Removal of organic matters in wastewater treatment by ferrate (VI)-technology

This paper presents the effect of ferrate-Fe(VI) on municipal secondary effluents derived from two different wastewater treatment plants. Experiments were carried out in laboratory using Fe(VI) and chlorine to compare the performance of these reagents regarding their organic matter and reactive phosphate compounds removal, and the formation of adsorbable organic haloids (AOX) as by-products. Additionally, the most probable number (MPN) of cultivable heterotrophic bacteria was also determined. In every case for 100% bacterial inactivation a low Fe(VI) concentration (5 mg L− 1) was enough and by this concentration 40% chemical oxygen demand (COD) and 20% total organic carbon (TOC) removal could be obtained on average. Higher Fe(VI) concentration (7–15 mg L− 1) resulted in an even higher organics reduction (depending on the water matrix up to 79% COD and 45% TOC removal). Applying chlorine treatment also resulted in a 99.9% inactivation, but only an approximately 30% COD and 2% TOC removal could be achieved at higher concentrations. Fe(VI) could also effectively diminish the reactive phosphate concentration in the investigated secondary effluents. Monitoring AOX concentration during Fe(VI)-treatment, it could be stated that AOX formation was in linear relationship with the applied Fe(VI) concentration, but at higher than about 10 mg L− 1 Fe(VI) concentration this increase became much less than at lower Fe(VI) concentration. Chlorine treatment also resulted in AOX formation, but using a low Fe(VI) concentration, which was already enough for 99.9% bacterial inactivation, the AOX concentration rise was lower than in the chlorine process.

► Ferrate technology resulted in similar disinfection performance than chlorination during secondary effluent treatment.
► TOC and reactive phosphate removal higher in Fe(VI)-process than in chlorination.
► Level of AOX compound formation lower in the case of Fe(VI)-treatment.