Elsevier

Water Research

Volume 38, Issue 2, January 2004, Pages 347-354
Water Research

Enhanced ammonia nitrogen removal using consistent biological regeneration and ammonium exchange of zeolite in modified SBR process

https://doi.org/10.1016/j.watres.2003.09.025Get rights and content

Abstract

The modified zeo-SBR is recommended for a new nitrogen removal process that has a special function of consistent ammonium exchange and bioregeneration of zeolite-floc. Three sets of sequencing batch reactors, control, zeo-SBR, and modified zeo-SBR were tested to assess nitrogen removal efficiency. The control reactor consisted of anoxic-fill, aeration-mixing, settling, and decanting/idle phases, meaning that nitrogen removal efficiency was dependent on the decanting volume in a cycle. The zeo-SBR reactor was operated in the same way as the control reactor, except for daily addition of powdered zeolite in the SBR reactor. The operating order sequences in the zeo-SBR were changed in the modified zeo-SBR. Anoxic-fill phase was followed by aeration-mixing phase in the zeo-SBR, while aeration-mixing phase was followed by anoxic-fill phase in the modified zeo-SBR to carry NH4+-N over to the next operational cycle and to reduce total nitrogen concentration in the effluent. In the modified zeo-SBR, nitrification and biological regeneration occurred during the initial aeration-mixing phase, while denitrification and ammonium adsorption occurred in the following anoxic-fill phase. The changed operational sequence in the modified zeo-SBR to adapt the ammonium adsorption and biological regeneration of the zeolite-floc could enhance nitrogen removal efficiency. As a result of the continuous operation, the nitrogen removal efficiencies of the control and zeo-SBR were in 68.5–70.9%, based on the 33% of decanting volume for a cycle. The zeo-SBR showed a consistent ammonium exchange and bio-regeneration in the anoxic-fill and aeration-mixing phases, respectively. Meanwhile, the effluent total nitrogen of the modified zeo-SBR showed 50–60 mg N/L through ammonium adsorption of the zeolite-floc when the influent ammonium concentration was 315 mg N/L, indicating the T-N removal efficiency was enhanced over 10% in the same HRT and SRT conditions as those of control and zeo-SBR reactors. The ammonium adsorption capacity was found to be 6–7 mg NH4+-N/g FSS that is equivalent to 40 mg NH4+-N/L of ammonium nitrogen removal.

Introduction

High concentration of organics and ammonia nitrogen is commonly present in industrial wastewaters such as tannery, textile, landfill leachate, and fertilizer wastewater. Biological processes for nitrogen removal is very important for wastewater treatment because discharge of nitrogen into surface water results in oxygen depletion and algae bloom. In order to enhance the nitrogen removal from ammonium-rich wastewater, several studies on pretreatment such as air stripping and chemical precipitation with magnesium ammonium phosphate have been conducted. These processes, however, require complicated configuration and have difficulties in maintenance due to the scale formation [1], [2], [3].

Zeolite is a well-known material for its ability to preferentially remove ammonium ions from wastewater. Unlike synthetic ion exchange resins, zeolite is known to possess a higher selective ion-exchange capability for ammonium ion than Ca2+ and Mg2+, even when the concentration of the latter is higher than the former [4]. Natural zeolite was mainly used to remove ammonium ions from secondary effluent by selective ion exchange [5], but it was rarely tested for the wastewater of high ammonium nitrogen level, due to the chemical regeneration cost of the used zeolite [6].

Several researchers have developed hybrid biological-ion exchange systems, using the zeolite as ion exchange material [7], [8]. Green et al. [9], [10] recently presented a dual mode process consisting of ion exchange and bioregeneration mode in a single reactor using zeolites for ammonium removal, followed by bioregeneration. In addition to the ammonium removal step with bioregeneration, however, a denitrification step should be provided for complete nitrogen removal from nitrogen stream generated from bioregeneration.

Jung et al. [11], [12] conducted studies on the bioregeneration and ammonium exchange capacity of the bio-flocculated zeolite, having powdered zeolite added to a sequencing batch reactor. However, they could not enhance overall nitrogen removal efficiency in a zeolite-added SBR. Therefore, modified zeo-SBR is recommended for nitrogen removal process that has a special function of consistent ammonium exchange capacity and bioregeneration of the bio-flocculated zeolite as described in Jung et al. [11], [12].

The objectives of this study were to test whether a modified zeo-SBR process could enhance the nitrogen removal more than control and zeo-SBR reactors could, by using the role of powdered zeolite in a sequencing batch reactor.

Section snippets

Principle of bioregeneration

The equilibrium exchange reaction between the NH4+ ion in the solution and the Na+ ion attached to the zeolite can be expressed as stoichiometric reaction:Z-Na++NH4+Z-NH4++Na+where Z=zeolite.

The selectivity of various ions is dependent on the size, electron, and electric structure of cations. Once the zeolite is saturated with ammonium, chemical regeneration is possible when the large amount of sodium chloride is added into the solution. As soon as the ammonium-saturated zeolite is placed in

Experimental apparatus

Three sets of sequencing batch reactors, control, zeo-SBR, and modified zeo-SBR were tested to assess nitrogen removal efficiency. 240 mg zeolite/L was daily added to zeo-SBRs. The powdered zeolite passed through a No. 100 sieve (0.15 mm). As shown in Table 1, true density and specific surface area of the powdered zeolite were 1.73 g/mL and 49.6 m2/g, respectively. The working volume of each reactor was 2.5 L. The anoxic condition was maintained with a mechanical mixer, while mixing and aeration

Mechanism and roles of the zeolite in the SBR

The roles of powdered zeolite in a sequencing batch reactor are summarized in Fig. 3 as described in our previous work [11], [12]. As the powdered zeolite was added to the SBR, microorganisms that were attached on the surface of zeolite or were entrapped the powdered zeolite particles formed zeolite-floc. These zeolite-flocs enhanced the settleability of microbial floc because of the higher specific gravity of zeolite. This zeolite-floc adsorbed ammonium nitrogen during the anoxic-fill phase.

Conclusions

Zeolite- floc in the sequencing batch reactor had the ammonium adsorption capacity of 6.0–7.4 mg NH4+-N/g FSS.

Control reactor with the sequential denitrification and nitrification during the anoxic-fill and aeration-mixing phases, respectively, showed a 70% of T-N removal at 33% decanting volume for one cycle (influent ammonia nitrogen=300 mg/L).

Zeo-SBR reactor represented the same nitrogen removal as the control reactor, but zeolite-folc in the reactor showed the ammonium adsorption and

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