Laboratories, especially chemical laboratories, are prone to produce toxic and harmful gases during experiments, threatening the safety of laboratory operators and laboratory equipment. Therefore, the disposal of laboratory waste is very important.
I. Laboratory exhaust gas
(a) the composition and harm of waste gas
There are many kinds of indoor air pollutants in chemical laboratories, including organic gases and inorganic gases. These gases are directly discharged into the atmosphere, which will aggravate the formation of acid rain and constitute a serious public hazard. If people inhale more, they will cause direct harm.
1. Inorganic waste gas mainly includes: nitrogen oxides, sulfuric acid mist, hydrogen chloride, hydrogen fluoride, hydrogen sulfide, sulfur dioxide and other inorganic waste gases.
2. Organic waste gas mainly includes aromatics: benzene toluene, xylene, styrene, etc.; Aldehydes and ketones: formaldehyde, acetaldehyde, glutaraldehyde, butyraldehyde, acetone, cyclohexanone, methyl ethyl ketone, acetophenone, etc.; Esters: Isobutyl acetate, ethyl acetate, butyl acetate, methyl acetate, banana oil, etc.; Alcohols: Methanol, ethanol, butanol isopropanol, ethanol, etc.
(two) the main principles and methods of waste gas treatment
At present, the treatment methods of gaseous pollutants can be generally divided into two categories: wet method and dry method. It is necessary to choose the method with high efficiency and low cost according to the characteristics of chemical laboratory waste gas.
A. Wet waste gas treatment wet method
Waste gas treatment adopts acid mist purification tower for waste gas treatment, It is suitable for purifying water-soluble gases such as hydrogen chloride gas (HCI), hydrogen fluoride gas (HF), ammonia gas (NH3), sulfuric acid mist (H2SO4), chromic acid mist (CrO3), hydrogen cyanide acid gas (HCN), hydrogen sulfide gas (H2S) and low-concentration NOx waste gas. It has the characteristics of good purification effect, compact structure, small occupied area, good corrosion resistance and anti-aging performance, convenient installation, transportation and maintenance management, simple equipment structure and less one-time investment, so it is widely used in the treatment of gaseous pollutants. Acid mist purification tower is suitable for installation on the roof of high-rise buildings. Its working principle is that acid mist waste gas is pressed into the purification tower by a fan, passes through spray and packing layer, and the waste gas and sodium hydroxide absorption neutralization liquid undergo gas-liquid two-phase full contact absorption neutralization reaction. After acid mist waste gas is purified, it is treated by deliquid layer and then discharged into the atmosphere. The purified acid mist waste gas can be lower than the national emission standard.
B. Dry waste treatment dry method
Waste gas treatment refers to the process of adsorbing a certain component or some components in the mixture on the solid surface by using the unbalanced molecular attraction or chemical bond force existing on the solid surface when the gas mixture contacts with the porous solid. The solid with adsorption is called adsorbent. The advantages of this method are simple equipment, convenient operation and easy to realize automatic control. However, because of the different physical and chemical properties of adsorbents, they have strong pertinence, so the waste containing different harmful substances must be equipped with adsorbents with different physical and chemical properties in order to play a good role in gas purification; If the waste gas passes through the adsorbent for a short time and the content of harmful substances in the waste gas is too high, the purification effect of the waste gas will not be ideal; When the exhaust gas passes through the adsorption medium, the air flow is blocked by the solid medium, so it is necessary to increase the power of the fan to ensure the normal wind speed of the ventilation system. Adsorbents need to be replaced or regenerated regularly to ensure the normal operation of the absorption device. Therefore, this method needs to invest certain cost and manpower in practical application. This method is generally used for waste gas treatment with relatively stable types and low content of harmful substances in waste gas, so it is convenient to adopt a targeted adsorbent.
Organic gas activated carbon adsorption device is generally used for dry waste gas treatment. Its principle is that activated carbon has many micropores and large specific surface area. Relying on molecular leading force and capillary action, solvent vapor and volatile substances can be adsorbed on its surface, and according to the boiling points of different substances, the adsorbed substances can be separated out by steam. When steam is used as the desorption medium, the precipitated organic solvent vapor and water vapor are condensed together through the condenser, and then enter the separation barrel to recover the organic solvent after separation.
Second, laboratory wastewater
1. Composition and harm of wastewater
The waste water produced in the laboratory includes surplus samples, standard curves and residual liquid of sample analysis, invalid storage liquid and washing liquid, and a large amount of washing water. Almost all routine analysis projects have wastewater pollution problems to varying degrees. The components in these wastewater are all-encompassing, including the most common organic matter, heavy metal ions and harmful microorganisms, and relatively rare cyanide, bacteria, toxins, various pesticide residues and drug residues.
Once the wastewater containing excessive heavy metals is discharged to the clean downstream, it will pollute a large area of water source. Because this kind of water polluted by heavy metals is no different from normal water in color and smell, once it is irrigated with these waters, it will inevitably make soil and crops polluted by heavy metals. People who eat crops grown on soil contaminated by heavy metals are easily poisoned by heavy metals.
2. Treatment methods of wastewater
Generally, there are physical methods, chemical methods and biological methods. Physical method mainly uses physical action to separate suspended solids in wastewater; Chemical method mainly uses chemical reaction to treat dissolved substances or colloidal substances in wastewater;
Biological method is to remove colloid and dissolved organic matter in wastewater. The above three basic treatment methods have their own characteristics and applicable conditions. When wastewater is discharged into surface water, the treatment degree should be determined according to the discharge requirements, and the self-purification ability of water body should be combined. Usually, the allowable load of water body should be determined according to the indexes of harmful substances and dissolved oxygen, that is, the allowable concentration discharged into water body.
A. Treatment of acidic wastewater:
Using alkaline wastewater for neutralization, the PH value of mixed wastewater is close to neutrality; Neutralizing agent is added to acidic wastewater, and acidic wastewater is filtered and neutralized by alkaline filter layer.
B. Treatment of alkaline wastewater:
Using acidic wastewater for neutralization, putting acidic neutralizer into alkaline substances: blowing flue gas (acidic gas carbon dioxide or sulfur dioxide) into alkaline wastewater; Using carbon dioxide in water to neutralize alkaline wastewater.
C, treatment of comprehensive waste liquid:
The process of water quality homogenization + neutralization filtration-neutralization coagulation-replacement internal electrolysis-biosorption tank-sedimentation tank and clear water tank is adopted for treatment. In wastewater treatment, in order to protect the pH on-line control system, neutralization and filtration technology is adopted to ensure that acid-alkali wastewater can reach the standard stably and save chemicals. Adopt combined packing to realize sludge immobilization; The disinfection treatment section adopts advanced ozone generator for disinfection; Sludge digestion adopts pulse water distributor to distribute water to realize sludge reduction. This process can decompose complex organic matter, and can stably treat the influence of chemicals produced in experimental wastewater on wastewater. Moreover, the operation cost of the process is low, and the management can minimize the floor area through reasonable layout: make a good greening design and make a reasonable planning for the sewage station, so as to make it a landscape in the laboratory center.
D. Treatment of special wastewater:
Where wastewater containing radionuclides, According to the half-life of nuclides, Divided into long-life and short-life radionuclide wastewater, And should be treated separately, long-life radionuclide, and high radioactive concentration of wastewater, the wastewater should be stored centrally, after a certain amount, the purification method can be used to treat a small amount of concentrated solution produced in the purification process, which can be treated by solidification method, short-life radionuclide wastewater should be treated by storage method; The treatment of wastewater containing radionuclides should comply with the current Regulations on Radiation Protection. The sewage of biosafety level 4 and biosafety level 3 laboratories must be disinfected. After treatment, the sewage should comply with the provisions of Hospital Wastewater Discharge Standard.
III. Laboratory solid waste
Solid waste generated by laboratories includes surplus samples, analysis products, consumed or damaged laboratory articles (such as glassware and gauze), residual or invalid chemical reagents, etc. These solid wastes are composed of complex components
Miscellaneous, covering all kinds of chemical and biological pollutants, especially many expired chemical reagents, which can easily lead to serious pollution accidents if handled carelessly.
The treatment method of laboratory pollutants is to prevent the diffusion of laboratory pollution. The general treatment principles of pollutants are: classified collection, storage and centralized treatment respectively. Use waste recovery and solid as much as possible
Chemical and incineration treatment, select appropriate methods for detection in practical work, and minimize the amount of waste and pollution. Waste discharge shall conform to the relevant national environmental discharge standards