Sulfide in the Anaerobic System: Source and Effects

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CHAPTER II: OPTIMIZATION OF THE CANNIBAL PROCESS: EFFECT OF HYDRAULIC RETENTION TIME AND SOLIDS INTERCHANGE RATE ON THE SOLIDS DESTRUCTION IN THE CANNIBAL ΤΜ SYSTEM

ABSTRACT

The Cannibal TM system, comprised of an activated sludge process integrated with a side stream anaerobic bioreactor, is capable of reducing excess sludge up to 60% compared to the conventional activated sludge process. The hydraulic retention time (HRT) in the Cannibal bioreactor and the interchange rate (the percent of sludge by mass interchanged between the activated sludge system and the bioreactor on daily basis) are the two important operational parameters in the optimization of the Cannibal process. This research was designed to investigate the effect of the Cannibal bioreactor hydraulic retention time and the interchange rate on the solids destruction in the system. The first phase of this study has looked at the effect of three different HRTs, 5 day, 7 day and 10 day. The interchange rate during phase I was 10%. The results showed that the 7 day HRT can be recommended as the minimum retention period for the Cannibal process.The 5 day HRT Cannibal system had some settling problems and high volatile fatty acid content compared to the 7 day HRT Cannibal system. The protein and polysaccharide tests showed that the Cannibal bioreactor is primarily involved in the release of biopolymers which are degraded in the aerobic environment.The second part of this study focused on the effect of the interchange rate (IR) on the solids destruction in the system. The interchange rates that were applied in the system were 15%, 10%, 7%, 5% and 4%.The HRT in the Cannibal bioreactor was 7 day. The results showed that the 10% interchange rate gave maximum solids destruction than the other interchange rates. This implies that 10% is an optimum IR for the Cannibal system. Apart from higher solids wastage, the 4% and 5% IR Cannibal systems had higher volatile fatty acid production.

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INTRODUCTION

The Cannibal TM process is an innovative wastewater treatment process that minimizes the excess sludge generation in a conventional activated sludge system. The Cannibal TM system is comprised of an activated sludge process integrated with a side-stream anaerobic bioreactor (Figure II-1). The actual operation involves an interchange flow of biomass between the activated sludge tank and the Cannibal (anaerobic) bioreactor. The biomass that enters the Cannibal bioreactor is retained for a specific retention period and recycled back to the activated sludge process. The Cannibal bioreactor is an anaerobic bioreactor in which a negative oxidation reduction potential (ORP) exists. The ORP plays a vital role in the sludge minimization in the Cannibal process (Saby et al., 2002).Research at Virginia Tech by Novak et al. (2006) has shown that the CannibalTM process compared to the conventional activated sludge process is capable of reducing excess sludge up to 60%. The yield, defined as mg of VSS per mg of COD, in the conventional system is about three times the yield in the CannibalTM system.The effect that the Solids Retention Time (SRT) exerts on the performance of the activated sludge system makes it a critical operational parameter. The minimum SRT is described as the value below which microorganisms are unable to proliferate because they are wasted from the system before they can produce a stable population. Likewise,in an anaerobic system the biochemical operations of hydrolysis, acidogenesis and methanogenesis are affected in a unique way when the retention period is not maintained above the minimum range. The detention times of the activated sludge system and the Cannibal bioreactor are important parameters in the working of the Cannibal TM process.The initial research on the Cannibal process conducted at Virginia Tech employed a hydraulic retention time (HRT) of 2 days for the activated sludge system. This HRT was later reduced to 1.5 days. The HRT for the anaerobic bioreactor was maintained at 10 day (Chon, 2005). These retention periods were selected to be representative of the onsite operational parameters.

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Abstract
Dedication
Acknowledgement
Table of Contents
List of Figures
List of Tables
CHAPTER I- LITERATURE REVIEW
Introduction
Cannibal Process: Mechanism
Anaerobic System: Fundamental Biological Reactions
Hydraulic Retention Time
Importance of Solids Retention Time
Effect of Iron and Aluminum
Volatile Fatty Acids
Sulfide in the Anaerobic System: Source and Effects
References
CHAPTER II: Optimization of the Cannibal Process- Effect of Hydraulic Retention Time and Solids Interchange Rate on the Solids Destruction in the Cannibal System
Abstract
Introduction
Methods and Materials
Results and Discussion: Phase I
Summary: Phase I
Specific Conclusions: Phase I
Results and Discussion: Phase II
Summary: Phase II
Specific Conclusions: Phase II
References

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