Biochar of distillers’ grains anaerobic digestion residue: Influence of pyrolysis conditions on its characteristics and ammonium adsorptive optimization

Abstract

To promote the sustainable development of the liquor/ethanol industry and environment protection, alternative ways to dispose of anaerobic digestion residue (ADR) are urgently required. This research aims at studying the effects of different residence times (RTs) (30, 60 and 120 min) and heating rates (HR) (2.5, 5.0 and 10.0°C min-1) under 700°C on characteristics of ADR biochar as well as the optimization of ammonium (NH4+) adsorption. Results showed that, with the increasing RT and HR, the aromaticity as well as the content of fixed carbon and elemental carbon of ADR biochar increased, but the pyrolysis yield, volatile matter content, elemental hydrogen, oxygen and polarity decreased. Biochar prepared at 60 min and 5.0°C min-1 under 700°C presented the best development of orderly and honeycomb shape structures, highest specific surface area and maximal amount of NH4+ adsorption (3.15 mg N g-1). The multilayer heterogeneous adsorption process dominated the NH4+ adsorption behaviour. And the maximal amount of NH4+ adsorption was achieved with 4 g biochar L-1 at pH 11.0 along with the order of the competitive effect of K+ > Na+ > Ca2+ > Mg2+. Furthermore, NH4+ adsorption was exothermic. Thus, the present study demonstrated that ADR biochar has potential to adsorb NH4+ from NH4+ polluted water to meet environmental standards.