Abstract
Heavy metals in high concentrations can cause health and environmental damage. Nanosilver is an emerging heavy metal which has a bright future of use in many applications. Here we report on the levels of silver and other heavy metals in municipal sewage sludge. Five towns in Limpopo province of South Africa were selected and the sludge from their wastewater treatment plants (WWTPs) was collected and analysed. The acid digested sewage sludge samples were analysed using Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES) and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) methods. The concentrations of silver found were low, but significant, in the range 0.22 to 21.93 mg/kg dry mass. The highest concentration of silver was found in Louis Trichardt town with a concentration of 21.93 ± 0.38 mg/kg dry mass while the lowest was Thohoyandou with a concentration of 6.13 ± 0.12 mg/kg dry mass. A control sludge sample from a pit latrine had trace levels of silver at 0.22 ± 0.01 mg/kg dry mass. The result showed that silver was indeed present in the wastewater sewage sludge and at present there is no DWAF guideline standard. The average Cd concentration was 3.10 mg/kg dry mass for Polokwane municipality. Polokwane and Louis Trichardt municipalities exhibited high levels of Pb, in excess DWAF guidelines, in sludge at 102.83 and 171.87 mg/kg respectfully. In all the WWTPs the zinc and copper concentrations were in excess of DWAF guidelines. The presence of heavy metals in the sewage sludge in excess of DWAF guidelines presents environmental hazards should the sludge be applied as a soil ameliorant.
Highlights
Technological advancement, increase in incomes and betterment of standards of living have resulted in the increased demand for almost everything
In all the wastewater treatment plants (WWTPs) the zinc and copper concentrations were in excess of DWAF guidelines
The results show that the heavy metals, Cr, Ni, Cd, Pb, Cu and Zn, were present in the sewage sludge and their concentrations were variable (Table 1)
Summary
Technological advancement, increase in incomes and betterment of standards of living have resulted in the increased demand for almost everything. With more income people use more resources and have more wants and needs [1]. Such a situation has led to an increase in the number of uses of heavy metals. More and more amounts of heavy metals are being used and incorporated into products. Over the past two decades the use has risen even more dramatically due to technological advancements [3,4]. Nanoparticles are very minute particles which have more anthropogenic origin than natural origin. Due to their size they find a vast number of uses in food processing, textile production, cosmetics, medical devices and many other fields. Due to the widespread use in consumer products, it is likely that nanoparticles are entering water streams and the treatment facilities that process wastewater [3]
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