Maintenance of sewers consists of the removal of obstructions, cleaning of sewers including sewer appurtenances and repair works.
Maintenance of sewers is generally of two types – (i) Preventive / Routine maintenance (ii) Corrective maintenance. Routine maintenance means precautions taken to prevent any breakdown of sewerage facilities. Preventive maintenance is more economical. Whereas corrective maintenance is provided when the breakdown occurs.
Read more about – How testing of sewer is done ?
Problems faced during maintenance of sewers
- Clogging of sewers
1. Clogging of sewers
Sewers may get clogged because of the following factors –
- Grit and other detritus may get deposit in the sewer. Thus this will create stagnation resulting in collection of organic matter, which provides bad odour and poisonous gases.
- Roots of nearby plants may penetrate through the joints or cracks in the sewer lines, so this might result in clogging.
- The growth of fungi forms tendrils which starts floating, thus offer an obstruction to the flow.
- Due to improper working of pumps; sewerage gets stagnated and thus clog sewers.
Persons engaged in operations and maintenance of sewers; are exposed to occupational hazards likewise –
- Physical injuries
- Injuries caused by chemicals and radio-active wastes
- Infections caused by pathogens present in sewage
- danger due to deficiency of oxygen
Safety precautions against gas hazards
While entering with manholes, the following precautions should taken care of –
- Traffic warning signs should be there, thus to avoid accidents.
- No smoking / however open flames allowed nearby.
- Explosion proof electric lighting equipment or mirrors for reflection of light used only.
- Oxygen amount should be taken care of, thus no oxygen deficiency should be there.
- If any noxious gas is found, forced ventilation should be restored.
- Allow safety equipments.
- Use of non-sparking shoes and non-sparking tools.
Safety equipments for maintenance of sewers
- Gas mask
- Oxygen breathing apparatus
- Portable lighting equipment
- Portable air blowers
- Non-sparking tools
- Safety belts
Sewer cleaning equipments and devices
- Portable pump set
- Sectional sewer rods
- Flexible sewer rods
- Ferret used in conjunction with a fire hose
- Sewer cleaning bucket machine
- Rodding machine with flexible sewer rods
- Automatic flushing tanks
- Hydraulically propelled devices (flush bags, sewer balls, sewer pills, sewer scooter)
Ventilation of Sewers
Ventilation of sewers thus done properly for the completion of following purpose –
- Continuous flow – Ventilation relieves air pressure, caused due to sudden rise or fall of sewage. Due to this, air locks will not be there in it and sewer flow will be continuous flow.
- Disposal of sewer gases – The sewer has gases like – NH3, CO, CH4, N2, H2S etc. and sometimes includes petrol vapor also. If methane gas (CH4, explosive in nature) is not removed, may blow off manhole’s cover. On the other hand, CO is poisonous in nature. Therefore all the above gases needed to remove by proper ventilation.
- Prevention of unpleasant odour – Ventilation prevents concentration of unpleasant odour which generally causes nuisance .
Methods of ventilation
- Man hole covers with gratings – The man hole covers generally have perforations / gratings through which sewer gases escape. The disadvantage of this method is that it mostly causes air pollution by spreading bad odour. It also allows the storm water, dust, debris etc. in it.
- Ventilating columns or shafts – Ventilating columns or shafts, generally provided at the end of every branch sewer.
- Proper design and construction of sewer – Sewer should be so design that they run half or 2/3 full. The space above sewage flow will provide ventilation.
- Proper house drainage system – House vent and soil pipes thus used to ventilate the house drains and lateral sewers.
- Unobstructed outlets – Unobstructed outlets provide partial ventilation to storm water drains and sewers.
- Use of mechanical devices – Forced drafts, provided by exhaust fans to expel out foul gases sewers.