At present, most urban sewage treatment plants around the world use activated sludge treatment. One of the common problems is that the microorganisms in activated sludge will be affected by various internal and external factors to reduce the proportion of activated sludge and float away, which not only increases the amount of suspended solids in the effluent, but also greatly reduces the biological reaction system. Activity and quantity of medium activated sludge. It makes the operation, operation and control of the sewage treatment plant have certain difficulties, which seriously affects the quality of the effluent water.

Causes of activated sludge floating

The causes of activated sludge floating can be roughly divided into two categories: one is caused by changes in the quality of the incoming water, and the other is caused by process operation control.

Influent water quality causes activated sludge to float

1. Excessive surface active substances and grease compounds

When normal sewage enters the aeration tank and operates, the partial degradation of organic substances by specific surfactants forms foams, and the foams grow rapidly. These foams are generally white and lightweight and disappear when the activated sludge reaches maturity. When there is an excessive amount of surface-active substances in the sewage, such substances can affect the stability and permeability of the plasma membrane of the cell, causing the loss of certain necessary components of the cell, resulting in stagnation and death of microorganisms. A large amount of foam (bubbles) is generated during aeration, and these bubbles are easily agglomerated on the bacterial micelles, which reduces the specific gravity of the activated sludge and floats. In addition, when the intake water contains too much oil and fat, after aeration and mixing, the oil and fat will agglomerate on the surface of the bacterial micelles, causing the bacteria to die of hypoxia, resulting in a decrease in specific gravity and floating.

2. PH shock

Too high or too low pH will affect the catalytic action of extracellular enzymes and enzymes present in the cytoplasm and cell wall of active sludge microorganisms, and the absorption of nutrients by microorganisms. When the pH of the continuous-flow aeration reaction tank is <4.0 or pH> 11.0, the microbial activity in the activated sludge is inhibited, lost, or even died in most cases, causing the sludge to float.

3. Influence of water temperature and salt content

The suitable temperature range of the microorganisms that make up the activated sludge is generally 15 ~ 35 ℃. Above 45 ℃, most of the microorganisms in the activated sludge will die and float (except after long-term domestication or special microorganisms).

Adjusting the pH value of the incoming water cannot eliminate the effect of alkalinity on activated sludge. The pH value of the alkaline influent was adjusted, and although the alkaline substance was neutralized, salt was generated. The osmotic pressure varies with the salt solution concentration. Osmotic pressure is one of the important factors affecting the survival of microorganisms. If the osmotic pressure of the solution in which the microorganisms are mutated, it will cause cell death.

4. Toxic substrates

Substrates that are toxic to aerobic activated sludge microorganisms include: COD, organic matter (phenols and their derivatives, alcohols, aldehydes and certain organic acids), sulfides, heavy metals and halides with excessive levels. High substrate concentrations can form stable compounds with active centers of cellular enzymes, causing the matrix to be inaccessible, unable to be degraded, and even cell poisoning to death. After entering into human cells, heavy metal ions mainly bind to -SH groups on enzymes or proteins to inactivate or denature them.

Trace amounts of heavy metal ions can also accumulate in cells and eventually cause toxic effects on microorganisms (micro-action). The most common halides are iodine and chlorine. Iodine irreversibly combines with the tyrosine of the bacterial protein (or enzyme) to form diiodotyrosine, which inactivates the bacterial body. Chlorine and water synthesize hypochlorous acid, which decomposes to produce a strong oxidant. In addition, the mutation of the organic matter in the wastewater reduces or eliminates the microorganisms that have been domesticated and can degrade organic poisons.

Floating activated sludge caused by process operation

sludge disposal

1. Excessive aeration

Microorganisms are starved and cause self-oxidation into the human aging stage, and the dissolved oxygen concentration (DO) in the pond increases; or due to poor sludge activity, the linear velocity of the aerated impeller is too high, and too much oxygen is supplied. In short, the DO rises, and the sludge activity may be very good in the short term, because the metabolism is fast and the organic matter is also decomposed quickly, but over time, the sludge is beaten light and broken (but no air bubbles), like a mist flower floating in the sedimentation pond The surface flows away with the water. The sludge is light in color, poor in activity, reduced in oxygen consumption rate, increased in sludge volume and sludge index, and the treatment effect is significantly reduced.

2. Sewage sludge caused by hypoxia and denitrification

When the content of organic ammonia compounds in the wastewater is high or ammonia nitrogen is high, it can be oxidized by nitric acid bacteria and nitrous acid bacteria to NO3- under suitable conditions. Adsorbed by activated sludge floc, the activated sludge floats. Because denitrification occurs in the secondary sedimentation tank or the place with insufficient aeration, the tiny N2 bubbles are released, so that the density of the sludge is reduced, which is conducive to the upward movement of the activated sludge. This phenomenon is apparent in the secondary sedimentation tank, and the suspended foam produced is usually unstable.

3. Sludge floating caused by too much backflow

The sudden increase of the return flow will make the gas-water separation incomplete, and the air bubbles in the aeration tank will float to the sedimentation area. The sludge is granular and the color remains unchanged.

4. Sludge floating caused by sludge accumulation in the bottom of the second settling pond

If the bottom sediment of the secondary sedimentation tank is fermented, the CO2 and H2 produced will also agglomerate on the activated sludge, which will reduce the specific gravity of the sludge and float up. After the sludge decays to produce CH4 and H2S, it floats. First, small bubbles escape from the water surface, followed by black sludge.

5. Floating sludge caused by excessive growth of filamentous fungi in activated sludge

Under the influence of various factors such as insufficient N, P in the feed water, too low pH, too low dissolved oxygen in the mixed solution, and too large fluctuations in the feed water, the growth of filamentous bacteria and actinomycetes and other microorganisms caused abnormal growth. The growth rate is higher than that of bacterial micelles, and because of the large specific surface area of ​​filamentous bacteria, filamentous bacteria are much more advantageous than bacterial micelles in obtaining the oxygen required for BOD5 and oxidizing BOD5 in sewage. As a result, the filamentous bacteria in the aeration tank became the dominant species and a large amount of value was added, leading to the generation of biological foam. In addition, most of these microorganisms are filamentous or branch-like, easy to form a net, can capture particles and bubbles, and float to the water surface. The air bubbles surrounded by the wire mesh increase the surface tension, making it difficult for the air bubbles to break, causing the sludge to float up.

Control of activated sludge floating

Reason of activated sludge expansion

According to the activated sludge floating mechanism and its influencing factors, physical chemical and biological methods can be used to control the sludge floating.

Physical and chemical methods to control foam

1. Spray water

Utilizing the return of the final water, the sprayed water flow can break the air bubbles and the floating sludge floating on the water surface of the secondary sink to reduce the floating of the activated sludge. But it can not eliminate the sludge floating phenomenon at all. It is the most common and simple physical method.

2. Adjust the pH value of sewage

The population of the aeration tank is equipped with a neutralization tank and an automatic pH adjustment system composed of an alkali pool, an acid pool, a pH detector, and an automatic pH adjustment valve, so that the pH value of the aeration tank inlet water is controlled within the required range.

3. Reasonable dosage

Due to the imbalance of the nutritional ratio in industrial wastewater, there are often sufficient carbon sources and insufficient nutrients such as nitrogen and phosphorus, so it must be added in the treatment of industrial wastewater. Urea and phosphate are generally used as nitrogen and phosphorus sources, but the dosage should not be excessive.

4. Set the conditioning tank

When the feed water contains excessive surface-active substances, grease compounds, and substrates that have a toxic effect on aerobic activated sludge microorganisms, a final water reflux adjustment tank should be set in front of the aeration tank to dilute and adjust the aeration tank The concentration of organic matter in the incoming water makes it stable within a certain range. The prerequisite for the return of final water is that the treatment capacity of the sewage treatment plant must be greater than the actual incoming water volume.

Biological method to control activated sludge floating

Reason of Sludge expansion

1. Add biological selector

There are two types of biological selectors: aerobic selector and anoxic selector. The purpose is to fully mix the sewage entering the aeration tank before the returning sludge. By adjusting F / M, DO and other factors, the selective development Flocculant-forming bacteria suppress excessive proliferation of filamentous bacteria and the like. When designing a selector, the selector needs to be divided into grids. Generally, 4 to 6 grids are used; the F / M value of the first grid of the selector is increased as much as possible to form an F / M gradient; It is usually 10-15 minutes.

2. Optimization of process selection

The microbial composition of activated sludge mainly depends on wastewater composition, flow form, operating conditions, and appropriate design. Since it is almost difficult to control the components of the wastewater in the actual treatment process, it is important to optimize the operating conditions to control the floating of activated sludge.

3. Increase aeration

Floating sludge due to lack of oxygen or sludge poisoning can increase aeration, reduce water inflow and remove dead sludge.

4. Reduce sludge age

Generally, the residence time of sludge in the aeration tank is reduced to inhibit the growth of actinomycetes with a longer growth period. Practice has proved that when the residence time of the sludge is 5 to 6 days, the problem of sludge floating caused by it is avoided.

Industrial wastewater refers to the wastewater, sewage and waste liquid produced in the industrial production process, which contains industrial production materials, intermediate products and products that are lost with the water and pollutants generated during the production process. It summarizes the chemical industrial wastewater and the printing and dyeing industrial wastewater. 15, paper industry wastewater, dye production wastewater, food industry wastewater and pesticide wastewater treatment process of 15 industrial wastewater.

1. Desulfurization wastewater from coal-fired power plants

Most desulfurization devices in power plants use flue gas limestone-gypsum wet desulfurization process. The process is mainly composed of a limestone slurry preparation system, a gypsum dehydration system, and a desulfurization wastewater treatment system. The water in the slurry of the desulfurization device will be enriched with heavy metal elements and Cl- in the process of continuous circulation. On the one hand, it accelerates the corrosion of the desulfurization equipment, on the other hand, it affects the quality of gypsum, and it is necessary to discharge the wastewater in a timely manner.

Desulfurization wastewater treatment process of power plant: desulfurization wastewater → wastewater tank → wastewater pump → pH neutralization tank → sedimentation tank → flocculation tank → clarifier → outlet tank → outlet pump → discharge to standard The desulfurization wastewater treatment system includes three parts: wastewater treatment, dosing, and sludge treatment. The waste water treatment system is mainly composed of waste water tanks, triple tanks, clarifiers, sludge pumps, outlet tanks, clean water pumps, fans, dehydrators and other equipment. In addition to a large amount of Cl-, Mg2 +, the impurities in the desulfurization wastewater also include: fluoride, nitrite, etc .; heavy metal ions, such as: Cu2 +, Hg2 +, etc .; insoluble CaSO4 and fine dust. In order to meet the wastewater discharge standards, corresponding wastewater treatment devices are required.

2. Chemical industry wastewater

Chemical industry wastewater mainly comes from: petrochemical industry, coal chemical industry, acid and alkali industry, chemical fertilizer industry, plastic industry, pharmaceutical industry, dye industry, rubber industry and other industrial wastewater.

The main measures for the prevention and control of chemical wastewater pollution are: first of all, production processes and equipment should be reformed to reduce pollutants, prevent waste water from being discharged, and be comprehensively used and recycled; waste water that must be discharged should be selected according to water quality and requirements.

The primary treatment mainly separates suspended solids, colloids, oil slicks or heavy oils in water. Water quality and quantity adjustment, natural sedimentation, floating and oil separation can be used.

The secondary treatment is mainly to remove biodegradable organic dissolved matter and some colloids, and to reduce the biochemical oxygen demand and some chemical oxygen demand in the wastewater. Biological treatment is usually adopted. A considerable amount of COD remains in the biologically treated wastewater, sometimes with high color, odor, and odor, or because of high environmental hygiene standards, a tertiary treatment method is required for further purification.

Tertiary treatment is mainly to remove organic pollutants and soluble inorganic pollutants that are difficult to biodegrade in wastewater. Common methods include activated carbon adsorption and ozone oxidation, and ion exchange and membrane separation technologies can also be used. Various chemical industry wastewater can choose different treatment methods according to different water quality, water quantity and external drainage quality requirements after treatment.

oil sludge

3. Printing and dyeing industry wastewater

The printing and dyeing industry has a large amount of water, and usually consumes 100 ~ 200t of water per 1t of printing and dyeing. 80% ~ 90% are discharged as printing and dyeing wastewater. Common treatment methods are recycling and harmless treatment.

Recycling: Wastewater can be recycled separately according to the characteristics of water quality, such as the diversion of bleaching and cooking wastewater and dyeing and printing wastewater. The former can be washed by convection. Multiple uses of one water can reduce the discharge;

The lye is recovered and reused, usually by evaporation method. If the amount of lye is large, it can be recovered by three-effect evaporation. If the amount of lye is small, it can be recovered by thin film evaporation.

Dye recovery, such as Shihlin dye can be acidified into cryptobasic acid, showing colloidal particles. Suspended in the residual liquid, it can be recycled after filtration.

Harmless treatment can be divided into physical treatment methods such as precipitation method and adsorption method. The precipitation method mainly removes suspended matter in wastewater; the adsorption method mainly removes dissolved pollutants and decoloration in wastewater.

Chemical treatment methods include neutralization, coagulation and oxidation. The neutralization method consists in adjusting the pH of the wastewater, and can also reduce the color of the wastewater. The coagulation method consists in removing the dispersed dyes and colloidal substances in the wastewater. The oxidation method consists in oxidizing the reducing substances in the wastewater to precipitate the sulfur dyes and reducing dyes.

Biological treatment methods include activated sludge, biological turntable, biological drum and biological contact oxidation method. In order to improve the quality of the effluent water and meet discharge standards or recycling requirements, it is often necessary to use several methods for joint treatment.

4. Wastewater from the paper industry

Papermaking wastewater mainly comes from the two processes of pulping and papermaking in the paper industry. Pulp is the process of separating fibers from plant raw materials to make pulp, which is then bleached; papermaking is to dilute, shape, squeeze, and dry the pulp to make paper. Both processes discharge large amounts of wastewater.
Polluted wastewater is the most severely polluted. The waste water discharged during washing is dark brown, which is called black water. The concentration of pollutants in black water is very high, BOD is as high as 5 ~ 40g / L, and it contains a large amount of fiber, inorganic salts and pigments. Wastewater from the bleaching process also contains a large amount of acid and alkali substances. The waste water discharged from the paper machine is called white water, which contains a large amount of fiber and fillers and rubber added during the production process.

Wastewater treatment of the paper industry should focus on improving the recycling rate, reducing water consumption and wastewater discharge. At the same time, we should actively explore a variety of reliable, economical and able to make full use of useful resources in wastewater treatment methods. For example, the flotation method can recover fibrous solid matter in white water with a recovery rate of 95% and the clarified water can be reused; the combustion method can recover sodium hydroxide, sodium sulfide, sodium sulfate, and other sodium salts combined with organic matter in black water.

Neutralization method to adjust the pH value of wastewater; coagulation sedimentation or flotation method can remove suspended solids in wastewater; chemical precipitation method can decolorize; biological treatment method can remove BOD, which is more effective for kraft paper wastewater; wet oxidation method is more effective success. In addition, there are also domestic and foreign treatment methods such as reverse osmosis, ultrafiltration, and electrodialysis.

Oil sludge pollution

5.Dye production wastewater

Dye production wastewater contains acids, alkalis, salts, halogens, hydrocarbons, amines, nitro compounds, dyes and their intermediates, and some also contain pyridine, cyanide, phenol, benzidine, and heavy metals mercury, cadmium, and chromium. The components of these wastewaters are complex, toxic and difficult to treat. Therefore, the treatment of dye production wastewater should be based on the characteristics of the wastewater and its discharge requirements. Select an appropriate treatment method.

6. Food industry wastewater

The food industry has a wide range of raw materials and a wide range of products. The amount and quality of discharged wastewater varies widely.
The main pollutants in wastewater are: solid substances floating in wastewater, such as vegetable leaves, peels, minced meat, poultry feathers, etc .; the substances suspended in wastewater include oil, protein, starch, colloidal substances, etc .; acids dissolved in wastewater , Alkali, salt, sugar, etc .; mud and other organic matter entrained by raw materials; etc .;

Food industry wastewater is characterized by high organic matter and suspended matter content, easy to spoil, and generally has no major toxicity. Its harm is mainly to make the water body eutrophic, which will cause the death of aquatic animals and fish, promote the odor of organic matter deposited on the bottom of the water, deteriorate the water quality and pollute the environment.

In addition to proper pretreatment according to water quality characteristics, the wastewater treatment in the food industry is generally suitable for biological treatment. If the quality of the effluent is very high or the organic matter content in the wastewater is high, a two-stage aeration tank or a two-stage biological filter, or a multi-stage biological turntable can be used. Or two types of biological treatment devices can be used in combination, or anaerobic can be used. -Aerobic series.

7. Pesticide wastewater

There are many types of pesticides, and the quality of pesticide wastewater is complex. Its main characteristics are: high concentration of pollutants, chemical oxygen demand (COD) can reach tens of thousands of milligrams per liter; high toxicity, in addition to pesticides and intermediates in wastewater, toxic substances such as phenol, arsenic, mercury and many other Bio-degradable substances; foul odor, irritating to the human respiratory tract and mucous membranes; water quality and quantity are unstable.

Therefore, the pollution of pesticide wastewater to the environment is very serious. The purpose of pesticide wastewater treatment is to reduce the concentration of pollutants in pesticide production wastewater, improve the recycling rate, and strive to achieve harmlessness. Pesticide wastewater treatment methods include activated carbon adsorption method, wet oxidation method, solvent extraction method, distillation method and activated sludge method. However, the development of new pesticides with high efficiency, low toxicity and low residue is the development direction of pesticides.

8.Cyanide-containing wastewater

The cyanide-containing wastewater mainly comes from electroplating, coal gas, coking, metallurgy, metal processing, chemical fiber, plastic, pesticide, chemical and other departments.

Cyanide-containing wastewater is a relatively toxic industrial wastewater. It is unstable in water and easily decomposes. Inorganic cyanide and organic cyanide are highly toxic substances. Human ingestion can cause acute poisoning. The lethal amount of cyanide to the human body is 0.18g, the potassium cyanide is 0.12g, and the mass concentration of cyanide to fish in water is 0.04 ~ 0.1mg / L.

The cyanide-containing wastewater treatment measures mainly include: reforming the process to reduce or eliminate effluent cyanide-containing wastewater. If cyanide-free electroplating is used, industrial wastewater in electroplating workshops can be eliminated. Wastewater with high cyanide content should be recycled. Wastewater with low cyanide content should be purified before being discharged. Recovery methods include acidification aeration-alkali solution absorption method, steam desorption method, and the like.

The treatment methods include alkaline chlorination method, electrolytic oxidation method, pressure hydrolysis method, biochemical method, biological iron method, ferrous sulfate method, and air stripping method. Among them, the alkaline chlorination method is widely used, the ferrous sulfate method is incomplete and unstable, and the air stripping method pollutes the atmosphere and the effluent does not meet the discharge standards. Less adopted.

9.Phenol-containing wastewater

Phenol-containing wastewater mainly comes from coking plants, gas plants, petrochemical plants, insulation materials plants and other industrial sectors, as well as the production of ethylene, synthetic phenol, polyamide fibers, synthetic dyes, organic pesticides and phenolic resins from petroleum cracking. The phenol-containing wastewater mainly contains phenol-based compounds, which are a protoplasmic toxicant that can solidify proteins.

10. Mercury-containing wastewater

Mercury-containing wastewater mainly comes from non-ferrous metal smelters, chemical plants, pesticide plants, paper mills, dye plants and thermal instrumentation plants. The toxicity of various mercury compounds is very different, such as methylmercury, methylmercury is easily absorbed into the human body, not easily degraded, excreted very slowly, and easily accumulated in the brain.

Industrial sludge

11.Heavy metal wastewater

The heavy metal wastewater mainly comes from the wastewater from mining, smelting, electrolysis, electroplating, pesticide, medicine, paint, pigment and other enterprises. The types, contents and existing forms of heavy metals in wastewater vary with different production enterprises.

The principle of heavy metal wastewater treatment is: the most fundamental is to reform the production process without using or reducing the use of toxic heavy metals; followed by the use of reasonable technological processes, scientific management and operation to reduce the amount of heavy metals and the amount of waste with wastewater, and minimize efflux Amount of wastewater. Heavy metal wastewater should be treated in situ at the place of production and mixed with other wastewater to avoid complicating the treatment. Moreover, it should not be discharged directly into urban sewers without treatment, so as to avoid expanding heavy metal pollution.

The treatment of heavy metal wastewater can generally be divided into two categories: one is to convert the heavy metals in the wastewater in a dissolved state into insoluble metal compounds or elements and remove them from the wastewater by precipitation and floating. Applicable methods such as neutralization precipitation method, sulfide precipitation method, floating separation method, electrolytic precipitation (or floating) method, diaphragm electrolysis method, etc .; second, the heavy metals in the wastewater are concentrated without changing their chemical form and For separation, applicable methods include reverse osmosis, electrodialysis, evaporation, and ion exchange. These methods should be used alone or in combination according to the quality and quantity of wastewater.

12. Metallurgical wastewater

The main characteristics of metallurgical wastewater are large water volume, many types, and complex and variable water quality. According to the source and characteristics of wastewater, there are mainly cooling water, pickling wastewater, washing wastewater (dust removal, gas or flue gas), slag washing wastewater, coking wastewater, and wastewater condensed, separated or overflowed during production.

The development trend of metallurgical wastewater treatment is to develop and adopt new processes and technologies that use no or little water and no pollution or pollution. Develop comprehensive utilization technologies, such as recovering useful substances and heat energy from waste water and waste gas, and reducing material and fuel loss; according to different water quality requirements, comprehensively balance and use in series, while improving water quality stabilization measures, and continuously improving water cycle utilization; The new treatment technology and technology of metallurgical wastewater characteristics, such as magnetic steel treatment of steel wastewater, has the advantages of high efficiency, small footprint, convenient operation and management.

13. Acid and alkali wastewater

Acid wastewater mainly comes from steel plants, chemical plants, dye plants, electroplating plants and mines, etc., which contains various harmful substances or heavy metal salts. The mass fractions of acids vary widely, ranging from less than 1% to as high as 10%.

Alkaline wastewater mainly comes from printing and dyeing plants, leather mills, paper mills, and oil refineries. Some of them contain organic bases or inorganic bases. Some of the mass fractions of alkali are higher than 5% and some are lower than 1%. In addition to acid-base wastewater, acid-base wastewater often contains acid salts, basic salts, and other inorganic and organic substances.
Acid-alkali wastewater is highly corrosive and can only be discharged after proper treatment.

The general principle for treating acid-alkali wastewater is: high-concentration acid-alkali wastewater should be prioritized for recycling. According to water quality, water volume and different process requirements, carry out plant or regional scheduling and try to reuse as much as possible: if reuse is difficult, or the concentration is too high Low, large amount of water, can be concentrated to recover acid and alkali.

Low-concentration acid and alkali wastewater, such as the washing water of the pickling tank and the rinse water of the alkali cleaning tank, should be neutralized.

For neutralization treatment, the principle of treating waste with waste should be considered first. Such as acid and alkaline wastewater neutralize each other or use waste alkali (slag) to neutralize acidic wastewater, use waste acid to neutralize alkaline wastewater. In the absence of these conditions, a neutralizing agent can be used.

14.Beneficiation wastewater

Beneficiation wastewater has the characteristics of large water volume, high suspended matter content, and many types of harmful substances. Its harmful substances are heavy metal ions and ore dressing agents. Heavy metal ions include copper, zinc, lead, nickel, barium, cadmium, and arsenic and rare elements.

The beneficiation wastewater is mainly passed through the tailings dam to effectively remove suspended matter in the wastewater, and the content of heavy metals and flotation reagents can also be reduced. If the discharge requirements are not met, further treatment should be carried out. Common treatment methods are: lime neutralization and roasted dolomite adsorption can be used to remove heavy metals; ore adsorption method and activated carbon adsorption method can be used as the main removal flotation agent; Cyanide wastewater can be chemically oxidized.

15. Oily wastewater

Oily wastewater mainly comes from industrial sectors such as petroleum, petrochemicals, iron and steel, coking, gas generation stations, and mechanical processing. Except for heavy tars with a relative density of 1.1 or higher, the remaining relative density of oily pollutants in the wastewater is less than 1. Oily substances usually exist in three states in wastewater.

Floating oil, the diameter of the oil droplets is larger than 100 μm, and it is easy to separate from the waste water.

Disperse the oil, the diameter of the oil droplets is between 10 and 100 μm, and float in water.

Emulsified oil, the diameter of the oil droplets is less than 10 μm, and it is not easy to separate from the wastewater.

Due to the large differences in oil concentration in wastewater discharged from different industrial sectors, such as wastewater generated during the refining process, the oil content is about 150 ~ 1000mg / L, the tar content in coking wastewater is about 500 ~ 800mg / L, and the wastewater from the gas generation station is discharged into the wastewater. The tar content can reach 2000 ~ 3000mg / L.

Therefore, the treatment of oily wastewater should first use an oil trap to recover oil slicks or heavy oil. The treatment efficiency is 60% to 80%, and the oil content in the effluent is about 100 to 200mg / L. Emulsified and dispersed oil in wastewater is difficult. Treatment, it should prevent or reduce the emulsification phenomenon.

The first is to reduce the emulsification of oil in wastewater during the production process;

The second is to minimize the number of times the pump is used to raise the wastewater during the treatment process, so as not to increase the degree of emulsification. Treatment methods usually use air flotation and demulsification.

1. Light ceramsite made of sludge

A ceramsite company in Kunming introduced advanced domestic technology and used Dianchi sludge as a raw material to develop high-quality artificial light aggregates–ceramsite and ceramsite hollow brick. Among them, the proportion of sludge in raw materials is as high as 30% to 40%. This kind of ceramsite hollow brick replaces the ordinary clay sintered solid brick, which not only saves land, but also saves energy and steel. At the same time, it also reduces pollution in Dianchi Lake, thereby improving comprehensive benefits and turning waste into treasure.

2. Sludge replacing asphalt fine aggregate

After a large number of experimental studies, the Sewer Bureau of Tokyo, Japan has shown that the asphalt mixture mixed with sludge ash is equivalent to the mixture made of traditional materials. Compared with the previous method which only used cement as raw material for cement, the new method can save an average of 10 million yen in cost per year, and can also reduce 9 tons of emissions per year carbon dioxide.

3. Use of other building materials

Melting sludge into molten stone: The dried sludge cake is quantitatively sent to a surface melting furnace for combustion (temperature up to 1300 ° C), and the resulting slag is cooled and solidified to become glassy, ​​and then heat-treated in a crystallizing furnace to make the slag Modified from glassy to crystalline. This molten stone can replace crushed stone, stone, etc., and is used as a subgrade, pavement, concrete aggregate and sewer liner. There are also studies that use sludge to replace part of the sand for the preparation of concrete. Studies have shown that replacing the appropriate amount of sand with pipe trench sludge after drying, crushing and sieving will not directly affect the mechanical properties and durability of the concrete.

In addition to organic matter, sludge usually contains 20% to 30% of inorganic matter, mainly calcium, silicon, iron, and aluminum. The construction of sludge is an effective method to make full use of inorganic matter in sludge.

In 1997, a company produced high-strength cement using sewage sludge and waste incineration fly ash as the main raw materials, and built the world’s first ecological cement plant. It also studied the use of dewatered sludge produced by urban sewage treatment plants as Raw material manufacturing cement technology. About 60% of its raw materials are waste materials, and the roasting temperature is 1000 ~ 1200 ℃, so the fuel consumption and CO2 emissions are also low, which is conducive to the reduction, harmlessness and resource utilization of municipal waste. Called “environment-friendly cement”. When burning cement with sludge, there is no need to pretreat the sludge, and at the same time, all organic matter can be decomposed and removed at high temperature without secondary pollution such as nitrogen oxides, soot and so on. Therefore, using sludge for burning cement is also an effective comprehensive utilization method.

1. Overview of sludge treatment and disposal

In the treatment of feed water and wastewater, various types of sediments and floating materials produced by different sludge treatment processes are collectively referred to as sludge. The composition and properties of the sludge mainly depend on the composition, properties and treatment process of the treated water. The composition of the sludge is complex, and there are various classification methods and different names.

1.1 sludge classification

According to the source, the sludge is roughly divided into three categories: feed water sludge, domestic sludge and industrial wastewater sludge.

According to the separation process of sludge from water, it can be divided into sediment sludge (including physical sedimentation sludge, coagulation sludge, chemical sludge) and biological treatment sludge (sludge produced by sewage in the secondary treatment process, including biological filtration). Humic sludge obtained by methods such as pool and biological turntable, and activated sludge obtained by activated sludge method). Most of the sewage from modern sewage treatment plants is a mixed pollution of sediment sludge and biological treatment sludge.

According to the sludge composition and quality, it can be divided into organic sludge and inorganic sludge.

More commonly used are classified according to the different treatment stages of sludge: biological sludge, concentrated sludge, digested sludge, dehydrated and dried sludge, dry sludge and sludge incineration ash.

1.2 Characteristics of sludge

(1) Moisture content and solid content The water content is the percentage of the water content in the sludge, and the solid content is the percentage of the solid or dry mud content in the sludge. When the water content is high and the sludge is in a fluid state, the volume of the sludge is inversely proportional to the solid content: V1V2=Ps1/Ps2=(100-Pw2y(100Pw1)
In the formula: V1 and V2 are the volume of wet sludge when the water content is Pw1 (solid content Ps1) and Pw2 (solid content Ps2).

Example: The original moisture content of the sludge is 99.5%, and the percentage of sludge volume reduction when the water content is reduced to 98.5% and 95% is obtained.

Solution: Let V1 be the volume of sludge when the water content is 99.5%, and the volume when V2 and V3 respectively have water content of 98.5% and 95%, and substitute each value into the above formula to obtain V1/V2=Ps1/Ps2= (100-98.5/(100-99.5)=3 V1/N3=Ps1/Ps2=(100-95/(100-99.5)=10 As can be seen from the above example, when the moisture content of the sludge is reduced from 99.5% to At 98.5%, the volume of the sludge is reduced to about one-third of the original sludge, and then reduced to 95% (when the solid content is 5%, the volume of the sludge is reduced to about one-tenth of the original sludge). .

(2) Volatile solids Volatile solids refer to the part of solids in the sludge that can be burned in a furnace at 600 ° C and escaped by gas, reflecting the degree of stabilization of the sludge.

(3) Toxic and harmful substances in sludge The sludge in urban sewage treatment plants contains a considerable amount of nitrogen, phosphorus and potassium, which has certain fertilizer effects and can be used to improve the soil, but it also contains germs.

Viruses, parasite eggs, etc., should be treated as necessary before application. The heavy metals in the sludge are the main harmful substances, and the sludge with a heavy metal content exceeding the prescribed amount cannot be used as the clothing fertilizer.

(4) Dewatering performance of sludge When the water content of the sludge is separated by filtration, the commonly used index is used to evaluate the sludge dewatering performance than the resistance value or capillary water absorption time.

(5) Sludge specific gravity refers to the ratio of the weight of the sludge to the weight of the same volume of water. The specific gravity of the sludge depends mainly on the water content and the specific gravity of the round body. The proportion of domestic sludge and similar industrial sludge is generally greater than one.

Sludge treatment is the process of filling, training, water, stability, incineration or incineration. With the development of the economy, the discharge of urban wastewater is increasing, and the amount of sludge generated is also increasing. Sludge treatment and disposal has gradually become the focus of attention at home and abroad.

(6) Existing treatment and disposal methods at home and abroad mainly include sanitary landfill, water body consumption, incineration, composting, and land use. In view of the existing technology, the main sludge disposal method is landfill. The most suitable sludge treatment method is land use. With the advancement of science and technology, it is bound to introduce more effective and reasonable treatment and disposal methods, and ultimately realize the reduction, harmlessness, stabilization and resource utilization of urban sludge treatment and disposal.

Sanitary landfill

The disposal method is simple, easy, and low in cost, and the sludge does not need to be highly dehydrated and has strong adaptability. However, there are also some problems with sludge landfill, especially the formation of landfill leachate and gas. Leachate is a heavily polluted liquid that can contaminate the underground water environment if the site is sited or not properly operated. The gas produced by landfills is mainly methane, which can cause explosions and combustion if appropriate measures are not taken.

Direct land use

Direct use of sludge land is considered to be the most promising disposal method due to the advantages of low investment, low energy consumption, low operating cost and organic component conversion into soil improver. Scientific and rational land use can be reduced. The negative effects of sludge. The use of forest land and municipal greening has become an effective way of sludge land use because it is not easy to cause pollution in the food chain. The use and use of sludge for the repair and reconstruction of heavily disturbed land (such as mine land, forest harvesting sites, landfills, and severely damaged areas) reduces the potential threat of sludge to human life. Both the sludge was disposed and the ecological environment was restored.

Incineration

The application of wet sludge to direct incineration is more common. It is not only difficult to directly incinerate without drying the sludge, but it is also extremely uneconomical in terms of energy consumption. The incineration-based sludge treatment method is the most thorough sludge treatment method, which can completely carbonize organic matter and kill pathogens, thereby minimizing sludge volume. However, the disadvantage is that the treatment facility has large investment and high treatment cost. .

Powdered organic and inorganic fertilizers Powdered organic and inorganic fertilizers refer to mechanically mixed fertilizers containing two or more nutrients; the ratio of nutrients is determined according to crop varieties, target yield, soil and climate, etc. Different crops have their own unique growth needs; and they can be blended with auxiliary additives (such as limestone, dolomite powder, etc.) and herbicides, insecticides, etc., which have improved soil physiological characteristics according to the specific needs of the crop in specific regions and seasons. Become a nutrient-rich, multi-purpose special organic and inorganic fertilizer.

2. Sludge treatment process

1. The treated sludge (living sludge, industrial sludge, etc.), inorganic raw materials (urea, monoammonium phosphate, etc.), trace elements (borax, ferrous sulfate, etc.) filler (shadow earth, vermiculite, etc.) ) and other raw materials are sent to the automatic lifting silo in proportion;

2. Transported to the organic fertilizer mixer (continuous), while the organic fertilizer mixer rotates, the material advances 2/3 forward, and the remaining 1/3 of the material reciprocates back and forth, and continues to mix with the newly delivered materials. After two to three times of circulating mixing; after the material has reached the purpose of uniform mixing, it is slowly pushed to the discharge port along the inclined direction of the organic fertilizer mixer;

3. Transported to the organic fertilizer special screening machine, special design can completely solve the problem of screen adhesion;

4. The large particles are pulverized by the pulverizer and returned to the horizontal mixer;

5. The finished product is transported to the finished silo, and the automatic packaging scale is weighed, packed and stored.

Metallurgical dust

The main components of metallurgical dust are gas dust, gas mud, steel-making dust and so on.

Blast furnace dust

The blast furnace dust mainly refers to the metal vapor captured by the dust collector in the metallurgical operation, such as the raw material dust generated along with the blast furnace gas movement, the fuel dust in the blast furnace, etc. There are two ways for dust collector to collect blast furnace dust and mud, namely dry and wet. Dry dust collector is used to collect powdery solid. It is called blast furnace gas ash. Wet collection is to collect the dust and mud in slurry state by using wet dust collector, which is called blast furnace gas mud. Blast furnace dust is rich in zinc, iron and other elements. At present, most enterprises in our country use weak magnetic iron separation technology for classification and selection, to recover the iron concentrate contained in the dust, and to recover the carbon concentrate contained in the dust by flotation technology.

Steelmaking dust

The steelmaking dust refers to the phenomenon that some metal impurities with lower melting point will burst or even splash the boiling molten iron due to the change of high temperature environment when the molten iron is heated and smelted in the metallurgical converter. When the molten iron is discharged from the high temperature furnace, a large number of fine metal liquids will exchange with the cold air outside the furnace rapidly, and will form when the air continues to cool Metal dust. The main component of steelmaking dust is metal dust, which contains calcium, iron and other elements, usually in the form of oxide. At present, there are three ways to deal with steel-making dust and mud in China. The first is to mix and shake the steel-making dust and other dry powder according to a certain proportion, and then add some sintering raw materials for de coagulation and reuse. Second, because there are a lot of iron elements in the steel-making dust, the metal in the dust can be turned into pellets, which can be put into the converter again for roasting and utilization. Third, because the steel-making dust contains calcium element, the steel-making dust can play the role of replacing quicklime.

Fly ash

Fly ash refers to the fine ash collected in the smoke generated after coal combustion. Because of its strong adsorption activity and water absorption performance, most of the coal dust is used as admixture of concrete to realize resource reuse. In the process of making concrete, adding a proper amount of coal dust can save cement and fine aggregate, reduce water consumption and workability of concrete, and improve the impermeability of concrete. Nowadays, fly ash has been widely used in building materials, municipal construction and other industries in China.

In recent years, soil heavy metal detection technology has been developed rapidly, but there is still a big gap with the actual demand, and there is a huge room for improvement in some key technologies. The spectral method can be used to analyze and determine the heavy metal content in various complex environmental samples with high sensitivity and accuracy. However, considering that most of them need large-scale expensive instruments, high cost of analysis, need to be digested, analysis time is long and safety factors, its application in the determination of heavy metal content in soil has not been popularized yet. The electrochemical method is used in the determination of heavy metal content in soil Trace element detection has good research and application, but there are still some problems in the current detection process, such as ion interference, wave peak overlapping, etc. in addition, soil sample digestion is needed in the pretreatment process of soil samples, and the use of strong acid may bring secondary pollution to the soil. How to overcome these problems has become the key to its popularization and application; new detection technologies show good response But considering that these technologies are relatively new, the preparation of specific antibodies is difficult, terahertz and other equipment are relatively expensive at present, these all urgently need interdisciplinary support of biology, optics and other disciplines and carry out more collaborative innovation research. These problems indicate the direction for the further research and development of soil heavy metal detection technology.

Pretreatment technology of heavy metal detection samples in soil is a very important link, which can have a great impact on the accuracy of the analysis results. In order to achieve a unified pretreatment technology for heavy metal samples, a large number of analysts need to further explore and study, synthesize the advantages of several methods, and effectively avoid the disadvantages, so as to propose an efficient, simple and non polluting treatment method.

In addition to organic matter, sludge usually contains 20% to 30% of inorganic substances, mainly calcium, silicon, iron and aluminum. Sludge building materials are an effective method for making full use of inorganic substances in sludge.

The research team incorporated 10% to 30% of the sewage sludge into clay bricks and burned it into an ordinary “ecological brick” for construction at 900 °C. This method not only treats the sludge, but also seals the toxic heavy metals in the sludge during the firing process, kills all harmful bacteria, decomposes toxic organic matter, and the brick does not have any odor. Professor Weng Huanxin of Zhejiang University, when presiding over the provincial key project “Study on the development and utilization of sludge resources in wastewater treatment”, based on a large number of experimental studies to obtain various technical parameters, the use of sludge has the characteristics of high calorific value and light texture. Successfully developed a lightweight brick. The main index of this kind of lightweight brick reaches the national standard of ordinary sintered brick, and has the advantages of high compressive strength, energy saving of 10%, light weight of ordinary bricks of the same volume, and saving 10% to 15% of clay resources. . Therefore, the use of sludge for burning bricks not only achieves waste utilization, but also relieves the pressure of sludge treatment, opening up a new path for the comprehensive utilization of sludge.

At present, the main disposal methods commonly used for sludge are sanitary landfill, incineration treatment, direct land use, etc. These disposal methods have played a certain role in practical applications, but as environmental standards become more stringent, their problems Exposed.

1. Sanitary landfill

The sanitary landfill of sludge began in the 1960s and has developed into a relatively mature sludge disposal method. Its advantages are low investment, simple method, quick effect and large processing capacity; the disadvantage is that it requires high soil mechanical properties of landfill sludge, and requires a large area of ​​space and a large amount of transportation costs, and at the same time, to prevent it from polluting groundwater. The foundation also needs to be treated with anti-seepage treatment.

However, there are many problems with sanitary landfills. The various toxic and harmful substances contained in the sludge will cause secondary pollution of groundwater and the atmosphere through the erosion and leakage of rainwater. In addition, due to the large output of municipal sewage sludge, there are fewer and fewer places that can be used for sludge landfill. The US Environmental Protection Agency predicts that 5,000 of the 6,500 landfills will be shut down in the next few decades.

2. Incineration treatment

The most important feature of sludge incineration treatment is that it can realize the harmlessness, reduction and resource utilization of sludge, and it is the most “complete” treatment. At present, developed countries such as the United States, Japan, France, Switzerland, and Germany mainly use incineration to treat sludge. In recent years, sludge incineration technology has gradually become the mainstream of sludge treatment, and it is increasingly favored by countries all over the world. However, sludge must be dehydrated before incineration. As far as the current technical level is concerned, the cost of mechanical dewatering is relatively high. Although natural dehydration is low in cost, it takes a long time, covers a large area, is affected by the climate, and pollutes the surrounding air during drying. In addition, the incineration treatment generally requires a heating value of 1000 kJ/kg or more. When incinerated, harmful gases such as sulfur dioxide and dioxins are generated, and heavy metals in the sludge also pollute the air with the diffusion of soot; the incineration cost is other treatment process 2 ~4 times.

3. Direct land use

The sludge contains a large amount of organic matter and nutrients required by plants, and is a very valuable resource for using sludge as a resource for land use. Direct use of sludge land has the advantages of low investment, low energy consumption, low operating cost, and organic components can be converted into soil improver components. It is mainly used in farmland, vegetable fields, orchards, grasslands, municipal greening, seedling substrates and severe disturbances. Land restoration and reconstruction. However, the composition and source of sludge are quite complicated. Including nutrients, it also inevitably contains harmful components such as a large number of pathogenic bacteria, parasites (eggs), and heavy metals such as copper, arsenic, lead, zinc, aluminum and mercury. And refractory organic compounds such as polychlorinated biphenyls and dioxins, and radionuclides, which are used without treatment, will cause soil or water pollution.

Municipal sewage sludge is solid, semi-solid and liquid waste generated in the sewage treatment process. The sludge composition is complex, including solid particles such as fibers, sediments and animal and plant residues mixed into domestic sewage or industrial wastewater. A solid substance of coagulated flocs, various colloids, organic matter, and adsorbed metal elements, germs, microorganisms, and eggs. If these sludges are discharged or disposed of improperly, they will cause serious pollution to the surrounding environment. Therefore, it is of great significance to seek economical and effective reduction, harmless and resource sludge treatment technologies.

With the acceleration of urbanization in China, the number of urban sewage treatment plants has increased year by year, and the sewage treatment capacity has gradually increased, and the production of sludge has also increased dramatically. According to the survey, as of the end of September 2010, a total of 2,631 sewage treatment plants have been built in cities, counties and some key towns, and the daily sewage treatment capacity has reached 1.22×108 m3. The urban sewage treatment project under construction in the country has reached 1849. The total design capacity is about 0.466×108m3/day. According to the sludge yield of 3.8%, the daily sludge discharge is about 6.4×106m3. The sludge disposal method of most sewage treatment plants is to transport the sludge to the landfill or form it directly by proper concentration. On the one hand, it is easy to cause secondary pollution, on the other hand, the useful resources in the sludge are lost, resulting in waste of resources.

Obviously, with the construction of urban sewage treatment plants, how to properly treat and dispose of sludge will become more and more important. At present, China’s traditional sludge disposal methods include landfill, incineration, and direct land use. These treatment methods do not effectively utilize the sludge, and there are many social and environmental problems, not sludge disposal. The best way. Therefore, the search for appropriate resource utilization methods is the most important research in sludge treatment and disposal.