Technical Evolutions in Sludge Treatment André Visser
What is sludge? Sludge of a WWTP DS percentage of 18-28 % Embedded energy 1,6 MJ/kg sludge (13,3 MJ/kg ds) Composition 62 % organics 38 % inorganics 50 g Nitrogen/kg ds 18 g Phosphate/kg ds Copper 430 mg/kg ds Zinc 1.016 mg/kg ds Mercury 1,1 mg/kg ds Fresh sludge also contains pathogens Page 2
Quality depends on? Type of municipality Type of industry Type of collecting system Type of treatment Type of sludge treatment Type of chemicals added to the system Page 3
Principles Sludge is an agglomerate of: Inorganic material Organic (dead) material Organic (living) material Water - intercellular water - extracellular bound water - capillary water - free water Unique per location Composition difficult to change INTERCELLULAR WATER EXTRACELLULAR WATER CAPILLARY WATER FREE WATER Page 4
Sludge production Treatment Specific Gravity of sludge Dry Solids (range) Production (range) kg/l % DS g/(p.e.d) Primary sedimentation 1.020 4-10 20-40 Activated sludge 1.005 0.6 1.2 25-50 Extended aeration 1.015 0.8 1.5 40-60 Operation and maintenance of wastewater treatment plants Page 5
Why sludge treatment? Reduction of transportation costs Reduction of final treatment costs Recovery of valuable components Wastewater treatment Wastewater transport Sludge treatment Page 6
Process scheme (very low loaded extended aeration) Screens Aeration tank Final clarifier Sand Filtration Influent Effluent return sludge Sludge transport for further treatment Secondary sludge thickening Mechanical Sludge Thickening or Dewatering Sludge storage Page 7
Process scheme (very low loaded extended aeration) Page 8
Process scheme (low loaded) Screens Grit & grease Primary Clarifier Aeration tank Final clarifier Influent Effluent return sludge Mechanical Sludge thickening Biogas Co-generation Energy Primary sludge thickening Anaerobic digestion Mechanical sludge dewatering Sludge storage Page 9
Process scheme (low loaded) Page 10
Situation in The Netherlands 17 million inhabitants 350,000 ton DS/year This means 56 g/inhabitant.day 360 WWTP, 90 with digester 50 % of sludge is digested Disposal costs 120.000.000 /year This means 340/t DS Energy content of sludge is 4.9 PJ P-content in sludge is 12.000 ton/y Page 11
DS scale for municipal sludge Page 12
DS scale for municipal sludge Page 13
Sludge thickening Gravity thickener Belt filter Drum thickener Decanter Flotation Page 14
Sludge thickening (gravitational) Sludge type DS-load (kg/(m 2.d)) DS % Primary sludge 50-80 5-7 Activated sludge 20-30 2-3 Extended aeration 20-30 2-4 Digested (P + S) 30-50 2-4 Page 15
Sludge thickening (gravitational)! Page 16
Sludge thickening (gravity belt) Page 17
Anaerobic Sludge digestion To reduce and stabilize solids Three main phases Hydrolysis Acidification Methanogenic phase Biogas production CH 4 (50 75 %), CO 2 and other gasses 400-900 l/kg ODS removed Parameters Temperature, loading, ph COD removal, fatty acids, micro-elements Page 18
Sludge digestion mesophilic thermophilic Page 19
Sludge digestion Page 20
Mixing systems a) Unconfined gasinjection b) Confined gasinjection c) Mechanical steering d) Mechanical pumping Page 21
Sludge dewatering Decanter Belt filter press Chamber press Membrane press Dewatering screw Operation and maintenance of wastewater treatment plants Page 22
Sludge dewatering Difference in specific weight Separation by floc size Page 23
Sludge dewatering Separation by floc size Difference in specific weight Page 24
Sludge conditioning Mineral reagents for FP (FeCl 3 & Ca(OH) 2 ) Synthetic polyelectrolytes (emulsions or powder) Combination Others like heat or freezing treatment, elektro-osmosis Page 25
Sludge conditioning Page 26
Sludge transport Page 27
Final sludge treatment Sludge inciniration Sludge drying (pellets) Sludge composting Fertilizer for agriculture Landfilling Page 28
Legislation NL < 1995 Sludge used as fertilizer on land 1995 Forbidden to use sludge as fertilizer 1998 Landfill ODS < 10 % of TS EU-legislation for use of biogas for fuel EU-Water Framework Directive (WFD) Kyoto agreement 20 % less CO 2 in 2020 National agreements on energy efficiency National agreements on P-recovery Page 29
M kg ds/a Final sludge treatment through the years 400 Afzet zuiveringsslib 1981-2003 350 300 drying 250 200 150 landfilling composting inciniration overig verbranden composteren stort Landbouw 100 50 0 agriculture 1981 1990 1995 2000 2003 Page 30
Final treatment (NL in 2012) Sludge incineration (60 %) at 2 locations. Ash is used as filler in asphalt and mines. Cooling agent and energy source in brown coal energy plants (13 %). Drying (13 %) and used as energy source and filler in the cement industry. Sludge composting (14 %), addition of dry organic matter and finally as energy source for a power plant.!!! Realize that at the end 100% of the sludge is incinerated Page 31
Some developments in sludge treatment ORGANIC WASTE SEWAGE SLUDGE PLANT A SEWAGE SLUDGE PLANT B MECHANICAL THICKENING MECHANICAL THICKENING SLUDGE REDUCTION ANAEROBIC DIGESTION BIOGAS EXTRA BIOGAS N, P RICH WATER CENTRAL DEWATERING CHP INSTALLATION WWTP THIRD PARTY FUEL CELL UPGRADING TO CNG RECOVERY OF NUTRIENTS FINAL TREATMENT ELECTRICITY HEAT GAS STATION FOR TRANSPORT; GAS NETWORK Page 32
Co-digestion Digestion of sewage sludge with other wastes, like: external sewage sludge; food waste; industrial organic wastes; livestock manure. Addition of extra biomass more biogas energy output increases; emission reduction; well stabilization of organic wastes. A few aspects should be paid attention to: infrastructure for co-digestion has to be available; monitor the materials that enter the digester; proper mixing of the different sources. Page 33 Mixer in sludge fermentation tank
COD-balance in a convential WWTP * Page 34 * by Dr Sara Isabel Pérez Elvira
Principle of sludge reduction technologies Sludge floc Energy Energy Energy Energy Bacterial cel Inert particle Extracellular polymers Improving the hydrolysis rate Increase the biodegradability of biomass Decrease the required retention time for digestion And in that case also an increase of the sludge loading rate Page 35 * by Dr Sara Isabel Pérez Elvira
Just some reduction technologies Ultrasound Thermal Hydrolysis Plug Flow Digestion Page 36
Thermal Hydrolysis (Cambi) Page 37
Thermal Hydrolysis (Cambi) Claims compared with conventional digestion: 40 to 60% increase in biogas reduction in total solids of 15 to 20% increase in dewatering with 8 to10% DS 100% increase in digester capacity pathogen free biosolids Page 38 Up to 30 world-wide references.
Developments in final treatment Sludge drying Low Temperature Drying Solar drying Gasification and pyrolysis Super critical wet oxidation Page 39
Warning!!! Just a few possible scenario s eerste trap voorbezinking preprecipitatie microzeven droging + vergassing lage temperatuur BABE Sharon 1-AX Demon bio P superkritische vergassing indirect thermisch meestoken MBR Nereda korrel 1 e trap + 1-AX actief slib Cannibal droging direct thermisch meestoken cementoven HTU biologisch storten gravitaire indikking mechanische indikking natte oxidatie ultrasone voorbeh. thermische voorbeh. thermische voorbeh. stoomlevering enzymvoorbeh. co-verbranding W K K groen gas mesofiele gisting rwzi thermofiele gisting ontwatering wormenreactor verbranding tegendrukturbine condensatieturbine damprecompressie eindverwerking Page 40 Manage this from the beginning.