Why the city is feeling flush

Most of Shanghai's 23 million inhabitants don't really know what happens when they flush the toilet, or watch their shower water go down the drain. But what happens in the sewage pipes beneath the city streets and the treatment plants where it all ends up is vital to keeping the city alive and healthy.

Every monthly household account for water use is divided into two sections so that householders pay for the water they use and for the treatment of the water they have flushed down the drain.

Treating sewage in the city is a 24-hour-a-day, 365-day-a-year battle so that our waste can be returned to nature in a safe condition. Most people have no idea how this happens.

Most sewage in Shanghai comes from domestic or industrial waste. With the rapid development of Shanghai, water consumption and sewage output has increased dramatically. Today domestic waste makes up more than 70 percent of all the city's sewage.

In 2010 the city discharged 2.31 billion cubic meters of sewage, nearly a fifth of the volume of the city's annual water usage.

Until the 1970s Shanghai had no modern facilities for sewage treatment. By 1990 only 24 percent of the sewage produced in the city could be treated. Most sewage was discharged directly into the rivers, according to government records.　

This was a disaster. Shanghai's major water sources, Suzhou Creek and the Huangpu River, were seriously contaminated. The sources for the city's drinking water had to be moved several times to keep the city supplied with potable water.

Over the past decade authorities have been working hard on water and sewage treatment. By the end of 2011, 53 sewage treatment plants had been built across Shanghai to treat 83 percent of the 6.30 million cubic meters of sewage the city produces every day, according to the Shanghai Water Authority. This government department was launched in 2000 to take overall charge of water and sewage in the city.　

"The percentage is expected to be up to 85 percent by the end of 2015," said Tang Jianguo, the deputy director of the Water Resources Management Department with the Shanghai Water Authority.

With World Water Day approaching on Thursday, the Global Times visited the largest sewage treatment plant in Asia to see how Shanghai is coping with its waste matter.

From sand to sewage

A decade ago Bailonggang was just a little-known sandbar at the mouth of the Yangtze River in Pudong. Few locals knew about it or cared. Today it is the site of the city's largest sewage treatment plant, handling 2 million tons of sewage every day - one third of Shanghai's output.

The Shanghai Chengtou Waste Water Treatment Co Ltd runs 18 sewage treatment plants handling half of all of Shanghai's sewage every day. Its general manager, Zhou Hua, told the Global Times that the plants were a leading contributor to the government's annual plan for energy consumption and for reducing the discharge of pollutants.

Progress has not been achieved overnight. In 1988 the Shanghai Water Authority began building four major underground water reticulation systems to deliver domestic sewage to the city's treatment plants.

Bailonggang was built to meet the burgeoning demand on the system. In 1999 the 680-million-yuan ($107 million) plant was opened and later was extended as one way of attacking the problem of dealing with the pollution that resulted from the huge amount of sewage.

This is the terminus for the millions cubic meters of sewage carried through the drains and sewerage system of Shanghai. This is where the sewage gets cleaned up, first with filters then a series of treatments to make the water safe to return to the sea or rivers.

Zheng Zheng, the director of the Water Pollution Control Research Center at Fudan University, has studied Shanghai's water services and said that at one time the city's treated sewage was far below lowest standards for water purity.

"If we applied the national standard of surface water sources, it was even worse than the lowest level - level five," Zheng said.　

But general manager Zhou from the Chengtou Group said the standards for treated sewage and surface water were totally different.

Jiang Lingyan, the deputy manager of the Bailonggang Sewage Treatment Plant, said: "At one time sewage could only be treated crudely by filtering larger impurities. The leftover water contained large amounts of pollutants."

Jiang said in 2004 the plant began using chemicals to eliminate nitrogen and phosphorus, a major cause of eutrophication in the Yangtze River and East China Sea. In 2008 a new biological treatment was introduced for further purification.

The sewage treated at the plant is discharged as water into the Yangtze River through two underground outlets. "We found the water quality within 500 meters of the discharge outlets has not been affected at all," Zhou said.

He said that nowadays the treated water from the plant meets the national level two standard for discharged pollutants for municipal sewage treatment and this level is above the national standard.

For untreated sewage, one of the key measures is the Chemical Oxygen Demand (COD) concentration which is usually around 350 milligrams per liter (the higher the figure, the more polluted is the water or sewage). The national level for treated sewage is 100 milligrams per liter and Shanghai last year passed its goal and is discharging sewage where the COD is 40 milligrams per liter.

A smelly problem

After the sewage has been treated and the water purified and discharged, one of the biggest treatment problems remains: sludge. This is the smelly by-product which is packed with dangerous bacteria and pollutants often including heavy metals and chemicals. It is not just a problem for Shanghai but a problem for cities everywhere in the world.

Shanghai produces 3,000 tons of sludge each day and most of this to date has been buried in solid waste landfill in rural areas, said general manager Zhou Hua from the Chengtou Group.

But burying sludge can pollute the soil. "More importantly, considering the reality of Shanghai's limited land resources, it is unrealistic and unsustainable to do this in the future," Zhou said. "Most of the sludge we produce in the future will be burned.

"Some people worry that this could produce cancer-causing dioxins. But we can assure you that scientifically burning sludge is very safe. Many Western countries are doing this already," Zhou said.　

Now only one third of the city's sludge is burned after a drying process. The Shanghai Water Authority's Tang also said several Western countries were also burning sludge.

Another solution involves using technology to recycle sludge as a fertilizer for farms. Although only a little of Shanghai's sludge is being treated this way at present, insiders say more will be adapted for fertilizer use in the future.

Working together

Compared to many other cities, Shanghai has done a good job treating its sewage. But Zhou from the plant added: "However advanced our technology is, we still need to encourage people to save water and to use it reasonably."　

Some experts like He Pinjing, a professor of environmental science at the Department of Engineering at Tongji University suggested sewage and sludge should not just be the province of treatment plants.　

"It's not just a simple technical problem. It is also work that needs all of society involved. The successful disposal and recycling of sewage and sludge involves different fields of expertise including environmental protection, water treatment and agriculture. No one can do it all by themselves," He said.

"Nobody touches sludge willingly. It has to be treated properly. Shanghai has done well so far and if we cooperate, the goal of safely treating and recycling all our waste can be realized," He said.Water, water, everywhere, nor any drop to drinkThis Thursday, March 22, World Water Day will be celebrated to promote the sustainable management of freshwater resources. The first World Water Day was in 1993 after the United Nations General Assembly approved an initiative from the 1992 UN Conference on Environment and Development.

Over the past few years the project has served to raise awareness of water quality, trans-boundary waters and water scarcity among many other important issues, with the increasing impact of rapid urban population growth, industrialization, climate change and natural disasters. This year a series of special events are being launched worldwide with the theme "water and food security."

In Shanghai the city's water authority will invite more than 10,000 citizens to visit its sewage treatment works to gain a better understanding of how the city looks after its water and waste.　

Shanghai is surrounded by some 20,000 waterways alongside the vast Yangtze River. The city is not lacking water. However, Shanghai is one of the cities in China seriously lacking good quality water resources. Many of Shanghai's water resources have been polluted, failing to meet the lowest national standards for surface water resources, according to a study by the Shanghai Environmental Protection Bureau in 2000.

One of the major reasons was the large amount of sewage which went through little treatment before being pumped into the rivers.

To mark the day, UN's Food and Agriculture Organization is holding a conference in Rome where experts and leaders in their fields will discuss "Water and Food Security."

Later conference delegates will attend a special forum: "From field to fork - reduce food waste and change to sustainable diets to reduce your water footprints. In the US several events have been planned including several "walks for water."