1. INTRODUCTION 1.1 Potsdam Plant

A sewage plant belonging to The City of Cape Town which is based in the Milnerton area in Cape Town is divided in to two sections. These section are divided in such way that one is called the 1997 plant and the other one being called 2008 plant based on the years which those plants were built. The water which was treated in the 1997 plant was being sold to the private companies by the City of Cape Town then because of high demand of this water the 2008 plant was built. There was a problem that was experienced considering the quality of water that was obtained from the 2008 plant. A research was conducted as to find the problem which lead to the quality of water being what it was.

1.2 Purpose of the report

The purpose of this report is to give feedback on what were the aspects that might have lead to the research being conducted and it will also look at what was found to be the problem when the research was conducted. The report will include also the solutions that were tried out on trying to overcome the problem that was found. A comparison between a literature review to what was found be operating at the plant will be discussed as to determine wherether the operating machines of the plant were used the way that they are suppose to and if the are place at right places or not.

1.3 The research

During the research that was done on what might be the problem on the water that it was of the quality that it was, it was found that the was less oxygen fed to the water when the water comes out of the surface area zone. This problem was assumed that it might be caused by the aerators that are installed in the 2008 plant. Trying to find a problem in the aerators was challenging as they are quiet a number of thing that are involve in the operation of the aerators. Looking at motors at the aerators, they were found to be ones of varying speeds which were changing automatically changing according the need of them doing so. Some of the things that were considered were wherether the aerators that were used were the right aerators and if they were at the required height to operate on the conditions at which they were operating. The fact that the motors could automatically change the speedy gave a suggestion that the aerators being the right type of aerators should be able to handle the water that enters the surface aerator area in high volumes 30ML to be specific.

This now lead to the other aspect which was what might cause the motors to run at a speed that is less or more than required. The first thing which was looked at was the probes that are responsible to be the ones that indicate to the motors what speed are they suppose to be running at according to the amount of the oxygen needed in the water. The probes at the time at which the research was conducted were under repair because of that they were found to be delivering the wrong massage to the motors as to what speedy they should be running at. The power consumption was one important aspect of the research when looking at what time was the problem of less oxygen occurring as it is understood that the oxygen available at the atmosphere during the 24hours of a day varies. Weather is also one of the aspects which were considered to be the ones that affect the availability of oxygen though the day.

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2. Literature reviewed

2.1 mechanical aeratorsMechanical aerators are commonly divided into two groups based on major design and operating features: aerators with vertical axis and aerators with horizontal axis. Both groups are further subdivided into surface and submerged aerators. In surface aerators, oxygen is entrained from the atmosphere; and in the submerged aerators, oxygen is entrained from the atmosphere and, for some types, from air or pure oxygen introduced in the tank bottom. In either case, the pumping or agitating action of aerators help to keep the content of the aerators tank or basin mixed. In the following discussion, the various types of aerators will be described, along with aerators performance and energy requirement for mixing. (George, Franklin, Stensel,2004;443)

Figure 1: top view of the new plant in Potsdam.(www.googlehealth.com).2.1.1 Type of aerators:2.1.1.1 Surface mechanical aerators with vertical axis.Surface mechanical aerators with vertical axis are design to induce either updraft or downdraft flows through a pumping action. Surface aerators consist of submerged or partially submerged impellers that are attached to motors mounted on float or fixed structures. The impellers are fabricated from steel, cast iron, noncorrosive alloys, and fiberglass-reinforced plastic and are used to agitate the wastewater vigorously to facilitate solution of the air. Surface aerators may be classified according to the type of impeller used: centrifugal, radial-axial, or axial; or the speed of rotation of the impeller: low and high speed. Centrifugal impellers belong to the low-speed category; the axial flow impeller type aerators operate at high speed. In low-speed aerators, the impeller is driven through a reduction gear by an electric motor. The motor and the gear box are usually mounted on a platform that is supported either by piers extending to the bottom of the tank or by beams that span the tank. Low speed aerators may also be mounted on floats. In high-speed aerators, the impeller is coupled directly to the rotating element of the electric motor. High-speed aerators are almost mounted on floats. These units were originally developed for use in ponds or lagoons where the water surface elevation fluctuates, or where a rigid support would be impractical. Surface aerators may be obtained in sizes from 0.75 to 100 kW (1 to 150 hp). (George, Franklin, Stensel, 2004; 443-444)

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Figure 2: mechanical aerators with vertical axis in Potsdam

In Potsdam waste water treatment, a TMA type of aerator is in use on the new plant.

2.1.1.1.2General Description:

The TMA Aerator is a vertical shaft surface aerator which provides a mechanical means of oxygen transfer to sewage or industrial effluent.Manual, or any required degree of automatic control can be provided, including adjustment of aeration intensity by dissolved oxygen monitoring.The TMA Aerators are easily constructed and are available for conventional bridge mounting, on tripods with light access bridges, in simple rectangular tanks or channels which can vary in size and arrangement.TMA Vertical Shaft Aerators can be installed in any configuration within aeration lanes thereby offering a broad range of treatment capabilities from small communities to major installations. (biwaterconsultancy.co.uk, 2006; 1)

2.1.1.1.3 Design: Biwater TMA aerators provide sufficient oxygen input and maximum mixing characteristics with a minimum expenditure of power. The proven operating characteristics mean that the installations are simple, inexpensive and efficient.Complete mixing and appropriate circulation velocities though the aeration tanks are achieved with the robust non-clog design. (biwaterconsultancy.co.uk, 2006; 1)

2.1.1.1.4 Process: Oxygenation of the fluid promotes cultivation and reproduction of micro-organisms which carry out the treatment process by breaking down organic matter.Oxygenation also re-establishes dissolved oxygen levels in the final effluent in order to sustain plant and animal life when discharged into rivers and lakes.Vertical shaft aerators achieve oxygen transfer by developing a large interface between air and liquid so that oxygen can diffuse from the air into the liquid. In achieving this it is necessary to prevent local build up of oxygen concentration by promoting good mixing within the liquid.The Simplex Aerator satisfies both these criteria by drawing up sub-surface liquid and discharging it in heavy torrents, thus creating heavy turbulence upon striking the liquid surface with great force. (biwaterconsultancy.co.uk, 2006; 1)

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Figure 3: Impeller of a vertical surface aerator in Potsdam

2.1.1.1.5 Technical Data: Biwater Treatment offers a standard design of Simplex Aerators in the range of 3KW to 200KW. All aerators are guaranteed for the standard aeration efficiency (SAE) into clean water (at 15 Deg. C) of 1.8Kg02/kW/hr (based on motor shaft power).

Splash protection can also be provided in the form of GRP or steel covers.

Full scale test conditions can be simulated for the majority of aerators at Biwater’s purpose built research test facility, which has an adjustable volume of up to 2250m³ and a maximum power input of around 100kW. (biwaterconsultancy.co.uk, 2006; 1)

2.1.1.1.6 Special specifications of a slow speed type of TMA aerator: • Power ratings from 3kW to 200kW.• Slow speed, range is 40 to 60 rpm.• Complete mixing• (SAE) into clean water 1.8 kgO2/kWhr• Up to 4.0m diameter• Bridge mounted or floating.( biwaterconsultancy.co.uk , 2006; 2)

2.1.1.1.7 OXYGEN TRANSFERThe design of the TMA aerator provides high levels of oxygen input with Maximum mixing characteristics while using minimum power. (biwaterconsultancy.co.uk, 2006; 2)

2.1.1.1.8 CONTROLManual or any require degree of automatic control can be provided, including adjustment of aeration intensity by dissolved air monitoring. This, when linked with immersion level changes or variable speed Motor control, enables optimum performance of the aeration plant to be obtained at all times. Consequent reductions in power consumptionResult in considerable savings. (biwaterconsultancy.co.uk, 2006; 2)

2.1.1.1.9 NON-CLOG DESIGNOpen aerator blades radiate from a central hub and debris cannot accumulate in the aerators. The efficiency of the aerator is thus maintained without the need to clean the blades. The

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aerators can operate in various volumes and are available in powers of up to 132 kW. (Gillard, biwaterconsultancy.co.uk, 2006; 2)

2.1.1.1.10 MOUNTING ARRANGMENTSThe TMA aerators are available for conventional bridge mounting, on tripods with light access bridges or on Floats. They are suitable fur use in simple rectangular tanks or channels which can vary in size and arrangement. In certain tank configurations baffles may be fitted if required. Low tip speeds allow for reduced platform heights. (biwaterconsultancy.co.uk, 2006; 1)

2.1.1.2 Mechanical aerators with horizontal axis.Mechanical aerators with horizontal axis are divided into two groups: surface and submerged aerators. The surface aerators are patterned after the original kessener brush aerator, device

used to provide both horizontal cylinders with bristles mounted just above the water surface. The bristles were submerged in the water and the cylinder was rotated rapidly by an electrical motor drive, spraying wastewater across the tank, promoting circulation, and entraining air in

the waste water. Angle steel, steel of other shape, or plastic bars or blades are now used instead of bristles.

Figure 4: Mechanical aerators with horizontal axis (freepatentsonline.com, 2009; 1)

Submerged horizontal-axis aerators are similar in principle to surface aerators except disks or paddles attached to rotating shafts are used to agitate the water. The disk aerator has been used in numerous applications for channel and oxidation ditch aeration. The disks submerged in the waste water for approximately one-height to three-eight of the diameter and enter the water in a continuous, nonpulsating manner. Recesses in the disks introduce entrapped air beneath the surface as the disk turns. Spacing of the disks can vary depending on the oxygen and mixing requirements of the process. Typical power requirements are reported as 0.1 to 0.75 kW/disk (0.15 to 1.00 hp/disk). (George, Franklin, Stensel, 2004; 445)

2.1.1.3 Aerators performance.Mechanical aerators are rated in terms of their oxygen transfer rate expressed as kilograms of oxygen per kilowatt-hour (pound of oxygen per horsepower-hour) at standard conditions. Standard condition exist when the temperature is 200 C, the dissolved oxygen is 0.0 mg/L, and the test liquid is tap water. Testing and rating are normally done under non-steady-state conditions using fresh water, deaerated with sodium sulfite. Commercial-size surface aerators range in efficiency from 1.20 to 2.4 kg O2/kW.h(2 to 4 lb O2/hp.h). Efficiency claims for

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aerator performance should be accepted by the design engineer only when they are supported by actual test data for the actual model and size of the aerator under consideration. (George, Franklin, Stensel,2004;446-447)

2.1.1.4 Energy requirement for mixing in aerators systems.As with diffused-air systems, the size and the shape of the aeration tank are very important if good mixing is to be achieved. Aeration tanks may be square or rectangular and may contain one or more aerators. The depth and width of the aeration tanks for the mechanical surface aerators are dependent on aerator size. Depths up to 11 m (35 ft) have been used with submerged-draft tube mixers. In diffuser-air systems, the air requirement to ensure good mixing varies from 20 to 30m3/103.min of the volume of the tank, for a spiral-roll aeration pattern. For a grid system of aeration in which the diffusers are installed uniformly along the aeration basin bottom, mixing rates of 10 to 15 m3/103 m3.min have been suggested. Typical power requirements for maintaining a completely mixed flow regime with mechanical aerators vary from 20 to 40 kW/103 m3, depending on the type and design of the aerator, the nature and concentration of the suspended solids, the temperature, and design of the geometry of the aeration tank, lagoon, or basin. In the design of aerated lagoons for the treatment of domestic wastewater, it is extremely important that the mixing power requirement be checked because, in most instances, it will be the controlling factor. (George, Franklin, Stensel, 2004; 448)

3. HISTORY OF POTSDAM WWTW.3.1 Introduction

The Potsdam Wastewater Treatment Works (WWTW) has been undergoing an upgrade from 32 mega litres per day (Mℓ/d) to 47 Mℓ/d. Currently the Plant is receiving an annual average of approximately 37 Mℓ of wastewater daily. Construction began towards the end of 2004 and was scheduled to be completed towards the middle of 2009.

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3.2 General

The upgrading and extension of the Potsdam WWTW comprises decommissioning the biofilter plant of 15Mℓ and extending the plant capacity to 47 Mℓ/d. The upgrade of the WWTW will result in a much improved effluent quality to meet the standard requirements set by the Department of Water Affairs and Forestry (DWAF).

The 8 Mℓ interim capacity plant which was commissioned in August 2007, to alleviated dependency on the existing biofilter plant and allow developments to continue, is no longer in use as the 30 Mℓ extension has been in operation since April 2008. Phase II of the main extension, which includes the bioreactor, various pumpstations, primary and secondary settling tanks, odour control and dewatering facilities, is now nearing completion.

3.4 UV DisinfectionThe Potsdam WWTW was essentially the pioneer for this technology in the Western Cape as it is only the second such installation in the country. The only other such installation is at the Daspoort WWTW in Tswane. The choice of the technology was based primarily on the fact that it is the more environmentally friendly in that it is not a major hazardous installation and it does not produce potentially harmful by-products. Although the UV disinfection unit at Potsdam was commissioned in 2006, it could not meet the required disinfection rate until the Biofilters were taken out of commission in June 2008 (when the new activated sludge plant capacity was in operation). This was because the Biofilter effluent could not meet the

3.3 30 Mℓ Plant Extension and Upgrade to Treatment Works

The raw sewage is split between the old (1997) 17 Mℓ/d plant and the new 30 Mℓ,/d plant. The new raw sewage pumpstation pumps the raw sewage to the 3 newly constructed primary settling tanks. The settled primary sludge from the settling tanks is pumped via the primary sludge pumpstation to the sludge holding tanks before it is dewatered and sent for composting or disposed of to a landfill site. The overflow from the primary settling tanks is discharge to the bioreactor. The newly constructed bioreactor consists of two identical streams each with a capacity of 15 Mℓ/d. The outflow from the bioreactor is settled in secondary settling tanks to separate the treated wastewater from the biomass solids. The underflow is returned to the beginning of the bioreactor as it contains organisms which are responsible for removing impurities from the wastewater. The treated overflow is discharged through a series of maturation ponds before it undergoes UV disinfection and either re-used or discharged to the Diep River.( friendsofrietvlei.co.za,2008;1)

The tanks, which were used for the interim 8Mℓ/d capacity, as discussed above, have been modified to operate as aerobic digester tanks. A certain quantity of sludge which is periodically removed from the bioreactor is thickened and with the use of oxygen further biologically degraded. This procedure is to ensure that the dewatered sludge meets beneficial re-use requirements. The commissioning of these tanks is under way.( friendsofrietvlei.co.za,2008;1).

Figure 1: Interim capacity prior to conversion

However, there is still construction work in progress on site. The sludge dewatering capacity of Potsdam is currently being further upgraded in order to accommodate the increased requirement for solids dewatering.The main extension has been operating in the manner described in the first paragraph since April 2008. The biofilter plant has since been decommissioned.

The extension of the odour control units on site is also underway (discussed in greater detail below). New odour control units will be provided at the new raw sewage pumpstation and the new and old primary settling tanks which are in general the main sources of odour at wastewater treatment works. .( friendsofrietvlei.co.za,2008;1)

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transmissivity specification. June 2008 marked the first time since in the history of the operation of the Potsdam WWTW that all the effluent discharged from it complied with the DWAF legislation.( friendsofrietvlei.co.za,2008;1).3.5 Single Discharge PointThe two sets of maturation ponds both discharged upstream of the Diep River / Rietvlei confluence. To minimise the negative impact that the effluent may have on the wetland, the maturation flow pattern was re-arranged so that the two separate process streams are combined before the UV disinfection unit and discharged into a final holding pond before overflowing to the Diep River by-pass channel.( friendsofrietvlei.co.za,2008;1)3.6 Increase Re-use of EffluentBefore the extension, the Works supplied institutions and industries such as Century City, Caltex, SAPPI, golf courses and several schools with treated effluent for industrial and irrigation purposes. This accounted for 30% of the summer flow that would otherwise be discharged to the Diep River. Most of the re-use water was abstracted from the Biofilter plant’s maturation ponds which meant that some of the customers were not always happy with the water quality and had to treat it further on their premises. The construction of the De Grendel reservoir and the 800mm supply pipeline built by the Reticulation Branch has extended the re-use capacity to supply several more customers, including farmers in the Durbanville area. Recent (2008) figures indicate that a weekly average of up to 76% of the effluent can be re-used in dry weather. With the new activated sludge reactors now on-line, an improved water quality will be supplied to the City’s customers.( friendsofrietvlei.co.za,2008;1)3.7 New Activated Sludge ReactorsThe continued operation of the Biofilters, which treated approximately half of the influent to the Works, was the major reason of the non-compliance of the treated effluent. They had to be replaced with more suitable treatment facilities. The two new Bioreactors are designed to biologically remove phosphorous and can each treat up to 15 Mℓ/d. This has essentially given the Works increased treatment capacity, up to 47 Mℓ/d. The flow diversion has now alleviated some of the load onto the older activated sludge plant, which has also shown some performance improvement.( friendsofrietvlei.co.za,2008;1)3.8 Effluent QualityTables 1 and 2 summarise the average performance of the Bioftiler Plant and the Activated Sludge Plants (ASP) respectively.

Table 1: Average performance of Biofilter Plant from Jan 01 – Apr 06

   Biofilter

Plant

Effluent standard

requirement

    Average  

COD mgCOD/ℓ 91 <75

Ammonia mgN/ℓ 11 <10

Nitrate mgN/ℓ 5.0 <15

Phosphate mgP/ℓ 6.0 <1.0

Total Suspended Solids

mgTSS/ℓ 23 <25

E.coli   3.1x105 <1.0x103

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It is clear from Table 1 that the effluent quality produced by the biofilters prior to the treatment works upgrade did not meet the effluent standard requirements.Table 2 indicates a notable improvement in the effluent quality produced by the 30 Mℓ ASP extension – which replaced the Biofilter Plant. (friendsofrietvlei.co.za, 2008; 1)

Table 2: Average performance of the ASP 97 and ASP 08.( friendsofrietvlei.co.za,2008;1)

    ASP 97 ASP 08Effluent standard

requirement

Sampling Period

 Jan 07 - Nov

08May 08 - Nov 08

 

    Average Average  

COD mgCOD/ℓ 58 44 <75

Ammonia mgN/ℓ 1.6 0.3 <10

Nitrate mgN/ℓ 3.3 3.7 <15

Phosphate mgP/ℓ 1.8 3.4 <1.0

Total Suspended Solids

mgTSS/ℓ 17 13 <25

The major public concern over the past few years has been the high E.coli levels in Milnerton Lagoon which is used heavily for recreational purposes. A graph in the print version of this newsletter shows the 4 stages of the construction period (2004 to present) in relation to the E.coli concentrations. The E.coli levels during Stage IV (June to November 2008) show a definite improvement over Stage III.The new acitivated sludge plant was optimised and is performing very well in terms of meeting the phosphate requirement. However, there is a slight increase in Phosphate during the effluent passage through the maturation ponds which sometimes causes the combined final effluent to just tip over the 1 mgP/ℓ mark. On going forward, we have to pay close attention to the Stage IV monitoring of the E.coli and phosphate concentrations in particular.3.10 Environmental ConsiderationsThe Record of Decision issued by the Department of Environmental Affairs and Development Planning (DEA&DP) attached various conditions to the authorization. Most importantly, the City of Cape Town was required to keep Interested and Affected Parties (I&APs) informed by constituting an Environmental Monitoring Committee (EMC) and to develop and implement an Env.( friendsofrietvlei.co.za,2008;1)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;

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» 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 18 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.Ironmental Management Plan (EMP) for the construction phase. ( friendsofrietvlei.co.za, 2008; 1)

Potsdam activated sludge reactor 2008 plant

DATES

Setteable S (ml/l)

TOTAL Suspended S (mg/l) Ph

RAS(ACT)SETTLEABLE SOLIDS (mg/l)

Incoming flow to the reactor(Ml)

21 December 2009 1000 5850 6.7   83.191

12 January 2010 960 4310 6.6 5240 81.423

19 January 2010 730 3580 6.5 6750 85.097

26 January 2010 550 3400 6.7 5280 90.644

02 February 2010 720 3420 6.9 5180 72.475

09 February 2010 450 2920 6.7 10880 94.246

16 February 2010 900 4500 6.7 6290 92.881

23 February 2010 960 4790 6.6 6180 93.025

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02 March 2010 800 4810 6.6 4770  

Figure 3.1: the data table obtained fro the 21december 2009 to 02 march 2010

4. RESULTS DISCUSSION

4.1 The Potsdam 2008 plant

4.1.1 Potsdam activated sludge reactor 2008 plant

Potsdam activated sludge reactor 2008 plant

21 December 200912 January 2010

19 January 2010

26 January 2010

02 February 2010

09 February 2010

16 February 201023 February 2010

02 March 2010

0

200

400

600

800

1000

1200

13December

2009

23December

2009

02January

2010

12January

2010

22January

2010

01February

2010

11February

2010

21February

2010

03 March2010

13 March2010

Dates

sett

leab

led

so

lids

(ml/l

)

Setteable S (ml/l)

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This section shows data of dates and settle-able solids that were managed to be settled at the dates between the 21 December 2009 and 02 March 2010 from the Potsdam activated sludge reactor 2008 plant see figure 3.1 above for the data table. Looking at the graph it shoes that towards the end of 2009 there was a high value of solids that were managed to be settled which that would give a suggestion that the plant was working fine at the time. As the time goes on going to the beginning of January 2010 towards the beginning of March 2010 the graph shows that the volume of solids that were managed to be settled was going up and down. Since it was already discovered that there was a problem with the surface aerator zone at this plant this could be the reflection of that as the plant was going through repairs at that area at that time.

Potsdam activated sludge reactor 2008 plant

6.7

6.6

6.5

6.7

6.9

6.7 6.7

6.6 6.6

83.19181.423

85.097

90.644

72.475

94.246 92.881 93.025

6.3

6.4

6.5

6.6

6.7

6.8

6.9

7

21 December2009

12 January2010

19 January2010

26 January2010

02 February2010

09 February2010

16 February2010

23 February2010

02 March2010

Dates

Ph

0

10

20

30

40

50

60

70

80

90

100

Inco

min

g flo

w to

the

reac

tor (

Ml/d

ay)

Ph Incoming flow to the reactor(Ml)

The above section contains a data table that has dates the ph and the incoming flow that comes to the surface aerator area. These readings are plotted in the graph above. Referring to

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the graph above the ph looks to be steady for all the dates which would have an average ph of 6.6. The incoming flow to the reactors also seems to be steady at all the dates.

incoming flow to the reactors and the settleable solid

12 January 2010

19 January 2010

26 January 2010

02 February 2010

09 February 2010

16 February 201023 February 2010

02 March 2010

21 December 20091 2

34

5

6 7 8

0

200

400

600

800

1000

1200

21December

2009

12January

2010

19January

2010

26January

2010

02February

2010

09February

2010

16February

2010

23February

2010

02 March2010

Dates

settl

eabl

e so

lid (m

l/l)

0

10

20

30

40

50

60

70

80

90

100

inco

min

g flo

w to

the

reac

tors

(ML)

Setteable S (ml/l) Incoming flow to the reactor(Ml)

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The data above contains certain dates which readings were taken of settle-able solids matching them up with the flow that came in at the same dates. Looking at the graph it shows that during the 12th of January 2010 is the volume of settle-able solids quiet high with only 81.423 ML coming in compared to the settle-able solids that were obtained on the 9 th on February 2010 with a high amount of incoming flow being 94.246 ML. This deference could be because around that time of 9th of February 2010 there were repairs which were taking place in the aerators. Going to the end of February 2010 the relationship between settle-able solids and the incoming flow seems to be stable which this could be because the repairing was done at the aerators.

Potsdam activated sludge reactor 2008 plant

5850

4310

3580 3400 34202920

45004790

5240

6750

5280 5180

10880

6290 6180

4810

4770

83.191 81.42385.097

90.644

72.475

94.246 92.881 93.025

0

2000

4000

6000

8000

10000

12000

21 December2009

12 January2010

19 January2010

26 January2010

02 February2010

09 February2010

16 February2010

23 February2010

02 March2010

Dates

(mg/

l)

0

10

20

30

40

50

60

70

80

90

100

Inco

min

g flo

w to

the

reac

tors

(ML/

day)

TOTAL Suspended S (mg/l) RAS(ACT)SETTLEABLE SOLIDS (mg/l) Incoming flow to the reactor(Ml)

The graph above shows a relationship between total suspended solids with the RAS (ACT) settle-able solids and the incoming flow to the surface aerators. Seemingly the relationship between the total suspended solids and the RAS (act) settle-able solids is quiet steady as the lines on the graphs show a relationship between the two where one increases the other one also increases. Again looking at these two lines on the 9 th of Feb. 2010 it shows that there must have been a problem around that time as there is a difference in the relationship between

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the two lines as the graph clear shows that. Looking at a relationship between the incoming flow and the total suspended solids, they form a good relationship which indicates that even though there was a problem with the probes on the days like the 9 th of Feb.2010 there was no effect on the total settle-able solids due to the high flow coming in.

    ASP 97 ASP 08

Effluent standard

requirement  ASP 08

Sampling Period  

Jan 07 - Nov 08

May 08 - Nov

08  

9-Feb-10- 2-

Mar-10    Average Average   Average

COD mgCOD/ℓ 58 44 <75 44.75

Ammonia mgN/ℓ 1.6 0.3 <10 0.525Nitrate mgN/ℓ 3.3 3.7 <15 2.525

Phosphate mgP/ℓ 1.8 3.4 <1.0 0.975

Total Suspended Solids mgTSS/ℓ 17 13 <25 9

Table 2: Average performance of the ASP 97 and ASP 08. (friendsofrietvlei.co.za, 2008; 1)

The table above shows the average of the ASP 97 and ASP 08 for a certain period of time which was taken from the internet, but the was an additional column which was put in. this column was of average performance of the ASP 08 at which an average numbers were taken from certain days which were between the period of time 9 th Feb.2010 to the 2nd March 2010. Looking at this table and comparing the results that were found when checking the average performance of the ASP 08 during the period of time from 9th Feb.2010 to the 2nd March 2010 the to column of the effluent standard requirement, one can say that the results meet the results meet the requirements. There is no much difference between the average performance of the ASP 08 between Jan.2008 to Nov.2008 and the average performance of the ASP 08

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between the 9th Feb.2010 to the 2nd March 2010 considering the fact that the average performance of the ASP 08 between the 9th Feb.2010 to the 2nd March 2010 was not taken for every day in that period of time. This would give an indication that even though there were problems with the probes but they did not have an effect on average performance of the ASP 08.

5. CONCLUDION ANS RECOMMENDATIONS

In conclusion it can be said that the research was a success as the problem that lead to the poor quality of water produces by the 2008 plant was found. It can also be said that the plant needs to be inspected so that if there are problems that are taking places they can be noticed by the people of the plant before the companies that the City of Cape Town sells this water to because that could have a high cost. Seemingly there were no complaints about the 1997 plant which its water was solid by the City. After the whole process of treating there water, the water that comes from the 2008 plant comes togetther with the water that comes from 1997plant so it was since there were no complaints before about the 1997plant then it was concluded that the quality of water is affected by the water that comes from the 2008 plant.

The plant of 2008 is a new plant so the kind of technology that is used on that plant is new compared to the one that is used to the 1997 plant but it is the one that is failing. A recommendation that can be made is that a company that gets to be employed must be researched on its previous jobs that it has done before. A number of quotations must be looked at and the company that should get a job should be a company that does a good job whether it’s expensive or not. It would be wise also to employ the company that built the 1997 plant to take over the job of building the 2008 plant even if they use the old technology building the plant because using the new technology while its not working accordingly would be a waste of money.

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6. Bibliography G.Tchobanoglous, F.Burton, H.stensel,2009, Wastewater engineering, 4thedition,

united State: Mc Graw Hill. Tony Gillard,2006, SURFACE AERATORS,[Friday 26st of 2010]

http://www.biwaterconsultancy.co.uk/products/TMA.htm Non,2008,Potsdam wwtw, [Wednesday 31st of 2010]

http://friendsofrietvlei.co.za/PotsdamNewsletter3.html Non,2009,Image of horizontal surface aerators, [Tuesday 30st of 2010] Non,2010,Cape Town , [Wednesday 31st of 2010]

www.google _earth.com