Biological-ion exchange process for ammonium removal from secondary effluent

Abstract

A new concept for ammonium removal from secondary effluent by zeolite followed by bio-regeneration has been studied. In contrast to other studies of hybrid biological-ion exchange multireactor systems, the proposed process uses the ion exchange material, zeolite, as the carrier for the nitrifying biomass. This enables the two mode process to be carried out in a single reactor. In the first mode (ion exchange), secondary effluent is passed through an ion exchange column where ammonium is concentrated in the zeolite. During the second mode (bioregeneration), the absorbed ammonium is released gradually and converted to nitrate by the active biomass residing on the zeolite. Nitrification is carried out batchwise and in a small volume reactor where optimal conditions can easily be maintained. Moreover, the addition of chemicals for the desorption of ammonium is minimal due to regenerant reuse during several cycles of nitrification. As a result, operational costs and production of large volumes of brine are minimized. Batch and breakthrough experiments showed that the amount of ammonium adsorbed on the chabazite is strongly affected by the presence of competing cations present in secondary effluent. A reduction of about 75% was observed when using a typical Israeli sewage ion composition. The attached biomass did not significantly effect the efficiency of the ion exchange column. Ammonium desorption experiments showed that regeneration with 10,000 mg/L Na+ is much faster than with 2440 mg/L (more than 90% ammonium recovery after 40 and 70 bed volumes, respectively). A nitrification rate of 6 g NH4-N/(L reactor *day) was obtained in a fluidized bed reactor with chabazite as the carrier. Although this rate is in the high range of reported values for biofilm reactors, desorption experiments proved that nitrification will be the process's rate limiting step, rather than the desorption rate when regenerant solutions as low as 2440 mg/L Na+ are used.

Ammonium removal from wastewaters using natural New Zealand zeolites

“…One of these factors would be the presence of Na + and other cations in wastewaters. These cations may compete with NH 4 + for the adsorption sites on zeolites and hence decrease the exchangeable sites available for NH4 + removal (Koon & Kaufman 1975;Schoeman 1986;Booker et al 1995;Green et al 1996;Singh & Prasad 1997). This competition effect could explain the lower NH4 + removal performance in both zeolites tested (particularly clinoptilolite) when Na + was added to NH 4 + solutions ( Fig.…”

“…9) and the effluent NH4" 1 " concentration was <8 g NH 4 -N m" 3 . If NH4 + breakthrough was defined at 8 g NH 4 -N/m 3 (Green et al 1996), instead of 1.2 g NH 4 N m" 3 , the operating NH 4 + removal capacity after 64 BVs represents the Number of bed volumes passed through columns …”

“…The change in this composition and concentration (and hence the ionic strength) is expected to influence the extent of anion and cation adsorption on zeolites and hence the zeolite surface charge Nguyen & Tanner-Natural zeolites for ammonium removal from wastewaters 441 available for NH4 + adsorption (Koon & Kaufman 1975;Jorgensenetal. 1976; (Koon & Kaufman 1975;Jorgensen et al 1976;Schoeman 1986;Booker et al 1996;Green et al 1996;Singh & Prasad 1997). Organic matter and suspended solids may also influence the surface charge density on zeolites by providing alternative cation exchangeable sites for NH 4 + adsorption (Nommik & Vahtras 1982) or coating and clogging the zeolite interstitial pores, thus blocking NH4"1" for adsorption sites on zeolites (Olah et al 1988).…”

“…6) Research, 1998, Vol. 41 from farm dairy pond discharge with NH4 + concentration of 75 g NH4-N m" 3 , assuming that clogging of zeolite pores by S S and hence blocking of adsorption-diffusion sites (Liberti et al 1979;Green et al 1996) is not a major problem.…”

“…Backwashing is unrealistic unless zeolite and sand filter beds are placed in appropriately designed holding tanks. This may be an attractive option for farmers since holding tanks can be readily removed and zeolites may subsequently be regenerated for further NH 4 " removal (Green et al 1996) or reused as saleable N fertilisers and soil conditioners (Barbarick & Pirela 1984). Research is therefore required to determine the most cost effective and suitable approach of using zeolites in fanning situations.…”