Effects of different potassium and nitrogen pretreatment strategies on anaerobic digestion performance of rice straw

Abstract

The effects of different potassium and nitrogen pretreatment strategies on the anaerobic digestion (AD) performance of rice straw (RS) were investigated. KOH, NH₃·H₂O and KOH + NH₃·H₂O combined pretreatments were applied. The results showed that KOH + NH₃·H₂O combined pretreatment achieved the highest biomethane production and TS (TS: total solid) removal rate of 274 mL g VS⁻¹ and 43.9%, which were 6.2–75.8% and 4.3–29.5% higher than that of single alkali pretreatments and untreated RS, respectively. The NH₃·H₂O groups improved the process stability, which maintained the NH₃–N concentration in the range of 265–580 mg L⁻¹. It was also found that Bacteroidetes and Firmicutes were the dominant bacterial at phyla level, and the populations of acetate methanogen (Methanosarcina and Methanosaeta) were enriched in the AD system by KOH + NH₃·H₂O pretreatment. Furthermore, the cost of pretreatment agents can be recovered by the increased digestate nutritional value due to the K and N remaining in the digestate after AD. The results indicated that the KOH + NH₃·H₂O combined pretreatment might be a promising method for efficient AD of straw in future industrial applications.