6. WASTEWATER. 6.1 Overview. 6.2 Darvill Wastewater Works

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1 6. WASTEWATER 6.1 Overview Umgeni Water currently owns and operates the Darvill and Ixopo Wastewater Works (WWW). The Howick and Lynnfield Park WWW are operated for umgungundlovu District Municipality and Msunduzi Municipality respectively under a management contract, and the Albert Falls North and South WWWs as part of the management of Albert Falls Dam. All existing operations are based on current technology, namely aeration basins for biological nutrient removal and clarifiers for the separation process. 6.2 Darvill Wastewater Works The Darvill WWW (Figure 6.1) serves the Msunduzi Municipality. This WWW has a current biological treatment capacity of 65 Ml/day. Current average daily inflow (Oct 2007 to Oct 2014) is approximately 81 Ml/day (Figure 6.2) which is more than the plant s capacity. The graph also indicates the spike in flow in the summer seasons when there is ingress of stormwater into the sewer system. Figure 6.1 Darvill Wastewater Works. 372

2 Volumes (Ml/day) Average Daily Inflow Poly. (Average Daily Inflow) 20 Jan-07 Jan-08 Jan-09 Jan-10 Jan-11 Jan-12 Jan-13 Jan-14 Month Figure 6.2 Average daily inflow (Ml/day) to Darvill WWW. Umgeni Water is currently in the process of upgrading Darvill WWW to cope with the increased inflows and predicted wastewater demands (Figure 6.3). The average dry weather flows (ADWF) within the Darvill WWW catchment are expected to grow to about 90 Ml/day by 2020 (Figure 6.3). 160 Influent Volume (Ml/day) ADWF Plant Capacity (Existing) Plant Capacity (Proposed) Scenario 1: TLS Scenario 2 : Projected based on Historical Growth Scenario 3 : Expected Developments YEAR Figure 6.3 Projected Inflow into Darvill WWW 373

3 The plant will initially be upgraded by 35 Ml/day. The upgrade design will make allowance for expansion in the future to a maximum capacity of 120 Ml/day, which is forecast to occur in Some of the proposed infrastructure upgrades are illustrated in Figure 6.4 As a summary the proposed civil and process infrastructure upgrades at Darvill are as follows:- Biological treatment o Convert the existing Aerobic Reactor to an Anaerobic / Anoxic reactor o Construct a new reinforced concrete Aerobic Reactor ( m 3 ) Air for Biological Treatment o Blower House o 4 x 645 kw Blowers each with a rated delivery of 7 m 3 90 kpa o Air Header Mains o diffusers in three aeration lanes Secondary Settling o 2 x 35 m diameter secondary settling tanks Advanced Treatment o Reinforced Concrete Submerged Membrane Tank o Submerged Ultra-Filtration (UF) Membrane System complete with suction pumps, backwash blowers and CIP chemical storage and dosing Additionally a new 2 Ml/day Ultra-Filtration (UF) membrane system will be designed, which will treat the final effluent to potable standards. The post-treatment facility will serve a dual purpose. Firstly, it will supply all the wash-water for the works. Secondly, the facility will be representative of a full-scale reclamation plant. As such it will provide opportunities for further research into wastewater reclamation and serve as a valuable example of reclamation in practice to stakeholders. More information is available on the Darvill Reuse project in Section 4. The present method of disposal of sludge by spray irrigation to land is operating adequately, but has its limitations especially as the capacity of the works increases to cope with growth. Alternative methods of sludge treatment and disposal are being investigated in order to determine the optimal future disposal strategy. A feasibility report, which looks at the management and disposal of sludge produced by the works has been completed and the following recommendations have been included in the proposed upgrade:- Refurbish the existing Gravity Thickeners Construct a new sludge treatment building with mechanical thickening of waste activated sludge and digester sludge dewatering plant. Construct a new sludge sump for blending thickened primary and waste activated sludge and new digester feed pump station Construct two new Egg-Shaped digesters. 374

4 Darvill Figure WWW 6.4 Proposed Darvill WWW Infrastructure proposed infrastructure Upgrades upgrades. 375

5 6.3 Ixopo Wastewater Works Ixopo WWW (Figure 6.5 and Figure 6.6) serves the town of Ixopo in the Harry Gwala (Sisonke) District Municipality. The WWW has a design capacity of 1.0 Ml/day and is designed to be doubled. Sludge is dried on beds and disposed of on a local farm that was owned by Umgeni Water, but has been sold to the Harry Gwala (Sisonke) District Municipality. The average daily inflow to the Ixopo WWW is shown in Figure 6.7 Figure 6.5 Ixopo Wastewater Works. 376

6 Figure 6.6 General layout of the Ixopo WWW. 377

7 1.40 Average Daily Inflows (Ml/day) Average daily inflow Polynomial Mar-02 Mar-03 Mar-04 Mar-05 Mar-06 Mar-07 Mar-08 Mar-09 Mar-10 Mar-11 Mar-12 Mar-13 Month Figure 6.7 Average daily inflow (Ml/day) Ixopo WWW Historically, an upgrade to the WWW had not been envisaged, until the inflow to the works climbed to 20% above the design capacity prior to Plans were in place to increase the works capacity with the construction of an additional clarifier (3.25 Ml/day), however, the urgency for this planned upgrade no longer exists as the inflows to the works decreased significantly in The reduced inflow is because of blockages in the Ixopo sewer network, which overflow into the environment. As a result return flows to the wastewater water works have reduced as is evident in Figure 6.7. Despite the aforementioned Umgeni Water will proceed with the construction of the new clarifier in Umgeni Water has provided assistance to the municipality in improving the condition of the sewer network in an effort to reduce the blockages. The increase in capacity at the works will also cater for planned new developments in Ixopo. 6.3 Howick Wastewater Works and Mpophomeni Wastewater Works Umgungundlovu District Municipality provides wastewater treatment services for the umngeni Local Municipality at the Howick WWW. A large pump station at the Mpophomeni WWW site and a set of six smaller pump stations in Howick transfer wastewater for treatment at Howick WWW. Umgeni Water has a management contract with Umgungundlovu District Municipality to operate this WWW on their behalf. Howick WWW (Figure 6.8) has a design capacity of 6.8 Ml/day and is currently treating on average 5.8 Ml/day (Figure 6.9) (Oct 2012 Oct 2014). Mechanical dewatering equipment installed in 2013 has alleviated operational problems to a degree but the works still has capacity problems during peak periods. If additional treatment capacity is required, the WWW will have to be upgraded. 378

8 Figure 6.8 Chlorine Contact Tank Howick Wastewater Works Average Daily Outflow (Ml/day Average daily outflow Polynomial 0 Sep-12 Nov-12 Jan-13 Mar-13 May-13 Jul-13 Sep-13 Month Nov-13 Jan-14 Mar-14 May-14 Jul-14 Sep-14 Figure 6.9 Average daily outflow (Ml/day) Howick WWW Mpophomeni WWW is currently not functioning, and is only used as a transfer station to Howick WWW. This WWW will be reinstated as a treatment facility by Umgeni Water who will recover costs through a management contract with the Umgungundlovu District Municipality. The proposed plant will be designed to treat 6 Ml/day with the possibility of upgrading the works to 12 Ml/day. The site has space for at least 20 Ml/day. 379

9 The Mpophomeni WWW upgrade is required to free up capacity at Howick WWW and to also cater for planned development in the area. The following developments initiatives by the municipality will be serviced by the Mphophomeni WWW in future:- Refurbishment of existing sewage reticulation system in Mphophomeni Township will increase wastewater flows to the works (ADWF 3.6 Ml/day) The development of the Khayelisha social housing development on the banks of Midmar Dam (ADWF 1.3 Ml/day) Planned light/mixed industrial development park (3 Ml/day) These major infrastructure developments and others have been taken into consideration in the planning for the upgrade of Mphophomeni WWW. Umgeni Water has been requested to manage the implementation of the upgrade to the works and to take over its operation on completion of construction. Construction is envisaged to take place towards the end of Lynnfield Park Wastewater Works The Lynnfield Park Wastewater Works (WWW) is a small (0.2 Ml/day) works that services part of the Ashburton area. Umgeni Water has recently taken over the operation of the works on behalf of the Msunduzi Local Municipality and has a three year management contract. Inflow to the works is estimated at approximately 0.15 Ml/day as there is no inflow meter. Umgeni Water is in the process of constructing a weir and flume to measure the outflow. 6.5 Albert Falls North and South Wastewater Works The two Albert Falls WWWs (Figure 6.10) are transportable activated sludge units installed for the construction of the dam in the early 1970s. They were probably originally designed for approximately 100 m 3 /day (0.1 Ml/day). The bulk of the current feed to these WWWs is from conservancy tank contents delivered by tanker from the Albert Falls and Bon Accord resorts. Umgeni Water refurbished the WWW to a Sequencing Batch Reactor (SBR) configuration with a treatment capacity of 40 m 3 /day to suit present demands. 380

10 Figure 6.10 Albert Falls Wastewater Works. 381