Production of Compost from Invasive Water Hyacinth
in Moragoda Canal, Galle-Sri Lanka

Executive Summary

Most of the wetlands in Sri Lanka have been affected by the water hyacinth (Eichhornia crassipes) which is an alien invasive aquatic weed species. Aquatic weeds have been extensively used to produce compost to address these problems encountered. However, accumulation of heavy metals can be occurred during the phytoremediation process. In this context, this study was carried out with the objectives to manage water hyacinth in Moragoda canal, Galle, while producing compost and to assess the heavy metals in the produced compost. The weeds were collected from the canal which is primarily serves for flood control. Heavy metal concentration was determined in separated parts of leaf, stem and roots before making compost. The separated parts were air dried and grounded into powdered form to make them for metal analysis. The other parts were composed by aerobic digestion. Water samples taken from 3 sites namely, Beligaha, Samagiwattha, Magalle, and plant parts and compost were analysed for Cu, Cd, Pb, Zn, Ni, Fe, and As by using inductively coupled plasma optical emission spectrometer (ICP). Finally, the obtained results were compared with the indices of the Sri Lanka Standards (SLS) to examine the harmful effects on human as well as the environment. The results showed that the average Cu content in leaf, stem, root samples and compost samples were 2.49±0.64 mg/kg, 2.56±0.74 mg/kg, 9.83±0.21 mg/kg and 9.75±0.02 mg/kg respectively. The Zn content in leaf, stem, root samples and compost samples were 13.89±0.61 mg/kg, 18.21±3.49 mg/kg, 10.22±1.07 mg/kg and 21.65±0.19 mg/kg. The As content in leaf, stem, root samples and compost samples were 0.148±0.02 mg/kg, 0.088±0.002 mg/kg, 0.702±0.21 mg/kg and 0.53±0.07 mg/kg respectively. In this study, Fe was observed to be the highest occurring metal in water hyacinth. However, according to the results it revealed that the heavy metals of the produced compost except Fe, did not exceed the permissible limits of SLS standards for compost. Although the canal was polluted by anthropogenic activities, heavy metal parameters detected in canal water was not exceeded the permissible limits. Results indicated that the produced compost using water hyacinth in Moragoda canal was within the standard levels of heavy metals.

Introduction and research problem/issue

Water hyacinth (Eichhornia crassipes) is an invasive aquatic weed which created global menace by making environmental and economic problems. It shows prolific growth on the surface of water bodies and act as a hyper-accumulator of heavy metals (Matindi, 2016). In Sri Lanka this weed has been invasively distributed in almost all wetlands. It causes complete blockage of canals making all activities very difficult (Bhattacharya and Kumar, 2010).Thus, these reasons have prompted to undertake various measures to control this weed. As the growth of the weeds is very robust it finds very hard to eradicate them. For instance, during drought periods, the plant sinks into the bottom of the water and remains dormant and thrives in the next season (Ndimele, 2011). It has been utilized by many countries to make livestock feed, compost, etc. However, producing compost is increasingly being opted as a sustainable solution towards eradication of the weed (Matindi, 2016). Moragoda canal is situated eastern direction of Greater Galle city in Galle district. It starts from Maagalle and ends in Hiriburegama area. Its coordinates are 6°1' 60" N and 80°13' 60". The total length of the canal is about 6 km which acts mainly for flood mitigation. However, as a result of uncontrolled landfill, and lack of maintenance of the canal the existing canal is insufficient for conveying the flood water even during low rainfall which eventually leads to flash flooding. Further, the canal flows through highly populated and urbanized areas, it gets polluted by effluents and none decaying pollutants like, plastic bags, cans, bottles. Thus it causes blockage of free flow of water and limit the conveyance capacity. The growth of water hyacinth has posed a health risk to the people in the vicinity of the canal because the mats are habitats for mosquitoes and snails which spread diseases. The eradication of water hyacinth is very expensive and would be in short term. The biological control method is used in South America by the weevil Neochetinaei chhorniae. The chemical control method is cheaper than the other methods. However, each of these have negative impact. Compared to other methods, compost production by this weed has positive impacts as they will all high N and P nutrients to the cultivation. However, due to the phytoremediation effect of these plants, water contaminated with heavy metals will accumulated in these weeds. Water hyacinth is among one of the most frequently utilized plant in marshlands for heavy metal elimination as it has a prolific growth rate as well as high absorption capacity of contaminants and nutrients (Rai, 2009). A research conducted by Shao and Chang (2004), indicated that water hyacinth is capable of absorbing, heavy metals like Pb, Cd, Ni, Zn, and Cu. Therefore, before using water hyacinth for producing compost, it is vital to analyze the heavy metal content in produced compost. If the metal content is too high in the plant material, it will be challenging to utilize water hyacinth as biomass. This is because the metals remain in the compost could pose a serious environmental hazard during the disposal of the organic fertilizer. Further assessment of heavy metals in produced compost is important before using as a fertilizer. Therefore, the objectives of this study were to manage water hyacinth in Moragoda canal, while producing compost and to assess the heavy metals in the produced compost.

Materials and Methods

Water hyacinth was harvested manually from Moragoda canal (Figure 1) and transported to the compost production facility at the Faculty of Agriculture, University of Ruhuna. Moragoda canal is situated eastern direction of Greater Galle city in Galle district. It starts from Magalle and ends in Hiriburegama area. meets sea between Southern Naval Base and Galle Harbour. Its coordinates are 6°1' 60" N and 80°13' 60". The total length of the canal is about 6 km which acts mainly for flood mitigation.

Part of the weeds was separated and air dried. Those samples were divided in to leaf, stem, and roots. Then it was crushed and powdered for analysis (Figure 2). The fresh water hyacinth was then chopped into small pieces of about 5-10 cm in length to increase the surface area for microbial action. These were then aerobically digested using heap method. The decomposition process was monitored around 12 weeks (Figure 3).

After complete digestion compost samples were collected and sieved by 2 mm sieve for heavy metal analysis. The samples were digested by conc. HNO3 and conc. HCl with 3:1 ratio and kept in a water bath while stirring and kept overnight. Then filtered by Whatmann No. 42 filter paper and the substrate was taken and analyzed the heavy metals using inductively coupled plasma optical emission spectrometer (ICP-OE) in the Faculty of Agriculture, University of Rajarata. The same procedure was followed for the dried leaf, stem and root sample to analyze heavy metals (Figure 4).

Since water hyacinth derives its nutrients from water, it will also be essential to analyze metal content in water from the canal. Analysis of heavy metals in water provided data on the metal concentration levels and helped to get a general view of the pollution levels of the canal. The water samples from Beligaha, Samagiwattha, and Magalle were collected from the Moragoda canal.

Results and findings

The obtained results of the compost heavy metal parameters were compared with the indices of the Sri Lanka Standards (SLS) to examine the harmful effects on human as well as the environment. The results of the plant samples, water samples and the compost are shown in Figure 5.

The results showed that the average Cu, Cd, Pb, Zn, Ni, As content in plant samples, compost samples and water samples are below the permissible levels. Some metals such as As and Cu were high in roots of water hyacinth. In this study, Fe was observed to be the highest occurring metal in water hyacinth. Iron was highly accumulated in the roots of the plants in comparison to other plant parts. As the canal was polluted by anthropogenic activities, detected heavy metal parameters such as Fe, in canal water was very high. Results indicated good quality compost free of heavy metals could be produced by water hyacinth in Moragoda canal.

Conclusions, implications and significance

According to the results of the present study, the concentrations of heavy metals are lower than the recommended standards. Further, the results indicated that compost free from heavy metals could be produced by water hyacinth (Eichhornia crassipes) collected from Moragoda canal Galle. Although the compost production technique is a promising one to eradicate water hyacinth, routine analysis should be done in produced compost to ensure that the compost mixture is free from heavy metals and are within the standard level.

References

1.Matindi C, N, (2016) analysis of heavy metal content in water hyacinth (eichhornia crassipes) from lake victoria and Assessment of its potential as a feedstock for biogas Production, Thesis submitted to University of Nairobi, Institute of Nuclear Science and Technology, p123

2.Ndimele, P. E., Kumolu- Johnson, C. and Anetekhai A. (2011). The invasive aquatic macrophyte water hyacinth {Eichhornia crassipes (Mart.) Solm- Laubach: Pontediriceae}: Problems and prospects. Research Journal of Environmental Sciences, 5, 509 – 520.doi: 103293/rjes.2011.509.520

3. Rai, P.K., (2009). Heavy metal phytoremediation from aquatic ecosystems with special reference to macrophytes. Critical Reviews in Environmental Science and Technology, 39 (9), 697–753.

4. Shao W.L., Chang, W. L. (2004). Heavy metal phytoremediation by water hyacinth at constructed wetlands in Taiwan. Journal of Aquatic Plant Management,42, 60 - 68.