| Vegetation-activated sludge process(V-ASP) was an ecological environmental-friendly technology for decentralized wastewater treatment. Previous experimental results displayed that involvement of vegetation into ASP process improved biological nutrients removal capability, and produced rather low excess sludge, whose underlying mechanisms need to be elucidated. Moreover, influential factors would affected the system performance in a certain level, which also was worthy of investigation and accordingly establishment of corresponding adjustment methods.In the present work, the impact of seasonal temperature, influent organic loading rate shocking and aeration intensity in aerobic tank on the system treatment performance and stability assessment were carried out in a large-scale V-ASP demonstrative project. A long-term examination demonstrated that all of influential factors had effect onto pollutants removal rate, especially that seasonal temperature fluctuation had significant impact onto ammonia and total nitrogen removal efficiency. During the winter when the room temperature kept around 2? that accompanied with an effluent with high ammonia and TN concentration, insulation methods were adopted to elevate room temperature increased from 2? to 9?, which had positive effect onto physiological activity of vegetation and activity of suspended sludge, and hence to improve the removal efficiency of nitrogen and phosphorus from wastewater. When the influent organic loading rate increased accidentally, synchronized regulation of sludge recirculation rate from 0.5 to 0.75 could effectively increase COD removal efficiency from 54.2% to 70.4%. As for the dissolved oxygen content of aeration tank changes, it was found that corresponded operation mode shift from continuous-feeding to intermittent-feeding was favorable to the NH4+-N removal performance.In contrary to conventional activated sludge process, V-ASP with its own hybrid-property involving suspended and attached sludge, carrier for vegetation installation and vegetation root, brought about a rather complicated ecological structure. From the examination and investigation of biomass distribution and variation with large-scale V-ASP plant, it was obvious that carrier adsorption and ecological predation were major reasons for its low sludge yield coefficient. Upon the system steady-state, more than 48.8% biomass was attached on the carriers to form an attached-growth dominated circumstance that accompanied with a such low sludge yield coefficient of 0.143 g VSS/g COD. Moreover, this complicated ecological structure was beneficial to a stable eco-system establishment that comprised of micro-animals(nematodes, rotifers, etc.) and larger animals(Tubificidae, worms, snails, etc.), both which took the role as ecological predator to activated sludge biomass to reduce excess sludge production.Based on the analysis of biomass distribution and yield profiles, process reduction methods and ecological disposal of excess sludge withdrawn from the V-ASP process were investigated. The experiments revealed that combination of OSA process into V-ASP process could reduce the sludge yield coefficient more than 24.1%. As for ecological treatment of excess sludge, Procambarus clarkia were dosed for evaluation of their effectiveness of ecological predation and sludge disposal rate. It was found that shallow water depth was favorable for Procambarus clarkia survival, and the optimum sludge predation rate could be obtained when HRT and sludge concentration was kept at 4 h and 1200 mg/L, respectively. Notwithstanding, there was slightly elevation of bulk nutrients concentration in the sludge mixture, due mainly to the sludge uptaking, digestion and excretion after ecological predation. |
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