The use of brown coal for the removal of nutrients from wastewater

Apart from the biological and health issues, excessive amounts of nutrients (P and N) in water causes eutrophication that can severely damage the water treatment facilities. Available methods for adsorbing these contaminants are expensive both at its production and regeneration stages, hence the development of cheaper alternative adsorbents without a need for their regeneration seems to be necessary.<br><br> Brown Coal (BC) is an inexpensive material, which - apart from its application as an alternative to fossil fuels - has been used as an effective ion-exchanger for the removal of pollutants from wastewaters and soils. For the first time, this study investigates the use of BC as an adsorbent to remove ammonium and phosphate from wastewater.<br><br> The influence of pH, initial adsorbate concentration, and adsorbent dose was studied in the removal of nutrients from both synthetic and real wastewater using BC, and it was found that although all these parameters were effective, pH had the most significant influence on removal efficiency of BC. This achievement resulted in creating the idea of treating of BC using NaOH solution. Several experiments were conducted in batch and column modes to investigate the nutrient removal efficiency associated with raw brown coal (RBC) and NaOH-treated BC, which was referred to as base-wash brown coal (BWBC). Experimental results were then assessed through analytical methods.<br><br> Chemical and physical characterizations of BC, before and after treating, were studied via Fourier transform infra-red (FTIR), scanning electron microscopy (SEM), X-ray powder diffraction (XRD), and Brunauer-Emmett-Teller (BET) test to explain the experimental results of this study.<br><br> BWBC showed increased ammonium removal efficiency (95.45% and 92%) compared to RBC (41.18% and 88.4%) in batch and column tests, respectively. FTIR spectroscopy confirmed the substitution of the acidic proton for Na+ in BWBC after alkaline treatment of RBC and the substitution of Na+ for NH4+ after application of BWBC to ammonium solution.<br><br> In agreement with FTIR results, scanning electron microscopy-electron diffraction scattering (SEM-EDS) of BWBC revealed reduced sodium content by 2.55 wt% and augmented nitrogen content by 9.61 wt% after application to wastewater. Crystallographic analysis showed 7.2% increase in crystallinity for BWBC compared to RBC due to the formation of new salt crystals as a result of alkaline treatment on the acidic BC.<br><br> The influence of metal ions in the removal of ammonium using BC from solution was also studied. BC selectivity for NH4+ in the presence of metal ions in both synthetic and real wastewater samples was in the following order: Mg2+ > NH4+ > K+ > Na+ > H+.<br><br> Fitting experimental adsorption data to kinetic models suggested that the ammonium removal mechanism was based on chemisorption. Experimental data showed high fit to both Freundlich and Langmuir isotherm models. In addition, the pseudo-second-order model was found to be a reliable model to describe the adsorption of NH4+ by RBC and BWBC. Both kinetic and isotherm studies confirmed higher ammonium adsorption capacity for BWBC compared to RBC. Finally, breakthrough curve modeling using the Yoon-Nelson model showed the best fit in comparison with the Thomas and Adams-Bohart models in both synthetic and real wastewater samples.<br><br> RBC exhibited very low phosphate removal efficiency (less than 20%) due to its low anion-exchange capacity, which results in low adsorption capacities when applied to media containing negatively charged ions such as phosphates.<br><br> All in all, results showed that RBC had promising results in the removal of ammonium rather than phosphate from both synthetic and real wastewater, and modified BC (BWBC) has higher ammonium capacity than RBC. Hence, BWBC can be used as a greener and efficient ammonium adsorbent for wastewater treatment.