Slaughterhouse Sewage Treatment Solution

Sources of Wastewater at Chicken Slaughterhouse

1) After live broilers are hung on the production line, empty chicken crates are automatically conveyed by conveyor to crate washing equipment for cleaning, generating washing wastewater laden with contaminants such as chicken manure.

2) Chicken slaughtering and defeathering processes include hanging live chickens, water-bath stunning, neck cutting, blood draining, scalding, plucking, claw cutting and rehanging. The wastewater produced in this stage features high COD concentration due to residual blood.

3) The overhead conveyor line for evisceration consists of eviscerating, viscera removal, head cutting and carcass rinsing, which yields wastewater mixed with grease and bloody water.

4) Chickens are put into pre-chilling units during pre-cooling procedure, resulting in oily wastewater.

Characteristics and Main Pollutants of Wastewater from Chicken Slaughterhouse

1. Wastewater Characteristics

The wastewater contains blood, grease, meat scraps, bone residues, stomach contents, feather and manure, alongside hot wastewater with varying pH values, organic solvents and solid residues. It is brownish-red in color and emits strong fetid odor.

Key characteristics include large total discharge volume, uneven effluent flow, high organic concentration, abundant impurities and suspended solids, high grease content, massive pathogenic microorganisms, as well as favorable biodegradability.

2. Main Pollutants

Primary pollutants in chicken slaughter wastewater consist of COD, BOD₅, ammonia nitrogen, suspended solids (SS) and animal & vegetable oil.

Typical index range for chicken slaughter wastewater: BOD₅: 750–1000 mg/L; COD: 1500–2000 mg/L; Ammonia nitrogen: 50–150 mg/L

Typical index range for meat product processing wastewater: BOD₅: 500–1000 mg/L; COD: 800–2000 mg/L; Ammonia nitrogen: 25–75 mg/L

3. Wastewater Production per Slaughter Unit (Statistical Data)

Statistical data on wastewater output per slaughtered animal:

Pig: 0.5–0.7 m³ wastewater per head

Cattle: 1.0–1.5 m³ wastewater per head

Sheep: 0.2–0.5 m³ wastewater per head

Chicken: 1.0–1.5 m³ wastewater per 100 birds

Duck/Goose: 2.0–3.0 m³ wastewater per 100 birds

Process Flow of Chicken Slaughter Wastewater Treatment

1. Pretreatment Unit

Grille: The incoming wastewater from chicken slaughter production features large water volume and a high concentration of suspended solids (SS). To reduce labor costs, mechanical grilles are adopted. Considering the uneven particle sizes of suspended solids in the wastewater, a combination of coarse and fine grilles is applied for graded interception of impurities.

Regulating Tank: Wastewater discharge from the workshop is concentrated in daytime with obvious fluctuation of water volume and water quality. Therefore, the regulating tank is designed with a long hydraulic retention time to balance water quantity and water quality of the system.

Air Flotation Unit: To ensure the long-term stable operation of the whole treatment system, especially the biochemical treatment unit, and reduce comprehensive operating costs, an air flotation unit is set as the primary physical treatment facility. The suspended solids in the wastewater have good floatability, which makes air flotation an efficient pretreatment process for solid-liquid separation.

2. Biochemical Treatment Unit

The anaerobic treatment adopts the Upflow Anaerobic Sludge Blanket (UASB) process to degrade most organic pollutants in the wastewater and reduce the organic load of subsequent aerobic treatment.

The aerobic treatment adopts the Anaerobic-Oxic (A/O) process, and the O-stage (oxic stage) applies the activated sludge method for further degradation of organic matters, ammonia nitrogen and other pollutants.

3. Comparison of Advanced Treatment Technologies for Sewage

The selection of advanced treatment processes is determined by the residual pollutant concentration of biochemically treated effluent and the local discharge standard requirements. Advanced treatment mainly includes physical and chemical treatment methods.

Physical treatment methods mainly include sedimentation, air flotation and filtration. The addition of chemical agents depends on the content of suspended solids, colloidal substances and their charge properties in the wastewater. Filtration technologies are divided into filter material filtration and membrane filtration. Chemical treatment methods are mainly catalytic oxidation technologies, including ultrasonic oxidation, ozone oxidation, supercritical water oxidation, Fenton oxidation and other mainstream processes.

Combined with the project effluent quality requirements and the actual water quality after biochemical treatment, coagulation and sedimentation is selected as the advanced treatment process in this design. Poly Aluminium Chloride (PAC) and Polyacrylamide (PAM) can be dosed as auxiliary chemicals when necessary to remove residual suspended solids and colloidal pollutants.

4. Selection of Sludge Dewatering Equipment

Common sludge dewatering methods are divided into mechanical dewatering and natural drying dewatering. Natural drying dewatering is only applicable to small-scale sewage treatment plants with low water and sludge yield.

Integrated mechanical concentration and dewatering equipment mainly includes belt filter presses, centrifugal sludge dewaterers and plate and frame filter presses. Centrifugal sludge dewaterers have the advantages of good operating environment, low flushing water consumption and no pressurization required. Although belt filter presses have disadvantages such as poor operating environment and easy filter cloth clogging, they are low in equipment cost, small in installed capacity and low in operation and maintenance costs.

The plate and frame filter press adopted in this design features small floor area, low water content of dewatered sludge, low equipment price, small installed capacity, low operation and maintenance cost, and no need for additional chemical agents for dewatering.