TECHNOLOGICAL PERSPECTIVES ON THE NEW SOUTH AFRICAN EFFLUENT

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					    Presented at the WISA 2000 Biennial Conference, Sun City, South Africa, 28 May – 1 June 2000

TECHNOLOGICAL PERSPECTIVES ON THE NEW SOUTH AFRICAN
       EFFLUENT (WASTE) DISCHARGE STANDARDS

                                 André M van Niekerk
         Wates, Meiring & Barnard (Pty) Ltd, P O Box 6001, Halfway House, 1685
                         Tel (011) 254 4800, Fax (011) 315-0317
                                  andrevn@wmb.co.za

1         REGULATORY BACKGROUND
          The new National Water Act, Act 36 of 1998 aims at the protection of the national water
          resources for long term sustainable use. Special attention is given to the availability of water
          in sufficient quantity and of acceptable quality for basic human needs and the natural aquatic
          environment.

          The National Water Act contains a new list of identified water users, including such water-
          related practices as:

          •=   water abstractions
          •=   effluent (waste) discharges
          •=   evaporation of effluent (waste)
          •=   land uses, which impact the natural runoff, etc.

          Setting of waste discharge standards is one of the regulatory tools available to influence the
          activities of waste dischargers. The formulation of such waste discharge standards requires a
          substantial effort, since the National Water Act covers a wide spectrum of waste discharges
          (treated effluents, leachates, polluted stormwater, etc.) taking place in different water
          environments (streams, rivers, dams, estuaries, groundwater and oceans) from a range of
          different residential, commercial, agricultural, mining and industrial sectors.

          This paper presents the technology input into the process of developing new waste discharge
          standards. The initial development of standards was specifically aimed at the municipal
          sector, since the majority of point source waste discharges is associated with the municipal
          sector. The development of waste discharge standards will be continued to address a range
          of point-source and diffuse source pollution from all significant waste-contributing sectors.

          Different tactical approaches, from a regulatory perspective, could be taken in developing
          waste discharge standards:

          •=   Minimum standards, based on a relatively low level of waste treatment which is
               enforced without exception. Such standards would be considered as the absolute
               minimum to be achieved, even if the treated waste discharge takes place into a large
               stream with ample dilution. For most waste discharges, this approach would then
               require an impact assessment and site specific negotiations with the regulator.
          •=   Protective standards, based on a relatively high level of waste treatment, aimed at
               achieving protection of the water environment in the majority of situations. Impact
               assessment for site-specific waste discharge standards would be restricted to large
               dischargers to sensitive water environments.




                                                    1
    The latter approach was selected in view of the specific emphasis in the National Water Act
    on the regulatory obligation to ensure protection of water resources and the lower level of
    regulatory intervention required to administer the system.

2   MUNICIPAL DOMESTIC WASTEWATER SECTOR
    No complete data base of all the wastewater treatment plants was available at the time
    (1998/99) of initiating the development of new waste discharge standards. The available
    data base included a total of 1 062 wastewater treatment plants, but excludes many of the
    plants located in the former homeland areas. The data base does, however, provide some
    perspective on the sector.

    The distribution with respect to the nominal size of the wastewater treatment plants,
    expressed in terms of a design flow is reflected in Table 2(a).

    Table 2(a) : Distribution of waste treatment plant sizes
             Treatment capacity of plant                          Percentage (%)
     less than 1 Mℓ/day                                                 47
     1 – 5 Mℓ/day                                                       19
     6 – 20 Mℓ/day                                                       9
     21 – 100 Mℓ/day                                                     5
     More than 100 Mℓ/day                                                2
     Not specified                                                      18


    Statistical analysis of the available information indicates that an estimated 8 000 Mℓ/day of
    municipal wastewater is treated and mostly discharged in South Africa.

    A variety of different treatment technologies is also employed in the waste treatment sector.

    Table 2(b) summarises the application of treatment technology and indicates that no single
    technology dominates the sector.

    Table 2(b) : Range of waste treatment technologies employed

               Treatment technology                               Percentage (%)
     Oxidation ponds                                                    16
     Biological filtration                                              23
     Activated sludge and biofiltration                                  6
     Activated sludge                                                   35
     Not specified                                                      20



3   GENERIC PROCESS FOR DEVELOPING TECHNOLOGY-
    BASED WASTE DISCHARGE STANDARDS
    The generic process for developing technology-based waste discharge standards is based on
    a sequence of steps involving the following considerations:

    •=   Selection of an appropriate waste treatment technology for a specific waste generating
         activity or sector
    •=   Evaluation of a selected waste treatment technology performance.
    •=   Socio-economic impact assessment of the selected waste treatment technology



                                             2
    It is essential to have input from the stakeholders involved in a specific waste generating
    activity or sector at critical milestones during the waste discharge standards development
    process. The generic process for the development of waste discharge standards is shown
    graphically on Figure 3.1

    The South African application of this generic process to municipal waste dischargers is
    summarised below:

    •=   The selected waste generating sector was the municipal sector, specifically focussed on
         the discharge of predominantly treated domestic waste
    •=   Municipal waste discharges are characterised by a typical diurnal flow pattern,
         primarily dictated by the water use pattern in the domestic sector. Wet weather storm
         events and associated ingress and infiltration into the sewer system will change the
         flow pattern.
    •=   The common water quality variables of concern in the municipal waste sector are COD,
         suspended solids, ammonia nitrogen, nitrate nitrogen, phosphate phosphorus, salinity
         and a range of trace metals. Microbiological quality is also important.

    A selection of an appropriate level of waste treatment, based on the general philosophy of a
    precautionary approach to protection of water resource was done. The level of waste
    treatment was selected to be advanced secondary treatment. This level of treatment can be
    achieved by ponds, biological filtration, activated sludge or a combination of these
    processes, with specific features dealing with nitrogen and phosphorus removal.

    The following steps were taken in evaluating the selected treatment technology:

    •=   Local and international information on the performance of advanced secondary
         treatment process was reviewed.
    •=   A number of sites at which the technology is applied was selected for evaluation. The
         financial constraints on the project restricted the number of technology sites, which
         could be included in the evaluation.
    •=   Performance data was retrieved from the different sites for an operations period of 12
         months to cover seasonal variation in technology performance.
    •=   The performance data was analysed and statements were prepared on the removal of
         different pollutants.
    •=   The proposed waste discharge standards were based on the reliable removal of
         pollutants at advanced secondary treatment plants.

    The financial constraints on the development of the waste discharge standards have not
    allowed a thorough evaluation of the social (skills development, retraining, job creation,
    etc.) or economic (capital expenditure, operating and maintenance costs, imported
    technology, affordability, etc.) impacts of the new proposed discharge standards at this
    point.

4   WASTE DISCHARGE STANDARDS FOR KEY SANITARY
    VARIABLES
    The main pollutants or indicators of pollution removed by advanced secondary treatment of
    municipal waste are COD, suspended solids, nitrogen and phosphorus. The microbiological
    quality (specifically the presence of potentially disease-causing agents) is also improved by
    waste treatment.




                                            3
The following protocol was followed in developing the proposed waste discharge standards
on the basis of technological considerations:

•=   A sample of 31 wastewater treatment plants, incorporating advanced secondary
     treatment, was selected. These plants were located in Gauteng, Mphumalanga, North-
     West and Northern Province.
•=   The variation in treated effluent quality over a period of 12 months was analysed for
     each plant in terms of 5 percentile, median and 95 percentile concentrations
•=   The plant performances were ranked in terms of both the median effluent
     concentrations (C50) and the ratio between the 95 percentile concentration (C95) and the
     median concentration (C95)
•=   The technologically achievable treated effluent concentration was based on the plant
     performance ranked as the 25 percentile.
The results of the survey of the advanced secondary treatment plants are shown graphically
as follows:

•=   COD concentrations on Figure 4(a)
•=   TSS concentrations on Figure 4(b)
•=   Ammonia nitrogen concentrations on Figure 4(c)
•=   Nitrate nitrogen concentrations on Figure 4(d)
•=   Phosphate phosphorus concentrations on Figure 4(e).

The proposed discharge standard was then calculated as:

               S       =       C50 (C95 /C50)
     where     S       =       proposed discharge standard (mg/ )
               C50     =       median concentration of treated effluent from plant ranked as
                               the 25 percentile plant (mg/ )
               C95 /C50 =      ratio of 95 percentile to median concentration of the plant
                               ranked as the 25 percentile plant.
In general, achievement of these proposed waste discharge standards would require
operation within the reliable plant treatment capacity, competent plant operations and
maintenance, control at source of toxic and inhibitory wastes discharged to the plant and
special measures to deal with peak waste flows and loads.




                                         4
Figure 3.1




             5
                                                                                Figure 4(a) Advanced Secondary Waste Treatment Plant Performance
                                                                                                Treated Waste COD Concentrations


                             200


                             180


                             160


                             140
COD Concentration (mg/l)




                             120
                                                                                                                                                                                       5%
                             100                                                                                                                                                       50 %
                                                                                                                                                                                       95 %
                                           80


                                           60


                                           40


                                           20


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                                                                                 Figure 4(b) Advanced Secondary Waste Treatment Plant Performance
                                                                                           Treated Waste Suspended Solids Concentrations


                                                     120




                                                     100
                           SS Concentration (mg/l)




                                                         80


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                                                         60                                                                                                                           50 %
                                                                                                                                                                                      95 %


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                                                                                 Figure 4(c) Advanced Secondary Waste Treatment Plant Performance
                                                                                               Treated Waste Ammonia Concentrations


                                                            25




                                                            20
                      Ammonia Concentrarion (mg NH3-N/l)




                                                            15
                                                                                                                                                                          5%
                                                                                                                                                                          50 %
                                                                                                                                                                          95 %
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                                                                                Figure 4(d) Advanced Secondary Waste Treatment Plant Performance
                                                                                               Treated Waste Nitrate Concentrations


                                                           25




                                                           20
Nitrate Concentration (mg NO3-N/l)




                                                           15
                                                                                                                                                                            5%
                                                                                                                                                                            50 %
                                                                                                                                                                            95 %
                                                           10




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                                                        Figure 4(e) Advanced Secondary Waste Treatment Plant Performance
                                                                      Treated Waste Phosphate Concentrations


                                       9


                                       8
Phosphate Concentration (mg PO4-P/l)




                                       7


                                       6


                                       5                                                                                   5%
                                                                                                                           50 %
                                       4                                                                                   95 %


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                                                                                  8
    The proposed new waste discharge standards, after evaluation by the receiving water impact
    specialists, are contrasted with the achievable performance of advanced secondary
    treatment.

                                                 Advanced secondary         Proposed waste
        Pollutant parameter          Units
                                                     treatment            discharge standard
     Chemical oxygen demand        mg/ℓ                  50                       65
     Suspended solids              mg/ℓ                  15                       20
     Ammonia nitrogen              mg N/ℓ                2,0                      3,0
     Nitrate nitrogen              mg N/ℓ                7,0                     15,0
     Phosphate phosphorus          mg P/ℓ                0,8                      1,0


    Public health considerations and the impact of free chlorine (the most commonly employed
    disinfectant in South Africa) on the natural aquatic environment, dictated the following
    proposed new waste discharge standards:

    Faecal Chloroform              < 100 #/100 mℓ

          Free chlorine            < 0,1 mg/ℓ

5   WASTE DISCHARGE STANDARDS FOR TRACE METALS
    A national survey of the presence of trace metals in the treated waste streams discharged to
    receiving waters was conducted. The survey covered a total of 63 plants with a geographical
    distribution across all the provinces – refer to Figure 5(a). All the surveyed plants had at
    least secondary level of treatment, with some plant also having a form of tertiary treatment.

    Trace metals are removed in advanced secondary treatment plants by oxidation,
    precipitation and adsorption to biomass. It is, however, not the current practice to install
    dedicated unit treatment processes, specifically focussed on the removal of trace metals in
    municipal treatment plants.

    The technology-based proposal for waste discharge standards was based on the observed
    95 percentile trace metal concentration in treated effluents from plants not receiving a
    significant industrial waste contribution. It was argued that plants receiving a significant
    industrial waste contribution must implement source-based pollution control (via
    enforcement of municipal Bylaws) to achieve the proposed discharge standards. The
    technology-based proposal was modified by the requirements for protection of other water
    users, in particular the natural aquatic environment. The modified proposed waste discharge
    standards are contrasted with the original technology-based proposals – refer to Table 5(a).




                                             9
Figure 5(a)




              10
Table 5(a) : Proposed waste discharge standards for metals
                                               Technologically*       Proposed Waste Discharge
              Trace Metal           Units          achievable                   Standards
                                                   Standards          Short term         Long term
         Aluminium                   ug/ℓ                45                 50               30
         Arsenic                     ug/ℓ                53                 60               30
         Cadmium                     ug/ℓ              <10                   8               1
         Chromium III                ug/ℓ               <5                 110              110
         Chromium VI                 ug/ℓ               <5                  20               20
         Copper                      ug/ℓ              <10                   6               2
         Cyanide                     ug/ℓ              N/A                  30               6
         Iron                        ug/ℓ               187                300              300
         Lead                        ug/ℓ              <50                  10               9
         Manganese                   ug/ℓ               277                400              400
         Mercury                     ug/ℓ              <10                   2               1
         Nickel                      ug/ℓ                13                N/S              N/S
         Selenium                    ug/ℓ              <100                 50               8
         Zinc                        ug/ℓ               114                 50               50
         * Based on advanced secondary treatment, no significant industrial contribution

6       TECHNOLOGICAL IMPLICATIONS OF NEW DISCHARGE
        STANDARDS
        The proposed new waste discharge standards have certain implications for municipal waste
        treatment. These implications can be categorised in terms of operations and maintenance,
        infrastructure and technology development.

        The proposed discharge standards will require a higher level of operations and maintenance
        of municipal waste treatment plants. In general, two options exist for competent operations
        and maintenance:

        •=   Allocation of more resources to further training and empowerment of human resources.
             Collaborative efforts or regional sharing of scarce trained resources may be required.
        •=   Outsourcing of operations and maintenance services to competent contractors.

        More attention will have to be given to control at source of potentially toxic and inhibitory
        waste and operations under abnormal operating conditions, such as peak wet weather flows,
        low temperature, etc.

        The South African wastewater treatment industry is well placed with respect to proven and
        reliable technology to meet the new proposed waste discharge standards. Development and
        implementation of new technology will, however, be required to achieve:

        •=   Nitrification (ammonia oxidation) and denitrification (nitrate reduction) for older
             treatment technologies such as ponds and biological filtration
        •=   Combination of different conventional “older” treatment processes such as ponds and
             biological filters, with “newer” treatment processes, such as activated sludge to reliably
             achieve the new waste discharge standards.
        •=   Alternative disinfection technology or if chlorination is applied, a form of
             dechlorination will be required.
        •=   Tertiary treatment using established technology as constructed wetlands may in future
             also be required, especially with respect to metals polishing.


                                                 11
    The new waste discharge standards will continue to place a burden on municipal authorities
    to invest capital for upgrading of old plants and construction of new plants. It is estimated,
    based on a current national municipal wastewater production of 8 000 M /day, that the
    replacement value of existing municipal treatment infrastructure amount to R16 billion. This
    substantial past investment will have to be maintained, retrofitted and expanded to meet the
    new waste discharge standards.

    It may be appropriate to launch a fresh initiative for the research and development of new
    and revolutionary treatment technology to renew the national infrastructure asset.

7   CONCLUSIONS
    The National Water Act, Act 36 of 1998 required a reconsideration of appropriate waste
    (effluent) discharge standards, specifically with respect to the protection of the natural
    aquatic environment.

    A precautionary approach was adopted and the new waste discharge standards will be
    protective under most conditions.

    The new waste discharge standards did take technological constraints into account and were
    tested, at least partially, on advanced secondary treatment of domestic wastewater.

    The new waste discharge standards do however pose a challenge with respect to competent
    operations and maintenance of wastewater treatment plants. Upgrading of existing
    treatment plants using older technologies such as ponds and conventional biological --------
    will be required. More advanced and new technologies will be required to achieve reliable
    compliance with certain aspects of the new standards:

    •= ammonia oxidation

    •= disinfection

    •= polishing




                                            12

				
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