In today’s rapidly evolving global landscape, the quest for water security transcends mere access, extending to the imperative need for purified water for diverse applications. Surface water bodies, contaminated by domestic and industrial waste, pose unprecedented challenges to conventional treatment methods leading to a growing reliance on groundwater. However, excessive groundwater abstraction, exacerbated by climate change, is greatly impacting water quality.
The World Health Organization’s (WHO) stringent standards for water quality combined with the ever-deteriorating water quality highlight the need for advanced treatment methods. To address these challenges, a paradigm shift toward innovative solutions, particularly Reverse Osmosis (RO) technology, has been ongoing. RO technology has been, for a long time now, a viable solution for treating water with high levels of salinity, as well as specific contaminants such as fluoride, hardness, bicarbonates, and heavy metals to acceptable standards, although misconceptions persist regarding its perceived high capital and operational costs.
Understanding the fundamental principle of osmosis is crucial in demystifying RO technology. The process involves forcing raw feedwater with high dissolved solids through a membrane against the natural osmotic process, resulting in purified water. Achieving a balance between high recovery (ratio of purified to feed water) rates and maintaining acceptable purified water quality is vital for system efficiency and sustainability.
RO units are categorized based on raw water salinity levels, ranging from low brackish, high brackish to seawater, each requiring specific membrane types and operating pressures, subsequently determining the energy requirements and costs. The capital and operational costs increase with rising salinity levels, emphasizing the importance of selecting the correct RO unit.
Effective pre-treatment before feeding water to the RO unit is critical to prevent damaging the heart of the system which are the membranes. Anti-scale chemical injection into the feedwater of the reverse osmosis unit plays a vital role in preventing scale deposition, ensuring the system’s optimal performance. However, periodical cleaning of the membranes may be necessary to restore system performance, especially after long periods of operation resulting in scale deposition which consequently reduces the production capacity of the RO unit.
In off-grid areas, power supply to RO systems is a challenge which has led to increased adoption of renewable energy sources, particularly solar power. Advancements in solar technology offer alternatives like solar grid-tie systems and off-grid battery-less RO units, to minimize energy costs and address power deficiencies. This alternative is also applicable to either supplement or replace grid power, where available, as a cost-reduction measure.
The latest advancement, the Closed-Circuit Reverse Osmosis (CCRO), operates in a closed-loop configuration, optimizing water recovery thus minimizing waste to between 10 – 20%. Traditional RO units can waste up to 70% of the feedwater depending on the salinity levels. While characterized by higher investment costs compared to traditional RO configurations, the CCRO enhances overall system efficiency and sustainability, resulting in significantly lower operational costs in the long run.
As the demand for purified water intensifies, demystifying RO technology becomes pivotal in the quest for water stewardship. A comprehensive understanding of different RO configurations, raw water quality classifications, energy requirements and alternatives, and pre-treatment processes is key to managing the water-energy nexus globally, especially in developing countries which are disproportionately affected by challenges of water insecurity.