Upgrade of the Ritchie WWTW was commissioned by Sol Plaatje Municipality as it is currently hydraulically overloaded and only running on a capacity of 0.5 Mℓ/d. 

Vela VKE’s Bloemfontein office is currently responsible for the design and site supervision of the Ritchie Wastewater Treatment Works (WWTW) upgrading, which forms part of the infrastructure upgrade by Sol Plaatje Municipality – initialised by the executive director of Infrastructure and Services, Boy Dhluwayo. Situated on the town of Ritchie in the Northern Cape, the WWTW currently consists of only oxidation dams, which are being used with a capacity of 0.5 Mℓ/d and was in need of an urgent upgrade. It was therefore necessary for the hydraulic capacity of the WWTW to be increased to 2 Mℓ/d.

Project overview

The current inflow at Ritchie WWTW consists of mainly residential sewerage that enters the works from a pump station – no gravity inflows take place. The WWTW was designed and constructed in a cost-effective manner without compromising quality or construction standards – to comply with national government’s obligation to uplift community hygiene standards and other general expectations.

The current works consist of:

• two anaerobic ponds each 1 450 kℓ and 4.3 m deep
• a primary pond of 13 000 kℓ and 1.3 m deep
• a secondary pond of 19 500 kℓ and 1.3 m deep
• two tertiary pondseach 800 kℓ and 1.3 m deep
• three tertiary ponds of 2 300 kℓ, also 1.3 m deep

The upgrading of Ritchie WWTW comprises of the following three sections:

WWTW design and construction: The works are currently being upgraded adequately to treat an average dry weather flow (ADWF) of 2 Mℓ/d. The proposed Ritchie upgrade entails the following process elements:

• construction of a truck dump facility
• construction of new inlet works complete with mechanical screen and manual standby screen
• two duty/standby horizontal flow grit channels
• inlet flow measuring station based on BS3680 flume
• upgrading of the two existing anaerobic ponds to 1 450 kℓ concrete activated sludge reactors, complete with mixing, surface aeration, mixed liquor and sludge recirculation
• construction of a new 16-diameter clarifier downstream of the two reactors for effluent clarification, settling and return of sludge from the clarifier to the anoxic reactor
• use of primary ponds as contact tank and maturation ponds after chlorine dosing
• flow from the last chlorination/maturation pond will be released to the adjacent vlei area
• a new measuring station
• last three ponds will be reconstructed and used as sludge lagoons
• electrical infrastructure complete with office buildings
• new 200 KVA, with a supply voltage of 400 V – Eskom line was built to supply the works.

Erection of a security fence around the WWTW: A security fence is being constructed to prevent unauthorised access to the works site while at the same time to protect the community of Ritchie from injuries associated with the treatment works. Flat razor mesh security fences (1.8 m high) with access gates are being installed. A new guardhouse consisting of a store room and operators control room was also newly build at the entrance gate.

Construction of a 2 km gravel access road to the WWTW: The need to upgrade the access road to the WWTW was also identified. Construction is currently underway and once complete will accommodate heavy vehicle traffic (sewer tanker trucks and waste compactor trucks), which travel to the WWTW and landfill site on a daily basis. The road consists of three layers with a final layer of 150 mm, C4 material compacted to 98% MOD AASHTO. A section of road of about 140 m starts adjacent to the current township and will be constructed with kerbs and channelling. The road also includes two stormwater culverts consisting of three 900x450mm box culverts.

Project funding

The project is funded from the Municipal Infrastructure Grant, and a community Project Steering Committee was formed to liaise with the contractor. This committee represents the interests of the community during the course of the construction and takes decisions on its behalf. Another objective identified by the client was to identify suitable local residents during construction for transferred skills training (in the various aspects of the construction) and to be trained as operators on the new plant. The estimate full construction amount will be R 17 820 000 (excluding VAT).

Progress

Construction is currently on track with 36% of the work complete and an anticipated final completion date of 31 August 2012. Although Vela VKE still envisages several engineering challenges ahead, the biggest concern is the time frame and unruly community problems, which the contractor is encountering. The company is however confident that the project will be completed within time and budget.

 

Photo: Stabilised base layer on access road

Photo: New clarifier construction underway

Photo: Excavation of existing anaerobic ponds for upgrade to concrete-lined activated sludge reactors