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Laboratory Wastewater Treatment

Laboratory wastewater treatment is one of the three waste treatments in the laboratory. The waste produced includes general washing wastewater and chemical experiment waste. Save water and keep the laboratory waste water treatment discharge to a minimum.

实验室三废处理之综合废水废液处理及水循环

The following introduces several common methods of laboratory waste liquid treatment.

①Sulphide precipitation method This precipitation method is mainly for inorganic waste liquids containing more heavy metals such as mercury, lead and cadmium in their composition. The specific method is generally to use Na2S or NaHS to convert such heavy metals in the waste liquid into insoluble water The metal sulfide is subsequently separated by co-precipitation with Fe(OH)3. Or you can first adjust the pH value of the waste liquid to 8.0~10.0, and then gradually add sodium sulfide to the waste liquid to excess until the precipitation of sulfide is formed. At this time, FeSO4 is added as a co-precipitant to promote the formation of FeS. The suspended mercury sulfide, cadmium sulfide, lead sulfide and particulates in the waste liquid are adsorbed and then co-precipitated, and the separation is achieved by standing and filtering.


②Flocculation sedimentation method  This method is mainly suitable for inorganic waste liquid containing more heavy metal ions. After initially determining the nature of the waste liquid and exploring the sedimentation characteristics of various ions, by selecting a suitable flocculant (such as lime, iron salt or aluminum salt, etc.), it can be formed under weak alkali conditions containing Fe (OH ) 3 and Al (OH) 3 component flocculation precipitation, this flocculation sediment has a certain adsorption effect, not only can remove heavy metal ions in the waste liquid, but also can also remove part of other organic pollutants in the waste liquid to achieve The purpose of reducing the chemical oxygen demand (COD) in the waste liquid.


③Redox neutralization precipitation method" This method is usually suitable for the treatment of hexavalent chromium (Cr6+) or reductive toxic substances, such as cyanide ion (CN-), etc., as well as some organic compounds containing metal elements. The common process can be summarized as follows: First, let the waste liquid undergo a series of oxidation-reduction reactions, thereby converting highly toxic pollutants into low-toxic pollutants, and then flocculate and precipitate the converted low-toxic pollution The substance is separated from the current reaction system; for the waste liquid containing hexavalent chromium, it is necessary to first reduce the hexavalent chromium to trivalent chromium (Cr3+) by the oxidation-reduction reaction, and then use a suitable precipitation agent to make it precipitate. To achieve the purpose of separation, or it can be treated together with other types of heavy metal waste liquid.


The reducing agent used in the above reaction is usually iron powder, sulfur dioxide, ferrous salt or bisulfite, etc. At the same time, it needs to be carried out under the condition of a pH value of less than 3.0, and then through neutralization and precipitation, the chromium element is converted into Insoluble salt is removed. When the solution contains cyanide ions, it is generally necessary to first use an oxidant under alkaline conditions to oxidize it to N2 and CO2. The usual methods include the chlor-alkali method and the Prussian blue method (that is, the method to generate ferricyanide compounds). To cause precipitation), ozone oxidation, electrolytic oxidation, and internal electrolysis of iron filings.


④Activated carbon adsorption method "This method is usually used to remove a small amount of dissolved organic matter that cannot be removed by biological, physical or chemical methods. The organic waste liquid in the laboratory usually contains a large amount of experimental residual liquid and waste solvent. Its main components are alkanes, aromatics or surfactants, and the concentration of the waste liquid is very high, which is very suitable for adsorption treatment with activated carbon. The processing process is usually to separate the organic phase in the waste liquid through a series of simple separation means, and then through the secondary adsorption of activated carbon to effectively remove the COD in the waste liquid. At the same time, the activated carbon can also adsorb together Part of inorganic heavy metal ions.


⑤ Ferrite precipitation method   This method is mainly suitable for inorganic waste liquid containing a variety of heavy metal ions. Ferrite refers to a type of composite metal oxide, its general chemical formula is M2FeO4 or MOFe2O3 (where M represents other metals), generally presenting a spinel-like cubic crystal structure. The best condition for the formation of ferrite is generally to provide sufficient Fe2+ and Fe3+, and its Fe2+:Fe3+=1:2 (molar ratio), at this time the most ideal pH value condition is 8.0~9.0; The peculiar wrapping and entrainment effect of the ferrite can make the heavy metal ions form a composite ferrite after entering the crystal lattice of the ferrite. The composite ferrite generally has strong stability. As long as it is under normal acid-base conditions, it can remove various metal ions in the waste liquid at one time, such as Cr3+, Fe3+, Pb2+, As3+, Zn2+, Hg2+, Cd2+, Mn2+, Cu2+, etc. all have good removal effects, so that harmful heavy metals contained in the waste liquid will not be leached.


⑥ Incineration method "Because organic matter generally has very good combustible properties, these organic solvents, organic residues or waste liquids are usually treated by incineration. The use of incineration to treat organic waste liquid refers to the oxidative decomposition of organic matter under high temperature conditions to promote the production of water, CO2 and other environmentally friendly products, and then discharge these products into the atmosphere. At this time, the removal rate of COD Usually it can reach 99% and above. It is worth mentioning that using incineration to treat organic waste liquid is an effective means to use air to perform advanced oxidation treatment of organic matter in waste liquid under high temperature conditions, and it is also one of the easiest methods to achieve industrialization.


Generally, the organic waste liquid discharged by the chemical industry is treated by incineration, especially for some waste liquids with high concentration and complex components, or pollutants with no recycling value and relatively high calorific value. Adopt incineration method for disposal. For those pollutants that are difficult to burn, they can be mixed with highly flammable substances before burning. However, special attention must be paid during this operation to prevent the incomplete combustion from producing new toxic substances or the toxic gas produced by combustion from escaping, thereby causing secondary pollution to the environment. Whether the combustion is complete depends on the temperature of combustion and the time of combustion. The residence time of the zone and the mixing state of the substances are determined.


⑦Solvent extraction method Solvent extraction method refers to the use of the solubility or partition coefficient of the compound in two immiscible solvents, so that the compound can be transferred from one solvent to another solvent, so that after repeated The compound can be extracted by multiple extractions; in general, the more hydrophilic the organic solvent, the worse the effect of two-phase extraction with water, because it can make more affinity Aqueous impurities follow, which will have a great impact on the further refinement of the active ingredients. For those low-concentration organic matter aqueous solutions, solvents with incompatible volatile properties can be used for extraction and separation, and then incinerated.


⑧Biochemical treatment method is usually suitable for the preliminary treatment of high-concentration organic waste liquid. Generally, microorganisms use pollutants as nutrients to grow, so that the dissolved or colloidal organic pollutants in the waste liquid are transformed into harmless Pollutants, so that the waste liquid can be purified. Biochemical treatment methods can be divided into aerobic biological treatment methods and anaerobic biological treatment methods. Among them, the aerobic biological treatment method refers to the use of aerobic microorganisms to decompose the organic pollutants in the waste liquid and the harmless treatment of the waste liquid; and the anaerobic biological treatment method uses anaerobic microorganisms. The biological function of the waste liquid is to degrade the organic pollutants in the waste liquid and achieve the purpose of purification of the waste liquid. The waste liquid that forms emulsion esters cannot be treated by biochemical treatment methods, but must be treated by incineration.

Generally speaking, the hazardous waste produced by the chemical laboratory mainly includes waste inorganic acid, waste lye, organic waste solvent, cyanide waste, heavy metal waste, mercury waste, chromium waste, arsenic waste, etc. , There are different treatment methods for different waste liquids.


Keywords: laboratory wastewater treatment, laboratory waste water treatment