The wastewater from slaughterhouses is difficult to treat due to its high concentration of organic matter, suspended solids (such as blood, grease, hair, internal organ debris, etc.) and strong fishy smell. Polyacrylamide (PAM), as an efficient high-molecular flocculant, plays a significant role in the treatment of slaughterhouse wastewater. This article will elaborate on aspects such as the characteristics of wastewater, the mechanism of action of PAM, key points for selection, treatment processes, and case analyses.
I. Characteristics and Treatment Difficulties of Slaughterhouse Wastewater
The water quality is complex: The wastewater contains a large amount of organic matter such as protein, fat, and blood, with extremely high COD (Chemical Oxygen Demand) and BOD (Biochemical Oxygen Demand), and also contains oils, suspended solids, and a small amount of heavy metal ions.
Strong biodegradability but large fluctuations: The wastewater has good biodegradability, but the water quality and quantity are significantly affected by factors such as slaughter volume and season. The treatment process needs to have strong adaptability. 69.
High viscosity and color: The wastewater is reddish-brown in color and has a relatively high viscosity, which limits the efficiency of traditional physical sedimentation or biological treatment.
Ii. Mechanism of Action of Polyacrylamide
Polyacrylamide achieves wastewater purification through the following mechanisms:
Adsorption bridging effect: The long-chain structure of PAM can adsorb suspended particles, form large flocs, and accelerate solid-liquid separation.
Charge neutralization: Cationic PAM neutralizes negatively charged colloidal particles through positive charge, reducing repulsive force and promoting flocculation.
Thickening and resistance reduction: PAM can reduce the viscosity of wastewater and improve the operational efficiency of subsequent treatment units (such as pipeline transportation and air flotation) by 57%.
Iii. Selection and Application Points of Polyacrylamide
Model selection
Anionic type (APAM) : It is suitable for wastewater with neutral or alkaline pH, especially in cases with low oil content. It is often used in combination with inorganic coagulants (such as polyaluminium chloride PAC) to enhance the removal rate of suspended solids by 26%.
Cationic type (CPAM) : It is more suitable for high-oil wastewater and wastewater with negatively charged colloidal particles. It can effectively remove COD and decolorize, and is especially suitable for enhanced treatment in low-temperature environments in winter.
Molecular weight and ion degree: High oily wastewater requires PAM with high molecular weight and low ion degree. When the water volume is large, choose products with low molecular weight and high ion degree.
2. Dosage method and dose optimization
The optimal model and dosage (usually 0.1-0.3% solution) should be determined through small-scale laboratory tests to avoid excessive sludge bulking or increased costs.
It is recommended to be used in combination with coagulants such as PAC to form a “coagulation-flocculation” synergistic effect and improve the treatment efficiency by 78.
Iv. Typical Processing Techniques and Case Analysis
1. Physical-chemical and biochemical combined process
Pretreatment stage: The grid intercepts large particle impurities, the regulating tank homogenizes and equalizes the volume, the air flotation device adds PAC and PAM to remove oil and suspended solids, and the COD removal rate can reach over 30%.
Biochemical treatment stage: The hydrolysis acidification tank decomposes large-molecule organic substances into small-molecule ones, and then further degrades them through the A/O process (anaerobic-aerobic). Finally, the standard discharge is achieved through chlorine dioxide oxidation or membrane separation technology.
2. Case reference
Case of a slaughterhouse in Henan Province: The process of “air flotation + anionic PAM+ hydrolysis acidification + contact oxidation” was adopted, with the removal rate of suspended solids reaching over 90%, and the COD of the effluent was reduced to below 100 mg/L, meeting the “Discharge Standard of Water Pollutants for Meat Processing Industry” 78.
Treatment plan for low-temperature environments in the north: In winter, add enhanced cationic PAM and combine it with Fenton oxidation technology to effectively solve the problem of low microbial activity at low temperatures and ensure stable treatment effects.
V. Precautions and Future Directions
Test first: The PAM model should be determined through beaker tests and on-site pilot tests to avoid directly applying the general solution 28.
Comprehensive treatment technology: PAM has a limited effect on the removal of heavy metals and needs to be combined with chemical precipitation, adsorption or membrane technology to achieve comprehensive purification.
Sludge disposal: The sludge produced by flocculation needs to be dewatered (such as through plate and frame filter press) for resource utilization to reduce secondary pollution by 78%.
In the future, with the increasing environmental protection requirements, the modification research of PAM (such as the improvement of salt resistance and shear resistance) and its integration with intelligent control systems will further enhance the efficiency and sustainability of slaughterhouse wastewater treatment.
Through reasonable selection and process optimization, polyacrylamide has demonstrated remarkable economic and environmental benefits in the treatment of slaughterhouse wastewater, providing important technical support for the industry to achieve green production.
