Simultaneous concentration of nutrients from anaerobically digested sludge centrate and pre-treatment of industrial effluents by forward osmosis

In the last years, forward osmosis (FO) has gained increasing prominence, new membranes are being developed and new applications are being considered. In this study, the recovery of nitrogen and phosphorus of the anaerobically digested sludge centrate was studied by FO using two industrial effluents characterized by high osmotic pressure (residual stream from an absorption process for ammonia elimination and brine from a seawater desalination facility) as draw solutions. The experiments were carried out in a laboratory plant testing two FO membranes (CTA-NW and Aquaporin Inside membrane). Results showed that nitrogen concentration was achieved with both membranes and both draw solutions. The use of the effluent from ammonia absorption enhanced of the nitrogen concentration in the feed stream to the FO membrane. The reached concentration factor in the laboratory tests was 1.61 when Aquaporin membrane was used. Phosphorus could not be concentrated because of its precipitation as calcium phosphate (confirmed by EDX analysis) as a consequence of the high calcium concentration of the municipal wastewater.