The Initiation And Control Of Activated Sludge Bulking In The Treatment Of Papermaking Wastewater By Oxidation Ditch

Wastewater generated by the paper industry is a kind ofunmanageable organic wastewater which has the characteristics oflarge amount, high concentration of suspended solids and organicmatter, high chromaticity and complex components. In thisexperiment, by causing and controlling the sludge bulking inoxidation ditch and determining the effluent quality, the relevantengineering parameters can be determined. The control methods fordifferent trigger factors can be found to treat sludge bulkingcost-effectively.Sludge bulking is a common phenomenon in activated sludgewastewater treatment process, especially sludge filamentous bulking.After sludge filamentous bulking, not only the sludge structure andsludge settling properties change, but also the treatment ability falls.This paper focuses on the changes in influent organic load, DO and pHwhich cause sludge filamentous bulking. The results show that,reducing the organic load operation to the9th day, reducing DO to the9th day and reducing pH value to the7th day have triggered sludgefilamentous bulking. The treatment time of the bulking caused bythese three factors differs with bulking time and extent.There are many ways to control sludge filamentous bulking andthe bulking caused by three factors above can be controlled by thefollowing methods:1. Improving a single factor and changingmanagement operation mode.2. Adding PAC into wastewater to treatsludge bulking.3. Adding bio-flocculants to treat sludge bulking.4.Adding H2O2to treat sludge bulking.The following methods are used to treat the sludge filamentous bulking caused by organic load:1. Raising organic load and changingoperation mode, on the7th day, SV30reduces to22%, SVI reduces to109mL·g-1, COD removal rate is83.03%, total protein is0.028mg·mL-1, SOUR is0.6578mgO2·(mgMLSS·h)-1, filamentousbulking gets effective control.2. Raising organic load and addingflocculants, while the system has run for5days, SV30reduces to22%,SVI reduces to109mL·g-1, COD removal rate is83.66%, total proteinis0.022mg·mL-1, SOUR is0.5035mgO2·(mgMLSS·h)-1. Comparedwith the method1above, method2uses less time and has betterperformance in controlling sludge filamentous bulking.The following methods are used to treat the sludge filamentousbulking caused by DO:1. Raising DO and changing operation mode,on the8th day, SV30reduces to20%, SVI reduces to109mL·g-1, CODremoval rate is91.94%, total protein is0.0479mg·mL-1, SOUR is0.6586mgO2·(mgMLSS·h)-1, sludge filamentous bulking gets effectivecontrol.2. Raising DO and adding flocculants, while the system hasrun for6days, SV30reduces to30%, SVI reduces to146mL·g-1, CODremoval rate is83.78%, total protein is0.0326mg·mL-1, SOUR is0.3875mgO2·(mgMLSS·h)-1. Method2has advantages over method1.The results show that raising DO to appropriate range is the key factorin controlling sludge filamentous bulking.The following methods are used to treat the sludge bulkingcaused by pH:1. Raising pH value and changing operation mode, onthe17th day, SV30reduces to32%, SVI reduces to130mL·g-1, CODremoval rate is80.39%, total protein is0.0483mg·mL-1, SOUR is0.3978mgO2·(mgMLSS·h)-1, sludge filamentous bulking gets control.2. Raising organic load and adding3.5g H2O2·(kgMLSS·d)-1H2O2,while the system has run for11days, SV30reduces to25%, SVIreduces to124.45mL·g-1, COD removal rate is89.21%, total protein is0.0423mg·mL-1, SOUR is0.2672mgO2·(mgMLSS·h)-1. Compared withthe method1above, method2can restrain the growth of filamentousbacteria in a shorter time so it is benefit to the operation of sewagetreatment plant. According to the experimental data, sludge filamentous bulkingcaused by low DO and low organic load can be controlled within onesludge age. By comparison, low DO and low organic load will notimpact the microorganism in sludge fatally, and problems being timelyidentified can improve the activity of microorganism in a shorter time.If sludge filamentous bulking is caused by low pH, the control periodis as long as two sludge age and the activity of microorganism onlycan be revived by themselves’ metabolic turnover.