The objective of the work presented here was to investigate the catalysing effect of iron oxyhydroxide on the redox reaction between ferrous iron and chromate. This was done in a bench-scale upflow reactor containing an expanded sand medium (fluid-bed reactor), where continous chemical addition, reaction and solid-liquid separation take place. Removal efficiencies of chromate in excess of 99% were attainable on spiked tapwater corresponding to an outlet concentration of 0.01 mg/l. Chromate polluted groundwater from a fly-ash disposal site was treated in the first full-scale plant (3 m3/h) with good results as well. The waste product generated by this method is a very compact granulate with a specific density of approx. 3 kg/l and low water content. Operation of the compact plant is simple and chemicals cost very little (approx. US D 1/400 per m3). The method (patent pending) is recommended for remediation purposes, but may also be applied in treatment of industrial wastewaters.

The calcium carbonate (CaCO3) precipitation potential (CCPP) can predict the potential for corrosion and lime scaling in drinking water systems. CCPP can be calculated by different standards, but none of these consider all of the conditions in drinking water systems where temperatures can reach 100 °C and the water exchanges CO2 with the atmosphere. We provided and demonstrated a procedure for CCPP calculations using the open-source software PHREEQC with the phreeqc.dat database at temperatures relevant for drinking water systems (10–90 °C) and for open systems in equilibrium with atmospheric CO2. CCPP increased by 0.17–1.51 mmol/kg when the temperature was increased from 10 °C to 90 °C and increased by 0.22–2.82 mmol/kg when going from closed to open systems at 10 °C. Thus, CaCO3 precipitation may be underestimated if CCPP is only considered for the lower sample temperature and for closed systems. On the other hand, CCPP10 decreased by 0.006–0.173 mmol/kg when including the ionic species from the German DIN 38404-10 standard in addition to calcium, alkalinity and pH, indicating that all relevant ionic species should be included in CCPP calculations. CCPP values should always be reported with the calculation procedure and temperature to avoid inconsistency in literature.