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• A quantitative method was proposed to assess the shear stability of AGS. • Parameter a had a strong positive linear correlation with the wet density of AGS. • LGS represented the equilibrium size for AGS after sheared for a period of time. • LGS was significantly and exponentially related to the parameter a. • The results were validated with the AGS samples from a pilot-scale AGS-MBR. This work established a quantitative method to access the shear stability of aerobic granular sludge (AGS) and validated its feasibility by using the mature AGS from a pilot-scale (50 tons/day) membrane bioreactor (MBR) for treating real municipal wastewater. The results showed that the changing rate (Δ S) of the peak area (S) of granule size distribution (GSD) exhibited an exponential relationship (R 2≥0.76) with the shear time (y = a − b · c x), which was a suitable indicative index to reflect the shear stability of different AGS samples. The limiting granule size (LGS) was defined and proposed to characterize the equilibrium size for AGS after being sheared for a period of time, whose value in terms of Dv50 showed high correlation (R 2=0.92) with the parameter a. The free Ca2+ (28.44–34.21 mg/L) in the influent specifically interacted with polysaccharides (PS) in the granule's extracellular polymeric substance (EPS) as a nucleation site, thereby inducing the formation of Ca precipitation to enhance its Young's modulus, while Ca2+ primarily interacted with PS in soluble metabolic product (SMP) during the initial granulation process. Furthermore, the Young's modulus significantly affected the parameter a related to shear stability (R 2=0.99). Since the parameter a was more closely related (R 2=1.00) to Δ S than that of the parameter b or c , the excellent correlation (R 2=0.99) between the parameter a and the wet density further verified the feasibility of this method. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Three photovoltaic-assisted composting systems were developed for rural waste treatment. • Monthly turning and ventilation-dehydration treatment is recommended as the optimized process for the system. • Oxygen disparity at gradient heights of the compost pile significantly affects the physicochemical properties and maturity process of composting. • Manual turning and ventilation-dehydration optimize compost maturity. • The humification process at gradient heights is influenced by oxygen disparity and has different mechanisms. This study constructs three different photovoltaic assisted composting systems to treat rural domestic waste, and explores the interaction pathways between biomacromolecules and other factors under oxygen disparity at gradient heights of the compost. The optimized mode of regular turning and ventilation-dehydration significantly reduced the moisture content by 53.6% and increased the seed germination index by 35.6%. The oxygen content at different heights under the optimized mode significantly affects the physicochemical properties of the compost, and the degradation of cellulose, hemicellulose, and protein in the middle is higher than other parts. The structural equation model shows that the physicochemical properties at the bottom are affected by biomacromolecules, which may be related to volatile fatty acids(VFAs) produced under low oxygen conditions.The research results show that using manual turning and ventilation-dehydration as the optimized process can promote compost maturity, and oxygen concentration has an important impact on the humification process of the compost. [ABSTRACT FROM AUTHOR]