Abstract: Non-co-digestion kitchen waste resource utilization projects often suffer from prolonged low-load operation due to complex acceptance procedures. The resulting operational stability and economic difficulties of the projects are common across the industry, yet systematic research on the full-process slurry treatment characteristics under such conditions remains lacking. Based on the operational data of a 660 t/d project in Nanjing in 2025, the organic matter distribution, anaerobic digestion performance, carbon source dependence of the biochemical treatment system, and operating costs of the slurry under low-load conditions were investigated. The results showed that approximately 0.89 m3 of slurry was produced per ton of feedstock. The slurry was acidic, with a pH ranging from 3.51 to 4.99. Owing to its high solids content, the total chemical oxygen demand (TCOD) was about 40% higher than the soluble chemical oxygen demand (SCOD), with values of （112 859.32±5 861.25） mg/L. Therefore, TCOD was preferable for expressing the organic loading. The continuous stirred tank reactor(CSTR) operated stably even at an organic loading rate far below the design value, achieved a TCOD removal efficiency of 93.13%±1.3%. While biogas production and methane concentration remained at normal levels. However, the excessively long hydraulic retention time caused the B/C ratio of the anaerobic effluent to drop below 0.2, which made nitrogen and phosphorus removal highly dependent on external carbon source addition. The carbon source cost accounted for over 50% of the direct cost of wastewater treatment. The overall direct cost of slurry treatment was 65.99 RMB/t. The loss of volumetric efficiency induced by low-load operation was the primary cause of the poor economic performance.

Key words: low-load conditions, kitchen waste, waste oils, slurry, CSTR, biochemical system