Post-digestion liquor treatment in the method combining chemical precipitation with reverse osmosis

The aim of the study was to develop an effective treatment of post-digestion liquors highly-loaded with biogenic and organic substances. The scope of the research project encompassed: mesophilic anaerobic digestion of waste activated sludge (WAS) as well as the treatment of post-digestion liquors, coming from the most appropriate HRT value of 25 days, in the process of ammonium magnesium phosphate (struvite) precipitation targeted at ammonia nitrogen binding and a subsequent reverse osmosis (RO) process. It was established that the method combining chemical precipitation and high-pressure fi ltration ensures a high degree of contaminants removal allowing for a direct release of treated liquors into the natural reservoir. However, in order to decrease the residual NH⁴⁺ concentration (6.1 mg NH⁴⁺/dm³) in the purifi ed post-digestion liquors below the level allowing for a direct release to the natural reservoir, it turned out to be necessary to apply increased molar ratio of magnesium and phosphates (Mg:NH⁴⁺:PO₄^3- =1.5:1:1.5).