Aqueous silica removal from agricultural drainage water and reverse osmosis concentrate by brackish water diatoms in semi-batch photobioreactors
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A novel aqueous silica removal process using naturally occurring diatoms for water and wastewater treatment, in particular water reuse and desalination, was developed. Brackish agricultural drainage water containing 39 mg L−1 of total silica and 10 g L−1 of total dissolved solids was used as a source of silica-assimilating diatoms. The drainage water was statically incubated in 500-mL and 7.5-L photobioreactors at 27 ± 2 °C under continuous illumination using two 13-W compact fluorescent light bulbs as a light source. After 10 days, brown algal biomass became noticeable and silica removal started to occur. Silica removal accelerated as algal biomass accumulated. In the fourth semi-batch cycle, more than 95 % of molybdate reactive silica was removed within 28 h. Removal of nonreactive silica was also confirmed. Reverse osmosis concentrate samples from advanced water reclamation facilities with high silica concentration (>120 mg L−1) were also tested. More than 75 % of silica was removed within 6 days. Microscopic analysis revealed the presence of Pseudostaurosira, Nitzschia, and Halamphora species in the photobioreactors. To the best of our knowledge, this is the first report on the use of diatoms for aqueous silica removal in water treatment.
KeywordsDiatoms Photobioreactor Silica Brackish water Desalination Water reuse
The authors would like to thank Dr. John P. Smol from Queen’s University, Kingston, ON, Canada, and Mr. Paul B. Hamilton from Canadian Museum of Nature, Ottawa, ON, Canada, for their kind helps with preliminary diatom identification. The authors would also like to thank Dr. Kenneth P. Ishida and Mr. Donald W. Phipps from the Orange County Water District, Fountain Valley, CA, and Dr. Cathy Chang and Dr. Paul Fu from the Water Replenishment District of Southern California, Lakewood, CA, for providing RO concentrate samples and valuable information and suggestions. Assistance of Ms. Kelly M. Huston, Ms. Yao (Fiona) Jin, and Yuan (Abby) Li, Pacific Advanced Civil Engineering, Inc., Fountain Valley, CA, is also gratefully acknowledged. This work was financially supported by Pacific Advanced Civil Engineering, Inc.
Conflict of interest
Two of the authors (Keisuke Ikehata and Andrew T. Komor) have applied for a US patent (application no. 20120175301) based on this discovery. The authors declare that there is no other conflict of interest.
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