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Polluted lake needs biological treatment

Update: November, 11/2013 - 11:40
Every summer, the masses of fish dying in Da Nang's polluted lakes leave a foul smell lingering in the air.

Da Nang's rapid urbanisation and industrialisation in the past 10 years might benefit some, but the central city's lakes tell another story. Biologists at Da Nang University of Technology found that nearly all the lakes contained toxic metals and other dangerous substances, the result of industrial wastewater and poor drainage systems.

Along with researchers from the University of Technology and Environment Research and Protection Centre, they have been working on a treatment process, Viet Nam News reports.

Tran Van Quang, deputy head of the environment faculty from Da Nang University of Technology

Tran Van Quang

The city has seen rapid urbanisation and industrialisation over the past decade. However, such development also results in environmental pollution. A vast amount of land was turned into urban and industrial parks. Pollutants from industrial parks, untreated drainage and wastewater in the city and industrial centres have polluted the water surface and water sources.

Hazardous heavy metals such as mercury, lead and copper were found in almost all 10 major lakes in the city. The worst polluted is September 23 Lake, situated in the city's largest park.

We found excessive heavy metals in lake sludge, which cause eurotrophication and kill fish.

Wastewater from the city's drainage system carries contaminants to the 11ha lake, which accumulate in sludge to contaminate the lake for a long time.

The Chemical Oxygen Demand (COD) content was 3.3-3.8 times the standard; methane content ranged from 3.26 to 5.58. There was also high Oxygen Demand (BOD).

Sulphur, mercury, lead, copper and hazardous metals in lakes are dangerous for people living in the area. Local people often fish in the lake despite warnings.

We proposed the city administration improve the quality of water with biological treatments, which can reduce pollution by 60 to 70 per cent.

We are examining pollution and classifying contaminants to find a suitable biological treatment. We try to grow plants that can treat the pollution while also improving the scenery.

Canna India bail, a plant grown at September 23 Lake as a pilot project, absorbs pollutants from sludge and blossoms colorfully.

Nguyen Thi Thanh Xuan, petro-chemical engineer from Da Nang University of Technology

Nguyen Thi Thanh Xuan

Organic substance pollution in lakes produces hydrogen sulfide, which is very hazardous to residents.

Inhaling too much hydrogen sulfide can lead to chronic respiratory inflammation. Heavy metal pollution affects lake plants, meaning residents can get seriously ill from eating fish or vegetables from the lake.

If we don't get water and air pollution in industrial centres under control, we could see a rise in diseases such as cancer.

However, creating a proper sewage treatment system requires prolonged investment and appropriate technology to deal with pollutants.

Punishments for environmental violators should be strengthened, while pollution needs to be constantly monitored in industrial centres.

Biological solutions for dealing with pollution are a sustainable way for Da Nang to develop as a green city. We have been involved in research on producing bio-fuels from green micro-algae (chlorella vulgaris).

We found that green algae grows well on the wastewater from seafood processing plants in the worst polluted areas in Son Tra District.

Not only does green algae help produce bio-fuels and limit water and air pollution, it also helps reduce carbon emissions and absorbs heavy metals in lake sludge.

However, we still need to find sponsors to produce bio-fuels from green algae in Da Nang.

Nguyen Dieu, director of the city's Environment and Natural Resources department

The city has invested VND15 billion (over US$700,000) in wastewater treatment, but that's still a modest amount.

We have built high-capacity centralised wastewater plants at seafood processing and industrial parks in the city.

We punished companies heavily for illegally draining off untreated wastewater at industrial parks. Bac Dau paid the biggest fine, VND300 million (US$14,000), for using an illegal drainage system.

Most businesses intentionally discharge untreated wastewater directly into the environment so they don't have to pay to treat it.

Da Nang has benefited from projects funded by the World Bank in past years.

The city has completed a US$218.4 million priority infrastructure project, 70 percent of which was funded by the World Bank. The project helped upgrade urban infrastructure, resettlement areas, the environment, wastewater treatment, bridges and roads as well as personnel training and management between 2008-13.

The city will benefit from a US$272.1 million project, of which $202.4 million will be provided by the World Bank, to improve public transport, build new roads and revamp the drainage system.

Last year, the city's sewage water treatment and Drainage Company in collaboration with Matewater company from Japan introduced a low cost sewage treatment system.

The system is a suitable choice for dealing with pollution and creating sustainable development.

Phan Minh Ke, resident of Thac Gian ward, near Thac Gian Lake

Pham Minh Ke

We have been living here for generations, but the pollution became serious seven years ago.

Sewage water from households, rubbish, dust and sand all run into the lake. The pollutants gradually accumulate in sludge and cause a stinky smell day and night. Most households around the lake have to close their doors. It's stuffy in summer. Although workers from an urban environment company have done dredging, the lake still pollutes air in the area.

We are expecting a complete solution for the worst pollution so we can live as well as we did in the past. The lake should be a gathering point for people after the working day, with beautiful scenery and a pleasant atmosphere. — VNS

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