Study On Cultivation Of Aerobic Granular Sludge And The Performance Of Adsorption Of Heavy Metals

The wastewater treatment technology with aerobic granules is a new technique developed within recent years, which can not only be applied to remove COD, ammonia, poisonous organic wastewater as well as the wastewater with phosphorus, but also be used to dispose the wastewater with heavy metal. Aerobic granule has become the highlight in the wastewater treatment study as a result of so many advantages it has.The research has two parts, including cultivation of aerobic granules and adsorption of heavy metals. We focus on the problems that aerobic granular sludge cultivated when seeding conventional activated sludge and the aerobic granular sludge adsorption effects on heavy metal ion concentration, adsorption time, pH, speed and adsorption temperature.Firstly, activated sludge was used as inoculated sludge in this experiment. Aerobic granular sludge in a sequencing batch reactor (SBR) fed with synthetic wastewater was cultivated by controlling operational conditions. Under the control of the parameters, such as the operational period, the settling time and velocity of uprising gas, aerobic granular sludge was successfully cultivated in 20 days. Aerobic granular sludge had compact strucyure, regular shape, good settling ability and microbic activity.The granular sludge became the main form of sludge in reactor after cultivated aerobic granular sludge preliminarily formed. At this time, outline of the granular sludge is clear and granular sludge has light-yellow appearance, compact structure and smooth surface, good settlement.SVI values of the granular sludge maintains approximately between 40-50mL/g, MLSS of the granular sludge attains 7.5mg / L, the settling rate of the granular sludge is about 29-72m/h, which are much higher than the conventional activated sludge.Cultivated the granular sludge in experiment is able to remove organic matter efficiently and stable, and has ability of removing nitrogen and phosphorus.The COD, NH₄-N and TP average removal rate achieves 92.75%, 75.8% and 95.1% respectively. The research indicated that aerobic granular sludge showed more efficient simultaneous nitrification and denitrification function and denitrification and phosphorus removal function because of its special structure.Secondly,cultivated the granular sludge in experiment as adsorbent for heavy metal ions.The results of the research indicated that aerobic granular sludge has a strong influence on adsorption of Cd²⁺,Cu²⁺ and Zn²⁺.PH value was one of important effect factors on heavy metal biosorption. The optimal pH value of adsorption heavy metal ions was different. The optimal pH value of three heavy metal ions biosorption is about 4 to 6. The results of contact time of biosorption indicated that the biosorption process could be divided into two phases: the surface biosorption course and the slow intracellular accumulation. The heavy metal ions concentrations of solution descend quickly through the first phase which just at the beginning of 30-60min. Adsorptive capacity increases very slowly and achieves gradually balances through the second stage, which is a slow process.Increasing temperature and rotating speed in the proper range can be benefit to the adsorption of three heavy metals. But, overhigh temperature and too fast rotating speed can reduce the adsorption of heavy metals.