Effect of organic matter on size and structural strain of nano-ZnS formed in organic waste

Anaerobic digestion (AD) is an interesting opportunityfor organic wastes (OW) treatment because of biogasproduction and agricultural valorisation of digestate asfertiliser. OW often contain large amounts of zinc (Zn),potentially toxic for soil living organisms on the long term.Therefore, it is crucial to understand the effect of AD on Znspeciation in OW to determine the risk of digestate recycling.ZnS have already been evidenced in digestates in varyingproportions according to past studies [1-2]. Besides, thedissolution in soil is faster for ZnS that precipitated in OWthan for ZnS from other origins [3-4].In order to better understand process influence on Znspeciation, a systematic study was needed. We have sampledOW in nine AD and composting plants that cover most of thecurrent practices. Zn k-edge ExtendedX-ray Absorption FineStructure (EXAFS) was used to determine Zn speciation. Weshowed that nano-ZnS is a major phase in all digestates. Thehigh reactivity of those nano-ZnS is reflected by the drasticchange of Zn speciation along the OW treatment chain.The OW is a too complex matrix to investigate theseprocesses. Therefore to go further into the mechanisms thatdrive ZnS reactivity, we used laboratory batch experiments.Nano-ZnS of different sizes have been synthetized inpresence of organic molecules in the laboratory andcharacterized by X-ray Diffraction (XRD) and Wide AngleX-ray Scattering (WAXS). Pair Distribution Function (PDF)analysis was perfomed on WAXS signals to obtain real-scaleinteratomic distances distribution. It has shown structuralsize-dependent properties and has underligned the influenceof OM on both size and strain