Heavy Metal Phytoextraction in Sewage Sludge using Sunflower
AbstractAgricultural application of sewage sludge is an effective disposal method as it is beneficial to agricultural productivity. However, there is a great need to regularly monitor the levels of heavy metals in sludge. Such monitoring is lacking in our sewage treatment plants. Thereby, leading to informal use of sewage sludge in agriculture and a lack of quality control. Furthermore, there is an absence of local technologies for heavy metal removal. Conventional processes for heavy metal removal such as chemical precipitation and membrane filtration are too expensive, require technologically advanced systems, are difficult to maintain, require a lot of expertise and are therefore not locally accessible. Heavy metals have adverse effects on human life when consumed. There is therefore a demanding need to come up with affordable, innovative technologies that can be locally used to remove heavy metals from sewage sludge used in agriculture. This study used phytoextraction, a process in which certain plants have the ability to absorb toxic contaminants from a soil matrix, to remove heavy metals from sewage sludge. The objectives entailed identifying and quantifying heavy metals present in sewage sludge samples before and after phytoextraction; identifying and quantifying heavy metals in the sunflower plant roots and shoots before and after phytoextraction and using the results to assess the efficiency of sunflower phytoextraction. The experimental set up was in three sets. The first containing soil and Kariobangi sewage sludge mix in the ratio 1:1. The second containing soil and Dandora sewage sludge mix in the ratio 1:1. The third set contained 100% soil and thus served as the control experiment. A ratio of 1:1 was used to closely emulate local farming practices. Sunflowers were grown in each of the sets and heavy metal levels were monitored for a period of four months using atomic absorption spectroscopy. After the four months, cadmium levels in the sewage sludge were reduced by 83.94%, manganese by 90.64%, copper by 85.27%, lead by 88.64% and zinc by 83.61%. The stated heavy metals were all brought down to levels acceptable for garden soil. Proving that sunflower phytoextraction is a technology that can be assimilated in sewage treatment plants to ensure safe use of sewage sludge in agriculture.
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