Strategic Management of Non-Point Source Pollution from Sewage Sludge L. Bolton 1 L. Heathwaite 1, P. Whitehead 2 and P. Quinn 3 1 Department of Geography, University of Sheffield 2 Aquatic Environments Research Centre, Reading University 3 University of Newcastle upon Tyne

Sewage Sludge Disposal UK, 1991/1992* 26% SEA DISPOSAL 9% OTHER 6% INCINERATION 11% LANDFILL 47% RECYCLING TO FARMLAND * WaterUK

UK, 2000* 12% OTHER 22% INCINERATION 11% LANDFILL 55% RECYCLING TO FARMLAND * WaterUK Sewage Sludge Disposal

Sewage Sludge or “Biosolids” Benefits of recycling to land –Fertiliser- agronomically useful quantities of nutirents and trace elements –Increases soil quality –Cheaper than mineral fertilisers (up to £100/ha) –Most environmentally sustainable method of disposal Best option in most circumstances: EU and UK government –Supported by environmental groups Surfers Against Sewage

Drawbacks of recycling to land –Accumulation in soil/transfer to groundwater/surface water Heavy metals –Diffuse nutrient pollution Fertiliser governed by nitrogen application can lead to excess phosphorus Controlled by 1986 EU Directive (86/278/EEC) and ADAS Safe Sludge Matrix Sewage Sludge or “Biosolids”

Critical Source Areas C S A HIGH TRANSPORT RISK HIGH SOURCE POTENTIAL

Soil P Index Sludge not applied when risk of P loss is identified Soil P index ≥3* UK 56% arable and 30% grassland soil P index ≥3 Current thinking has little understanding of the vulnerability of sludge P loss to receiving waters Is it possible to minimise nutrient loss by applying sludge to land outside CSAs regardless of soil P index status? * UK Code of Good Agricultural Practice, 1998

Study Area Arable farm receiving regular sewage sludge treatments, SE England Upper Chalk Perched water table Groundwater dominated system 20m unsaturated zone

Field A P index Prior to Application 30ha field, ephemeral ditch Mean soil Olsen’s P 38.8 mgL -1, areas of soil P index 5 Digested sludge cake and lime stabilised sludge treatment September 2001 Dominated by subsurface flow

Field A Post application P index Mean ditch total phosphate mgL -1 Mean soil water total phosphate mgL -1

Field B Field B treated with digested sludge cake, October 2003 –Soil Olsen’s P prior to treatment 22.00mgL -1 Adjacent control field not treated Both fields are tile drained Nutrients concentrations in tile drains from both fields monitored

Field B: tile drains control (untreated) sewage sludge treated

Field A and Field B Field A P concentration in ditch water relatively low P not lost from this field: retained in soil or no connectivity High initial soil P is not coincident with transport No CSAs for surface water

Field A and Field B Field B Rainfall occurred during application Incidental loss of P very important in this situation Land drains effectively turned the whole field into a CSA

Modelling Field Scale Connectivity Modelling TopManage –Digital terrain analysis to visualise the effects of land management on hydrology TOPCAT –timeseries modelling of flow and nutrients Catchment Scale Modelling INCA-N and P models

P leaching: 100% cereal catchment; low connectivity low initial P medium initial P high initial P low initial P medium initial P high initial P Total P leaching kg ha -1 y -1 Biosolids P input kg ha -1 y -1

low initial P medium initial P high initial P Total P leaching kg ha -1 y -1 Biosolids P input kg ha -1 y -1 P leaching: 100% cereal catchment; high connectivity low initial P medium initial P high initial P

Nutrient Export Risk Matrix SOIL TYPE FLOW CONNECTIVITY FERTILISER APPLICATION AND SOIL MANAGEMENT Low risk High risk Output gained from scenario tests with plot and field scale INCA is being used to fill in the nutrient availability axis on the NERM

Phosphorus Export Risk Matrix FERTILISER APPLICATION AND SOIL MANAGEMENT FLOW CONNECTIVITY Low risk High risk

Phosphorus Export Risk Matrix Series of questions are asked relating to: Flow Connectivity –Hill slope form –Hedgerows –Remediation options Fertiliser Application and Soil Management –How much P do you intend to apply –Current soil P index Prototype PERM available on and

Conclusions Sewage sludge has an environmental and economical use when applied to land Export of P occurs when transport and source factors coincide as CSAs P export can be controlled by strategic management of applications of sewage sludge

Acknowledgements EPSRC (GR/N26074/01) The SEAL Project: Strategic Management of Non-point Source Pollution from Sewage Sludge Roger Pryor for access to field site Lister Noble (Farm Systems) for P index data Thames Water and Terra Ecosystems for sludge data