Advantages of anaerobic digestion of sludge in microaerobic conditions P. Jenicek, J. Koubova, J. Bindzar and J. Zabranska ABSTRACT P. Jenicek (corresponding author) J. Koubova J. Bindzar J. Zabranska Department of Water Technology and Environmental Engineering, Institute of Chemical Technology Prague, Technicka 5, 166 28 Prague, Czech Republic E-mail: jenicekp@vscht.cz The paper reviews results and experience of microaerobic experiments at both high and low sulphide concentrations and evaluates advantages and drawbacks of the anaerobic digestion of sludge in microaerobic conditions as regards biogas quality, digested sludge quality, organic pollutants biodegradability and methanogenic activity of biomass. The innovative microaerobic modification of the anaerobic sludge digestion technology was studied in both laboratory and full scale. Microaerobic conditions are obtained by dosing of a limited amount of the air into the liquid phase of the anaerobic digester. It was shown that anaerobic bacteria including methanogens can be active also in such system. In a mixed culture, even strict anaerobes can survive without inhibition, if the facultative microorganisms are able to consume the present oxygen quickly and fully. Until now, the microaerobic conditions were predominantly used for hydrogen sulphide removal from biogas. In the paper the role of the surplus oxygen was studied also at low sulphide concentration, when the oxygen is consumed in high extent for other processes beside sulphide oxidation. Key words | anaerobic digestion, biodegradability, methanogenic activity, microaerobic conditions, sulphide oxidation INTRODUCTION Among sludge treatment technologies anaerobic digestion is established and well-proven technology. The innovative microaerobic modification of anaerobic sludge digestion technology combines the anaerobic and in micro-scale the aerobic condition. In the field of biological wastewater treatment the combination of anaerobic and aerobic processes is well known and often used. It brings many benefits, mostly related to excellent treatment efficiency and low energy consumption. In the field of sludge treatment the combination of different operational conditions is much scarcer. The successive combination of anaerobic sludge treat- ment followed by post-aeration was successfully tested to improve nitrogen removal (Parravicini et al. 2008), however in this case both processes are separated in time and space. Untill lately, there was a lack of knowledge about the possibility of combining both anaerobic and aerobic (or anoxic) processes ( Jenicek et al. 2002) at the same time simultaneously in one biological reactor. The coupling of oxidative and reductive environments is common in natural environments since the homogeneous distribution of oxygen is rare (Stephenson et al. 1999). Conjunction and symbiosis of anaerobic and aerobic processes into the microaerobic operation of anaerobic digestion presents a special case ( Jenicek et al. 2005). It was found out that limited and controlled presence of oxygen inside a digester is not dangerous, it can even have a positive effect in some aspects (Stephenson et al. 1999; Zitomer & Shrout 2000; Khanal & Huang 2003a; Tang et al. 2004; van der Zee et al. 2007). The microaerobic condition is obtained by dosing of a limited amount of air (oxygen) into an anaerobic reactor. doi: 10.2166/wst.2010.305 427 Q IWA Publishing 2010 Water Science & Technology—WST | 62.2 | 2010 Downloaded from https://iwaponline.com/wst/article-pdf/62/2/427/446300/427.pdf by guest on 19 June 2020