Assessment of Heavy Metals in Municipal Sewage Sludge: A Case Study of Limpopo Province, South Africa

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.

Quantification of Cd, Cu, Pb and Zn from sewage sludge by modified-BCR and ultrasound assisted-modified BCR sequential extraction methods

“…This value is similar to that obtained in municipality sludge (3.10 mg kg from Limpopo Province (Shamuyarira and Gumbo, 2014 ) were higher compared to their corresponding DWAF threshold and MPL standards. The higher values of Pb, Cu and Zn in the clarifier sludge is matter of concern due to toxicity associated with these metals.…”

“…Figure 1 shows that the concentrations of the investigated metal ions in the raw and clarifier sludge obtained by total digestion exceeded both the DWAF threshold and the MPL, with the exception of Cd in clarifier sludge and Zn in raw sludge. The amounts of Cu (500-700 mg kg -1 ) were similar to those reported by Shamuyarira and Gumbo (2014) from Louis Trichardt and Musina sludge samples in the Limpopo Province in South Africa. Similarly, the amounts of Zn in the clarifier sludge (2300 mg kg -1 ) were also similar to that reported by the same authors from Louis Trichardt and Polokwane.…”

“…Similarly, the amounts of Zn in the clarifier sludge (2300 mg kg -1 ) were also similar to that reported by the same authors from Louis Trichardt and Polokwane. Heavy metals that exceed the DWAF guidelines is a cause for concern since this could be hazardous to both humans and the environment (Shamuyarira and Gumbo, 2014). Table 1a shows the comparison of the pseudototal digestion results with the sum of the 4 fractions obtained from the modified-BCR and UA-BCR method.…”

“…The higher values of Pb, Cu and Zn in the clarifier sludge is matter of concern due to toxicity associated with these metals. Shamuyarira and Gumbo (2014) ). These values also exceeded the DWAF guidelines.…”

Mineral Nanoparticles in Waste: Potential Sources, Occurrence in Some Engineered Nanomaterials Leachates, Municipal Sewage Sludges and Municipal Landfill Sludges

“…According to the literature, these elements were considered to be the most relevant. [31][32][33][34][35][36][37]. The common range of Ag for soils is 0.01-5 mg/kg, with a representative average of 0.05 mg/kg [38], 200 times less than the mean concentration observed in the sludge.…”