Page 295 - Materials Chemistry, Second Edition

276 Life Cycle Assessment of Wastewater Treatment

(Spirito et al., 2014). To maximize the selectivity of the elongated prod-
ucts, three technological possibilities are emerging: (1) artificial removal
or addition of electrons by microbial electro-catalysis, (2) separation of the
products by in-line extraction technology to enhance product yield, and (3)
immediate conversion of the elongated products to increase the product
value (biorefinery concept).
• Use of anoxygenic purple phototrophic bacteria (PPB). PPB are very
versatile bacteria, able to perform a wide range of metabolic pathways,
though their most interesting mechanism is anaerobic photoheterotrophy,
in which simple organics such as VFAs, alcohols, and sugars are assimi-
lated, with infrared (IR) light as the energy carrier of the process (Puyol
et al., 2017a). It has been proposed to use these bacteria as the key part
in the partition step of the partition-release-recovery concept due to their
high redox and C recycle efficiencies, high biomass yield, and high C/N/P
growth ratio, thus optimizing C and nutrient recovery via assimilation
instead of dissipation (Batstone et al., 2015a). Compared with other pho-
totrophs such as algae and cyanobacteria, PPB can use low-energy IR
light, which greatly decreases the energy demand of the process (Hülsen
et al., 2014). These bacteria have been used for both domestic (Hülsen
et al., 2014) as well as industrial (Chitapornpan et al., 2013) wastewater
treatment with resource recovery. Also, their metabolism can be altered
to enhance biohydrogen production with an excess of organic electron
sources, nutrient deficiency, and lack of ammonium in the medium
(Ghosh et al., 2017).
• Use of the anammox process to low-energy main line with complete nitro-
gen depletion in a single-stage process. The anammox process entails the
anaerobic oxidation of ammonium to dinitrogen gas with nitrite as the elec-
tron source. In domestic wastewater applications, complete removal of C
and N is feasible with partial oxidation of ammonium to nitrite (nitritation)
and anammox with concomitant C removal by fermentation and microaero-
philic organic oxidation in a delicate equilibrium, where the pH and the
temperature play a critical role. Anammox bacteria are very sensitive to
temperature changes and concentrations of unionized nitrogen forms (free
nitrous acid and free ammonia), so that pH must remain in a narrow range
of 7–8.5 (Cao et al., 2017).
• Engagement of sulfate reduction with methanogenesis. The sulfur cycle
in bacteria is key for very high-strength and sulfate-rich wastewater treat-
ment by AD technologies, basically including the sulfate reduction and the
sulfide oxidation processes (Batstone et al., 2015b). Many food industry
wastewaters, such as those coming from distilleries and fermentation pro-
cesses, contains high amounts of COD and sulfate, the latter coming from
the use of sulfuric acid in chemical processes. Sulfate reduction implies the
oxidation of hydrogen or VFA with concomitant sulfate reduction to hydro-
gen sulfide. This means that sulfate reduction bacteria (SRB) can com-
pete directly with methanogens for substrate (hydrogen and acetate) and
therefore, critically affects the methane potential in the treatment of these