Confined Growth of Water Hyacinth for Bio-remediation in Caohai, Dianchi Lake , China: The Effects on Water Quality The topic of my presentation today Dr. Zhiyong Zhang Institute of Agricultural Resources and Environment Jiangsu Academy of Agricultural Sciences

1. Introduction of Caohai, Dianchi Lake Dongfengba Neicaohai Waicaohai Laogan yutang Waihai N 1 km Ship lock Caohai: Inner lake of Dianchi, a total area about 10.5 km2, consists of Neicaohai (area ~1.8 km2), Dongfengba (area ~2.4 km2), Waicaohai (area ~5.8 km2) and Laoganyutang (area ~0.5 km2), Average water depth: 2.5 m; gross storage capacity: 25 million m3 water. 6 rivers are connected to Caohai, receiving the wastewater discharged from wastewater treatment plants. Xi Yuan is the only water outlet. In the Years of 2007 to 2009, the concentrations of TN and TP were 12-20 and 1.2-1.6 mg/L, respectively.

2. Ecological Engineering of large-scale growth of water hyacinth in Lake The principle for eutrophication control using water hyacinth in Dianchi lake can be summarized in three words: Confined Growth―Mechanical Harvest―Safe Utilization Confined Growth: in the area with high concentrations of pollutants, water hyacinth was cultivated in the man-made enclosures. Mechanical Harvest: the macrophytes will be harvested using a specially designed vessel after a certain period of growth; Safe Utilization: the harvested biomass of the macrophytes was processed to produce biogas and organic fertilizer.

Fig. 2 Confined Growth of water hyacinth at Caohai, Dianchi Lake（13 Aug. 2011） The coverage of water hyacinth in the lake was about 0.3 km2 (~9 kilotons) in May, and the coverage had reached ~5.3 km2 (~211 kilotons) in the November , 2011.

3. The Sampling Sites Totally, there are 11 sampling sites. 6 sites at river inlets: 6 rivers that receive wastewater discharge（R1~R6） 5 sites in the Caohai lake: designed along the flow of wastewater from river inlets to Neicaohai (C5, C4)-Waicaohai (C3, C2)-Xiyuan outlet (C1). C5 is located at the central of Neicaohai；C4 (at Duanqiao, Neicaohai) is the location monitored by China National Environmental Monitoring Centre； C3 is located at Waicaohai which is close to Neicaohai；C2 is located the central of Caohai and is also the location monitored by China National Environmental Monitoring Centre；C1 (Xiyuan channel) is the water outlet channel of caohai。

4. Sample and Data Collection Water sample collection: May, 2011-April, 2012. Water sample collection frequency: 1-3 times per month. The coverage of water hyacinth was monitored using GPS. The biomass of water hyacinth was weighted in 1m2 quadrat. water and plant samples were collected for analyzing TN and TP contents.

5 Results and Discussion

Temporal Changes of DO, TN and TP in Caohai

5.1 Changes of DO in Caohai over the past 5 years Waters at rivers inlets: 1.8±0.8 mg L-1 in 2007 and gradually increased to 4.5±1.6 mg L-1 in 2011. Neicaohai: ranged from 4.1±2.9 to 5.2±1.7 mg L-1. Waicaohai: changed significantly from 5.5±1.9 to 7.9±1.9 mg L-1. especially in 2011 with growth of water hyacinth, it increased significantly over 33.3% compared to that in 2010. River estuary: 1.8±0.8 mg L-1 in 2007 and gradually increased to 4.5±1.6 mg L-1 in 2011. This may be the result of river improvement works.

5.2 Changes of TN concentration in Caohai over the past 5 years Year 2007~2009: TN concn. was 18.3 and 13.0 mg/L in Neicaohai and Waicaohai, respectively. Year 2010: TN concn. (13.3 and 9.0mg/L) in Neicaohai and Waicaohai were decreased by 27.3% and 30.8%, respectively. This may be due to the natural growth of water hyacinth to the scale of ~2 km2； Year 2011: TN concn. at Neicaohai (9.86±1.32 mg L-1) and at Waicaohai (4.13±1.49 mg L-1) were further significantly lower (p < 0.01) than those in the year of 2010。This may be a result of more large-scale confined growth of water hyacinth.

5.3 Changes of TP concentration in Caohai over the past 5 years Year 2007~2009: TP Concn. kept a steady trend of decreasing at river inlets. This may be due to the control of point source pollution. Year 2010: TP Concn. In Neicaohai and Waicaohai decreased by 58.6% and 58.3%, respectively, when compared with 2009. Year 2011: TP Concn. In Neicaohai and Waicaohai further decreased by 60.3% and 55.2% respectively, when compared with 2010. The extents to which TP was decreased in Neicaohai and Waicaohai were higher than that at river inlets (37% in 2010, 28.8% in 2011). This may be a result of natural growth and confined growth of water hyacinth.

Spatial Distribution of TN and TP in Caohai

5.4 Effect of water hyacinth on spatial distribution of TN Before the confined growth of water hyacinth in 2011: The concentration of the TN had a 39% reduction (p < 0.05) from river inlets (12.3 mg L-1) to Xi Yuan outlet (7.5 mg L-1). After the confined growth of water hyacinth: it had a further reduction of 76.1% (p < 0.05) from river inlets (13.8 mg L-1) to the Xi Yuan outlet (3.3±0.90 mg L-1).

5.5 Effect of water hyacinth on spatial distribution of TP After the confined growth of water hyacinth: TP concentrations had a further reduction of 97.3% (p < 0.05) from river inlets (0.6 mg L-1) to the Xi Yuan outlet (0.16 mg L-1).

Year-round Changes of TN and TP in Caohai

5.6 2011-2012 year-round changes of TN concentration in Caohai since growth of water hyacinth TN concentration at the 6 river inlets: 11.7~14.3 mg/L (May, 2011-May, 2012) During fast growth period of water hyacinth (from May to Aug., 2011): TN concentrations in Neicaohai and Waicaohai were decreased rapidly. Waicaohai: TN concentration decreased rapidly from 7.7 mg/L in May to 2.6 mg/L in Aug, 2011. After Sep.: the growth of water hyacinth slow down, but TN concentrations in Neicaohai and Waicaohai remained stable with little fluctuation.

5.7 2011-2012 year-round changes of TP concentration in Caohai since growth of water hyacinth TP concentrations at 6 river inlets: about ~0.4 mg/L each month, with exception of 1.5 mg/L in July， Neicaohai and Waicaohai: TP concentrations were significantly lower than that at river inlets, and also decreased rapidly during fast growth period of water hyacinth. Example: TP Concentration in Waicaohai decreased sharply from 0.94 mg/L in Apr. to 0.22 mg/L in Jun., which was decreased by 76.6%，Lowest concentration was 0.12 mg/L in Oct.

To what extent water hyacith assimilation can contribute to N and P removal from Caohai?

5.8 Estimation of contribution of water hyacinth assimilation on N and P removal in Caohai The total amount of N and P removal can be calculated: (total amount of N or P in effluence waters-total amount of N or P in drainage water)+(initial amount of N or P storage in the lake-final amount of N or P storage in the lake) As it is hard to directly get the data of water inflow from rivers at their inlets, the water inflow from rivers is derived from the “water effluence at Xiyuan outlet+ amount of evaporation in Caohai-average amount of rainfall in Caohai”. Total amount of N or P in effluence waters=average concentration of N or P in effluence waters × water inflow from rivers at inlets。

5.8 Estimation of contribution of water hyacinth assimilation on N and P removal in Caohai Amount of N or P in drainage water at Xiyuan=water effluence at Xiyuan outlet×N or P concentration in the effluence Amount of N or P in water hyacinth biomass=N or P concentration in water hyacinth tissues at Nov. when harvesting × total biomass of water haycinth at Nov. The biomass of water hyacinth reached 211 kilotons in Nov., 2011., water content was 94.4%，N content was 4.11% on dry weight basis，P content was 0.29% on dry weight basis. Amount of N or P storage in the lake=N or P concentration in water each moth × water volume of Caohai

Table 1 Contribution of water hyacinth assimilation on nitrogen removal in Caohai from May, 2011 to April, 2012

5.9 Estimation of contribution of water hyacinth assimilation on N removal in Caohai According to the calculation based on 2011-2012 year-round data: the total amount of TN removal and the TN assimilation by water hyacith were 990.6 and 485.6 tons, respectively. The N assimilated by water hyacinth counted for 49% of TN removal. According to the mass balance calculation: there was 51% of TN may be removed via denitrification. The results indicated that there were two major pathways through which N was removed from water in Caohai: water hyacinth assimilation and denitrification

5.10 Estimation of contribution of water hyacinth assimilation on P removal in Caohai Table 2．Contribution of water hyacinth assimilation on phosphorus removal in Caohai from May to November in 2011 Removed P in water hyacinth biomass counted for 139% of total phosphorus removal. The result indicated that water hyacinth assimilation may take away a portion of P released from sediment.

Table 3 Nitrogen assimilated and removal by E Table 3 Nitrogen assimilated and removal by E. crassipes in Caohai from May to November in 2011 Table 4 P assimilated and removal by E. crassipes in Caohai from May to November in 2011 Nitrogen removed by water haycinth assimilation and harvest was about 485.6 tones, and we did the rough calculation that nitrogen removed by waterhaycinth accounted for bout 64% of total nitrogen removal.

6. Conclusion Large-scale confined growth of water hyacinth could significantly improve the water quality in the lake with continuous influent of external pollutants. TN concentrations in the water body of Caohai was significantly (p<0.05) decreased by confined growth of water hyacinth. According to the calculation based on 2011-2012 year-round data, the results indicated that there were two major pathways through which N was removed from water in Caohai: water hyacinth assimilation and denitrification Removed P in water hyacinth biomass counted for 139% of total phosphorus removal in Caohai. The result indicated that water hyacinth assimilation not only took away P in water but also a portion of P released from sediment.

Mechanical Harvest

Organic Fertilizer Production

Biogas production and application of digested water hyacinth slurry on farmland

Utilization of water hyacinth： silage to feed sheep and goose

Thank you for your attention！