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Effluent reuse demo plant tested at KZN works

FLAGSHIP DESIGN
The Darvill wastewater treatment works upgrade will include a significant capacity increase, from approximately 55 Mℓ/d to 120 Mℓ/d

FLAGSHIP DESIGN The Darvill wastewater treatment works upgrade will include a significant capacity increase, from approximately 55 Mℓ/d to 120 Mℓ/d

9th October 2015

By: Mia Breytenbach

Creamer Media Deputy Editor: Features

  

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Engineering, project and construction management services supplier Hatch Goba will – in addition to managing the refurbishment of the Darvill wastewater treatment works, in KwaZulu-Natal – install a demonstration final effluent reuse plant on site to showcase the efficiency of effluent reuse.

The reuse plant, with a capacity of 2 Mℓ/d, will treat final effluent to potable water standards, says Hatch Goba principal engineer Jason Browne, who tells Engineering News that this will be the first plant of its kind in the province.

“Detail design of the plant has been completed and construction is expected to start before the end of the year,” he notes, adding that, while other water resource options are available in the area, the increasing cost of additional bulk water resources will drive the attractiveness of reuse plants.

Hatch Goba’s demonstration plant will incorporate several advanced technologies – such as advanced oxidation and biologically activated filters and ultrafiltration membranes – thereby providing multiple barriers against bacteria, viruses and endocrine-disruptor breakthrough. The plant will function as a separate facility for the next five years; a portion of final effluent will be taken from the secondary clarifiers at the Darvill wastewater treatment plant and diverted to the reuse plant.

Meanwhile, Browne notes that the upgrade and expansion of the Pietermaritzburg-based Darvill wastewater treatment works, which is owned and operated by water utility Umgeni Water, are currently about 50% complete. The construction phase is due for completion in December 2016, provided there are no unforeseen delays, he adds.

The project scope comprises a significant capacity increase, from about 55 Mℓ/d to 120 Mℓ/d, as well as upgrades of the preliminary, secondary and tertiary treatment process units, including the sludge-treatment process, which will require the construction of two additional ellipsoid-shaped anaerobic digesters.

Browne emphasises that, by implementing a fine-bubble diffused air aeration system during the upgrade of the Darvill waste- water treatment works, Hatch Goba has achieved a forecast energy cost saving of about 40% in the life-cycle costing of the project.

“A key project driver is energy efficiency in the wastewater treatment plant, which is why the fine-bubble diffused aerator was the suggested and preferred solution.”

The fine-bubble diffused aeration system supplies oxygen to the metabolising microorganisms.

“For the first time in South Africa, a 7-m-deep aerobic reactor was used, owing to space constraints, which has resulted in an increase in the oxygen transfer efficiency for the treatment process,” Browne explains.

This system allows for smaller air bubbles to be introduced into the reactor, creating a larger surface area for the mass transfer of oxygen into liquid. This reduces power use while increasing capacity.

Upgrades to the existing works include reconfiguring the existing basin, which has been modified to become an anaerobic-and-oxic zone where nitrate and phosphate removal occurs.

Hatch Goba’s other implementations of fine-bubble diffused aeration systems include those for water utility Johannesburg Water’s Bushkoppie wastewater treatment works facility, in Soweto, Gauteng. The facility accounts for about one-sixth of the city’s total wastewater treatment capacity.

The company was appointed to provide design and construction management services for the replacement of the existing below-water infrastructure of the Bushkoppie wastewater treatment works’ fine-bubble diffused aeration system.

“Owing to the increased efficiency of the new system, the plant’s original treatment capacity of 200 Mℓ/d has also been increased to 250 Mℓ/d,” Browne says.

He reiterates that a feasibility study, including a process design analysis, identified that the biological treatment capacity could be increased by 25% using efficient technologies instead of constructing an additional biological reactor. This would also achieve a 20% saving in energy costs. According to Hatch Goba’s website, this represents a saving of about R250-million.

Browne notes that Hatch Goba replaced the old ceramic diffuser domes with new 9" ethylene propylene diene monomer discs for the entire fine-bubble diffused aeration plant.

The project started in June 2013 and was commissioned in November 2014.


Hatch Goba water business unit regional director Andrew Officer notes that 90% of the company’s current work is for the public sector, supported by an increasing focus on bulk infrastructure, as well as water and waste-water treatment works.

The company is involved in water treatment projects in Botswana, Mozambique and Lesotho; and big transfer schemes, such as Limpopo’s R13.4-billion two-phase Mokolo Crocodile Water Augmentation Project, and the North–South carrier pipeline project Phase 2, in Botswana, which will transport water 360 km south to the capital city of Gaborone. The company is also undertaking several large-scale, rural water supply projects in the Eastern Cape and KwaZulu-Natal.

Hatch Goba maintains its outlook on expanding its market, and regards Africa as a significant focus area on which to build. Officer notes that the company is considering expanding its footprint more into the neighbouring States and into East and Central Africa, where it plans to focus on larger-scale bulk water supply and treatment projects.

Edited by Samantha Herbst
Creamer Media Deputy Editor

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