Engineering of Water Quality Control Theory and performance of Deep-Bed Filtration
Engineering of Water Quality Control Theory and Performance of Deep-Bed Filtration
1. An overview of potable Water filtration 1.1 Concept of filtration The filtration processes discussed in here are used primarily to remove particulate material from water
1. An overview of potable Water filtration 1.1 Concept of filtration The filtration processes discussed in here are used primarily to remove particulate material from water
the classification of filtration filtration style granular bed filtration precoat filter filter media sand, anthracite coal GAC de filtration hydraulic: gravity filters pressure filters rate of filtration: rapid granular bed filter, slow sand filter distribution of deposit: depth filtration, cake filtration
the Classification of filtration: filtration style: granular bed filtration, precoat filter filter media: sand, anthracite coal , GAC, DE filtration hydraulic: gravity filters, Pressure filters rate of filtration: rapid granular bed filter, slow sand filter distribution of deposit: depth filtration, cake filtration
Dominant Mechanisms, Performance, and Applications (1)Cake filtration Cake filtration of particulates involves physical removal by straining at the surface The mechanism of cake filtration is largely physical straining Chemical pretreatments such as coagulation and sedimentation are not generally provided The source water must be of quite good quality
Dominant Mechanisms, Performance, and Applications (1) Cake filtration ▪ Cake filtration of particulates involves physical removal by straining at the surface. ▪ The mechanism of cake filtration is largely physical straining. ▪ Chemical pretreatments such as coagulation and sedimentation are not generally provided. ▪ The source water must be of quite good quality
(2)Slow sand filtration The surface cake of accumulated particulates includes a variety of living and dead micro-and macroorganisms The biological metabolism of the organisms enhances removal of particulates As the filter cake develops, the cake itself assumes a dominant role in particulate removal Because of this filtrate turbidity improves as the filter run progresses, and deterioration of the filtrate turbidity is normally not observed at the end of the filter cycle
(2) Slow sand filtration ▪ The surface cake of accumulated particulates includes a variety of living and dead micro- and macroorganisms. ▪ The biological metabolism of the organisms enhances removal of particulates. ▪ As the filter cake develops, the cake itself assumes a dominant role in particulate removal. ▪ Because of this, filtrate turbidity improves as the filter run progresses, and deterioration of the filtrate turbidity is normally not observed at the end of the filter cycle
(3 Rapid granular deep-bed filtration Depth filtration involves a variety of complex mechanisms to achieve particulate removal The small particles could be captured in bed by transport and attachment process in series Transport process are needed to carry the small particles into contact with the surface of the individual filter grains Attachment mechanisms hold the particles to the surfaces Chemical pretreatment is essential to particulate removal in depth filtration
(3) Rapid granular deep-bed filtration ▪ Depth filtration involves a variety of complex mechanisms to achieve particulate removal. ▪ The small particles could be captured in bed by transport and attachment process in series. ▪ Transport process are needed to carry the small particles into contact with the surface of the individual filter grains. ▪ Attachment mechanisms hold the particles to the surfaces. ▪ Chemical pretreatment is essential to particulate removal in depth filtration
Regulatory Requirements for Filtration community water systems must disinfect all surface waters and filtration for most surface water sources The U.S. Environmental Protection Agencys Surface Water Treatment Rule (SWTR)
Regulatory Requirements for Filtration “community water systems must disinfect all surface waters and filtration for most surface water sources……..” The U.S. Environmental Protection Agency’s Surface Water Treatment Rule (SWTR)
TABLE 8. 1 SwTR Assumed log removals and turbidity requirements Log removals Filtration process giardia Virus Turbidity requirement Conventional 2.5 2.0 =or 5 ntu Direct 2.0 or5 ntu Slow sand 2.0 =or. n Diatomaceous earth 2.0 1.0 =or5 ntu s From Table IV-2 in Supplementary Information, p. 27511 sw Special provision was made for slow sand filters to exceed 1 ntu in some cases, providing effective dis infection was maintained Filtration processes that do not function on the principles of the processes defined in the SWTR are called alternative filtration processes, and the log removal for Giardia cysts or ruses that can be allowed for alternative processes must be determined for each alternative process
Filtration processes that do not function on the principles of the processes defined in the SWTR are called alternative filtration processes, and the log removal for Giardia cysts or viruses that can be allowed for alternative processes must be determined for each alternative process
Removal of Microorganisms by Granular Bed and precoat Filtration 在北美,贾第虫卵和隐孢子虫囊胞所引起的水糸传播疾病,以及 水中一些致病微生物的抗氯性等问题,促使大家开始关注不同工 艺对水中微生物去除效果,许多的研究集中在过滤以及相应的泥 凝处理技术。 模型试验研究发现 通过改善泥凝和过滤来降低滤后水的浊度,可以有效去除贾第虫 和隐孢子虫囊胞。滤后水浊度越低,对贾第虫和隐孢子虫囊胞的 去除率越高。 运转良好的传统处理工艺,通过有效的沉淀或其他的固液分离, 加上随后的过滤处理,可以组成对原生生物的有效屏障
Removal of Microorganisms by Granular Bed and Precoat Filtration 在北美，贾第虫卵和隐孢子虫囊胞所引起的水系传播疾病，以及 水中一些致病微生物的抗氯性等问题，促使大家开始关注不同工 艺对水中微生物去除效果，许多的研究集中在过滤以及相应的混 凝处理技术。 模型试验研究发现： ▪ 通过改善混凝和过滤来降低滤后水的浊度，可以有效去除贾第虫 和隐孢子虫囊胞。滤后水浊度越低，对贾第虫和隐孢子虫囊胞的 去除率越高。 ▪ 运转良好的传统处理工艺，通过有效的沉淀或其他的固液分离， 加上随后的过滤处理，可以组成对原生生物的有效屏障
小结 可以去除原生微生物的过滤工艺包括快滤、慢砂滤、硅藻土过滤和 膜过滤,但应用最为广泛的处理工艺当属凝聚和普通快滤的组合, 通常还涉及絮凝和沉淀。对于常规处理或直接/直流过滤来说,微生 物有效去除的前提是,必须很认真的控制混凝和过滤过程,以期获 得非常低的滤后水浊度。 根据模型研究和生产试验,去除水中微生物的过程可以归纳为: 滤后水浊度应为0.1ntu或更低 。出水浊废较高的滤池成熟期的持续间应该尽量缩短(少于1小时); 滤后水浊度一旦超过0,2ntu,即视为滤池浊度穿透,随即迸行反冲 洗
小结： 可以去除原生微生物的过滤工艺包括快滤、慢砂滤、硅藻土过滤和 膜过滤，但应用最为广泛的处理工艺当属凝聚和普通快滤的组合， 通常还涉及絮凝和沉淀。对于常规处理或直接/直流过滤来说，微生 物有效去除的前提是，必须很认真的控制混凝和过滤过程，以期获 得非常低的滤后水浊度。 根据模型研究和生产试验，去除水中微生物的过程可以归纳为： ▪ 滤后水浊度应为0.1ntu或更低； ▪ 出水浊度较高的滤池成熟期的持续时间应该尽量缩短（少于1小时）； ▪ 滤后水浊度一旦超过0.2ntu，即视为滤池浊度穿透，随即进行反冲 洗