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Membrane Water Treatment
  Volume 8, Number 3, May 2017, pages 279-292
DOI: http://dx.doi.org/10.12989/mwt.2017.8.3.279
 


UF pretreatment at elevated temperature within the scheme of hybrid desalination: Performance and environmental impact
Sergey Agashichev and Jayesh Kumar

 
Abstract
    This study was aimed at ultrafiltration (UF) as a pretreatment before reverse osmosis (RO) within the scheme of hybrid reverse osmosis-multistage flush (RO-MSF) desalination. Seawater at elevated temperature (after MSF heat-exchangers) was used as a feed in this process. The pretreatment system was represented as a set of functionally-linked technological segments such as: UF filtration, backwashing, chemical- enhanced backwashing, cleaning, waste disposal, etc. The process represents the sequences of operating cycles. The cycle, in turn, consists of the following unit operations: filtration, backwashing and chemical-enhanced backwashing (CEB). Quantitative assessment was based on the following indicators: normalized permeability, transmembrane pressure, specific energy and water consumption, specific waste generation. UF pre-treatment is accompanied by the following waste streams: W1=1.19x10 power of -2 m3 (disposed NaOCl with 0.0044% wt.)/m3(filtrate); W2=5.95x10 power of -3 m3 (disposed H2SO4 with 0.052% wt.)/m3 (filtrate); W3=7.26x10 power of -2 m3(disposed sea water)/m3(filtrate). Specific energy consumption is 1.11x10 power of -1 kWh/m3 (filtrate). The indicators evaluated over the cycles with conventional (non-chemical) backwashing were compared with the cycles accompanied by CEB. A positive impact of CEB on performance indicators was demonstrated namely: normalized UF resistance remains unchanged within the regime accompanied by CEB, whereas the lack of CEB results in 30% of its growth. Those quantitative indicators can be incorporated into the target function for solving different optimization problems. They can be used in the software for optimisation of operating regimes or in the synthesis of optimal flow- diagram. The cycle characteristics, process parameters and water quality data are attached.
 
Key Words
    hybrid desalination; elevated temperature; UF pre-treatment; UF cycle; chemical-enhanced backwashing; performance indicators; waste intensity indicators
 
Address
Sergey Agashichev and Jayesh Kumar : NEWRC (ADWEA), PO Box 54111, Abu Dhabi, UAE
 

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