Land application of sewage sludge (biosolids) in Australia: risks to the environment and food crops

Abstract

Australia is a large exporter of agricultural products, with producers responsible for a range of quality assurance programs to ensure that food crops are free from various contaminants of detriment to human health. Large volumes of treated sewage sludge (biosolids), although low by world standards, are increasingly being recycled to land, primarily to replace plant nutrients and to improve soil properties; they are used in agriculture, forestry, and composted. The Australian National Biosolids Research Program (NBRP) has linked researchers to a collective goal to investigate nutrients and benchmark safe concentrations of metals nationally using a common methodology, with various other research programs conducted in a number of states specific to regional problems and priorities. The use of biosolids in Australia is strictly regulated by state guidelines, some of which are under review following recent research outcomes. Communication and research between the water industry, regulators and researchers specific to the regulation of biosolids is further enhanced by the Australian and New Zealand Biosolids Partnership (ANZBP). This paper summarises the major issues and constraints related to biosolids use in Australia using specific case examples from Western Australia, a member of the Australian NBRP, and highlights several research projects conducted over the last decade to ensure that biosolids are used beneficially and safely in the environment. Attention is given to research relating to plant nutrient uptake, particularly nitrogen and phosphorus (including that of reduced phosphorus uptake in alum sludge-amended soil); the risk of heavy metal uptake by plants, specifically cadmium, copper and zinc; the risk of pathogen contamination in soil and grain products; change to soil pH (particularly following lime-amended biosolids); and the monitoring of faecal contamination by biosolids in waterbodies using DNA techniques. Examples of products that are currently produced in Western Australia from sewage sludge include mesophilic anaerobically digested and dewatered biosolids cake, lime-amended biosolids, alum sludge and compost.

Field‐Scale Evaluation of Biosolids‐Derived Organomineral Fertilizers Applied to Winter Wheat in England

“…However, in practice, recycling biosolids to agriculture presents both the wastewater industry and end-users with several challenges, including: land-bank availability in the proximity of wastewater treatment works, soil P status and potential P enrichment of surface waters, the concentrations and phyto-availability of nutrients in biosolids, potential build-up of heavy metals in soil, their uptake by crops grown on the soil and subsequent transfer to the food chain, and logistics issues such as cost of transport, storage, handling and field application (Hogan et al, 2001;Elliott et al, 2002;O'Connor et al, 2004;Clarke and Cummins, 2015). A concern of routine application of biosolids to soil is that the loading rate of P can be higher than that commonly applied through mineral fertilizers because of their low N/P ratio (Higgs et al, 2000;Pritchard et al, 2010). This can lead to progressive build-up of soil P, a problem commonly observed in areas close to production sites, where soils frequently have relatively high soil P Indices that are above the recommended target index for the soil and cropping system (Skinner and Todd, 1998;DEFRA, 2010;Antille et al, 2014aAntille et al, , 2014b.…”

Nutrient recovery technologies for anaerobic digestion systems: An overview

“…Recovery of phosphates through precipitation with aluminium, iron, calcium and magnesium is technically possible; however aluminium and iron sources are expensive and makes phosphorus unavailable to plants [148]. Calcium phosphates are a poorer fertilizer (particularly in alkaline soils) [149,150], while recovery as struvite requires a higher P concentration in the solution [151].…”

Soil properties and microbial ecology of a paddy field after repeated applications of domestic and industrial sewage sludges

“…The land application of sludge involves effects on soil properties, soil microbes, plants, and animal by the accumulation of these pollutants. This may threaten the safety of agricultural production and human health through the food chain (Pritchard et al 2010;Bondarczuk et al 2016;Harder et al 2016). Thus, the use of sewage sludge as a source of plant nutrients for crop production needs to be carried out carefully to protect the environment and human health.…”