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Water is becoming a scarce resource in terms of quantity and quality. Water supply enhancement measures are being taken with less attention given to wastewater management, leading to increased discharge of untreated wastewaters. Wastewater is emerging as an affordable and reliable alternative water supply for urban agriculture, supporting thousands of farmers. Extensive use of untreated wastewater for irrigation will without a doubt lead to accumulation of heavy metals in soils and crops, resulting in overwhelming risks to both public health and the environment. This paper deals with determination of the strength and compositions of the wastewater from a public university in the tropical semiarid region for rainy and dry seasons, based on a number of key parameters including heavy metals. Furthermore, it identified the real advantages of treated water use and issues pertaining to untreated wastewaters use for irrigation purposes. An independent t test showed significant differences in concentrations of all the tested metals, excluding lead, copper, and cadmium during dry and wet seasons. Similarly, differences were significant for electrical conductivity, biological oxygen demand, total nitrogen and total phosphorus. Salinity and concentrations of organics, nutrients, copper, cadmium, iron, manganese and to some extent copper exceeded the allowable thresholds for irrigation water. Lead, zinc, nickel and chromium, on the other hand, were lower than their respective limits. Wastewater used for irrigation purposes is unsafe, and urgent policy interventions on the use of untreated wastewater are required.

This study investigated the concurrent accumulation of eight heavy metals by two floating aquatic macrophytes (Lemna minor and Azolla filiculoides) cultivated in ambient media and blended wastewaters in the semiarid regions of Ethiopia. Both species accumulated heavy metals in varying degrees with a significant concentration gradient within the immediate water media. Highest bioconcentration factor (BCF) was determined for Mn and Fe in both plants. Results revealed that L. minor was high phytoaccumulator for Fe, Mn, Zn, and Co but moderate for Cd, Cu, Ni, and Cr. On the other hand, A. filiculoides was a high accumulator for Fe, Mn, Zn, and Cu, but its potency was moderate for Co, Cr, and Ni, but lower for Cd. Both species exhibited significant difference in accumulating Co, Zn, and Mn (p < 0.05). In general, the BCFs for both plants were comparable within the same treatment. In this study, stronger associations between the heavy metal concentrations in the plant tissues and in the grown water media were observed for A. filiculoides.

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