Study of using fine fraction excavated from Kudjape landfill as landfill cover material

Prügilad põhjustavad mitmeid keskkonnakaitselisi probleeme. Üks tõsisem on prügilas tekkiv prügilagaas ning selle koostises olev metaan, mis on kasvuhoonegaas. Probleemi lahendamiseks on vaja nõuetele mittevastavad prügilad sulgeda ja katta ning seal tekkiv prügilagaas koguda ja ära põletada. Väikeste prügilate puhul ning prügilates, kus ei teki suurtes kogustes prügilagaasi on mõistlik see oksüdeerida metaanilagunduskattes. Antud magistritöö eesmärgiks oli uurida Kudjape prügilast välja kaevatud jäätmete sõelumisel saadud peenfraktsiooni ja sellest valmistatud prügila kattekihi omadusi. Uuriti mõlema füüsikalis-keemilisi omadusi, määrati pH, elektrijuhtivus, kuivaine ja orgaanilise aine sisaldus. Materjalide bioloogilise aktiivsuse hindamiseks määrati 7-päeva hapnikutarve kasutades OxiTop meetodit. Peenfraktsiooni proovid Kudjape prügilast koguti esmalt kaevetööde alguses ning seejärel laiaulatuslike välitööde ajal 2013. aasta jaanuaris. Peenfraktsiooni proovide keskmised tulemused jäid küll soovituslike piirmäärade sisse, kuid selgus samuti, eri kohtadest ja sügavuselt kaevatud materjal võis mõne parameetri (elektrijuhtivus, hapnikutarve) korral olla väga erinev. Valmis kattekiht koosnes prügilast välja sõelutud peenfraktsioonist, reoveesettekompostist ja pinnasest (suhtes 3:1:1). Et kattekihi maht on välitingimustes väga suur ning selle omadused muutuvad ajas, tasuks kattekihi omadusi kontrollida ka pärast katmistööde lõppu. Valmis kattekihi proovid koguti katmistööde ajal ning seejärel kahel korral pärast sulgemistööde lõppu. Kudjape kattekihi proovide füüsikalis-keemilised omadused olid ühtlasemad ning suuremaid kõikumisi, mis peenfraktsiooni proovidel esines, enam ei tuvastatud. Kattekihi proovide hapnikutarve on 10 kuu jooksul langenud. Kudjape prügila kattekihi proovide uuritud füüsikalis-keemilised omadused ja hapnikutarve vastavad Keskkonnaameti nõuetele, vaid orgaanilise aine sisaldus on mõnevõrra nõutud väärtusest madalam. Antud töö tulemused on olulised, kuna varasemalt ei ole peenfraktsiooni nii suuremahuliselt prügila metaanilagunduskattes kasutatud. Uute prügilakaevandamise projektidele on seetõttu Saaremaal asuva Kudjape prügila peenfraktsiooni ja kattekihi omaduste tulemused väga oluliseks teabeks.Kudjape landfill was covered with methane degradation layer, which was excavated from the same landfill. The aim of this master thesis was to investigate the properties of fine fraction from Kudjape landfill as well as landfill cover layer made from this fine fraction. To achieve the aim, the following tasks were performed: Physical and chemical analyzes (pH, electrical conductivity, dry matter, organic matter) of the fine fraction landfill mined from Kudjape landfill; Determination of oxygen demand of the fine fraction landfill mined from Kudjape landfill; Physical and chemical analyzes (pH, electrical conductivity, dry matter, organic matter) of the Kudjape landfill cover layer; Determination of oxygen demand of the Kudjape landfill cover layer; Comparison of Kudjape landfill cover layer with requirements. During the fieldwork in Kudjape landfill, samples of solid material were collected at six occasions. First samples were taken from fine material in August 2012. In January 2013, large number of systematically collected samples from fine fraction were collected and taken to laboratory for detailed analyses. Electrical conductivity, pH, dry matter, organic matter and oxygen demand were measured for determining spatial characterisation of fine material. After the excavation and sieving work at Kudjape landfill, it was covered with biologically active cover, consisting of landfill fine fraction, mineral soil and sewage sludge, in ratio 3:1:1. Samples of cover layer were taken first during the covering works and three times during next 11 months. Similar to fine fraction samples, also electrical conductivity, pH, dry matter, organic matter and oxygen demand were measured. Overall the results showed that fine fraction from Kudjape landfill was heterogeneous and differs in different parts of landfill (pH values varied 7,44–8,24, electric conductivity 1,56– 6,03 mS/cm, dry matter 60,9773,25%, organic matter 12,2924,70%). The average electric conductivity of fine fraction was 2,62±1,05 mS/cm, average pH was 7,82±0,21, dry matter content was 66,10±2,83% and average organic matter 18,84±2,45%. The biological activity was measured by OxiTop measurement system and gave the average oxygen demand in 7 days 5,86±4,08 mg O2/g DM. Despite of heterogeneity, all the average results fitted within the recommended values by Huber-Humer et al. (2009). Because of differences between sampling holes and layers, it is recommended to mix the fine fraction with other materials before using it as a methane degradation cover. The results of landfill cover layer samples showed that the final coverage material was more stable and homogeneous than fine fraction. The first cover layer samples from May 2013 had average pH value 7,54±0,06, electric conductivity 1,13±0,47 mS/cm, dry matter content was 69,74±1,00% and average organic matter 11,08±1,76%. The last cover layer samples from April 2014 had average pH value 7,92±0,07, electric conductivity 0,87±0,29 mS/cm, dry matter content was 71,04±2,71% and average organic matter 11,08±1,76%. The average oxygen demand between cover layer samples has shown decline in past 10 months, as it has decreased from 5,39±2,47 mg O2/g DM to 2,82±1,33 mg O2/g DM. Overall the analyzed parameters of landfill cover layer samples fitted to the recommended values by Huber-Humer et al. (2009) and the requirements given by Estonian Environmental Board (Keskkonnaamet, 2011), except the content of organic matter, which had a bit lower values as expected. Each landfill needs personal solutions and it is important to find the best way for closure and mitigation considering landfill speciality (area, age, location of the landfill) in each case. Before using the fine fraction as cover material it is necessary to make sure it is probable to use. Moreover it is important to investigate and monitor the cover layer also after the closure. As there are not a lot of information about landfill fine fraction and only few of them are describing using it as landfill cover material. Therefore the results of this study are very important for future landfill mining projects. To incorporate some scientific research in future landfill mining projects should consist similar study of landfill mined fine fraction in case it is considered to be used as landfill cover material. Proper investigation of fine fraction gives certainty to the owner of the landfill and also environmental board that it is safe to use fine 46 fraction as cover material and also good way to find a new usage for landfilled material. Moreover, recycling of landfill mined fine fraction is the key issue for future landfill mining projects