Sewage Treatment & Disposal
Water should never be regarded as waste. Even in countries with abundant rainfall, water remains a valuable resource that should be conserved and reused whenever possible.
However, human activities inevitably contribute to water pollution. Everyday activities such as washing introduce dirt and other contaminants into water.
More serious pollution results from human waste products, particularly urine and faeces, which are carried away by water to form a polluted liquid known as sewage. In many areas, animal waste and industrial effluents further complicate wastewater management.
The most effective and widely used treatment methods utilise natural biological processes to purify sewage and decompose the sludge produced during treatment. Through these processes, the impact of human waste on the environment can be significantly minimised.
RATJOMOSE SEWAGE TREATMENT PLANT
The Ratjomose Sewage Treatment Plant is the largest sewage treatment facility in Lesotho. The plant uses both conventional treatment methods and waste stabilisation pond systems to treat and purify sewage.
It is located southwest of Maseru on the banks of the Mohokare (Caledon) River. The plant serves a collection area of approximately 20 square kilometres, representing about one-fifth of the current inhabited Maseru urban area.
Due to the topography of Maseru, eleven pumping stations have been installed to assist in transporting sewage to the treatment plant.
The drainage areas served include Lesotho College of Education, Phahameng and BEDCO, Maseru East, Moshoeshoe II, Cathedral and Stadium areas, Sea Point, Maseru Central, Maseru West, Industrial and Hoohlo areas, Europa, Hillsview, Thetsane, and the Thetsane Industrial Area.
The population served is estimated to be over 12,000 people.
Sewage flows through two main sewers with a diameter of 1.5 metres, which are capable of handling a flow capacity of approximately 20,000 cubic metres per day, equivalent to 20 million litres of sewage per day.
The plant can handle an average dry-weather flow of 10,000 cubic metres per day, equivalent to 10 million litres per day. It is also capable of handling peak flows exceeding 20,000 cubic metres per day.
PRELIMINARY TREATMENT
Screening
Upon arrival at the treatment works, large debris such as rags, maize cobs, and other solid materials are removed from the sewage through screening.
The plant uses one bar screen with bars spaced at 25 mm intervals. The screenings are manually removed using rakes and are either dried and burned or buried in trenches that are covered with a layer of soil at the end of each day.
Grit Channels
Two grit channels, each 12 metres long and operating in parallel, are used alternately to allow grit, sand, and other mineral solids to settle.
The channels are designed to allow organic solids to continue flowing with the sewage while heavier inorganic materials settle.
The collected grit is removed using shovels, placed into wheelbarrows, and buried in trenches that are covered with a layer of soil.
PRIMARY TREATMENT
Primary Sedimentation
Four circular primary sedimentation tanks are used in parallel to slow down the flow of effluent from the preliminary treatment stage. This allows suspended solids to settle before the wastewater proceeds to the next treatment stage.
The solids may consist of granular materials, salts, or flocculated particles. The tanks are designed to allow these materials to settle effectively.
Approximately 40% of the effluent from preliminary treatment flows into the old primary sedimentation tanks (#19 on the site plan), while the remaining 60% is diverted to the new primary sedimentation tanks (#17).
The settled material, known as raw sludge, is collected from the tank floors into sludge hoppers using mechanical scrapers. Floating debris is removed by skimmers and transferred into scum boxes.
The resulting effluent, now known as settled sewage, flows to the next treatment stage. Effluent from the old primary sedimentation tanks flows to the biological filters (#20), while effluent from the new primary sedimentation tanks flows directly to the pond feed chamber (#18).
TERTIARY TREATMENT
Maturation Ponds
The effluent from the first facultative pond bypasses the second facultative pond and flows into the first maturation pond (#3). Effluent from the second facultative pond also flows into the first maturation pond.
Maturation ponds serve two main purposes:
• Provide further reduction of BOD (Biochemical Oxygen Demand).
• Provide further reduction of bacteria found in faecal matter, known as faecal coliforms, through exposure to ultraviolet radiation from sunlight.
Maturation ponds operate in series. The effluent from the final maturation pond (#18) flows into the river.
Currently, effluent from the humus tanks bypasses the first facultative pond and flows directly to the second facultative pond before passing through the maturation ponds and finally reaching the outlet.
SLUDGE HANDLING
Sludge Digestion Tanks
Two sludge digestion tanks are used in series to stabilise sludge. This process allows anaerobic microorganisms to break down the organic matter present in the sludge, making it more stable and suitable for further handling.
Digested Sludge Drying Beds
The drying beds are the only units at the plant where actual filtration takes place. Digested sludge from the digestion tanks is spread in thin layers across the beds and allowed to dry through filtration and evaporation.
The filtrate is pumped back to the inlet works, while the dried sludge is collected by individual farmers for potential reuse in agricultural land.
Guidelines for the safe reuse of treated sludge are currently under development.
Digested Sludge Lagoons
The purpose of the sludge lagoons is to retain digested sludge while reducing moisture content through evaporation and drainage of liquid into a holding tank.
The separated liquid, known as liquor, is pumped back to the inlet works for further treatment.
VIP Contents Lagoons
The purpose of the VIP contents lagoons is to retain VIP (Ventilated Improved Pit) latrine contents for further digestion and drying.
PUMP ROOM
The pump room contains the following pumping equipment:
• Two pumps for transferring raw sludge from the primary sedimentation tanks (PSTs) to the sludge digestion tanks.
• Two pumps for transferring:
a) Humus sludge from the secondary sedimentation tanks;
b) Filtrate from the sludge drying beds; and
c) Liquor from the digested sludge lagoons and VIP contents lagoons.
SUMMARY AND OTHER FACTS ABOUT THE PLANT
Population served:
• Users of VIPs: approximately 60,000 people.
• Users of conservancy tanks: approximately 4,940 people.
• Customers connected to the sewer network: approximately 12,000 people.
Collection area served: More than 20 square kilometres.
Current average flow to the works: Approximately 7 million litres per day.
The plant consists of the following treatment units:
a) One screening unit.
b) Two grit channels.
c) Four primary sedimentation tanks (PSTs).
d) Four biological filters.
e) Two secondary sedimentation tanks.
f) Two facultative ponds.
g) Six maturation ponds.
h) Two sludge digestion ponds.
i) Forty-eight sludge drying beds.
j) Four sludge lagoons.
k) Two VIP contents lagoons.
l) One pump room containing four pumps.
Staff employed: 5 employees.
Samples are collected weekly from different stages of the treatment process and sent to the Central Laboratory for analysis.
The Sewerage Network
Property owners are responsible for maintaining and repairing their private drains up to the point where they connect with the public sewer system.
WASCO regularly inspects and maintains public sewers to ensure that they operate as effectively as possible.
Public and Private Sewers
Public sewers are sewer lines owned and maintained by WASCO. These include lateral sewers that collect sewage from private properties and transport it to sewage pumping stations and wastewater treatment plants.
Homeowners are responsible for private sewers and drains located within their properties, including the connection from the premises to the public sewer manhole.
When a public sewer becomes blocked, WASCO clears the blockage without charge. However, when a private sewer or drain becomes blocked, the property owner is responsible for arranging and paying for the repair service.
Disposal of Unwanted Material
The drains connecting homes to the main sewer system are designed to carry only wastewater, toilet paper, and human waste. They are not designed to transport other materials or solid waste.
Unfortunately, many people use the sewer system as a waste disposal facility. As a result, inappropriate materials cause sewer blockages, leading to overflows and creating risks to public health and the environment.
Some products may be labelled as disposable but are not suitable for flushing down the toilet. These items should be placed in a bag or bin instead of being flushed.
Proper disposal helps prevent unnecessary repair costs and reduces expenses associated with plumbing problems.
What to Do with Disposable Products?
All disposable products should be placed in a bin or bag and should never be flushed down the toilet, as they may eventually enter the environment and cause pollution.
The following items should be disposed of using the recommended methods:
Cotton buds, bandages, plasters, and dental floss: Dispose of these items in a bin.
Sanitary towels and pads: Use special sanitary disposal bags available from pharmacies and place them in rubbish bins.
Disposable nappies: Wrap them properly and dispose of them in a bin or use dedicated nappy disposal bags available from supermarkets.
Razors and blades: Place them in a rigid container before disposing of them in a bin.
Plastic bags and newspapers: Dispose of them in a bin.
Sewer Blockages
Causes of Sewer Blockages
WASCO sewers are designed to transport sewage from properties to treatment facilities. However, placing inappropriate waste materials into toilets and drains can result in blockages within the sewer system.
Who Is Responsible for Sewage Overflow?
WASCO is responsible for sewage overflows caused by blockages within public sewers and ensures that such blockages are cleared.
If an overflow is caused by problems within a customer’s private sewer or drain, the property owner is responsible for resolving the issue.
Where a sewer serves more than one property, WASCO remains responsible for addressing the problem.
Customers should contact the Sewage Division immediately if they experience a blockage within their property.
Telephone: 22312213 / 22312449 / 22313943
Toll Free: 800 22 011
Precautions During Sewage Blockages or Overflow
The following precautions should be taken to protect you and your family:
• Wear protective clothing and cover any open cuts or wounds.
• Dispose of vegetables and fruit from gardens affected by sewage flooding, or wash affected areas thoroughly using a hosepipe.
• Keep children away from flooded areas until the area has completely dried and is safe.
• Consult a doctor or healthcare professional if you experience vomiting, diarrhoea, or other illness symptoms following exposure to sewage flooding.
