Nitrate and nitrite reduction by adsorbed Fe(II) generated from ligand-promoted dissolution of biogenic iron minerals in groundwater.

Chemical denitrification by redox-active Fe(II) species is pivotal in the coupled iron and nitrogen cycles. The reductive dissolution of ferric minerals by ligand can generate Fe(II)-ligand complexes, but their reducing capability for electrophilic pollutants like nitrate and nitrite remains uncertain. Here, biogenic secondary iron minerals (SIM) after dissimilatory iron reduction were reductively dissolved by oxalate and the siderophore desferrioxamine B, and subsequently the partially-dissolved SIM (SIMD) effectively removed NO2- from groundwater via reduction, while exhibiting much lower reactivity towards NO3-. The dissolution and removal processes were well-fitted with the Kabai model and the pseudo-second-order adsorption model, respectively. The equilibrium NO2- removal capacity (qe) of SIMD reached 0.146-0.223 mmol/g, accompanied with the rate constants as 0.433-0.810 g/(mmol·h). The emission of N2O and NO verified the occurrence of chemical denitrification during NO2- removal by SIMD. From the perspective of Fe(II) reactivity, SIMD exhibited higher densities of surface Fe(II) and more negative Eh values than SIM, and these two indicators showed linear correlations with the removal rates. Combined with microscopic, electrochemical and spectral analysis, our results indicated the redox reaction of adsorbed Fe(II)-complexes with NO2- on SIMD surface. The concurrent substance biochar was also considered, as it indirectly influenced dissolution and pollutant removal by shifting the iron mineral phase in SIM from magnetite to goethite. These findings highlight the significant role of reductive dissolution of iron mineral in N transformation, expand the electron pool available to support chemical denitrification, and have implications for Fe and N cycling coupling with pollutant reduction.

Coupling of polyhydroxybutyrate and zero-valent iron for enhanced treatment of nitrate pollution within the Permeable Reactive Barrier and its downgradient aquifer.

Permeable Reactive Barriers (PRBs) have been utilized for mitigating nitrate pollution in groundwater systems through the use of solid carbon and iron fillers that release diverse nutrients to enhance denitrification efficiency. We conduct laboratory column tests to evaluate the effectiveness of PRBs in remediating nitrate pollution both within the PRB and in the downgradient aquifer. We use an iron-carbon hydrogel (ICH) as PRB filler, which has different weight ratios of polyhydroxybutyrate (PHB) and microscale zero-valent iron (mZVI). Results reveal that denitrification in the downgradient aquifer accounts for at least 19.5 % to 32.5 % of the total nitrate removal. In the ICH, a higher ratio of PHB to mZVI leads to higher contribution of the downgradient aquifer to nitrate removal, while a lower ratio results in smaller contribution. Microbial community analysis further reveals that heterotrophic and mixotrophic bacteria dominate in the downgradient aquifer of the PRB, and their relative abundance increases with a higher ratio of PHB to mZVI in the ICH. Within the PRB, autotrophic and iron-reducing bacteria are more prevalent, and their abundance increases as the ratio of PHB to mZVI in the ICH decreases. These findings emphasize the downgradient aquifer's substantial role in nitrate removal, particularly driven by dissolved organic carbon provided by PHB. This research holds significant implications for nutrient waste management, including the prevention of secondary pollution, and the development of cost-effective PRBs.

[Sacrococcygeal gap injection for the treatment of failed back surgery syndrome].

OBJECTIVE: To explore the clinical effect of the sacrococcygeal space injection for the treatment of failed back surgery syndrome. METHODS: From July 1998 to October 2012,47 patients with failed back surgery syndrome were treated and included 39 males and 8 females with an average age of 61.5 years old ranging from 35 to 89 years old. Among them,41 patients experienced one time of operation, 6 patients with twice of operation. Forty-one patients underwent single,bilateral fenestration or central laminectomy decompression, discectomy. Six patients underwent total laminectomy discectomy and inter body fusion and pedicle screw fixation. All patients were examined by X-ray plain film, CT or MRI before treatment. The anticoagulation was discontinuation before treatment. The needle was put into the sacrococcygeal gap at prone position in the sense of frustration,suction without cerebrospinal fluid and blood,with injection of Mailuoning (Chinese characters: see text) 15 ml. The pain was assessed by VAS before and after treatment. The Oswestry low back pain disability index and survival quality interference degree were evaluated. RESULTS: At 1 month after treatment,the pain VAS decreased from 59.24 +/- 17.35 before treatment to 19.19 +/- 11.19 after treatment (P < 0.05); The Oswestry low back pain disability index decreased from (41.35 +/- 9.87)% before treatment to (23.17 +/- 17.56)% after treatment (P < 0.05); The survival quality interference degree decreased from 6.5 +/- 2.2 before treatment to 2.6 +/- 1.4 after treatment (P < 0.05). CONCLUSION: The sacrococcygeal gap injection for treatment of failed back surgery syndrome has advantages of simple, safe, fewer complications, and low treatment cost.