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

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. http://ec.europa.eu/environment/waste/sludge/sludge_disposal.htm

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

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%)

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.

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 16,000-24,000 kJ kg-1 DS Digested 11,000-14,000 kJ kg-1 DS

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

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

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

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

Wastewater Treatment: Sludge disposal Proposed new directive includes both metals and organics: Potentially toxic elements (PTEs) Massive reduction over past 10-15 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 0.008-0.01 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.

Wastewater Treatment: Sludge disposal

Wastewater Treatment: Sludge disposal

Wastewater Treatment: Sludge disposal

Wastewater Treatment: Sludge disposal Sludge injection (USA)

Wastewater Treatment: Sludge disposal

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

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 https://www.youtube.com/watch?v=vdw-fCHFtcg https://www.youtube.com/watch?v=3zNMmxJw6-s

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)

Wastewater Treatment: Sludge disposal Safe Sludge Matrix (UK) Conventional treatment: 99% pathogen destruction Enhanced treatment: Thermal drying; Sludge hydrolysis; microwave oxidation 99.9999% 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

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 www.adas.co.uk/home/matrix/html Amendment to Code of Practice (2002): Microbial standards formal record keeping HACCP procedures (Hazard analysis and critical control) Similar Code for Ireland published 2008

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

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

Wastewater Treatment: Sludge disposal Further Reading Read Chapter 15 of Course text Read Irish Code of Practice as example US conference on biosolids use https://www.youtube.com/watch?v=nx99V3vkeaI Latest EU overview: http://ec.europa.eu/environment/waste/sludge/sludge_disposal.htm Latest Irish overview: http://www.environ.ie/en/Environment/Water/WaterServices/SludgeManagement/ http://www.environ.ie/en/Publications/StatisticsandRegularPublications/AnnualReports-Departmental/FileDownLoad,33724,en.pdf Future in Ireland: http://erc.epa.ie/safer/iso19115/displayISO19115.jsp?isoID=129 Leachate: http://leachate.co.uk/main/leachate-chemistry-testing/landfill-leachate-composition/