WASTEWATER TREATMENT AND DISPOSAL
This section includes reference to the work undertaken by BCHOD involving the treatment of domestic, industrial, commercial and other types of wastewater for safe disposal or re-use. Projects involving the reticulation of wastewater (or sewage) to urban and rural developments including many 100’s of schemes in Zimbabwe alone are covered under the general infrastructure section of the document.
Types of works and processes designed and constructed by the firm under BCHOD supervision have included:
- Conventional works, incorporated Screens, grit channels, comminutors, primary sedimentation tanks, biological filters, humus settlement tanks, slow sand filters, chlorination and secondary digesters and sludge drying beds.
- Modified activated sludge treatment works including aeration, primary settlement tanks, clarifiers, sludge digesters, sludge thickeners and all related machinery and controls.
- Wastewater treatment Systems for industrial, Commercial and Mining clients that have ranged in size from a few cubic meters of raw sewage per day to more than 70ML/day.
- Pond systems incorporating facultative and maturation oxidation ponds with the inclusion in many facilities of additional facilities like anaerobic pre-treatment, effluent re-cycling and sludge disposal.
Brian Colquhoun, Hugh O’Donnell & Partners now (BCHOD) pioneered the use of oxidation ponds and anaerobic treatment for wastewater in the Central African Region.
The firm designed the first large-scale anaerobic/aerobic ponds system [including effluent recirculation] of its type in Zimbabwe for the City of Harare at Mabvuku. The anaerobic part of this design was later adopted with a conventional works design at Zengeza by the City of Harare.
In the mid-70’s the firm designed one of the first modified activated sludge sewage treatment facilities at Gath’s Mine, Mashave, from which effluent was reclaimed for use in the Mill. This necessitated partial nutrient removal and effluent very low in solids content.
Treatment and Disposal of Wastewater
The type of sewage treatment installed has often depended upon the availability of land, whether effluent reclamation would be required, and the degree of expertise needed for operation. Generally, therefore, the various forms of wastewater treatment available in the country has been explored and reported to our clients with recommendations, designs and construction implementation.
Of specific interest the firm has been involved in sewage treatment projects throughout its time of operation in Zimbabwe for which the following more recent references are included.
Large Scale Projects:-
Thorngrove Sewage Works was designed in three stages for an ultimate dry weather flow of 14 500 m³/day [3 200 000 MGD] for the City of Bulawayo. It comprises conventional works consisting of screens, grit channels, comminutor, primary sedimentation tanks, biological filters, humus settlement tanks, slow sand filters, chlorination, primary and secondary digesters and sludge drying beds. All effluent is used for irrigation of the City’s Parks. In a recent foreign aided project which included a review of the City of Bulawayo’s sewage works it was described by a visiting specialist Public Health Engineer, as the best sewage installations in Bulawayo in design, construction quality and operation
Llewellyn Barracks, Bulawayo – Activated sludge sewage treatment plant and consists of horizontal flow grit channel and screens, aeration basin, clarifier, return activated pump station, sludge drying beds and effluent pump station. The effluent is sold to a local farmer.
Design and construction of ponds for Ngezi Mine Village including treatment of effluent for irrigation.
Design and construction of sewage treatment for Murowa Mine Village including first stage septic tanks and second phase BNR plant and wetlands.
Chinhoyi – Modified conventional sewage treatment works was designed for a dry weather flow of 3 250 m³/d and consists of screens, vertical flow grit channels, raw sewage pump station, 2 anaerobic ponds, primary settlement tank, 2 biological filters, humus settlement tank, sludge drying beds, maturation ponds and effluent and sludge recirculation pump station.
Gimboki Sewage Treatment Works Stage III for City of Mutare to increase capacity by approximately 20 Mℓ/d [current].
Shurugwi, Mtoroshanga, Mazowe, Essexvale, Plumtree – Oxidation Ponds with and without anaerobic pre-treatment.
Temporary Oxidation Ponds – Epworth Area, Harare [Sewage works ultimately required].
Previous projects, some of which involved continuing input from time to time include:
Firle Sewage Works, Harare – Design and supervision of 72 Mℓ/d extension (Phase V) for Modified Activated Sludge Treatment Works for City of Harare.
Modified activated sludge sewage treatment works for Renco Gold Mine where agreement was reached for effluent to be discharged into the Mtilikwe River.
Mechanical or modified activated sludge sewage treatment at Maphisa, Tsholotsho, Hwange Safari Lodge, Chiredzi, Ntabazinduna, ZRP Camp Bulawayo and Kamativi Mine.
At Beit Bridge an existing anaerobic/aerobic pond system became overloaded, and in order to extend its lift, five floating aerators were installed at approximately one-third of the cost of additional ponds.
Oxidation ponds at Plumtree, Gwanda, Beit Bridge, Esigodini, Chiredzi, Bank, Sanyati and Zimunga.
Report into the existing modified conventional sewage works and industrial estate ponds at Chitungwiza in relation to the present condition and operation and future potential for the Chitungwiza Council.
Report into existing Pasveer ditch treatment plant at Mvuma in relation to its present state and recommendations for reinstatement and future operation.
Report into proposed new sewage works for Chinhoyi including comparison of activated sludge, modified activated sludge and modified conventional sewage works.
Report into existing pond system at Chikonohono area of Chinhoyi related to present condition and capacity.
Smaller Scale Projects
The more recent projects for Industrial, Commercial, Mining and other Clients often requiring more specialized ways of dealing with effluent are included below
Nestle trade effluent treatment plant in Southerton, Harare.
Carrefour, DRC Wastewater treatment including grease separators and anaerobic treatment for a large food court in Kinshasa 2014.
Mine workshops oil/grease separators for Zimplats Ngezi Mines 2014.
Unki Mine Housing complex wastewater treatment plant commissioning in 2014.
Chivhu Food-court wastewater separation and disposal 2014.
Old Mutual Properties, oil/grease separator for bus wash-down areas.
British Embassy Complex – Package Wastewater Treatment Plant for safe discharge of final effluent to the environment.
Border Timbers, Mutare: Trade effluent investigations and proposals.
Selous Metallurgical Complex, Zimplats treatment and disposal of leachate effluent 2014.
SMC Village investigation into existing aeration type wastewater plant and ultimate design and implementation of effluent disposal.
Delta Beverages – Coca Cola Bottling Factory Harare: Investigation and proposals for wastewater separators and disposal.