Actiflo+Steel+Plant+Paper.docx

1、Actiflo+Steel+Plant+PaperTREATMENT OF STEEL PLANT EFFLUENTWITH HIGH SPEED MICROSAND SETTLINGCharles D. Blumenschein and Kashi BanerjeeUSFilter CorporationNorth American Technology CenterPittsburgh, PA 15108INTRODUCTIONTotal suspended solids (TSS) and oil and grease (O&G) are two major pollutants tha

2、t are present in the wastewater generated from the steel making operations. The release of these substances into the environment must be controlled to minimize effects on aquatic life and downstream uses. Increasingly stringent environmental regulations pertaining to discharges containing TSS and O&

3、G necessitate the development of technically and economically feasible processes for the removal of these pollutants from industrial wastewater prior to discharge. Iron or alum coagulation followed by conventional clarification is a common process for removal of TSS and O&G from industrial wastewate

4、r. The overflow rate of a conventional clarification system ranges between 0.25 and 1.0 gallons per minute per square foot (gpm/sf). This design criterion often results in a large system footprint. Additionally, conventional treatment methods cannot handle sudden increases in hydraulic loading that

5、may be caused by storm events. Direct discharge of contaminated storm water can be avoided by building large storage reservoirs at the facility and treating the water gradually, or by treating the peak flow continuously. Typically, installation of a large storage tank is cost prohibitive. Vivendi Wa

6、ter/USFilter Corporation has developed a cost-effective system, known as ActiFlo, for treating wastewater. The process has an extremely small footprint, typically requiring less than 10% of the space needed for a conventional sedimentation process. Even at a high wastewater flow rate, this process i

7、s capable of producing excellent treated water quality. Pilot-scale operation of this system was conducted to verify the applicability of the ActiFlo process for efficiently handling wastewater from a steel making facility. The primary objectives of this study were to demonstrate the effectiveness o

8、f this ballasted coagulation process for the removal of TSS and O&G in a continuous-flow system as well as to determine the desired operating conditions of the ActiFlo system. PROCESS DESCRIPTIONActiFlo is a compact, conventional-type water clarification system that utilizes microsand as a seed for

9、floc formation. The microsand provides surface area that enhances flocculation and acts as a ballast or weight. The resulting sand-ballasted floc displays unique settling characteristics, which allow for clarifier designs with high overflow rates and short detention times. These designs result in sy

10、stem footprints that are between 5 and 20 times smaller than conventional clarification systems of similar capacity. The use of microsand also permits the unit to perform well under dramatically changing flow rates without impacting final effluent quality. The overflow rate can vary from 20 gpm/sf t

11、o as high as 60 gpm/sf within short periods of time (less than one-half hour) without sacrificing performance.Raw water enters the ActiFlo system in the first flash mix tank (coagulation tank). Here, chemical coagulant (alum, ferric ion, etc.) is added to destabilize suspended solids and colloidal m

12、atter in the influent stream. Typical hydraulic detention time in the coagulation tank is around two minutes. The coagulated water then passes into the second flash mix tank (injection tank) where polymeric flocculant and microsand are added to initiate floc formation. These serve as “seed” for floc

13、 formation and development in the next process step. ActiFlo treatment continues as water passes through the underflow passage from the injection tank into the maturation tank. In the maturation tank, relatively gentler mixing provides ideal conditions for the formation of polymer bridges between th

14、e microsand and the destabilized suspended solids. This process is further augmented by the large specific surface area of the microsand, which provides enhanced opportunity for polymer bridging and enmeshment of microsand and floc already in suspension. The fully formed ballasted flocs leave the ma

15、turation tank and enter the settling tank. Here, laminar upflow through the lamellar settling zone provides rapid and effective removal of the microsand/sludge flocs. Clarified water exits the ActiFlo system via a series of collection troughs or weirs.The ballasted floc sand-sludge mixture is collec

16、ted at the bottom of the settling tank and withdrawn using a rubber-lined centrifugal slurry pump. The sand-sludge mixture is then pumped to the hydrocyclone for separation. Energy from pumping is effectively converted to centrifugal forces within the body of the hydrocyclone, causing the sludge to be separated from the higher density microsand. Once separated, the microsand is concentrated and discharged from the bottom of the hydrocyclone, and re-injected