Removal of Ammonium and Organic Compounds by Ion Exchange and Adsorption

Adsorption using activated carbon and ion-exchange is used to remove a range of organic compounds and ammonia respectively from treated wastewaters. Such treatment may follow secondary biological treatment to reduce BOD. Organic nitrogen (e.g. proteins) is degraded to ammonia and residual organic compounds may also be present following secondary treatment. Residual organic compounds may be those which are recalcitrant and may include fatty acids, aromatic compounds, and detergents. Adsorption and ion exchange may offer an alternative to further biological treatment. Possible advantages include good response to shock loading, and low sensitivity to variations in temperature, pH, and anti-microbial activity. Three areas of investigation were undertaken and are described here; adsorption of organic acids onto activated carbon, the adsorption of aromatic compounds and proteins onto activated carbon and onto ion exchange resins, and the ion exchange removal of ammonium from an actual waste-water in the presence of organic compounds. Three cationic ion exchangers were studied: Clinoptilolite, Dowex 50w-x8 and, Purolite MN500. Three adsorbents were evaluated: two samples of activated carbon: Norit GAC 1240, and Aldrich activated carbon; and crushed glass (AFM). The results show that phenol, benzoic acid, methanoic, ethanoic, and propionic acid were successfully adsorbed on to the activated carbon. AFM was an ineffective adsorbent. It was also shown that successful ammonium removal by ion exchange in the presence of organic compounds was possible. In the presence of real wastewater, there were significant variations in the removal performance. Introduction As discharge limits for treated waste-water continue to become more stringent, tertiary treatment will become a requirement. The Council of the European Community [1] has set a guide level of 0.05mg/l and a maximum level of 0.5mg/l. New Zealand discharge standards vary from 0.22mg/l to 0.77mg/l [2]. In some cases biological methods may fail if the water contains antimicrobial chemicals. Some compounds may not be biodegradable and its also possible that the pH and temperature are outside suitable ranges for biological treatment. One possibility is the use of activated carbon to remove organic compounds and ion exchange to exchange ammonium with the less toxic sodium [3,4,5,6]. Applications range from the petrochemical sector to industries such as woolscouring. Ammoniacal nitrogen along with other organic compounds (some of which may be recalcitrant) also contributes to the overall BOD. Three aspects are considered here:(1) Removal of short chain fatty acids onto activated carbon by adsorption, (2) Adsorption of aromatic compounds and proteins onto activated carbon, AFM (crushed glass), and onto cationic exchange resins (3) The potential of ion exchangers for removal of ammonia and simultaneous sorption of organic compounds.