Sewage treatment technology

About:

Under normal circumstances, the actual sewage often contains a variety of pollutants, and only a single treatment method can not achieve the desired effect. In order to obtain a better treatment effect at a lower treatment cost, it is often necessary to combine several treatment technologies according to a certain primary and secondary relationship and order according to a variety of factors such as the quality of sewage, the amount of water, the degree of treatment, the possibility of recycling useful substances and the conditions of the capital site, to form a complete purification treatment system.

Process application:

The type of domestic sewage treatment process not only determines the sewage purification effect, but also determines the sludge generation and sludge treatment method in the sewage purification process [3]. sewage treatment (wastewater treatment) : The process of purifying sewage in order to make it meet the water quality requirements for draining a body of water or reuse. Sewage treatment is widely used in construction, agriculture, transportation, energy, petrochemical, environmental protection, urban landscape, medical, catering and other fields, but also more and more into the daily life of ordinary people.

Selection criteria:

1) The municipal sewage treatment process should be optimized and determined according to the treatment scale, water quality characteristics, environmental functions of the receiving water body and the actual situation and requirements of the local area after a comprehensive technical and economic comparison.

2) The main technical and economic indicators of process selection include: investment per unit of water treatment, investment reduction per unit of pollutants, power consumption and cost per unit of water treatment, power consumption and cost reduction per unit of pollutants, land area, reliability of operation performance, management and maintenance difficulty, overall environmental benefits, etc.

3) The effluent water quality should be determined realistically and the process design parameters should be optimized. It is necessary to conduct detailed investigation or determination of the current water quality characteristics and pollutant composition of sewage, and make reasonable analysis and prediction. When the water quality is complex or special, the dynamic test of wastewater treatment process should be carried out, and pilot study should be carried out if necessary.

4) Actively and prudently adopt efficient and economical new processes. For the new process applied for the first time in China, it must go through pilot and production tests to provide reliable design parameters before being applied [1].

By process:

Classification of Water Pollution Control Engineering

Separation technology of insoluble pollutants:

1, gravity sedimentation: sedimentation tank (advection, vertical flow, swirl, aeration), sedimentation tank (advection, vertical flow, radial flow, oblique flow);

2, coagulation and clarification;

3, buoyancy floating method: oil separation, air floating;

4, others: resistance retention, centrifugal force separation method, magnetic separation method

Biochemical transformation technology of pollutants:

1, Activated sludge method: SBR, A/O, A/A/O, oxidation ditch, etc

2, biofilm method: biological filter, biological turntable, biological contact oxidation pool, etc

3. Anaerobic biological treatment: anaerobic digestion, hydrolytic acidification pool, UASB, etc

4. Biological treatment under natural conditions: stabilization pond, ecosystem pond, land treatment method

Chemical conversion technology of pollutants:

1. Neutralization method: acid-base neutralization

2, chemical precipitation method: hydroxide precipitation, ferrite precipitation, other chemical precipitation

3, REDOX method: chemical oxidation method, chemical reduction method, electrochemical method

4, chemical and physical disinfection method: ozone, ultraviolet, chlorine dioxide, chlorine gas, sodium hypochlorite

Physicochemical separation technology of dissolved pollutants:

1. Adsorption method

2. Ion exchange method

3, membrane separation method: diffusion dialysis, electrodialysis, reverse osmosis, ultrafiltration, nanofiltration, microfiltration

4, other separation methods: blowing and gas extraction, extraction, evaporation, crystallization, freezing

Classification according to common sewage treatment methods

Physical method: Physical or mechanical separation process. Filtration, precipitation, centrifugal separation, floating, etc

Chemical method: The conversion process of adding chemical substances to react with harmful substances in sewage. Neutralization, oxidation, reduction, decomposition, coagulation, chemical precipitation, etc

Physicochemical method: physicochemical separation process. Gas stripping, blowing, adsorption, extraction, ion exchange, electrolytic electrodialysis, reverse osmosis, etc

Biological method: The metabolic process in which microorganisms oxidize and decompose organic matter in sewage. Activated sludge, biological filter, biological turntable, oxidation pond, anaerobic digestion, etc

Chemical classification of wastewater

coagulate

Add electrolyte to the colloidal turbid liquid to condense the colloidal substance in water and separate the sum of water

Coagulants are aluminum sulfate, alum, polyaluminum chloride, ferrous sulfate, ferric chloride and so on

Oily wastewater, dyeing wastewater, gas station wastewater, wool washing wastewater, etc

neutralize

Acid-base neutral,pH neutral

Lime, limestone, dolomite, etc. neutralize acidic wastewater,CO2 neutralize alkaline wastewater

Sulfuric acid plant wastewater with lime neutralization, printing and dyeing wastewater, etc

REDOX

Oxidizing (or reducing) agents are added to oxidize (or reduce) substances in wastewater into harmless substances

Oxidants include air (O2), bleaching powder, chlorine gas, ozone, etc

Containing phenol, cyanide, chromium sulfide, mercury wastewater, printing and dyeing, hospital wastewater, etc

electrolysis

When an electrode plate is inserted into the waste water, the charged ions in the waste water become neutral atoms

Power supply, electrode plate, etc

Chromium containing cyanide (electroplating) wastewater, wool spinning wastewater

extraction

The solvent that is insoluble in water is put into the wastewater, so that the solute in the wastewater is dissolved in the solvent, and then the solvent is separated by the relative density difference between the solvent and water

Extractant: butyl acetate, benzene, N-503 and other equipment has pulse sieve plate tower, centrifugal extractor and so on

Phenolic wastewater, etc

Adsorption (including ion exchange)

The waste water is passed through a solid adsorbent, so that the dissolved organic or inorganic matter in the waste water is adsorbed on the adsorbent, and the passed waste water is treated

Adsorbents are activated carbon, cinder, soil and so on

Adsorption tower, regeneration device

Dyeing, pigment wastewater, can also adsorb phenol, mercury, chromium, cyanogen and color removal, odor, taste and so on for deep treatment.

Craft level editor broadcast

Modern sewage treatment technology, according to the degree of treatment, can be divided into primary, secondary and tertiary treatment.

Primary treatment is mainly to remove the solid pollutants in the suspended state of sewage, and most of the physical treatment methods can only complete the requirements of primary treatment. After primary treatment of sewage, BOD can generally be removed about 30%, can not meet the discharge standards. Primary treatment belongs to the pre-treatment of secondary treatment.

Secondary treatment, the main removal of colloidal and dissolved organic pollutants (BOD, COD substances) in the sewage, the removal rate can reach more than 90%, so that organic pollutants meet the discharge standards.

Tertiary treatment, further treatment of refractory organic matter, nitrogen and phosphorus can lead to water eutrophication of soluble inorganic matter. The main methods include biological nitrogen and phosphorus removal, coagulation and precipitation, sand filtration, activated carbon adsorption, ion exchange and electroosmotic analysis.

The whole process is that the raw sewage through the coarse grid is lifted by the sewage lifting pump, passes through the grid or sand filter, and then enters the sand sedimentation tank, and the sewage separated by sand water enters the primary sedimentation tank, which is a primary treatment (that is, physical treatment), and the effluent from the primary sedimentation tank enters the biological treatment equipment, including activated sludge method and biofilm method. (The reactor of activated sludge method has an aeration tank. The effluent from the biological treatment equipment enters the secondary sedimentation tank, and the effluent from the secondary sedimentation tank is disinfected and discharged or enters the tertiary treatment. The tertiary treatment ends here as the secondary treatment. The tertiary treatment includes biological nitrogen and phosphorus removal method, coagulation sedimentation method, sand filtration method, activated carbon adsorption method, etc. Ion exchange and electrodialysis. Part of the sludge in the secondary sedimentation tank is returned to the primary sedimentation tank or biological treatment equipment, part of it goes into the sludge thickening tank, and then into the sludge digestion tank. After dehydration and drying equipment, the sludge is finally used.