Heavy metals in untreated/treated urban effluent and sludge from a biological wastewater treatment plant.
OBJECTIVE
The presence of heavy metals in wastewater is one of the main causes of water and soil pollution. The aim of the present study was to investigate the removal of Cd, Cu, Pb, Hg, Mn, Cr and Zn in urban effluent by a biological wastewater treatment, as well as to quantify the levels of As, Be, Cd, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Sn, Tl, V and Zn in dewatering sludge from the Biological Wastewater Treatment Plant of Ribeirão Preto (RPBWTP), Brazil.


METHODS
Concentrations of Cd, Cr, Cu, Mn and Pb in wastewater and those of Ni in sludge were determined by atomic absorption spectrophotometry with graphite furnace atomization. Mercury concentrations in wastewater were measured by hydride generation atomic spectrophotometry, and Zn levels were determined by atomic absorption spectrophotometry using acetylene flame. In sludge, the levels of As, Be, Cd, Cr, Cu, Fe, Hg, Mn, Pb, Sn, TI, V and Zn were determined by inductively coupled plasma-mass spectrometry. Results. The percentages of removal efficiency (RE) were the following: Hg 61.5%, Cd 60.0%, Zn 44.9%, Cu 44.2%, Pb 39.7%, Cr 16,5% and Mn 10.4%. In turn, the mean concentrations (mg/kg) of metals in dewatering sludge followed this increasing order: Tl (< 0.03), Hg (0.31), Be (0.43), As (1.14), Cd (1.34), V (59.2), Pb (132.1), Sn (166.1), Cr (195.0), Mn (208.1), Ni (239.4), Cu (391.7), Zn (864.4) and Fe (20537).


CONCLUSIONS
The relationship between metal levels in untreated wastewater, as well as the removal efficiency are in agreement with previous data from various investigators. It is important to note that metal removal efficiency is not only affected by metal ion species and concentration, but also by other conditions such as operating parameters, physical, chemical, and biological factors.


CONCLUSIONS
Metal values recorded for treated wastewater and sludge were within the maximum permitted levels established by the Environmental Sanitation Company (CETESB), São Paulo, Brazil.


CONCLUSIONS
There is an urgent need for the authorities who are responsible for legislation on sludge uses in agriculture of establishing safety levels for As, Be, Hg, Sn, Tl and V.


CONCLUSIONS
According to the current metal levels, RP-BWTP sludge might be used for agriculture purposes. However, for an environmentally safe use of sewage sludge, further studies including systematic monitoring are recommended. Annual metal concentrations and predicted variations of those elements in the sludge should be monitored.
Environmental Health Laboratory, Department of Maternal-Infant Nursing and Public Health, Ribeirão Preto College of Nursing, University of São Paulo, Brazil.
Aline da Silva
Ada S
Oliveira
Ana
A
Bocio
Tânia M Beltramini
TM
Trevilato
Angela M Magosso
AM
Takayanagui
José L
JL
Domingo
Susana I
SI
Segura-Muñoz
D019216:Metals, Heavy / Q000032:analysis* / Q000737:chemistry; D012722:Sewage / Q000737:chemistry*; D014867:Water / Q000737:chemistry*; D018508:Water Purification
D019216:Metals, Heavy; D012722:Sewage; D014867:Water