Kenya Water Hyacinth

In partnership with Kenyan government authorities, the University of Nairobi, U.S.-based business interests, and local community representatives, Ecologists Without Borders has conceived of a plan to mitigate ecological, disease, and economic problems caused by the proliferation of water hyacinth, an invasive, perennial, free floating aquatic plant, in Lake Victoria.  Native to the Amazon Basin, water hyacinth was introduced as an ornamental plant in Lake Victoria the late 1980’s, and thereafter spread rapidly as the lake became increasing polluted.  Large, dense, floating mats of water hyacinth, some covering hundreds of hectares, have altered habitat along the lake’s shoreline (to the detriment of locally adapted fishes), disrupted navigation and fishing, and increased the incidence of malaria, schistosomiasis, and other water-borne diseases among people living around the lake.  The environmental, social and economic impacts caused by the spread of water hyacinth have been extremely deleterious, particularly in Winam Gulf, a relatively small ( xx ha) embayment in the northeast portion of Lake Victoria that receives large amounts of untreated sewage and agricultural runoff.

In April of 2017 an EcoWB representative met with government officials and university researchers in Nairobi and subsequently visited several Kenyan towns, cities, and rural communities that border Winam Gulf on Lake Victoria.  The information provided to us, the distressing signs of adverse environmental and socioeconomic effects, and the entreaties and assurances received from affected parties convinced us to take action.

We learned, among other things, that past attempts to control the spread of water hyancith using biological, chemical, and physical means were all unsuccessful. Clearly, the solution lies in reducing nutrient inputs to levels that will not sustain the plant.  Unfortunately, those levels will not be reached anytime soon, even with the imposition of more stringent pollution control measures.

While pollution abatement is the ultimate goal, the availability of a nearly inexhaustible supply of water hyacinth well into the foreseeable future provides an opportunity that, if pursued, would help reverse, at least at the local level, some of the weed’s more deleterious impacts.  Water hyacinth, as it turns out, is high in nutrients and caloric value; it therefore is valued as animal feedstock, compost, and a soil amendment.   We propose to harvest 0.7 ha ( ) of WH each day (140K mt of WH per year, equivalent to 0.7 ha d-1.  The harvested WH would be used to produce biogas in two anaerobic digesters, each capable of producing the equivalent of 1 MW in electricity.

(WH) (Eicchornia crassipes) is a perennial, free floating aquatic plant that is native to the Amazon basin in South America, but is now widespread in subtropical and tropical freshwater systems throughout the world, where it has caused considerable ecological and economic damage.  WH invaded Lake Victoria in Africa in the late 1980’s and has since spread rapidly as the lake has become increasingly polluted from urban and agricultural runoff.  The proliferation of WH has contributed to a dramatic reduction in the diversity and abundance of native species of flora and fauna in Lake Victoria, including numerous endemic species of fish that formerly supported thriving fisheries.  Despite millions of dollars spent to rid Lake Victoria of WH over the past three decades, attempts to eradicate the plant using assorted mechanical, chemical, and biological means have failed.

Homa-Bay County (formerly, Nyanza Province) is located in western Kenya along the northeast shoreline of Lake Victoria.  Its capital and largest town is Homa-Bay.  The county is bordered on the north by Winam Gulf, a 56 km long, 24 km wide, shallow bay connected to the main lake by a 5 km wide inlet.

A majority of residents of Homa-Bay County depend on fish and other resources from Winam Gulf for sustenance and their economic livelihoods.  Because the water in Winam Gulf is eutrophic and only slowly replenished through hydraulic mixing with Lake Victoria, WH has proliferated, with attendant impacts on local fish populations and fishermen.  Kateregga and Sterner (2008) reported that “the impact of the hyacinth on the catchability of fish was greatest in the Kenyan section of Lake Victoria.” Fishermen find it nearly impossible to fish in the dense mats of WH that grow in their traditional fishing areas (Figure 1).  In addition to interfering with fishing, dense growths of WH have also negatively affected navigation, water withdrawals, and other beneficial uses.

We propose to pay fishermen and their wives from Homa-Bay County to use their boats and nets to harvest (physically remove) WH from nearby Winam Gulf (Figure 2).  The floating aquatic plant is ubiquitous and grows very quickly.  In places where it has become well-established, an estimated 200 tons per hectare of fresh WH, on average, is available for harvest on a sustainable basis (Hasan and Chakrabarti 2009).  Our goal is to reduce the amount of WH present in Winam Gulf and to maintain it at levels that would allow the nearshore ecosystem and associated fisheries to recover to some semblance of their former state, while realizing additional benefits for local communities.

Figure 1.  Evidence of rapid growth of water hyacinth in Winam Gulf, Kenya, in 2005-2006.  (Source: NASA’s Earth Observatory website: Water Hyacinth Re-invades Lake Victoria: http://earthobservatory.nasa.gov/IOTD/view.php?id=7426).

The harvested plant material would be loaded onto barges, ideally using nets to corral the WH, which would then be winched aboard with a powered drum.  Once loaded, the barges would transport the WH to onshore storage and processing facilities in northern Homa-Bay County.  A portion of the WH can optionally be processed and used as livestock fodder[1].  As shown in Figure 3, however, the majority of the WH would be pre-treated with inoculant and digested anaerobically to produce biogas and sludge, following batch digestion methods described by Oosterkamp (2012). Several studies have shown that WH, either digested alone in combination with cow dung or other suitable organic material, produces biogas[2] that is comparable in quality to that generated from manure and other conventional feedstocks (Njogu et al. 2015; Patil et al. 2011; Sudhakar et al. 2013).

 

Figure 2.  Key steps in the proposed project.

In addition to biogas, the anaerobic digestion process produces a sludge that is rich in nutrients (nitrogen, potassium, and phosphorous) and can be used as a fertilizer with no detrimental effects on the environment.  The biogas and other byproducts of digestion will be sold at a steeply discounted price to residents of Homa-Bay County and willing buyers from other regions.  The operation would generate enough revenue to pay workers for their services; maintain and operate the barges, processing facilities, and related infrastructure; while providing incentives for fishermen and other stakeholders to ensure that fisheries and other beneficial uses of the restored Lake Victoria nearshore ecosystem are conserved and managed appropriately over the long-run.

In the first phase of the project, a small digestion facility would be constructed to demonstrate the technical feasibility; refine methods, costs, and revenue projections; and determine the appropriate size and number of processing facilities needed for the built-out project.   The pilot project would be capable of generating enough biogas to meet the needs (i.e., cooking fuel and methane gas sufficient to run a 25 kW generator) of a village of 600 inhabitants. Oosterkamp (2012) estimates that approximately 12,000 m³ of methane would be required to meet this goal.  Using the conventional 1:10 storage volume to methane production ratio, the required 1,200 m³ storage volume could be achieved by a single digestion chamber measuring 7 m high, 7 m wide, and 20 m long.

Figure 3.  Process for producing biogas and sludge (fertilizer) from water hyacinth.  The plant can also be processed into livestock fodder.  (Source: Njogu et al. 2015).

The production of biogas through the anaerobic digestion of WH offers an attractive alternative to fossil fuels for meeting local energy needs.  By making biogas and solar power available as the primary sources of energy used locally, the project will reduce energy costs and dependence on fossil fuel, with the additional benefit of helping to counteract the negative socioeconomic and environmental effects caused by global warming.

In addition to producing a potentially abundant supply of inexpensive biogas and fertilizer, the proposed project offers a means of restoring fish populations in the Winam Gulf and other nearshore areas in Lake Victoria.  As long as the water quality and habitat of the gulf are restored and proper conservation measures are put in place, local fishermen will be able to start fishing again, make a reasonable income, and fish sustainably for generations to come.  Ecologists Without Borders would assist in the development of a sustainable fisheries plan and the adoption of community-based resource management plans.

In summary, this proposal envisions a self-financing “payment for environmental services” scheme whereby revenue generated from the production of biogas and fertilizer from harvested water hyacinth would be used to compensate local residents (primarily fishermen and their families) for assisting in the restoration and conservation of the aquatic ecosystem in Winam Gulf, as well as provide new, long-term economic opportunities and a cascade of benefits for fishers, their families, and other members of the local community.  The WH removal and processing system will be both scalable and replicable, so that resources can be redirected in response to local circumstances.  Water hyacinth is not a renewable resource in the conventional sense; it is an invasive species that should be eradicated.  However, it is likely that, despite our best efforts, WH will never be completely eradicated due its high productivity, the presence of near optimal growing conditions, and its continual transport into Winam Gulf from other (untreated) areas of Lake Victoria.  For these reasons, it will be important to develop long-range conservation and economic exploitation strategies that ensure that costs are avoided and benefits are sustained indefinitely.

Literature Cited

Hasan, M.R., and R. Chakrabarti.  2009. Use of algae and aquatic macrophytes as feed in small-scale aquaculture: A review. FAO Fisheries and Aquaculture technical paper, 531. FAO, Rome, Italy

Kateregga, E., and T. Sterner.  2008.  Lake Victoria Fish Stocks and the Effects of Water Hyacinths on the Catchability of Fish.  Environment for Development Discussion Paper Series. EfD DP 08-05.

NASA Earth Observatory website: Water Hyacinth Re-invades Lake Victoria: http://earthobservatory.nasa.gov/IOTD/view.php?id=7426).  Accessed September 4, 2016.

Njogu, P., R. Kinyua, P. Muthoni, and Y. Nemoto.  2015.  Biogas Production Using Water Hyacinth (Eicchornia crassipes) for Electricity Generation in Kenya.  Energy and Power Engineering, 2015, 7, 209-216.

Oosterkamp, W.J.  2012.  Batch digestion of aquatic weeds in tropical countries.  Downloaded on September 1, 2016 from the website: http://www.oosterkamp.org/aquaticweeds.pdf.

Patil, J.H., M.L.A. Raj., S. Bhargav, and S.R. Sowmya.  2011.  Anaerobic co-digestion of water hyacinth with primary sludge.  Research Journal of Chemical Sciences.  Vol. 1(3).

Sudhakar, K., R. Ananthakrishnan, and A. Goyal.  2013.  Biogas Production from a Mixture of Water Hyacinth, Water Chestnut and Cow Dung. International Journal of Science, Engineering and Technology Research 2: 35-37.

Center for at the University of Nairobi, the Kenya Fisheries, and the Beach Management Unit

[1] Fresh or dried WH is usually chopped and fed directly to animals.  Ensiling enhances its palatability.

[2] Biogas consists of a combustible mix of methane and carbon dioxide that can be used to generate electricity and power internal combustion engines, or simply used as a direct heat source.

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