Basic knowledge of sewage treatment

08 How to precipitate colloidal particles?

To precipitate colloidal particles, it is necessary to promote colloidal particles to contact each other, so that it becomes a large particle, that is, condensed, so that its specific gravity is greater than 1 and precipitation.

There are many methods used, and the commonly used technologies in engineering are: condensation method, flocculation method and coagulation method.

09 What is condensation?

Adding a coagulation agent with positive ions in the wastewater, a large number of positive ions exist between colloidal particles to eliminate the electrostatic exclusion between colloidal particles, so that the particles coalesce, this method by adding positive ion electrolyte, the process of coalescing colloidal particles is called condensation. Coagulants commonly used are aluminum sulfate, ferrous sulfate, alum, ferric chloride and so on.

10 What is flocculation?

Flocculation is the addition of polymer coagulant to wastewater. After the polymer coagulant is dissolved, polymer will be formed. The structure of this polymer is a linear structure, one end of the line pulls a tiny particle, and the other end pulls another tiny particle, which plays the role of bonding and bridging between the two particles far apart, making the particles gradually larger, and eventually forming a large particle floc (commonly known as alum flower), accelerating the particle settlement. Commonly used flocculants are polyacrylamide (PAM), polyiron (PE) and so on.

11 What is coagulation?

Coagulation is a process in which coagulation and flocculation are combined. Coagulation is often used in experiments or engineering, such as adding ferrous sulfate and other agents in water to eliminate the electrostatic exclusion between colloidal particles, and then adding polyacrylamide (PAM), so that the particles gradually become larger, forming visible alum flowers, and finally settling.

12 What is adsorption?

The use of porous solids (such as activated carbon) or flocs (such as polyiron) to adsorb toxic and harmful substances in wastewater on the surface of solids or flocs or in micropores to achieve the purpose of purifying water quality, this treatment method is called adsorption treatment. The object of adsorption can be an insoluble solid substance or a dissolved substance. The efficiency of adsorption treatment is high, and the effluent quality is good, so it is often used as a deep treatment of wastewater. Adsorption treatment can also be introduced into the biochemical treatment unit to improve the efficiency of biochemical treatment (such as PACT method is one of them).

13 What is the biochemical treatment of wastewater?

The biochemical treatment of wastewater is one of the most important processes in the wastewater treatment system, referred to as biochemical treatment. Biochemical treatment is the use of microbial life activity process to effectively remove soluble organic matter and some insoluble organic matter in wastewater, so that the water can be purified.14 In what way do microorganisms decompose organic pollutants in wastewater?

Due to the presence of carbohydrates, fats, proteins and other organic matter in the wastewater, these inanimate organic matter is the food of microorganisms, part of the degradation, synthesis into cellular substances (combined metabolites), the other part of the degradation oxidation into water, carbon dioxide and other (catabolites), in this process, the organic pollutants in the wastewater are degraded and removed by microorganisms.

15 What factors are microbes associated with?

In addition to nutrients, microbes also need the right environmental factors, such as temperature, pH, dissolved oxygen, osmotic pressure, etc., to survive. If the environmental conditions are not normal, it will affect the life activities of microorganisms, and even mutate or die.

16 What temperature range is the most suitable for microbial growth and reproduction?

In the biological treatment of wastewater, the most suitable temperature range for microorganisms is generally 16-30 ° C, the highest temperature is 37-43 ° C, and when the temperature is below 10 ° C, microorganisms will no longer grow.

Within the appropriate temperature range, the metabolic rate of microorganisms will increase correspondingly with the increase of 10℃, and the removal rate of COD will also increase by about 10%. On the contrary, when the temperature is reduced by 10℃, the removal rate of COD will be reduced by 10%. Therefore, the biochemical removal rate of COD will be significantly lower in winter than in other seasons.

17 What is the most suitable pH condition for microorganisms?

The life activity and metabolism of microorganisms are closely related to pH value. The pH range of most microorganisms is 4.5-9, while the optimal pH range is 6.5-7.5. When the pH is lower than 6.5, fungi begin to compete with bacteria, and when the pH is 4.5, fungi will occupy a complete advantage in the biochemical tank, which will seriously affect the settling result of sludge. When pH exceeds 9, the metabolic rate of microorganisms will be hindered.

The range of pH requirements for different microorganisms is different. In aerobic biological treatment, pH can vary between 6.5 and 8.5; In anaerobic biological treatment, the pH requirements of microorganisms are relatively strict, and the pH should be between 6.7 and 7.4.