Mesophilic and thermophilic anaerobic digestion of acid whey into biogas

Kisla sirotka je tekoč stranski produkt mlekarske industrije in je zaradi nizkega pH, visoke vsebnosti organske snovi in nizke alkalinitete težaven substrat za obdelavo, zato pogosto konča v odpadnih vodah, kjer zaradi visoke vsebnosti organske snovi predstavlja veliko okoljsko obremenitev. Kljub temu ima kisla sirotka zaradi svoje sestave velik potencial za povečanje proizvodnje bioplina in donosa metana v procesu hkratne anaerobne razgradnje z odpadnim biološkim blatom, ki nastane pri čiščenju odpadne vode na čistilnih napravah. Namen magistrske naloge je bil s pomočjo testa biometanskega potenciala proučiti vpliv različnih obremenitev poskusnih mešanic s kislo sirotko v kombinaciji z mešanico primarnega in sekundarnega odpadnega biološkega blata na proizvodnjo bioplina v mezofilnih in termofilnih pogojih, in nato na podlagi dobljenih rezultatov simulirati proces anaerobne razgradnje v laboratorijskih bioreaktorjih. Test BMP smo izvajali v litrskih poskusnih steklenicah, 32 dni pri mezofilnih (39 C) in 28 dni pri termofilnih (55 C) pogojih. V poskusne steklenice smo poleg mešanice primarnega in sekundarnega blata (0,3 g KPKbata/1 g OSmikrobne biomase) dodali še različne koncentracije kisle sirotke (0,1, 0,3 in 0,5 g KPKsirotke/1 g OSmikrobne biomase). Poskus v laboratorijskih bioreaktorjih smo izvajali 42 dni v dveh litrskih bioreaktorjih pri mezofilnih pogojih (39 C). V oba smo na tri dni dodajali mešanico primarnega in sekundarnega blata, v poskusni bioreaktor smo poleg blata (0,3 g KPKblata/1 g OSmikrobne biomase) dodajali tudi največjo koncentracijo kisle sirotke (0,5 g KPKsirotke/1 g OSmikrobne biomase). Ugotovili smo, da dodana kisla sirotka poveča proizvodnjo bioplina v mezofilnih in termofilnih pogojih. Mezofilna anaerobna razgradnja kisle sirotke in odpadnega blata se je izkazala za učinkovitejšo, saj so bili izpleni metana 17 % večji kot pri termofilnih pogojih, kljub temu, da pri mezofilnih pogojih dodana kisla sirotka ni povečala proizvodnje metana v primerjavi z mešanicami s samim blatom. S poskusom v laboratorijskih bioreaktorjih smo ugotovili, da kontinuirno dodajanje kisle sirotke poveča proizvodnjo bioplina in metana in ne zavira procesa anaerobne razgradnje.Acid whey is a liquid by-product of the dairy industry, which is due to its low pH, a high organic matter content and a low alkalinity a difficult substrate when it comes to its processing. Therefore, it often ends up in wastewater, where it represents a high environmental burden because of its high organic matter content. Despite the mentioned fact, it is the acid whey\u27s structure that makes the liquid a great potential to increase biogas production and methane yield in anaerobic co-digestion process with sewage sludge, which is generated during wastewater treatment at wastewater treatment plants. The aim of this thesis was to examinate the influence of different burdens of experimental whey mixtures in combination with a mixture of primary and secondary sludge on biogas production in mesophilic and thermophilic conditions, by using the biomethane potential test, and then to simulate the process of anaerobic degradation in laboratory bioreactors based on the obtained results. The BMP test was carried out in 1-L test bottles which had been under mesophilic conditions (39 C) for 32 days and under thermophilic conditions (55 C) for 28 days. Besides the mixture of the primary and secondary sludge (0.3 g CODsludge/1 g OSmicrobial biomass), we also added different concentrations of the acid whey (0,1, 0,3 and 0,5 g CODwhey/1 g OSmicrobial biomass) to the test bottles. The experiment that took place in laboratory bioreactors was being carried out in 42 days, in two 1-L bioreactors under mesophilic conditions (39 C). Both of them received an addition of the primary and secondary sludge mixture every three days, while experimental bioreactor did not only receive the sewage sludge (0.3 g CODsludge /1 g OSmicrobial biomass), but also the maximum concentration of acid whey (0,5 g CODwhey/1 g OSmicrobial biomass). The results had shown that the added acid whey increased the biogas production under mesophilic and thermophilic conditions. Therefore, we concluded that mesophilic anaerobic decommissioning of acid whey and sewage sludge was more efficient, as methane yields had been 17 % higher than under thermophilic conditions, even though the added acid whey did not increase methane production under mesophilic conditions in comparison with the mixtures that contained only sludge. By having carried out this experiment in the laboratory bioreactors, we have realized that the continuous addition of the acid whey increases the production of biogas and methane and does not inhibit the process of the anaerobic decommissioning