Laboratory three waste treatment

Environmental Engineering

The exhaust gas, waste liquid, and waste residue generated during the experimental process are mostly harmful and must be treated before being discharged. In order to reduce the pollution of the laboratory to the environment, the Laboratory Environmental Protection System Engineering RoomLaboratory Design and ConstructionA very important link in it.

1、 Laboratory exhaust gas

During the process of inspection, identification, and testing in the laboratory, various exhaust gases are generated due to the needs of the experiment. The composition of the exhaust gases is relatively complex, including aromatic compounds such as benzene, toluene, xylene, styrene, etc; Ketones: Acetone, Cyclohexanone, Methyl Ethyl Ketone, etc; Esters: ethyl acetate, butyl acetate, methyl isoacetate, banana water, etc; Alcohols: Organic waste gases such as methanol, ethanol, butanol, isopropanol, etc. This also includes inorganic waste gases such as nitrogen oxides, sulfuric acid mist, hydrogen chloride, hydrogen fluoride, hydrogen sulfide, sulfur dioxide, etc; At the same time, there are also high-temperature combustion exhaust gases, dust, etc. The exhaust gas generated during the experimental process often has complex and diverse components, and the degree of damage to human health varies according to this characteristic.

Laboratory exhaust gas treatment methods

At present, the treatment methods for gaseous pollutants can generally be divided into two categories: wet and dry, and the specific selection of high-efficiency and low-cost methods needs to be based on the characteristics of chemical laboratory waste gas.

(1) Wet waste gas treatment

Wet waste gas treatment adopts acid mist purification tower for waste gas treatment, which is suitable for purification, hydrogen fluoride gas (HF), ammonia gas (NH3), sulfuric acid mist (H2SO4), chromic acid mist (CrO3), hydrogen cyanide gas (HCN), hydrogen sulfide gas (H2S), low concentration NOx waste gas and other water-soluble gases. It has the characteristics of good purification effect, compact structure, small floor area, good corrosion resistance, anti-aging performance, convenient installation, transportation, maintenance and management, simple equipment structure, low one-time investment, and is widely used for the treatment of Qitai pollutants.

The acid mist purification tower is suitable for installation on the roof of high-rise buildings. Its working principle is that the acid mist waste gas is pressed into the purification tower by the fan, and passes through the spray and packing layer. The waste gas and sodium hydroxide absorption neutralization liquid are fully contacted, absorbed and neutralized by gas-liquid two-phase reaction. After purification, the acid mist waste gas is subject to the dehydration treatment in the dehydration layer, and then discharged into the atmosphere. The purified acid mist exhaust gas can be below the national emission standards.

(2) Dry process exhaust gas treatment

Dry process exhaust gas treatment refers to the process of adsorbing a certain component or components of a gas mixture onto a porous solid surface by utilizing the unbalanced molecular gravity or chemical bonding forces present on the solid surface. Solid materials with adsorption properties are called adsorbents, and the advantages of this method are simple equipment, easy operation, and easy implementation of automatic control. However, due to the different physical and chemical properties of adsorbents, they have strong specificity. Therefore, in order to effectively purify gases containing different harmful substances, adsorbents with different chemical properties must be configured; If the time for the exhaust gas to pass through the adsorbent is short and the content of harmful substances in the exhaust gas is too high, the purification effect of the exhaust gas will not be ideal; When the exhaust gas passes through the adsorption medium, due to the obstruction effect of the solid medium on the airflow, it is necessary to increase the power of the fan to ensure the normal wind speed of the ventilation system. The adsorbent needs to be regularly replaced or regenerated to ensure the normal operation of the absorption device. Therefore, this method requires a certain amount of cost and manpower in practical applications. This method is generally used for the treatment of exhaust gases with relatively stable types and low content of harmful substances, which facilitates the use of a targeted adsorbent.

Dry exhaust gas treatment generally uses organic gas activated carbon adsorption devices. The principle is that activated carbon has many micropores and a large surface area. By relying on molecular gravity and adsorption, solvent vapor and volatile substances can be adsorbed on its surface. Depending on the boiling point of different substances, the adsorbed substances are precipitated by steam. When steam is used as the desorption medium, the organic solvent vapor and water vapor that precipitate are condensed by the condenser and enter the separation tank for separation before recovering the organic solvent.

Adsorption of activated carbon

a. Physical adsorption

This mainly occurs during the process of removing impurities from liquid and gas phases using activated carbon. The porous structure of activated carbon provides a large surface area, making it very easy to achieve the purpose of absorbing and collecting impurities. Just like magnetism, all molecules have mutual attraction. Because of this, a large number of molecules on the pore walls of activated carbon can generate strong attraction, thereby achieving the goal of attracting impurities from the medium into the pore size.

It must be pointed out that the molecular diameter of these adsorbed impurities must be smaller than the pore size of activated carbon in order to ensure that the impurities are absorbed into the pore size. That's why we create activated carbon with different pore structures by constantly changing raw materials and activation conditions, making it suitable for various impurity absorption applications.

b. Chemical adsorption

In addition to physical adsorption, chemical reactions often occur on the surface of activated carbon.

Activated carbon not only contains carbon, but also has a small amount of chemically bound oxygen and hydrogen in the form of functional groups on its surface, such as carboxyl groups, hydroxyl groups, phenols, lipids, quinones, ethers, etc. These surface oxides or complexes can undergo chemical reactions with the adsorbed substances, thereby binding and accumulating on the surface of activated carbon.

The adsorption of activated carbon is the result of the combined action of the two types of adsorption mentioned above.

When the adsorption rate and desorption rate of activated carbon in solution are equal, that is, the amount of activated carbon adsorbed per unit time is equal to the amount of desorption, the concentration of the adsorbed substance in the solution and on the surface of the activated carbon no longer change, and equilibrium is reached. At this point, the dynamic equilibrium is called activated carbon adsorption equilibrium, and the concentration of the adsorbed substance in the solution is called equilibrium concentration.

2、 Laboratory wastewater

1. Composition and hazards of wastewater

The wastewater generated in the laboratory includes excess samples, standard curves and sample analysis residues, expired storage liquids, and washing water. Almost all routine analysis projects have varying degrees of wastewater pollution issues. These wastewater contain a wide range of components, including common organic compounds, heavy metal ions, and harmful microorganisms, as well as relatively rare ones such as bacteria, toxins, various pesticide residues, and drug residues.

According to the main components of chemical laboratory wastewater, it can be divided into inorganic wastewater, organic wastewater, and comprehensive wastewater. Inorganic wastewater mainly contains heavy metals such as mercury, lead, chromium, arsenide, fluoride, etc. Organic wastewater mainly contains carcinogens such as phenols, benzene, nitro compounds, polycyclic aromatic hydrocarbons, polychlorinated biphenyls, etc. Comprehensive wastewater refers to wastewater that contains both organic and inorganic pollutants, and both have high levels. Most experimental wastewater is comprehensive wastewater, and the treatment of these wastewater should be tailored to the specific needs of the water.

Once wastewater containing excessive heavy metals is discharged downstream, it will pollute large areas of water sources. Due to the fact that water contaminated with heavy metals is no different from normal water in terms of color, odor, etc., once used for irrigation, it will inevitably make soil and crops contaminated with heavy metals. Crops grown on soil contaminated with heavy metals are easily poisoned by heavy metals when consumed by humans.

2. Treatment methods for wastewater

There are generally chemical methods, physical methods, and biological methods.

The physical method mainly utilizes physical actions to separate suspended solids in wastewater;

Chemical methods mainly use chemical reactions to treat soluble or colloidal substances in wastewater;

Biological methods are used to remove colloidal substances and dissolved organic substances from wastewater.

The above three basic processing methods each have their own characteristics and applicable conditions. When discharging wastewater into surface water, the degree of treatment should be determined according to the discharge requirements, while taking into account the self purification capacity of the water body. The allowable load of the water body is usually determined based on indicators of harmful substances and dissolved oxygen, that is, the allowable concentration of the discharged water body

According to the degree of treatment, wastewater treatment (mainly urban domestic sewage and certain industrial wastewater) can generally be divided into three levels:

The task of primary treatment is to remove suspended solid pollutants from wastewater. For this reason, physical processing methods are often used. After primary treatment, the removal rate of suspended solids is generally 70% to 80%, while the removal rate of biochemical oxygen demand (BOD) is only about 25% to 40%, indicating a low degree of wastewater purification.

The task of secondary treatment is to significantly remove organic pollutants from wastewater. Taking BOD as an example, after secondary treatment, 80% to 90% of BOD in wastewater can be removed. For example, the BOD content in urban sewage treatment water can be less than 30 milligrams per liter. Most of the various treatment units of aerobic biological treatment methods can meet this requirement.

The task of tertiary treatment is to further remove pollutants that cannot be removed by secondary treatment, including organic matter, phosphorus, nitrogen, and soluble inorganic matter that cannot be degraded by microorganisms. Third level processing is synonymous with advanced processing, but the two are not consistent. Third level treatment refers to one or more additional treatment units added after secondary treatment to remove a specific pollutant, such as phosphorus, nitrogen, etc., from wastewater; Advanced treatment is often a treatment unit or system added after secondary treatment for the purpose of wastewater recovery and reuse. The third level treatment is costly and complex to manage, but it can fully utilize water resources. A few countries have built some tertiary sewage treatment plants.

3、 Laboratory solid waste

The solid waste generated in the laboratory includes excess samples, analytical products, consumed or damaged laboratory supplies, residual or expired chemical reagents, etc. These solid wastes have complex compositions, covering various chemical and biological pollutants, especially many expired and ineffective chemical reagents. A slight carelessness in handling can easily lead to serious pollution accidents.

Principles of laboratory waste disposal

According to the characteristics of laboratory waste, it should be classified, collected, stored, and centrally processed. The processing method should be simple and easy to operate, with high processing efficiency and not requiring a lot of investment.

A small amount of toxic gas can be discharged outdoors through ventilation equipment, and the ventilation duct should have a certain height to dilute the discharged gas with air. When the amount of toxic gas generated is large, it must undergo absorption treatment before being discharged. Acidic oxide gases such as nitrogen, sulfur, phosphorus, etc. can be introduced into the alkaline solution through a conduit to be absorbed and discharged.

For certain toxic organic compounds with small quantities and high concentrations, sufficient oxygen can be supplied to the combustion furnace to ignite them, producing carbon dioxide and water. High concentration waste acid and alkali liquids should be neutralized to near neutrality before being discharged. For high concentration organic solvent waste liquids containing small amounts of analyte and other reagents, they should be recycled and reused.

Waste liquids used for recycling should be stored separately in clean containers. High concentration waste liquids of the same type should be centrally stored for the purpose of recycling certain components, while low concentration waste liquids can be discharged after appropriate treatment to meet standards.

Choose appropriate containers and storage locations based on the nature of the waste. Waste liquid should be stored in sealed containers and mixed storage is prohibited to avoid accidents caused by violent chemical reactions. Containers should be leak proof to prevent volatile gases from escaping and contaminating the laboratory environment.

The storage of waste liquids containing highly toxic, flammable, and explosive drugs should be carried out in accordance with corresponding regulations. Waste liquid should be kept away from light and heat sources to avoid accelerating the chemical reaction of the waste liquid. Storage containers must be labeled, indicating the type, storage time, etc. The storage time should not be too long.

Laboratory waste disposal methods

Laboratory waste reagent bottles such as ethanol, acetic acid, and other non-toxic and harmless reagent bottles can be washed clean with tap water before being discarded and disposed of by the garbage disposal personnel in the acid meal department.

Other reagent bottles should be washed clean with tap water and discarded. The waste liquid generated should be uniformly treated by the garbage disposal personnel of the sour meal department, and the same as 3. 3 Processing.

Other glass waste such as straws, triangular bottles, test tubes, etc., if there are residual chemical reagents, must also be washed clean and discarded.

Environmental Engineering