4.1 活性污泥工艺概论

1 Definition
活性污泥（Activated Sludge）：
Story about Activated Sludge:
In 1912, Clark and Gage in England found that prolonged aeration produced sludge and improved water quality. Then, Arden and Lockett found that the Sludge has a key role on improving water quality, so called this sludge as Activated Sludge (1914).
2）Sludge settling performance parameters：
Settling Velocity，又称30min沉淀率 SV It's generally expressed as %. For most urban sewage treatment
plants, the value is between 20% and 30%.
The DO concentration in the aeration tank of activated sludge system should be maintained at 2-4mg/L, and should not be lower than 1mg/L.
DO consumption rate: DO consumption per unit time and volume (mg/L·min), which can be regarded as a quantitative indicator of sludge activity.
4 components of activated sludge: Active microbial population (Ma);Oxidizing residues (Me);Organic matter (Mi) that cannot be degraded by microorganisms or is not degraded temporarily;An inorganic substance (Mii) carried by raw sewage.
Slurry Volumn Index SVI
Volume of precipitated sludge formed by 1g of dry sludge.
SVI

1L混合1L液混3合0 液min中沉悬淀浮后固的体活干性基污质泥量容（积g）（ml）
SV MLSS
3）Dissolved oxygen (DO) and the rate of oxygen consumption：
Aeration tank: the core of activated sludge process, where activated sludge is fully mixed with organic pollutants in water, and then decomposed and absorbed.
活动能力强、沉淀性能差
静止期
变小 生长速度减慢
絮体开始形成，凝聚、吸附以 及沉淀性能提高。
衰老期
最低
开始分解代谢、代谢微生物自身 数量减少、絮凝、吸附沉淀性 能好，处理水质好。
一般投配比在0.1－0.2左右可以保证活性污泥稳定在工艺需要期。
5）Removal rate loading
Volume removal rate load: unit working volume, amount of BOD or COD removed per unit time, unit (kgBOD/m3·d or kgCOD/m3·d)
The most basic form of bacteria
globular rhabditiform
heliciform
肉足类：可以任意改变形状
原
amoeba
生 动 鞭毛类：有一根或多根鞭毛
物
flagellates
protozoon
纤毛类：分为自由游泳型和固着型
infusorians
线虫 轮虫
Method: DO values of the mixed solution were measured at different times, and the slope of the curve was the rate of dissolved oxygen consumption. The above five parameters (MLSS, MLVSS, SV, SVI and DO consumption rate) are important indicators for monitoring in process operation.
The first activated sludge process sewage treatment plant was built in 1916.
In fact, activated sludge is not the traditional mud. Under the microscope, in the brown flocculated activated sludge, there are a large number of bacteria, fungi, algae, protozoa and other microorganisms, which constitute a special ecosystem. This particular ecosystem turns organic pollutants in water into cellular materials or oxidizes into low-energy compounds.
Mixed Liquor Volatile Suspended Solid/Sludge混合液挥发性悬 浮固体浓度, Represents the concentration of organic suspended solids, mg/L或kg/m3。MLVSS=Ma+Me+Mi
In general, MLVSS/MLSS values are relatively stable, and urban sewage is generally between 0.75 and 0.85. This value is different for different wastewater.
水 处 理 系 Metazoan in water 统 treatment systems 中 的 后 生 动 物
2 Characteristics of activated sludge
Activated sludge is usually yellow-brown (sometimes iron red), flocculated granules, generally with a diameter of 0.02-2mm and a moisture content of 99.2%-99.8%. The density varies with the moisture content, generally within a range of 1.002-1.006g/cm3, with a larger surface area of about 20-100cm2/mL.
Mixed Liquor Suspended Solid/Sludge（混合液悬浮固体浓度）,
MLSS mg/L或kg/m3，Represents the concentration of activated sludge
in the aeration tank。MLSS=Ma+Me+Mi+Mii
MLVSS
Disadvantages: Process operation is relatively complex, requiring qualified and experienced personnel to operate and maintain, while the investment and operation costs, though reasonable, are still relatively large.The successful operation of an activated sludge system needs sufficient financial and human resources to guarantee.
4）投配比F/M（kgBOD或COD/kgMLSS·d）
活性污泥的营养物或有机底物量(F)与微生物量(M)的比值(F／M)是活性污泥 微生物增厚、增殖的重要影响因素。
增值期
活性污泥微生物各增值期特点比较
F/M 微生物变化情况
活性污泥性能

停滞期
适应新环境，没有量的增值，有 质的变化
对数增殖期 >2.2 以很高的速度增值
活性污泥的性质
颜色 味道 状态 相对密度 粒经 比表面积
黄褐色
土腥味
似矾花絮绒颗粒 曝气池混合液：1.002～1.003 回流污泥：1.004～1.006 0.02～0.2mm 20～100cm2/mL
3 parameters of activated sludge system
1）Sludge concentration parameters：
Aeration device: supply oxygen to aeration tank to meet microbial demand.
Secondary sedimentation tank: separation of activated sludge from treated water.
Chapter 4 Activated sludge process 第四章 活性污泥法
§4.1 Summarize
Activated sludge process is one of the most widely used biochemical wastewater treatment technologies.
Sludge removal rate: amount of COD or BOD was removed per unit of quality and unit of time (kgBOD/kgMLSS·d or kgCOD/kgMLSS·d)
4 Activated sludge system composition (Conventional activated sludge process, CAS)
Advantages: this process is flexible, reliable, easy to control, and the effluent quality is high. In addition to organic pollutants, some N and P can be removed.The ability to resist short-term organic and hydraulic loading is also relatively strong.
What is activated sludge?
The activated sludge, which is composed of microorganism groups such as bacteria, mycelia, protozoa and metazoan as well as organic and inorganic substances in the adsorbed sewage, has certain vitality and has a good function of purifying sewage.