Water & Wastewater Treatment Magazine
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32 | OCTOBER 2018 | WWT | www.wwtonline.co.uk (0.5g of dry sludge in 50ml solution) and later filtered with the same filter paper in preparation for ICP analysis. The average concentrations (5 samples) of the detected ele- ments in the liquid and solid portions are presented in Table 1. The results showed a wide spectrum of valuable materials that are present in raw sewage sludge including heavy metals (aluminium, arsenic, cobalt, chromium, iron, mercury, nickel, lead, manganese, and zinc), noble metals (silver, gold and platinum), and other elements with potential commercial value (potassium, magnesium, sodium, silicon). It is very early at this stage of the research to accurately quantify the amount of valuable materials that can be extracted. However, if we assume that all the identified elements are chemically available for full extraction, the quantities presented in Table 2 can be theoretically recovered from the sewage sludge generated in England and Wales each year. The next stage of this study is to carry out wider research to identify and quantify valu- able materials on a national scale for a minimum period of 12 months. This will help the research team to understand the impact of seasons, loca- tion and demography on the chemical composition of raw sewage sludge. The data from this stage will also be used to prepare feasibility studies to assess the financial viability, practicality, efficiency and pos- sibility of recovering identified materials. The final stage, and ultimate goal of this research, is to develop a one-point pro- cess where optimal extraction of precious materials can be obtained from sewage sludge. The recovery processes may include physical, chemical and biological applications and the overall cost will depend on the efficiency and complexity of each recovery method. The research team welcomes input from and col- laboration with our colleagues in the water and wastewa- ter industry. Get in touch: a.hamood@wlv.ac.uk The Knowledge Sludge treatment Caption Table 1: Concentrations of valuable materials in Raw Sewage Sludge samples Element Average concentrations (5 samples) in Parts Per Millions (PPM) or mg/kg of water The liquid portion The solids portion Silver 0.022 0.019 Aluminium 0.81 0.509 Arsenic 0.042 0.028 Gold 0.012 0.003 Cadmium 0 0.005 Cobalt 0.024 0.000 Chromium 0.008 0.015 Copper 0 0.219 Iron 14.502 34.928 Mercury 0.014 0.020 Potassium 56.146 21.850 Magnesium 3.542 0.212 Manganese 0.012 0.015 Sodium 84.476 13.143 Nickel 0.332 0.019 Phosphorus 0 0.185 Lead 0.052 0.024 Platinum 0 0.005 Silicon 1.894 0.120 Zinc 0.09 1.253 Table 2: Estimated quantities of precious materials in Raw Sewage Sludge (tonnes per year) Element Mass of element (tonnes) from the liquid portion Mass of element (tonnes) from the solids portion Total in tonnes per year in England and Wales Silver 0.091 2.413 2.504 Aluminium 3.344 64.065 67.408 Arsenic 0.173 3.510 3.684 Gold 0.050 0.439 0.488 Cadmium 0 0.658 0.658 Cobalt 0.099 0 0.099 Chromium 0.033 1.975 2.008 Copper 0 32.361 32.361 Iron 59.864 4501.198 4,561.062 Mercury 0.058 2.633 2.691 Potassium 231.770 3047.018 3,278.789 Magnesium 14.621 27.425 42.046 Manganese 0.050 1.975 2.024 Sodium 348.716 1792.712 2,141.428 Nickel 1.370 2.413 3.784 Phosphorus 0 40.955 40.955 Lead 0.215 3.291 3.506 Platinum 0 0.658 0.658 Silicon 7.818 16.016 23.835 Zinc 0.372 158.626 158.997