Publication: Nutrients recovery and sodium removal from aquaculture effluent via vacuum membrane distillation-nanofiltration
Date
2024-02-01
Authors
Loh Chian Yong
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Abstract
The aquaculture industry expansion has led to excess nutrient discharge
causing eutrophication. Recovery of such trace nutrients is inefficient using
conventional treatment methods. The presence of high sodium content (osmotion) in
aquaculture effluent has also been another primary challenge that limiting nutrient
recovery and its application for reuse. To address these issues comprehensively, this
study focused on the development of an effective membrane-based treatment
sequence, combining vacuum membrane distillation and nanofiltration. In the
preliminary study, an acid-stripping-enhanced vacuum membrane distillation (eVMD)
was developed for improving ammonia recovery and concentrating performance while
nanofiltration (NF) in diafiltration mode was introduced for simultaneous
concentrating phosphate and removing sodium. The eVMD demonstrated exceptional
performance, surpassing conventional VMD. Within 2 hours, it achieved a 16-fold
increase in the ammonia separation factor (SF) and concentration factor (CF), enabling
the complete recovery of dilute ammonia at high concentrations in an acid solution.
For enhanced nutrient recovery and sodium removal, diafiltration-nanofiltration (DF-
NF) proved superior to nanofiltration-diafiltration (NF-DF), effectively concentrating
phosphate (2 factors) and removing sodium (97 wt%). The membrane sequence,
whether through eVMD followed by VMD or NF, underwent evaluation using various
synthetic and real aquaculture effluent sources. VMD demonstrated superior
performance as a second-stage process, achieving a phosphate CF of 4.67 with over 99.74% rejection. For fresh aquaculture effluent, a two-stage VMD operation (eVMD-
VMD) effectively concentrated both ammonia and phosphate, resulting in a
remarkable 77-fold increase in recovered ammonia (from 49.33 to 3,790 mg/L) with
an SF of 554, and up to a 6-fold increase in phosphate (from 16.67 to 92.52 mg/L).
When dealing with mixed effluent from both fresh and brackish sources, a membrane
sequence combining eVMD-VMD and DF-NF was proposed for nutrient recovery and
sodium removal. The first-stage eVMD concentrated ammonia (from 20.37 to
1,046.67 mg/L) in an acid solution, while the subsequent NF in diafiltration modes
selectively separated the concentrated retentate, yielding phosphate-rich (from 10.33
to 50.50 mg/L) and sodium-lean (from 510 to 44.50 mg/L) retentates after the second-
stage VMD. These innovative membrane sequences excel in efficiently recovering
nutrients at high concentrations while simultaneously removing sodium from various
aquaculture effluent sources. It opens new possibilities for utilizing the recovered
nutrients as liquid fertilizers or soil conditioners.