Biodesalination: A Case Study for Applications of Photosynthetic Bacteria in Water Treatment  

Abstract

Shortage of freshwater is a serious problem in many regions worldwide, and is expected to become even more urgent over the next decades as a result of increased demand for food production and adverse effects of climate change. Vast water resources in the oceans can only be tapped into if sustainable, energy-efficient technologies for desalination are developed. Energization of desalination by sunlight through photosynthetic organisms offers a potential opportunity to exploit biological processes for this purpose. Cyanobacterial cultures in particular can generate a large biomass in brackish and seawater, thereby forming a low-salt reservoir within the saline water. The latter could be used as an ion exchanger through manipulation of transport proteins in the cell membrane. In this article, we use the example of biodesalination as a vehicle to review the availability of tools and methods for the exploitation of cyanobacteria in water biotechnology. Issues discussed relate to strain selection, environmental factors, genetic manipulation, ion transport, cell-water separation, process design, safety, and public acceptance.

Removal of Sodium from Seawater Medium Using Photosynthetic Bacteria

“…This suggests that the use of photosynthetic bacteria offers a convenient, low-cost approach for the desalinization of seawater. In other desalinization processes that use photosynthetic bacteria, for example, cyanobacteria, large ponds are required to provide sunlight for growth of cells [10].…”

“…However, the process by Rhodovulum sp. removes Na by its Na transport system of cells compared with the adsorption by EPS of negative charge [10] [13]. The functions of Na removal by Rhodovulm sp.…”

“…However, the precise function of Na reduction wasunclear [9]. Amezago et al reported low-cost bio-desalinization of seawater using photosynthetic bacteria [10].…”

Biodesalination: an emerging technology for targeted removal of Na+ and Cl− from seawater by cyanobacteria

“…In addition, cells should be just depleted of energy and therefore not able to actively export Na + . As discussed in a recently published case study on using cyanobacteria for biodesalination [6], one of the bottlenecks in the production process is the efficient removal of the salt laden cells from the desalinated water without affecting the integrity of the cell membrane. Cell-liquid separation techniques such as sedimentation or flotation require, as a first step, the formation of robust cell aggregates.…”

“…At the same time, extreme weather events have increased the occurrence of droughts, most notably in arid regions in close proximity to the sea [3,4]. In addition, developing countries are more prone to these effects [5] and these factors put together allowed for the conception of "Biodesalination: From cell to tap" [6]. This project envisages the utilisation of photosynthetic bacteria for the removal of specific ions from seawater, thus, providing a sustainable alternative to seawater desalination, when compared to current methods [7,8].…”