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Recommendations for the Design Details of Sewage Pond Effluent Refuse or Disposal Facilities to Prevent Mosquito Breeding Medical Entomology

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Recommendations for the Design Details of Sewage Pond Effluent Refuse or Disposal Facilities to Prevent Mosquito Breeding Medical Entomology Powered By Docstoc
					Recommendations for the Design
 Details of Sewage Pond Effluent
  Refuse or Disposal Facilities to
      Prevent Mosquito Breeding




                            Medical Entomology
                      Centre for Disease Control
               Department of Health and Families
                  Northern Territory Government
                                      April 1998
                Recommendations for Design Details of
               Sewage Pond Effluent Reuse or Disposal
                Facilities to Prevent Mosquito Breeding

         Background
         Sewage facilities are one of the most prolific sites for mosquito breeding around
         many towns in the NT. This mosquito breeding can produce a public health threat by
         producing conditions for the transmission of a number of arboviruses including Ross
         River virus and Murray Valley encephalitis.


         There are a number of sewage treatment and sewage effluent projects proposed in
         Central Australia under the HIP program. A number of questions have been raised on
         the appropriate design of effluent reuse facilities to disperse or use treated effluent
         from aerobic treatment ponds. General recommendations on the prevention of
         mosquito breeding in sewage ponds or effluents can be found in the general
         reference listed below. Any proposal to build sewage ponds or dispose or reuse
         sewage effluent should be in accord with the “Policy for the design of off site sewage
         ponds and the disposal or reuse of sewage pond effluent” by Department of Health
         and Community Services.


         In general inland treatment and disposal of effluent requires tertiary and final
         evaporation ponds to be as small as possible in accord with the expected seasonal
         effluent production and rainfall considerations, to avoid large shallow expanses of
         effluent in standing vegetation. Large expanses of shallow effluent are ideal for
         breeding a range of mosquito species and make the efficient control of mosquito
         larvae very difficult.


         Some form of sprinkler system for the disposal or reuse of effluent is the preferred
         option, as this method can increase evaporation, and be managed for various
         effluent disposal or reuse requirements.


         The following recommendations are brief replies to specific questions raised by
         Environmental Health in Central Australia.




Recomendations for Design of Sewage Pond Effluent Dsiposal                                         Page 1
         Recommendations for effluent reuse areas

         1. Appropriate design of sprinklers and the reticulation system
         The design of a sewage reuse reticulation system should be undertaken by a
         recognised irrigation specialist. Generally the reticulation system will depend on
         wether the effluent is to be used for a beneficial use or to be disposed.


         For disposal, the irrigation system should aim to spread the water evenly over an
         area such that it can be efficiently disposed in dry and wet season conditions without
         pooling of effluent or ecologically deleterious run off. Generally the sprinkler heads
         should be of a higher volume capacity and in a number of lines so that areas can be
         spelled before reapplication. The disposal area should ideally have native or other
         suitable trees in the area to increase evapo-transpiration, but pasture irrigation is a
         suitable alternative if the ground is level and long term infiltration is possible.


         For beneficial use, under tree or spray irrigation with ground sprinklers is generally
         more suitable than overhead sprinklers as it reduces water loss by evaporation.
         Beneficial use systems may additionally require excess effluent disposal systems to
         dispose of effluent during rainy periods when effluent is not required for the beneficial
         use.


         Generally the irrigation system should be underground to reduce fire and
         maintenance damage after vegetation growth. In areas of tree or shrub irrigation
         where ground maintenance may not be regular or possible, the sprinklers should be
         metal with metal uprights to promote spray distribution and to reduce fire damage by
         accident or use as a management tool.


         2. The use of appropriate plants in the disposal area
         The species of plants in the disposal area will depend on species local suitability, the
         beneficial use of the plants, and the degree of maintenance that can be carried out.


         Irrigation to grass for ovals and landscape areas may require a higher standard of
         effluent for public health reasons and to prevent algal or other blockages in the
         sprinkler system.


          Pasture species such as lucerne can be suitable in some areas, as it is more hardy
         and perennial than most grasses. Irrigation for pasture is generally only suitable if it
         can be slashed and mown regularly so that it can be fed to off site animals or animals
         can be rotated to various areas. Irrigation to pasture for enclosed animals is generally
         not recommended as they may trample the vegetation and compact the soil which
         can lead to ponding of effluent.




Page 2                                                 Recomendations for Design of Sewage Pond Effluent Dsiposal
         Tree species such as Eucalyptus camaldulensis, (the ‘River red gum’) is suitable for
         use over a wide area of inland Australia and can have a beneficial use as firewood or
         shelter. They can handle increased water application and high nutrient loads. Many
         arid native species can not handle long term water application and high nutrient
         loads. Other suitable species can be provided by the Parks and Wildlife Commission
         of the NT. Generally high volume sprinkler irrigation to trees requires less
         management than other methods of dispersal.



         3. Suitable types of fencing around the disposal area
         All reuse areas should be fenced to demark the application area to prevent
         application of effluent or drift to people. Suitable signs will be required around the
         reuse or disposal area. Standards and requirements should be checked in the code
         of practice and various guidelines mentioned in the policy document above.



         4.Ongoing maintenance issues with the disposal area
         Some of the maintenance issues have been dealt with in the above sections. The
         main requirement for inland areas is to design disposal or reuse systems that require
         minimum maintenance. Usually this will involve underground distribution systems and
         fire proof above ground components.


         Generally tree forest or bush irrigation systems require high stand metal risers and
         relatively high volume metal sprinklers to avoid grass interruption to the spray
         pattern, fire damage, maintenance damage and the need for regular grass mowing.
         Fire resistant tree species such as native Eucalyptus species are often more suitable
         than Acacia species, as fire can be used as a cheap and easy management tool.


         Under tree sprinkler systems generally require a lot more mowing maintenance and
         application of weedicide such as glyphosate, and may need fire protection to protect
         poly pipe take offs or plastic spinners. Larger sprinkler heads are generally less
         prone to blockages. Higher volume under tree sprinklers are generally more efficient
         in preventing blockages compared with small volume sprinklers, with drippers posing
         the most maintenance problems with root growth and ant blockages. Smaller
         sprinkler systems generally require some form of filter to prevent blockages and
         these filters generally require regular maintenance.



         5. Project Advice
         The Medical Entomology Branch is available for specific project advice on the
         prevention of mosquito breeding in effluent disposal or reuse systems. This is best
         considered at the initial planning stage and would require as much documentation as
         possible to be sent direct to the Medical Entomology Branch by the relevant
         environmental health officer in the various regions.




Recomendations for Design of Sewage Pond Effluent Dsiposal                                        Page 3
         Written By:
         Peter Whelan
         Senior Medical Entomologist
         Department of Health and Families




         References
          ‘Mosquito breeding and sewage treatment in the Northern Territory’, Peter Whelan
         Department of Health and Community Services. Reprinted from ‘Water’, Journal of
         the Australian Water and Wastewater Association. Vol 15, No. 5, Dec 1988, pp 34-
         38.


         Policy for the design of off site sewage ponds and the disposal or reuse of sewage
         pond effluent. Department of Health and Community Services, June, 1997.




Page 4                                               Recomendations for Design of Sewage Pond Effluent Dsiposal

				
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