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3.5 Slaughterhouse WastewaterTreatment

Technical Description

Slaughterhouse effluent is usually high in organic contaminants. The BOD5 oscillates between 1 500 and 2 200 mg/l or higher, which typically creates problems for traditional purification plants. To overcome these problems, this technology uses a chemical coagulation technique to precipitate the organic materials from the wastewater stream. The technology uses flow equalization tanks equipped with pneumatic agitators, chemical dosing systems, and a separator. In the first stage, a continuous chemical injection system adds an acidic coagulating agent known as T.I. In the second stage, a continuous chemical injection systems adds lime milk. After an initial T.I. mixture reaction time of 5 minutes (at pH = 4.4) in the first stage reaction tank, the effluent is transferred to the second stage reaction tank where it is neutralized (to pH = 7.0) by the injection of the lime milk. In the third stage, the effluent is placed in a vertical reaction column where separation of the coagulated sludge and supernatant water takes place. The supernatant is then siphoned off for further biological purification in aerated activated sludge tanks. Aeration is achieved with surface turbines. The sludge in the chemical stage separator, together with the excess activated sludge, is dehydrated under vacuum in rotary filters.

The T.I. coagulating agent is prepared daily from ground metallurgical slag and diluted sulphuric acid, H2SO4. The residual, exhausted slag is neutralized with lime milk, and, together with the dehydrated sludge, is used as fertilizer for agriculture. The principle active elements of this coagulating agent are the ferric sulphate and silicic acid which act as accelerators of flocculation.

Extent of Use

The technology is used in Romania.

Operation and Maintenance

The technology uses well known principles of wastewater treatment, and is easy to build and maintain. Level of Involvement This technology is implemented at the individual company level.

Costs

The costs depends on the desired discharge quality of the treated wastewater and number of stages need to achieve the required effluent quality.

Effectiveness of the Technology

This technology can achieve about an 80% reduction in BOD5 in the chemical stages and a further 80% reduction in the biological stage. The overall purification efficiency of the technology was over 99%, and achieved between 99.5% and 99.6% effectiveness at times. The product effluent was clear, colourless, and free of odours, with a BOD5 of about 5 to 10 mg/l.

Suitability

This technology is suitable for treating slaughterhouse effluents.

Advantages

This is an highly efficient method of waste water treatment.

Disadvantages

No known disadvantages have been identified.

Cultural Acceptability

This technology is accepted as a wastewater treatment technology.

Further Development of the Technology

Technology is fully developed.

Information Sources

Nikolic Vasilie, Food Chemistry Institute, Str Girlei 1, sector 1, Bucharest, Romania, Tel. (40-1) 679 20 40.

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