Sewage sludge is a residue of the treatment of municipal wastewater. Sewage sludge can be disposed on landfills, incinerated and utilized as energy or it is used as an agricultural fertilizer.
The disposal of untreated sewage sludge on landfills is banned within the EU since 2005 by the amendment of the Sewage Sludge Ordinance – amongst other things due to the high content of organic material. The utilization as fertilizer in agriculture is increasingly being subjected to restrictions, as the sewage sludge contains a variety of different pollutants with health effects on humans and nature. The harmful substances range from inorganic pollutants, through toxic heavy metals to organic pollutants and contaminants. Some examples are mercury or residues of medicines or household chemicals.
The acceptance for the utilization as an agricultural fertilizer is therefore dropping significantly within the EU. Long term considerations aim to end the material utilization of sewage sludge to protect human and natural resources. Instead, disposal processes that ensure the destruction of organic pollutants should be used for sewage sludge. Proper thermal treatment of the sewage sludge warrants for the destruction of these toxic substances.
To allow the incineration of sewage sludge at all and to improve its efficiency, the sludge has to be dewatered. In a first step, this is realized by mechanical dewatering. However, the mechanical dewatering alone is usually not sufficient and should be usefully complemented by a thermal drying of the sludge. When looking on the economic feasibility of the drying process its worth to mention that by drying the volume of the sludge is significantly reduced. This results in lower costs for transportation, storage and material handling.
Among the variety of drying applications, EnviroMin Technologies offers different technologies that will be customized according to your needs and requirements:
- Thermal treatment of sewage sludge in a rotary kiln
- Thermal treatment of sewage sludge in a rotary tube dryer
- Thermal treatment of sewage sludge in a tumble dryer
- Pyrolysis of sewage sludge in a tube bundle dryer
A more than interesting economical and technical aspect is the use of waste heat from upstream or downstream thermal processes or the use of solar energy. The energy balance of drying can thus be reduced considerably and therefore the efficiency increases.
Alternatively, we offer low-temperature drying processes. By gentle drying of the sewage sludge no harmful cracking products will be set free chemically and any odour emissions are avoided.
The sanitation of sewage sludge according to U.S. EPA standards is is a considerable option – an important aspect as most of the germs and pathogens present in the sludge survive the biological wastewater treatment.
In contrast to the low-temperature drying, during the pyrolysis the sludge is directly converted into usable heat and inert dumping ash. The Pyrolysis is carried out at significant higher temperatures – between 600 ° C and 800 ° C – and almost under the exclusion of oxygen.
In addition to the stand-alone drying technology EnviroMin Technologies offers turnkey solutions including conveying systems, material and condensate handling, vapour and exhaust gas treatment and the entire process control.