Scientists want to save water and make smelly waste vanish

Local researchers' plan would cut consumption of a rapidly dwindling resource and keep what goes into our toilets out of the ground and waterThe lush tropical landscape of Hong Kong is one of the most water-scarce places on earth.self storage The land may not be parched, and country parks and ocean make up much of the territory, but the amount of freshwater available in the reservoirs and water-catchment areas each year falls far below the global scarcity level.The rest of the water needed in Hong Kong is shipped in from Guangdong province through massive pipes that start at a tributary of the Dongjiang, or East River. But there may be competition soon, as the mainland's continuing urbanisation puts stress on water resources."Hong Kong only has around 125-150 cubic metres of fresh water capacity per person [each year]," says Chen Guanghao, a professor of civil engineering at the Hong Kong University of Science and Technology.The UN Food and Agriculture Organisation says that 500 cubic metres per person per year is the bare minimum needed. North Africa and the Middle East all hover around the 1,100 cubic metres mark, according to a 2007 report by the World Bank.Hong Kong is not alone in its predicament. The Beijing government has started the first phase of an ambitious and controversial 50-year project that will divert freshwater from the southern provinces to the more arid north, as the rapid growth of Beijing and other cities means there is less water to go around.Even as China's water consumption rises, climate scientists are warning of the fast retreat of glaciers in the Himalayas and the Tibetan Plateau, which feed the Yangtze, Yellow and Mekong rivers. The glaciers supply water to about 1.4 billion people in Asia, and have shrunk by 9 per cent in the past 30 years, according to data published last year in the journal Nature Climate Change.To help Asia deal with this looming water crisis, Chen and his colleague Dr Samuel Chui have a solution that would greatly reduce urban consumption of the precious resource. It's a three-part water conservation and treatment system that will also reduce energy usage and carbon dioxide emissions, and produce a phosphorous-based fertiliser called struvite.Chek Lap Kok airport has already been using one part of Chen and Chui's water strategy since the mid-1990s. The system has allowed the airport to halve its freshwater demand, save 30,000 MWh of energy and reduce its carbon-dioxide output by 17,000 tonnes.The key is using seawater and reusing and recycling grey water, the dirty freshwater from people washing their hands and doing their dishes. The seawater cools buildings and is used to flush toilets. The dirty freshwater gets treated and is then used to irrigate grass and clean the outside of aircraft and other surfaces that people don't normally touch.Just a few minutes away in迷你倉the new town of Tung Chung, the second part of the equation is in action. Sewage sludge is being digested by several different colonies of slow-growing bacteria, which convert the sewage into harmless sulphates, nitrogen and carbon dioxide.Chui points to a trial run of the process at a small plant in Tung Chung, which has been treating around 10 cubic metres of sewage a day for months.Chui said the system is guaranteed to eliminate about 90 per cent of the sludge, but can be even more effective, and that the Tung Chung plant has accounted for virtually all the sewage fed into it for 225 days.Hong Kong produces around 1,150 tonnes of sewage sludge daily. Thick crumbly truckloads are carted away from Hong Kong's wastewater treatment facilities to landfills, and mixed in with the 13,500 tonnes of discarded plastic bottles, construction waste and other detritus of city life generated each day. With space in the city's three landfills set to run out within the next decade, Hong Kong is looking to reduce the amount of waste that is dumped each day.A larger plant able to treat 1,000 cubic metres of sewage a day is being built in Sha Tin. The project, costing HK$24.5 million, is expected to begin trials in 2015.The Drainage Services Department promised wide-scale implementation across Hong Kong if the plant is successful, HKUST's school of engineering says.The final part of the water strategy is a process that converts phosphorus in urine to fertiliser, by adding one part hydrolysed urine to one part seawater. With the help of bacteria in the seawater, magnesium in the seawater reacts with ammonia to create the struvite within 15 minutes."It doesn't need energy, or the addition of expensive chemicals. All the elements needed are already in the seawater," Chen said.The process could also recover 30,000 tonnes of phosphorus, worth around US$150 million. Phosphorus is an essential nutrient, and also a vital part of commercial fertilisers that are currently in use.But it is in our interests to keep phosphorus from being washed back into the ocean. Like nitrates, phosphorus can cause harmful algal blooms that over time cause dead zones in coastal areas by depleting the amount of dissolved oxygen in the water.These dead zones are a growing problem in coastal areas worldwide. In 2008, there were 405 of them recorded, up from 162 in the 1980s and 49 in the 1960s."We're going from bad pee to good P," Chen said, referring to the chemical symbol for phosphorus.Were 120 million people to adopt the integrated water strategy, it could save 4.7 billion cubic metres of freshwater and US$450 million per year.It would also eliminate 10 million tonnes of sludge and save US$290 million in incineration costs, according to an article by Chen and his colleagues in Water21, the magazine of the International Water Association.Christy Choi文件倉