Enzymes commonly used in the degradation of phenol-containing wastewater

Peroxidase is one class of oxidoreductase produced by microorganisms or plants.It can catalyze the oxidative decomposition of peroxides, and peroxidase can be activated by hydrogen peroxide (H:O:). In the catalytic process,H:O: first the oxidase, then the enzyme oxidizes the substrate. 
1. Horseradish Peroxidase (HRP) and Lignin Peroxi-dase (LIP) are two kinds of peroxidase that have been studied and applied widely.The former can catalyze the oxidative degradation of many toxic aromatic compounds in the presence of hydrogen peroxide, including phenol, aniline, benzidine and related isomers.
HRP has two important characteristics in the treatment of wastewater pollutants:
The first is that the catalyzed product is an insoluble precipitate, which is conducive to subsequent process filtration or precipitation removal.
The second is the wide range of active temperature and pH.
Industrial wastewater containing aniline, hydroxyquinoline, carcinogenic aromatic compounds (such as benzidine, naphthylamine) is often treated by HRP.
In addition,HRP can also form polymers with some difficult to remove pollutants and precipitate, which can improve the removal efficiency. For example, PCBS can precipitate with phenols at the same time, and both are removed at the same time.
2. Lignin peroxidase (also called lignin enzyme,Ligninase) is a peroxidase produced by white rot fungi that can be used to treat a variety of refractory aromatic compounds.
Lignin enzyme plays an important significance in the process of lignin depolymerization, and its mechanism is similar to that of HRP. The relationship between the stability of the enzyme and pH should be mainly considered, because the activity of the enzyme is suppressed at low pH, and the stability increases with the increase of pH. Generally, the phenol removal system is composed of high concentration of enzymes, pH greater than 4.0 and a certain amount of hydrogen peroxide.
The results showed that the lignin peroxidase immobilized by porous ceramics did not affect the activity, and the degradation performance of aromatic substances was good. When plant peroxidase is used to treat wastewater containing 2, 4-dichlorophenol with concentration up to 850mg/L, the removal rate is close to that of pure HRP.
3. Polyphenoloxidase is a oxidoreductase that catalyzes the oxidative degradation of phenolic substances.
Polyphenoloxidase is divided into two types: tyrosinase and laccase, and the catalytic reaction requires the participation of molecular oxygen, but does not require coenzymes. Tyrosinase, also known as phenolase or catecholase, catalyzes the two successive reactions:
①Monomolecular phenol and molecular oxygen form catechol by REDOX;
②Catechol dehydrogenation form to benzoquinone, benzoquinone is very unstable, through non-enzymatic catalytic polymerization to form water insoluble products, simple filtration can be removed.
Tyrosinase has been successfully used to remove industrial wastewater with phenol concentration of 0.01~1.0g/L. Chitin immobilized tyrosinase treatment phenol containing wastewater, removal rate reach up to 100% within 2 hours, it is still active after it is repeated use 10 times. Laccase can remove toxic phenols through polymerization reaction and can catalyze the degradation of many phenolic substances at the same time.

Enzymes commonly used in the degradation of pollutants in papermaking wastewater

Peroxidase and laccase horseradish peroxidase and lignin peroxidase can also be used for decolorization of papermaking wastewater.
The mechanism of lignin peroxidase is to oxidize benzene ring units into cationic groups that can be automatically degraded. The treatment effect of immobilized peroxidase and laccase was better than that of free enzyme. Laccase can also remove chlorophenols and chlorinated lignin from bleaching wastewater by precipitation.
There are a lot of mixed colloids of starch and clay in the wastewater of papermaking with cellulase and amylase.
The immobilized a-amylase can hydrolyze the colloidal suspended starch continuously and precipitate the suspended fiber to separate and remove it. Batch method or column loading method can be used for continuous treatment of paper mill wastewater by immobilized a-amylase.
100mg/L alum is added to the former, which can remove 80% of suspended matter in wastewater. In the latter, it is immobilized a-amylase is placed in a plexiglass reactor, and the wastewater flows through the reactor from bottom to top.
The high content of cellulose in papermaking wastewater can be used as raw material for ethanol production. The mixed enzyme system consisting of cellobiose hydratase, cellulase and β-glucoase can be used for waste cellulose conversion.

Enzymes commonly used in the degradation and treatment of cyanide-containing wastewater

Cyanide in plants is usually found in the form of Cyanogenic glycosides, such as amygdalin in almonds. Cyanide is also widely used in chemical synthesis, artificial fabrics, rubber industry, pharmaceutical industry, ore leaching, coal treatment, electroplating and other fields. Cyanide is an inhibitor of metabolism, which is fatal to humans and other organisms. The enzymes commonly used in the harmless treatment process of cyanide mainly include:
①Cyanase converts cyanide to ammonia and formates in a one-step reaction.
The cyanase activity was not affected by common cations such as Fe and Zn and organic substances such as acetic acid, formamide and acetonitrile. The optimal pH range is 7.8~8.3.
②Cyanide hydratase is also called formamide hydrolase.
This enzyme hydrolyzes cyanide to formamide. After immobilization, the stability is obviously improved, which is more conducive to the treatment of cyanide-containing wastewater.

Enzymes commonly used in the treatment of food processing wastewater

Food industry wastewater is generally non-toxic and easily decomposed or converted into economically valuable products.
①Protease belongs to a group of hydrolases
Protein in wastewater can be converted into animal feed after hydrolysis by protease. Some species of the genus Bacillus are often sources of proteases, such as alkaline proteases from Bacillus Subti-lis that treat poultry feathers after slaughter to produce high-protein feed.
②Starch in amylase waste is hydrolyzed by amylase and converted into monosaccharides, which can be used as fermentation raw materials
Amylase is divided into a-amylase, β-amylase and so on. A-amylase converts starch into small molecule compounds, which are further degraded into glucose by glucosylase. Lactic acid was obtained by fermentation of lactic acid bacteria with glucose as raw material, and the polymerized polylactic acid could be used to produce degradable plastics.

Other pollutants

It is very important to develop effective microbial and enzymatic treatment techniques for pesticide contaminants.
Because of the specificity of enzyme action, it can only remove one or several specific pollutants, and the pollutants in wastewater are diverse, and the development of multiple enzyme systems is more obvious than the use of a single enzyme. The immobilized enzyme technology can also extend the service life of the enzyme and reduce the operating cost.
German research institutions immobilized 9 kinds of enzymes degrading parathion pesticides on porous silica gel to make enzyme columns. The removal rate of parathion pesticides in wastewater reached more than 95%, and the enzyme activity was not significantly lost after continuous work for 70 days.
It is reported that the National Institute of Resources and Environment of Japan has successfully used tyrosinase, peroxidase and laccase to treat toxic compounds in wastewater. Potentially dangerous chemicals are oxidized by enzymes and converted into precipitates that can be degraded by anaerobic bacteria, thus achieving the purpose of detoxification.
French Industrial Research Institute uses immobilized enzymes to treat industrial wastewater, and the immobilized enzymes are made into enzyme cloths, enzyme sheets, enzyme granules or enzyme columns. When treating static wastewater, use enzyme cloth or enzyme sheet directly. When treating mobile wastewater, the height and inner diameter of glass or plastic enzyme column are determined according to the type and amount of sewage contained in the wastewater.
Different immobilized enzymes were selected according to the different substances treated. The immobilized cyanide-degrading enzyme and the fixed phenol-removing enzyme were loaded into one column to achieve the common removal of cyanide and phenols, and the enzymes that could not coexist could be loaded into the column separately.
Mobite GmbH of Germany and Agrecol of the United States use immobilized enzymes to remove nitrates from groundwater. The enzyme is fixed to the polymer matrix. Catalyze the reduction of nitrate to nitrite, which is converted to nitrogen in the bioreactor.
The immobilized composite enzyme system of Candida tropicalis can be used to treat phenol-containing wastewater, and the immobilized enzyme system of Clostridium butyricum can be used to treat alcohol production wastewater, and the hydrogen produced is an important energy material, realizing the transformation from waste to treasure.
Lysozyme is an enzyme that can catalyze the cracking of some bacterial cell walls. Japanese scholars have successfully treated biodegradable black humic acid and organic substances similar to black humic acid in wastewater by immobilizing lysozyme technology.
The basic requirements of enzyme reactor wastewater treatment are as follows:High volumetric productivity; The reaction conditions are easy to control; Easy continuous and automatic operation; Low energy consumption, less pollution; Easy processing, low investment.
Enzyme technology treatment of environmental wastewater need to pay attention to the below problems:
①The effect of toxic substances on enzyme activity. The toxic substances here may be original, or they may be produced by enzymatic processes. Therefore, the biochemical mechanism of enzyme-catalyzed process, especially the production of toxic substances, should be fully studied before constructing the process route.
②Proper disposal of solid substances such as phenolic precipitates produced during enzyme treatment. The secondary environmental pollution caused by combustion or burial process should be fully considered.
③Low-cost preparation of enzymes. At present, due to the high investment in enzyme separation, purification and production, the application of enzymes in environmental protection is limited to a certain extent.
④Development of efficient enzyme preparations. Because the treatment of high concentration of pollutants requires high enzymatic catalytic activity and strong stability.