Recovery of ammonia from domestic wastewater effluents as liquid fertilizers by integration of natural zeolites and hollow fibre membrane contactors

Abstract

The integration of up-concentration processes to increase the efficiency of primary sedimentation, as a solution to achieve energy neutral wastewater treatment plants, requires further post-treatment due to the missing ammonium removal stage. This study evaluated the use of zeolites as a post-treatment step, an alternative to the biological removal process. A natural granular clinoptilolite zeolite was evaluated as a sorbent media to remove low levels (up to 100 mg-N/L) of ammonium from treated wastewater using batch and fixed bed columns. After being activated to the Na-form (Z-Na), the granular zeolite shown an ammonium exchange capacity of 29 ± 0.8 mg N-NH4+/g in single ammonium solutions and 23 ± 0.8 mg N-NH4+/g in treated wastewater simulating up-concentration effluent at pH = 8. The equilibrium removal data were well described by the Langmuir isotherm. The ammonium adsorption into zeolites is a very fast process when compared with polymeric materials (zeolite particle diffusion coefficient around 3 × 10- 12 m2/s). Column experiments with solutions containing 100 mg N-NH4+/L provide effective sorption and elution rates with concentration factors between 20 and 30 in consecutive operation cycles. The loaded zeolite was regenerated using 2 g NaOH/L solution and the rich ammonium/ammonia concentrates 2–3 g/L in NaOH were used in a liquid-liquid membrane contactor system in a closed-loop configuration with nitric and phosphoric acid as stripping solutions. The ammonia recovery ratio exceeded 98%. Ammonia nitrate and di-ammonium phosphate concentrated solutions reached up to 2–5% wt. of N.