TUTCRIS - Tampereen teknillinen yliopisto


Start-up of sulfide-oxidizing bioreactors under autotrophic denitrification conditions

Tutkimustuotos: Konferenssiesitys, posteri tai abstrakti


TilaJulkaistu - 19 tammikuuta 2017
TapahtumaThe 1st International ABWET Conference on Waste-to-Bioenergy: Applications in Urban Areas - Université Paris-Est Marne la Vallée - 5, Champs-sur-Marne, Ranska
Kesto: 19 marraskuuta 201720 marraskuuta 2017


ConferenceThe 1st International ABWET Conference on Waste-to-Bioenergy: Applications in Urban Areas


Biogas produced from anaerobic degradation of organic wastes commonly contains contaminants, such as carbon dioxide (CO2), hydrogen sulfide (H2S), ammonia (NH3) and siloxane, which should be removed before utilizing the biogas as an alternative energy source. H2S concentrations in biogas can range from a few ppm in facilities processing, such as landfill and off-gas from wastewater treatment plant, to several thousand ppm when treating liquid manure and biological wastes. The biological oxidation of the H2S present in biogas, under aerobic conditions, has been extensively studied in the past decade and applied in full-scale industrial systems. However, oxygen present in the aerobic bioreactors can dilute methane concentration in biogas and, when present in natural gas stream, can cause various problems, including the degradation of process chemicals and corrosion of pipelines. For safety reasons, it is also necessary to control the ratio of oxygen to methane in order to avoid reaching explosive limits (Petersson and Wellinger 2009; Fernández et al. 2013).
Recently, anoxic bioreactors have been introduced for H2S removal from biogas (Soreanu et al., 2008). A comparison between anoxic and aerobic bioreactors for H2S removal has indicated that anoxic bioreactors are more practically applicable than the conventional aerobic bioreactors, in terms of ease of use and operational costs (Fernández et al. 2013). Among the different bioreactor configurations tested, the biotrickling filter has been widely studied during the last few years (Almenglo et al. 2016; Fernández et al. 2014; Fernández et al. 2013; Soreanu et al. 2008). However, a combination of both suspended and attached growth bioprocesses for eliminating H2S from biogas streams has not been studied yet. The use of a moving bed biofilm reactor (MBBR), a hybrid bioreactor that combines the operational advantages of the conventional activated sludge and trickling filter processes, was proven to be successful for the treatment of domestic and industrial wastewater (Borkar et al. 2013). The MBBR was originally developed to solve the problems of periodic backwashing and clogging usually occurring in biofilm reactors and has been recently tested under anoxic, aerobic or anaerobic conditions (Rusten et al. 2006). The main objective of this research was to study sulfide oxidation in the liquid phase in order to enhance the fundamental understanding of the growth of sulfide oxidizing bacteria (SOB) in continuous bioreactors. For this purpose, two anoxic bioreactor configurations, i.e. a MBBR and fluidized bed reactor (FBR), were studied (Fig 1).
The MBBR and FBR were operated under the same conditions, i.e. room temperature (20 ± 2°C), hydraulic retention time (HRT) of 5 h, feed pH of 7.0 (±0.2) and nitrogen-to-sulfur (N/S) ratio of 0.5. The synthetic influent consisted of nutrients and micronutrients as described by Di Capua e al. (2017), in which sodium thiosulfate, Na2S2O3 (370 mg S2O32- L-1) and potassium nitrate, KNO3 (200 mg NO3- L-1) were used as substrate and electron acceptor, respectively. To study sulfide oxidation in liquid phase, Na2S2O3 was used as sulfur substrate instead of NaS2 in order to prevent S2- loss as gaseous H2S (Luo et al., 2013). The FBR start-up was done as described by Zou et al. (2016). The biofilm formation in the MBBR was initiated by transferring 10 mL of biofilm-coated (0.16 g VS mL-1) granular activated carbon (GAC) taken from the FBR after 705 operational days to allow the colonization of the plastic carrier (Kaldnes-K1). The batch tests were carried out in 60 mL serum bottles in order to determine the kinetic parameters of biomass present in both bioreactors at steady state conditions. The initial biomass concentration used in the batch tests was approximately 500 mg VSS L-1.
The bioreactor performances were evaluated for 120 days after the start-up of the MBBR. The thiosulfate removal efficiencies in both bioreactors were higher than 97% and all the removed thiosulfate was converted to sulfate. Similarly, nitrate was completely consumed in both bioreactors over time. The experimental data obtained from the batch tests were fitted with a Monod equation and the kinetic parameters for nitrate and thiosulfate uptake were determined (Table 1). The results of this study showed that the maximum specific nitrate and thiosulfate uptake rate (rmax) of the MBBR biomass were higher than those of the FBR biomass. This difference was probably related to the biomass carrier characteristics of both reactors, . The rmax and half saturation constant (Ks) obtained from the test can be used as a guide for operating the sulfide oxidizing reactors in further studies.