Abstract
The increasing concern of biogas slurry disposal and nitrogen loss in soils has brought back the interest in using biochar as an adsorbent of biogas slurry in soils. Three types of biochars, commercial activated carbon, pyrolysis productions derived from rice husk, and nut shell, were added as adsorbents in two types of soils (sandy and loamy) at solid weight ratio of 5%, 10%, 15%, and 20% to investigate the effects of biochars on soils adsorbing ammonium nitrogen (NH4+-N) in biogas slurry using oscillation method. There was no difference of NH4+-N adsorbability for sand soil and loamy soil. The NH4+-N adsorption capacity of soils increased as the additive biochars increased from 0 to 20%. The smaller particle size of biochars led to the shorter stable adsorption time and the better NH4+-N adsorption capacity. Commercial activated carbon showed the best NH4+-N adsorption capacity in biogas slurry, followed by the nut shell carbon. The rice husk carbon was the worst. The results in this study provide a feasible and cost-effective assessment method of biochars for increasing the NH4+-N adsorption capacity of soils in biogas slurry, as well as good insight into effects of different biochars on improving NH4+-N adsorption capacity of soils.
Highlights
Biogas derived from anaerobic digestion (AD) of biomass has been comprehensively utilized because of energy production, environmental protection, and favorable ecological cycle [1, 2]
The objective of this study is to evaluate the effects of three biochars on NH4+-N adsorption capacity of two soils in biogas slurry on laboratory scale
The BET surface areas of commercial activated carbon were much higher than rice husk carbon and nut shell carbon
Summary
Biogas derived from anaerobic digestion (AD) of biomass has been comprehensively utilized because of energy production, environmental protection, and favorable ecological cycle [1, 2]. Some researchers utilized biogas slurry as a superior organic fertilizer in arable crop production [7]. Biogas slurry offers many advantages including (1) promoting the granular structure formation of soil and improving the physical and chemical properties of soil [8, 9]; (2) providing nitrogen, phosphorus, potassium, amino acid, auxin, and ionmicroelement for crop’s sprouting and growing [10]. Biogas slurry has higher inorganic nitrogen content and the mineralization rate than biogas residue (solid remains of digestate after solid-liquid separation) [11]. More than 90% weight of biogas slurry is liquid, where up to
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