Snyman H G
Department of Chemical Engineering, University of Pretoria, South Africa.
Water Sci Technol. 2001;44(10):107-14.
The South African sludge guidelines were revised in 1997 with considerable amendments to the heavy metal loading and usage restrictions. The industry continued using the aqua regia extraction method to characterise and classify sewage sludge. This meant that a Class D sludge (most stable class and sellable product) could not be generated at any South African plant. This caused the industry to seek alternative nonbeneficial disposal methods. It was then realised that the metal limits were in fact the TCLP (Toxicity Characteristic Leaching Procedure) extractable limit. This method was developed to determine the potential of a waste to contaminate ground and/or surface water. The agriculturists, however, use the NH4EDTA extractable fraction to establish metal concentration in soils. This paper specifically aims to establish the feasibility of using the available metals extraction methods such as NH4EDTA and TCLP to determine the fate and therefore the risk of sludge-borne metals (Cd, Pb, Zn, Cu). The results show that the TCLP extraction method could potentially underestimate the impact of sewage sludge-borne metals when amended to agricultural soils. The extraction efficiency of the NH4EDTA and TCLP methods relative to the aqua regia extraction method was presented for Cd, Pb, Zn and Cu. The NH4EDTA extraction method seems to be an alternative to the aqua regia method, especially since the NH4EDTA measures the fraction of the metal that may become available in the environment. It is recommended that the aqua regia and NH4EDTA be used to classify and characterise the metal content of South African sludges.
南非的污泥指南于1997年进行了修订，对重金属负荷和使用限制进行了大量修正。该行业继续使用王水萃取法对污水污泥进行表征和分类。这意味着南非的任何工厂都无法产生D类污泥（最稳定的类别和可销售产品）。这导致该行业寻求替代性的非有益处置方法。随后人们意识到，金属限值实际上是毒性特征浸出程序（TCLP）可萃取限值。该方法旨在确定废物污染地下水和/或地表水的可能性。然而，农业学家使用乙二胺四乙酸铵（NH4EDTA）可萃取部分来确定土壤中的金属浓度。本文具体旨在确定使用诸如NH4EDTA和TCLP等现有金属萃取方法来确定污泥中金属（镉、铅、锌、铜）的归宿以及因此产生的风险的可行性。结果表明，当将污水污泥中的金属用于改良农业土壤时，TCLP萃取方法可能会低估其影响。文中给出了NH4EDTA和TCLP方法相对于王水萃取法对镉、铅、锌和铜的萃取效率。NH4EDTA萃取方法似乎是王水法的一种替代方法，特别是因为NH4EDTA测量的是可能在环境中变得可用的金属部分。建议使用王水法和NH4EDTA法对南非污泥的金属含量进行分类和表征。
