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A derivation of a dynamic Electric Arc Furnace (EAF) model is shown in Bekker 1) and Bekker, Craig and Pistorius.2) This model describes the time-evolution of EAF furnace and off-gas system variables. A preliminary verification of this model with measurements taken from an industrial EAF, is discussed in Bekker, Craig and Pistorius. 3) In this note the Bekker model is improved and expanded to include some process variables not modelled previously. Improvements are made to the off-gas temperature model, and a slag foam depth model is added.The off-gas model as derived by Bekker 2) is sufficient as far as the CO production rate is concerned. The mass flow through the cooling duct is also fairly accurately modelled. The off-gas temperature model, however, still had room for improvement.There are two main processes in the cooling duct which affect the temperature of the off-gas mixture. Of these, combustion adds heat to the gas, and convective heat transfer to the duct sides extracts heat from the gas. The rates of both processes were initially modelled 2) as being proportional to the difference between the off-gas temperature at the entrance to the cooling duct, and the temperature of the cooling duct walls. These two processes were remodelled to better describe the mechanics of the heat transfer that occurs.In the duct the off-gas from the furnace mixes with the air from the atmosphere that enters at the slip-gap. The CO then combusts with oxygen that enters with the air. The mass fraction of CO in the off-gas (QC CO ) reacting with the O 2 gas in the cooling duct is given by Eq. (1), where g is given by Eq. (2)

Not all phosphorus removed in activated sludge systems can be accounted for by polyphosphate accumulating organisms (PAO). A method for the qualitative and quantitative in situ characterization of PAO cell clusters and closely associated extracellular polysaccharides (EPS) is described. X-ray microanalysis was performed on samples from four activated sludge plants situated in Pretoria, South Africa. Analyses were done by means of Scanning Electron Microscopy (SEM) combined with Energy Dispersive Spectrometry (EDS). Cell clusters with associated EPS on average contained between 57 and 59% phosphorus, while EPS alone contained on average between 23 and 30% phosphorus. Results suggest that phosphorus removal in activated sludge might be due not only to PAO, but also by EPS acting as a phosphorus reservoir. Extraction of EPS from two different activated sludge plants yielded different amounts of EPS, which, in combination with SEM-EDS, may shed light on different phosphate uptake abilities of different activated sludges.

Model Predictive Control (MPC) of an Electric Arc Furnace (Em off-gas process combined with temperature control is investigated. A more predictable process, safer working environment, cleaner emission gasses and reduced energy wastage are some of the advantages obtained by controlling relative furnace pressure, CO-emission and temperature.