Potsdam WWTW - Upgrade & Extension

Newsletter No 2 - November 2007

Introduction The Potsdam Wastewater Treatment Works (WWTW) is located opposite the Caltex Oil Refinery in Table View. In response to the significant development occurring in the Blaauwberg Area, the City of Cape Town identified the need to upgrade and extend the Potsdam WWTW. Environmental approval was obtained in December 2002, authorising the proposed activities. Interested and Affected Parties (I&APs) subsequently appealed against Department of Environmental Affairs and Development Planning’s (DEA&DP) decision. Accordingly the then acting MEC of Environmental Affairs reviewed his Department’s Record of Decision. The MEC issued his ruling on 27 June 2003 in which he upheld the original Record of Decision, with various modifications to the Conditions of Approval. Construction activities at the Potsdam WWTW commenced towards the end of 2004, and considerable progress had been made since then. In light of the keen public interest attached to this project, both during the Environmental Impact Assessment (EIA) process and since the initiation of construction, the first Potsdam Newsletter was circulated in March 2006 to update the I&APs with of the project’s progress. This second publication serves as a further progress update on the future development of the project.

General The upgrading and extension of the Potsdam WWTW comprises various improvements to some of the existing facilities and a capacity increase from 32 mega litres per day (Mℓ/d) to 47 Mℓ/d. The works are currently receiving approximately 35 Mℓ of wastewater daily. The additional 8 Mℓ interim capacity plant was commissioned in August 2007 and has alleviated dependency on the existing biofilter plant, thereby improving the overall quality of effluent leaving the plant. Construction for the Phase II Main Extension of the works is progressing well and is on track towards providing the full 47 Mℓ/d plant by April 2008. The following sections provide a more detailed overview of the key components of the upgrades currently being undertaken on site.

Interim Capacity Plant Since it was anticipated that the proposed activities at Potsdam WWTW would take the better part of four or five years to complete, the City and its consulting engineers devised an approach to construction where an additional 8 Mℓ/d could temporarily be provided to relieve pressure from the existing process capacity. Once the main extension is commissioned the interim capacity plant will fall away and its structures will be modified to serve as aerobic digestors instead. From this point the biofilter plant will no longer be used. The interim capacity contract is currently in its maintenance period which will continue until August 2008. The works’ staff and engineer are working together to achieve the operating conditions that will treat the effluent to Department of Water Affairs and Forestry (DWAF) standards. It is expected that the correct balance meeting these standards will be established shortly.     Figure 1: Effluent from Interim Capacity plant, October 2007.

Disinfection of Final Effluent The Final Scoping Report for the Potsdam WWTW reported that the Ecoli present in the final effluent leaving the WWTW significantly exceeded the standards set by DWAF. Although the impact of this on Rietvlei and the Diep River must be contextualised against the background of the poor quality of water travelling down the Diep River and entering the Milnerton Lagoon from the Theo Marias stormwater outfall and other sources, the City recognised that this was unacceptable and accordingly provided for the disinfection of the final effluent. The contract for disinfection of the final effluent from the works was completed in February 2007. The system uses a set of lamps which emit ultraviolet radiation into the effluent stream to neutralize any bacteria present. The effectiveness of this treatment is dependant on the effluent clarity which is measured using a transmissivity index (UVT). The Ecoli are removed to within acceptable limits when the effluent has a UVT of 45%. A portion of effluent, approximately 30%, is still treated through the biofilter plant with the result that the overall effluent clarity is less than ideal. Once the main extension of Potsdam WWTW is commissioned and the biofilters are decommissioned the overall effluent UVT is expected to exceed 45% which will lead to excellent disinfection performance within the permitted limits (set at 1000/100ml). Figure 2: Ultraviolet treatment of final effluent.

Table View East Odour Control Biofilter During the EIA process concerns were raised by the various I&APs, regarding odours emanating from the works. In light of these concerns, amelioration of this impact was prioritised by the City and a comprehensive approach to odour control was adopted. Figure 3: Odour control biofiltration plant at the Table View East pumpstation The first phase of the odour control strategy was implemented at Tableview East Pumpstation, a prime source of odours at Potsdam WWTW. The pumpstation is located on the banks of the Diep River, opposite a residential area. The pumpstation was sealed and air extracted through a dedicated biofiltration plant. The biofilter contains bacteria which remove odorous compounds from the air stream before it is released to atmosphere. The contract for odour control at the Tableview East Pump Station was completed in August 2007 with the biofilter successfully achieving the specified treatment levels. The plant was evaluated in four quarterly tests over a one year period which started in August 2006. The performance of the biofilter was calculated by measuring the hydrogen sulphide (H2S) levels in the inlet and outlet air streams. The odour control biofiltration plant was initially fed by treated effluent to humidify the biofilters. At one point the department controlling the effluent reuse introduced hypochlorite into the effluent stream to prevent algae growing in their pipelines and filters. This hypochlorite effectively poisoned the bacteria in the biofilters. It took some time to determine the cause of the problem, at which point we reverted to using potable water in the humidification process. Having switched to potable water it took a further month or two for the biofilters to recover to their normal balance. It should be noted that the Table View East pumpstation odour treatment facility is only one of the planned odour abatement measures. Pursuant to the completion of the main extension, a main odour treatment contract will be implemented to deal with the off-gases from the other odour-producing sites which include the new inlet works, the new and existing primary settling tanks and the new sludge dewatering facility. Moreover, the decommissioning of the biofilter works will also reduce odours as these are open to the atmosphere.

Electrical Supply Upgrade Work has been completed on the medium voltage electricity supply to the works which is now on a ring main ensuring that power to any part of the plant is not interrupted should a portion of the supply cable require maintenance. Furthermore, there is now a standby electrical generator on site which allows the Tableview East pump station and the UV disinfection facility to function independently in the event of a power failure. A generator is also planned to provide emergency power to the new inlet works and raw sewage pump station. These generators will ensure that critical processes can operate at all times and that the risk of overflowing under power failure conditions will be dramatically reduced.

Budget The project is now in its fifth year with a total of R150 million of the budget having been spent thus far. This represents 64% of the total budget available for the six year project. There are a number of contracts currently under preparation or out to tender that will further upgrade the works as follows: • The construction of a new dewatering plant to increase the sludge handling capacity of the plant. • The construction of a new inlet works to increase and improve the screening process. • The installation of odour control measures as part of the current main extension contract. • The installation of a further generator as a contingency in the event of power failure.

Environmental Considerations The Record of Decision issued by DEA&DP attached various conditions to the authorisation. Most importantly, the City of Cape Town was required to keep I&APs informed by constituting an Environmental Monitoring Committee (EMC) and to develop and implement an Environmental Management Plan (EMP) for the construction phase: • The Potsdam EMC was constituted in July 2004, and comprises the following: » City of Cape Town; » Ward Councillors; » Friends of Rietvlei; » Table View Residents Association; » Milnerton Residents Association; » Milnerton Ridge Residents Association; » Parklands Homeowners Association; » Wildlife and Environment Society of South Africa; » Representative for developers; » Representative for effluent re-users; » DEA&DP; » The Department of Water Affairs and Forestry (DWAF); and » The Environmental Control Officer (ECO), who also acts as Chair and fulfils the secretarial functions of the EMC. The role of the EMC is to monitor and report to the City of Cape Town, DEA&DP, DWAF and their organisational constituents on the construction activities associated with the upgrading and extension of the Potsdam WWTW, in terms of the environmental requirements set in the Record of Decision and the EMP. Since its constitution, the EMC has held 14 meetings, the frequency of which has been dictated by the EMC members. As per the requirements of the Record of Decision, an EMP was compiled and approved by the DEA&DP. The EMP takes the form of a series of environmental specifications that are integrated into Tender Documentation for each contract. ANA were appointed as the Environmental Control Officer (ECO) for the construction phase, and are responsible for monitoring day-to-day compliance by the various Contractors with the requirements of the EMP. The ECO reports on a monthly basis to the City of Cape Town, the EMC and DEA&DP. As per the requirements of the Record of Decision and good practice, the ECO and EMC will continue to monitor compliance with the environmental requirements. [ANA is a joint venture comprised of ASCH, Ninham Shand and Africon. Michael Mangnall and Tinka Shapiro from the Ninham Shand Environmental Discipline Group are acting as the ECO.]

The Way Forward The Phase II Main Extension of the activated sludge works is on programme for completion in April 2008. This will see a dramatic improvement in the quality of the effluent produced by Potsdam WWTW and will increase the capacity of the plant to 47 Mℓ/d. Next Year (2008) will be a busy year at Potsdam WWTW with a number of contracts to be awarded before the year end that will culminate in completion of the project in April 2009. Interested and affected parties will be kept informed on a quarterly basis by projects newsletters issued by the City of Cape Town. However, should more frequent or detail information be required, I&APs should feel free to contact their representatives on the EMC or the ECO (Michael Mangnall or Tinka Shapiro Tel: 021 481 2400, Email: enviro@shands.co.za).

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