Research On A New Reactor For Sludge Reduction Using Oligochaete Worm With Simultaneous Nitrification And Denitrification Process

Biological wastewater treatment has many advantages, but it generates surplus sludge. The high cost of sludge treatment and disposal is the key economic factor limiting the operation of sewage treatment plant. Therefore, the sludge reduction has become the most talked topic of scholars all around the world. Compared with other strategies, micro-fauna's predation with the advantages such as energy saving and no secondary pollution has begun to receive increasing attention.This paper aims to design a novel oligochaete worm reactor with simultaneous nitrification and denitrification process to achieve the stabile sludge reduction and minimum nutrient release. This paper focused on study of optimization of process conditions; performance of sludge reduction; variations of the sludge characteristic; and simultaneous nitrification and denitrification process. All of above provided the foundation of engineering application about this novel reactor.The influences of change in frequency of high-intensity aeration(FHIA), dissolved oxygen(DO) content, initial sludge concentration(ISC) and sludge retention time(SRT) on the immobilization of worms and sludge reduction were evaluated. Furthermore, response surface method was applied to optimize the process conditions using the sludge reduction rate and stable immobilization of worms as the target parameters to optimize, and DO as the control factors to be optimized with the fluctuation of influent ISC, while keeping FHIA and SRT at optimum level. The optimum conditions were found to be DO of 1.0¹.6 mg·L^-1 and ISC of 3000⁴000 mg·L^-1 respectively, while keeping FHIA at 12 times·d^-1 and SRT at 2 d.The research on the long-term operation of the oligochaete worm reactor showed that: attractive sludge reduction rate (43.71 g·d^-1) can be obtained. From the consideration of sludge characteristic, the reactor can improve the sedimentation performance of activated sludge. Furthermore, the filter performance and the stability of sludge characteristic had been improved in this reactor. Oligochaete worm reactor can stabilize sludge characteristic while reducing the sludge. The results also showed that worms can reduce the rate of EPS-sugar and EPS-protein. From the consideration of water quality, the predation of worms led to the release of COD, ammonia nitrogen and phosphorus. Strong denitrification promoted in oligochaete worm reactor because of its special operation mode. The metabolism of worms led to the release of organic carbon can strengthen greatly denitrification and improve the nitrogen removal efficiency.The further research on the simultaneous nitrification and denitrification showed that: Effective simultaneous nitrification and denitrification were obtained owing to the stratified sludge layer containing aerobic and anoxic microzone formed on each carrier during most of the operation time in the reactor, which created suitable conditions for remarkable sludge reduction and nutrient removal. And the soluble chemical oxygen demand released by sludge predation was also proved to provide a carbon source for denitrification leading to carbon release control and substantial cost savings.