| Eutrophication has become the major environmental problem throughout the world. Phosphorus is a fundamental factor that restricts eutrophication, and it is difficult to remove from wastewater. Therefore, phosphorus removal from wastewater is an important means to prevent eutrophication. It’s a very important and pressing task to develop efficient and affordable methods to prevent and control phosphorus pollution.Activated sludge-based technology is widely used in urban wastewater treatment; it can remove organic pollutants effectively, purify water and reduce content of pollutants in water. However, its capability for removal of nitrogen and phosphorus needs to be improved. The inner part of the constructed wetland system is in the anaerobic state, anaerobic denitrification improved the removal of nitrogen, and wetland substrate is beneficial to phosphorus removal. Therefore, combination of activated sludge-based technology and the constructed wetland system could strengthen the purification of sewage capacity; it is also a promising technology for urban sewage treatment in our country.Phosphorus removal can be reached by adsorption through attachment at adsorbent surface, ion exchange or surface precipitation on the large surface area provided by adsorbent. Adsorption promises low investment and high treatment efficiency, and is suitable for the removal of phosphorus from wastewater. In this study, we are focused on the removal of phosphorus in wastewater; the main contents are as follows:1. The removal efficiency of phosphorus was analyzed in the pre-activated sludge and constructed wetland hybrid system, and the major factors affecting phosphorus removal was also discussed.2. The possibility of the biologically originated iron oxide from the vertical subsurface flow constructed wetlands was used as adsorbent for phosphorus removal was investigated. The iron oxide adsorbent was characterized by XRD, SEM and FT-IR. Various factors affecting the phosphorus removal, such as initial phosphorus concentration, adsorbent dosage, pH and temperature, were investigated in detail. In addition, the adsorption kinetics and adsorption isotherms were also used to study the adsorption mechanism of the biological iron oxides for phosphorus removal.3. The Fe3O4nanoparticles used as adsorbent for phosphorus removal were investigated, and effects of various factors were also analyzed. Meanwhile, the adsorption kinetics and adsorption isotherms of Fe3O4on phosphorus were investigated.On basis of the above analysis, the major results are as follows:1. The pre-activated sludge and constructed wetland hybrid system can removal some of phosphorus, but the removal efficiency of phosphorus is not obvious. Therefore, looking for and developing a better adsorbent for phosphorus removal is a key challenge to improve the system performance for phosphorus removal. Statistical analysis suggested that conductivity caused significant effect on phosphorus removal.2. The biologically originated iron oxide is a biological material. Compared with other reported iron-based adsorbent for phosphorus adsorption, the biological iron oxide has good adsorption ability. The phosphate adsorption rate is fast in the first3h, and reaches the adsorption equilibrium at5h. The adsorption process was good fitted to quasi-two-order dynamics and Langmuir isotherm equation. The acidity pH value was beneficial to the phosphate adsorption. With the increasing of temperature, the maximum phosphate adsorption capacity increased from9.40mg/g to14.08mg/g.3. The phosphorus removal with Fe3O4nanoparticles as adsorbent materials increased with the increase of contact and reached adsorption equilibrium at5h. This suggested that FeaO4nanoparticles can be used for phosphorus-containing wastewater. Additionally, with their special magnetic properties and rapid solid liquid separation, Fe3O4nanoparticles have great potential application in the phosphorus removal from wastewater. |
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