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Abstract:
 
The removal and treatment of sludge from municipal wastewater treatment plants is important due to environmental factors, so there is a significant incentive to discover and develop strategic plans to reduce excess sludge production in sewage treatment processes. Activated sludge system is used as the main biological process for municipal and industrial wastewater treatment and an excess sludge production rate in this process is between 15-100 liters per kilogram of removed BOD₅. One of The usages an anaerobic reactor in the activated sludge system known as the Cannibal process that is one of the conventional methods used to reduce the sludge production rate at the sewage treatment line, which has low operating costs and relative simplicity to process design. The system's overall reducing efficiency is generally up to 50%. The purpose of this process is less production of sludge and also improvement of wastewater quality. In order to achieve reduction in excess sludge production, different mechanisms are considered which include microbial predation, uncoupling metabolism, endogenous metabolism and lysis-cryptic growth. The microbial predation mechanism is one of the important mechanisms in the cannibal process that is a suitable choice for reduction of excess sludge because of its low strategic cost and environmental compatibility. The objective of this research is the applicability of Quorum quenching (QQ) phenomenon in a conventional Cannibal process for enhancing the microbial predation mechanism to improve the efficiency of reducing sludge and other effective sludge parameters. Quorum sensing system is a new method of managing social behavior of microbial Population. The decomposition of Acyl Homosserine Lactones (AHL) is the most usable and practical way for creating disturbance in Quorum sensing system. For increasing the free bacteria population, Quorum quenching agent is used in the aerobic tank. These enhance microbial predation and show decrease in Extracellular Polymeric Substances (EPS). So far many bacteria with QQ feature are reported in biological wastewater treatment reactors. The basis of this project was designed in two laboratory phases and the reactors were operated with synthetic wastewater. In the first phase, the cannibal process was used in the form of a laboratory reactor, and in the second phase, by installing a separate aeration reactor and adding the Rhodococcus sp.BH4 bacteria, a quorum quenching bacteria, in a polymeric structure of alginate and introduced as QQ beads. The modified Cannibal process was designed. Microbial predation mechanism is one the methods that increase population of eukaryotic predators by changing the microbial structure of activated sludge system; by this method, efficiency of reduction of excess sludge production is increased. The results showed that the presence of QQ grains led to an increase in the number of eukaryotic species. The yield coefficient (Y_obs) in the modified Cannibal and the control Cannibal was 0.389 and 0.092, respectively, with a significant decrease of 77%. Also, the results of EPS, which indicates the proper functioning of this system, has been analyzed and investigated. The applied QQ primary treatment enhances the Microbial predation mechanism in Cannibal system, significantly improve the efficiency of this system, and biological excess sludge notably is decreased.
 
Keywords: Excess Sludge, Cannibal Process, Microbial Predation, Quorum Sensing/Quenching
 

Keywords: excess sludge, Canibal Process, Microbial predation, Quorum Quenching

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