Elsevier

Water Research

Volume 34, Issue 14, 1 October 2000, Pages 3675-3681
Water Research

Ammoniacal nitrogen removal from water by treatment with clays and zeolites

https://doi.org/10.1016/S0043-1354(00)00113-5Get rights and content

Abstract

The objective of the present study was to investigate the removal of nitrogen in the form of ammonium ions (N-NH+4) from aqueous solutions using natural clay and zeolite. The Croatian zeolite clinoptilolite from the area of Donje Jesenje and Croatian bentonite clay from the Kutina area were used as natural filtration materials. Alkaline and acid modification of natural clay was performed. The N-NH4+ removal efficiency by clays in a dry state as well as in a liquid colloidal state have been investigated. The highest removal efficiency value for N-NH+4 (61.1 wt%) was achieved with the natural zeolite at the lowest used initial concentration, i.e. at a concentration of 100 mg N-NH+4/l. With the increase of the initial concentration of ammoniacal nitrogen, the removal efficiency quickly decreases. This is expected as zeolites and clays have limited sorption capacities. The practical aspect is important since an ammoniacal nitrogen elimination of more than 60.0 wt% for water containing less than 100 mg N-NH+4/l can be achieved. The ammoniacal nitrogen removal efficiency is higher for clays in a liquid colloidal state compared to the clays in a dry state. It has been found that the acid modification of the clay decreases the efficiency of ammoniacal nitrogen removal.

Introduction

Nitrogen is a nutrient essential to all forms of life as a basic building block of plant and animal proteins. Although it is an essential nutrient for living organisms, too much of it can be toxic. The presence of nitrogen excess in the environment has caused serious distortions of the natural nutrient cycle between the living world and the soil, water, and atmosphere. Nitrogen in the form of nitrous oxide, nitric oxide, nitrate, nitrite or ammonia/ammonium is soluble in water and can end up in ground water and drinking water. One of the best documented and best understood consequences of human alterations of the nitrogen cycle is the eutrophication of estuaries and coastal seas (Oenema and Roest, 1998, Banens and Davis, 1998, Forsberg, 1998).

Various methods of ammoniacal nitrogen removal from waters have been developed, but the aim of worldwide investigation has been to discover new possibilities for ammoniacal nitrogen removal in waters.

Natural clays and zeolites gained significant interest in the scientific community over the last two decades. The discovery of natural clay and zeolite deposits has lead to an increasing use of these minerals for the purpose of eliminating, or at least reducing, many long standing pollution problems (Cerjan-Stefanović and Ćurković, 1997, Jorgensen and Libor, 1976, Koon and Kaufman, 1975; Mellah and Chegrouche, 1997; Gharaibeh and Dwairi, 1996; Schoeman, 1986, Smith and Galan, 1995, Mercer and Ames, 1970, Ćurković et al., 1997, Barrer, 1987).

Zeolites are similar in their composition to clay minerals. More specifically, both are hydrated aluminosilicates. They differ, however, in their crystalline structure. Natural zeolite framework consists of symmetrically stacked alumina and silica tetrahedra which results in an open and stable three dimensional honey comb structure with a negative charge. The negative charge within the pores is neutralized by positively charged ions (cations) such as sodium. These cations are exchangeable with certain cations in solutions such as heavy metals as well as ammonium ions (Ćurković et al., 1997, Barrer, 1987).

Clays are composed of extremely fine crystals or particles of clay minerals. Because of their fineness, clay particles exhibit chemical properties of colloids. Clay minerals are sandwiches of tetrahedral and octahedral sheet structures. They are classified into layer types, distinguished by the number of tetrahedral and octahedral layers. The 2:1 layer type has two silicon-oxygen tetrahedral sheets that sandwich an aluminum-oxygen-hydroxyl octahedral sheet. The three mineral groups with this structure are illite, vermiculite, and smectite (Barrer, 1989, Skipper et al., 1995).

The isomorphous substitutions of Al3+ for Si4+ in the tetrahedral sheet and Mg2+ or Fe2+ for Al3+ in the octahedral sheets result in a negative surface charge on the clay. These charges are permanent, do not vary with change in pH, but do vary depending on the type of clay. This unbalanced charge is compensated by exchangeable cations (most often, Na+ or Ca2+) which are relatively loosely held, although stoichiometrically, and give rise to major cation exchange properties. A second negative charge occurs as a result of dissociation of the hydrogen in various hydroxyl groups which include SiOH and AlOH groups. The tendency for dissociation increases with an increase in pH. Another source of charge on the clays are the low coordination number edge atoms. Their charges are neutralised by compensation cations.

The layered structure of the clay allows expansion (swelling) when contacted with water, which exposes an additional mineral surface capable of cation adsorption.

The aim of this paper was the investigation of the possibility of using natural Croatian clay and zeolite as a filter medium for water treatment with regard to ammoniacal nitrogen.

Section snippets

Reagents

1000 mg N-NH+4/l and 10 000 mg N-NH+4/l stock solutions were prepared by dissolving anhydrous ammonium chloride salt, respectively, in distilled water. The expression “N-NH+4” is defined as “nitrogen in the form of ammonium ion”. The exact concentration of ammoniacal nitrogen solutions were verified by spectrophotometry at wave length λ=377.89 nm where the absorbance is the maximal one.

Characterization of zeolite and clay samples

The clay samples (samples 2, 3 and 4) were investigated by differential thermal analysis (DTA),

Results and discussion

Chemical composition of tested zeolite and clay samples (wt%) is presented in Table 1. All samples contain sodium ions as the main exchangeable ions. Other ions are strongly held by all samples as opposed to sodium (Table 2, Table 3).

Acid treatment leads to dealumination, i.e. an increase of the silica to alumina ratio. With Al removal, ions such as Na+, Ca2+, K+ which were bound to clay were also removed. The rate of the ammoniacal nitrogen removal process is very important, and small rates

Conclusion

Only natural zeolite (sample 1) removes more than 50 wt% of ammoniacal nitrogen (61.1 wt% N-NH+4) at the solution concentration of 100 mg N-NH+4/l. By increasing the initial ammoniacal nitrogen concentration the removal efficiencies decreased on all samples. Na+, K+, Ca2+ and Mg2+ cations which compensate the negative charge of aluminosilicate frameworks of clay and zeolite can be exchanged with other cations and with H+ ions. The Na+ ions in aluminosilicate structure of zeolites and clays are

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