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Abstract
Occurrence of conventional pollutants and more than seven hundred emerging pollutants have seriously contaminated the aquatic ecosystem and further threaten human health. To satisfy access to safe drinking water, scientists need to explore applicable technology to cleaning contaminated water. In chapter 2 and chapter 3, two common but important pollutants, ammonium and phosphate, were investigated through being adsorbed on biochar surfaces with the aim of cleaning wastewater produced in agricultural fields and manufacture industry. Ammonium, as a precursor to atmospheric ammonia, which is released over large areas of the United States, the European Union, and China, has brought undesirable consequences affecting carbon fixation, eutrophication, and biodiversity. According to the latest EPA assessment, forty percent of national rivers and streams in U.S. have an evaluated level of phosphate, causing a persistent threat to waterways. Both ammonium and phosphate are nonpoint source pollutants from human waste, food, soaps, and other detergent, and their myriad inputs undoubtedly cause the United States to be challenged politically, technologically, and financially to treat such widespread nutrient pollution.
Coincidently, Biochar, as a renewable adsorbent, not only can mitigate the mass transfer of either inorganic or organic contaminants, but also may be co-applied with inorganic NPK fertilizer to generate biochar-based fertilization. We attempted to focus on the adsorptive behavior, characterization, and mechanisms of ammonium and phosphate upon biochar in Chapter 2 and Chapter 3, individually. The main conclusions are: 1) pH was the dominant parameter controlling the adsorption characteristics and their optimum adsorption capacities; 2) The Freundlich model was more favorable for describing the adsorption of either ammonium or phosphate onto the hydrous bamboo biochar compared to the Langmuir model; 3) Particle size didn’t significantly affect the adsorbing ability of biochar towards either ammonium or phosphate although smaller size biochar particles to some extent have improved adsorption capacity compared to that of larger particles; 4) A pseudo-second-order model was a better fit than a pseudo-first-order model of the process of either ammonium or phosphate adsorption upon biochar; 5) Higher ionic strength was unexpectedly able to improve the uptake of either ammonium or phosphate upon biochar; 6) Higher temperature can enhance the adsorption uptake of either ammonium or phosphate upon biochar, which indicated that this adsorption process was spontaneous and endothermic; 7) A stronger phosphate peak appeared and thin and stick-shaped particles were observed on the whole range of post-adsorption samples compared to that on pre-adsorption samples, using SEM-EDX to scan biochar surfaces. Although the nitrogen peak was hard to detect due to its light weight, indeed, it was found existing on mesh lattice particles, which also hinted there was precipitate formation during the adsorption process of ammonium upon bamboo biochar. In brief, this study clearly has verified that biochar can be as an effective adsorbent for ammonium and phosphate removal from simulated wastewaters. Secondly, this study systematically has demonstrated the adsorption characteristics and mechanisms between hydrous biochar and ammonium/phosphate. Thirdly, the results implicate that sustainable fertilizer can be synthesized through an adsorption pathway between hydrous biochar and ammonium/phosphate.
Piranha solution, also known as piranha etch, a mixture of sulfuric acid and hydrogen peroxide, is particularly used to clean sintered glassware in semiconductor manufacturing. Unlike chromic acid solutions, piranha can clean many organic residues without damaging and contaminating glassware. However, much attention has been paid to how to reduce sulfuric consumption and how to reclaim waste sulfuric acid produced in the cleaning process because sulfuric acid is not only extremely valuable but also a troublesome contaminant if it released to the environment. To recycle and purify sulfuric acid, hydrogen peroxide needs to be removed from the mixture. As a renewable resource, Biochar, an electron donor, has potential to reduce the oxidizing agency of hydrogen peroxide. A major aim of this work was to investigate whether biochar can remove hydrogen peroxide from simulated waste acid and learn the reaction mechanisms.
Batch experiments on the removal of hydrogen peroxide by biochar from the simulated industrial waste are studied in detail in chapter 4. The results were: 1) Hydrous biochar with smaller scaled particles can accelerate the removal efficiency of hydrogen peroxide from the mixtures; 2) Greater amounts of hydrous biochar more readily remove hydrogen peroxide from the mixtures; 3) pH can obviously affect the removal effectiveness of hydrogen peroxide, and pH values higher than 6.0 can completely remove hydrogen peroxide from the mixtures within four hours; 4) Higher temperature can enhance removal of hydrogen peroxide from the mixtures, and temperature in the range from 30 °C to 40 °C facilitates total removal of 10–2 M hydrogen peroxide on 193-µm biochar in less than four hours. (Abstract shortened by ProQuest.)
