Meat processing wastewater treatment equipment

　　Meat-processing wastewater is industrial effluent generated during meat processing. It typically comprises two main components—slaughtering and meat processing—and may also include ancillary facilities for producing by-products such as edible oils, gelatin, and soap. The wastewater originates primarily from processes including slaughter, dehairing, carcass splitting, evisceration, and cleaning, as well as from rinsing workshop equipment and floors. It contains blood, hair, fats, meat fragments, and various impurities, resulting in poor water quality: BOD5 ranging from 300 to 2,200 mg/L, suspended solids from 600 to 3,000 mg/L, oil and grease concentrations of 200 to 1,000 mg/L, and coliform counts between 2.38 × 10^6 and 2.38 × 10^7 CFU/L. The volume of wastewater is substantial; approximately 10 tons of wastewater are produced per ton of live livestock slaughtered. Treatment should preferably employ a segregated‑flow approach, with separate streams for oily, non‑oily, and fecal‑containing wastewaters, followed by combined treatment in a secondary biochemical stage. Common methods include the activated sludge process, biofilters, rotating biological contactors, and integrated anaerobic–aerobic lagoon systems.

　　Overview of Meat Processing Wastewater

　　Sources of Meat Processing Wastewater

　　The production process of slaughter and meat processing generally proceeds as follows: prior to slaughter, livestock undergo quarantine inspection and acceptance; upon entering the slaughter area, they are first stunned using mechanical, electrical, or chemical methods, then hung by their hind legs, their veins are severed, and they are bled. Cattle are skinned mechanically, whereas pigs are typically not skinned—instead, their carcasses are immersed in a scalding tank at 60°C to loosen the hair before it is removed. Next, the carcass is eviscerated, with edible and non‑edible parts separated; the carcass is then washed, cut into portions, chilled, and further processed into various meat products, such as fresh meat, marinated or seasoned preparations, and cured, smoked, or canned meats.

　　Wastewater from slaughterhouses and meat processing plants is primarily generated during the slaughtering and pre‑processing stages. It originates mainly from pen‑washing, pre‑slaughter rinsing, and operations such as slaughter, bleeding, dehairing, carcass breakdown, cavity opening and splitting, and the cleaning of viscera and intestines. Certain wastewater is also discharged from processes like fat extraction, boning, cutting, and the production of by‑products. In addition, meat processing facilities produce cooling water from refrigeration rooms, as well as domestic sewage from workshop sanitation equipment, laundry facilities, office buildings, and on‑site welfare amenities.

　　Water Quality Characteristics of Meat Processing Wastewater

　　Meat-processing wastewater contains substantial amounts of blood, fats, grease, hair, meat scraps, organ debris, undigested feed, and fecal matter. It exhibits an unappealing reddish‑blood color and a repulsive, bloody odor. Furthermore, this wastewater harbors pathogenic bacteria such as fecal coliforms, fecal streptococci, and Salmonella, which pose risks to human health; however, it typically does not contain toxic substances.

　　The pollutants in meat-processing wastewater are primarily organic substances existing in dissolved, colloidal, and suspended forms. The main pollution indicators include pH, BOD, COD, and SS, along with total nitrogen, organic nitrogen, ammoniacal nitrogen, nitrate nitrogen, total solids, total phosphorus, sulfate, sulfide, and total alkalinity. Microbiological indicators comprise Escherichia coli.

　　Like typical industrial wastewater, the quality of meat-processing effluent is influenced by factors such as the type of raw material processed, the production process, water consumption, the skill level of workers, and the sophistication of equipment, resulting in considerable variability. Not only do domestic and international datasets exhibit substantial differences, but even within China, effluents from different manufacturers can vary significantly in their characteristics.

　　Wastewater Treatment Plan for Meat Processing

　　There are many treatment options for meat-processing wastewater. However, for a specific meat-processing plant, selecting the most appropriate treatment scheme is a question that warrants careful study. Consequently, there is no single “best” treatment solution that fits every situation; each approach has its own limitations and requires particular operating conditions. The design of an optimal treatment plan can only be accomplished through a thorough understanding of the wastewater’s characteristics, coupled with comprehensive analysis and consideration of all relevant factors. In general, when determining a treatment strategy, it is essential to assess and take into account the following issues:

　　1. Can the factory’s wastewater be discharged directly into the municipal sewer system for treatment at a city‑level wastewater treatment plant, or can it be combined with other nearby wastewater streams of similar characteristics for joint treatment?

　　2. Are there any readily available stabilization ponds or land‑based systems nearby that can treat meat‑processing wastewater, and can they be operated year-round? How will the issue of wastewater treatment during non‑peak water‑use seasons be addressed? When assessing feasibility, it is essential to consider not only technical and economic factors but also environmental and social considerations.

　　3. Is it feasible to reduce water consumption through in-plant controls, thereby minimizing the discharge of associated wastes and lowering the load on wastewater treatment?

　　4. After determining that an on-site wastewater treatment plant is required, the following factors should be considered when selecting a treatment process: whether wastewater recycling will be implemented; the characteristics of the wastewater in terms of quality and quantity; the level of treatment needed to meet discharge standards; local regulatory requirements; capital and operating‑maintenance costs; the availability of electrical power; the level of operational management; the destination of sludge disposal; and land‑use considerations, among others.

　　When evaluating whether to implement wastewater reuse, it is essential to take the plant’s water supply situation into account holistically to determine whether such reuse is necessary and economically and technically feasible. At the same time, a clear understanding of the potential applications and anticipated volumes of reused water is required to select a treatment scheme that is both technically viable and economically sound. In general, when wastewater has high concentrations, large flow rates, or stringent discharge standards, an anaerobic–aerobic serial treatment process is recommended; if anaerobic treatment is not feasible due to environmental constraints, an aerobic process should be adopted; when capital and operating costs are tight, simplified treatment technologies should be prioritized; under conditions of limited power supply, anaerobic treatment should be given preference; and when operational management capabilities are uncertain, simpler treatment methods are advisable. In practical applications, these principles should be integrated and balanced to ensure the selection of the most appropriate treatment solution for the specific circumstances.

　　Meat Processing Wastewater Treatment Process

　　Meat-processing wastewater is a highly biodegradable, high‑suspended‑solids organic effluent with significant variability in both water quality and flow rate. First, it exhibits pronounced seasonality, with discharge volumes fluctuating markedly over the course of a year. Second, it is characterized by non‑continuous operation, with substantial diurnal variations; the hourly variation coefficient typically exceeds 2.0. Treatment of this type of wastewater generally relies on biological processes, encompassing aerobic, anaerobic, and facultative systems. Among these, the activated sludge process is currently the most widely applied and mature technology for treating meat‑processing wastewater in China. Aeration methods may include shallow aeration, jet aeration, extended aeration, and oxidation ditches. Meanwhile, the sequencing batch reactor (SBR) process has gained widespread recognition and adoption worldwide in recent years as an advanced biological treatment technology. It integrates equalization, primary sedimentation, biological degradation, and secondary sedimentation into a single tank, without a sludge recirculation system, thereby offering advantages such as simplicity of operation, reduced land footprint, lower capital investment, and strong resistance to shock loads. This makes it particularly well suited to meat‑processing facilities, which often operate on a single shift and experience substantial fluctuations in both water quality and quantity.

　　Slaughterhouse Wastewater Treatment Process Flow

　　Slaughterhouse wastewater first passes through a screen to remove large debris such as bone fragments, organ pieces, and skin and meat scraps, thereby ensuring the proper operation of the pumps and reducing wear. It then flows into an oil‑removal and grit‑removal tank, where oils and floating scum are removed before entering the equalization basin. The equalization basin not only homogenizes flow and volume and stores the wastewater but also houses submersible mixers that thoroughly blend the wastewater with sludge, facilitating hydrolysis and acidification. From there, gravity‑fed flow carries the wastewater into the SBR reactor, where aeration, oxidation, sedimentation, decanting, and excess sludge discharge are sequentially carried out. Removal rates for key pollutants are approximately 95% for BOD₅, 95% for CODCr, and 90% for suspended solids (SS). The clarified effluent is directed to a contact clarifier to further remove fine suspended particles and residual oils. Excess sludge from the clarifier is pumped by submersible pumps into a sludge thickening tank; the supernatant from this tank is returned to the equalization basin. After digestion and stabilization in the sludge thickening tank, the remaining sludge is periodically removed by vacuum suction trucks and can be used as agricultural fertilizer.