Chapter 19 - Dewatered sludge treatment (86 pages)

1.Sludge composting
1.1.Principle and conditions governing its use
1.1.1.Dry solids contents of the initial mixture and of the final compost
1.1.2.Nutritional balance
1.1.3.Selecting the carbonaceous support
1.1.4.Maturation
1.1.5.Main sludge composting processes
1.2.Thermoposting
2.Heat treatment used on dewatered sludge - General comments
2.1.Introduction
2.2.Sludge characterisation on the energy level
2.3.The heat balance
3.Drying
3.1.Principles
3.2.Sludge behaviour as it dries
3.3.Drying technologies
3.4.A few specific technologies
3.4.1.The drum dryer
3.4.2.The Naratherm dryer (photo 5)
3.4.3.The thin layer dryer (figure 6)
3.4.4.The Innodry dryer
3.5.Drying unit design
3.6.Drying unit energy consumption
3.7.Running drying plant
3.8.Drying to an intermediate dry solids content
3.8.1.Specific case of the Centridry unit (figure 13)
3.8.2.Special case of Hélianthis solar drying
3.8.3.Dimensioning
3.9.Drying and cogeneration
3.10.Safety and drying units
3.10.1.Self-heating and dried sludge
3.10.2.Main properties of dust created by dried sludge
3.10.3.Consequences for engineering
4.Thermal processes used to destroy the organic matter contained in sludge
4.1.General
4.2.Dedicated fluidised bed incineration: the Degrémont Thermylis- HTFB incinerator (figur 21)
4.2.1.Sizing
4.2.2.The heat balance
4.2.3.General operating principles
4.2.4.The incinerator construction principle
4.2.5.Energy consumption optimisation
4.2.6.Industrial concern
4.3.Pyrolysis and thermolysis applied to sludge
4.3.1.General comments and definition
4.3.2.The pyrolysis process in multiple hearth furnaces
4.3.3.The process involving thermolysis in a rotary furnace with liquefaction
4.3.4.Processes involving thermolysis with the production of syngas
4.4.Organic matter destruction treatment using coincineration processes
4.4.1.Co-incineration of wet cake sludge with household waste: the IC850 process
4.4.2.Co-incinerating pre-dried sludge processed with household waste
5.Processes involving flue gas treatment downstream from the thermal processes
5.1.Data required to design a flue gas processing unit
5.2.Flue gas treatment types
5.2.1.The wet process
5.2.2.The dry process
5.2.3.The semi-wet system
5.2.4.Processing nitrogen oxide (NO_x) pollution
6.Organic matter destruction using the wet oxidation method (OVH in French)
6.1.General description of the subcritical wet oxidation method
6.2.The main subcritical wet oxidation operating parameters: Mineralis
6.2.1.Selecting the pressure-temperature combination
6.2.2.Selecting the oxidant
6.2.3.Catalysts
6.3.The specific operation of the Mineralis process
6.3.1.Sludge concentration levels (DM and COD) at the wet oxidation inlet
6.3.2.Reactor without phase separators
6.3.3.Solid/liquid separation
6.4.Ammonia treatment
6.4.1.Ammonia treatment inside the reactor
6.4.2.Ammonia treatment outside the reactor
6.5.Engineering precautions
7.Regulations
7.1.French legislation
7.1.1.The administrative body responsible for ICPE
7.1.2.The basic principles of ICPE regulations
7.1.3.ICPE regulations applied to sludge heat processes
7.2.European regulations on incineration (extracts)

Introduction

Following on from chapter 18 that was devoted to processes applied to liquid sludge (stabilisation and dewatering), this chapter now describes all dewatered sludge treatments implemented so that sludge can be put to its end usage (agricultural, re-vegetation, recycled energy, disposal on ultimate waste sites...). These treatments are now severely governed by the regulations that had already been discussed in chapter 2 § 6.3. or, more specifically, under the heat treatments (drying, incineration, gasification) included in this chapter.
There are two exceptions to this logic:

the lime treatment of dewatered sludge was discussed in chapter 18 § 4;
although wet oxidation is applied to liquid sludge, it is included in this chapter : in fact, it is first and foremost a heat process.

Therefore, this chapter is devoted to composting and to all processes involved in thermal drying or in the destruction of the organic matter contained in sludge.