15.2 Photobiological Agents and Methods Used in PhotoBiological Reactors

237

and C3–C4 (photo). The long-term impact of main operational parameters (i.e. HRT

of 6, 12, and 24 hours at initial pH of 5.5 and 6.5) was measured. Maximum hydro-

gen yield (HY) of 0.4 l/g COD, COD removal of 82%, and organic-N removal of 95%

were obtained at HRT of 24 hours and initial pH of 6.5. Increasing HRT was found to

maintain the reactor efficiency at ambient temperature. Lowering initial pH to 5.5

worsened the dark treatment at C1 and C2, resulting in lower local HY and ammoni-

fication efficiency. Further, the results established that higher HY was achieved in

the photo-fermentation, as the protein hydrolysis was mainly achieved in the dark

fermentation. The residual free ammonia (<0.36 mg/l), under all inspected condi-

tions, was below the inhibition limit of PSB. The microbial community analysis

revealed the development of purple non-sulfur bacterial family Rhodospirillaceae at

C3. The economic efficiency of DP-CBR was also assessed by considering the capi-

tal cost, annual costs (i.e. lightning, pumping, nutrients, and gas purification), and

revenues (bio-hydrogen energy and removal of added-value). Overall, the technoe-

conomic assessment of DP-CBR performance highlights its feasibility (affordable

removal of organics and bioenergy recovery) when commenced with gelatin-rich

wastewater. The use of integrated dark photo-fermentation reactor is also sensible,

since the conventional bio-methanization strategy faces the risk of ammonia inhibi-

tion when dealing with protein-rich substrates [22].

15.2.3

Membrane Bioreactor

Membrane bioreactors will have an ultrafiltration membrane module inside to sep-

arate the sludge and liquid by membranes. Management of concentrate and waste

streams for membrane-based algal separation during water treatment is discussed.

Frequent occurrence of harmful algal blooms (HABs) and red tides in freshwater and

seawater poses serious intimidations to water treatment, energy recovery, and the

application of membrane-based technologies during algal separation. Despite the

high elimination efficiency of algal cells and their metabolites (e.g. organic matter

and toxins) by membranes, the generation of concentrate and waste streams presents

a major challenge. Currently membrane-based processes are integrated with algal

separation and particular attention was given to

(i) drinking water production and desalination at low algal concentrations and

(ii) Cyanobacteria-laden water treatment/desalination.

The concentrate and waste streams from backwashing and membrane cleaning in

each scenario are characterized, and this information facilitates a better understand-

ing of the transport of algal cells and metabolites in membrane processes. Current

strategies are (i) recycling of MF/UF(microfiltration/ultrafiltration) concentrate

and beneficial use of RO (reverse osmosis) concentrate in the lower concentration

scenario, (ii) decontamination of MF/UF concentrate (wastes) and pretreatment

for RO feed in the high concentration and high toxicity (Hc–Htox) scenario. Hence,

identification of the knowledge gap provides insights to future studies of treating

wastewater [23].