Slaughterhouse Wastewater Treatment Process

1. Water quality types and characteristics

In this project comes from pen washing, leaching, slaughtering and factory floor washing, scalding, dissection, side dish processing, animal residues, blood water, etc. It has the characteristics of large water volume, uneven drainage, high concentration, many impurities and suspended solids, and good biodegradability. At the same time, the biggest difference compared with other high-concentration wastewater is that its NH3-N concentration is higher (about 120mg/L).

1.1 Design water volume

Designed water volume: 150m³/d, i.e. 7.5m³/h (daily operation time is 20 hours)

1.2 Influent water quality

According to the pollutant water quality index data provided by the owner , the designed influent water quality index of this project is shown in the following table :

Table 1 Design influent water quality index table

1.3 Outlet water quality

Table 2 Designed effluent water quality index table

2. Process design plan

2.1 Process

( Process flow chart )

2.2 Process Overview

Basket grille: filter out large particles in the water, such as garbage, leaves, minced meat, etc.

Pre-sedimentation regulating tank: regulate water quality and quantity.

Solid-liquid separator: separates hair, feces, etc. from wastewater.

Grease trap: removes floating oil from water.

Intermediate water pool: water storage function.

Coagulation flotation tank: by adding PAC and PAM, the tiny particles and colloids in the water are condensed into larger suspended matter under the action of the agent, and are carried to the water surface by the floating tiny dissolved air bubbles, and then scraped to the sludge tank by the scraping system to achieve solid-liquid separation . Remove suspended matter, colloids, and some organic matter in the water .

Hydrolysis acidification tank: Degrade some organic matter through hydrolysis and acidification reactions of microorganisms to improve the biodegradability of organic matter.

Two-stage A/O /precipitation system: Microorganisms degrade and remove organic matter, ammonia nitrogen, total nitrogen and total phosphorus in wastewater under alternating anoxic and aerobic environments .

Sludge treatment system : mainly composed of sludge tank and sludge dewatering system . The scum and residual sludge produced by the flotation tank, hydrolysis acidification tank and two-stage A/O /sedimentation system are discharged into the sludge tank. After further gravity concentration in the sludge tank , the sludge is pressurized by the sludge feed pump and pumped into the sludge dewatering machine to reduce the moisture content of the sludge and make the moisture content of the mud cake less than 75 %. The dehydrated sludge is outsourced for treatment .

2.3 Operation Effect and Analysis

The project started to be debugged in early 2013. After three months of system debugging, all process sections have been put into normal operation at full capacity. The monitoring and acceptance department has continuously monitored the wastewater treatment project and the water quality monitoring results are averaged. The results are shown in Table 3 .

It can be seen from Table 3 that all indicators of effluent are better than the first-level emission standard of "Emission Standard of Water Pollutants for Meat Processing Industry" (GB13457-1992).

3. Engineering technology and economic analysis

3.1 Technical Analysis

This process uses a combination of secondary anoxic + high-efficiency aerobic bacteria to achieve efficient nitrogen and phosphorus removal. This process can eliminate traditional anaerobic reaction units (UASB, IC) and other anaerobic reaction towers, which can reduce investment costs and land area while ensuring stable operation in the later stage.

This process has the advantages of impact resistance, high load, stable water quality and quantity, etc. Secondary anoxic treatment can not only effectively remove nitrogen and phosphorus, but also has the functions of deodorization and decolorization. This process is formed by combining traditional sewage treatment units, and has the characteristics of simplicity, stability, low technical difficulty, and easy replacement of accessories.

This process has the potential for upgrading and transformation, and the effluent water quality is high, which is convenient for effluent reuse. If multi-stage filter tanks and ultrafiltration, disinfection and other equipment are added to the end effluent, the produced water can be reused in the production line.

3.2 Operation Cost Analysis

The total investment of this project is 1.6 million yuan, of which equipment investment is 1.3 million yuan, civil engineering facilities and other investment is 300,000 yuan. It covers an area of 300m2 ^and can treat 150m3 of sewage per day ^. The specific project operation costs are: electricity fee is 0.65 yuan/m3 ^, chemical fee is 0.36 yuan/m3 ^, labor fee is 0.18 yuan/m3 ^, and the actual operation cost is 1.19 yuan/ ^m3 .

4. Conclusion

(1) Based on the high organic matter load of slaughter wastewater, flotation can be used as the pre-treatment to remove most of the grease, suspended matter, etc. The subsequent hydrolysis and acidification treatment technology can hydrolyze and acidify the large molecular organic matter in the water into small molecules, and degrade most of the insoluble organic matter into soluble substances, thereby reducing the subsequent biochemical treatment load.

(2) Highly active aerobic bacteria are added to the contact oxidation tank and highly active return sludge produced by the ordered aerobic reaction tank to adsorb most of the biodegradable organic pollutants in the sewage and effectively remove COD and BOD5 in the water.

(3) The flotation-hydrolysis acidification-contact oxidation process has been put into actual operation in multiple projects for treating slaughterhouse wastewater. The entire treatment system operates stably and has created good economic, social and environmental benefits.