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This paper investigates biological denitrification using autotrophic microorganisms that use elemental sulfur as an electron donor. In this process, for each gram of nitrate-nitrogen removed, approximately 4.5 g of alkalinity (as calcium carbonate) are consumed. Because denitrification is severely inhibited below pH 5.5, and alkalinity present in the influent wastewaters is less than the alkalinity consumed, an external buffer was needed to arrest any drop in pH from alkalinity consumption. A packed-bed bioreactor configuration is ideally suited to handle variations in flow and nitrate loading from decentralized wastewater treatment systems, as it is a passive system and thus requires minimal maintenance; therefore, a solid-phase buffer packed with the elemental sulfur in the bioreactor is most suitable. In this research, marble chips, limestone, and crushed oyster shells were tested as solid-phase buffers. Bench- and field-scale studies indicated that crushed oyster shell was the most suitable buffer based on (1) the rate of dissolution of buffer and the buffering agent released (carbonate, bicarbonate, or hydroxide), (2) the ability of the buffer surface to act as host for microbial attachment, (3) turbidity of the solution upon release of the buffering agent, and (4) economics. 相似文献
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Sukalyan Sengupta Sarina J. Ergas Erika Lopez-Luna Asish K. Sahu Kumaravel Palaniswamy 《Water, Air, & Soil Pollution: Focus》2006,6(1-2):111-126
The overall objective of this research was to develop a reliable, robust, and maintenance-free passive system for biological
denitrification in on-site wastewater treatment systems. The process relies on sulfur oxidizing denitrifying bacteria in upflow
packed bioreactors. Since this process consumes alkalinity, it is necessary to add a solid-phase buffer that can scavenge
the H+ as it is generated by the biologically-mediated reaction and arrest the drop in the pH value. This study investigated the
use of limestone, marble chips and crushed oyster shell as solid-phase buffers that provide alkalinity.
Two bench-scale upflow column reactors and two field-scale bioreactors were constructed and packed with sulfur pellets and
an alkalinity source. The pilot scale bioreactors (∼200 L each) were installed at the Massachusetts Alternative Septic System
Test Center (MASSTC) in Sandwich, MA. The pilot-scale bioreactors performed better when oyster shell was used as the solid-phase
buffer vis-à-vis marble chips. In both (pilot-scale and laboratory-scale) systems, denitrification rates were high with the
effluent NO3
− —N concentration consistently below 8 mg/L. 相似文献
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Many silver(Ag)containing consumer-products(e.g.textiles)release Ag into the environment,posing ecotoxicological risks.Ag recovery mitigates environmental hazards,recycles Ag,and leads to sustainability.In the present work,Ag has been recovered as Ag~0nanoparticles from the spent solution(thiourea(TU)~0.5 mol/L pH~1.1–1.2,and Ag~550 mg/L)obtained from the regeneration of an Ag-loaded resin using a simple undivided electrolytic cell.The reclaimed regenerant solution has been recycled and reused in a closed-loop scheme over multiple cycles.The process parameters,i.e.,current(0.05 A)and stirring speed(600 r/min),have been optimized for Ag recovery of~94%and TU loss of~2%.The reclaimed regenerant solution has been shown to regenerate Ag-loaded resin samples with90%regeneration efficiency over 4 cycles of consecutive extraction and regeneration.The recovered Ag~0nanoparticles are monodisperse,consistently spherical in shape,and have a mean diameter of~6 nm with standard deviation of the Gaussian fit as~2.66 nm. 相似文献
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