Transformation and migration of phosphorus in excess sludge reduction pretreatment by alkaline ferrate oxidation combined with anaerobic digestion.

Recently, more and more attention has been paid to the strong oxidation ability of newly prepared potassium ferrate (NAPF) in sludge reduction process, but less attention has been paid to the change of phosphorus in this process. The feasibility of phosphorus migration and transformation during excess sludge reduction pretreatment using NAPF pre-oxidation combined with anaerobic digestion was investigated. After 70 mg/g suspended solids NAPF pretreatment and 16 days anaerobic digestion, the solid-phase volatile suspended solids decreased by 44.2%, and much organic matter had been released into the liquid-phase and then degraded during digestion by indigenous microorganisms. As the sludge pre-oxidation process was performed, solid-phase organic phosphorus and chemically combined phosphorus also released into the liquid-phase as PO43-, peaking at 100 mg/L. During anaerobic digestion, the Fe3+ in the liquid-phase was gradually reduced to Fe2+, and then formed Fe2+-PO43- compound crystals and re-migrated to the solid-phase. The concentration of PO43- decreased to 17.08±1.1 mg/L in the liquid-phase after anaerobic digestion. Finally, the phosphorus in the Fe2+-PO43- compound accounts for 80% of the total phosphorus in the solid-phase. A large number of vivianite crystals in sludge were observed. Therefore, this technology not only effectively reduces sludge, but also increases the proportion of PO43- in the sludge in the form of Vivianite.

[Improved on Nitrogen Removal of Anaerobic Ammonia Oxidation by Coupling Element Sulfur-based Autotrophic Short-cut Denitrification].

In order to enhance the removal of NO3--N in the ANAMMOX process, an element sulfur-based autotrophic short-cut denitrification (short-cut S0-SADN) was introduced by adding elemental sulfur to an ANAMMOX continuous flow reactor. The effects of different influent NH4+-N/NO2--N ratios on the nitrogen conversion and NO2--N competitive characteristics in the coupled system were investigated at (33±2)℃ and a pH of 7.8-8.2. The results showed that under different influent NH4+-N/NO2--N ratios (1:1.3, 1:1.5, 1:1, and 1:1.1), the average total nitrogen (TN) removal efficiency of the coupled system reached 96.78%, 97.21%, 94.68%, and 97.72%, respectively, which were much higher than the highest TN removal efficiency of the ANAMMOX theory (89%). Among them, the stable operation of deep nitrogen removal of the short-cut S0-SADN coupled with ANAMMOX was successfully achieved with an influent NH4+-N/NO2--N ratio of 1:1 or 1:1.1. Under the optimal influent NH4+-N/NO2--N ratio of 1:1.1, the concentrations of influent NH4+-N and NO2--N were 240 mg·L-1 and 265 mg·L-1, respectively, the TN removal rate reached 1.50 kg·(m3·d)-1, and the TN removal efficiency of ANAMMOX and S0-SADN pathways were stable at (95.68±1.22)% and (2.04±0.77)%, respectively. During the entire operational process, ANAMMOX always occupied an absolute advantage in the competition of substrate NO2--N, and the activity of ANAMMOX bacteria (NH4+-N/VSS) was stable at (0.166±0.008)kg·(kg·d)-1.

[Phosphate Adsorption from Water on CaO2-loaded Magnetic Diatomite].

In this study,magnetic diatomite was used as a carrier to load calcium peroxide(CaO2) nanoparticles,fabricating a high efficiency phosphate adsorption and recovery composite material(MDCP).The micromorphology, inner structure,crystalline constituents and element composition of MDCP were characterized by SEM,EDX-mapping,XRD, XDS, and VSM,respectively.The adsorption isotherm data of MDCP exhibited good agreement with the Langmuir isotherm model. According to the Langmuir model,when T=20℃,the maximum monolayer phosphate adsorption capacities can reach 191.84mg·g-1 for MDCP. The isotherm and kinetics studies showed that MDCP has a regulating effect on the pH of the solution,which can maintain the pH of the solution at the level where adsorption of phosphate occurs on MDCP as a chemisorption process. pH plays a important role on the adsorption of phosphate by MDCP,the pH of effective adsorption ranges from 4 to 10,and the pH of the adsorbed solution can still be maintained in the range of 7 to 9.The MDCP exhibited a high selective adsorption for phosphate in the presence of anions,including Cl-, SO42-, CO32-, HCO32-, F-, and NO3-.The recovered MDCP could be desorbed by HCl solution,and after desorption, the phosphate removal rate of MDCP after re-loading CaO2 could still reach 70% of the initial adsorption.