Assessment of selected agrochemicals in wastewater from horticultural farms in Arusha and their removal by constructed wetlands
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Date
2014
Authors
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Publisher
The Nelson Mandela African Institution of Science and Technology
Abstract
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.
Description
Keywords
Agrochemicals, Horticultural farms, Macrophyte plant types, Fertilizers imports, Fertilizers use, Arusha