BIOLOGICAL-ION EXCHANGE PROCESS FOR AMMONIUM REMOVAL FROM SECONDARY EFFLUENT

A new concept for ammonium removal from secondary effluent by zeolite followed by bio-regeneration has been studied. In contrast to other st udies of hybrid biological-ion exchange multireactor systems, the prop osed process uses the ion exchange material, zeolite, as the carrier f or the nitrifying biomass. This enables the two mode process to be car ried out in a single reactor. In the first mode (ion exchange), second ary effluent is passed through an ion exchange column where ammonium i s concentrated in the zeolite. During the second mode (bioregeneration ), the absorbed ammonium is released gradually and converted to nitrat e by the active biomass residing on the zeolite. Nitrification is carr ied out batchwise and in a small volume reactor where optimal conditio ns can easily be maintained. Moreover, the addition of chemicals for t he desorption of ammonium is minimal due to regenerant reuse during se veral cycles of nitrification. As a result, operational costs and prod uction of large volumes of brine are minimized. Batch and breakthrough experiments showed that the amount of ammonium adsorbed on the chabaz ite is strongly affected by the presence of competing cations present in secondary effluent. A reduction of about 75% was observed when usin g a typical Israeli sewage ion composition. The attached biomass did n ot significantly effect the efficiency of the ion exchange column. Amm onium desorption experiments showed that regeneration with 10,000 mg/L Na+ is much faster than with 2440 mg/L (more than 90% ammonium recove ry 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 wi th chabazite as the carrier. Although this rate is in the high range o f reported values for biofilm reactors, desorption experiments proved that nitrification will be the process's rate limiting step, rather th an the desorption rate when regenerant solutions as low as 2440 mg/L N a+ are used. Copyright (C) 1996 IAWQ.