Biological Denitrification of High Nitrate Processing Wastewaters from Explosives Production Plant

Wastewater samples originating from an explosives production plant (3,000 mg N l−1 nitrate, 4.8 mg l−1 nitroglycerin, 1.9 mg l−1 nitroglycol and 1,200 mg l−1 chemical oxygen demand) were subjected to biological purification. An attempt to completely remove nitrate and to decrease the chemical oxygen demand was carried out under anaerobic conditions. A soil isolated microbial consortium capable of biodegrading various organic compounds and reduce nitrate to atmospheric nitrogen under anaerobic conditions was used. Complete removal of nitrates with simultaneous elimination of nitroglycerin and ethylene glycol dinitrate (nitroglycol) was achieved as a result of the conducted research. Specific nitrate reduction rate was estimated at 12.3 mg N g−1 VSS h−1. Toxicity of wastewater samples during the denitrification process was studied by measuring the activity of dehydrogenases in the activated sludge. Mutagenicity was determined by employing the Ames test. The maximum mutagenic activity did not exceed 0.5. The obtained results suggest that the studied wastewater samples did not exhibit mutagenic properties

Speciation and sorption structure of diphenylarsinic acid in soil clay mineral fractions using sequential extraction and EXAFS spectroscopy

Purpose The mobility of arsenic (As) in soils is fundamentally affected by the clay mineral fraction and its composition. Diphenylarsinic acid (DPAA) is an organoarsenic contaminant derived from chemical warfare agents. Understanding how DPAA interacts with soil clay mineral fractions will enhance understanding of the mobility and transformation of DPAA in the soil-water environment. The objective of this study was to investigate the speciation and sorption structure of DPAA in the clay mineral fractions. Materials and methods Twelve soils were collected from nine Chinese cities which known as chemical weapons burial sites and artificially contaminated with DPAA. A sequential extraction procedure (SEP) was employed to elucidate the speciation of DPAA in the clay mineral fractions of soils. Pearson's correlation analysis was used to derive the relationship between DPAA sorption and the selected physicochemical properties of the clay mineral fractions. Extended X-ray absorption fine structure (EXAFS) L-III-edge As was measured using the beamline BL14W1 at Shanghai Synchrotron Radiation Facility (SSRF) to identify the coordination environment of DPAA in clay mineral fractions. Results and discussion The SEP results showed that DPAA predominantly existed as specifically fraction (18.3-52.8%). A considerable amount of DPAA was also released from non-specifically fraction (8.2-46.7%) and the dissolution of amorphous, poorly crystalline, and well-crystallized Fe/Al (hydr)oxides (20.1-46.2%). A combination of Pearson's correlation analysis and SEP study demonstrated that amorphous and poorly crystalline Fe (hydr)oxides contributed most to DPAA sorption in the clay mineral fractions of soils. The EXAFS results further demonstrated that DPAA formed inner-sphere complexes on Fe (hydr)oxides, with As-Fe distances of 3.18-3.25 angstrom. It is likely that the steric hindrance caused by phenyl substitution and hence the instability of DPAA/Fe complexes explain why a substantial amount of DPAA presented as weakly bound forms. Conclusions DPAA in clay mineral fractions predominantly existed as specifically, amorphous, poorly crystalline, and crystallized Fe/Al (hydr)oxides associated fractions. Amorphous/poorly crystalline Fe rather than total Fe contributed more to DPAA sorption and DPAA formed inner-sphere complexes on Fe (hydr)oxides