<h1 class="pgc-h-arrow-right" data-track="1" > pay more attention to the public name: environmentally friendly water treatment (hbscl01).</h1>
The activated sludge method is essentially the artificial strengthening of the self-purification effect of natural water bodies, which can remove dissolved and colloidal biodegradable organic matter from sewage and suspended solids and other substances that can be adsorbed by activated sludge, and has the characteristics of wide adaptability to water quality and quantity, flexible and diverse operation mode, and good controllability, and has become the main body of biological treatment methods.
First, the basic principles
Activated sludge is composed of bacteria, fungi, protozoa, protozoa, protozoa and other microbial groups mixed with suspended matter in the sewage, colloidal substances mixed together to form, with a strong ability to adsorption and decomposition of organic matter and good sedimentation performance of the flocculent sludge particles, because of its biochemical activity, so it is called activated sludge.
Properties of activated sludge
From the appearance point of view, the activated sludge is like alum flower-like floc particles, also known as biological flocculants, flocculant diameter is generally 0.02 - 0.2 mm, in the standing can immediately condense into larger velvet particles and sink. The color of activated sludge varies according to the quality of sewage water, generally yellow or tea brown, black when oxygen supply is insufficient or anaerobic state occurs, star gray white when oxygen supply is too much nutrient deficiency, slightly acidic, slightly soil odor and entrained - some musty odor. Activated sludge moisture content is very high, generally above 99%, its specific gravity varies according to the moisture content, the relative density of the aeration tank mixture is 1.002-1.003, while the relative density of reflux sludge is 1.004-1.006.The surface area of activated sludge is generally 20-100 cm2/mL.
Composition of activated sludge
The solid substance in the activated sludge is less than 1%, which is composed of two parts, organic matter and inorganic matter, and its composition ratio varies according to the different properties of the original sewage. The organic components are mainly the microbial population inhabiting the activated sludge, but also include some inert and difficult to be taken up by bacteria in the incoming sewage, the so-called "refractory organic matter", and the residues of microbial oxidation.
Activated sludge microbiota is a mixed group dominated by aerobic bacteria, other microorganisms include yeast, actinomycetes, molds and protozoa, epizoans, etc., the bacterial content of normal activated sludge is generally 107-108 /mL, and protozoa is about 100/mL.
In the activated sludge microorganisms, protozoa feed on bacteria, and the protozoans feed on protozoa and bacteria, forming a food chain between them, forming an ecologically balanced biological group. Activated sludge bacteria often exist in the form of bacterial gel groups, which are less free, which gives bacteria the ability to resist external unfavorable factors.
Free bacteria are not easy to precipitate, but can be preyed upon by protozoa, making the effluent of the sedimentation tank clearer. The inorganic components of the activated sludge are all carried in by the original sewage, and as for the inorganic salts present in the microbial body, the amount is negligible due to its small number.
In summary, activated sludge is composed of the following four parts:
(1) Microbial populations with metabolic functional activities (M);
(2) microorganisms (mainly bacteria) self-oxidation residues (M);
(3) Difficult biodegradable organic matter (M;);
(4) Inorganic substances (M;) carried in by the original sewage. Among them, the active microbial population is the main component of activated sludge.
Second, the activated sludge purification reaction process
The reaction process of activated sludge purification is more complex, including physical, chemical or physical chemical processes such as adsorption and flocculation of organic pollutants by the activated sludge itself, as well as biological or biochemical processes such as the biotransformation and absorption of organic pollutants by microorganisms in the activated sludge, which can be roughly divided into the following two stages.
Initial adsorption removal phase
In the short period of time (5-10 min) after the sewage is in contact with the activated sludge and mixed, the organic pollutants in the sewage, especially the organic matter in the suspended and colloidal state, show a high removal rate, and this initial high-speed removal phenomenon is the result of the comprehensive action of physical adsorption and biological adsorption. In this process, the organic substrate in the mixture is rapidly reduced and the BOD is rapidly reduced, as shown in the adsorption zone curve in Figure 2. This is due to the large surface area of the activated sludge, and a large number of microorganisms are enriched on the surface, and the outside is covered with a clay layer of polysaccharides, and when the suspended and colloidal organic substrate in the sewage comes into contact with the activated sludge floc, it is quickly condensed and adsorbed and removed. This phenomenon is the "initial adsorption removal" effect.
The initial adsorption process is carried out quickly, generally within 30 minutes can be completed, the adsorption removal rate of sewage BOD can reach 70%, for sewage containing suspended and colloidal organic matter, BOD can be reduced by 80%-90%. The initial adsorption rate mainly depends on the activity of microorganisms and the degree of hydraulic diffusion in the reactor and hydraulic dynamics, the former determines the adsorption and agglomeration efficiency of activated sludge microorganisms, and the latter determines the degree of contact between activated sludge flocs and organic substrates. The high adsorption activity of activated sludge microorganisms depends on the large specific surface area and suitable microbial proliferation period, in general, endogenous respiratory microorganisms in the "starved" state have the strongest adsorption activity.
Metabolic stabilization phase
Organic pollutants adsorbed on the surface of the activated sludge microbial cells, under the action of permeable enzymes, dissolved and small molecule organics directly through the cell wall into the cell body, while colloidal and suspended macromolecular organic matter such as starch, protein, etc. are first under the action of extracellular enzyme hydrolases, hydrolyzed into dissolved small molecules and then enter the cell body, at this time part of the dissolved simple organic matter produced by hydrolysis will spread into the mixture, resulting in an increase in the BOD value of the mixed liquid, as shown in the extracellular hydrolysis zone curve in Figure 2.
Organic pollutants entering the cell body, under the catalytic action of various intracellular enzymes (such as dehydrogenase, oxidase, etc.), are oxidized and decomposed into intermediate products, some intermediate products are combined into new cellular substances, others are oxidized into stable inorganic products, such as CO2 and H2O, etc., and release energy for the synthesis of cells, this process is the oxidative decomposition process of the substance, also known as the stabilization process. In this process, the unstable polymer organic material is converted into a simple and stable low molecular inorganic substance through biochemical reaction, and the mixture BOD is gradually reduced, as shown in the intracellular biological oxidation zone curve in Figure 2. The time required for the stabilization process depends on the degree of transformation of the organic matter and is much longer than the adsorption process