Adsorption of BiOBr microspheres to rhodamine B and its influence on photocatalytic reaction.

Adsorption and its influence are often neglected during photocatalytic degradation of organic pollutants. To call attention to these issues, a novel bismuth oxybromide (BiOBr) microsphere with hierarchical flower-like structure was fabricated through a facile hydrothermal process using polyvinyl pyrrolidone (PVP) as additive in this work, and then the adsorption of the BiOBr microspheres to RhB and its influence on the photocatalytic degradation of RhB were investigated in detail. Experimental results show that the BiOBr microspheres have a very strong adsorption capacity to RhB. The adsorption behavior follows the Langmuir model and the quasi second order kinetic equation. Tests of the photocatalytic degradation of RhB under visible irradiation verify that the adsorption of the BiOBr microspheres to RhB greatly boosts the degradation of RhB due to the "enriching effect", and a complete degradation of 20 mg L-1 RhB only requires 37 min.

Acute impact of Hg2+, Cu2+, and Ag+ on the formation of biopolymers and nitrogenous soluble microbiological products in activated sludge for wastewater treatment.

In the present work, acute impact of heavy metals on activated sludge was investigated, specifically the release of biopolymers and nitrogenous soluble microbiological products (N-SMP) that significantly impact tertiary effluent quality. Based on the previously reported studies, Hg2+ and Ag+ were selected as representative "non-essential" heavy metals, while Cu2+ was selected as the "essential" heavy metal. Stress tests show that under the present experimental conditions, adding a higher concentration of heavy metals to the activated sludge increases the concentration of biopolymers and SMP in the supernatant; N-SMP increased more significantly than carbonaceous products, implying a greater risk of formation of toxic nitrogenous disinfection by-products or membrane fouling in relevant tertiary treatment processes. The severity of the release of SMP into the supernatant depended on the heavy metal, with an order of Hg2+ > Ag+ > Cu2+ ("non-essential" > "essential") under identical molar concentrations. The mass balance of typical organics (e.g., biopolymers) in SMP and extracellular polymeric substances (EPS) in activated sludge was analyzed, and a negative correlation between the organics in the SMP and tightly bound EPS was observed, implying that a significant fraction of the SMP could be quickly released from the tightly bound EPS under heavy metal shock conditions and could be related to cell response or damage.