This research project aimed at evaluating four internationally accepted leachate extraction tests to determine their applicability on sewage sludge samples. Furthermore, the present analytical method to determine the leachable fraction of sludge for compliance to South African sludge legislation was evaluated. Leaching tests are done on sludge samples to determine element mobility. This is important since land application of sewage sludge is an accepted and regulated sludge management practice. A literature survey was done to evaluate the mobility over time of metals originating from sludge-amended soils. Mobility is initially due to the organic content of the soil and after organic matter decomposition, it is dependant on the inorganic content. Mobile metals in sludge-amended soil can cause potential environmental risks like groundwater contamination and metal accumulation in soil. Metal accumulation can further lead to increased plant uptake of metals. To determine the partitioning or fractionation of metals found in sludge-amended soil, selective sequential extractions and single extractions can be used. Since South African sludge legislation specifies a single extraction procedure, four were selected for comparative studies. The selected procedures were the USA Environmental Protection Agency (EPA) Toxicity Characteristic Leaching Procedure (TCLP) the Australian Standard Bottle leaching Test (AS 4439.3) the Nederlands Normalisatie-Insitiuut availability test (NEN 7341) and the Deutches Institut für Normung water leachability test (DIN 38 414-S4). A variation of the TCLP is specified for use in South Africa. Three sewage sludge sample lots were collected. The first consisted of 24 sub-samples that were collected from 24 different wastewater treatment works on the East Rand. Both leachable (TCLP) and total (aqua regia) extraction was done on these samples for Cd, Co, Cr, Cu, Hg, Mo, Ni, Pb, Zn, Se, B and Fe. A relationship between the leachable and total extractions was found for Co and Pb but could not be tested by literature values due to a variation in the sample preparation. The TCLP leachates were also analysed by Atomic Absorption and Inductively Coupled Plasma techniques to compare the applicability of the two. It was found that both techniques are acceptable for leachate analysis. The second sample lot collected from a single wastewater treatment plant was used to determine the leachable effect of the difference between the South African adapted TCLP and the USA EPA procedure as well as the NEN procedure. The EPA specifies all samples be extracted on an “as is” basis while the South African adaptation specifies dry samples. It was found that no element was comparative between dry and wet sample for both extraction procedures. It was observed that wet extractions yield generally higher values than dry extractions. A third sample lot was collected two months after the second sample lot at the same wastewater treatment works. It was used to compare the four extraction procedures. From this it was found that the DIN yielded the highest results for the specified elements. This procedure could not be recommended since the experimental difficulties and the duration of the test make it an unsuitable regulatory compliance tests protocol. / Dissertation (MSc (Environmental Technology))--University of Pretoria, 2006. / Chemical Engineering / unrestricted

The use of treated waste water for irrigation of vegetable crops is on the increase in Botswana especially in the Glen Valley farms, a peri-urban settlement of Gaborone city. However, the effects of this practice on heavy metals uptake by vegetable crops are uninvestigated. Chromium and nickel have been reported to be accumulating in Gaborone crop soils and cultivating vegetables in these soils with treated waste water could potentially lead to an increased bio-availability of the heavy metals in the vegetable crops. The main aim of this study was therefore to compare the uptake of chromium and nickel in tomato plants, a vegetable grown in sludge amended Glen Valley soils, to those grown in sludge absent Glen Valley soils using treated waste water at different pH values and tap water for irrigation. The high water uptake and high water consumption rate of tomato plants made it suitable for this study. Twenty five pots each containing 2.5 kg sludge amended Glen Valley soils and 5 pots each containing 2.5 kg sludge absent soils were utilized. Fresh treated waste water in a 50 L plastic container on a need by need basis was used. For the control experiments 5 pots each containing 2.5 kg standard commercial soils and fresh tap water were used. The potted tomato plants were cultivated from early May to middle of October 2009. One leaf and one fruit from each tomato plant was harvested and tested in this study. The highest uptakes of chromium (0.819 mg/L) and nickel (0.327 mg/L) were experienced in the leaves where the tomato plant were cultivated in standard commercial soil and irrigated with tap water at pH 7.0. The least uptake of chromium (0.052 mg/L) and that of nickel (-0.030 mg/L) was found in the fruits, where the tomatoes were grown in sludge amended Glen Valley soil and irrigated with normal Glen Valley treated waste water at pH 8.5. Increasing the pH of the treated waste water from 5.0 to 6.0 caused increased bio-accumulation of chromium and nickel in the leaves and the fruits of the tomato plants. Normal treated waste water (pH 8.5) and treated waste water at pH 9.0, however, reduced the chromium and the nickel uptake by the tomato plants. Treated waste water at pH 10.0 bio-accumulate more chromium and more nickel in the leaves and fruits of tomato plants. The pH variation experiments suggested that the fruit tissues accumulated more chromium and the leaf tissues accumulated more nickel. The mean chromium uptake in the tomato plants exceeded the Food and Agriculture Organization permissible limits but the Botswana Bureau of Standards effluent limit was not exceeded. The mean nickel concentrations were below the threshold limits for both local and international standards. Statistical analysis showed no significant difference between the mean chromium and the mean nickel concentration in the leaves and the fruits of the tomatoes at the 5% significant level. It can be concluded from this study that cultivating tomatoes with sludge amended Glen Valley soil combined with normal treated waste water at pH 8.5 could reduce the uptake of chromium and nickel uptake in tomato plants. However, an increase in the uptake of chromium and nickel in the leaves and fruits of the tomato plants could be triggered at slightly low pH (pH 5.0 and pH 6.0) and high pH (pH 10.0) of the treated waste water. It is recommended that the current practices of using treated waste water combined with sludge amended Glen Valley soil to cultivate tomatoes at the Glen Valley farm is good practice and should be continued. Nonetheless, further studies need to be carried out at the farm to establish possible phytotoxicity effects of these heavy metals on tomatoes when using treated waste water combined with sludge amended and sludge absent soils. / Dissertation (MSc)--University of Pretoria, 2011. / Chemical Engineering / unrestricted