(564f) Emergy Method Analysis On Sludge Residues For Use From Waste-WATER Treatment Plant

Cano, N. A., Universidad Nacional de colombia
Velásquez, H. I., Universidad Nacional de Colombia
Gallego, D., Universidad Nacional de Colombia




It was confirmed that the emergy analysis method allows comparison between the two alternatives for biosolids disposal while integrating disposition the energy, economic and environmental aspects. Therefore, by using the method of emergy analysis as a tool for sustainability assessment for environmental decision making, and understanding the sustainability of a disposal process that would reach a greater economic benefit with minimal environmental load, the actual benefit of biosolids "using biosolids as Soil Fertilizer" was evaluated and compared against a suitable alternative referenced in the literature as “energy recovery from Biosolids using fluidized bed gasification" under two scenarios: biosolids considered as a renewable resource and as an imported resource.

Being the best alternative according to the sustainability indices “Energy Recovery from Biosolids Using Fluidized Bed Gasification", ie, this alternative is energetically profitable, economically viable and environmentally acceptable; It does not mean that the actual use of the biosolids is economically or environmentally inappropriate. On the contrary, it does not produce environmental stress because its economic performance is not being taken advantage of at its full potential.

The analysis of emergetic levels not only allow us to evaluate the sustainability of a project, It also offers the possibility to improve the practice, so for example for the current use of biosolids the sustainability index allows us to say that a pretreatment of sewage sludge before its disposal improve to the alternative and become the most acceptable [1]

KEYWORDS: Emergy, sustainability, indicators, waste water, disposal, sludge

In Colombia, it is not uncommon to rely on plants for waste-water treatment purposes followed by the  anaerobic  stabilizing of  biosolids as an alternative source of treatment. This practice is due to  the many topographical limitations and conditions that  do not allow mainstream treatment such as the use of oxidation ponds.

However, during waste-water treatment processing, large significative quantities of highly putrescible bio-solids with  a higher energy concentration as well as organic charge/volume are produced; such is the case-example of the waste water treatment plant in  San Fernando (an EEPPM-owned plant) where more than 70 tons of bio-solid material are generated, to be used to treat  the 1.100m l/s of water needed to be released on a permanent basis [2].

Although bio-solid materials processed in this particular example is known for carrying similar traits to those found in urban areas, as well as being defined as neither toxic nor hazardous, they do in fact carry contaminants that required treatment and profitable use of such. Based on these findings, many alternative traditional methods for treatment and use of bio-solids have been implemented, those being for energy production, materials for construction purposes, restoration of natural habitat as well as agricultural uses  [3]. However they have proven to be ineffective in their result.

In retrospect; it can be said that management of waste-water treatment is ultimately lacking and inconclusive, lest treatment of its additional waste product is carried-on in a sustainable fashion. defining  sustainability of course,  as the process of obtaining the highest financial return with a minimum effect in the environment; for such reason, the use of the emergy analysis method is a reliable gauging tool to measure level of sustainability to take full advantage of such, as proposed by [4] [5] [6] [7], as the most prominent and noteworthy method used in other countries [8]  [9]  [10]  [11] [12]   for sustainability based practices, in a  manageable  and equitative way  in the economic, energy and environmental areas.

The emergy analysis approach is known as an analytical method, that through its integration of economy, ecology and thermodynamics concepts allows the assessment of economic, social and environmental impacts in a theoretical form, on development-driven projects, thus becoming a stronghold system in the fields ecological economy and environmental engineering.

As an emergy analysis method-based research, its ultimate intent is to weigh-in the efficient level of sustainability of any processing system used to make decisions concerning the environment. this method  will be used in a way whereby a correct approach to evaluate all sludge residues found in any waste-water treatment plant can be identified in order to choose an assessment alternative that is  ´applicable´. that is to say, an alternative that is ´´energy-suitable´´, ´´financially viable´´, and ´´environmentally friendly´´, in accordance to sustainability indicators; this research means to assess the use of the emergy analysis method as a sustainability appraisement tool of bio-solids production at a waste-water treatment plant in Colombia, while being able to  satisfy  all economic, environmental and energy levels of sustainability. Having as contrast, an already existing method of assessment found in the table of reference, allowing evidential proof of its utility on projects of a similar nature, as well as measuring if current alternative methods of waste-water treatment used in Colombia fit the standards of sustainability, by using the following parameters.

In order to meet such general objective, the application and results of the emergy analysis method used in a waste-water treatment plant in Colombia is analyzed, followed by an analysis of the system of sustainability. Then, by comparing the assessment of the two chosen alternatives of bio-solids used, through the estimate of emergy of both alternatives, the better method for bio-solid analysis is defined and accepted as the best one.

Thus, based on the sustainability indicators, the recovery of bio-solids energy through fluidized bed gasification becomes the best alternative for sustainability. That is to say, this alternative, meets all three standards of sustainability when compare to the alternative of using bio-solids as ground fertilizer.


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