Study On Sludge Reduction Technologies With Thermophilic Bacteria Based On The Cryptic Growth Of Microorganism

Now the actived sludge process has been used more and more extensively, but a large quantity of excess sludge was produced. The problems of treatment and disposition to the excess sludge become difficult and troublesome, the cost can account for 25% to 40%, up to 60% of total plant operation costs. The final sludge disposal became more and more difficult with potential pollution to the environment as well as the limitation of the land area available for the disposal. The sludge reduction technologies are studied in lately decades.The sludge reduction are some technologies which can reduce the quantity of sludge priduction, ensuring the same sewage quantity and treatment quality with having been taken some measures.The possible approaches for sludge reduction may be based on three aspects: uncoupling metabolism, cryptic growth enhanced through cell lysis and microfauna pry. Relevant research works were reviewed, characteristics of each technology were compared, and the sludge reduction based on cryptic growth was discussed particularly.The sludge reduction technology with thermophilic bacteria was divided into two parts, including sludge digestion by the aerobic Thermophilic bacteria was compared with the conventional aerobic sludge digestion at 60, 65, 70℃, and the influences of temperature, the initial concentration values of sludge, dissolved oxygen and the inoculation quantity of thermophilic bacteria were each studied in this paper.The research results indicated that the digestion effect and efficiency of sludge by the aerobic thermophilic bacteria were much better than the conventional aerobic sludge digestion at each three temperature as said before. The removal rate of TSS and VSS was just 40% and 50% for the conventional aerobic sludge digestion process, but in the thermophilic bacteria sludge digestion, The removal rate of TSS and VSS respectively reached 55% and 65%, corresponding to the before both higher fifteen percents. In addition, the digestion cycle was declined from 96 hours to 72 hours, and was shortened by 1/4 than the simple aerobic digestion. The changes about the parameter of TCOD,SCOD,NH4+-N et al. in the thermophilic bacteria sludge digestion were more clearly and better than the conventional process.Temperature was an important effect factor to the thermophilic bacteria sludge digestion. The cycle of sludge digestion was shortened, and the efficiency of sludge digestion was enhanced. But, it was oppositely, not endless. When temperature reached 70℃, its tend of improvement became so unconspicuous. The best temperature for the excess sludge digestion with thermophilic bacteria appeared at 65℃, when the biodegradation for sludge was more completely, The removal rate of TSS and VSS were higher.The thermophilic bacteria sludge digestion with the different initial concentration values of sludge was studied. When the initial concentration values of sludge was very low, higher removal rate of TSS and VSS has been achieved; when the initial concentration value was very high, the removal rate of TSS and VSS was also very low, the aim to remove much VSS from the excess sludge through digestion method with the thermophilic bacteria will be not obtained. Further more, the phenomenon that removal quantity of TSS and VSS was increased along with the increasing initial concentration value of sludge was indicated in the research results.Dissolved oxygen was one more important effect factor to the thermophilic bacteria sludge digestion. When the dissolved oxygen concentration was around 2mg/L, the thermophilic bacteria could be enriched and the removal rate of TSS and VSS was increasing along with the DO. The DO reached one value while the removal rate of TSS and VSS became steady gradually, no increasing. With the increasing DO, the removal had even declined. The best DO concentration value for the excess sludge digestion with thermophilic bacteria appeared at around 2 mg/L.The inoculation quantity of thermophilic bacteria was one effect factor to the thermophilic bacteria sludge digestion. But the research results indicated that its influence was not so important and obvious. There were no different changes in the removal rate of TSS and VSS if the inoculation quantity changed, and the best inoculation quantity to the thermophilic bacteria or sludge of this study was 5% (volume ratio).