Machining

Analysis of wastewater characteristics

1. Wastewater is discharged intermittently, and there is a certain range of fluctuation in water quality and quantity, with a certain impact load, so it is necessary to set up a reasonable regulation system.
2. Because the production process uses a large amount of nitric acid, hydrofluoric acid, etc., the wastewater contains many fluoride ions, which are strongly acidic and corrosive. Therefore, the equipment and instrumentation selection need to pay special attention to the choice of materials.
3. The characteristics of pollutants in multi-stranded wastewater differ greatly, so it is necessary to carry out qualitative pre-treatment.
4. For wastewater with high nitrate-nitrogen content and low COD content, adding a certain amount of carbon source is necessary to ensure the growth of microorganisms in the biochemical system.

Wastewater treatment process analysis
Fluoride wastewater treatment
For high-concentration fluorine-containing industrial wastewater, the calcium salt precipitation method is generally used, i.e., lime is injected into the wastewater to make fluoride ions and calcium ions generate CaF2 precipitation and remove. This process has the advantages of a simple method, convenient treatment, and low cost. Still, there are shortcomings, such as difficulty in meeting the standard of treated effluent, slow sedimentation of mud and slag, and difficulty in dewatering.
The solubility of calcium fluoride in water at 18 ℃ is 16.3 mg/L and 7.9 mg/L according to fluoride ion, and calcium fluoride in this solubility will form precipitates. When the residual amount of fluorine is 10-20 mg/L, precipitate formation slows down. When water contains a certain amount of salts, such as sodium chloride, sodium sulfate, and ammonium chloride, the solubility of calcium fluoride will increase. Lime is cheap, but the solubility is low, and it can only be dosed in emulsion, and the dosage is high due to the production of CaF2 precipitate wrapped on the surface of Ca(OH)2 particles, so it can not be fully utilized. The total fluorine content in the wastewater can be reduced to about 10 mg/L by adding the mixture of lime and calcium chloride in the fluorine-containing wastewater after neutralization, clarification, and filtration with a pH of 7 to 8.
At present, various treatment methods are used for fluorine-containing wastewater at home and abroad, mainly chemical sedimentation, adsorption, mud coagulation and sedimentation, electrocoagulation, ion exchange resin method, reverse osmosis, liquid membrane method, electrohydraulic dialysis, etc. The methods adopted by the band are chemical sedimentation, adsorption, coagulation, and sedimentation, and other methods are less applied.

method	principle	Removal Effect	advantage	shortcoming
Chemical precipitation method	Add lime and other compound agents to the water	The fluoride content in water is 10~20mg/L.	Simple operation and low cost	A large amount of sludge
Activated Alumina Method	The process of removing fluoride from water by adsorbing and exchanging fluoride ions with activated alumina filter media	The fluoride content in water is 1-10 mg/L	General operation and low-cost	Requires regeneration, high operating cost
Resin defluorination	Conventional anion exchange resins are introduced into the polishing treatment of F- F-containing wastewater	Suitable for low-concentration fluoride wastewater treatment or deep treatment	Simple process and easy to use	Resin regeneration, high operating cost
Membrane separation	Mainly nanofiltration and reverse osmosis	The nanofiltration fluoride ion rejection rate is 50%; Reverse osmosis can completely remove fluoride ions. It is suitable for deep defluorination.	High defluorination efficiency and simple operation	High cost and high energy consumption
Fluoride removal agent	Fluorine removal is carried out using high molecular weight polymer as a defluorinating agent.	It can achieve the removal of low-concentration fluorine and is suitable for deep defluorination.	The fluoride ion concentration can be reduced to less than 1.5 ppm.	Slow settling

Comparison of various fluoride removal
Nitrogenous wastewater treatment
At present, the main treatment technology for nitrate wastewater can be divided into the physical method, chemical reduction method, and biological denitrification method, in which the physical-chemical method is to separate the nitrate in the original water so that the water meets the standard, chemical reduction and biological denitrification through chemical and biological effects on nitrate reduction so that the nitrate is converted into nitrogen to achieve the removal of nitrate. From the treatment point of view, the physical and chemical method is only the transfer of nitrate, but also needs to further deal with the separation of nitrate, and does not fundamentally remove nitrate pollution, the use of chemical reduction or biological denitrification of nitrate into nitrogen is the fundamental method of treatment of nitrate pollution.

Process flow description
(I) Machining wastewater
(1) Wastewater is firstly collected in the workshop to the collection pool for temporary storage and then elevated to 1# adjustment pool by pump, which plays the role of regulating water quantity and quality and sets mixer in the pool to prevent precipitation.
(2) The sludge feed pump is pumped into the filter press, and after pressing, the filtrate flows into the filtrate collection tank, disinfected with sodium hypochlorite filtered by bag filter, and sent to the water point of the machining workshop. When the water quality of the machining reuse pool deteriorates, it enters the mixing pool for discharge.

(II) Comprehensive wastewater
(1) Acid-washing wastewater (manual) and acid-washing wastewater (automatic) are firstly collected in the workshop to the collection tank for temporary storage and then lifted by pump to the 3# adjustment tank for mixing.
(2) Acid absorption tower wastewater is discharged to the 3# regulating pool for mixing, and then into the subsequent treatment unit.
(3) Into the pH adjustment pool, through the addition of lime, adjust the pH to about 10, the fluoride in the wastewater under alkaline conditions and Ca2 + generated insoluble CaF2, losing strong corrosive properties. Then PAC and PAM for a coagulation reaction to form a larger alum flower precipitation, precipitated in the form of sludge. After complete precipitation, the supernatant flows into the pH adjustment pool, and the sludge produced is transported to the materialized sludge tank, and then sent by the sludge pump to the plate and frame filter press for filtration, the filtrate is self-flowing to the filtrate collection pool, and then enters the adjusting pool for re-treatment.
(4) Reagent cleaning wastewater is collected in the workshop to the collection tank for temporary storage and then lifted to the 4# conditioning tank by the pump, and then mixed with the pre-treated pickling wastewater in the pH reconditioning tank.
(5) Living wastewater and single crystal furnace wastewater are collected and lifted to the 5# adjustment pool for mixing, and then enter the blending pool to mix with the pre-treated acidic wastewater to replenish the carbon source for the subsequent biochemical system.
(6) The effluent from the blending tank enters the AO biochemical system for COD degradation and biological nitrogen removal. The anoxic section mainly removes most of the total nitrogen by denitrifying bacteria, and the aerobic section further degrades the excess carbon source. The effluent flows into the secondary sedimentation tank, where mud and water are separated, the supernatant flows into the discharge tank, part of the settled sludge flows back to the anoxic tank, and the remaining part is discharged to the biochemical sludge tank by the pump.
(C) Make pure water concentrated water
(1) The concentrated water of pure water is collected in the workshop and stored in the collection pool and then lifted to the 6# regulating pool by the pump.
(2) The water from the regulating pool enters the coagulation and precipitation system, and further reduces the suspended matter and other pollutants in the wastewater by adding PAC and PAM. After precipitation, the wastewater is filtered by the filter into the reuse pipeline, and the sludge is discharged into the materialized sludge tank.
(D) Sludge dewatering
The sludge is pressed by a sludge dewatering machine, the mud cake is entrusted to a professional disposal organization for proper disposal, and the filtrate is returned to the conditioning tank for re-treatment.

Process design:
1. Machining wastewater treatment system
(1) Workshop wastewater collection tank
(2) Conditioning tank
(3) Filter liquor collection tank

2. Silicon core processing wastewater treatment system
(1) Workshop wastewater collection tank
(2) Conditioning tank
(3) Filtrate collection tank

3. Comprehensive wastewater treatment system
(1) Acid washing wastewater collection tank
(2) Reagent cleaning wastewater collection tank
(3) Domestic wastewater collection tank
(4) Single crystal furnace wastewater collection tank
(5) Conditioning tank
(6) pH adjustment tank
(7) Defluoridation reaction tank
(8) Flocculation reaction tank
(9) Sedimentation tank
(10) pH adjustment tank
(11) Blending tank
(12) Hypoxia tank
(13) Aerobic tank
(14) Secondary sedimentation tank
(15) Discharge tank

4. Pure and concentrated water treatment system
(1) Conditioning tank
(2) Coagulation and sedimentation tank
(3) Intermediate tank

5. Sludge dewatering system