New technology for productive and sustainable reuse of wastewater for irrigated cropping

• Tianjin Water Conservancy Bureau, China
• China Institute of Water Resources and Hydropower Research, China

Valuable irrigation water supplies in China and many other countries are increasingly being diverted for city use and industry. As well as reducing water available for agriculture, the discharge of wastewater from urban and industrial uses contributes to environmental pollution.
Reuse of wastewater for irrigation in China could save scarce water supplies and produce the same economic benefits that have come out of many effluent irrigation projects around the world. It would also help deal with the serious environmental problems caused by the dumping of untreated sewage and industrial effluent into watersheds. However, inappropriate treatment and reuse techniques can result in agricultural products being contaminated with pollutants from the wastewater, or cause land degradation in the irrigated area or downstream.
CSIRO developed the FILTER (filtration and irrigated cropping for land treatment and effluent reuse) technique for Australia to overcome some of the problems in land treatment of wastewater. The system was designed to treat primary or secondary sewage and to use the nutrients from it for intensive annual crop-growing. The initial work tested the technique on clay soils in Australia, where it was found to reduce pollutant loads in wastewater and also ameliorate salinised land. However, its performance on non-clay soils and with different wastewaters has not been tested.
The FILTER technique allows wastewater to filter through the soil to a sub-surface drainage system. The filtration reduces the pathogen load and the phosphorus content so that the drainage waters are of a quality that can be safely discharged to any water body.

This project explored the potential of FILTER and other new technologies and assessed how they dealt with the wide range of wastewater treatment problems faced by managers in China and Australia. Project aims were to develop new and simple procedures for treating wastewater on land so that it could be productively reused. The FILTER technique, developed in Australia, would be tested for use in China and further tested in Australia.

The researchers field-tested FILTER at three sites: near Tianjin in China, on a farm near Griffith in New South Wales, and at the Griffith sewage works. Plots were set up either with or without FILTER and then soil status and wastewater quality compared.
Computer modelling was used to help improve the design and operation of FILTER and to aid in the evaluation of other treatment techniques. The work developed programs to help wastewater managers choose the best combination of treatment systems and optimise their operations.
There was close consultation with wastewater managers in Australia and China throughout the project. The field experimental sites were used for demonstration and training, and published information described the techniques and their relative advantages and restrictions.

Results of trials at both the Griffith and Wuqing sites showed marked reductions in pollutant loads to acceptable standards; crops removed high levels of nutrients and yielded well. The results confirmed that when the FILTER system is installed at sites featuring soil with a high capacity for phosphorus uptake, with a stable soil structure to maintain hydraulic flows, and appropriate groundwater conditions it can reduce pollutants markedly and make the drainage water suitable for reuse, other than for human consumption.
The research component of the commercial FILTER development in Griffith successfully demonstrated the extension of FILTER to sites which are less than ideal. Based on previous research on these soils the FILTER design was modified by the researchers to effectively address the on-field practical management problems on these soils and to increase the efficiency of the FILTER operations.
The FILTER technique produced water that meets Chinese standards, and also NSW Environment Protection Agency standards, for biological and chemical hazards. This has led to a further project LWR1/2002/113 Application of innovative irrigated cropping and soil filtration technology for wastewater reuse and treatment in China, in part a response to the heavy investment in the technology from the Chinese. The FILTER system technology alone will not solve all wastewater treatment problems in China. However, the research to date has shown that it forms an excellent, innovative component of a suite of potential solutions.