1. Wastewater Treatment Sludge disposal
Professor Nick Gray
Centre for the Environment
Trinity College
University of Dublin
© Tigroney Press

2. Disposal dictates the treatment sludge must receive
Wastewater Treatment: Sludge disposal
Disposal dictates the treatment sludge must receive
Disposal limited by:
Presence of toxic compounds
Pathogens
Volume
Location of WWTP
Cost
Key factors in selection: cost and environmental protection/health
Main options: Disposal to agricultural land; Landfill; Disposal to sea; Incineration
Other options (<10%): Compost; Land reclamation; Top soil manufacture; Forestry; Sacrificial land use; building materials; foodstuff; Pyrolysis.

3. Wastewater Treatment: Sludge disposal
Current UK disposal routes (2006)
62% Agricultural land
19% Incineration
11% Land reclamation
1% landfill
7% Other
4% gasification
2% industrial cropping
1% compost
1,000,000 t (DS) produced from WWTPs
Current Irish disposal routes (2010)
76% Agricultural land
17% Landfill
7% Other
42,298 t (DS) produced from WWTPs with PE>500

4. Wastewater Treatment: Sludge disposal
Landfill
Landfill undesirable:
Contamination of leachate with metals and trace organics
Enhanced H2S production
Pathogen transfer risk
Enhanced decomposition leading to excessive methane production
Minimum 35% DS
Reduce biodegradable input to 75% of 1995 level by 2010; 50% 2015; 35% 2020
Still major route in many countries e.g. Greece (>50%)

5. Wastewater Treatment: Sludge disposal
Typical Composition of Leachate from Domestic Landfilled Wastes at Various Stages of
Decomposition (all results in mg/l except pH-value)
Determinand
Leachate A
Leachate B
Leachate C
(recent wastes)
(aged wastes)
(bioreactive wastes)
pH-value
6.2
7.5
8.0
COD
23 800
1 160
1 500
BOD5
11 900
260
500
TOC
8 000
465
450
Fatty Acids
(as C)
5 688 5 12
Ammoniacal-N
790
370
1 000
Oxidises -N 3 1
1.0
o-phosphate
0.73
1.4
Chloride
1 315
2 080
1 390
Sodium
(Na)
960
1 300
1 900
Magnesium
(Mg)
252
185
186
Potassium
(Kg)
780
590
570
Calcium
(Ca)
1 820
250
158
Managanese
(Mn) 27
2.1
0.05
Iron
(Fe)
540 23
2.0
Nickel
(Ni)
0.6
0.1
0.2
Copper
(Cu)
0.12
0.03 -
Zinc
(Zn)
21.5
0.4
0.5
Lead
(Pb)
0.40
0.14
A)  Recently emplaced domestic wastes, in the active “acid-forming” stage of anaerobic decomposition, with rapid production of readily degradable organic materials such as fatty acids.
B) Relatively aged wastes in latter stages of stabilization, containing a lower proportion of biodegradable organic materials (as indicated by the low ratio of BOD: COD), but with continuing biological activity as shown by the concentration of ammoniacal nitrogen.
C) Leachate from rapidly degrading domestic wastes, with active generation of methane, in water saturated conditions. Low concentrations of volatile fatty acids indicate efficient conversion of these to landfill gases, and very high concentrations of ammoniacal nitrogen show a high rate of anaerobic biological activity with the landfill.

6. Wastewater Treatment: Sludge disposal
Incineration
Sludge v coal
Contains more volatile combustible matter
Less fixed carbon
Once dried burns to release considerable heat
Calorific Value of sludge
Raw ,000-24,000 kJ kg-1 DS
Digested ,000-14,000 kJ kg-1 DS

7. Wastewater Treatment: Sludge disposal
Sludge Incineration
High capital cost and high operational cost
Sludge dewatering/drying required
Only used for large cities where other options unfeasible

8. Wastewater Treatment: Sludge disposal
DS >30% reaction is autothermic
DS<30% additional fuel required (i.e. amount of energy released during combustion is less than that required to remove water

9. Wastewater Treatment: Sludge disposal
Land Treatment
Used for decades
Returning plant nutrients and biomass forming material back to soil now recognized as Best Practical Environmental Option (BPEO)
UK one million tonnes of DS produced annually, 62% to land (820,000 t)
Only represents 5% of total organic matter returned to land (90% animal manure and slurry rest industrial wastes)
Supports government waste strategy to recycle
Supports Landfill Directive by progressively reducing amount of biodegradable material going to landfill
Biosolids contain N, P, S, Mg and trace elements
UK 80,000 ha-1 treated annually

10. Wastewater Treatment: Sludge disposal
Directive on the protection of the environment and in particular the soil when sewage sludge is used in agriculture (86/278/EEC)
Controls on sludge spreading based on concentrations either in soil or sludge
Soil quality control (environmental quality standards)
Sludge quality control (emission standards)
Directive defines:
Limit values (G and I) for metals in soil
Limit values (G and I) for metals in sludge
Limit values on application rates over 10 years

11. Wastewater Treatment: Sludge disposal
Proposed new directive includes both metals and organics: Potentially toxic elements (PTEs)
Massive reduction over past years due to stricter controls at source and changes in manufacturing base.
Main sources now diffuse (run off) and households
All sludges contain PTEs with up to 96% of all PTEs in wastewaters retained in sludge
e.g. Cd in sewage at mgl-1
Assume 85% removal of metal during treatment; Assume 350 mg of 1o and 2o sludge solids generated per litre of sewage treated
Therefore sludge will contain 20 mg Cd kg-1 DS
Most countries now have specific codes of practice for use of biosolids on agricultural land which includes pathogen as well as PTE controls.

12. Wastewater Treatment: Sludge disposal

13. Wastewater Treatment: Sludge disposal

14. Wastewater Treatment: Sludge disposal

15. Wastewater Treatment: Sludge disposal
Sludge injection (USA)

16. Wastewater Treatment: Sludge disposal

17. Wastewater Treatment: Sludge disposal
Sludge injection (Europe) using chisel plough and roller.
25-50 mm below surface
180 t ha-1 at single pass
Floatation tyres

18. Wastewater Treatment: Sludge disposal
US Sludges
Rule 503
Class A (Enhanced Treatment)
Pathogens largely eliminated
Unrestricted use
Class B (Conventional treatment)
High pathogen risk
Very restricted use

19. Wastewater Treatment: Sludge disposal Safe Sludge Matrix (UK)
Resulted from consumer pressure
Agreement between Water Companies and British Retail Consortium
Came into force Dec. 1998
Outcomes:
Use of raw/untreated biosolids phased out on land used for food crops (Dec. 1999)
Use of raw/untreated biosolids phased out on land used for non-food crops (i.e. hemp (fibre); Miscanthus (biomass) etc.)(Dec. 2005)
All biosolids disposed to agricultural land must be either conventionally treated or receive enhanced treatment (Dec. 2005)

20. Wastewater Treatment: Sludge disposal Safe Sludge Matrix (UK)
Conventional treatment:
99% pathogen destruction
Enhanced treatment: Thermal drying; Sludge hydrolysis; microwave oxidation
% pathogen destruction plus no Salmonella
Conventionally treated biosolids
Only on grassland using direct injection and 3 week no grazing or harvest
12 month gap after application if vegetables grown
30 month gap after application if salads grown
Enhanced treated biosolids
10 month gap for vegetables or salads

21. Sludge (Use in Agriculture) Regulations 2001
Wastewater Treatment: Sludge disposal
Sludge (Use in Agriculture) Regulations 2001
Code of Practice for Agricultural use of Sewage Sludge 2001
Amendment to Code of Practice (2002):
Microbial standards
formal record keeping
HACCP procedures (Hazard analysis and critical control)
Similar Code for Ireland published 2008

22. Wastewater Treatment: Sludge disposal
Key Irish legislation and actions required for sewage
sludge disposal to agriculture
legislation
Content
Impact on the sludge recovery conditions
SI 148 of 1998
SI 267 of 2001
The use of sewage sludge in agriculture
Conditions of use
Sludge must be treated
Nutrient requirements of crops have to be taken into account
Limit values
Heavy metals in sludge and soils
Maximum loads of heavy metals
Soil pH >6
Sludge register
Sludge quantity an quality
Contact details of sludge users
Location of the landbank
Waste Management Act
General duty of waste holder
Sludge disposal or recovery shall not cause environmental pollution
Collection and movement of waste
Waste collection permit is necessary for sludge haulage
SI 610 of 2010:
Good agricultural practices for protection of water
Prevention of water pollution
Determination of buffer zones to protect sensitive area
Sludge spreading is forbidden in certain weather conditions
Definition of spreading period
Nutrient balance
Maximum organic nitrogen is limited to 170 kg/ha
NMP to be established and records kept on the farm holding
Definition of fertilisation rates
SI 32 of 2010:
Registration of sewage sludge facilities
Establishment of sewage
sludge facilities register
Registration of any storage facility
Specific requirements regarding the protection of the environment shall be issued by local authorities
Records shall be kept by the operator

23. Comparison of major disposal options in EU
Wastewater Treatment: Sludge disposal
Comparison of major disposal options in EU
Outlet
Cost to customer
Environmental sustainability
Public perception
Landfill
Medium
Low
Poor
Incineration and energy recovery
High
Recycling to land
Medium-high

24. Wastewater Treatment: Sludge disposal
Further Reading
Read Chapter 15 of Course text
Read Irish Code of Practice as example
US conference on biosolids use
Latest EU overview:
Latest Irish overview:
Future in Ireland:
Leachate: