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's 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.
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