Development of biological filtration process for effective advanced treatment of sewage

다국어 초록 (Multilingual Abstract)

Lowering of nitrogen and phosphorus levels in wastewater discharges has been a continuing trend in the wastewater treatment filed as a result of regulatory requirements becoming increasingly stricter. The objectives of this study are to develop advanced biological filtration processes and to establish design and operational parameters of them for removal of nutrients from two kinds target water: (1) effluent from grit chamber and (2) secondary effluent of a municipal wastewater treatment plant.
Utilization of pre-coagulated sludge, obtained by adding coagulant at the primary sedimentation tank, as the hydrogen donor for denitrification in biological filtration process, which consists of a pre-coagulation, a sedimentation tank, an anoxic filter, an aerobic filter with a side stream to the anoxic tank and a polishing filter with anoxic and aerobic parts, is discussed with a pilot plant treating actual municipal sewage. To utilize pre-coagulated sludge as the hydrogen donor for the first denitrification, nitrified liquid from the following aerobic filter is re-circulated either to the anoxic filter (Flow A) or, to the bottom part of the sedimentation tank of pre-coagulation (Flow B). Flow A and Flow B are compared from the viewpoints of treatment performance. Concentration of SS, T-C-BOD, T-N and T-P in the effluent are less than 3 mg/L, 5 mg/L, 2 mgN/L and 0.5 mgP/L, respectively, under total hydraulic retention time of 3.0∼3.5 h in the biological filtration part in both Flow A and Flow B. DO of 2∼5 mg/L is consumed and NO_(x)^(-)-N of 1∼3 mgN/L is denitrified in the sedimentation tank in Flow B. The amount of discharged sludge and required water during backwashing is not affected by the Flow. When ratio of S-COD_(Cr)/S-N in the influent wastewater is 5.0 mgCOD/mgN, the methanol of 32 mg/L concentration addition is required at 29 mL/㎥-treated water for the anaerobic part of the polishing filter in Flow A but, at 22 mL/㎥-treated water in Flow B. 31% reduction of methanol addition per ㎥-treated water is achieved by changing from Flow A to B.
A biological filtration process applicable to tertiary treatment of sewage for effective removal of nitrogen is also developed. The biological filtration system developed for tertiary treatment consists of a nitrification filter (Filter 1) and/or a polishing filter with anoxic and aerobic part (Filter 2). Filter 1 is required only when nitrification is not accomplished in secondary effluent. A pilot plant set at a municipal sewage treatment plant is operated for 525 days with feed of real sewage. Denitrification is accomplished with linear velocity (LV) of 50∼202 m/d in a 1 m anoxic filter-bed. As a result, T-N concentrations at the outlet are 1∼5 mgN/L for the influent concentrations of 12∼30 mgN/L. LV of 202 m is considered to be the upper limit. Methanol addition is controlled based on COD/N ratio and McCarty's equation. Constant COD/N control sometimes results in excess or less addition of methanol because of consumption by DO and large diurnal fluctuation of NO_(x)^(-)-N concentration, and McCarly's equation control gives appropriate amount of methanol. The maximum denitrification rate is reached at 4.0 kgN/(㎥-filter-bed·d) at water temperature of 15∼20℃ in Filter 2. The ratio of backwashing to the treated water is about 5∼10%. No significant effect of HRT (LV) on the ratio is observed. The yield coefficients are only 0.1∼0.3 kgSS/kgCOD in Filter 2. These results prove that this process is both convenient to install as tertiary treatment and cost effective to build and operate.
The mathematical model of biological filtration proposed by Hidaka and Tsuno (2004) is applied for tertiary treatment. The model is applicable to explain the experimental performance with biological filtration reactors, in which continuous treatment of actual sewage is carried out. The simulated results about long-term treatment performance in continuous treatment, details of water quality profiles through the filter bed, and biomass are similar to the measured value and well reproducted. This model predicts that McCarly's equation ratio of 1.1 is to be required to accomplish denitrification and avoid excess carbon with remaining S-C-BOD of less than 5 mg/L under the conditions that HRT in the filtration part and the linear velocity (LV) of Filter 2 are set at 0.30 h and 160 m/d, respectively. This model shows that constant COD/N control results in an excess or shortage addition for larger diurnal fluctuation of NO_(x)^(-)-N. McCarty's equation can be used to add the appropriate amount of methanol and make the plant operation cost-effective. This biological filtration process should be operated less than ammonium loading rate of 0.5 kgN/(㎥-filter-bed·d) in Filter l and NO_(x)^(-)-N loading rate of 4.4 kgN/(㎥-filter-bed·d) in the winter season. No significant effect of height on nitrification, denitrification, and organic removal was observed when HRT is constant.
These results show that the stability of treatment performance and applicability of these processes to advanced treatment of sewage have been confirmed.

목차 (Table of Contents)

• ABSTRACT = ⅰ
• TABLE OF CONTENTS = ⅲ
• LIST OF FIGURES = ⅵ
• LIST OF TABLES = ⅹ
• CHAPTER 1 INTRODUCTION = 1
• 1.1 Research Background = 1
• 1.2 Literature Review = 3
• 1.2.1 Pre-coagulation process = 3
• 1.2.2 Biological filtration system = 4
• 1.2.3 Modelling in biological filtration = 13
• 1.3 Objectives and structure of this dissertation = 14
• CHAPTER 2 UTILIZATION OF PRE-COAGULATED SLUDGE FOR DENITRIFICATION IN THE BIOLOGICAL FILTRATION PROCESS = 16
• 2.1 Introduction = 16
• 2.2 Materials and Methods = 16
• 2.2.1 Experimental devices = 16
• 2.2.2 Automatic operation = 18
• 2.2.3 Operational conditions = 20
• 2.2.4 Experiment analysis = 23
• 2.2.5 Estimation of bacterial mass and potential activity = 23
• 2.2.6 Batch test for pre-coagulated sludge = 26
• 2.2.7 Tracer test in the sedimentation tank = 26
• 2.3 Results and Discussion = 28
• 2.3.1 Treatment Performance = 28
• 2.3.2 Characteristics of sedimentation tank and pre-coagulated sludge = 43
• 2.3.3 Investigation of the first step denitrification = 49
• 2.3.4 Investigation of nitrification rate = 49
• 2.3.5 On-line nitrate measurement device = 51
• 2.3.6 Biomass and potential activity = 51
• 2.3.7 Backwashing = 55
• 2.4 Summary of Results = 58
• CHAPTER 3 A BIOLOGICAL FILTRATION PROCESS FOR EFFECTIVE NITROGEN REMOVAL IN TERTIARY TREATMENT OF SEWAGE = 60
• 3.1 Introduction = 60
• 3.2 Materials and Methods = 61
• 3.2.1 Experimental devices = 61
• 3.2.2 Operating condition = 63
• 3.2.3 Experiment analysis = 65
• 3.2.4 Estimation of bacterial mass and potential activity = 65
• 3.3 Results and Discussion = 67
• 3.3.1 Treatment Performance = 67
• 3.3.2 Profiles of water qualities with height of filter-bed = 79
• 3.3.3 Nitrification in Filter 1 = 87
• 3.3.4 Denitrification and SS removal in Filter 2 = 91
• 3.3.5 Characteristics of microorganisms = 95
• 3.3.6 Backwashing = 102
• 3.4 Summary of Results = 106
• CHAPTER 4 MODELING OF BIOLOGICAL FILTRATION SYSTEM AND DISCUSSION ON OPERATIONAL PARAMETERS FOR TERITERAY TREATMENT = 108
• 4.1 Introduction = 108
• 4.2 Mathematical model = 108
• 4.2.1 State variables and transformation paths = 108
• 4.2.2 Rate equations = 110
• 4.2.3 Mass balance = 116
• 4.3 Experimental methods = 124
• 4.4 Results and Discussion = 125
• 4.4.1 Rate constants and coefficients = 125
• 4.4.2 Verification = 125
• 4.4.3 Discussion of operational parameters = 134
• 4.5 Summary of Results = 141
• CHAPTER 5 CONCLUSIONS = 144
• REFERENCE = 149
• ACKNOWLEDGMENTS