激活的污泥过程- Activated Sludge Wastewater Treatment Process

It is a:

• Unit process
• Biological treatment process
• Suspended growth process
• Aerobic process

Activated Sludge:

Definition

Is defined as a ‘Suspension’ of microorganisms, both living and dead’ in a wastewater. The microorganisms are active by an input of air (oxygen) thus known as activated-sludge. Activate-sludge is that sludge which settle down in a secondary sedimentation tank after the sewage has been freely aerated and agitated for a certain time in an Aeration tank.

工作机制

The activated-sludge contains numerous bacteria and other microorganisms, when it is mixed with raw sewage saturated with oxygen, the bacteria perform the following function.

1. Oxidize the organic solids.

2. 促进凝血和絮凝，并将溶解，胶体和悬浮固体转化为固定固体。在实践中，以下操作是在激活的污泥过程中进行的。

3. The sewage is given treatment in the primary sedimentation tank. The detention time is kept as short as 1-1/2 hours.

4. The settled sewage form thePrimary Sedimentation Tank是与所需数量的曝气罐中所需的活化污泥混合的。充气罐中活化污泥和废水的混合物称为“混合酒或混合酒悬浮固体MLSS或者MLVSSmixed liquor volatile suspended solids’.

5. TheMixed Liquor Suspended Solidsis aerated for 6-8 hours in the aeration tank, called the液压拘留时间according to the degree of purification. About 8 m³of air is provided from each m³of wastewater treated. The volumes of sludge returned to the aeration basin is typically 20 to 30% of wastewater flow air supply 8-10 m³of sewage

6. The aerated Mixed Liquor Suspended Solids resulting in the formation of floc particles, ranging in size from 50 to 200pm.which is then removed in the secondary sedimentation tank by gravity settling, leeching a relatively clear liquid as the treated effluent. Typically greater than 99% of suspend solids can be removed in the clarification step.

7. Most of the settled sludge is returned to the aeration tank (and is called return sludge) to maintain the high population of microbes that permits rapid breakdown of the organic compounds. Because more activated-sludge is produced tan is desirable in the process, some of the return sludge is diverted or wasted to the sludge handling system for treatment and disposal.

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f/m比的推导:

Q = Flow of Sewage ( m³/day)
BOD =有机物（mg/l）
FOOD = Q ( m³/day) x BOD (mg/l)
FOOD = Q x BOD / 1000 (Kg of BOD/ day)
V = Volume of Aeration ( m³)
MLSS = Mixed liquor suspended solids (mg/l)
Micro-organisms = V ( m³) x MLSS (log/l) / 1000 = V x MLSS / 1000 (kg of MLSS in aeration tank)

F/M ratio:

A parameter of organic loading rate in the design aerated sludge parameter in the design of Trickling Filter in organic loading rate = kg of BOD / m³-d

F/M ratio =

F/M ratio = BOD / MLSS x t kg of BOD / Kg of MLSS/day
FM ratio varies between 0.2 -0.5 day^-1

• F/M ratio -0.5 day-1 has a good settleabilty of a sludge. ( even in some cases it can go to 1)
• f/m比率 - <0.2食物非常有限，因此细菌会死亡。
• F/M ratio 70.5 day^-1食物更是如此，细菌会移动流出物（系统故障）
• If high F/M ratio, filamentous bacteria will also grow. They not settle easily because of long tails, get entangled with each other. Food to micro organism ratio(F/M) is a common used parameter in the activated-sludge process which is defined as

激活的污泥过程Design

Design of Activated Sludge Systems:

Design of activated-sludge process involves details of sizing and operation of the following main elements.

1. 曝气箱（反应堆） - 容量和尺寸。
2. 曝气系统 - 氧的需求和氧气转移系统。
3. Final sedimentation tank – (deifier)
4. Return activated sludge system.SV1
5. Excess activated sludge withdrawal system and subsequent treatment and disposal of waste sludge. Since the whole process takes place in al liquid medium the hydraulic regime essentially in the aeration tank and final sedimentation tank.
6. MLSS - 沉淀污水 +活化污泥溶解氧的混合物<2mg/l

Design Criteria

1. F/M ratio = 0.2 – 0.5 day -1 or 0.2 – 0.5 kg BOD's / kg MLSS – d
2. Detention time (aeration time) of sewage = 6 to 6 hours
3. MLVSS or MLSS = 1500 -3000 mg/l
4. Air supply = 10 m³/ m³sewage treated
5. return sludge = 0.25 -10 of Q (influent sewage flow) Qr / Q = 0.20-0.30 = Vs/100Vs (Volume of sludge)
6. Depth = 3-5m
7. L=W ratio =5:1
8. SVI 50-150 ml/gm

Sludge Volume Index (SVI-TEST)

It is the measure of the settleability and compatibility of sludge and is made from a laboratory column setting test.

Definition

The sludge volume index is defined as ‘the volume in mm occupied by 1 gm of sludge after it has settled for a specified period of time’ generally ranging from 20 min to 1 or 2 hr in a 1 – or 2-l cylinder. One-half hour is most common setting time allowed to the mixed liquor to settle for 30 min. ( larger cylinder is desirable to minimize bridging of sludge floe and war effects). Take the reading let Vs is the settled volume of sludge (ml/l) in 30 min.

* If SVI is 50 - 150 ml/mg, the sludge settle ability is Good.

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Return Activated Sludge System:

1. The activated sludge form the underflow of the final setting tanks should be returned to the inlet of the aeration tanks at a rote sufficient to maintain the MLSS concentration at the design value.
2. 返回污泥所需的流量是确定的，构成了传入的污水流量和污泥与最终设置储罐的污泥的浓度。

因此，需要简单地测量底流浓度形式的设置储罐。常规用于此目的的参数是污泥体积指数，SVI定义为4的体积，含有1.0克污泥（干重）的污泥占据，因此在30分钟后，因此具有HT单位ml/g。一段时间代表SDI，即sludge density index. Once the SVI and operating MLSS concentration (x) is known, the required rate of activated sludge return can be determined

R = 100 / [ 106/ (x) (SVI) -1] where r = return sludge flow rate as a % age of incoming sewage flow.

SEDIMENTATION:

It is the removal of solid particles form a suspension by settling under gravity.

CLARIFICATION:

It is a similar termn which refers specifically to the function of a sedimentation removal.

THICKENING:

It means the separation of water from Suspended Solids

where R = return sludge flow rate (ML/D) for Q in ML/D)

最终沉积罐的表面几何形状：

VARIATION OF THE ACTIVATED SLUDGE PROCESS:

1. Activated sludge was introduced in 1941 and has undergone many variations and adaptations.
2. The main objective of many modifications has been to increase the loading capacity of the basic plug flow activated sludge plant by provision of optimum condition design parameters for different variations are summarized in table. It is worthy of note that 5 modifications tapered aeration step aeration the CMAS process, the pure oxygen system and the deep shaft process all aim at either the improvement of oxygen transfer efficiency t the efficient distribution of available oxygen to match demand. A flow sheet of most of the commonly used variations is similar to that ofCAS(Conventional Activated Sludge).

CONVENTIONAL ACTIVATED SLUDGE:

Volumetric loading =kg of BOD
m³-d
Aerial loading rate =gm of BOD
m³-d
Td = V/Q in days and grater than 5 days.

ALGAL-BACTERIAL SYMBOPSTS:

The combined and mutually- been facial action of algae and bacteria in this process is called algal-bacterial symbioses.

• Shock loading (CSTR)
  
• BODu

Aerated Lagoons:

充气泻湖是活性污泥的单元操作without sludge return. Historically they were developed from waste stabilization ponds in temperate climate where mechanical aeration was used to supplement the algal oxygen supply in winter. It was found, however that soon after the aerations were put into operation the algal disappeared and the microbial flora resembled that of activated sludge. Aerated lagoons were now usually design as completely mixed not-return activated sludge units. Floating aerates are most commonly used to supply the necessary oxygen and mixing power.

Sludge Treatment:

Anaerobic sludge treatment cell Primary Sedimentation Tank and Secondary Sedimentation Tank are basically organic these can treated to aerobic.

• 厌氧池塘和瀑布化粪池是浪费r treatment .
• Sludge treatment = Anaerobic sludge treatment.

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COLD DIGESTION:

• Two stage digestion up
• High rate digestion up
• 固定膜过程。SWM区域

SLUDGE DIGESTION:

SLUDGE: the concentrated impurities settled at the bottom of the flower bed of sedimentation tanks.

消化：

To decompose or breakdown by heat and moisture or chemical action. (to invent food equable forms)

Sludge treatment:

Aerobic digestion it is defined as ‘it is the use of microbial organisms in the absence of oxygen I for the stabilization of oxygen materials by conversion to mean and inure produce including CO₂.

Organic matter + H₂O amoebas CH₄+ CO₂+ NH₃+ H₂S + heat

Benefices of anaerobic digestion. Types of anabolic detectors. It’s of two types:

• Conventional (stranded) or low-rate digester or cold digester.

• High rate digesters / two stage digester are characterized by continuous miring except at time of sludge with draw.