The use of properly designed and operated pond systems and irrigation with
treated effluent is generally accepted as the most cost-effective, method of waste
water treatment and disposal for sugar mills, provided that suffiCient land is available
at low cost for the ponds, and that land is available which is capable of being
irrigated. To minimise the amount of land used for ponds while still obtaining
adequate treatment, the geometric design of the ponds must be optimised. In
addition, to ensure that the use of ponds followed by irrigation remains available as
a treatment option for the Australian sugar industry, an industry~wide database on
the effect of storage and treatment of waste water in ponds on the local groundwater
should be established.
This paper reports on the development of a three-dimensional model of the
flows in a sugar mill effluent pond, and the design tools with which to optimise the
geometric design of new or existing ponds. It demonstrates that the technique is able
to predict hydraulic flow patterns in ponds and therefore calculate expected waste
water retention times for a specific pond geometry. The paper further reports on the
potential for waste water to migrate or seep from the storage ponds into the local
groundwater, and the development of procedures to monitor potential seepage. The
results show that in the pond studied, there was no indication of any pollutants
entering the groundwater. As seepage is influenced by many local factors, similar
monitoring at individual mills will need to be carried out to establish an industrywide
database on the effect of waste water storage and treatment on local groundwater.