Achieving the nitrite pathway using aeration phase length control and step-feed in an SBR removing nutrients from abattoir wastewater

Aeration phase length control and step-feed of wastewater are used to achieve nitrogen removal from wastewater via nitrite in sequencing batch reactors (SBR). Aeration is switched off as soon as ammonia oxidation is completed, which is followed by the addition of a fraction of the wastewater that the SBR receives over a cycle to facilitate denitrification. The end-point of ammonia oxidation is detected from the on-line measured pH and oxygen uptake rate (OUR). The method was implemented in an SBR achieving biological nitrogen and phosphorus removal from anaerobically pre-treated abattoir wastewater. The degree of nitrite accumulation during the aeration period was monitored along with the variation in the nitrite oxidizing bacteria (NOB) population using fluorescence in situ hybridization (FISH) techniques. It is demonstrated that the nitrite pathway could be repeatedly and reliably achieved, which significantly reduced the carbon requirement for nutrient removal. Model-based studies show that the establishment of the nitrite pathway was primarily the result of a gradual reduction of the amount of nitrite that is available to provide energy for the growth of NOB, eventually leading to the elimination of NOB from the system.     

Kinetic analysis on the two-step processes of AOB and NOB in aerobic nitrifying granules

Complete granulation of nitrifying sludge was achieved in a sequencing batch reactor. For the granular sludge, batch experiments were conducted to characterize the kinetic features of ammonia oxidizers (AOB) and nitrite oxidizers (NOB) in the granules using the respirometric method. A two-step nitrification model was established to determine the kinetic parameters of both AOB and NOB. In addition to nitrification reactions, the new model also took into account biomass maintenance and mass transfer through the granules. The yield coefficient, maximum specific growth rate, and affinity constant for ammonium for AOB were 0.21 g chemical oxygen demand (COD) g⁻¹ N, 0.09 h⁻¹, and 9.1 mg N L⁻¹, respectively, whereas the corresponding values for NOB were 0.05 g COD g⁻¹ N, 0.11 h⁻¹, and 4.85 mg N L⁻¹, respectively. The model developed in this study performed well in simulating the oxygen uptake rate and nitrogen conversion kinetics and in predicting the oxygen consumption of the AOB and NOB in aerobic granules.     

Reactions of nitrosobenzene with reduced glutathione.

Nitrosobenzene (NOB) formed acid labile conjugates with reduced glutathione (GSH) and hemoglobin within red cells. In vitro, NOB rapidly reacted with GSH with formation of phenylhydroxylamine (PH), oxidized glutathione (GSSG), and a water-soluble compound identified as glutathionesulfinanilide (GSO-AN). Free aniline (AN), aminophenols and azoxybenzene were not detected. The proportion of PH formed increased with increasing GSH concentration and at higher pH values. Spectroscopic analysis revealed the formation of a labile adduct following a second order reaction (K = 5 x 10(3) M-1 . sec-1 at pH 7.4 and 37 degrees). This reaction was reversible because nearly all NOB could be extracted with ether from the labile intermediate. On the other hand, the labile intermediate was transformed into GSO-AN (with increasing rate at lower pH values) or it was cleaved by GSH with formation of GSSG and PH. Intermediate formation of NOB and thiol radicals was ruled out by analysis of the equilibrium data. A tentative scheme is presented for the proposed reaction mechanism.     

Characterization of a new marine nitrite oxidizing bacterium, Nitrospina watsonii sp. nov., a member of the newly proposed phylum “Nitrospinae”

Nitrite oxidizing bacteria are an integral part of the nitrogen cycle in marine waters, but the knowledge about their diversity is limited. Recently, a high abundance of Nitrospina-like 16S rRNA gene sequences has been detected in oceanic habitats with low oxygen content by molecular methods. Here, we describe a new strain of Nitrospina, which was sampled in 100 m depth from the Black Sea. It coexisted with a not-yet cultivated chemoorganotrophic gammaproteobacterium and could be purified by classical isolation methods including Percoll density gradient centrifugation. The new Nitrospina-like bacterium grew lithoautotrophically at 28 °C in diluted seawater supplemented with inorganic salts and nitrite. Gram-negative rods were characterized morphologically, physiologically and partly biochemically.