Exploring the roles of zero-valent iron in two-stage food waste anaerobic digestion.

This research investigated the roles of zero-valent iron (ZVI) in a two-stage food waste digestion process. ZVI was added separately to hydrolytic-acidogenic (HA) and methanogenic (MG) stages to understand its impacts on FW hydrolysis-acidification, methanogenesis and bioenergy recovery efficiency. Results showed that ZVI effectively enhanced the overall performance of digestion as compared with the controls without ZVI. Supplementing with ZVI could facilitate the HA process along with faster hydrogen generation. In addition, ZVI shortened the lag phase of MG stage by 42.43-57.23% and raised the maximum methane production rate and yield by 33.99-38.20% and 11-13%, respectively, compared with the controls. Supplementing ZVI to the HA stage could simultaneously raise the bioenergy recovery efficiency of the HA and MG stages by 71.92% and 96.96%, respectively. Further studies demonstrated that iron corrosion contributed little to hydrogen and methane production. The enrichment of syntrophic bacteria, Pseudomonas, and methanogens, and the enhancement of electron transfer among those microbes was supposed to be the main possible mechanism for the enhancement of methanogenesis with ZVI assisted.

Enhancement of hydrogen production using untreated inoculum in two-stage food waste digestion.

This research investigated the possibility to enhance H2 production using untreated inoculum in a two-stage hydrogen-methane process from food waste. Batch experiments were conducted to evaluate the H2 production efficiency at different F/M ratios (ranging from 1:1 to 64:1). The results showed that when a proper F/M ratio was selected, significant H2 production was feasible to be achieved even inoculated with untreated anaerobic sludge. Among the F/M ratios studied, maximum H2 yield (217.98 mL H2 g VS-1 FW) was found in the digester at the F/M of 64:1, which was 93.75 times higher than that of the digester at the F/M of 1:1. Higher hydrogen yield was achieved at the greater F/M ratio, due to the enrichment of the H2 producing bacteria and the reduction of the antagonistic bacteria. The two-stage process allowed more stable methane production and higher overall energy yield compared to the single-stage process.

H2S adsorption by municipal solid waste incineration (MSWI) fly ash with heavy metals immobilization.

As a byproduct of municipal solid waste incineration (MSWI) plant, fly ash is becoming a challenge for waste management in recent years. In this study, MSWI fly ash (FA) was evaluated for the potential capacity of odorous gas H2S removal. Results showed that fly ash demonstrated longer breakthrough time and higher H2S capacities than coal fly ash and sandy soil, due to its high content of alkali oxides of metals including heavy metals. H2S adsorption capacities of FA1 and FA2 were 15.89 and 12.59 mg H2S/g, respectively for 750 ppm H2S. The adsorption of H2S on fly ash led to formation of elemental sulfur and metal sulfide. More importantly, the formation of metal sulfide significantly reduced the leachability of heavy metals, such as Cr, Cu, Cd and Pb as shown by TCLP tests. The adsorption isotherms fit well with Langmuir model with the correlation coefficient over 0.99. The adsorption of H2S on fly ash features simultaneous H2S removal and stabilization and heavy metals found in most MSWI fly ash, making fly ash the potential low cost recycled sorbent material.