Sewage sludge ash to phosphorus fertiliser (II): Influences of ash and granulate type on heavy metal removal

Ashes from monoincineration of sewage sludge suggest themselves as an ideal base for inorganic fertiliser production due to their relatively high phosphorus (P)-content. However, previously they need to be detoxified by reducing their heavy metal content. The core process considered in this paper consists of three steps: mixing of the ashes with suitable chlorine-containing additives, granulation of the mixture and thermochemical treatment in a rotary kiln. Here relevant heavy metal compounds are first transformed into volatile species with the help of the additives and then evaporated from the granules.In this study two chemically different ashes and their mixture were agglomerated to two different granulate types, briquettes and rolled pellets. The resulting six different materials were subjected to thermal treatment at different temperatures. The heavy metals examined were Cu and Zn due to their strong dependence on treatment conditions and their relevance concerning thermal treatment of sewage sludge ashes. Besides, the behaviour of Cl and K was monitored and evaluated.The experiments showed that ash type and temperature are more influential on Cl and heavy metal chemistry than granulate type. Temperature is a primary variable for controlling removal in both cases. Cu removal was less dependent on both ash and granulate type than Zn. The Cl utilization was more effective for Cu than for Zn. Depending on the treatment conditions some K could be retained, whereas always all P remained in the treated material. This satisfies the requirement for complete P recycling.     

Photochemical production of methane in natural waters: implications for its present and past oceanic source

We conducted irradiation experiments with riverine, estuarine, and marine water samples to investigate the possibility of photochemical methane (CH4) formation. CH4 photoproduction was undetectable under oxic conditions or in the absence of methyl radical precursors indicating that its photochemical formation is negligible in the present ocean. Significant photochemical CH4 production was observed in the presence of a methyl radical precursor such as acetone under strictly anoxic conditions. Our results indicate an indirect formation mechanism with coloured dissolved organic matter acting as photosensitizer. We suggest that photochemical CH4 formation might have occurred in the anoxic ocean surface layer of the Archean prior to the onset of O2 accumulation in the atmosphere at around 2300 million years ago. Oceanic CH4 photoproduction via methyl radical (CH3) precursors and its subsequent release to the atmosphere may have contributed to high CH4 mixing ratios in the Archean atmosphere.