Study On CAST-Inclined Plate Worm Reactor Combined Process For Sludge Reduction

Activated sludge wastewater treatment process is the most importantcontemporary biological wastewater treatment method. Usually it has a good waterpurification effect, but the process is accompanied by amount of excess sludge. From aholistic point of view of environmental protection, sewage treatment on the one handshould to achieve the goal of purifying wastewater, on the other hand excess sludge alsoshould be got effective treatment and disposal to avoid its secondary pollution. In theearly, our country’s sewage treatment industry is in a “attention sewage, sludge ignored”development model, its potential risks has become increasingly prominent in thebackground of the surge in the amount of sewage and excess sludge. Sewage treatmentindustry’s demand for the method of sludge reduction is becoming more intense.Currently, a variety of methods for sludge reduction has be proposed. They achieved thesludge reduction through regulate the transfer processes of matter and energy. However,there are many difficulties of most of these methods, such as large amount of investment,high energy consumption and the risk of secondary pollution. The microfauna predationtechnology, which based on the principle to extend the food chain to promote theextension of the energy consumed, has an excellent environment-friendly and lowenergy consumption characteristics. At present, the types of the reactors, whichdeveloped based on this concept, is still relatively small. In addition, the relativelycomplex operation and maintenance also makes it difficult to apply to practicalengineering.This subject came from the social development project of Zhenjiang MunicipalScience and Technology Bureau (FZ2011022). It based on the CAST of Zheng Runzhousewage treatment plant, issues carry out the sludge reduction tests with using Tubifextubifex to prey excess sludge. Test got the best habitat for the growth of Tubifex tubifexand the predation of sludge by small scale experiment. According to the test resultsauthor develop the multilayer inclined plate worm reactor and its operating conditions.Unit volume of the reactor has a large adhesion area, the ratio of area to volume up9.7m2/m3. The test result shown worms grew well on the filler. Using the inclined plateworm reactor coupled with CAST to compose a medium-size test model. In a continuitytest examine the combined process’s sewage treatment effect and sludge reductionperformance, which using the optimal working parameters. Examine the impact of environmental factors on the worm’s growth and thepredation effects of sludge. Test results shown the optimal environmental factor includeintermittent aerated to maintain DO=2mg/L, water temperature=20~25℃, pH=6~7,MLSS/worm≥0.2, MLSS=2~6g/L, worm growing region SRT=1~2d, worm populationdensity maintained at10~15g/L. In the laboratory scale tests, the system running withthe optimal working parameters, the sludge reduction rates up to21.4%and the worm’spredation rate was0.031g-TSS/(g-worm·d) every cycle after the worm’s growth wasbecoming steady. After worm predation, the supernatant TN concentration increased18.8%, the ammonia concentration increased56.3%, nitrate concentration decreased by34.2%, TP concentration increased2.53times, COD concentration increased89.3%. Inaddition, the MLVSS/MLSS of sludge decreased to0.49from0.56. TN and TP insludge decreased by3.7%and2.8%, respectively. Sludge system could maintain part ofthe ability of denitrification.74.2%of the decrement of TP in sludge were transferred toworm, and the rest were release into aqueous phase.In the second stage, we ran the CAST-Inclined Plate Worm Reactor CombinedProcess for a continuity test. Operating parameters of the process: CAST operationcycle was4h, influent/micro-aeration0.5h, vigorous aeration2h, settle1h, decant0.5h,micro-aeration maintained DO=1mg/L, vigorous aeration maintained DO=2mg/L; fillratio was0.28; MLSS=3000~4000mg/L; SRT=2d in worm reactor; sludge returned ratiowas15%; beginning of every cycle MLSS=4500~5000mg/L in worm reactor; theoperation mode of aeration system in worm reactor was also aeration2h and standby2h,maintained DO=2mg/L when system was aerating. Initial inoculation density of Tubifextubifex in worm reactor was11.4g/L.The results showed: sludge yield coefficient of CAST was0.45gTSS/gCOD;sludge yield coefficient of CAST-Inclined Plate Worm Reactor Combined Process was0.37gTSS/gCOD, it was17.8percent lower than the former. The concentration ofCOD, TN, ammonia, TP and SS in treated water could meet Category B, Class1underthe standard of “Discharge standard of pollutants for municipal wastewater treatmentplant”(GB18918-2002). SS in the effluent of worm reactor was significantly reduced, itcould the standard of Category A, Class1. Compared with CAST effluent water quality,concentration of TN and ammonia in the in the effluent of worm reactor increasedslightly, but they all meet the standard of Category B, Class1. But TP released seriouslyin worm reactor. Chemical method was recommended to treat TP in tail water of thesystem. After the predation of Tubifex tubifex, SVI value of sludge decreased by14.1%, specific resistance of sludge increased by78.9%, specific oxygen uptake rate decreasedby24.2%. Therefore, the sludge settling performance enhanced, dewateringperformance of sludge became weakened, and sludge activity also became weakened.