Page 299 - Materials Chemistry, Second Edition

280 Life Cycle Assessment of Wastewater Treatment

Inputs (materials, energy)

Biogas Recovered
electricity
and heat
Urban wastewater
Anaerobic
tank
Membrane E uent Methane E uent
Carbon source recovery
unit

Digested sludge

Outputs

FIGURE 13.2 Scheme of SAnMBR process for urban WWTPs.

the submerged anaerobic membrane bioreactor (SAnMBR) technology, recently
explored as a promising technology for urban wastewater treatment.
Pretel et al. (2013) report an environmental study of SAnMBR technology at
different temperatures using LCA analysis. The process scheme is illustrated in
Figure 13.2.
The reported SAnMBR system is constituted by an anaerobic reactor connected
to two membrane tanks, which include commercial ultrafiltration membranes. The
plant operates with an SRT of 70 days, and the studied temperatures are 20 and
30°C.
The following system boundaries are considered in that work in the context of
LCA evaluation:

• The wastewater treatment process is included. The contribution of the
stages involved in this phase to the environmental impact is decisive for
LCA studies.
• The operating phase is also included, as it significantly contributes to envi-
ronmental impact (the construction phase, including membrane investment
cost, is not considered).
• Final effluent composition is determined to evaluate whether nutrient recov-
ery is possible.
• Pre-treatment processes are not included in this LCA analysis, because they
are well known for all the WWTP LCA studies.
• The demolition phase is not taken into account, as it has been demonstrated
that it shows a negligible contribution.