Paarl's wastewater works upgraded
2011-01-27
WITH the total population of 500 000 people in the catchment area of the Berg River, the Paarl Wastewater Treatment Works (WWTW), on the banks of this river, plays a very important role in the economic activity of the area.
These works have recently been upgraded, with the second phase due to start next week, due to the expanding population of the Paarl area.
Says Ronald Brown, water services manager of Drakenstein Municipality: “It is inevitable that development results in the generation of wastewater."
There is a legal obligation on ‘the polluter’ to treat wastewater to the required standard before discharging it into the environment. In the case of an urban area the local authority accepts this responsibility on behalf of its tax payers.”
“The quality of water in the river has been a subject of investigation for many years. The potential sources of pollution of the river are diffused sources such as return flow from agricultural activity or general storm water run-off from informal settlements, while point sources are defined outlets into the river such as the Paarl wastewater treatment works.
"Most of the wastewater arising out of the residential and industrial developments end up at the sewage works,” he said
“Due to the level of pollution already observed in the river, as well as the importance of the river for economic activity, the required quality of water to be released into the river is very strictly controlled.”
“The wastewater treatment works at Paarl consists of a biofiltration system for domestic wastewater and a series of evaporation ponds for industrial wastewater, with further maturation ponds to treat the effluent before it is discharged into the Berg River
The Paarl WWTW was not designed for dedicated nutrient removal and, due to the fact that the bioreactor, which over the years developed from a pond system, was not lined, there has always been suspicion that the works could contribute to the elevated E.Coli level in the river via groundwater infiltration.
In 2003 Drakenstein Municipality appointed Ninham Shand, in association with Lyners and Associates, to investigate options to reduce the nutrient load from the works on the Berg River.
The report that followed recommended that the treatment process be amended to remove nutrients from the wastewater biologically as well as that a proper biological reactor be constructed which will eliminate the risk of groundwater pollution.
In 2005 it was also recommended that the capacity of the works be increased in capacity to 35 Ml/d
“An investigation showed that economically it would be more beneficial for the Council to convert the existing unlined biological reactor to a concrete lined reactor. A temporary biological reactor had to be constructed to allow for continuous treatment of the wastewater while construction work was in progress.
“As a further cost saving measure it was decided to use the floating aerators from the original works on the temporary reactor as well as in the new extended works. Normally new works are provided with new aeration equipment.
"The fact that these aerators are still in a condition to be used in the upgraded works is a feather in the cap of the municipality’s operating and maintenance personnel.
“The utilisation of existing aerators reduces the capital cost of the new works by at least R7 million. This emphasises the value of well-trained and dedicated maintenance and operating personnel. They do save taxpayers millions of rands."
The first phase extension, which was completed last year, represents a capital investment of about R75 million.
This will increase by a further R50 million at the completion of phase 2 for a total capital investment of about R125 million.
At the end of phase 2 the capacity of the works will increase by 17 Ml/d to 35 Ml/d. Typically an increase in capacity of this magnitude would cost about R170 million.
"The reduced cost can be ascribed to the utilisation of surplus capacity in existing infrastructure, the utilisation of the existing bioreactor as well as the ability to incorporate existing mechanical equipment into the upgraded works,” he added.
The replacement value of the upgraded works, at the end of phase 2, will be be-tween R300 million and R350 million. At the completion of the second phase of the proposed extensions, the Paarl works will, according to estimates, have sufficient treatment capacity up to the year 2020.
The Municipality has already started a process to identify a site for a new treatment works to the south of the town as well as to upgrade the capacity of the Wellington waste water treatment works.
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