Studies On The Treatment Mechanism Of Two Typical Dyes By Aerobic Granular Sludge

Synthetic dyes were widely used in medical, textile, leather, paper and other fields. These industrial wastewaters were difficult to be biodegraded by conventional biological degradation methods. Aerobic granulation for the treatment of wide range of applications, complex composition and good stability of dyeing wastewater was investigated. Granules had characteristics of hierarchical structure, with aerobic zone, oxygen zone and anaerobic zone. Nitrification and denitrification could be performed simultaneously.Aerobic granulation for methylene blue (MB) biodegradation with glucose, soluble starch and sodium acetate as a co-substrate was examined to explore the MB biodegradation property and mechanism. Aerobic granulation with congo red (CR) wastewater was determined to predict its full-scale application in dyeing wlstewater treatment. The batch biosorption of CR and MB onto aerobic granule was conducted to evaluate the feasibility of aerobic granule as a biosorbent. At the same time, the influence of adsorption on biodegradation was studied.(1) The selective pressure from the increasing organic loadings, improving hydraulic shear stress and decreasing of settling time were added to a sequencing batch reactor (SBR) to enhance the formation of granular sludge. Aerobic granular sludge to treat wastewater containing MB was successfully developed in the SBR using activated sludge as inoculum. Aerobic granules were first observed on day44as irregular spherical particles, and the granules became dominant in the reactor on day87. After cultivation for87days, stable aerobic granules were obtained with a clearly defined shape and a diameters ranging from2to4mm. Meanwhile, compact well-settling aerobic granules were developed for biological removal of CR using activated sludge as inoculum. After55-day operation, aerobic granules were first observed as irregular spherical particles. On day121, the aerobic granules gradually matured forming a strong compact structure and showing a well-defined appearance with diameters ranging from0.2to0.5mm. With the granulation, the SVI value decreased from124to42mL/g.(2) The mechanism of aerobic granular sludge removal of MB was investigated. The aerobic granules had the ability to withstand CODCr and MB. When the influent MB concentration increased from4to10mg L-1, the Mixed Liquid Suspended Solids (MLSS) and the Sludge Volumetric Index (SVI) were about4.3g L"1and about43mL g-1, respectively. The removal efficiency of CODCr and MB reached93%and56%, respectively. The biodegradation kinetics showed that the presence of MB at the concentration of66.67mg L-1inhibited the biodegradation rate of MB and the inhibition increased with the increase of MB concentration. Specific MB biodegradation rates followed the Haldane model and the associated kinetic parameters were as follows:Vmax=184.15mg L-1h-1, Ks=209.96mg L-1, and Ki=21.23mgL-1.(3) The mechanism for the removal of CR by aerobic granular sludge was studied. Stable granules with size of0.2-0.5mm were obtained from CR wastewater on day121. The MLSS and SVI were maintained around3.3g L-1and42mL g-1. The granule had an excellent settling ability with the settling velocity over113m h-1. Aerobic granule exhibited good performance in the organics and CR removal from the wastewater. After granulation, high and stable removal efficiencies of91%CODCr,93%CR were achieved at the volumetric exchange ratio of50%and cycle duration of8h. The average CODCr and CR of the effluent were43and4.6mg/L, respectively. The granules had specific CR degradation rates that increased with CR concentration from0to379mg L-1, peaked at326.89mg CR g-1VSS-1h-1, and declined with further increases in CR concentration as substrate inhibition effects became significant. The data obtained through biodegradation experiments was fitted with Haldane model. Degradation process showed new intermediate products appeared, and the cleavage of azo bond should be one of the steps in the process of biochemical reactions. Meanwhile, the CR granular sludge had some potential capability to biodegrade other azo dyes.(4) The adsorption effect during dye degradation process was investigated. Aerobic granulation was successfully developed in a SBR with glucose, soluble starch and sodium acetate as a co-substrate. Irregular spherical particles appeared on the day84, and on day93, the mature aerobic granular sludge became the dominant with the diameter of0.8-1.1mm. The result showed that aerobic granules exhibited large capacity for the biosorption of CR and MB from aqueous solutions, which was175.44mg/g SS and256.41mg/g SS at the initial concentration of80mg/L, respectively. pH value had great effect on biosorption process. In the alkaline environment, the removal rate of MB was higher, while in the acidic environment, CR removal efficiency became higher. The Freundlich model provided a better fit to the experimental data than the Langmuir model. The adsorption process was endothermic reaction. Adsorption kinetics showed that the adsorption process was more suitable for the pseudo-second-order kinetic model. After the adsorption reaction process, degradation reactions didn’t proceed, indicating that without the culture and effective aggregation of the dominant bacteria, the degradation reactions of the dye could not take place.