Evaluation of slow pyrolyzed wood and rice husks biochar for adsorption of ammonium nitrogen from piggery manure anaerobic digestate slurry

Due to its high adsorption capacity, the use of biochar to capture excess nutrients from wastewater has become a central focus in environmental remediation studies. In this study, its potential use in adsorption and removal of ammonium in piggery manure anaerobic digestate slurry was investigated. The adsorbed amount of NH4+-N (mg·g−1) and removal percentage as a function of adsorbent mass in solution, adsorbent particle size, NH4+-N concentration in the effluent, contact time, pH and temperature were quantified in batch equilibrium and kinetics experiments. The maximum NH4+-N adsorption from slurry at 1400mgN·L−1 was 44.64±0.602mg·g−1 and 39.8±0.54mg·g−1 for wood and rice husk biochar, respectively. For both biochars, adsorption increased with increase in contact time, temperature, pH and NH4+-N concentration but it decreased with increase in biochar particle size. Furthermore, the sorption process was endothermic and followed Langmuir (R2=0.995 and 0.998) and Pseudo-second order kinetic models (R2=0.998 and 0.999). Based on the removal amounts, we concluded that rice husk and wood biochar have potential to adsorb NH4+-N from piggery manure anaerobic digestate slurry, and thus can be used as nutrient filters prior to discharge into water streams. •Biochar adsorbed 60% NH4+-N from piggery slurry.•Absorption was sensitive to changes in particle size, pH and temperature.•NH4+-N adsorption from slurry followed the Langmuir and Pseudo second order models.•Monolayer chemisorption was the major NH4+-N adsorption mechanism from piggery slurry.