Assessment of selected agrochemicals in wastewater from horticultural farms in Arusha and their removal by constructed wetlands

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The Nelson Mandela African Institution of Science and Technology


Commercial horticulture has been growing rapidly and has a significant contribution to food security and economic growth in Tanzania. The growth of horticulture industry has been associated with an increase in consumption of agrochemicals on farms. 1 lowever. wastewaters containing agrochemicals are usually discharged from horticulture farms into the environment without proper treatment. Apparently, the effects of these agrochemicals on the environment are very complex, and therefore, their undesirable transformations can contaminate water, soil, sediments and biota and consequently cause adverse effects on human health and the environment. This study was aimed at investigating the levels of agrochemicals in wastewater discharged from selected horticultural farms in Arusha and their removal by constructed wetlands. The study reviewed literature on the use of agrochemicals in Tanzania and analysed wastewater discharged from horticulture farms for nutrients and pesticide levels. The literature review on agrochemical use showed that inorganic fertilizers, insecticides, fungicides and herbicides arc mostly used in horticultural fields. The analysis of wastewater from live horticulture farms detected NOj'. PO/\ BOD5 and permethrin in the wastewater discharged into the environment at concentration levels above the Tanzanian allowable limits for discharge. The mean concentration levels ranged from (4.5 - 64) ppm for NO.f, (3 - 48) ppm for POq3’. (57-119) ppm for BOD5 and (0.4 - 0.8) ppm for permethrin insecticide. This study investigated the influence of macrophyte type towards removal of Cu, Fe, Mn. Zn. Endosulfan, L-Cyhalothrin and Permethrin by using bucket experiments and influence of flow rate towards removal of Cu. Zn and Mn in horizontal subsurface flow constructed wetlands (HSSFCWs). The results from the bucket experiments showed a significant positive effect of macrophytes on the removal of Cu, Fe, Mn and Zn. In the HSSFCWs experiments, the removal of heavy metals was as high as 95 % on the average and was found to be independent of flow rate and the difference was statistically insignificant (P>0.05). It w'as observed that regardless of the mechanisms involved in the removal of heavy metals in the HSSFCWs, the overall removal is not limited to transport processes within the wetlands. The conclusion drawn from this research is that agrochemicals are a problem in the environment and constructed wetlands can be used as treatment options for wastewater before it is discharged into the environment.



Agrochemicals, Horticultural farms, Macrophyte plant types, Fertilizers imports, Fertilizers use, Arusha