Diagnose And Control Of Sludge Floating In UASB For Beverage Wastewater Treatment

Anaerobic biological treatment technology is characteristized by low energy consumption,high treatment load and low investment,has been widely used in high organic load wastewater and industrial wastewater treatment.Normally,Beverage wastewater,with high organic concentration(2000-3000mg/L),good biodegradability and low SS concentration,was treated by combined anaerobic(Up-flow Anaerobic Sludge Blanket,UASB)and aerobic process to meet the discharge standard.However,the huge fluctuation of the influent load and operation conditions will cause reactor instability,acidification and sludge floating.In this study,investigation on sludge floating in UASB in Xi’an Coca-Cola Beverage Company was carried out.by analyzing the changes of influent water quality,gas production,sludge structure,maximum methanogenic activities and microbial community,As the influent organic load decreased,microorganisms in the granular couldn’t get enough substrate for normal growth.The inner part of the granular will be consumed by endogenous respiration and get into empty,which led to the decrease of sludge density and deterioration of settling performance.The sludge floating taken place.Therefore,a control strategy that aimed at to increasing the organic load by shortening the hydraulic retention time under the condition of constant influent organic concentration was put forward.Based on this control strategy,a lab-scale UASB reactor was used to simulate the treatment of the beverage wastewater.Granular sludge with floating characteristics was used as the inoculation.COD,VFA,SS,gas production and other conventional indicators were monitored to prove the validity of the strategy.At the same time,theparticle size distribution,average sedimentation rate and density,specific methanogenic activities,sludge morphology,hydrogen partial pressure,hydrogen utilization rate(HUR)and microbial community were analyzed.The validity of the strategy was proved.The results showed that the reactor is stable when the hydraulic retention time of UASB reactor is shortened from HRT of 10 h to 2.5h.COD concentration in the effluent could reachless than 300mg/L and the removal rate did more than 82%,which was equal to the efficiency of actual reactor.The average settling velocity of granular sludge increased from 41.3 m/h to 74.8 m/h,and the density increased from 1030.6kg/m3 to 1093.3 kg/m3.The settling performance of sludge was improved and floating sludge disappeared.The maximum methanogenic activities for acetate and propionate of the granular sludge increased from 0.493 to 0.669 g COD/(g VSS·d)and 0.398 to0.588 g COD/(g VSS·d),respectively.The hydrogen partial pressure decreased from23.8 Pa to 5.75 Pa and the maximum hydrogen utilization rate(HUR)of sludge was0.48 g COD/(g VSS·d).FISH results showed that the proportion of methanogens in the granular sludge increased by 1.8 times and that of acetate utilizing Archaea increased by1.5 times.The number of hydrogen utilizing Achaea was significantly higher than that in inoculation(3.2 times),which would benefit interspecific syntrophic metabolism.Reducing the hydraulic retention time and/or increase the organic load can be used as an effective strategy to improve the settling performance of the sludge in the UASB reactor and control the sludge floating.