Bulent Inanc

Community Changes During Start-up in Methanogenic Bioreactors Exposed to Increasing Levels of Ammonia

To investigate the methanogenic population dynamics during the start-up under gradually increasing free ammonia levels, five mesophilic UASB reactors seeded with different sludges were operated for 140 days. Changes in the methanogenic community investigated by using 16S rDNA/rRNA based molecular methods such as denaturing gradient gel electrophoresis (DGGE), fluorescent in-situ hybridization (FISH), cloning and DNA sequencing. Free ammonia nitrogen (FAN) in the reactors was gradually increased from 50 to 130 mg l-1 by increasing total ammonia nitrogen (TAN) from 1000 to 2500 mg l-1 in the feed and keeping reactor pH at 7.7 in the active zone. Even at highest FAN level, COD and VFA removal efficiencies above 90 and 98% were obtained, respectively. However, Methanosaeta-related species mainly prevailing in seed sludges were substituted for Methanosarcina as the abundant methanogens although reactor performances were almost comparable and constant.

Molecular Analysis of Microbial Communities in Nitrification and Denitrification Reactors Treating High Ammonia Leachate

Abstract Molecular analysis of microbial populations in two bench-scale nitrification and denitrification reactors fed with high ammonia landfill leachate was conducted in this study by using DGGE, cloning, and FISH techniques in addition to classical efficiency control parameters. Nitrification tank was operated with a computer-controlled alkalinity dosing system to supply the alkalinity intermittently as consumed on the basis of on-line pH monitoring. By keeping the pH at 7.0 with this system, 99% nitrification efficiency and rates of about 0.14–0.18 mg -N/mgVSS day were obtained. Meanwhile, as ammonia oxidizing bacteria Nitrosomonas and Nitrosococcus mobilis-like cells and as nitrite oxidizing bacteria Nitrobacter-related cells were intensively indicated. Moreover, some aerobic denitrifiers as Thauera species were also identified. After the termination of pH adjustment in the preceding anaerobic reactors, nitrification tank was loaded with more biodegradable COD as a result of reduced COD removal in anaerobic reactors. Microbial diversity was immediately affected from this alteration and heterotrophic carbonaceous bacteria and aerobic denitrifiers have dominated. To provide the former high efficiencies, retention time has increased from 24 to 48 h and a second pump dosing HCl was included to the automatic control system. Subsequent to these precautions, numbers of ammonia (Nso190) and nitrite oxidizing bacteria (NIT3) were comparatively increased. In denitrification system, about 98% denitrification efficiencies were obtained at 2000 mg/L NO x -N concentrations if sodium acetate was supplied as carbon source. Meanwhile, with 20 gVSS/l biomass concentration, denitrification rates of about 1.34 mgNO x -N/mgVSS day were obtained. All sludge samples have represented similar DGGE patterns and Paraccoccus-related species were identified as dominant denitrifying bacteria.

Comparative Analysis of Nitrifying Bacteria in Full–Scale Oxidation Ditch and Aerated Nitrification Biofilter by Using Fluorescent In Situ Hybridization (FISH) and Denaturing Gradient Gel Electrophoresis (DGGE)

In this study, nitrification performances and composition of nitrifying populations in a full–scale oxidation ditch and a high–rate submerged media nitrification biofilter were comparatively analyzed. In addition to different reactor configurations, effects of differing operational conditions on the nitrification efficiency and bacterial diversity were also explored and evaluated thoroughly. In microbial analysis of sludge samples fluorescent in situ hybridization (FISH) and denaturing gradient gel electrophoresis (DGGE) techniques were used complementary to each other. The extended aeration oxidation ditch subjected to the study is operated as a nitrogen and phosphorus removal system consisting of anaerobic, anoxic, and aerobic zones. The high–rate submerged media aerated filter is operated as nitrification step following the conventional activated sludge unit and the nitrified wastewater is discharged to the sea without complete nitrogen removal. In situ hybridization results have indicated that Nitrosomonas–like ammonia oxidizing and Nitrospira–related nitrite oxidizing bacteria were intensively present in vigorous flocs in nitrification biofilter while carbonaceous bacteria belong to beta subclass of Proteobacteria were considerably dominant in oxidation ditch. Low quantities of nitrifiers in oxidation ditch were also confirmed by the dissimilarity in intensive bands between two systems obtained with DGGE analysis.