Name: Larissa Bastos Paulino
Type: MSc dissertation
Publication date: 04/03/2020
Advisor:

Namesort descending Role
Ricardo Franci Gonçalves Advisor *

Examining board:

Namesort descending Role
Adrianus Cornelius Van Haandel External Examiner *
RAQUEL MACHADO BORGES Co advisor *
Ricardo Franci Gonçalves Advisor *
Sérvio Túlio Alves Cassini Internal Examiner *

Summary: This research aimed to study the influence of the variation of the configuration of a column of
bubbles, filled with effluent from a high rate algae pond treating anaerobic effluent from UASB,
regarding biogas purification. The effect of the column configuration was verified by varying the
type of diffuser (fine and thick bubbles) and the effect of the presence of packing. The
purification of biogas using microalgae-based processes allows the transfer of CO2 to the liquid
phase, preventing its emission to the atmosphere, as well as increasing the energy potential of
biogas, while simultaneously providing the recovery of CO2 as algal biomass. The effect of
column configuration by varying the type of diffuser (thin and thick bubbles) and the effect of
the presence of packing using a randomly distributed synthetic granular medium consisting of
pieces of high-density polyethylene corrugated tubes was verified. Thereunto, two columns
were designed and constructed: one of thin bubbles, without packing, and another of thick
bubbles, with packing. The height of the liquid column (0.55, 1.55 and 2.55 m) and the biogas
aeration flow rate (2.12, 5.31, 10.6, 15.91 e 21.22 m³.m-2h
-1
) were also varied. The increase of
the biogas injection flow presented a greater increase of the carbon dioxide concentration in
the liquid medium and an increase of the values of the volumetric coefficient of global transfer
KLa to the CO2 in the fine bubble column without packing (3,58, 4,13, 6.22, 6.92 and 10.48 h-1
for
flow rates of 2.12, 5.31, 10.6, 15.91 e 21.22 m³.m-2h
-1
, respectively) and in the thick bubble
column with packing (2.71, 7.51, 9.44, 14.53 and 14.93 h-1
for flow rates of 2.12, 5.31, 10.6, 15.91
e 21.22 m³.m-2h
-1
, respectively). In addition, the increase in the flow rate resulted in an increase
in overall transfer capacity (STR) for the fine bubble column without packing (0.17, 0.33, 0.51,
0.75 and 1.05 gh-1 for flow rates of 2.12, 5.31, 10.6, 15.91 e 21.22 m³.m-2h
-1
, respectively) and
for the bubble column with packing (0.15, 0.68, 0.86, 1 , 39 and 2.17 for flow rates of 2.12, 5.31,
10.6, 15.91 e 21.22 m³.m-2h
-1
respectively), however, reduced the mass transfer efficiency (STE)
39, 24, 29.54, 22.95, 22.60 and 23.68% for the fine bubble column without packing at 2.12, 5.31,
10.6, 15.91 e 21.22 m³.m-2h
-1
, respectively. On the other hand, for the column filled with thick
bubbles, there was an increase in the STE of 34.33, 61.40, 38.74, 41.53 and 48.75%, in flows of
2.12, 5.31, 10.6, 15.91 e 21.22 m³.m-2h
-1
, respectively. The height of the liquid column had
influence on the transfer parameters, and the height increase presented higher values of the
kinetic coefficients. Overall, the thick bubble column with packing performed better than the
thin bubble column without packing. This result was related to the presence of packing, which
acted as a barrier to the passage of the bubbles, avoiding coalescence and increasing the
detention time. On the other hand, the columns presented higher KLa values for methane with
increasing biogas flow rate, as well as the percentage of loss of methane ranging from 6.33 to
27.82%. Although the filled bubble column had higher KLa values, both column configurations
showed similar methane losses. The energetic potential of the crude and purified biogas for each
column was estimated, and the results indicated that for the thick bubble column the biogas
purification was not advantageous due to the high oxygen uptake and methane loss; therefore,
the maximum energy production was from crude biogas (72.67W). On the other hand, for the
fine bubble column, biogas purification obtained better energy results than crude biogas, having
its maximum value (79.38 W) for the biogas flow rate of 2.71 m³.m-2h
-1
. Also, for all flows tested
in both columns, the results indicated a positive energy balance.

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