Excess Sludge Reduction By High Speed Rotary Disk Disintegration With A/O/A-SBR Process

Activated Sludge Process (ASP), is the most widely applied biological technique both to domestic and industrial wastewater treatments all over world. But, a major disadvantage still remains unsolved in conventional ASP, that is a large amount of excess sludge (ES) will be generated within the wastewater treatment process, which is difficult to disposal. From the perspective of sustainable development and recycling economy, ES treatment and disposal should be a kind of environmental friendly method following the priority strategy of reduction, recycling, innocuity and stabilization. So, based on the theory of Lysis-Cryptic Growth, a sludge reduction process, combining mechanical or physical disintegration pretreatment with aerobic digestion, has become a hot spot in the field of wastewater treatment. However, the process is still not widely applied, because of the economic and technical bottleneck in the sludge disintegration technologies, and the effluent water quality deterioration problem caused by recirculation of the disintegrated sludge which contains high nitrogen (N) and phosphorus(P)load.In this study, based on the disintegration mechanism analysis of a variety of mechanical and physical methods, a new kind of ES disintegration technology, High Speed Rotary Disk (HSRD) method, was brought forward. And an Anaerobic/Oxic/Anoxic-Sequencing Batch Reactor (A/O/A-SBR) process was also put forward, with the purpose of synchronous removal of N and P in the disintegrated sludge. So, by recirculating the N-and-P-removed disintegrated sludge back to the original ASP system, an ES reduction system combined HSRD disintegration with A/O/A-SBR process was established. In this research, HSRD disintegration mechanism, the structural and operational parameters optimization of HSRD, the anaerobic and aerobic biodegradation properties analysis of disintegrated sludge, the operational parameters determination of A/O/A-SBR process, and the feasibility analysis for the reduction system, were systematically studied, in order to explore a new way to achieve the purpose of ES reduction treatment.Grind Rotary Disk (GRD) was an original model of HSRD. Through the experiment of ES disintegration test by GRD, it was found that:The MLSS concentration of ES, the spacing between the disks and treatment times were the main factors influencing the disintegration effect of GRD. The fluid shear force generated between the rotating disk and the fixed disk, the grinding effect, and the hydrolytic enzyme released from the lysed cells, the three functions together were the main reason which caused the ES disintegration. When the disks spacing of 0.25 mm, rotating speed of 3500 r/min, ES MLSS concentration was 11300 mg/L, after treatment of 25 cycles, the dissolved organic carbon (DOC) concentration of disintegrated sludge treated by GRD improved from 7.4 mg/L up to 310.9 mg/L, and the median diameter decreased to about 10 ?m.Through structure improvement from GRD, HSRD ES disintegration apparatus was developed and manufactured. Through the experiment of ES disintegration test by HSRD, disintegration mechanism analysis and operational parameters optimization was studied. It was found that:Because of the viscosity of ES, the huge shear force generated by the high-speed-rotating disk, mainly caused the disintegration of sludge floc and extracellular polymeric substances (EPS), and the lysis of bacteria and other microorganisms. ES MLSS concentration, rotating speed were the main factors influencing the HSRD disintegration effect. When the rotating speed of 5000 r/min, ES MLSS concentration was 18800 mg/L, after treatment of 45 min, the solubilisation degree (DOC/TOC, ratio of DOC to Total Organic Carbon) of disintegrated sludge treated by HSRD reached up to more than 50%, with energy consumption of 14500 kJ/kg-DS. In the treatment process of HSRD, EPS disintegration, cell lysis and lysate releasing would cause the transformation of the dispersion system in the disintegrated sludge suspension, and also caused the composition changing of the dissolved and suspended substance in the disintegrated sludge. So, a kind of complex dynamic non-Newtonian fluid viscosity characteristics of the disintegrated sludge would be discovered. Accordingly, the intensity of fluid shear force would be reduced because of declining of apparent viscosity of the disintegrated sludge, so solubilisation degree would not increase any more. Besides, the rise of temperature has a promoting effect on the ES disintegration in HSRD process. HSRD treatment time would be shortened when combined with 80? thermal hydrolysis. And the combined disintegration process would achieved a solubilisation degree of more than 50%, when energy input of 17200 kJ/kg-DS.Through the experimental test, it was found that:the anaerobic and aerobic biodegradation characteristics were improved after HSRD disintegration, which indicated that no inert nonbiodegradable compounds was produced in the HSRD disintegration process. The 10 d batch anaerobic digestion test indicated that, CH4 production was increased by 18.8% and MLSS reduction rate was improved by 10.7 percentage points, when compared with untreated sludge. The semi-continuous anaerobic test showed that, digestion rate promotion, hydraulic retention time reduction, sludge reduction would be achieved if HSRD disintegrated sludge combined with anaerobic digestion process. Deterioration of effluent water quality was not found if recirculation of disintegrated sludge back to aeration system.By altering the anaerobic/oxic/anoxic conditions, A/O/A-SBR for synchronous removal of N and P from disintegrated sludge was brought forward base on the biological reactions:i.e. anaerobic biodegradation and ammonification, oxic nitrification, anoxic denitrification reactions, and anaerobic P release, oxic (or anoxic) P accumulation reactions. After multiple cycles of microorganisms domestication, DOC, soluble total nitrogen and soluble total phosphorus removal rate were reached by 40.9%,38.6%, and 31.5%, respectively, when the anaerobic/oxic/anoxic time were set to 5 d,1 d,1 d, with the disintegrated sludge and seed sludge mixing ratio of 2:1. According to the theoretical analysis of material balance simulation,45.5% of sludge reduction can be achieved by the system combined HSRD disintegration with A/O/A-SBR process, and without influence on the effluent water quality in the original wastewater treatment system.