Removal of nutrients from stormwater using a mixed biochar-alum sludge adsorbent

Abstract

A series of batch tests was conducted to remove nutrients (NO3-N, NO2-N, NH3-N and PO4-P) of varying concentrations (1-5 mg/l) from synthetic stormwater using an adsorbent mixture of Eucalyptus Wandoo Biochar (8g) and alum sludge (2g) of 2.36 mm diameter. Test results confirmed the effectiveness of these mixed adsorbents for removing NO2-N (92-100%), NH3-N (87-97%) and PO4-P (>90%) from aqueous phase but not effective for NO3-N (<1% removal). The percentage removal was found to increase with increasing initial concentration. Adsorption isotherm showed that the NO2-N adsorption followed both Langmuir and Freundlich models (R2= 0.99) while NH3-N and PO4-P followed only Langmuir (R2=0.95-0.97). The adsorption intensities (RL) were found to be in the range 0< RL< 1 showing favourable adsorption behaviour. The biochar and alum sludge mix may be used as a potential adsorbent in treating stormwater.