Core processing technology flow (quality based processing)

1. Domestic sewage treatment process (mainly standard discharge)

Domestic sewage has strong biodegradability, and the treatment goal is to meet the third level standard (discharge into municipal pipelines) or first level standard (direct discharge, special requirements required) of the Comprehensive Wastewater Discharge Standard (GB8978-1996). Typical process:

Grille → regulating tank → septic tank/biochemical treatment unit → sedimentation tank → disinfection tank → discharge/reuse

Grille: intercepts large impurities (such as paper scraps and plastic bags) in sewage to prevent blockage of subsequent equipment;

Regulating pool: Balance water quality and quantity (with large fluctuations in domestic sewage discharge) to avoid impacting subsequent biochemical systems;

Biochemical treatment unit: the core process that utilizes microorganisms to degrade organic matter and ammonia nitrogen. Common processes include:

Sedimentation tank: Separate activated sludge or biofilm generated by the biochemical system to reduce effluent SS;

Disinfection pool: sodium hypochlorite or chlorine dioxide is used for disinfection to kill pathogenic microorganisms such as Escherichia coli, ensuring that the effluent meets the hygiene standards.

2. Treatment process of production wastewater (equipment cleaning+ground flushing water) (mainly for recycling)

Production wastewater contains high salt and high pollutants, making it difficult to discharge directly and wasting water resources. The "treated and reused" mode is preferred (such as for workshop flushing, equipment cooling, and spray dust reduction). Typical process:

Preprocessing → Main processing → Advanced processing → Reuse/compliant emissions

(1) Pre treatment stage: Removing suspended solids and some pollutants

Grille → sedimentation tank → coagulation sedimentation/air flotation → regulating tank

Grille+sedimentation tank: first intercept large impurities and sand and gravel to avoid wear on subsequent pump bodies and pipelines;

Coagulation sedimentation/air flotation: core pretreatment process to solve high SS problems:

Regulating tank: Adjust the water quality of production wastewater (such as pH and pollutant concentration) to create stable conditions for subsequent treatment. At the same time, acid-base regulators (such as sulfuric acid and sodium hydroxide) can be added to adjust the pH to 6-9 (suitable for subsequent treatment).

(2) Main processing stage: degradation of organic matter and denitrification and phosphorus removal

High salt, high COD, and high ammonia nitrogen in production wastewater require a combination of "physicochemical+biochemical" processes to avoid high salt inhibiting microbial activity

Emulsification/oxidation pretreatment → high salt biochemical system → deep desalination unit

Emulsification/oxidation pretreatment (optional): If the wastewater contains recalcitrant organic compounds or oils, the "Fenton oxidation method" (H ₂ O ₂+Fe ² ⁺) or "ozone oxidation method" can be used first to oxidize and decompose large molecular organic compounds, improve the biodegradability of the wastewater, and reduce some COD;

High salt biochemical system: The core link requires the selection of salt tolerant microorganisms (through domestication and cultivation), commonly used processes are "salt tolerant A/O process" or "MBR (membrane bioreactor) process":

Deep desalination unit: If high reuse requirements are needed (such as low salt water for equipment cleaning), high salt in the wastewater needs to be removed. The commonly used processes are "reverse osmosis (RO)" or "electrodialysis":

(3) Deep processing and reuse

Filtering unit: After deep treatment, it is necessary to use a "quartz sand filter+activated carbon filter" to remove small suspended solids and residual chlorine from the water, protecting the reuse pipelines and equipment (avoiding scaling or corrosion);

Reuse system: The treated production wastewater is preferentially reused for "workshop floor flushing, equipment cleaning, granulation section spraying and dust reduction" to achieve water resource circulation. The remaining small amount of wastewater (if it meets the standard) can be discharged into the municipal pipeline network (in accordance with the first level standard of the "Comprehensive Wastewater Discharge Standard").

3、 Key process control points

Microbial domestication of high salinity wastewater: When the salinity of production wastewater is high, it is necessary to domesticate the microorganisms in the biochemical system in advance (gradually increase the inlet salinity to allow the microorganisms to adapt), otherwise it will lead to microbial inactivation and affect the treatment effect;

PH adjustment: The pH of wastewater from compound fertilizer production may be slightly acidic (such as containing residual phosphoric acid) or alkaline (such as containing residual potassium salt). It is necessary to strictly control the pH in the adjustment tank at 6-9 to avoid damaging the biochemical system or corroding equipment;

Sludge treatment: The sludge generated during the treatment process (such as coagulation and sedimentation sludge, biochemical sludge) contains unreacted fertilizer components and needs to be temporarily stored in accordance with the "General Industrial Solid Waste Storage and Landfill Pollution Control Standards" (GB18599-2020). After dehydration (plate and frame filter press), it can be returned to the fertilizer production system for re granulation (resource utilization) to avoid solid waste pollution;

Reuse water quality monitoring: The recycled wastewater needs to be regularly monitored for salinity, SS, pH and other indicators to prevent long-term reuse from causing equipment scaling (high salt is prone to crystallization) or pipeline corrosion (abnormal pH).

4、 Principle of process selection

Small production line: With a small daily discharge of wastewater (such as less than 50m ³), the process can be simplified to "grid+coagulation sedimentation+activated carbon filtration" and reused for ground flushing; Domestic sewage is discharged into the municipal pipeline network after being treated with "septic tank+disinfection";

Medium to large production lines: A complete "pretreatment+salt tolerant biochemistry+deep desalination" system is required to achieve high proportion reuse of production wastewater (with a reuse rate of over 70%), and A/O process is used for domestic wastewater to ensure compliance;

Special requirement scenario: If the local environmental protection requirements are strict (such as not allowing discharge into the municipal pipeline network), it is necessary to add an "evaporation crystallization" unit (to treat high salt concentration water) to achieve "zero discharge" of wastewater (but with high investment and operating costs, suitable for areas with high environmental standards).

In summary, the core of wastewater treatment in compound fertilizer production lines is "quality separation treatment and resource utilization", which solves the problems of high salt and high pollutants through targeted processes, while also considering environmental compliance and cost control.