Samenvatting

Nutrient enrichment, scientifically known as eutrophication, is a worldwide problem. Eutrophication is one of the main drivers for cyanobacteria blooms. Cyanobacteria blooms can have a negative effect on ecology, economy and human health, as a result of to the ability of some species to release toxins. Due to the absence of water treatment plants in developing countries, cyanobacteria blooms causes increasing problems as the surface water is often the only source for drinking water. Lacking financial resources keeps this situation critical, which is why an instant cheap and effective solution is needed.
Geo-engineering is the manipulation of biogeochemical processes (mainly targeting phosphorus) using different materials such as metals or clay. A flocculant is combined with a ballast product to sink the flocks. Ballast products can be P-sorbents or natural materials such as soil or clay. Flocculants can be e.g. polyaluminiumchloride or natural materials, such as chitosan and recently Moringa oleifera has been used. In this study the flocculation performance of the natural flocculant Moringa oleifera seeds was investigated.
In the general experiment design crushed Moringa seeds extracted with different solvents were added to cyanobacteria cultures in different concentrations and after 1 hour chlorophyll-a, PSII and pH were measured.
During a series of experiments the effects were studied of different Moringa extraction methods, initial chlorophyll-a concentrations, inorganic turbidity, pH, addition of ballast, seed variability and different cyanobacteria species on the flocculation performance of Moringa oleifera seeds. Furthermore, it was explored how Moringa oleifera seeds influence the pH of the water and the nutrient release by Moringa. Additionally, the flocculation time of Moringa oleifera extract was measured and the optimum Moringa seed concentration was found for a cyanobacteria solution with an initial chlorophyll-a concentration of 200µg/L.
Filtered Moringa extract showed a better flocculation performance than unfiltered MO extract. Furthermore, the reliability of 1M NaCl MO extract was higher than that of MO water extract. The pH affect the flock size, but had no effect on the removal efficiency. The optimum MO concentration depended on the initial chl-a concentration, but for removing 200µg/L cyanobacteria the optimum concentration was 80mg/L. Moringa did not influence the pH. Moringa seemed to be unable to flock inorganic turbidity. A high removal efficiency does not automatically mean that Moringa is a good flocculant, because at some species Moringa influences the PSII and toxins can be released. In that case, it is recommended not to use Moringa. The flocculation performance and removal efficiency can be influenced by both the flocculant and the ballast. Moringa releases nutrients to the water and might contribute even more to eutrophication if added in the system. Seed variability might cause variation in flocculation performance, since it was observed that in repeated experiment with similar treatments sometimes flocculation occurred and sometimes not.
It can be concluded that at this point Moringa seeds are not yet a reliable flocculant, but there is potency in this natural flocculant. Undoubtedly, more research is needed to better understand the flocculation process of Moringa oleifera seeds.