Case Study SA-EM2

RELOCATION OF THE POINT PUMP STATION

Present Point Road Pump Station and surrounding development

Bio-filtratiion odour control system at the present Point Road Pump Station

Aerial view showing current Point Road Pump Station

Relocation of Point Pump Station, Durban, South AfricaThe upgrade of the Point Road Waterfront area in Durban, South Africa, has resulted in significant development taking place in the area over the past few years, especially in terms of upmarket residential buildings. As a result Durban’s largest sewage pump station is now surrounded by high end developments, some only 20 m away from the pump station, necessitating an urgent solution to the odour impact of this 60 ML/d pump station.

Background:

The Point pump station is, at 60 ML/d, Durban’s largest sewage pump station, servicing a large part of the Durban CBD and surrounding areas, including the Berea, parts of Maydon Wharf, Umbilo and the area south of the Umgeni River. However, due to development in the area, odour has become a serious issue and as a result, the pump station is being relocated to the harbour entrance, some 200 m away from its current site. The pumps were in need of refurbishment and maintenance in any case, so the cost of relocation and replacement of the pumps will be offset to some extent by saving on refurbishment costs. Although this project was in no way motivated by energy savings, eThekwini Municipality saw this as an ideal opportunity to install new, more efficient pumps and to ensure better control of these pumps through the use of variable speed drives.

The present pumps were commissioned in the 1970’s, so are now some 40 years old and needed to be refurbished. The new pump station will be equipped with new, more energy efficient pumps with variable speed drives to enhance energy savings still further. The existing biofilter-type odour control unit will be replaced with a new chemical system, consisting of scrubbers with a much smaller footprint than the current system (about 10% of the current footprint)

Description of Process:

At present around 60 ML/d of sewage is pumped by the Point Road Pump Station under the harbour entrance to the Central Wastewater Treatment Works on the Bluff. This wastewater treatment works services an extensive collection system, so by the time the sewage reaches the Point Pump Station it is low in dissolved oxygen and has become malodorous.

The pump station consists of four wet-wells situated three stories underground, but despite this, the turbulence associated with pumping results in significant amounts of hydrogen sulphide being released into the atmosphere, which the current biological odour control unit is failing to contain adequately.

The new pump station will be located some 200 m away from the current site at the harbour mouth. A new sewer line will be constructed to join the trunk sewer between the present site and the new site and will involve micro tunneling under Mahatma Gandhi Road (Point Road). The new pump station will be equipped with more efficient chemical scrubber systems for odour control, which will occupy an area of only around 10% of that occupied by the current odour control system.

Potential Interventions

Optimal energy savings are achieved by combining newer, more efficient pumps with variable speed drives. Without the variable speed drives, optimal energy savings cannot be achieved

Range of potential Savings

The real incentive for this project was odour control, however the new pumps will be far more energy efficient and it will be possible to have better operational control of them due to the variable speed drives. It has been calculated that replacement of the old station with the new one will bring about an energy saving of around 1 100 kWh/d (i.e. 401MWh/annum).eThekwini Municipality purchases electricity from Eskom at around R0.50c/kWh, so this amounts to a savings of approximately R200 000/annum.

The new pumps will be more efficient than the old pumps, but most of the energy saving is due to the variable speed drives and since the current pumps needed to be replaced or refurbished in any case, the payback period has been calculated based on the capital cost of the variable speed drives only. The cost of the pumps has not been taken into account.The tender submission date for the new pumps and variable speed drives had not been advertised by March 2013 and therefore prices were not available when finalizing this case study. However, using approximate costs and based on electricity tariffs of R0.50c/kWh and an annual escalation of 8% on electricity cost (the increase allowed to ESKOM for the next 5 years)s, the payback is estimated at around 11 years.

Case Study SA-EM2

RELOCATION OF THE POINT PUMP STATION

Ref Case Study SA-EM2 Response information, description and remarks

1Location:

eTthekwini Metropolitan, Durban, South Africa.High density urban population.

2 Sector: Wastewater

3 Works Owner or Operator: The pump station is owned and operated by the eThekwini Municipality, Durban, South Africa

4 Size: The pump station presently has a capacity of 60 ML/d. There are 4 pumps (3 duty and 1 standby), although usually only 1 or 2 pumps are in operation, except at periods of peak flow.

5 Energy Provider: Electricity is presently purchased from Durban Electricity, which in turn purchases electricity from Eskom, the national electricity agency. Electricity tariffs are expected to increase significantly over the next 7-10.However of more concern to eThekwini Municipality is the increased demand for electricity countrywide and the resultant power outages that occur during periods of high demand.

6 Process: This is a pump station, so it is a physical process. The current odour control system is biological, but the new system will consist of chemical scrubbers.

7 Component: The project involves the entire pump station and odour control system. This is the only pump station on this particular sewer trunk line.

8Motivation for the case study: The motivation for construction of a new pump station at a new site was not

due to energy savings. However the municipality saw an opportunity to reduce energy consumption and the new pumps will be variable speed pumps which are not only more energy efficient, but will also allow for more efficient operation. The potential for energy saving here made the project more attractive and will reduce the payback period.

9 Process/Plant changes: The old pumps will be replaced with new pumps with variable speed drives and a new pump station will be constructed about 200m away from the present station, which will then become redundant. The new pump station will need to be equipped with all the necessary electrical fittings and operational controls.

10 Civil/Physical Changes: A completely new pump station will be constructed together with a new chemical scrubber system for odour control. The new odour control system will have a much smaller footprint than the existing system (about 10% of the current system)

11Operational Changes: Fundamentally the process will not change, but the new pumps will be

operated through a SCADA system, which means It will be more advanced in terms of control tools, but otherwise there will be no real changes to the process. eThekwini Municipality already has the skills in-house for operation of the scada system, but some additional training of the existing operator will be required.

12 Risks and Dependencies: The real risk lies in not undertaking this project. Maintenance costs are increasing as the pump station ages, the current pumps are not energy efficient, the cost of electricity has increased by some 25% over the past 3 years and are expected to treble again over the next 7 to 10 years and of course, the odour problem, the initial motivator, will also become greater as development in the area increases.

13 Implementation: A tender has already been awarded to Group Five Construction for the civil contract and is presently underway. This is a 2 year contract that started in October 2011 and is due for completion by October 2013.

14 Energy Efficiency gains: Energy efficiency gains will be due to the new, more efficient variable speed pumps. Not only do these pumps use energy more efficiently, but variable speed control allows better control of the pumps, so reducing energy usage when flows are low.It has been calculated that the energy savings due to the new pumps will be 1100 kWh/d (401MWh/annum) compared to the energy consumption of the present pumps.

15 Cost/Benefit analysis: Based on the cost of variable speed drives only (and excluding the cost of the new pumps), an energy savings of 1 100 kWh/d (401MWh/annum) at a cost of R0.50/kWh for 2013 and an annual escalation of 8% in electricity tariffs, the payback period has been calculated as around 11 years.

16Project review: The relocated pump station will in fact be a completely new one, so will

include the latest in design and technology, including the most efficient pumps and odour control systems available, so at this stage, there are no improvements that could be made.

17 Confidence grade: High. The technology being used has been successfully used elsewhere, so although the project has not been completed yet, the confidence grade is high.

18Reference/Information source Peter von Brandis, eThekwini Municipality, Durban, South Africa.

GOBA Consulting Engineers.