Transfer Line and Second Module of Birjand Sewage Treatment

Features of Plan

Birjand has arid desert-like climate with average temperature of +28 centigrade in summer and average of +5 centigrade in winter. Most of raining happens in winter.

Regarding the existing river,the total inclination of Birjand is from north and south towards the center of city and also from east to west. The north section of Birjand has a new made sewage network, thus by knowing this fact in the design of wastewater collecting network of studied area, it is tried to consider the topography of city, regional divisions are conducted in a way that the sewage of each section is entered to the main collector by use of the natural gradient of ground through the shortest way, and from there it transfers into the treatment through gravity. Based on this fact regarding the existing natural ridges, the sewage-taking areas are selected in a way that the sewage of each section starts from ridges by the help of secondary sewers and it leads towards a collector at the final line of each section and after that, all collectors are guided into the outside of city through main transfer line. Moreover, the intersection of sewer ways with city ways shall be minimum.

In the plan of Birjand sewage, regarding the development of city and by considering developing areas and in order to optimal transfer of sewage to treatment, two transfer lines have been considered that one of them has been made and implementing the other is in the range of this contract.

The sewage of northern part of the city is transferred to the treatment through transfer line with diameter of 900-1000 millimeters. By regarding the total gradient of city and the location of treatment which has been in south, sewage transfer of the southern half of the city with discharge of 870 liter per second and for a crowd of 244500 people is transferred from the output place of sewage network into a treatment by gravity and through a sewer with diameter of 1000-1200 millimeters. This transfer line has been started from the early of Ebadi boulevard after the housing cooperative of police force in the direction of Birjand-Khusf road with diameter of 1000 millimeter and by entrance of collector c with diameter of 500 millimeter, it is converted into a road with diameter of 1200 millimeter at the kilometer 0+ 398 before passing the path under bridge.

Purification method is as follows: active sludge with removal of Nitrogen (MLE without primary sedimentation and without separately sludge digestion) sludge must be consolidated in the aeration basin; therefore, it doesn’t need any separate consolidation system. To supply consolidation of sludge in aeration unit, time as a cell in aeration basin shall be considered so high till the sludge stabilizes. Return of sewage to anoxic area should be conducted by pumps which are located out of the basin.

The general outline of services’ description

  • Services of planning, determination of implementation method, control of work advancement
  • Engineering services
  • Services of work reference
  • Services of coordination, execution and temporary delivery
  • Services of quality control
  • Services of estimation, control, payments and costs, legal affairs of contracts
  • Services related to the period of experimental operation (guarantee period) and definite delivery

The main components of plan

1 – Second transfer line of sewage

  • Line diameter is 1000 and 1200 millimeter
  • Line material: two-shell polyethylene
  • Line length: 5/9 kilometers

2 –Sewage treatment plant:

The most important units of treatment are as follows:

Large-opening trash rack, input pump house, small-opening trash rack, taking beans with aeration (all these units are common for existing treatment and two development modules are designed), parshall flume, beam-taker blower building, Anoxic unit, aeration unit, final sedimentation, sewage return pump house, sludge return pump house and additional sludge pump hou, final sedimentation, parshall flume, chloride contact tank, administrative building and central control room, diesel and trans building, aeration blower building, concentration and mechanical dehydration, dryer bed of emergency sludge, pump house for transferring sludge, building of provision and injection of sodium hypochlorite, laboratory building of smell removal system, compost and other lateral buildings).

Aims of plan

In irrigation seasons, the output sewage will be used for agriculture and in non-irrigation seasons, it is discharged into the nearest way; therefore it is necessary to consider the output sewage quality is discharged to the surface levels according to discharge standards.