Biological wastewater treatment Unit


A various wastewater streams are formed at the  “Atyrau Refinery” LLP. Wastewater from "mechanical treatment facilities” (MTF) comes in biological wastewater treatment system. The unit "Biological treatment facilities " (BTF) with capacity 15.48 ths. m3 / day was built and put into operation in 2006. Two main streams, wastewater, arriving from the unit of MTF and domestic sewage runoff are processed at the biological wastewater treatment unit. 

Following processes are applied for water purification in system:

  • Flocculation and flotation;

  • Biological purification;

  • Filtration and chlorination;

  • Sludge drying.

At the first stage of the block of flocculation and  flotation (BFF), coagulation- flocculation process, which improves removal of suspended solid particle and colloidal substances, is carried out. Process of flotation is carried out at the final stage of separation of solid and liquid particles in the  floatation block. Additional biological sediment is entered for improvement of process of flotation.

For removal of large and heavy particles, which are  saved up at the bottom of the container, the unit is equipped with the system of removal of bottom  sediment. 

Surface sediment at the flotation moves  by gravity to  general settler, and then it is pumped over  in the block of sludge drying. Treated wastewater in the BFF moves by gravity to the block of biological treatment.

Also wastewater  from the channel of separate sewerage goes to the  block of biological treatment. Biological processes, used at the water purification, are similar to phenomenons, which occur in habitat. At sufficient aeration organic carbon turns into carbon dioxide and biomass.  Basic elements are necessary for reproduction of bacteria: С, H, O, N, secondary elements P, K, S, Mg, and also vitamins, hormones, microelements, etc.  Content of N and P in wastewater, arriving on the  unit of biological treatment, isn't enough.

A  carbamide and phosphoric acid is added for maintenance of minimum ratio of BPK:N:P. A suspension of sediment in the aeration tank,  containing clearing bacterial flora, is called as  "activated sediment ". The water,  intended for  cleaning, contacts to a bacterial flocculant in the  presence of oxygen (aeration process), then process of separation of water from the flocculant  (clarification process) is carried out. 

Sand filters are used for removal the excess of  suspended solid particle from purified water. It is necessary to carry out the process of  chlorination of water to reduce the number of  coliform bacteria, for this purpose sodium hypochlorite is dosed into water.  Resulting sediment is subjected to dehydration by using two centrifuge of the sludge dewatering unit,  and polymer T3 is added for improving the separation of solid and liquid particles. 

Dried sediment is stored in bunkers and dried  sediment is taken out by dump trucks to the ground  of waste disposal of the refinery. The part of cleared wastewater of 20-23% comes back to production for reuse and rest comes back  on dumping to the pond evaporator of wastewater  from the biological treatment construction.