Highly collaborative of wasted activated sludge deconstruction and incineration gas utilization in the presence of nitrogen oxides

With the rapid urbanization in China, the volume of urban sewage continues to increase, resulting in large quantities of waste activated sludge (WAS). Anaerobic digestion (AD) is a widely used method for stabilizing WAS, but its efficiency is often hindered by the limited degradability of sludge. Researches have identified free nitrous acid (FNA) as an effective pretreatment for enhancing WAS degradability, though its sources remain insufficiently explored. This study introduces a novel method for sludge pretreatment, harnessing nitrogen oxides (NO_x) from waste combustion as a source of FNA to facilitate highly efficient deconstruction of WAS and utilization of incineration gas. Key optimization pretreatment factors including NO_x oxidation ratio (50%), concentration (5000 ppm), aeration time (4 h), as well as pH (>6.8) and temperature (60 °C), were evaluated. Findings revealed that the soluble chemical oxygen demand (SCOD) of the NO_x pretreatment sludge was 2.47 times higher than that of the untreated sludge. The mechanism underlying the NO_x pretreatment involves conversion of NO_x into nitrite within the sludge, disrupting sludge cells and resulting in the production of biodegradable substrates, thereby improving AD for methane production. All the results demonstrate that the innovative and chemical-free pretreatment strategy has synchronization benefits of incineration gases reutilization and organic solid recovery, offering substantial environmental and economic benefits.