Microbial biotechnologies for potable water production

The WHO suggests that humans require an absolute minimum of 7.5 L of water per day, while a minimum of about 20 L of water per person per day is recommended to ensure adequate hygienic standards. With a population of 7.5 billion, this works out to 150 billion litres of safe freshwater daily, globally. Much more than this is generally consumed in developed nations, while less than adequate amounts of safe water are available in some regions. Although sufficient freshwater resources exist to meet global water needs, the major limitation is the lack of infrastructure in some regions for production and distribution of safe water. The global provision of safe water is a key aim of UN Sustainable development goal (SDG) 6, but this goal also intersects closely with SDG 13, climate change, requiring energy efficiency and minimal GHG emissions, and SDG 12, requiring sustainable global water consumption and production patterns and reductions in pollution of water resources. Safe drinking water has a quality that would not present any significant risk to health over a lifetime of consumption. While physical and chemical disinfection processes may remain essential to reduce the pathogenic burden during water treatment, we believe that increased exploitation of microbiological processes for drinking water treatment is the most sustainable way forward for the global provision of safe water. Biological drinking water treatment processes are available for the removal of a wide range of chemical contaminants, are less costly and less energy intensive than advanced chemical or physical treatment methods and are robust over a wide range of operating conditions and water qualities. Furthermore, they reduce the use of potentially hazardous chemicals and typically result in complete mineralization of contaminants, rather than concentration in a waste stream, which then necessitates specialized treatment and/or disposal. In addition, recent and ongoing research indicates that providing biologically stable water can be accomplished by fostering the presence of a natural resident, non-pathogenic drinking water microbiome that can resist pathogen invasion in water supplies, which can be achieved through the use of biological drinking water treatment processes. The major sources of drinking water are surface water and groundwater. Both forms of water are generally not safe at the source and require some form of treatment to be considered potable. To ensure adequate water quality, regulatory guidelines exist for (i) biological contaminants (pathogenic bacteria, protozoa, viruses and helminths), (ii) inorganic chemicals (metals, oxyanions, nitrogen species and radionuclides), and (iii) organic chemicals (natural organic matter and synthetic organic chemicals from agricultural, industrial and residential use). In regions where disinfection is used in drinking water treatment, disinfectant residuals and disinfection by-products are also typically regulated due to their potential adverse health effects. In addition, physical aspects of the water including colour, odour and taste also contribute to water quality. Historically and up to the present day, microbial processes have been used in the production of potable water. Biological drinking water treatment has been widespread since the 1800s in the form of slow sand filtration or bank filtration (Schubert, 2002; Logsdon et al., 2011). While historically, biological water treatment was empirical, we now have the technology and tools to understand the structure and function of the microbial communities involved in biological water treatment, potentially enabling control and optimization, making these processes even more attractive. Unfortunately, the use of biological processes for drinking water production has been in decline in recent years due to misconceptions regarding a relationship between the presence and exploitation of microbes in drinking water treatment and the presence of pathogens. In North America (and many regions around the world), disinfection is routinely used in an effort to sterilize drinking water. Despite the use of disinfectants and the presence of disinfectant residuals in distribution systems, 10–10 bacteria per mL are still present in drinking water at the tap (Hammes et al., 2008; Lautenschlager et al., 2010; Nescerecka et al., 2014). It is virtually impossible to completely remove microbes in water while delivering a safe product to consumers, and the use of disinfectants results in selection Received 21 July, 2017; accepted 21 July, 2017. *For correspondence. E-mail [email protected]; Tel. +45 45251600; Fax +45 45932850. Microbial Biotechnology (2017) 10(5), 1094–1097 doi:10.1111/1751-7915.12837 Funding Information Villum Fonden.