SPECIATION OF COPPER, LEAD, MANGANESE AND ZINC AND CHARACTERISATION OF SEWAGE SLUDGE FROM WUPA TREATMENT PLANT, ABUJA, NIGERIA

ABSTRACT

Speciation of Copper, Lead, Manganese and Zinc ions in three sewage sludge samples (fresh, digested and dry) from Wupa sewage treatment plant, Abuja were investigated using sequential extraction  methods. Flame atomic absorption spectrophotometer was used for instrumental analysis. The sludge physicochemical parameters, total metal concentration using aqua regia digestion, speciation of metals under study, using   single extraction with EDTA and sequential extraction analytical methods were determined. Analysis of variance (ANOVA) on data obtained from the work was also carried out. Study on physicochemical parameters showed that; Samples   had mean pH values   of   8.48±0.13.8.50 ±0.02 and 8.37±0.17 for fresh,treated and dry sludge respectively. Samples had electrical conductivities of 520.00±0.01, 340.00±0.01 and 320.00±0.00 µScm-1 for fresh,treated and dry  sludge respectively.  Samples  had    nitrate  contents  of;  5.20±0.0,  4.80±0.01  and 2.50±0.01 gkg-1 for fresh, treated and dry sludge respectively. Aqua regia digestion for total metal concentration results showed values of;1418.13, 237.50, 4510.00 and 8289.60 mgkg- 1  for Cu, Pb, Mn an d Zn respectively. Single extraction with EDTA results showed; 66.89, 6.90, 298.46 and  8.10  mgkg-1 for Cu, Pb, Mn and Zn respectively. Results for extraction of ions in five operational phases in sequential extraction showed; 202.15, 66.91, 385.59 and 418.79 mgkg-1 for Cu, Pb, Mn and Zn respectively. The metals; (Cu, Pb, Mn and Zn) were   bound in five operational phases; (exchangeable, acid extractable, reducible, oxidizable and residual) in the sequential extraction method. Pb, Mn and Zn speciated more in  the  acid  extractable,  and  reducible  phases  which  were  the  carbonate and  Mn/Fe oxide/hydroxide bound respectively. Cu speciated prominently   in acid extractable and residual phases which were carbonate bound and occluded in organic matter respectively. The Solubility of all the metals (Cu, Pb, Mn and Zn) ranked highest in  the acid extractable phase. Mn and Zn ranked lowest in the residual phase while Cu and Pb ranked lowest in the exchangeable and oxidizable phases respectively. Speciated ions in the exchangeable and acid extractable phases as soluble metal acetates and chlorides respectively are bioavailable to plants and vegetables for  uptake. From the results of Cu, Pb, Mn and Zn ions obtained in the three extractions carried out it can be deduced that both ion concentrations are within the limits of regulatory agencies. However, a new method of speciation in handling trace metal pollutants will assist Wupa Treatment Plant in treating sewage sludge better. This will also boost agriculture and human health  in the Federal Capital Territory in particular and in Nigeria in general which falls in line with the current  Federal Government policies on  food  security and  environmental sanitation.

CHAPTER ONE

1.0      INTRODUCTION

1.1      Background to the Study

Frequent discharge of sewage sludge without a proper treatment could have a serious negative impact on the environment, because it is a difficult material to manage (Nessa et al., 2016). Sewage sludge is the residue or waste generated from treatment of wastewater (Emmanuel and Edu, 2017). It is a dark grey deposit, which is a byproduct of treated sewage from homes, offices and abattoirs (Sungur et al, 2019). It is also an unavoidable by product of wastewater treatment plants (Hu et al., 2015). Dewatering and disposal of waste sludge is a major economical factor in the operations of wastewater treatment plants (Obianyo, 2015). Sewage contains among other things, toxic metals like copper, lead, manganese and zinc (Duarte and Noguiera, 2014). Heavy metals are mostly present in sludge as they are attached to the solid portion of the wastewater (Abdul-Aziz et al., 2017). The analysis of metal concentrations found in sewage sludge constitutes an important issue in terms of both human health and environmental hazards.

Toxic heavy metals associated with sewage sludge include mercury, cadmium, manganese, nickel, copper, iron, lead and zinc (Daniel, 2017). When the metals are exposed to the environment could pose serious risk to both plants and animals.  Cu, Mn, Zn, Pb and Cd pose persistent threat to the ecosystem and human health (Xiaofel et al., 2017). Blood-Mn levels are related to the prevalence of chronic diseases (Koh et al., 2014). Controlling sludge is of essence here, because soil is usually the final destination of metals emitted in to the environment (Ibrahim and Nafiu, 2017).

Metal  speciation  describes  the measure  of  existence  of heavy metals  as  hydroxides, biomolecules,  or  even  organometallic  compounds  (Faustin  et  al.,  2018).  Operational determination of the various species of Cu, Pb, Mn and Zn in different portions of sludge sample is achieved using both single and sequential extraction techniques (Luana et al., 2015). Sewage sludge can vary from mixed fresh, digested (aerobic or anaerobic) sludge and bed sludge in the sewage treatment plants.   Sewage sludge could be hazardous to environment due to its chemical and biological contents but can be useful if well treated (Liang et al., 2016). On the other hand, sewage sludge can be beneficial for both agricultural purposes and landfill, to avoid erosion and landslide (Adam, 2018). The knowledge of chemical speciation of heavy metals in sewage sludge disposed in sanitary landfill sites is of great importance to assess the ecological risk of land application of stabilised sewage sludge from the sites (Tyagi and Lo, 2016).

1.2       Statement of the Research Problem

Physicochemical parameters of sewage sludge such as pH, electrical conductivity, moisture and nitrate content can  increase the danger posed by sludge to agricultural soil and environment if not controlled properly during sludge treatment (Xavier et al., 2019).

Study on the total concentration of a metal alone does not provide adequate information to allow for assessing the bioavailability or toxicity of heavy metals (Egorova and Ananikov, 2017). Understanding metal risk in the environment should go beyond metal measurement (John, 2018).

Species of metals in soil are a potential risk to environment (Reis, 2015).  The potential toxic risks from heavy metals of sludge depend on their chemical speciation (Santoro et al., 2017).

1.3       Justification of the Study

Safer utilisation of sludge could be achieved only if there is a mechanism in place to control resultant pollution of sludge disposal by controlling its  physicochemical parameters.

Effects of pH, electrical conductivity and nitrate contents of sewage sludge can contribute to its potential risk to environment (Li and Yang, 2018).

Understanding the effect of heavy metals in the soil is the key factor to realize the safe utilisation of sewage sludge (Hei et al., 2016). Cu, Pb, Mn and Zn concentration will be analysed using aqua regia digestion to extract them (Vhangwale and Miraslav, 2018). Aqua regia method proves suitable for metal extraction for solid phases to have a fair understanding of effect of metals in the environment (Das and Teng, 2016).

Proper understanding and application of the knowledge of chemical speciation of Cu, Pb, Mn and Zn in sanitary landfill can assist greatly in assessing the ecological risk of application of stabilized sewage sludge (Kai et al., 2016). Single and sequential extraction techniques in the speciation of Cu, Pb Mn and Zn in sewage sludge can help in evaluating the fractionations of these metals (Shuman, 2015).

1.4       Aim and Objectives of the Study

The aim is to study speciation of Copper, Lead, Manganese and Zinc and characterisation in sewage sludge from Wupa treatment plant, Abuja, Nigeria.

The objectives of this study were:

i.      Characterisation of physicochemical parameters of Wupa sewage sludge samples. ii.      Determination of the concentrations of Cu, Pb, Mn and Zn in sewage sludge samples.

iii.      Speciation of Cu, Pb, Mn and Zn ions in the sludge using single and sequential extraction analytical techniques.

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