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With the aim to investigate the main pollution characteristics of exhaust gases emitted from plastic waste recycling granulation plants, mainly volatile organic compounds (VOCs), polycyclic aromatic hydrocarbons (PAHs) and phthalate esters (PAEs) were analyzed in Xingtan Town, the largest distribution center of plastic waste recycling in China. Both inside and outside the plants, the total concentrations of volatile monocyclic aromatic hydrocarbons (MAHs), PAHs and PAEs ranged from 2000 to 3000 μg m−3, 450 to 1200 ng m−3, and 200 to 1200 ng m−3, respectively. Their concentration levels inside the plants were higher than those outside the plants, and PAHs and PAEs were mainly distributed in the gas-phase. Notably, highly toxic benzo[a]pyrene (BaP) could be detected inside the plants, and harmful PAEs could be detected not only inside but also outside the plants, although PAEs are non-volatile. The exhaust gas composition and concentration were related to the plastic feedstock and granulation temperature.

Microbial fuel cells (MFCs) represent a new method for simultaneous wastewater treatment and biological electricity generation. In this study, an air-cathode MFC with membrane electrode assembly was operated over four batch cycles (a total period of 140 d) and results indicated that starch processing wastewater containing 4852 mg/l of chemical oxygen demand could be used as substrate to produce electricity with this MFC. Maximum voltage output and power density of 490.8 mV and 239.4 mW/m2 (a current density of 893.3 mA/m2) were approached in the third cycle, which also had the minimum internal resistance of about 120 Ω and maximum coulombic efficiency of 8.0%. Removal efficiencies of chemical oxygen demand and ammonia-nitrogen increased as a function of time, and maximum amounted to 98.0% and 90.6%, respectively. Scanning electron microscope image revealed that short rod shaped bacillus were the dominant bacteria on the biofilm of the anode, whose electrochemical activity was proved by cyclic voltammetry. These results demonstrate that starch processing wastewater can be used for power generation in MFCs and also can be treated with high removal efficiencies of chemical oxygen demand and ammonia-nitrogen.

Bioleaching of Cr(III) from tannery sludge using the mixture of ingenuous iron-and sulfur-oxidizing bacteria was investigated in batch flasks. Experiments involved the adaptation of indigenous iron- and sulfur-oxidizing bacteria, the pre-acidification the sludge to pH 6.0 and the addition of energy substrates. Results showed the inoculation of mixture of ingenuous iron- and sulfur-oxidizing bacteria and co-addition of Fe2+ and elemental sulfur accelerated acid production and increase of oxidation-reduction potential originating from the bio-oxidation of Fe2+ and elemental sulfur. Dissolved Cr concentration increased concomitant with pH decreased in the sludge and reached its maximum removal of 95.6%. The amelioration of the odor of bioleached sludge could be noted. However, 20.4% of N, 24.5% of P and 14.3% of organic matter were lost in the bioleaching process. The residual Cr content in the leached tannery sludge was acceptable for use in agriculture. This study had shown the feasibility of applying the bioleaching process, developed for sewage sludge, to tannery sludge with high Cr.