WaterTreatment Sludge: Potential for Use as a Soil Ameliorant

ReportNo WSAA 106

May 1997

SUMMARY

Thisreport outlines the investigations conducted between 1993 and 1996 to identifythe potential for water treatment sludges, which are subject to stringent EPAguidelines with respect to handling and disposal, to be used as a soilameliorant in preference to dumping it in municipal landfill sites. Before thesludge can be utilised in an unregulated manner, however, it was necessary toestablish whether it had any physical or chemical properties that might pose anenvironmental health hazard when released. While there was no evidence in theliterature of any such problems, much of the literature was from overseas, andthus applicable to different soils and environmental conditions. It wasconsidered necessary to establish up-to-date local evidence to govern thedisposal of sludges generated in Australia. The four objectives of the projectwere therefore to 1) determine the magnitude of soluble aluminium in alumsludge in comparison with naturally occurring soils, 2) determine the magnitudeof soluble aluminium in an acidic soil at the Waite Research Institute with andwithout sludge and lime in various proportions, 3) determine the effects ofadding sludge to soils in different proportions on the establishment and growthof lawn grasses, and 4) evaluate the utility of sludge as an ingredient incommercial potting mixes.

Inall laboratory, glasshouse and field experiments, the sludge was found topossess no serious detrimental properties, and in particular no solublealuminium by comparison to other natural soils in Australia. On the contrary, anumber of beneficial properties were identified, including low bulk density,high infiltration rate, plenty of available nitrogen, a neutral to alkaline pH,and a modest calcium carbonate equivalence. When mixed as a potting ingredientwith sand and other materials, the sludge imparted favourable properties whencompared with commercially available mixes. Plant yields from sludge and fromsludge-based mixes were as high or higher than those in just soil. The mainagronomic limitation of the sludge was its large P-fixing capacity, whichnecessitated large quantities of added P-fertiliser. From an environmentalviewpoint, however, this could be regarded as an advantage, as the sludge mightbe used to remove P from contaminated water sources; further research toquantify its effectiveness is being planned. In short, once the sludge has beenair dried, its disposal need not be stringently regulated and can be safelyused in many ways, only a few of which have been identified here (eg. to raisesoil pH of acidic soils, or as a potting mix ingredient).

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