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This paper introduces a superstructure-based simultaneous optimum design and operation of seawater reverse osmosis (RO) system with boron removal under time-variant constraints. Three operational strategies are utilized to improve operability of the system under boron restrictions, including changing the activated number of pressure vessels, permeates split ratio, and pH values. Moreover, exergo-environmental and exergo-econoenvironmental analysis models are integrated. The economic efficiency, energy utilization, and environmental impact could be optimized in both design and operation phases. The effect of water tank area, membrane type, and boron concentration on water production are investigated with constant feed conditions. Choosing proper water tank volume and type of membrane could not only reduce cost but also better operation conditions, such as improving the efficiency of pumps and reducing feed pH of RO pass 2. When both the eco-costs/value ratio and emergy rate of product are added as a penalty, the annual operation cost (a reduction of 5.50 %), emergy rate (a reduction of 7.02 %) and eco-costs/value ratio (a reduction of 7.48 %) of the product could be reduced with only a small amount of water cost increment (about 2.66 %). Improving the efficiency of pumps would be an effective method to improve overall performance of the RO plant. [Display omitted] • Optimal design and operation of RO networks with boron removal are considered. • Economic, thermodynamic, and environmental analysis are integrated in model. • Economic efficiency, energy utilization, and environmental impact are optimized. • Improving efficiency of pumps could improve emergy performance of the RO plant. • Operational cost, emergy rate and eco-costs/value ratio are effectively reduced. [ABSTRACT FROM AUTHOR]

In this work, an operational optimization designed to reduce the operational cost of a full-scale seawater reverse osmosis (SWRO) system was studied under variable operating conditions. To increase operational flexibility and cost savings potential, the storage tank was used as the buffer between freshwater production and supply. With a well-developed mathematical model, which included reverse osmosis (RO) process equations, the storage tank equations and operational cost equations, the optimal problem was formulated in the form of nonlinear DAOPs (differential algebraic optimization problems). To solve the problem effectively, a simultaneous approach was introduced in which the differential and algebraic variables were fully discretized. Then nonlinear solver of IPOPT was used to solve the discretized large-scale nonlinear programming (NLP) problem. Computational results show that the operational optimization has significant potential of more than 26% cost saving over conventional method. Based on the successful solution, the impacts of variable parameters, such as feed temperature, seawater salinity, electricity price and freshwater demand were analyzed in detail. The effect of these parameters on operational cost savings and corresponding key performance indicators was determined, which enhances the understanding of the SWRO process and its optimal control. [ABSTRACT FROM AUTHOR]

Closed-circuit reverse osmosis (CCRO) was piloted to treat RO concentrate from a potable reuse facility to increase the RO recovery beyond 85%. The study determined optimum operating conditions and maintenance requirements for sustained performance at maximum recovery including flux, cross-flow velocity, and membrane cleaning intervals. The CCRO pilot included a "side conduit" to displace spent concentrate without depressurizing the membrane elements. Performance was evaluated in terms of recovery, clean-in-place (CIP) frequency, and permeate quality. Adaptive control strategies were implemented to manage feed water quality fluctuations by operating in variable recoveries where cycle-to-cycle recovery was controlled by concentrate conductivity, feed pressure and volumetric recovery. An important contribution of this study is the long-term pilot dataset collected over two years of operation, which showed the treatment of RO concentrate by CCRO to be technically feasible and operationally sustainable. The pilot operated continuously with a CIP interval greater than two months and produced permeate that met potable reuse requirements. At theoretical full scale, CCRO could increase the facility RO recovery from 85% to 91% (92% was demonstrated in a short-term run). At the future expanded plant capacity of 130 million gallons per day (MGD) (5.7 m3/s), this corresponds to a production increase to 139 MGD (6.1 m3/s). [Display omitted] • Closed-circuit reverse osmosis (CCRO) was piloted to treat RO concentrate. • Pilot is operationally sustainable from a two year study in a water reuse facility. • Adaptive control strategies were employed to manage fluctuations in water quality. • CCRO treating RO concentrate could increase the overall RO recovery to 91%. [ABSTRACT FROM AUTHOR]