Abattoir Effluent Treatment

ABATTOIR EFFLUENT TREATMENT

  • Effluent means dirty water with organic matter such as blood, dung, urine, fat, trimmings, fascia, etc.
  • The disposal of effluent of abattoir is essential because of possibility of pollution leading to human health hazards.
  • Large quantity of water is utilised in the abattoir to clean blood from slaughter section, pen manure and similar material containing organic matter as suspended solids.
  • This wastewater has got a high pollution capacity and hence should not be connected to municipal sewer line.
  • However, water from the toilet lines and cooling towers should be directly connected to sewer system.
  • The concentration of effluent solids is measured in terms of biological oxygen demand (BOD) usually expressed in parts per million (ppm) or mg/litre.

BOD5

  • Biological oxygen demand is the amount of O2 required during the first five days for decomposition of organic matter at 20°C by aerobic biological action.
  • Higher the BOD level, greater is the organic matter content and greater its pollution capability.
    • Domestic sewage – BOD5 = 250-300 mg/litre  normal and permissible one
    • Slaughterhouse - BOD5 = 1500-2000 mg/litre  normal and permissible one

In general, abattoir effluent treatment involves the following steps

  • Primary treatment
    • This consists of screening out solids and removing fat by hands.
    • It is carried out in a tank constructed below the ground level.
    • It is divided by a partition of strong steel meshes.
    • The main trunk line drainage of meat plant or abattoir opens into the first part.
    • The gross solid materials like bits of fat, flesh, stomach, intestine, hide, etc., are filtered through the mesh.
    • The waste water free of gross solids is pumped to the secondary filtration unit.   
  • Secondary treatment
    • This system depends upon cost, BOD level required, land area available, odour level etc.
    • This unit is erected at the first floor level and contains two vibrating screens with fine mesh which are arranged at an angle.
    • This unit separates the suspended solids. Subsequent treatment is done in tanks erected at the ground level.

 Fat separation

  • It is a specially designed tank where waste water is agitated by pumping the air at several points.
  • The separated fat rises to the top and is skimmed off at regular intervals.

Equalization tank

  • It is a large tank fitted with floating level mechanical aerator.
  • Here waste water is continuously agitated to have a uniform quality for proper biological oxidation.
  • As a biological stimulant, a small quantity of activated sludge is also recycled into this tank.
  • This method is capable of reducing up to 90% of the fats, 65% of the solids and BOD5 by 35%.

Biological oxidation tanks or ponds

  • Further treatment of waste water depends on the availability of land or open space.
  • In limited land area, anaerobic process and if enough land area is available, aerobic process is adopted.

 Anaerobic process

  • This is used in which reduction of BOD5 is performed by bacteria in the absence of O2.
  • Ponds of 4.5 m deep and loaded to 7.5 kg BOD5 per 5000 litres pond volume will give a BOD5 reduction of 60-80% at temperatures of 32.5 – 35°C.
  • The effluent is digested in enclosed digester at 32.5°C.
  • The gas being burnt and heat generated for heating.  

Aerobic process

  • In this the process, O2 assists bacterial action to reduce the BOD5.
  • Shallow ponds 0.9 – 1.2 m deep having a loading of 7.3 – 9.3 kg BOD­5 per day per hectare of pond surface are mainly restricted to final treatment following other processes.

 Activated sludge process

  • Involves utilizing biologically active sludge in small amount mixed with screened, pre-settled effluent and then agitated in presence of ample supply of aeration tank. This is a well-known method of treating domestic sewage but it is not commonly used for meat plants.

  The oxidation ditch system

  • It was developed by Dr. A. Pasveer in Holland in 1953.
  • It is an one-stage process for purification of sewage by oxidation using an aeration rotor.
  • The raw sewage flows into the aeration zone where it is mixed with ditch contents; oxidation is effected by the rotor.
  • Flow of the mixed liquor from the ditch to the final settlement tank is controlled by means of an adjustable outlet weir which can regulate rotor blade depth and thereby oxygen input.
  • Settled sludge from the final settlement tank is returned continuously to the oxidation ditch.

 Biological filtration process

  • Percolating filters consists of 1.8 -2.4 meter beds of stones 50 -1000 mm in diameter.
  • Purification is accomplished by the action of a film of microorganisms covering the stones on the organic matter.
  • At loadings of 75-87 kg BOD5 per 5000litres of packing per day a BOD5 reduction of 40% is possible.
  • This system is costly since it has a tendency to block and require a large area.
  • Before treating the effluent, data on flow rate, BOD levels, fat, solids should be determined over a period of time. 
Last modified: Wednesday, 12 October 2011, 7:02 AM