Enhancing Anaerobic Digestion of Simulated Plateau Blackwater with Highland Barley Straw Biochar

Abstract

Background: Anaerobic digestion of blackwater is attractive for sanitation and resource recovery in high-altitude regions, but low pressure, low oxygen availability and cold stress can slow hydrolysis, acid conversion and methanogenesis. Aims: This study evaluated whether biochar produced from locally available highland barley straw can improve blackwater digestion under simulated plateau conditions. Study Design: Batch adsorption and anaerobic digestion experiments were performed using highland barley straw biochars prepared at 300-700 ℃, with the 600 ℃ biochar selected for digestion tests. Methodology: Ammonium removal was monitored for 4320 min using an initial NH4+-N concentration of about 30 mg/L. Anaerobic digestion was conducted in 2 L reactors at 65 kPa, with a highland control (HC) and a biochar-amended group (HB, 5 g/L). Chemical oxygen demand (COD), pH, volatile fatty acids (VFAs) and cumulative methane were followed for 30 d. Results: The 600 ℃ biochar achieved 98.77% NH4+-N removal and an equilibrium adsorption capacity of 2.54 mg/g. Adsorption followed a pseudo-second-order model (R2 = 0.981), indicating a dominant chemisorption contribution. Biochar raised final COD removal from 96.09% to 98.01% and shortened the time needed to reach COD below 60 mg/L from 24 to 18 d. Cumulative methane  increased from 118.96 to 146.35 mL/g COD, while the fitted maximum methane production rate increased by 88.31%. Conclusion: Highland barley straw biochar can simultaneously retain ammonium, accelerate COD removal and improve methane recovery from simulated plateau blackwater. The approach links sanitation improvement with straw valorization and provides a low-cost route for decentralized treatment in plateau agricultural and pastoral settlements.