• Energy Research

Abstract The environmental impacts of brine disposal from seawater desalination plants and wastewater treatment plants represent a subject of growing concern; thus, determining the potential applicability of zero liquid discharge (ZLD) for water treatment is crucial. Membrane-based technologies are a potentially attractive strategy that can be used to reach this goal. Recent studies have highlighted that integrating a series of membrane processes is a viable approach to achieving ZLD for industrial use. However, a relatively limited number of reports have been published on the challenging problems encountered with ZLD approaches. Here, we provide a review of membrane processes that may be used in ZLD approaches and describe their problems as well as potential solutions and innovative technologies for improving their performance. Furthermore, the energy consumption of the different approaches is calculated and analyzed because it represents a major contributor to the total cost, and investments in innovative technologies are discussed. Finally, the prospects for membrane-based ZLD and further research are highlighted.

The manufacture of egg yolk powder by spray drying requires regular cleaning in order to remove fouling deposits and prevent microbiological growth on the pasteurisation heat exchanger and the spray dryer. A life cycle assessment (LCA) study on a typical powder manufacturing plant, using literature data, indicated that the egg breaking, storage and pasteurisation steps were the major contributors to the plant's environmental impacts rather than the cleaning-in-place (CIP) operations owing to their high water and electricity consumption (for refrigerated storage). CIP impacts on thermal energy and wastewater emissions were nevertheless significant, and the benefits of using intermittent flows of aqueous NaOH solution in the dryer CIP stage, reported by Yang et al. (2019), were assessed. The latter gave a 21% improvement in terrestrial ecotoxicity impact. Optimising the NaOH/temperature conditions based on experimental data gave more efficient cleaning with lower water, chemicals and energy consumption. Over-cleaning had significant impacts on terrestrial and marine ecotoxicity as well as reducing productivity. Three changes in cleaning technology were considered briefly: electrical heating, solar heating and pumping, and membrane treatment of wastewater. These gave little overall global improvement, partly due to the polluting nature of the available electricity supply (coal-fired) and local benefits to the factory being offset by impacts associated with equipment manufacture.

Membrane distillation (MD) is an interesting process for desalination; however high thermal energy consumption remains one of the main obstacles in its widespread adoption. The current study presents multipass hollow fiber membrane modules to improve thermal efficiency of MD process. Fundamentally three module designs are considered: conventional one shell and one tube (fiber) pass (A), 1 shell and multiple tube passes (B/C) and equal but multiple shell and tube passes (D). The performance of the proposed designs is analyzed as a function of length of each pass, number of passes and operating conditions by using Aspen Plus simulator. The results demonstrate that the traditional design A yields the highest flux — up to 92 % higher than the multipass design D. On the other hand, the multipass design D is the most energy efficiency and shows up to 35 % less thermal energy consumption than the conventional single pass design of the same length. Single shell and multiple tube pass designs (B/C) show higher flux than D; however, their specific thermal energy consumption remains the highest among all the designs investigated. The pressure drop in multipass modules was marginally (1.5 %) higher than the conventional single pass modules.