Evaluation of a sequential biological concentration system in natural resource management of a saline irrigated area

Wastewater need not be disposed to an evaporation basin until all useful benefit has been extracted from the waste stream. Sequential Biological Concentration (SBC) of saline drainage streams offers the ability to create a number of financial opportunities, whilst concentrating the waste stream to a manageable volume. In this paper, we present field data from the first three cells of a six-cell SBC system, to evaluate the potential for sustainable management of saline drainage on irrigated lands. The field data indicate that the progressive increase in salinity can be accommodated by using suitable cropping choices, although yields and hence financial returns could be smaller in the cells with the highest salinity water applications. Significant reductions in other pollutants were achieved during flow through the first cell of the SBC system, with appropriate irrigation and drainage management. In the SBC system we are motivated to grow the highest value crops at the different salinities, provided that adequate yields are maintained. Crop yield levels were maintained up to stage 2 which was irrigated with 3.6 dS/m water, but declined to about half in stage 3 when irrigated with 10.8 dS/m water. Changes in soil profile salinity show that a saline soil was progressively ameliorated due to leaching of the excess salts through provision of a subsurface drainage system and irrigation with 1.2 dS/m water. The SBC stage 1 soil salinity changes were very marked during leaching in the first two years, and very gradual in the subsequent years. A similar pattern of soil salinity changes was observed in the other SBC stages. An advantage of the FILTER type systems over traditional land-based sewage treatment is that the FILTER system can operate without building up salt in the soil profile, and thus ameliorate previously salinised sites not considered suitable for irrigated cropping. The performance of the last three cells of the proposed SBC system has been successfully tested in Australia and overseas. This SBC system with suitable modifications could potentially be used to handle saline drainage from other sources in Australia, such as dry land and urban areas.