Exergy saving and exergy production in municipal wastewater ...

Exergy saving and exergy production in municipal wastewater treatment
ABSTRACT
This report represents an overall view on thermodynamical studies of wastewater
treatment plant, concepts like exergy, emergy and entropy. In addition, there has been
an introduction of calorimetry. A common unit of measurement of organic contents
in wastewater treatment facilities is COD. However, the unit of measurement which
shows the sustainability of an industry is exergy and emergy. According to the
calculations represented in this report it has been tried to make a correlation between
the COD and exergy in order to make it easier to assess the sustainability of a
treatment plant. The calorific measurement methods which have been used in the
food science can also be used in wastewater treatment industry. Therefore, it is
possible to replace COD and BOD measurement devices with online calorific
measurements. It has been tried to find a correlation between exergy value and
calorific contents. Accordingly, if the calorific values in wastewater input and output
are known they can be transferred into exergy values. The energy and exergy
production from wastewater has been observed in a Microbial Fuel Cell made in the
laboratory and the measured values of current produced by the microbial activities has
been analyzed in this report. For future studies, exergy can be used directly in
modeling a wastewater treatment plant and improving an already made one.
Keywords: calorimetry, emergy, exergy, Microbial Fuel Cell
1. INTRODUCTION
Domestic wastewater contains 10 times the energy required for
treatment (Pant et al, 2009). According to California energy commission
WasteWater Treatment Plants are the largest electricity (exergy)
consumers in a single municipality (Cited from electric power research
institute (Pesific Gas And Electric Co., 2003). 2% of total US electricity
consumption is used in activated sludge processes. In Sweden 1% of
total electricity is used in these processes (Jonasson, 2007).besides,
Today’s technology has not been able to fully facilitate the use of
renewable energy sources economically as their facilities need large area
and they need high technologies which are not available
yet (Jonasson, 2007).
As the population is increasing, the amount of the wastewater produced
and consequently the amount of the energy needed for treatment will
increase. Moreover, the more strict discharge regulations have also led to
more energy need in the treatment plants. This should be consider also
that larger treatment plants use energy more efficient than smaller
treatment plants (pe