Effect of influent COD/N ratio on biological nitrogen removal (BNR) from high-strength ammonium industrial wastewater

doi:10.1016/j.procbio.2003.10.005

Process Biochemistry

Volume 39, Issue 12, 29 October 2004, Pages 2035-2041

https://doi.org/10.1016/j.procbio.2003.10.005 Get rights and content

Abstract

The effect of influent COD/N ratio on biological nitrogen removal (BNR) from high-strength ammonium industrial wastewater was investigated. Experiments were conducted in a modified Ludzack–Ettinger pilot-plant configuration for 365 days. Total nitrification of an influent concentration of 1200 mg NH₄⁺–N l⁻¹ was obtained in this period. Influent COD/N ratios between 0.71 and 3.4 g COD g N⁻¹ were tested by varying the nitrogen loading rate (NLR) supplied to the pilot plant. An exponential decrease of nitrification rate was observed when the influent COD/N ratio increased.

The experimental COD/N ratio for denitrification was 7.1±0.8 g COD g N⁻¹ while the stoichiometric ratio was 4.2 g COD g N⁻¹. This difference is attributable to the oxidation of organic matter in the anoxic reactor with the oxygen of the internal recycle. The influence of influent COD/N ratio on the treatment of high-strength ammonium industrial wastewater can be quantified with these results. The influence of COD/N ratio should be one of the main parameters in the design of biological nitrogen removal processes in industrial wastewater treatment.

Introduction

Several activities generate high-strength ammonium wastewater including human waste, agricultural waste and industrial effluents.

Uncontrolled disposal of these effluents can cause great damage to the environment, primarily through eutrofication of receiving waster and because ammonium freely dissolved in the water is one of the worst polluting agents for aquatic life [1]. For this reason removal of ammonium from wastewater is explicitly required under the European Directive on the disposal of urban wastewater. The biological nitrogen removal (BNR) process is frequently used to treat urban wastewater. This process involves two stages: (1) conversion of ammonium into nitrate (nitrification) and subsequent transformation of nitrate into nitrogen gas (denitrification).

One of the most critical parameters of the nitrification process is the influent chemical oxygen demand to nitrogen ratio (COD/N), because it directly influences the growth competition between autotrophic and heterotrophic microorganism populations [2], [3], [4]. Some authors report that the influence of this ratio is greater in an aerobic activated sludge process than in the BNR process [5]. In the latter case, organic matter is mainly consumed in the first anoxic stage, which apparently allows lower competition between nitrifiers and heterotrophs in the next aerobic stage. In the early 1990s, McClintock et al. reported similar nitrification rates in both aerobic activated sludge and BNR systems operated with the same COD/N ratio [6]. Their results showed no differences in competition among microorganism populations in the BNR and aerobic activated sludge systems. Consequently, the influence of COD/N ratio on nitrification rate is similar in both systems.

Competition among microorganisms has been clearly observed in some other biological nitrogen removal processes, such as immobilized biomass systems [7]. In this case, the COD/N ratio causes growth competition among all different microbic populations and therefore defines the biofilm composition. This may cause undesirable nitrification inhibition in the global process for two reasons: (1) the majority presence of heterotrophic microorganisms in the biofilm, (2) oxygen diffusion problems in immobilized biomass [8], [9].

The aim of this paper was to quantify the influence of influent COD/N ratio on a BNR process of an industrial high-strength ammonium wastewater (N-wastewater) produced during the frosting process of bottles in a winery. The company also generates a zero-nitrogen containing wastewater, mainly containing of organic matter (C-wastewater). The main objective of this work was to determine the optimum proportion between both types of wastewaters in order to achieve maximum nitrogen removal. The study was conducted in an on-site pilot-plant fed with industrial wastewater from the site.

Section snippets

Wastewater features

The basic composition of both types of industrial wastewater is shown in Table 1. The N-wastewater contained 4000–6000 mg NH₄⁺–N l⁻¹, and the C-wastewater contained 800–3000 mg COD l⁻¹. This organic matter was mostly ethanol and readily biodegradable. Both C- and N-wastewaters also have high chloride and sulphate anion concentrations.

Experimental settings

Experiments in the present paper were conducted in a modified Ludzack–Ettinger configuration pilot-plant (Fig. 1). This plant consisted of an anoxic reactor (27 l), two

Results and discussion

Operational parameters affecting nitrification rate are diverse. In order to study the influence of influent COD/N ratio, parameters such as temperature, DO, and mean cell residence time (MCRT) were maintained constant throughout the study. Temperature is one of the most influential parameters on nitrification rates [12]. The study was performed at 25 °C. DO can become a limiting factor on nitrification if its value is <2 mg O₂ l⁻¹ and the floc size is bigger than 200 μm [13]. In order to prevent

Conclusions

Competition for substrates among different microorganisms populations in a BNR system causes a decrease in effectiveness of nitrification and denitrification processes.

Nitrification is highly influenced by competition established between heterotrophic and autotrophic microorganisms. This competition depends on the COD/N ratio of wastewater. The influence of COD/N ratio on system nitrification capacity can be quantified by means of nitrification rate or nitrifying biomass fraction. The

Acknowledgements

The Generalitat de Catalunya provided financial support for J. Carrera through a pre-doctoral fellowship. We wish to express our gratitude to project CYCIT: REN2000-0670/TECNO and the company FREIXENET S.A. The Department of Chemical Engineering of UAB is member of the CeRBa of the Generalitat de Catalunya.

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Effect of influent COD/N ratio on biological nitrogen removal (BNR) from high-strength ammonium industrial wastewater

Abstract

Introduction

Section snippets

Wastewater features

Experimental settings

Results and discussion

Conclusions

Acknowledgements

Water Res

Water Res

Water Res

Environ Modelling Software

Water Sci Technol

Water Res

Water Sci Technol

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Enzyme Microbiol Technol