STRATEGIES FOR FLOW RECOVERY OF
ULTRAFILTRATION MEMBRANES APPLIED TO THE SEPARATION OF MICROALGAL BIOMASS CULTIVATED WITH DOMESTIC WASTEWATER

Name: LUDIMILA ZOTELE AZEREDO
Type: PhD thesis
Publication date: 13/02/2023
Advisor:

Namesort descending Role
Ricardo Franci Gonçalves Advisor *

Examining board:

Namesort descending Role
Eduardo Lucas Subtil Co advisor *
Regina de Pinho Keller Internal Examiner *
Ricardo Franci Gonçalves Advisor *
Sérvio Túlio Alves Cassini Internal Examiner *

Summary: The improvement of sustainable technologies based on the NEXUS and Circular
Economy concepts is a strategic need to mitigate water and energy insecurity in
various regions of the planet. The objective of this work was to optimize the
ultrafiltration of a microalgae suspension through the implementation of flow
recovery strategies using coagulants and steel industry residues to control the
formation of deposits. This suspension corresponds to the effluent from a sanitary
sewage treatment plant on a pilot scale through a UASB reactor and followed by
two high rate lagoons. The average concentration of SSV in the suspension
produced in the LAT was 120 mg/L, being composed of a heterogeneous
biomass with the majority presence of Chlorella sp. In the first stage of the
research, physical methods such as aeration, relaxation and backwashing were
tested to recover the flow and control deposits on the ultrafiltration membranes.
Aeration at the base of the membranes increased the tangential velocity by 47%
compared to filtration without any technique for reducing and controlling deposits.
The average flows were 68.9 L/m².h, 63.2 L/m².h and 55.7 L/m².h, aeration,
relaxation and backwash, respectively. In the second stage, the use of coagulants
and steel industry residues in the pre-treatment of the suspension with
microalgae and their effects on flow recovery and deposit control were studied.
The coagulation-flocculation-sedimentation process influenced the
characteristics of the flocs, and the average final normalized fluxes of the
coagulated suspensions. The tannin-based coagulant increased the resistance
imposed by deposits on the membrane, even though most deposits were
reversible. Finally, the influence of pre-treatment of the suspension on the
ultrafiltration of microalgae grown in sanitary sewage on the physical methods of
flow recovery and deposit control was verified. The use of residues rich in calcium
as coagulants caused lower membrane resistance. Although there was an
increase in irreversible deposits with the addition of inorganic coagulants based
on aluminum and calcium, the predominant mechanism in the formation of
deposits was the formation of the cake layer. For the three control strategies
investigated, the lowest formation of deposits on the membrane was observed in
the backwash filtration of the suspension coagulated with 10 mg/L with bag filter
powder.

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