Environmental Evaluation of Different Treatment Processes for Sludge from Urban Wastewater Treatments: Anaerobic Digestion versus Thermal Processes (10 pp) |
| |
Authors: | Almudena Hospido Teresa Moreira María Martín Miquel Rigola and Gumersindo Feijoo |
| |
Institution: | (1) Ing. Almudena Hospido Dept. of Chemical Engineering Institute of Technology University of Santiago de Compostela 15782–Santiago de Compostela SPAIN,;(2) Dr. María Teresa Moreira Dept. Chemical Engineering School of Engineering University of Santiago de Compostela 15782–Santiago de Compostela SPAIN,;(3) María Martín Laboratory of Chemical and Environmental Engineering Faculty of Sciences University of Girona 17071 Girona Spain,;(4) Miquel Rigola Laboratory of Chemical and Environmental Engineering Faculty of Sciences University of Girona 17071 Girona Spain,;(5) Dr. Gumersindo Feijoo Department of Chemical Engineering University of Santiago de Compostela 15782–Santiago de Compostela SPAIN, |
| |
Abstract: | Background, Aims and Scope Huge amounts of sewage sludge, that need to be handled, are generated all around the world from wastewater treatment plants
and its management in an economically and environmentally acceptable way has become a matter of increasing importance during
the last few years.
In this paper, we make use of Life Cycle Assessment (LCA) to compare biological and thermal processes, that is to say, anaerobic
digestion versus pyrolysis and incineration. This paper will complete the analysis performed in a wastewater treatment plant,
where sludge post-treatment was identified as one of the main contributors to the environmental impact on the global system.
Methods LCA is a tool for evaluating the environmental performance of goods as well as processes or services (collectively termed
products). ISO 14040 defines LCA as a compilation and evaluation of the inputs, outputs and the potential environmental impacts
of a system throughout its life cycle: from the production of raw materials to the disposal of the waste generated.
In this study, data relating to the actual scenario from an existent wastewater treatment plant were considered. Both bibliographical
and real data from existing facilities were used for the thermal processes proposed.
The Centre of Environmental Science (CML) of Leiden University's methodology was chosen to quantify the potential environmental
impacts associated with the different scenarios under study. The software SimaPro 5.1 was used and CML factors (updated in
2002) were chosen for characterisation and normalisation stages.
Results and Discussion In a previous study, sewage sludge was found to be a critical point in the environmental performance of a wastewater treatment
plant, so different alternatives have been tackled here. Anaerobic digestion followed by land application of pasty sludge
comprises both energy recovery and nutrient recovery. Other thermal processes, such as incineration or pyrolysis, allow energy
recovery (both electrical and thermal) and, although nutrients are lost, new co-products are produced (tar and char at pyrolysis).
Here, the most adverse case (that is to say, the total amount of heavy metals is supposed to be released from the sludge and
reach the environment) was applied to consider the most negative impact due to sludge spreading in agricultural soils; so
more research is required in order to establish the precise amount of heavy metals that is effectively uptaken by the plants
and crops as well as the amount that is transferred to another phase as a leachate.
Thermal processes are presented here as a good option to recover energy from the sludge; although the value of nutrients is
lost. Tar and char, co-products from pyrolysis, are good examples that were evaluated here, recycling of bottom ashes from
sludge incineration or manufacture of ceramic materials from sludge are other options to be studied in the near future.
Conclusion During the last few years, several opinions have been declared in favour of land application, incineration or pyrolysis,
but many voices have also spoken out against each one. To obtain general conclusions for an overall comparison of different
post-treatment of urban wastewater sludge is not easy as there are many contradictory aspects. The most effective utilisation
of sewage sludge implies both energy and material re-use, but this is not always possible. Nevertheless, we think that land
application of digested sludge is an acceptable option, probably not the best but at least a good one, for sludge treatment
as long as efforts are focused on the minimisation of heavy metal content in the final cake. |
| |
Keywords: | wastewater pyrolysis sludge treatment processes sewage sludge incineration anaerobic digestion urban wastewater treatments |
本文献已被 SpringerLink 等数据库收录! |
|