How Safe for Re-Use is Treated Sewage?

The subject of just how safe treated municipal sewage is for re-use often crops up and has recently been questioned more as the world’s freshwater resources become scarcer and with an increasing world population. Much attention has been given to removing pathogens from drinking water in the last century and the discovery of chlorination as a means of disinfecting water for human consumption has been responsible for saving many millions of lives. Various new disinfections methods have also subsequently been discovered, such as the use of ultraviolet light, ozone and ultra-filtration, however none of these methods, nor chlorination, adequately removes substances in water that have come to be known as endocrine disruptor compounds, or EDCs. An endocrine disruptor is a foreign substance or mixture that alters the functioning of the endocrine system and can consequently causes adverse health effects in humans and their offspring, as well as other organisms.

Cosmetics, pharmaceutical drugs and hormones like oestrogen from birth control pills are considered to be endocrine disruptors and can accumulate in water as it is repeatedly passed through the human body and don’t get diluted away through enough contact with larger bodies of cleaner water. Regulations in South Africa permit treated municipal effluent to be discharged almost anywhere in the natural environment, including rivers and dams, provided its quality is compliant with the necessary standards required of the particular discharge point. These standards are some of the most rigorous in the world and include adequate disinfection to kill off pathogens, however there is currently no consideration for the impact of endocrine disruptors in the water, as is currently the case virtually worldwide. Local regulations also allow treated sewage to safely be used as wash-down water, such as at car wash outlets, or to irrigate plants that aren’t consumed by humans: e.g., golf courses and playing fields. However, the vast majority of treated effluent is returned to rivers and other surface water bodies where it can be taken up again after dilution to be treated for use as drinking water. Underground aquifers are also receiving treated sewage effluent by natural ground seepage at effluent discharge points. In many places in the world it is still permitted to use treated effluent to irrigate pastures for livestock that is subsequently sent to the abattoir, or in some cases on crops that are directly consumed by humans.

There aren’t many places that recycle their sewage effluent directly for drinking water purposes, as can be done in the International Space Station. Windhoek in Namibia recycles up to 50% of its domestic waste water effluent and typically the use of sophisticated energy-intensive ultra-filtration processes such as reverse osmosis (RO) are employed for this purpose. The resulting filtrate from this process usually needs to be blended with fresh water before human consumption though as RO effectively renders the water so sterile that it is unpalatable. RO has the advantage, however, of being able to remove virtually everything in water except ammonia which shares a similar chemical structure to that of water.

Conventional drinking water treatment processes don’t actively remove endocrine disruptors and these substances can be re-consumed repeatedly with their concentrations increasing as they pass through the body each time. Andrew Hulsman, owner of HWT, a local specialist water treatment company comments: “Endocrine disruptors are, at the moment, unquantifiable – which means we don’t really know exactly what they do to us and how serious their effects are. What we do know is that in sufficient quantities over a prolonged period of time they contribute to the onset of hermaphroditism.” Currently there are concerns about both the female and male populations in some places in the world being subjected to too many human hormones where extensively recycled water is ingested. It is also claimed that the accumulation of oestrogen in particular is leading to a much earlier onset of puberty in young females but an increasing amount of infertility in men as part of the ‘feminisation of nature’. The author Deborah Cadbury used this term as the title of her book where she explains the feminisation phenomenon in great detail. Concerns such as these are starting to gain more attention more recently though with small amounts of money starting to be made available for EDC contamination research, although more significant amounts of money for such research will likely only be made available once the issue reaches crisis proportions.

The Canadian Water Network is one authority that is taking a greater interest in EDCs to the extent that they are funding two Carleton university professors in Ottawa, Canada to find ways to cleanse water of drugs, personal care products, cosmetics, fragrances and other endocrine-disrupting compounds that are found in products such as birth control pills. According to the Canadian researchers, extremely low concentrations of endocrine-disrupting compounds are able to affect the human endocrine system and pose a threat to both foetal development and to young children. They also cite the example of the feminization of male fish, documented as being linked to the presence of EDCs in surface waters, as positive proof that these substances have an adverse and undesirable effect on aquatic organisms and that humans are also most likely to be adversely affected as well. The Carleton researchers are reportedly using polymeric particles with nano-structures that they intend to engineer either to remove several of the compounds simultaneously or selectively remove targeted harmful compounds from effluent water.

According to HWT’s Hulsman, it is because EDCs are currently difficult to quantify that it is not easy to engineer an appropriate unit treatment process for removing them from waste streams. Therefore the first step towards achieving an engineered solution would be the standardization of the measurement of EDCs. At present, certain long chain molecules associated with orally ingested contraceptives, for example, can successfully be identified in a private laboratory owned by the patent holder. However there is currently no practical means whereby accredited water treatment laboratories would have the equipment, skills and knowledge available to recognize EDCs, even if they wanted to measure them. A suitable EDC test would need to be a broad catch-all to ensure that it gains acceptance and is adopted widely, much like the Chemical Oxygen Demand (COD) test that is currently used by water quality test laboratories. In this well-established test procedure, COD measurements do not discriminate between an easily assimilable sugar or starch from brown bread, however each can be represented by a specific COD concentration, which in turn can then be used as an easily measured input and output variable for an engineered solution. It is possible that filtration, chlorination or ozonation could remove or destroy EDCs, however with no agreed-upon measurement technique currently available process variables such as loading rates and exposure times to different treatment regimes will have no meaningful value.