The Shift Of The Microbial Commuinity In Activated Sludge With Calcium Treatment And Its Implication To Sludge Settleability

The activated sludge process is by far the most widely used biological treatment for pollutant removal from sewage water.The sludge settleability and dewaterability are obvious concerns in the daily operation of activated sludge wastewater treatment plants.Given the addition of Ca2+ in influent is efficiency,relatively simple operation and low cost,it becomes to be a simple approach to improve the bioactivity of activated sludge.However,the mechanisms about the effects of Ca2+ in influent on sludge settleability is not available.This study investigated the relationship between Ca2+ and biological performance of activated sludge,and attempted to understand how Ca2+ content in wastewater affects microbial community structure of sludge using PCR-DGGE,high-throughput sequencing analysis and Q-PCR.The main conclusions were as follows.1.The effect of calcium ion on the biological performance of sludge was investigated in a lab-scale activated sludge system with 0-200 mg/L Ca2+ concentration.The seed sludge sampling from Jiangxinzhou WWTP(Wastewater Treatment Plant)and Lucun WWTP.Results indicated that 150 mg/L Ca2+ in the influent obviously improved the settling characteristics and biological performance of activated sludge:The SVI significantly decreased from 45 to 35 g/mL and the average removal efficiencies of TN,NH4+-N,TP and COD were kept above 71%,89%,71%,and 96%in the reactors seeding sludge sampling from Jiangxinzhou WWTP.The SVI significantly decreased from 45 to 40 g/mL and the average removal efficiencies of COD were kept above 96.8%in the reactors seeding sludge sampling from Lucun WWTP.2.PCR-DGGE and high-throughput sequencing techniques confirmed some appreciable changes in diversities and microorganism population with the increase of Ca2+concentation.Clostridium,Flavobacreria,Rhodobacteraceae and other bacteria which can secrete more EPS are gradually enriched in the sludge samples treated with 0-150 mg/L Ca2+,the seed sludge of the reactors sample from Jiangxinzhou WWTP and Lucun WWTP.Acinetobacter,Devosia and Zoogloea were enriched in the sludge samples along with Ca2+concentration enhancement,the seed sludge of the reactors sample from Lucun WWTP.Acinetobacter could excrete EPS,while Devosia and Zoogloea play important roles in the formation and the stabilization of the granules.3.This study showed that Ca2+ contributed to the floe formation and improved sludge community diversity when the concentration of Ca2+ treatment was 0-150mg/L,but the community diversity index Shannon and Chaol was decreased to 3.12 and 1074 when the concentration of Ca2+ treatment was 200mg/L.Bacillus and Pseudomonas which have high proteolytic activity may make the difference.Bacillus may secrete a large number of proteolytic enzymes,which break the bridging of EPS and Ca2+,and even lead to the instability of activated sludge floes.4.Ca2+ feeding also alter the abundance of the speciflc nitrifying and denitrifying genes.The abundance of napA,nirK and nosZ was increased to 2.45×106 Copies/mL,2.32×106 Copies/mL and 8.00×104 Copies/mL in the sludge samples treated with 0-150 mg/L Ca2+.A large number of the Nitrifying and denitrifying bacteria were enriched and removal efficiencies of TN,NH4+-N were reached highest(68.6%and 91.1%)when the concentration of Ca2+ treatment was 150mg/L,5.Ca2+ increased the production of the EPS and facilitated the development of microbial cluster in the bioreactor.The binding of Ca2+ with EPS may result in higher cell density and more compact structure or the formation of microbial clusters and finally improved the sludge settleability.