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

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.

Removal of phosphate from aqueous solution using MgO-modified magnetic biochar derived from anaerobic digestion residue.

A novel MgO-modified magnetic biochar (MgO@MBC) was made by chemical co-precipitation of Mg2+/Fe3+ on anaerobic digestion residue (ADR) and subsequently pyrolyzing at different temperatures. MgO@MBC was used for phosphate recovery from aqueous solution. The physicochemical properties of MgO@MBC were comprehensively investigated using TEM-EDS, FT-IR, XRD, VSM, N2 adsorption-desorption and TGA. Results showed that MgO/γ-Fe2O3 nanoparticles were successfully deposited onto the surface of BC. The effects of reaction temperature, initial solution pH, MgO@MBC dosage, coexisting anions and phosphate concentration on the removal of phosphate by MgO@MBC were researched. Additionally, the adsorption process of phosphate onto MgO@MBC was well described by the pseudo second-order and pseudo first-order models, which indicated a chemisorption and physisorption process. Besides, the maximum adsorption capacity of MgO@MBC for phosphate by the Langmuir model were 149.25 mg/g at 25 °C. Moreover, the thermodynamic study suggested that the adsorption of phosphate onto MgO@MBC was a spontaneous and endothermic process. The adsorption mechanisms including physical absorption, surface electrostatic attraction, surface complexation and precipitation were revealed. It could be concluded that MgO@MBC exhibited high removal efficiency of phosphate and excellent magnetic property for the recovery. MgO@MBC could be utilized as a magnetically recoverable adsorbent to realize phosphate recovery and MgO@MBC after the adsorpion of phosphate could be applied in agricultural production as a fertilizer.

Distillers' grains anaerobic digestion residue biochar used for ammonium sorption and its effect on ammonium leaching from an Ultisol.

The aim of this work was to explore the potential application of biochar from distillers' grains anaerobic digestion residue pyrolyzed at 700 °C (ADR-DG700) to ammonium (NH4+) adsorption from aqueous solution, as well as its effect on NH4+ leaching from an Ultisol. The adsorption kinetic of NH4+ on the ADR-DG700 could be described by an Elovich model (R2 = 0.995), and the combined Langmuir-Freundlich model (R2 = 0.997) fitted the isotherm data better than the Langmuir, Freundlich, Redlich-Peterson, and Temkin models with a maximum adsorption of 11.41 mg N g-1. The NH4+ adsorption on ADR-DG700 was mainly controlled by the cation exchange, the surface complexation with oxygen-containing functional groups of carboxyl C〓O (C▬O) and carbohydrate C▬OH, as well as the electrostatic interactions with Si▬O▬Si functional group. In addition, the ADR-DG700 soil application reduced 2.48-20.67% of NH4+-N leaching loss after nitrogen fertilizer application in an Ultisol. These results suggested that the ADR-DG700 could be a sorbent for NH4+-contaminated water as well as an inhibitor for soil NH4+ leaching.