Replace contamination, not the pipes Wolfgang Rauch and Manfred Kleidorfer Science 345, 734 (2014); DOI: 10.1126/science.1257988

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INSIGHTS | P E R S P E C T I V E S

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Undernutrition

WATER TREATMENT

Replace contamination, not the pipes Rethinking water treatment additives can have synergistic benefits for urban water management systems By Wolfgang Rauch and Manfred Kleidorfer

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astewater from urban settlements contains—among a multitude of other substances—sulfate (SO42–). Under anaerobic conditions, SO42– can be biologically converted into toxic hydrogen sulfide gas (H2S) and further to corrosive sulfuric acid (H2SO4), which results not only in noxious odors but also health issues and damage to sewer systems. This “sulfide problem” in sewers has long been recognized, but until recently, efforts have focused only on mitigation strategies for sulfide emissions in sewers. On page 812 of this issue, Pikaar et al. (1) provide an alternative to current technical measures—source control. They argue that by using substitutes for SO42–, which is often used as a coagulant in the treatment of water, the SO42– concentration in the wastewater can be reduced such that H2S no longer affects sewer infrastructure. Traditional urban water management usually involves the following (illustrated in the figure). After the uptake and treatment of raw water, drinking water is distributed to the end users. Waste and stormwater are then collected from the end users and surrounding environment and treated for release. An observer may see this as one technical system for managing water, but in reality, it is segmented into the subsystems of water supply and sanitation. Such partitioning into “clean” and “dirty” water is not only administrative but fundamental and is found at all levels, from operators to research. The advantages of taking a more integrated view of the urban water cycle have been noted (2), but barriers to implementation remain. Institute of Infrastructure Engineering, University Innsbruck, Technikerstrasse 13, 6020 Innsbruck, Austria. E-mail: [email protected]

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in which a slight differential methylation at the Lxra locus was maintained in the F2 generation (9). That study, however, used a candidate approach by F0 first identifying transcriptional differences between control and undernutrition groups and then Fetal primordial Fetal primordial assaying candidate sequences. germ cell DNA germ cell DNA Differences in mouse chow inNormal remethylation Incomplete remethylation gredients and husbandry conditions could also contribute to the discrepancies between studies. How nutritional deficiency F1 in utero leads to multigenerational phenotype transmission Sperm DNA remains unclear. The presence of hypomethylated regions in Normal methylation Reduced methylation the F1 sperm suggests that DNA methylation initially mediates Brain Inheritance. The undernutrition model environmental per turbation – suggests that DNA methylation alone induced developmental changes, cannot govern the transmission of but secondary epigenetic mechaF2 multigenerational phenotypes. Because nisms must be involved. DNA Liver of incomplete remethylation during methylation changes at other primordial germ cell development in regions not detected by MeDIP Normal utero, F1 sperm have reduced locussequencing may also be relevant methylation specific DNA methylation. Methylation to the affected developmental in the F2 mice is normal. loci. Alternatively, other epigenetic modifications operate perturbed the epigenome nonrandomly. at these loci and mediate the inheritance Furthermore, 21% of the hypomethylated of phenotypes. Histone H3 Lys4 and Lys27 regions overlapped with regions previously trimethylation (H3K27me3 and H3K4me3, shown to be nucleosome-enriched (8), which respectively) are found in nucleosome-enis striking, because 99% of histones are norriched developmental loci in sperm (8), immally replaced by protamines in mature plicating histone modifications as a potential sperm to facilitate packaging. The observamechanism for paternal transmission to the tion suggested that nutritional restriction in next generation. Another possible mechautero may have altered chromatin architecnism could involve small RNAs, as shown in ture of the sperm. a Caenorhabditis elegans caloric restriction To determine whether the altered F1 sperm model (10). epigenetic state could be transmitted to the Radford et al. provide a model of how F2 generation, Radford et al. mated young, whole-genome approaches followed by indeprediabetic F1 males with control females pendent validation should be conducted in and then assessed DNA methylation in F2 analogous studies. Although DNA methylaliver and brain at embryonic day 16.5 (E16.5). tion plays an important role in nutritional The use of a paternal transmission strategy restriction–induced developmental changes, excluded maternal effects during pregnancy. other epigenetic mechanisms mediating Analysis of late embryonic F2 tissues demmultigenerational inheritance should be inonstrated that DNA methylation at the difvestigated. ■ ferentially methylated regions was reset and reprogrammed such that, by E16.5, methylaREFERENCES 1. T. J. Roseboom et al., Mol. Cell. Endocrinol. 185, 93 (2001). tion between control and food-restricted F2 2. G. Kaati, L. O. Bygren, S. Edvinsson, Eur. J. Hum. Genet. 10, offspring was similar. However, a few genes 682 (2002). in close proximity to the differentially meth3. K. A. Lillycrop, E. S. Phillips, A. A. Jackson, M. A. Hanson, G. C. Burdge, J. Nutr. 135, 1382 (2005). ylated regions still displayed differential ex4. E. J. Radford et al., Science 345, 1255903 (2014); 10.1126/ pression at E16.5. Together, the data suggest science.1255903. that DNA methylation may not be the pri5. J. C. Jiménez-Chillaron et al., Diabetes 58, 460 (2009). 6. H.-J. Park et al., J. Clin. Invest. 118, 259 (2008). mary epigenetic mechanism underlying the 7. S. Seisenberger et al., Mol. Cell 48, 849 (2012). inherited gene expression profile and phe8. S. Erkek et al., Nat. Struct. Mol. Biol. 20, 868 (2013). notypes in the F2 offspring, although this re9. D. Martínez et al., Cell Metab. 19, 941 (2014). 10. O. Rechavi et al., Cell 158, 277 (2014). mains to be determined. These observations are in contrast to results from a study that used a similar undernutrition mouse model 10.1126/science.1258654 Control

This network-based water system is commonly seen as a technological success story and as a main contributor to improved human health. For example, for sanitation, around 64% of the world population lives in a dwelling connected to sanitation systems (3). However, the underground sewer system comes at a price. Assuming typical replacement values for sanitation systems at ~$3000 per capita (without wastewater treatment), we can assess global investments of more than $10 trillion for sewer networks that need to be maintained. This amounts to 10 to 20% of the annual global gross domestic product (4).

rates on the order of several millimeters per year. Although the mechanism is undisputed (6), it is relevant to ask about the sources for this “sulfide problem.” Sulfate is found in all types of urban wastewater. It originates from geologically induced background concentration in source water, from municipal waste products, and, when applied, from the use of aluminum sulfate or ferric sulfate as a coagulant in treatment of raw water. Hydrogen sulfide emission in sewers is favored by oxygenlimited conditions and warm temperature. Such circumstances are found in many

H2SO4 Raw water

There are many other examples that outline the benefits of a holistic view to urban water management. For the past three decades, the phosphate content of laundry detergents has been steadily reduced by switching to substitutes, thus decreasing the phosphorus concentration in the wastewater. Because this source control measure is successfully mitigating eutrophication in inland waters (8), it is a commonly cited successful intervention. One could even ask whether decentralized solutions in water management (4) could avoid the sulfide problem altogether. This is certainly true when all wastewater is treated or reused

H2S

SO42

Aluminum sulfate AI2(SO4)3

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Wastewater treatment Water supply Sewer pipes

Natural water cycle

ILLUSTRATION: P. HUEY/SCIENCE

Breaking the link. Pikaar et al. show that substitution of aluminum sulfate as a coagulant prevents H2S formation and resulting corrosion by H2SO4 in downstream sewer pipes.

More than a century after the implementation of modern sewer systems, the age of much of this infrastructure already makes their maintenance a challenge. The deterioration of sewer pipes depends mainly on factors such as type and quality of construction material, soil and sewage quality, and external impacts such as traffic loads or climate. Typically, engineers estimate the average life span of sewers at 50 to 100 years, which leads to necessary annual investments of 1 to 2% of the replacement values. Thus, any technological improvement that helps to increase the service life of sewers by 1 year would save globally more than $1 billion per year. For concrete pipes, the reduction of sulfide can be seen as such a technology. The detrimental effect of SO42– to sewer pipes was first described in 1900 (5). SO42– in the wastewater is reduced by anaerobic bacteria (primarily Desulfovibrio in biofilm and sediments) to H2S. Once emitted to the sewer atmosphere, H2S is not only a health and odor issue but also oxidized to H2SO4 by aerobic bacteria from the family Thiobacillus. In concrete pipes, H2SO4 leads to concrete corrosion with deterioration

sewer systems, particularly in pressurized pipe sections after pumping stations. Combined systems (which collectively discharge stormwater and sewage) are generally less affected because of sufficient ventilation in dry weather and elevated flow during rain conditions. The corrosion caused by H2SO4 is essentially limited to concrete pipes that prevail in highly urbanized areas as being the dominant material for large-diameter pipes. Because none of the influencing factors stated above is seemingly easy to control, mitigation measures have usually focused on H2S removal after formation (7). The costs arising from such technical interventions are on the same order as the loss in asset value caused by sulfide-induced deterioration. Pikaar et al. took a wider look at the problem and identified the obvious link between water supply and sanitation. Replacing the SO42– in water treatment by sulfate-free coagulants (e.g., ferric chloride or polyaluminum chloride) or alternative measures (e.g., membrane-based nanofiltration) is a simple source control measure that can at least counteract if not solve the sulfide problem.

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on site, thus completely avoiding the piped sanitation system. However, a combination of decentralized solutions and existing sewers will most likely prevail. The resulting decrease in sewage flow can exacerbate H2S problems in existing systems. There is a long history of making wrong decisions in complex technical systems if the components are viewed in a segregated way. Understanding processes, interlinkages, and consequences in the complete urban water cycle allows identification of optimal solutions. ■ REFERENCES

1. I. Pikaar et al., Science 345, 812 (2014). 2. P. M. Bach, W. Rauch, P. S. Mikkelsen, D. T. McCarthy, A. Deletic, Environ. Model. Softw. 54, 88 (2014). 3. World Health Organization, Progress on Drinking Water and Sanitation: 2014 Update (WHO and UNICEF, WHO Press, Geneva, 2014). 4. T. A. Larsen, K. M. Udert, J. Lienert, Eds., Source Separation and Decentralization for Wastewater Management (IWA Publishing, London, 2013). 5. F. H. Olmsted, H. Hamlin, Eng. News 44, 19 (1900). 6. T. Hvitved-Jacobsen, J. Vollertsen, A. H. Nielsen, Sewer Processes: Microbial and Chemical Process Engineering of Sewer Networks (CRC Press, Boca Raton, FL, ed. 2, 2013). 7. L. Zhang et al., Water Res. 42, 1 (2008). 8. A. W. Maki et al., Water Res. 18, 893 (1984). 10.1126/science.1257988 15 AUGUST 2014 • VOL 345 ISSUE 6198

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