Study on dynamic sorption characteristics of modified biochars for ammonium in biogas slurry

Jingtao Ding,Jian Wang,Haibo Meng,Hongsheng Cheng,Yanru Ma,Yujun Shen,Xi Zhang,Pengyue Zhang

doi:10.25165/j.ijabe.20201301.4697

Abstract

The objective of this study was to investigate the relationship between ammonium (NH4+-N) dynamic sorption capacity and physicochemical properties of modified biochars. Biochars, producing from three species of agricultural wastes of cornstalk (A), corncob (B) and sawdust (C) at 550°C, 600°C and 650°C, were modified by four methods of NaOH plus microwave (NaM), KOH (K), FeCl3 (Fe) and HNO3 (H). The static and dynamic adsorption experiments were conducted to investigate sorption characteristics of modified biochars on NH4+-N in slurry of piggery manure anaerobic digestate. Four modified biochars with better NH4+-N adsorption rates were selected through static kinetics adsorption tests, which showed that chemical reactions might have occurred during the NH4+-N sorption process and the maximum NH4+-N removal rates of B-550-Fe, A-550-NaM, A-550-K and C-600-NaM were 66.64%, 57.50%, 52.39% and 45.20%, respectively. The dynamic adsorption column experiment was conducted in a three-stage adsorption column packed with the selected three modified biochars. NH4+-N dynamic adsorption depended on the slurry inflow flow rate, the type of biochar and the depth of packed biochar. The optimal adsorption process was elected by the method of orthogonal experiment. The data showed that using deeper packed biochar and applying lower flow rates could be a better strategy to increase NH4+-N adsorption. The maximum NH4+-N removal rate in the slurry could reach 85.60% in the three-stage adsorption process. It concluded that NH4+-N adsorption in three-stage adsorption process could be an effective method to recover nitrogen from piggery manure anaerobic digestate. Keywords: modified biochar, biogas slurry, ammonium adsorption, sorption characteristics DOI: 10.25165/j.ijabe.20201301.4697 Citation: Ding J T, Shen Y J, Ma Y R, Meng H B, Cheng H S, Zhang X, et al. Study on dynamic sorption characteristics of modified biochars for ammonium in biogas slurry. Int J Agric & Biol Eng, 2020; 13(1): 234–240.

Highlights

Anaerobic digestion technology is the worldwide applied technology for treating livestock manure[1]
The biogas projects produced about 1.12 t of slurry every year
The slurry pollution puts a lot of pressure on the environmental protection

Summary

Introduction

Anaerobic digestion technology is the worldwide applied technology for treating livestock manure[1]. Anaerobic digestion projects produce a large amount of digestates, which are renowned for containing high nutrients mainly nitrogen and phosphorus compounds that often pollute the environment[2,3,4]. In China, the chemical oxygen demand (COD), total nitrogen (TN) and total phosphorus (TP) from the livestock breeding industry accounted for 96%, 38% and 56% of the total pollutants from agricultural sources respectively and were 2.3 times that of industrial sources, according to the China pollution source census carried out in 2010. The biogas projects produced about 1.12 t of slurry every year. Chinese biogas projects produce about 1.12 t of anaerobic digestate slurry every year[5], in which the content of ammonia nitrogen (NH4+-N) is as high as 80% of TN[6]. The slurry pollution puts a lot of pressure on the environmental protection

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Conclusion