Measurement of Surface Runoff of Mixed Contaminants Arising from the Landspreading of Treated Sewage Sludge.

Measurement of surface runoff of mixed contaminants arising from the landspreading of treated sewage sludge

 

Mark G. Healy¹, Dara Peyton^1,2, Gerard Fleming³, Martin Danaher⁴, Liam Morrison⁵, David Wall², Jim Grant⁴, Martin Cormican⁶ and Owen Fenton²

 

¹Civil Engineering, National University of Ireland, Co. Galway, Rep. of Ireland.

²Teagasc, Johnstown Castle, Environment Research Centre, Co. Wexford, Rep. of Ireland.

³Microbiology, National University of Ireland, Galway, Rep. of Ireland

⁴Teagasc Research Centre, Kinsealy, Co. Dublin, Rep. of Ireland.

⁵Earth and Ocean Sciences, National University of Ireland, Galway, Rep. of Ireland

⁶University College Hospital, Galway, Co. Galway, Rep. of Ireland

The landspreading of treated sewage sludge (‘biosolids’) offers an excellent source of nutrients and metals required for plant and crop growth. Due to the increasing awareness regarding risks to the environment and human health, the application of biosolids to land as a fertilizer has come under increased scrutiny. Therefore, any potential benefits accruing from the reuse of sludge must be considered against possible adverse impacts associated with its use. The aim of this project was to examine, under controlled conditions in the field, the impact of landspreading of biosolids on grassland on surface runoff of nutrients, metals, faecal and total coliforms, and pharmaceuticals with a known link to poor human health (triclosan and triclocarbon).

Three types of biosolids (anaerobically digested (AD), lime stabilised (LS) and thermally dried (TD)) were applied to replicated (at n=5) hydraulically isolated micro-plots, each 0.9 m-long x 0.4 m-wide. Prior to application, the biosolids and the plots were fully characterised for the nutrient, metal, microbiological and pharmaceutical parameters of interest. Rainfall with an intensity of approximately 10 mm hr^-1 was applied to each plot, in 30-min durations, over three rainfall events at time intervals of 24, 48 and 360 hr from the time of application, and the surface runoff was fully characterised.

The flow-weighted mean concentrations measured in the surface runoff indicate that nutrient loss is similar to other organic wastes, metals are well below the drinking water limits, total and faecal coliforms are below 1.8x10⁶ MPN per 100 ml. Pharmaceutical testing is on-going, but may be crucial in determining whether biosolids may be safely applied to land.