Evaluating the potential for zero discharge from reverse osmosis desalination using integrated processes : a review

Desalination processes used worldwide produce a large amount of waste concentrate, the disposal of which can have significant environmental impacts. As such, there has been research carried out into the development of zero liquid discharge technologies which recognise that the waste concentrate streams contain valuable salts, minerals and water. These technologies include the proprietary SALPROC systems, as well as other integrated systems that use a variety of different technologies for the extraction of salts and minerals from waste concentrates. Research has also been conducted on using forward osmosis as a means of treating the waste concentrate in order to produce additional product water and thus reduce the volume of waste concentrate. This article provides a review of these technologies and evaluates the potential for achieving zero liquid discharge by combining these technologies with conventional desalination technologies into integrated processes.

Advances in membrane distillation for water desalination and purification applications

Membrane distillation is a process that utilizes differences in vapor pressure to permeate water through a macro-porous membrane and reject other non-volatile constituents present in the influent water. This review considers the fundamental heat and mass transfer processes in membrane distillation, recent advances in membrane technology, module configurations, and the applications and economics of membrane distillation, and identifies areas that may lead to technological improvements in membrane distillation as well as the application characteristics required for commercial deployment.

Carbon nanotube based composite membranes for water desalination by membrane distillation

New technologies are required to improve desalination efficiency and increase water treatment capacities. One promising low energy technique to produce potable water from either sea or sewage water is membrane distillation (MD). However, to be competitive with other desalination processes, membranes need to be designed specifically for the MD process requirements. Here we report on the design of carbon nanotube (CNT) based composite material membranes for direct contact membrane distillation (DCMD). The membranes were characterized and tested in a DCMD setup under different feed temperatures and test conditions. The composite CNT structures showed significantly improved performance compared to their pure self-supporting CNT counterparts. The best composite CNT membranes gave permeabilities as high as 3.3 x 10-12 kg/(m x s x Pa) with an average salt rejection of 95% and lifespan of up to 39 h of continuous testing, making them highly promising candidates for DCMD.

Drought and desalination: Melbourne water supply and development choices in the twenty-first century

Sharply reduced catchment inflows across Australia around the end of the twentieth century led to a sequence of water restrictions followed, as the drought persisted, by approximately $10 billion of investments in desalination plants near Perth, Adelaide, Melbourne, Sydney and Brisbane. This Deakin University project jointly with Griffith University, for the National Centre of Excellence in Desalination (NCEDA), follows these new investments. We ask how best to manage bulk water supply and retail supply given the facts and fears of uncertain rainfall, modelled over a 100 year simulation period. We use Monte Carlo style studies aiming to capture the new tensions and trade-offs regarding uncertain climate, rainfall and water supply. There are presently no comprehensive life-cycle approaches to model city water balances that incorporate economic feedbacks, such as tariff adjustment, which can in turn create a financing capacity for such investment responses to low catchment levels, models that could provide significant policy implications for water planners. This project addresses the gap, and presents excerpts from a system dynamics model that augments the usual water utility representation of the physical linkages and water grids. We add inter-connected feedback loops in tariff structures, demand levels and financing capacity. Tariffs are reset in association with drought and the modelling of responses both in terms of reduced consumption and increased revenue to the utility, depending on the elasticities of demand responses to higher tariffs, both short and long term, while also allowing effects from any transitional restrictions. Before reporting on parts of the simulations applied to Melbourne, this paper will first review the general issues surrounding whether desalination is or can be a “game changer” for economic development that hinges on secure water supply. We then explore options in bulk water supply management when desalination augments the choices, including catchments, dams, recycling, pipelines from rivers and savings in irrigation. Finally, the paper addresses the intriguing and important question of the value and cost of providing water for environmental uses.

Long-term water supply planning in an Australian coastal city : Dams or desalination?

Water resource managers and planners are continually involved in defining and evaluating alternative policies to better meet changing water supply conditions and the expectations of society. To undertake such long-term water supply planning, this study developed a novel integrated system dynamics model to combine economic, social and scientific variables and considerations within the planning horizon. Extensive sensitivity analysis for these variables was considered in this long term water resource planning process. The analysis suggests that over a longer time horizon, desalination provides a more viable, cost effective and secure bulk water supply alternative when compared to building large rain-dependent dams.