Dianchi Lake in the Province of Yunnan covers an area of 320 km2 and is thus one of the largest lakes in China. The lake is divided in two parts by a dam into the northern Inner Lake and the larger southern Outer Lake. The mean water depth is 4.5 metres. Regarding topography, Dianchi Lake is located at latitude 24° north (eastern Himalayan rift valley) on a highland with an elevation of approx. 1,990 meters above sea level. Its catchment covers 2,920 sqkm with a population of 2.2 million, of which 1.8 million live in the capital Kunming. All the rivers, canals, industrial and agricultural effluents are finally discharged into the lake. Intensive land cultivation on the western and southern shores of the lake with two to three harvest cycles contributes particularly to its pollution.
Consequently, eutrophication is the major environmental problem and the water quality is constantly deteriorating. Since drinking water is extracted from the lake, this situation directly affects the population – on the one hand the local economic development is impaired and on the other the quality of life is lessened.
Already in 1988 did the water of the lake show a green-yellowish colour and visibility was less than 1 m deep in the Outer Lake and in the Inner Lake even 0.5 m. The trophication parameters in the northern part of the Outer Lake were in the eutrophic, in the Inner Lake in the hypertrophic range. Between 1988 and 1999 the water quality deteriorated to such an extent that the entire Outer Lake is in a hypertrophic state today. The determining parameters are total phosphorus (TP) at 4,000 mg/ml, nitrogen at 2,500 mg/ml and chlorophyll-a at 120 mg/ml; visibility is now 0.4 m. As to the Inner Lake the parameters are even worse; the highest chlorophyll-a concentration measured amounted to 250 mg/ml.
The Provincial and Central Governments are meanwhile well aware of the problem and have already invested billions of Yuans in canals and sewage treatment plants. The World Bank presently supports water management measures amounting to EUR 330 million. More investments are to follow in the future.
A fact-finding mission, undertaken in co-operation with our Chinese representative, brought Austria into the "game", which finally led to a co-operation agreement signed in October 1999 between the local Kunming Institute of Environmental Science and Monitoring and "my" company, the UTL Ltd. Subsequently, an Austrian expert group for lake clean-ups was formed, whose activities were financed by the Study Fund of the OeKB by order of the Federal Ministry of Finances and which prepared the study, which is now available.
Profound monitoring initiated
The enormous amount of 254 million cubic metres of wastewater is discharged into Dianchi Lake every year; 1/3 of this amount into the Inner Lake and 2/3 into the Outer Lake. Our evaluation (for the balance) of the monitoring programme carried out by the Kunming Institute showed the following detailed results: the total amount of COD discharge in 2000 amounted to 52,000 tons, of which 55 percent were faecal effluents, 36 percent industrial effluents, and 9 percent came from diffuse sources. When balancing the inflow and the outflow, it showed that, depending on precipitation conditions, 75 to 90 percent of the COD load remain in the lake.
In addition, the total amount of about 10,000 tons of nitrogen and about 1,000 tons of phosphorus were discharged last year. The discharge of suspended matter depends on precipitation and fluctuates between 140,000 tons and 440,000 tons annually, of which up to 90 percent remain in the Lake. Taking samples from and analysing the bottom sludge at a total of 11 sampling sites is also part of the monitoring programme, since sludge is one of the main sources of releasing processes, or rather of recontamination with nitrogen or phosphorus. In addition, sludge is enriched with heavy metals. The sludge layer in Dianchi Lake is up to 1 m thick.
Drinking water & wastewater situation
There are eight waterworks in Kunming. Drinking water consumption amounts to a total of 230 million m3 per year. Waterworks No. 3 is located in the western part of the city in the immediate vicinity of the Inner Lake and had to be closed down due to excessive water pollution.
The region is supplied primarily from precipitation in summer, which is stored in reservoirs along the rivers north and west of Dianchi Lake. The Songhuaba Reservoir stores the biggest amount of water with 120 million cubic metres annually. Up to 1998, 91 million cubic metres were taken from the Outer Lake. Due to the deterioration of the lake water quality, more water has been taken since from the Dahe and Chaihe River Water Reservoir south of Dianchi Lake and treated in Waterworks No. 5. This plant lies in the south of the city of Kunming near the Mingtonghe River and has a capacity of 300,000 cubic metres per day.
In Kunming, there are four wastewater treatment plants. The oldest among them, the Sewage Treatment Works No. 1, went into operation in 1992 with a capacity of 55,000 cubic metres per day. The biological purification plant works according to the circular activated sludge method with phosphorus reduction. The Sewage Treatment Works No. 2 started operation in 1996 and is designed for a capacity of 100,000 cubic metres per day or 560,000 PE. The Sewage Treatment Works No. 3 and 4 work with intermittent ventilation processes to reduce nitrogen. Their capacity amounts to 150,000 cubic metres per day or 60,000 cubic metres per day, respectively. The Sewage Treatment Works No. 1 is presently being enlarged by a new plant section (capacity 40,000 per day); the existing parts are being qualitatively upgraded.
No. 5 is presently under construction (capacity 75,000 cubic metres per day), and No. 6 is in the planning phase (capacity 50,000 cubic metres per day). The total capacity of the five treatment plants will thus amount to 480,000 cubic metres per day – corresponding to 2.7 million PE – as of the year 2002. All the treatment plants will work according to the activated sludge method and will be equipped with nitrogen and phosphorus reduction facilities. The older treatment plants only achieve a BOD5 reduction of 75 to 85 percent; the new ones will reach reduction rates of 95 to 97 percent.
Emission and immission targets
According to the Austrian expert team the immission targets set by the Chinese are aimed too high. In addition, the division into an Inner Lake with high limit values and an Outer Lake with lower limit values is not functional from the current ecological and hydrological point of view. There should be only one water body and uniform standards.
The immission values suggested should also consider the geogenic condition and have to be adjusted to it. As soon as the immission values worked out by our experts are implemented, the Lake will have a mesotrophic/eutrophic status. To achieve a Chl-a concentration of 30 mg/m3 the TP immission would have to be reduced to 300 to 700 mg/m3. This corresponds to a TP discharge into the Lake of 110 to 290 t/year. To achieve these immission targets every discharge into the Lake or its feeders has to comply with the emission targets. In this respect the Austrian wastewater emission guidelines for direct and indirect dischargers will be suggested.
The catalogue of measures to achieve these targets comprises administrative and legal improvements, as well as ecological and technical measures. A period of 15 to 20 year is assumed for their implementation and – as a consequence – for the noticeable improvement of the water quality of Dianchi Lake.
(Source: aqua press 4-5/2001)
Dipl. Ing. Dr. Willibald Lutz
Information & Contact:
The study "Bewertung der derzeitigen Situation der Sanierungsmaßnahmen sowie Erstellung von Vorschlägen zur Verbesserung des Dian Chi Sees in der Provinz Yunnan, VR China" (233 pages, English, EUR 189,-) is available from
Österreichische Kontrollbank AG,
Tel. +43 1 53 127-824
Fax +43 1 53 127-411
UTL-Umwelttechnik Leopoldau Planungs- und Vertriebs-Ges.m.b.H.
Dipl. Ing. Dr. Willibald Lutz
Leopoldauer Platz 5
A-1210 Vienna
Tel. +43 1 25 71 939
Fax +43 1 25 71 939-29
