Treatment Methods for Slaughterhouse Wastewater

Amid the roar of machinery, streams of reddish wastewater laden with grease and blood foam continuously discharge from the slaughtering workshop. However, at the treatment station on the other end of the factory premises, through a series of "mysterious" processes, this foul-smelling wastewater gradually clarifies, eventually transforming into a clear, flowing stream. This scene epitomizes the modern slaughter industry's response to environmental challenges and its pursuit of green development. Slaughterhouse wastewater treatment has evolved from a headache-inducing problem into a new starting point for resource recycling.

Slaughterhouse wastewater is far from ordinary sewage. It primarily originates from pre-slaughter rinsing, bleeding during slaughter, offal processing, carcass washing, and floor cleaning, resulting in exceptionally complex composition.

"High load" is its primary characteristic.The wastewater contains substantial amounts of blood, grease, meat scraps, feces, and undigested food, leading to extremely high concentrations of organic matter. Its Chemical Oxygen Demand (COD) typically ranges from 2000 to 8000 mg/L, or even higher, which is several tens of times that of ordinary domestic sewage."High hazardous potential" follows closely. The wastewater is rich in proteins, fats, etc. If discharged untreated, it would severely deplete oxygen in water bodies, causing fish and other aquatic life to die, emitting foul odors, and damaging the ecological environment. Furthermore, it may contain pathogenic microorganisms, posing public health risks.

Faced with such "formidable" wastewater, traditional simple sedimentation or direct discharge methods have long been strictly prohibited. Efficient, systematic treatment processes have become imperative for the survival and development of slaughter enterprises.

Today, mainstream slaughterhouse wastewater treatment is like a precise "purification relay race," employing a combined process of "pretreatment + primary treatment + advanced treatment."

Pretreatment: Intercepting the "Big Pieces." Wastewater first passes through screens to intercept large debris like feathers and bone fragments. It then enters a grease trap/grit chamber, where gravity causes grease to float and sand particles to settle for preliminary separation. To further remove finer suspended solids and some grease, the dissolved air flotation (DAF) process is commonly used. Tiny bubbles adhere to impurities, causing them to float to the surface for skimming. This stage is akin to giving the wastewater a "coarse screening" and "degreasing" pretreatment.

Primary Treatment: Tackling the "Core Fortress."This is the main battlefield for removing organic pollutants, with the core being the "devouring" action of microorganisms. The most widely applied method currently is the anaerobic-aerobic biological combined process.

Anaerobic Treatment: Under oxygen-free conditions, anaerobic microorganisms break down complex organic matter in the wastewater into methane, carbon dioxide, etc. This stage efficiently removes a large portion of the COD, and the generated biogas can be recovered for energy use. Reactors like the Upflow Anaerobic Sludge Blanket (UASB) function as highly efficient "biological digesters."

Aerobic Treatment:Wastewater after anaerobic treatment enters the aerobic stage. Aeration equipment (e.g., blowers) injects oxygen into the water, "activating" aerobic microorganisms that further decompose the remaining organic matter into carbon dioxide and water, forming sludge that settles easily. Common choices include the Sequencing Batch Reactor (SBR) or biological contact oxidation processes.

Advanced Treatment and Disinfection: Ensuring "Safe Effluent." Water after biological treatment may still contain residual nutrients (like nitrogen, phosphorus), color, and pathogens. Therefore, advanced treatment is often added, such as coagulation-sedimentation, biofiltration, or membrane filtration, to ensure stable, compliant effluent quality. Finally, disinfection using chlorine dioxide or ultraviolet (UV) light is essential to completely kill pathogenic microorganisms, guaranteeing the safety of the discharged water.

Thus, the turbid, foul-smelling slaughterhouse wastewater finally completes its "transformation" into compliant, clear water.