Strategic Management of Non-Point Source Pollution from Sewage Sludge

1
Strategic Management of Non-Point Source
Pollution from Sewage Sludge

• L. Bolton1 L. Heathwaite1, P. Whitehead2 and P.
  Quinn3
• 1Department of Geography, University of Sheffield
• 2 Aquatic Environments Research Centre,
• Reading University
• 3 University of Newcastle upon Tyne

2
Sewage Sludge Disposal
UK, 1991/1992
9 OTHER
6 INCINERATION
26 SEA DISPOSAL
11 LANDFILL
47 RECYCLING TO FARMLAND
WaterUK
3
Sewage Sludge Disposal
UK, 2000
22 INCINERATION
11 LANDFILL
12 OTHER
55 RECYCLING TO FARMLAND
WaterUK
4
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

5
Sewage Sludge or Biosolids

• 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

6
Critical Source Areas
C S A
7
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
8
Study Area

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

9
Field A
Prior to Application

• 30ha field, ephemeral ditch
• Mean soil Olsens 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

P index
2
3
4
5
10
Field A
Post application

• Mean ditch total phosphate 0.475 mgL-1
• Mean soil water total phosphate 0.451 mgL-1

P index
2
3
4
5
11
Field B

• Field B treated with digested sludge cake,
  October 2003
• Soil Olsens 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

12
Field B tile drains
control (untreated)
sewage sludge treated
13
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

14
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

15
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

16
P leaching 100 cereal catchment low
connectivity
Total P leaching kg ha-1 y-1
Biosolids P input kg ha-1 y-1
17
P leaching 100 cereal catchment high
connectivity
Total P leaching kg ha-1 y-1
Biosolids P input kg ha-1 y-1
18
Nutrient Export Risk Matrix
Output gained from scenario tests with plot and
field scale INCA is being used to fill in the
nutrient availability axis on the NERM
High risk
FERTILISER
APPLICATION AND
SOIL
MANAGEMENT
Low risk
SOIL TYPE
FLOW
CONNECTIVITY
19
Phosphorus Export Risk Matrix
High risk
FERTILISER APPLICATION AND SOIL MANAGEMENT
Low risk
FLOW CONNECTIVITY
20
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 www.sheffield.ac.uk/SE
  AL and www.ncl.ac.uk/wrgi/TOPCAT/

21
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

22
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