Laboratory pure water & waste water treatment system
Grading of lab water
Grade III pure water: The physical purity of Grade III pure water is generally less than 50uS/cm, and single distilled water, double distilled water, ordinary deionized water and reverse osmosis water all belong to this level. It is generally prepared by purifying tap water. The main uses of grade III pure water are to clean bottles and dishes, water for high-pressure disinfection devices, water for high-pressure disinfection devices, and water for artificial environment rooms, such as water supply to ultra-pure water meters.
Grade II pure water: Grade II pure water is a vague range, commonly expressed as 5-15M-cm. However, grade II pure water is not strictly limited to this range, and the range of 1-17M-cm can be regarded as grade II pure water. Grade II pure water is generally prepared by ion exchange or electrodialysis of Grade II pure water. It is mainly used for the preparation of general reagents, water for general chemical experiments and water supply for ultrapure water meters.
Grade I ultrapure water: Grade I ultrapure water refers to water with a physical purity greater than 18M-cm. It is customary to say that the resistivity of 18.2M-cm is the index of Grade I ultrapure water. Grade I ultrapure water must be purified from grade III or grade II pure water through nuclear-grade ion exchange resin. It is mainly used for high-precision analytical experiments and life science experiments that require high water purity.
Characterization parameters and international standards of water quality:
Characterization parameters:
1) Inorganic content - resistance value/conductivity
2) Organic Content - TOC (Total Organic Carbon)
3) Microbial content - bacterial count Particulate matter content - particle number (with particle size requirements, often refers to the remaining number of particles less than 0.2um)
Water purification methods and combined applications:
Laboratory pure water can be prepared by the following methods, and ultrapure water can fully meet the indicators only by comprehensively using a variety of technical means.
Distillation: Distillation is a traditional and commonly used method to make drinking water into pure water. The method is divided into single distillation, double distillation and triple distillation according to the number of distillations, and the purity of water increases with the increase of the number of distillations. The advantage of the distillation method is that the method is simple, the one-time investment of the preparation equipment is small, and the disadvantage is that the energy consumption is relatively large, the purity of the produced water is limited, and the output is limited.
Filtration method: This method adopts reverse osmosis technology. Reverse osmosis (RO) membrane is usually used to filter out pollutants with a diameter of less than 1nm. A typical reverse osmosis method can filter out 90c ionic pollution, most organic pollutants and almost all Particulate contaminants. The removal capacity of reverse osmosis for non-ionic pollutants with molecular weight less than 100 Daltons is low, and the filtration capacity of RO membrane increases with the increase of the molecular weight of pollutants. In theory, this method can filter out molecules with a molecular weight greater than 300 Daltons and particles including colloids and microorganisms at 100Vo, but dissolved gases cannot be removed.
In the reverse osmosis process, the influent water is pumped A in a tangential flow mode from the influent surface of the RO membrane under a certain pressure (usually 415bar, 60220psi). RO membranes are generally thin polyamide membranes that are stable in the pH range of the chamber but may be destroyed by hydrogenating agents such as chlorine in municipal water supplies. Microporous depth filters and activated carbon filter columns for influent pretreatment, typically used to protect RO membranes from large particles, heavy metals and free chlorine. The amount of influent is 15V0-25Y0 to generate reverse osmosis water, and the concentrated water intercepted upstream of the membrane contains most of the salt, organic matter and almost all particles. The volume ratio of reverse osmosis water and influent water is called water production rate.
The performance of RO membranes in water purification systems is usually monitored by measuring the ion removal rate, which is the percentage difference between the influent and effluent conductivity divided by the influent conductivity. The ion removal rate and water production rate depend on the water quality, inlet pressure, water temperature and RO membrane state.
Due to its excellent purification efficiency, reverse osmosis is a very efficient technique for removing most impurities. However, its water production rate is relatively low, so it is usually equipped with a water storage tank to temporarily store the produced water for use or further purification. The reverse osmosis device protects the subsequent system from blockage or contamination by colloids and organics, and its subsequent system is usually equipped with an ion exchange or electrodialysis device.
1) Ultrafiltration (UF): The continuous filtration method with a molecular cutoff of 5000 Daltons is called ultrafiltration. It is mainly used for purification or impurity removal of biological macromolecules. In the ultrapure water meter, this method is mainly to remove biological macromolecules such as nucleases and endotoxins in ultrapure water, so as to meet the strict requirements for ultrapure water in biological experiments.
2) Microfiltration (MF): The filtration of materials with a pore size between Olum.5um or 8um is called microfiltration. This method is used to remove particles and microorganisms in pure water, and there can be a flow path in-line microfilter or a water outlet microfilter.
3) Pre-filtration: The filtration of materials with a pore size above 5-8um is called pre-filtration. This method is mainly used in the water inlet of pure water instruments to remove large particles of impurities in tap water.
Adsorption method: Adsorption method refers to the adsorption and removal of some microorganisms, free chlorine and other impurities by the high porosity of activated carbon.
Photo-oxidation method: The photo-oxidation method uses 185nm or 254nm ultraviolet rays to kill and oxidatively decompose microorganisms in water, thereby controlling the total organic carbon (TOCI level) of ultrapure water.
Ion exchange method: With the continuous improvement of industrial production level, ion exchange resins are also being updated. It can be combined with several other technical means to produce electrodialysis, which can be regenerated online, which is higher than the exchange method.
1) Classical ion exchange (SDI): Generally, the anions and cations are placed in different containers, and after a period of use, they are basically in a saturated state, and off-line regeneration can be performed at this time. The purity of deionized water produced by this means is approximately 1 M-cm.
2) Ion exchange of nuclear grade resin: This is the most efficient one among ion exchange resin products so far, and pure water can reach 18.2M-cm grade I ultrapure water after its treatment. In the ultrapure water instrument, the nuclear grade anion and cation exchange resin is mixed and filled in a container for use. It is disposable and cannot be recycled.
3) Electrodialysis (EDI): This is a polymer exchange method that can be instantly regenerated under the action of an electric field, which is developed by integrating several technologies of ion exchange, ion selectivity through membrane and electric field. The method of electrodialysis is an upgraded version of the ion exchange method.
The biggest advantage of this technology is that in theory, there are no consumable materials, but it is characterized by a large one-time investment and EDI components have high purity requirements for heavy metal plasma in the influent water, otherwise it is very easy to be poisoned, and under the action of an electric field , unable to regenerate active ion exchange resin, had to replace EDI components. The real significance of the use of EDI lies in pharmaceutical factories and other enterprises that have strong requirements for certification, and can ensure continuous production. In the laboratory field, the use of EDI modules to produce water will increase the purchase cost and is not the most efficient choice. As an ion exchange, the longer the flow of water in the ion exchange resin, the better the exchange effect.
Wastewater Treatment System
It is to use physical, chemical and biological methods to treat wastewater to purify wastewater and reduce pollution, so as to achieve wastewater recycling and reuse, and make full use of water resources.
According to the degree of treatment, wastewater treatment (mainly urban domestic sewage and some industrial wastewater) can generally be divided into three levels:
Primary processing:
The task is to remove suspended solid pollutants from wastewater. For this reason, physical treatment methods are often used. Generally, after primary treatment, the removal rate of suspended solids is 70%~80%, while the removal rate of biochemical oxygen demand (BOD) is only about 25%~40%, and the purification degree of wastewater is not high.
Secondary treatment: The task is to greatly remove organic pollutants in wastewater. Take BOD as an example. Generally, after secondary treatment, BOD in wastewater can be removed by 80%~90%, such as the BOD content in water after urban pollution treatment. Can be lower than 30 ml/g. Most of the various treatment units of aerobic biological treatment can meet this requirement.
Tertiary treatment: The task is to further remove pollutants that were not removed by secondary treatment, including organic matter, phosphorus, nitrogen and soluble inorganic matter that were not degraded by microorganisms.
Tertiary processing is synonymous with advanced processing, but the two are not exactly the same. Tertiary treatment is to add one or several additional treatment units in order to remove certain pollutants, such as phosphorus, nitrogen, etc. from wastewater after secondary treatment; A processing unit or system added after secondary processing for the purpose of use. The tertiary treatment is more expensive and more complicated to manage. But it can make full use of water resources. A few countries have built some tertiary sewage treatment plants.
Laboratory wastewater mainly comes from the laboratory laboratories of various scientific research units and the scientific research and teaching laboratories of colleges and universities. Laboratory wastewater, especially its own special properties, is small in quantity, strong in discontinuity, high in hazard, and has complex and changeable components.
According to the nature of the main pollutants contained in wastewater, it can be divided into two categories: laboratory organic and inorganic wastewater:
Inorganic wastewater: mainly contains heavy metals, heavy metal complexes, acid and alkali, cyanide, sulfide, halogen ions and other inorganic ions.
Organic wastewater: Contains commonly used organic solvents, organic acids, ethers, polychlorinated biphenyls, organophosphorus compounds, phenols, petroleum, and grease substances.
In comparison, organic wastewater has a wider range of pollution than inorganic wastewater and brings more serious harm. Different wastewater has different composition of pollutants and different treatment methods and degrees. The treatment of laboratory wastewater is based on the principles of classified collection, local and timely in-situ treatment, simple operation, waste treatment and cost reduction.
The treatment of laboratory wastewater cannot be equal to the treatment of industrial wastewater, but a multi-unit treatment process system or targeted classification treatment is used to reduce the difficulty of treatment as much as possible, so that the treatment cost is lower and the operation is relatively simple. Laboratory organic wastewater treatment methods can learn from other organic wastewater treatment.
Generally speaking, organic wastewater treatment technologies mainly include biological methods and physicochemical methods:
For laboratory wastewater with high concentration of organic matter, strong toxicity and unstable water quality, biological method is not effective in treatment, while physicochemical method shows obvious advantages in the treatment of such wastewater. Laboratory drug recovery, sorting and recycling laboratory waste, can not only reduce environmental pollution, but also reduce chemical waste. For high-concentration laboratory organic wastewater, the organic solvents such as alcohols, lipids, organic acids, ketones and ethers are recycled and reused, and then treated by chemical methods; for high-concentration, toxic and unrecyclable organic wastewater , which requires centralized incineration.
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