In this study, the dependence between volumetric exchange rate (n) in an SBR (Sequencing Batch Reactor) with a modified cycle and simultaneous nitrification and denitrification (SND) efficiency during the treatment of anaerobic sludge digester supernatant was determined. In the SBR cycle alternating three aeration phases (with limited dissolved oxygen (DO) concentration up to 0.7 mg O2/L) and two mixing phases were applied. The lengths of each aeration and mixing phases were 4 and 5.5 h, respectively. Independently of n, a total removal of ammonium was achieved. However, at n = 0.1 d-1 and n = 0.3 d-1 nitrates were the main product of nitrification, while at n = 0.5 d-1, both nitrates and nitrites occurred in the effluent. Under these operational conditions, despite low COD/N (ca. 4) ratio in the influent, denitrification in activated sludge was observed. A higher denitrification efficiency at n = 0.5 d-1 (51.3%) than at n = 0.1 d-1 (7.8%) indicated that n was a crucial factor influencing SND via nitrite and nitrate in the SBR with a low oxygen concentration in aeration phases.

The paper presents the results of anaerobic digestion and co-digestion under mesophilic conditions in the OxiTop system and in lab-scale fermentors. The goal of the study was to determine the effect of reaction-based oil waste on biogas production in co-fermentation with sewage sludge (mixture of thickened primary and excess sludge). The average water content in sewage sludge was 97 %, with 70 % of total volatile solids concentration (TVS) in total solids. Weight content of oil waste in the mixture of sewage sludge ranged from 15 to 45 % (w/w) and the increase in TVS to 83.7 % was observed. The primary investigations of gas productivity by manometrie method (OxiTop) showed that biogas production increased with increasing content of oil waste in the mixture with sewage sludge. The rate constant of the first-order kinetics for biogas production was determined. To determine the yield parameters of cofermentation, the experiment was performed in four continuously stirred anaerobic reactors with a working volume of IO drrr'. Organic loading rate (OLR) changed from 0.9 to 3.1 kg TVS/m3•d. High correlation between biogas flow rate and OLR was observed. Volumetric biogas production rate and the average methane content in the biogas increased from 0.79 to 1.98 m3/m3-d and from 52.3 to 62.3 %, respectively, as OLR increased. The results obtained in lab-scale fermentors are promising and open the possibilities of the implementation of co-fermentation of sewage sludge and oil waste.

The impact of mechanical pre-treatment of municipal solid waste (MSW) on its biogas production potential was examined. Mechanical separation allowed the following size-fractions to be obtained: fine fraction - mineral fraction of municipal solid waste (MFMSW) (cf> < 20 mm), middle fraction - organic fraction of municipal solid waste (OFMSW) (20 mm< cf>< 80 mm), and coarse fraction (cf>> 80 mm). The most suitable fraction for biological treatment was OFMSW, containing about 76 % of high rate biodegradable organic fraction (HRBOF). The rate constant of degradation for organic compounds in OFMSW was 0.23 d·1• It was shown that total gas production (TGP) during 10 years may achieve 550 m3/Mg OFMSW. Mechanical pre-treatment may allow an 45 % decrease of the amount of landfilled MSW resulting in a reduction of greenhouse gas emissions of up to 70 m3/Mg over 10 years of landfilling (in contrast to MSW landfilling - 213 m3/Mg). The experimental results revealed that gas production potential should be determined on the basis of HRBOF content and measurements of the biogas production.