Development of humic acid based adsorbents for fast and efficient removal of ammonia and organic nitrogen from super magnetic separation treated wastewater

Although super magnetic separation technology (SMS) displayed great potential in removing pollutants from wastewater, the effluent was failed to meet wastewater discharge standard due to relatively high ammonia (AN) and organic nitrogen (ON). In this study, the carbonated and sulfonated humic acid (SCHA) adsorbent was optimally prepared for removing AN from wastewater. Then, based on the carbonated HA with iron loading (CHA-Fe) in our previous study, HA based mixed adsorbent, combining SCHA with CHA-Fe was directly used to simultaneously adsorb AN and ON in wastewater. The optimally prepared SCHA showed fast and efficient adsorption of AN with removal efficiency of around 60% within 40 min, which was ascribed to the function of strong electrostatic interaction by the successfully introduced -SO3-, but cations like Ca2+, Mg2+ and Al3+ significantly reduced AN adsorption. The adsorption data were adjacent with the Langmuir adsorption model with monolayer coverage and pseudo-second-order kinetic model. The calculated maximum adsorption capacity on AN was 12.84 mg/g at 298 K, which was higher than most of the other forms of materials. The thermodynamics of AN adsorption was found to be a spontaneous and exothermic process. In addition, the mixed adsorbent could simultaneously and efficiently adsorb AN and ON from wastewater with the removal efficiency of more than 75% under a wide pH range from 6 to10. It was mainly because the mixed adsorbent could automatically regulate solution pH to neutral range, in which electrostatic adsorption of AN by SCHA and coordinated adsorption of ON by CHA-Fe was intensified. When applied in treating actual wastewater after SMS, the mixed adsorbent could fast and effectively make the wastewater meet the discharge standard (level A) in China (GB18918-2002) through regulating mixed adsorbent dosage. This work provided theoretical and technical basis for physicochemical wastewater treatment processes and developed a new strategy for treating wastewater containing AN and various organics.