Cadmium Toxicity To The Performance And Bacterial Community Shift Of Activated Sludge Microorganisms

With the rapid development of electroplating, dyestuffs and mining and refining industries, a large amount of heavy-metal contaminated wastewater has been produced, resulting in a large amount of heavy metals entering the wastewater treatment plants (WWTPs) , which has a negative effect on the performances of the WWTPs. Thus, focusing on cadmium, the inhibition effect on the wastewater treatment systems and the microbial community structure of activated sludge were studied by using sequencing batch reactor (SBR) to simulate municipal wastewater in wastewater treatment system.The effect of short-term exposure to cadmium on the water treatment efficiency of SBR system showed that the change trend of water quality indices in the experimental group was consistent with that of blank group, and the inhibition of cadmium on activated sludge was related to its concentration.While exposed to cadmium in the long term, the inhibition on the SBR system appeared gradually with time. Based on the results of long-term exposure experiments, it is shown that different concentrations of cadmium could significantly inhibited the denitrification and dephosphorization capacities of the activated sludge system, and the degree of inhibition is enhanced with the increase of cadmium concentration, however during the whole process the cadmium have little effects on the removal of organic matter. In accordance with the removal efficiency, the MLVSS/MLSS and activities of microorganism were effected directly by the cadmium in the influent, also the protein and carbohydrate in extracellular polymeric substances were inhibited.After the long exposure, the surface of the activated sludge was observed and the release of lactate dehydrogenase was measured. It was found that the sludge surface and the cell membrane integrity of sludge microbes were destroyed with the increase of cadmium concentration. Further study for the impacts of cadmium on the bacterial community structure was conducted by using MiSeq sequencing. The results illustrated that cadmium obviously reduced the abundance and diversity of microbial community in activated sludge, while exposed to cadmium that in system with 10 mg·L-1 cadmium in the influent existed significantly affected the functional microbes such as nitrifying bacteria, denitrifying bacteria and poly-P acuumulation bacteria,which lead to the poor removal of nitrogen and phosphorus, also the floc-forming bacteria (Triothrix and Microthrixaceae bacteria) causing sludge bulking was enriched.