Two thirds of China's total crop production is from irrigated lands. There is, however, increasing pressure on water supplies from the spread of urbanisation and industrialisation. There is also increasing production of wastewater, resulting in environmental pollution. Most rivers, lakes, bays and groundwater sources are showing increasing signs of severe pollution, including from organic matter, nutrients, heavy metals and other toxic chemicals. As a result water use in agriculture, fisheries and recreation is greatly limited. Reusing effluent in suitable agricultural conditions is a possibility, provided appropriate land treatment and reuse techniques are in place. Soils with impeded drainage are particularly vulnerable to degradation and pollution unless properly managed.
The Australian Filtration and Irrigated cropping for Land Treatment and Effluent Reuse (FILTER) technique was developed for using effluent on soils with impeded drainage. FILTER uses nutrient-rich effluent for intensive annual cropping in combination with filtration of excess effluent through the soil to a sub-surface drainage system during periods of low-intensity cropping and high rainfall. A past ACIAR project proved the potential of the FILTER technique in China and Australia for sustainable irrigated cropping and nutrient reuse. This project promoted the use of FILTER in Shanxi Province.
The project had three main objectives:
to develop and field-test innovative FILTER techniques for sustainable irrigation with wastewater at a demonstration site in Shanxi Province;
to promote the application of FILTER technology for sustainable irrigation with wastewater in Shanxi and other Chinese provinces;
to develop simple integrated approaches for siting, design and operation of FILTER and related technology in China and Australia.
The project team developed and field-tested innovative FILTER techniques at a demonstration site in Shanxi Province by installing the irrigation system and instrumentation at the field site and establishing crops. Soil hydraulic and hydrological properties were characterised and irrigation applied on a preliminary schedule. Hydrology, crop performance and pollutant removal, along with cold weather infiltration performance were monitored. The drainage system was designed and an annual irrigation/drainage schedule and practices developed prior to the installation of either horizontal or vertical drainage, as required. Irrigation and drainage schedules were implemented and their effects on effluent, crops and pollutants were monitored.
For Objective 2, the Australian and Chinese scientists promoted the application of FILTER technology for sustainable irrigation with wastewater in Shanxi and other Chinese provinces by visiting potential sites and assisting wastewater managers with plans to apply the new technology. An inventory on wastewater problems in western China was prepared.
For Objective 3, the scientists developed approaches for siting, design and operation of FILTER and related technology in China and Australia. They collected data to use in existing models and to evaluate and apply models prior to testing existing models at other sites.
Objective 1 At Yanggao County near Datong city in Shanxi province, a field site consisting of three plots was installed on a farmer's field to evaluate the catchment-FILTER technology. The scientists studied summer, winter and groundwater components, using instrumentation to monitor wastewater and pollutant flows through the soil. During the summer season a very high hydraulic loading rate of domestic wastewater, around three times the crop's water requirement, was applied to a maize crop established on the FILTER plots. The pollutant removal in the process of wastewater movement through the soil and beyond the crop rooting depth was monitored. Concentrations of the major pollutants in the wastewater - Total P, Total N, NH4-N, Organic-N, and COD concentrations - were markedly reduced (by 97, 77, 99, 50 and 75% respectively) in the drainage water flows beyond the root zone.
These pollution removal rates in the Catchment-FILTER system are similar to those previously observed in land-FILTER sites with high watertables in Australia and China. However, due to better soil aeration conditions at this Catchment-FILTER site with deep watertables, the concentration of NO3-N levels in drainage water increased from zero to around 9 mg per litre, which needs close monitoring in future studies on field adoption of Catchment-FILTER technology. In spite of the high hydraulic loading rates of wastewater, the maize crop yields of 9.6 t per ha in FILTER plots compared well with district yields of 10.7 t per ha.
During the first winter season, shallow-ponding systems for wastewater infiltration used in north America under freezing conditions were tested at the Yanggao field site, but failed due to the heavy frosts in Datong. During the second winter season, an alternative deep-ponding approach was successful in maintaining an infiltration rate of around 0.2 m per day, with the formation of a 0.3 m floating ice-cap at the wastewater surface.
Soil-water-crop-solute models were applied for predicting wastewater and solute movement through the soil during the summer cropping season. In the second cropping season, the model provided accurate predictions of wastewater and solute flows through the soil profile. Application of the MAIZEMAN model provided accurate estimates of crop biomass accumulation, crop duration, soil water movement and nitrogen leaching.
The potential hydrogeologic impacts of the proposed FILTER system on the surrounding area were investigated. Data available from an existing long-term pond experiment were used to characterise aquifer properties. Boundary flux analysis carried out to quantify the net impact of FILTER on the surrounding areas indicated that a well designed and managed vertical drainage system could be used in a catchment-FILTER approach for domestic wastewater renovation at the site. There is a need to combine the hydrology modelling with detailed monitoring of biological and chemical contaminants present in the wastewaters, under the management practices proposed and adopted for the Catchment-FILTER site to ensure long-term sustainability.
Objective 2 Promotion of the application of FILTER technology for sustainable irrigation with wastewater irrigation in Shanxi and other Chinese provinces was carried out by the IWHR and SIWR researchers. The IWHR researchers in collaboration with Beijing Water Resources Bureau developed and successfully field-tested an innovative FILTER-polyhouse system to combine the FILTER technology with greenhouse agriculture systems to overcome the low infiltration during winter freezing conditions in north China. They also field-evaluated a modified land-FILTER system for treating domestic wastewater, in collaboration with Yunnan Environment Research Institute. The FILTER technology was also promoted at discussions with the Ministry of Science and Technology (MOST) and provincial authorities.
Objective 3 Simplified integrated approaches for siting, design and operation of the new FILTER and related technology in China and Australia were developed. These approaches are incorporated into the guidelines for using Land-FILTER and Catchment-FILTER systems for using wastewater in China and Australia.
Links:
[1] http://www.aciar.gov.au/country/China
[2] http://www.aciar.gov.au/programarea/Land and Water Resources