusnosti određeni su neizravno, na osnovu primjene
Terzaghi-jeve teorije jednodimenzionalne konsolidacije. Postupci određivanja koeficijenta
konsolidacije uključuju standardno korištenu Taylor-ovu i Casagrande-ovu metodu te
nestandardnu metodu nelinearne optimizacije uz ograničenja (Bardet, 1997). Utvrđene su značajne
razlike u rezultatima primijenjenih metoda te je potvrđena visoka pouzdanost metode nelinearne
optimizacije pri određivanju koeficijenta konsolidacije. Ugrađenim potopnim mjerilom sile
izmjereno je trenje koje se javlja na kontaktu oboda uzorka i unutarnje stjenke ćelije edometra te
je analiziran njegov utjecaj na rezultate ispitivanja.
Na kraju je provedena detaljna analiza rezultata ispitivanja vodopropusnosti. Utvrđen je utjecaj
različitih metoda određivanja, različitih parametara ispitivanja i fizikalnih odnosno geotehničkih
karakteristika kao i veličine i starosti ispitanih uzoraka na vrijednost koeficijenta vodopropusnosti.
Za pojedine relacije između analiziranih parametara određene su funkcijske zavisnosti. |
| Abstract (english) | According to the current Waste Management Plan of the Republic of Croatia for the period 2023 -
2028 (NN 84/2023), three out of a total of eleven planned centers for the management of mixed
solid municipal and other waste that cannot be directly recycled are in operation in the Republic of
Croatia (WMC). Of the existing centers, WMC Kaštijun and WMC Marišćina apply the technology
of biological-mechanical treatment (BMT), while WMC Bikarac applies the technology of
mechanical-biological treatment (MBT) of waste. Both applied technologies combine both
mechanical and biological processes of municipal waste treatment. During BMT, municipal waste
is subjected to a biodrying process, where one of the processing products is a partially bio-stabilized
fine-grained fraction, the so-called "methanogenic fraction", suitable for disposal at the bioreactor
landfill (BL) within the WMC. In BL, by introducing a liquid (most often landfill filtrate - eluate)
into the body of the landfill, the processes of biological decomposition of the disposed waste are
stimulated. Microbiological decomposition processes, stimulated by moistening, take place in
anaerobic conditions. The product of anaerobic decomposition is landfill gas - methane, which is
used for energy needs, i.e. for the production of electricity. Optimal functioning of the BL implies
management of the process of collection, extraction and recirculation of filtrate in the body of the
BL. Recirculation accelerates the biological decomposition of the organic component of the waste
and increases the production of landfill gas. The necessary prerequisite for recirculation, i.e.
constant continuity in the liquid phase, is realized in such a way that the lower parts of the BL are
permanently saturated with filtrate.
Permeability is a hydraulic property that conditions the possibility of continuous fluid movement
within the porous medium, that is, in the context of BL, it enables the unimpeded flow of filtrate
within the body of the landfill. The aim of the research carried out as part of this doctoral
dissertation is to determine the hydraulic properties of BMT waste in a saturated state by
determining the coefficient of permeability of the material. The conducted research can be divided
into three phases, described in more detail below.
The first phase of the research includes the preliminary characterization of BMT waste by
determining its basic physical and geotechnical parameters. For this purpose, laboratory tests were
carried out to determine: moisture content, organic matter content, composition by components,
composition by particle shape, grain size analysis and particle density. The conducted tests
established that BMT waste is a well-graded material with a wide range of grain sizes, and in this
respect is comparable to coarse-grained soil. The high determined value of the share of organic
matter of 38.39%, as well as the low initial value of the share of moisture, which is 13.93% (in
relation to the dry mass), confirms the suitability of the tested BMT waste for incorporation into
BL and methane production.
In the second phase of the research, the modernization of the non-standard hydraulic oedometer of
the Environmental Engineering Laboratory at the Geotechnical Faculty was carried out. It is a
large-sized oedometer with a cell diameter of 500 mm and height of 200 mm. The device is
designed for testing large-grained materials such as processed municipal waste. In addition to nonstandard
dimensions, the specificity of the so-called "large oedometer" is also its loading system,
which consists of a hydraulic aggregate with a pressure cylinder and a torus rubber membrane filled
with water. The modernization of the large oedometer included the implementation of two
significant improvements, namely the installation of a completely new system for loading and
measuring vertical displacements and the installation of a submersible force gauge.
The new loading system is based on the electric force actuator GDSFA, manufactured by GDS
Instruments Ltd. The system is mounted on the upper plate of the large oedometer using a newly
designed support structure. The upgrade made it possible to carry out a fully automated test and
significantly more precisely measure the test parameters: vertical loads and vertical displacements,
with the maximum amount of stress on the sample being 254.78 kPa.
Submersible force gauge Omega LSHD-50K-60FT, which is connected by a cable to the digital
gauge Omega DP41-S-230, is installed at the bottom of the oedometer cell with the aim of
measuring the friction force that occurs between the sample rim and the inner wall of the cell. The
influence of friction on the test results was analyzed taking into account the deviation of the axis
of action of the main stresses from the horizontal plane.
In the third phase of the research, laboratory tests were conducted to determine the water
permeability coefficient of BMT waste in a saturated state. The tests include: direct determination
of the coefficient of water permeability in a standard Rowe & Barden type hydraulic oedometer,
then indirect determination of the coefficient of water permeability based on the results of triaxial
tests and indirect determination of the coefficient of water permeability based on the results of tests
carried out in a large oedometer.
In the standard hydraulic oedometer, 3 samples of fresh BMT waste and 3 samples of decomposed
BMT waste were tested. The subject material was sieved through a 3 mm sieve and incorporated
into samples with a diameter of 63.69 mm and a height of 19.11 mm with an initial dry density
value of 380.23 kg/m3. The coefficients of permeability were determined by direct measurement
of the vertical water flow through the sample, induced by an imposed pressure gradient, at
consolidation pressure values of 50, 100, 200 and 400 kPa, and after unloading to a value of 200
kPa.
Triaxial tests were performed on fresh samples of BMT waste with an initial mean value of dry
density of 378.65 kg/m3 and 487.64 kg/m3. The mean values of the diameter and height of the less
compacted samples are 100.26 mm and 100.00 mm, respectively, while the mean values of the
diameter and height of the more compacted samples are 100.51 mm and 100.00 mm, respectively.
8 less compacted and 7 more compacted samples were tested, which were subjected to
consolidation pressures from 45 to 304 kPa and from 18 to 203 kPa, respectively. Coefficients of
permeability were determined indirectly, based on the results of tests conducted under isotropic
consolidation conditions.
Tests in a modernized large oedometer were performed on 3 fresh samples of BMT waste with a
diameter of 500 mm and a height of 95 mm and an initial dry density value of 379.75 kg/m3. The
samples were tested at stress increments ranging from 4.74 to 124.74 kPa and stress decrements of
64.76 and 4.74 kPa. Water permeability coefficients were determined indirectly, based on the
application of Terzaghi's theory of one-dimensional consolidation. Procedures for determining the
consolidation coefficient include the standard Taylor and Casagrande methods and the nonstandard
method of nonlinear optimization with constraints. Significant differences in the results
of the applied methods were determined, and the high reliability of the nonlinear optimization
method in determining the consolidation coefficient was confirmed. The friction occurring at the
contact between the sample rim and the inner wall of the oedometer cell was measured with a builtin
submersible force gauge, and its influence on the test results was analyzed.
Finally, a detailed analysis of the results of the permeability test was carried out. The influence of
different determination methods, different test parameters and physical or geotechnical
characteristics as well as the size and age of the tested samples on the value of the coefficient of
permeability was determined. Functional dependencies were determined for certain relations
between the analyzed parameters. |
