Monitoring s fermentation processes of producing biogas on wastewater treatment plant on the basis of chemical and biochemical methods PhD thesis Levente Kardos Supervisor: Dr. Gyula Záray, professor, DSc Consultant: Dr. Katalin Barkács, adjunktus Dr. József Oláh, tudományos tanácsadó (FCSM Zrt.) PhD School of Environmental Studies Environmental Chemisty Program PhD School of Environmental Studies Head of the Doctoral School: Dr. Kiss Ádám, professor, DSc Environmental Chemisty Program Head of the Program: Dr. Turányi Tamás, professor, DSc Eötvös Loránd University Faculty of Natural Science Cooperative Research Center for Environmental Sciences 2012
1. Objectives My aim was to study the applicability of enzyme activity measurements with classical plant controlling parameters in the course of anaerobic biogas producing fermentation. The reason was that through enzyme activity measurements the decisive steps of the anaerobic decomposition speed; i.e. process of the hydrolysis can be followed properly. With the used enzyme activity measurements it is possible to follow up those changes (temperature, specific organic matter load) - occurring in the anaerobic fermenters - which have influences on the quantity of the produced biogas. 2. Methods and experimental periods The experimental work was carried out at a communal sewage treatment plant in Budapest (Budapest Sewage Works Ltd., South-Pest Wastewater Treatment Plant). It was possible to test enzyme activity of sludge samples deriving from pilot plants and full scale fermenters. My laboratory works were in the communal sewage treatment plant and in the laboratory of Eötvös University. It was tested by applying usual control parameters (ph, volatile acid content, alkalinity, gas composition) and enzyme activity (dehydrogenase, protease, lipase) measurements. I wanted to examine six periods during my researches. These are the followings: 1. Comparing of mesophilic and thermophilic fermentation based on enzyme activity tests in pilot plants and full scale reactors. 2. Measurements of the effects of the temperature changes in pilot plants fermentors based on chemical and biochemical parameters. 3. Relation between the sewage sludge loading (specific organic material load) and the enzyme activity under pilot plant and plant conditions. 4. Mechanical pre-treatment s effect of experiment for sludge fermentation under pilot plant fermenter. 5. Possibility of using enzyme preparation because of increasing biogas production under laboratory conditions. 6. Examination of sewage sludge and organic materials (dairy industrial sludge, vegetable waste) cofermentation in pilot plant reactors based on enzyme activity measurements.
3. New scientific results 1. On the basis of the semi-plant- and plant experiments at mesophilic and thermophilic temperature I stated that - of the classical control parameters used in the practice of sludge putrefaction only the concentration of the volatile acid showed any correlation with the specific organic material load and the temperature change, respectively. I stated a negative correlation between the concentration of the volatile acid and the specific gas quantity. 2. On the basis of the semi-plant- and plant experiments at mesophilic and thermophilic temperature I stated that - of the classical control parameters used in the practice of sludge putrefaction (dry material content, organics content, chemical reaction, volatile acid, alkalinity, redoxipotential) - only the concentration of the volatile acid showed any correlation with the specific organic material load and the temperature change, respectively. I stated a negative correlation between the concentration of the volatile acid and the specific gas quantity. 3. My measurement for the specific dehydrogenase enzyme activity proved suitable for the biochemical characterization of the waste sludge fermented in an anaerobic way; i.e. for the follow up of changes in the total activity of the sludge cells. As proved by my experiments completed under pilot plant- and plant conditions, determination of the specific protease-, specific lipase- and specific cellulase enzyme activities optimized for the specification of the anaerobic sludge can be applied for presenting the frequent composition changes of substrates fed in the fermenters. If a substrate with large protein- and fat content is fed, the checking of the protease and lipase is suitable to follow up the effect, while in the case of vegetable waste supply, checking of the cellulase activity proved suitable. 4. Within pilot plant conditions I verified that the specific dehidrogenase enzyme activity is suitable to follow up the effects of the temperature changes, and that it has a correlation with the quantity of the produced biogas. 5. Based on my experiences gained in the course of tests completed under pilot plantand plant conditions at both mesophilic- and thermophilic temperatures, the proteaseand lipase enzyme activities showed strong correlation with the specific organic material load. The protease enzyme activity with a time lag of one/two day(s) while lipase enzyme activity with a time lag of maximum one day reflected the change in the specific organic material load. Under pilot-plant- and plant conditions I found correlation between the protease- and the lipase enzyme activities and the specific gas
volume at both the mesophilic and thermophilic temperatures. The protease- and lipase enzyme activities indicated the change in the specific gas volume with a time lag of one or two day(s). 6. On the basis of the pre-treatment tests completed under mesophilic pilot plant conditions I stated that - under the influence of ultrasonic preliminary treatment - a gas volume increase of 33 % can be experienced if compared to the specific gas volume of the control reactor. For the fermentation with preliminary treatment I experienced a significant relation between the dehydrogenase enzyme activity and the specific gas volume. And - on the basis of the preliminary treatment tests completed under laboratory conditions at mesophilic temperature in the interest of increasing the biogas quantity - I stated that with the used enzyme product it is possible to increase the dehydrogenase-, protease-, lipase- and cellulase enzyme activities of the sludge. 7. During the pilot-plant test - completed with vegetable co-substrate - I stated that for the effect of grass added to the waste sludge under optimum loading conditions it is possible to increase the specific gas quantity with 33 %. Within stable grass feeding period I found a significant relation between the specific gas quantity and the proteaseand cellulase enzyme activities, respectively.
4. Publications 4.1 Scientific papers in refereed journals in English Levente Kardos Ágota Juhász György Palkó József Oláh Katalin Barkács Gyula Záray (2011): Enzyme activity analyses of anaerobic fermented sewage sludges. In: Applied Ecology and Environmental Research, 9(4), pp. 333-339. ALÖKI Kft., Budapest, Hungary. ISSN 1589-1623 (print), ISSN 1785-0037 (online) Levente Kardos Ágota Juhász György Palkó József Oláh Katalin Barkács Gyula Záray (2011): Comparing of mesophilic and thermophilic anaerobic fermented sewage sludge based on chemical and biochemical tests. In: Applied Ecology and Environmental Research, 9(3), pp. 293-302. ALÖKI Kft., Budapest, Hungary. ISSN 1589-1623 (print), ISSN 1785-0037 (online) Levente Kardos György Palkó József Oláh Katalin Barkács Gyula Záray (2009): Operation control of anaerobic digesters on basis of enzyme activity tests. In: Water Science and Technology, 60(4), pp. 957-964. IWA Publishing, London, UK. ISSN 0273-1223 Levente Kardos Szilvia Tarjányi-Szikora József Oláh György Palkó Katalin Barkács Gyula Záray (2008): Co-digestion of sludge and organic wastes followed up by chemical and biochemical methods. In: Acta Pericemonologica Debrecina rerum ambientum, pp. 70-74. Debrecen, ISSN 1588 2284 4.2. Studies and conference proceedings Kardos Levente Palkó György Oláh József Barkács Katalin Záray Gyula (2011): A termofil és a mezofil hőmérsékletű kommunális szennyvíziszap rothasztás összehasonlítása kémiai és biokémiai vizsgálatok alapján. Erdei Ferenc VI. Tudományos Konferencia Tanulmánykötete, I. kötet, pp. 574-579. GyomaPress Kft. Kecskemét. ISBN 978-963-7294-99-0. Kardos Levente (2011): Az enzimaktivitás vizsgálatok szerepe az anaerob iszaprothasztás folyamatának ellenőrzésében. Erdei Ferenc VI. Tudományos Konferencia Tanulmánykötete, III. kötet, pp. 359-363. GyomaPress Kft. Kecskemét. ISBN 978-615-5192-01-2. Kardos Levente (2009): A biogáz mennyiségének növelése fizikai és kémiai módszerekkel egy kommunális szennyvíztisztító telepen. In: Szabó V. Fazekas I. (szerk.): Települési Környezet, pp. 234-238. Debreceni Egyetem (Tájvédelmi és Környezetföldrajzi Tanszék) és az Alföldi Nyomda Zrt., Debrecen, ISBN 978-963-473-336-2 Kardos Levente Juhos Katalin Palkó György Oláh József Barkács Katalin Záray Gyula (2009): Biogáz-kihozatal növelése egy kommunális szennyvíztisztító telepen. In: Orosz Z. Szabó V. Fazekas I. (szerk.) Környezettudatos energiatermelés és felhasználás, pp. 83-88. Alföldi Nyomda Zrt., Debrecen. ISBN 978-963-7064-20-3
Kardos Levente Tarjányiné Szikora Szilvia Oláh József Palkó György Barkács Katalin Záray Gyula (2008): Szennyvíziszap és szerves hulladékok együttrothasztásának nyomon követése kémiai és biokémiai módszerekkel. In: IV. Kárpát-medencei Környezettudományi Konferencia, I. kötet, pp. 173-177. Debrecen, REXPO Kiadó Kft. ISBN 978-963-06-4625-3 Kardos Levente Barkács Katalin Záray Gyula Palkó György Oláh József (2008): Anaerob rothasztók üzemének ellenőrzése biokémiai paraméterek alapján. In: Vízmű Panoráma, 2008/2. szám (16. évfolyam), pp. 3-8. Budapest, Magyar Víziközmű Szövetség, ISSN 1217-7032 Kardos Levente (2007): A szennyvíztelepi biogáztermelés optimálása és az üzemelés nyomon követése. In: Orosz Z. Fazekas I. (szerk.) Települési Környezet, pp. 266-271. Debrecen, Kossuth Egyetemi Kiadó, ISBN 978-963-473-101-6.