外文原文-混凝剂和絮凝剂.pdf

1、 CHAPTER 13 TREATMENT PROCESSES:COAGULATION AND FILTRATION Contents 13.1 Introduction 13.2 Coagulation process 13.3 Coagulants and flocculants 13.3.1 Definitions 13.3.2 Coagulants 13.3.3 Flocculants 13.3.4 Health effects 13.4 Coagulation and flocculation 13.4.1 Overview 13.4.2 Jar testing 13.4.3 Per

2、formance and control 13.5 Clarification and sedimentation 13.5.1 Overview 13.5.2 Clarifier types 13.5.3 Optimisation and performance issues 13.6 Two-stage lime softening 13.7 Rapid gravity filtration 13.7.1 Overview 13.7.2 Turbidity monitoring 13.7.3 Filter operation 13.7.4 Optimisation of the filtr

3、ation process 13.8 Second stage filtration REFERENCES Draft Guidelines for Drinking-water Quality Management for New Zealand,October 2005 Figures and Tables Figure 13.1:Conventional coagulation with sedimentation and filtration Figure 13.2:Direct filtration Figure 13.3:Lamella plate clarifier Figure

4、 13.4:Upflow adsorption clarifier Figure 13.5:Dissolved air flotation Figure 13.6:Actiflo process Figure 13.7:Rapid gravity filtration Draft Guidelines for Drinking-water Quality Management for New Zealand,October 2005 Chapter 13 Coagulation with Filtration 1 13.1 INTRODUCTION This chapter covers th

5、e water treatment process of chemical coagulation,with or without sedimentation.It also covers the situation where sedimentation is not followed by rapid gravity sand filtration.The discussion on coagulation includes details of chemical coagulants and polyelectrolytes used in the process.The separat

6、e stages of coagulation,flocculation and conventional sedimentation(also called clarification)are included.In current terminology sedimentation is one of a number of processes that are grouped as clarification.New high-rate clarification processes,(lamella plates,tube settlers,buoyant media clarifie

7、rs,dissolved air flotation(DAF)and Actiflo)are also covered in this chapter.The discussion on filtration covers only rapid gravity sand filtration(pressure sand filters are used sometimes).This is the most common filtration method following coagulation in New Zealand.Other filtration methods that do

8、 not involve coagulation,e.g.diatomaceous earth,cartridge,slow sand and membrane filtration,are discussed separately in Chapter 14.Although coagulation is commonly practised with membrane filtration to remove colour,membrane filtration does not rely on coagulation for removal of protozoa and is ther

9、efore classified separately as filtration without coagulation,in terms of the Drinking-water Standards for New Zealand 2005(DWSNZ).The combined process of coagulation and filtration is commonly used throughout New Zealand and is effective at removing dissolved and colloidal colour(natural organic ma

10、tter),turbidity(suspended solids),algae(phytoplankton),bacteria,viruses and protozoa(e.g.Giardia and Cryptosporidium).The DWSNZ outlines new turbidity criteria and turbidity monitoring requirements that must be met by water treatment plants to ensure compliance with the protozoa criteria.Further gui

11、dance on compliance with respect to coagulation and filtration is discussed in Chapter 8:Protozoa Compliance,Section 8.3.2 of these Guidelines.Risk management issues related to the treatment processes in this chapter are discussed in the:MoH Public Health Risk Management Plan Guide PHRMP Ref.P5.1:Tr

12、eatment Processes Coagulation/Flocculation/Sedimentation.MoH Public Health Risk Management Plan Guide PHRMP Ref.P5.2:Treatment Processes Dissolved Air Flotation.MoH Public Health Risk Management Plan Guide PHRMP Ref.P5.3:Treatment Processes Direct Filtration.MoH Public Health Risk Management Plan Gu

13、ide PHRMP Ref.P6.1:Treatment Processes Rapid Sand Filtration.MoH Public Health Risk Management Plan Guide PHRMP Ref.P8.1.Treatment Processes pH Adjustment.MoH Public Health Risk Management Plan Guide PHRMP Ref.P11:Treatment Processes Plant Construction and Operation.Draft Guidelines for Drinking-wat

14、er Quality Management for New Zealand,October 2005 Chapter 13 Coagulation with Filtration 2 13.2 COAGULATION PROCESS Coagulation,flocculation and clarification,followed by rapid gravity sand filtration,are the key steps in conventional water treatment systems.This is a well-proven technology for the

15、 significant removal of colour and particulate matter including protozoa(e.g.Cryptosporidium oocysts and Giardia cysts),viruses,bacteria,and other micro-organisms.Iron,manganese,tastes and odours may also be removed from the water by these processes.If not removed,natural organic matter can react wi

16、th chlorine to reduce disinfection efficiency and form chlorinated organic species,e.g.disinfection by-products(DBPs),some of which are chemical contaminants of health significance,see Chapter 10:Chemical Compliance and Chapter 15:Treatment Processes,Disinfection.Micro-organisms remaining in treated water may also pose risks to public health.Conventional treatment(coagulation,sedimentation and sand filtration),as illustrated in Figure 13.1,has several distinct stages.A coagulant is added to neut