Seval Sözen

Propionate Oxidation by and Methanol Inhibition of Anaerobic Ammonium-Oxidizing Bacteria

ABSTRACT Anaerobic ammonium oxidation (anammox) is a recently discovered microbial pathway and a cost-effective way to remove ammonium from wastewater. Anammox bacteria have been described as obligate chemolithoautotrophs. However, many chemolithoautotrophs (i.e., nitrifiers) can use organic compounds as a supplementary carbon source. In this study, the effect of organic compounds on anammox bacteria was investigated. It was shown that alcohols inhibited anammox bacteria, while organic acids were converted by them. Methanol was the most potent inhibitor, leading to complete and irreversible loss of activity at concentrations as low as 0.5 mM. Of the organic acids acetate and propionate, propionate was consumed at a higher rate (0.8 nmol min−1 mg of protein−1) by Percoll-purified anammox cells. Glucose, formate, and alanine had no effect on the anammox process. It was shown that propionate was oxidized mainly to CO2, with nitrate and/or nitrite as the electron acceptor. The anammox bacteria carried out propionate oxidation simultaneously with anaerobic ammonium oxidation. In an anammox enrichment culture fed with propionate for 150 days, the relative amounts of anammox cells and denitrifiers did not change significantly over time, indicating that anammox bacteria could compete successfully with heterotrophic denitrifiers for propionate. In conclusion, this study shows that anammox bacteria have a more versatile metabolism than previously assumed.

Respirometric analysis of activated sludge behaviour - I. Assessment of the readily biodegradable substrate

Abstract Respirometric analysis of domestic sewage together with textile, dairy, meat processing, tannery and confectionery wastewaters were carried out for the experimental assessment of the readily biodegradable COD. The accuracy and the reliability of the experimental procedure was tested using synthetic sewage and different wastewater mixtures. The merit of OUR and NUR measurements was investigated in parallel aerobic and anoxic batch reactors. The OUR data was analysed with specific emphasis to identify the lower plateau associated with the hydrolysis of slowly biodegradable substrate. The NUR data was corrected for nitrite formation to provide an accurate account of electron acceptor consumption. The respirometric procedure and especially the effect of the initial substrate to biomass F M ( C T1 X T1 ) ratio was investigated using model simulation of the respirometry curve together with the collected experimental data.

Characterization and COD fractionation of domestic wastewaters

Results of a comprehensive study are reported for wastewater characterization in relation to modelling and design of biological nutrient removal systems for the Metropolitan Area of Istanbul. Domestic sewage quality was experimentally assessed in terms of major polluting parameters. Size distribution and calculation of significant ratios such as BOD5:COD and COD:N were used to evaluate the merit of candidate physical, chemical and biological treatment alternatives. COD fractionation was effected to assess biological treatability and to yield the necessary process components to the recent modelling approaches.

The effect of residual microbial products on the experimental assessment of the particulate inert COD in wastewaters

Abstract This study mainly investigated the conceptual and experimental aspects related to the assessment of the particulate inert COD in tannery, domestic and synthetic wastewaters. The assumption of a constant fEX coefficient defining the residual fraction of endogenous biomass was not justified. Experimental proof was provided for the effect of residual microbial products generation, both soluble and particulate, on the assessment of inert COD fractions of different wastewaters. The results enabled the description of a unified procedure for the experimental assessment of inert COD fractions of wastewaters, as well as residual microbial products.

Respirometric analysis of activated sludge behaviour—II. Heterotrophic growth under aerobic and anoxic conditions

Respirometric analysis of domestic sewage and textile, dairy, meat processing, tannery and confectionery wastewaters were carried out for the experimental assessment of the maximum specific growth rate of heterotrophic biomass and the correction factors for biological growth and hydrolysis under anoxic conditions. The accuracy and reliability of the experimental procedure was tested using synthetic sewage and different wastewater mixtures. The merit of adopting a lower yield coefficient associated to nitrate utilization under anoxic conditions was theoretically discussed and verified with the experimental results obtained. The kinetic basis of respirometric analysis was evaluated for interpretation of the experimental data on the basis of major mathematical methods currently defining activated sludge modelling.

Dual hydrolysis model of the slowly biodegradable substrate in activated sludge systems

Experimental assessment of the hydrolysis rate coefficients for both domestic sewage and a number of industrial wastewaters was performed with emphasis on two different hydrolysis mechanisms associated with the readily and slowly hydrolyzable COD fractions. The adopted dual hydrolysis model was justified on the basis of significantly different rate constants. The hydrolysis rate of particulate COD occurred at such a slow rate that would significantly interfere with endogenous decay.

The effect of nitrite correction on the evaluation of the rate of nitrate utilization under anoxic conditions

The nitrogen utilization requirement (NUR) test is a useful respirometric procedure for the assessment of major kinetic constants in activated sludge systems designed for nitrogen removal. The electron transfer mechanism of nitrogenous compounds often involves significant nitrite accumulation which impairs the accuracy of the NUR test. Experimental results revealed no meaningful correlation between nitrite accumulation and the initial nitrate concentration or the food/microorganism (F/M) ratio. Significant impact of nitrite accumulation was observed both on the assessment of the readily biodegradable COD component, the correction factor for anoxic growth and the denitrification rates applicable to domestic sewage and a number of industrial wastewaters. © 1999 Society of Chemical Industry

Implementation of the anammox process for improved nitrogen removal

Abstract Stringent standards for nitrogen discharge necessitate the implementation of new systems for the sustainable removal of ammonium from wastewater. One of such systems is based on the process of anaerobic ammonium oxidation (Anammox), which is a new powerful tool especially for strong nitrogenous wastewaters. In this study, the Anammox process performance was tested with synthetic wastewater in a completely stirred tank reactor (CSTR). The reactor was operated for 511 days and fed with increasing amounts of ammonium and nitrite. In this period, an increase of ammonium and nitrite utilization rates were observed as a result of the increase of nitrogen loads in the influent. After 272 days, about 60% of the biomass was removed from the reactor and the system was restarted. Throughout 511 days 90% of the ammonium and more than 99% of the nitrite were converted mainly to dinitrogen (N2) and nitrate. The microbial community in the reactor was characterized with Fluorescence in situ Hybridization (FISH). The study showed that the population in the reactor was dominated by the deep-branching planctomycete Candidatus “Brocadia anammoxidans” strain Dokhaven 2.

A new approach for the evaluation of the maximum specific growth rate in nitrification

Monitoring the generation of oxidized nitrogen concentration in batch reactors is the preferred approach for the assessment of the maximum specific growth rate for autotrophic biomass. The simplifying assumptions associated with the currently available methods are not always justifiable and may lead to misleading results. This paper provides a critical appraisal of the relevant conceptual basis and proposes a new approach for the experimental determination of the maximum specific growth rate in nitrification. The proposed method is successfully tested on domestic sewage. It is also tested with synthetic substrate, a meat processing plant effluent individually and in different mixtures with domestic sewage.

Respirometric evaluation of biodegradation characteristics of dairy wastewater for organic carbon removal.

This study evaluates the biodegradation kinetics of an integrated dairy wastewater, with the main purpose of defining the experimental basis for modelling of the activated sludge process. Besides conventional characterization, the experiments involved detailed chemical oxygen demand (COD) fractionation and assessment of major kinetic and stoichiometric coefficients, by using respirometric methods. A multi‐component model based on the endogenous decay concept was used for the kinetic interpretation. The results of conventional analyses and respirometric evaluations together with the assessment of residual components showed that the organic carbon content of the dairy wastewater was mostly soluble and biodegradable. The soluble, slowly biodegradable COD was the major COD fraction, representing around 50% of the total COD. Model calibration of the oxygen uptake rate profiles were consistent and revealed the existence of dual hydrolysis kinetics for soluble and particulate COD components. The hydrolysis rate associated with the main COD component – the soluble, slowly biodegradable COD fraction – was found to be 1.2 d−1, which is quite low and underlines the role of this COD fraction as the rate‐limiting factor for effluent quality. Simulation of process efficiency by the adopted model, calibrated with the experimentally determined parameters, indicated that effective control of the biodegradation of the soluble biodegradable COD components could be done by selection of appropriate values for the sludge age and hydraulic retention time. In this way, the total effluent soluble COD level could be lowered to 30–40 mg L−1 range, in conformity with effluent limitations.