Application of Polyacrylamide in API Production Wastewater Treatment

The characteristics of API(active pharmaceutical ingredient) production wastewater are summarized as "three highs, two poors and one fluctuation": high concentration, high toxicity, high salinity, poor biodegradability, complex components, and drastic fluctuations in water quality and quantity.

• Core Water Quality Features

1. Extremely high pollutant concentration‌: Its COD usually ranges from thousands to tens of thousands mg/L, and some high-concentration mother liquor even exceeds 100,000 mg/L;
2. Extremely complex components‌: It contains unreacted raw materials, intermediates, by-products, residual solvents, catalysts and heavy metal ions;
3. Strong biological toxicity‌: Residual antibiotics, bacteriostatic agents, nitro compounds and halogenated hydrocarbons have strong inhibitory or lethal effects on microorganisms;
4. Poor biodegradability‌: The BOD/COD ratio is generally lower than 0.3, and some chemical synthesis wastewater is even lower than 0.2, containing a large number of refractory heterocyclic and benzene ring structures;
5. High salinity‌: The total dissolved solids (TDS) concentration is often 1% to 5% or even higher, and high osmotic pressure will cause ordinary microorganisms to dehydrate and deactivate;
6. Large fluctuations in pH and temperature‌: The pH of discharged water varies widely (from 2 to 12), and some process wastewater has a relatively high temperature and is discharged intermittently in a pulse mode.

• Differences in Characteristics by Category

1. Chemical synthesis type‌: It has the highest toxicity and the most prominent refractory property, containing a large amount of organic solvents and synthetic intermediates, with the lowest B/C ratio and high salinity;
2. Fermentation type‌: It has high ammonia nitrogen and sulfate content. Although its biodegradability is relatively good, high sulfate will be reduced to sulfide under anaerobic conditions, inhibiting methanogens;
3. Extraction type‌: It has high suspended solids (SS) and chroma, containing plant fibers, pigments, tannins, etc., with SS concentration up to thousands of mg/L and deep color.

• PAM role in API production wastewater treatment

Polyacrylamide (PAM) is mainly used as a ‌high-efficiency flocculant‌ and sludge dewatering agent in the treatment of wastewater from active pharmaceutical ingredient (API) production. Through charge neutralization and adsorption bridging effects, it addresses the challenges posed by pharmaceutical wastewater, such as complex composition, stable colloids, and poor biodegradability, significantly improving solid-liquid separation efficiency and reducing sludge moisture content.

Coagulation-sedimentation Pretreatment‌: Combined with inorganic flocculants (e.g., polyaluminum chloride, polyferric sulfate), it rapidly removes suspended solids, colloids, and part of the COD in wastewater, enhancing the biodegradability of subsequent biochemical treatment.

Advanced Sludge Dewatering‌: Dosed during filter pressing or centrifugal dewatering, it remarkably reduces sludge moisture content (down to 80%-85%), cuts down sludge volume and subsequent disposal costs.

Advanced Effluent Purification‌: Applied in secondary sedimentation tanks or final sedimentation tanks to further remove fine suspended particles, ensuring the effluent quality meets discharge standards.

• Selection and Dosing Strategy

Due to the large variation in characteristics of API wastewater, the model must be precisely selected according to pH value, organic matter concentration and charge properties:

1. Cationic PAM (CPAM)‌: The ‌most commonly used type‌. Suitable for sludge dewatering and wastewater containing a large amount of organic colloids. It is recommended to choose products with an ionic degree of ‌60%-70%‌ and a molecular weight of about ‌9 million‌, which can effectively neutralize negatively charged organic sludge particles.
2. Anionic PAM (APAM)‌: Applicable to wastewater with ‌neutral or alkaline‌ pH, positively charged suspended particles or high inorganic content. Its long-chain structure accelerates sedimentation.
3. Non-ionic PAM (NPAM)‌: Suitable for ‌acidic‌ environments (pH < 7) or low-temperature refractory wastewater, avoiding charge interference.

Dosing Principle‌: Always follow the principle of "bench test before field application". Usually, add inorganic flocculants first to destabilize colloids, then add PAM for flocculation. The dosage of PAM is generally 1/50 of that of inorganic flocculants; excessive dosage will cause colloids to restabilize.

• Key Operational Precautions

Dissolution Specifications‌: Prepare a ‌0.1%-0.2%‌ aqueous solution, control the stirring speed at 70-100 r/min, and the dissolution time at 40-60 minutes. Never pour the powder all at once to avoid caking.

Water Quality Adaptation‌: For antibiotic wastewater with high salinity and high toxicity, select salt-tolerant and high-purity products, with residual monomer content below 0.1% to prevent secondary pollution.

Dynamic Adjustment‌: Fine-tune the dosage regularly with the fluctuation of inlet water quality, avoiding fixed dosage that causes chemical waste or poor treatment effect.

In practical applications, it is recommended to conduct beaker tests first to determine the optimal model and dosing point, so as to balance the treatment effect and operating cost.