Increased water demands due to population growth, increased urbanisation and urban intensification especially in dry countries such as Australia, has led to increased adoption of various water reuse practices. Irrigation of greywater (all water discharged from the bathrooms, laundry and kitchen apart from toilet waste) is one potential means of easing water demands. Despite widespread adoption, there is limited knowledge of greywater reuse and the accumulation and potential impacts of the constituents of greywater (nutrients, major ions, metals and micro-pollutants) in soil, groundwater and surface water. This study compared four residential lots that had been irrigated with greywater for four years and adjacent non-irrigated lots that acted as controls to assess the sustainability of greywater irrigation. The irrigation volumes of greywater applied, the physicochemical water quality parameters and soil chemistry profiles were assessed for each lot. Assessments were made by comparing measured concentrations to national and international guidelines and determining whether organic micro-pollutants in irrigated greywater were transferred to shallow groundwater and an adjacent surface waterway. In assessing the sustainability of greywater irrigation, the data clearly showed benefits as the volume of water saved was 1.6 million litres of potable water from the four lots over four years (i.e., 100 000 L per household per year). However, the environmental sustainability of greywater irrigation from a potential contamination point of view differs depending on the water quality of the greywater.
Incorrect use and/or lack of understanding of how household products affect irrigated greywater can result in phosphorus posing a risk to the environment. Irrigated greywater from some lots displayed a risk of phosphorus interacting with the surrounding environment where as some showed minimal impacts and thus demonstrated sustainability. Greywater also increased concentrations of some metals in irrigated soil and resulted in As, B, Cr and Cu exceeding soil quality guidelines after only four years of irrigation. Movement of metals from the irrigation areas resulted in metal concentrations in groundwater (Al, As, Cr, Cu, Fe, Mn, Ni and Zn) and surface water (Cu, Fe and Zn) that exceeded environmental quality guidelines within four years. These results indicate the need to consider metals in greywater in order to minimise potential adverse environmental effects from greywater irrigation.
A total of 22 organic micro-pollutants were detected in greywater. Six of these (acesulfame, caffeine, DEET, paracetamol, salicylic acid and triclosan) were selected as potential tracers of greywater contamination. Three of these chemicals (acesulfame, caffeine, DEET) were detected in the groundwater, while salicylic acid was also detected in adjacent surface water. Caffeine and DEET in surface water were directly attributable to greywater irrigation. Thus the practice of greywater irrigation can act as a source of organic micro-pollutants to shallow groundwater and nearby surface water.
This research found greywater irrigation contributes substantially to surface water loads of caffeine, DEET, salicylic acid, SO42-, Al, B, Cu, P and N and indicates greywater irrigation can impact the aquatic environment. This research and holistic data set (organic micropollutants,nutrients, major cations and anions as well as metals and metalloids) as a result of irrigated greywater impacting three connected environment compartments (soil, groundwater and surface water). This data will be useful to validate and calibrate specific models and algorithms, allowing the modelling of catchment management scenarios for greywater land use and assessing the potential environmental impacts on aquatic environments.
This Doctoral dissertation is, to the authors’ best knowledge, the first to study the practice of sub-surface greywater irrigation in Australia and the potential impacts of its physicochemical properties, major ions, nutrients, metals, metalloids and organic micro-pollutant concentrations, loads and yields in three connected environmental compartments — soil, groundwater and surface water. It provides the first comprehensive assessment of the environmental fate of greywater constituents irrigated to land.
The results clearly demonstrate that with knowledge, appropriate household product use and responsible use of greywater, that greywater irrigation can be a sustainable practice. However, if the treatment of greywater is not suitable for long-term irrigation, and the retention of greywater constituents within the soil sub-surface irrigation zone is not achieved, then environmental harm is likely to occur.