'Room for decentralized greywater reuse in future'
Israel leads in use of treated wastewater, but doesn’t allow household systems, unlike other highly developed nations.
By SHARON UDASIN
While Israel’s authorities allow almost no decentralized water systems, experts stressed that there would be a place for such structures – particularly greywater recycling mechanisms – in the country’s future, at a conference in the Negev last week.The third Sde Boker Conference on Advanced Water Management Technologies was held at Ben-Gurion University Sde Boker campus.Other highly developed countries, such as the United States, Australia and Germany, allow at least to some extent the reuse of household greywater, but the Health Ministry still takes issue with such practices due to fears of health risk, according to Prof.Amit Gross, of the Environmental Hydrology and Microbiology Department at BGU’s Zuckerberg Institute for Water Research.While Israel reuses a higher proportion of treated wastewater than any country by far – more than 80 percent – and its desalinated water industry also thrives, all of these mechanisms are performed in a centralized, large-scale form. Decentralized greywater reuse, on the other hand, would mean individual homes reusing sink and shower basin water to flush their toilets and water their gardens, experts explained.“In Israel we neglect almost completely the discipline of decentralized water treatment,” Gross said.To put it simply, blackwater is defined as feces with flushing water and urine, yellowwater is urine with or without flushing water, brownwater is feces with flushing water without urine, and greywater is other domestic sewage – such as used shower or sink water, Prof. Jörg Londong of the Bauhaus-Universität Weimar said.AdvertisementLondong spoke of projects in Germany and Switzerland where waste products are being separated into streams right from the home – deriving nutrients such as nitrogen, phosphorus and potassium from urine, organic content for biogas and fertilizer from feces, and reusable water from greywater. The ideal situation, he said, would be “using everything, not just water but the nutrients.”About 70% of urban water demand in developed countries is for domestic consumption, and of that 70%, about 60% to 70% becomes greywater, said Prof. Eran Fridler, of the Environmental, Water and Agricultural Engineering Department at the Technion-Israel Institute of Technology.Of that greywater, about two-thirds is deemed light greywater – bath, shower and wash-basin water – and about one-third is dark greywater – water from the kitchen sink, the dishwasher and the washing machine, Fridler explained.By using greywater to flush toilets, countries can reduce the demand for potable water by 30%, and by using it to both flush toilets and water gardens, countries can reduce the demand by 40%, Fridler said.“When planning our systems we have to think about how to save and use more efficiently our water,” said Eli Cohen, CEO and an engineer at the Tzipori-based Ayala Water and Ecology, which develops natural biological systems for wastewater treatment.While a centralized approach might be easier to control, it requires more infrastructure, longer-range transport, more piping, pumping, maintenance, water loss, energy and contamination, Cohen explained. Decentralized approaches lack those disadvantages but still are often seen as a nuisance to the surrounding community and also require complex technological skill to install, he said.“It’s starting to get its place in the world, but it’s too slow,” he said.Gross and a team have been experimenting with greywater flow for three years, using installed constructed wetlands for further purification to irrigate landscapes and gardens. While there have been failures – only 45% of the systems experienced no failure during the entire period – fecal coliform levels met stringent Israeli standards, and soil treated with the greywater was similar in quality to soil treated with freshwater, he said.Gross stressed his hope that Israeli authorities would warm up to the idea of using decentralized greywater systems.“One major issue is that there is a lack of long-term quantitative information, and if we introduce that I think we can convince the authorities that it is possible,” he said.On a national scale, using greywater could reduce urban water consumption by an annual 140 million cubic meters by 2050 (around 10%), as well as reduce electricity usage by 560 gigawatthours (about 0.5%) by that time, according to Gross.Meanwhile, the country would be able to eliminate the need of one large desalination plant, reduce carbon dioxide emissions by about an annual 6 to 8 tons and save about $3 billion-$4b. in direct costs by that same year, he added.“Even in a single-house operation, water reuse can be economical and it can increase water savings by 40%,” Gross said. “It is recommended that the Israeli authorities will firmly advance and adopt current initiations for greywater reuse.”
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