| Arsanilic acid (p-ASA) and roxarsone are two widely used organic arsenics in livestock and poultry industry to treat dysentery and coccidiosis, promote growth and color. Because those organic arsenics are scarcely adsorbed by animals, most of the added organic arsenics enter into feces, which might impact the later manure treatment. Once those organic arsenics are released into the environment, they will be further diffused into the surface water through raining and runoff, or immersed in groundwater. In this thesis, the effects of p-ASA on anaerobic co-digestion of pig manure (PM) with fruit and vegetable waste (FVW) and food waste (FW) were investigated; The inhibition on methanogens by high concentration of p-ASA under the existence of Fe(Ⅲ), Cu(Ⅱ) and phosphate were explored; The adsorption removal of roxarsone by Fe/La-modified montmorillonite (Fe/La-Mt) from aqueous solution was investigated. The following conclusions were obtained:Firstly, the effects of p-ASA on anaerobic co-digestion of PM with FVW and FW were investigated. The results showed that 0.1 mmol L-1 p-ASA has no obvious effects on the digestion process and arsenic concentration in aqueous solution was very low. While with the addition of 0.5 mmol L-1 p-ASA, the inhibition on methane production was enhanced with the increased proportion of FVW or FW. At the high concentration of p-ASA, the maximum methane yields of 386.3 mL g-1 VS was obtained with PM alone. The methane production was modeled using the modified Gomperts equation with relatively high fitting coefficients. The cumulative methane yields of co-digestion calculated from the model were relative higher than digestion PM alone. Most of arsenics was absorbed or/and precipitated in the sludge, only a small part of arsenics existed in the aqueous solution (-2%) after the completion of the digestion. Arsenite and arsenate were the two main species in each component.Secondly, under the existence of Fe (Ⅲ), Cu (Ⅱ) and phosphate, the degradation of p-ASA was investigated. When the digestion process lasted to 60 days, the degradation efficiency of p-ASA in the solution were 99.0%,99.3%,38.3% and 98.6% with the corresponding inhibition rates on methane generation of 97.49%,96.38%, 13.84%, and 95.13% in the assays without addition ions, and with the addition of Fe (Ⅲ), Cu (Ⅱ) and phosphate, respectively. In addition, with the addition of Cu (Ⅱ),the content of inorganic arsenic in the solution was low. When sucrose was used as substrate, the digestion process suffered serious acidification. After the completion of the digestion, the distributions of arsenics in the solution were also relatively low, and even lower than the assay with the addition of Fe (Ⅲ). Arsenite and arsenate were the main species. While under the existence of Cu (Ⅱ) using pig manure as substrate, 74.27% of arsenics existed in the solution with the main form of p-ASA.Finally, the adsorption of roxarsone by Fe/La-modified montmorillonite was investigated. Brunauer-Emmett-Teller (BET) analysis confirmed the increased specific surface area and pore volume, FESEM analysis showed that Fe/La-Mt formed flake structure and collapsed after modified montmorillonite being calcined (C-Fe/La-Mt). Fe/la-Mt and C-Fe/La-Mt were investigated for the removal of roxarsone from aqueous solutions. The results showed that the adsorption capacity of Fe/La-Mt was higher than C-Fe/La-Mt. The sorption process of roxarsone onto Fe/La-Mt and C-Fe/La-Mt can be well described using pseudo-second-order model and interpreted using the Langmuir isotherm. Thermodynamic analysis indicated that the adsorption process was spontaneous and endothermic. The adsorption capacity reduced slightly when solution pH increased from 2.5 to 8.0. The existence of PO43-greatly decreased the adsorption of roxarsone onto Fe/La-Mt. And the high adsorption capacity in a wide pH range demonstrated that Fe/La-Mt can be used potentially for the removal of roxarsone from aqueous solution. |
PDF Full Text Request