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Remediation and Control Technologies
Water Recovery from Advanced Water Purification Facility Reverse Osmosis Concentrate by Photobiological Treatment Followed by Secondary Reverse Osmosis Keisuke Ikehata, Yuanyuan Zhao, Harshad Kulkarni, Yuan Li, Shane A. Snyder, Kenneth P Ishida, and Michael A. Anderson Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.8b00951 • Publication Date (Web): 19 Jun 2018 Downloaded from http://pubs.acs.org on June 21, 2018
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Environmental Science & Technology
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Water Recovery from Advanced Water Purification
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Facility Reverse Osmosis Concentrate by
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Photobiological Treatment Followed by Secondary
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Reverse Osmosis
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Keisuke Ikehata†*, Yuanyuan Zhao†, Harshad V. Kulkarni†, Yuan Li†, Shane A. Snyder‡, Kenneth
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P. Ishida§, and Michael A. Anderson⊥
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†
Pacific Advanced Civil Engineering, Inc., Fountain Valley, California 92708, U.S.A.
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‡
Department of Chemical and Environmental Engineering, University of Arizona, Tucson,
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Arizona 85721, U.S.A.
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Nanyang Environment & Water Research Institute, Nanyang Technological University,
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Singapore 637141
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§
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⊥
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U.S.A.
Orange County Water District, Fountain Valley, California 92708, U.S.A. Department of Environmental Sciences, University of California, Riverside, California 92521,
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*
Corresponding Author: Tel: +01-714-270-0824; email:
[email protected] 17 18
ABSTRACT
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Reverse osmosis (RO)-based desalination and advanced water purification facilities have
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inherent challenges associated with concentrate management and disposal. Although enhanced
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permeate recovery and concentrate minimization are desired, membrane scaling due to inorganic
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constituents such as silica, calcium, phosphate, and iron hinders the process. To solve this
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problem, a new diatom-based photobiological process has been developed to remove these
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scaling constituents by biological uptake and precipitation.
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samples were collected from a full-scale advanced water reclamation facility in California and
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were treated in 3.8- and 57-L photobioreactors inoculated with a brackish water diatom
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Pseudostaurosira trainorii PEWL001 using light-emitting diode bulbs or natural sunlight as a
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light source. The photobiological treatment removed 95% of reactive silica and 64% of calcium
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and enabled additional water recovery using a secondary RO at a recovery rate up to 66%. This
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represents 95% overall recovery including 85% recovery in the primary RO unit. In addition to
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the scaling constituents, the photobiological treatment removed twelve pharmaceuticals and
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personal care products, as well as N-nitrosodimethylamine, from RO concentrate samples
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primarily via photolysis. This novel approach has a strong potential for application to brackish
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water desalination and advanced water purification in arid and semi-arid areas.
In this study, RO concentrate
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Environmental Science & Technology
TOC/ABSTRACT ART
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1. Introduction
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According to the membrane water treatment facility database maintained by the American
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Membrane Technology Association, there are approximately 1000 reverse osmosis (RO)-based
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desalination and advanced water purification facilities (AWPFs) in the United States.1 Although
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the RO technology has been proven very useful and reliable to produce very high quality, near
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drinkable permeate from non-potable water resources, such as brackish groundwater and
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recycled water,2, 3 it generates a concentrate stream of 15 to 25% needing disposal. Concentrate
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generation and management has been one of the major challenges for utilities that own and
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operate RO-based water treatment facilities.3, 4 The availability of economical methods for
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concentrate disposal is becoming a critical factor for successful RO-based water reclamation and
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groundwater desalination projects, especially in the inland areas where ocean discharge is not an
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option.
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One way to reduce the concentrate volume at an RO facility is to increase permeate recovery.
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However, the solubility limits of inorganic constituents, such as calcium carbonate, calcium
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phosphate, silica, and calcium sulfate, are often exceeded in the RO concentrate when the
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permeate recovery rate is increased. This causes scaling on the membrane surface and a
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reduction in permeate flux making higher recovery impractical. Several technologies have been
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proposed and tested to improve the permeate recovery, including use of antiscalants and
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secondary RO,2, 5 removal of scaling constituents by ion exchange or chemical softening,6
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variation of the RO process with mechanical vibrations or precise control of concentrate
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discharge,7, 8 and non-RO based desalination processes, such as forward osmosis and
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electrodialysis reversal.9-12 However, these technologies are highly chemical and/or energy
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intensive. In addition, the permeate quality in terms of dissolved constituent concentrations
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tends to decline at a higher recovery because more passage of dissolved constituents occurs as
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the reject stream becomes more concentrated unless a softening process is employed. Also, no
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trace organic removal could be expected by any of the existing methods.
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Recently, a new photobiological process using brackish water diatoms has been developed to
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treat RO concentrate.13, 14 This unique process utilizes the natural biology of diatoms
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(Bacillariophyceae), which are a class of photosynthetic microalgae whose cells are enclosed by
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a rigid silicon dioxide (silica; SiO2)-based structure called frustule.15, 16 Diatoms are capable of
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absorbing aqueous silica requiring the silicon for growth and cell division. It is also known that
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up to 70% of the dry weight of the cell is silica.17 Our previous studies demonstrated the rapid
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removal of aqueous silica from silica-rich agricultural drainage water RO concentrate from two
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AWPFs and one brackish groundwater desalination facility using a mixed culture14 or isolated
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diatom strains.13 In addition to aqueous silica and macronutrients, orthophosphate, ammonia,
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nitrate, calcium, bicarbonate, iron, and manganese were also effectively removed by the
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photobiological treatment. Since many of these constituents are known RO scalants/foulants, it
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was speculated that the photobiologically-treated RO concentrate could be desalinated further by
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a secondary RO to recover more water.14
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Environmental Science & Technology
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The main objective of this study was to explore the feasibility of additional water recovery from
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AWPF RO concentrate by photobiological treatment followed by secondary RO. The
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photobiological treatment was conducted indoors with light-emitting diode (LED) bulbs or
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outdoors with natural sunlight. In addition to the laboratory-scale photobioreactors previously
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described,14 a new 57-L pilot-scale photobioreactor was designed, constructed, and used in this
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study. The removal of important trace wastewater contaminants, including pharmaceuticals and
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personal care products (PPCPs), as well as metals and N-nitrosodimethylamine (NDMA) by the
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photobiological process was also examined.
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2. Experimental Section
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Diatom Strain and RO Concentrate Samples
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A brackish water diatom Pseudostaurosira trainorii E. Morales PEWL001 previously isolated
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from agricultural drainage water14 was used in this study. RO concentrate samples were
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obtained from the third stage of a full-scale RO unit at the Groundwater Replenishment System
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(GWRS) of the Orange County Water District (OCWD) in Fountain Valley, CA in January–May
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2017. The RO concentrate samples were analyzed for water quality parameters upon arrival
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(Table 1) and refrigerated until use. The RO concentrate samples were typically used 4 to 5 days
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after the collection to ensure the absence of chloramine residual (
