The inhibitory effects of heavy metals and organic compounds on the net maximum specific growth rate of the autotrophic biomass in activated sludge

Estimating the combined effects of copper and phenol to nitrifying bacteria in wastewater treatment plants

The inhibition of nitrification by phenol and copper mixtures was studied to investigate the differences between individual and mixture inhibition as the change of phenol and copper speciation due to their reactions. This study showed a decrease in the ammonium removal rate (k, first-order rate coefficient), indicating an increase in the relative % inhibition on nitrification, as the phenol and mixed liquor suspended solids (MLSS) concentrations were increased. In the case of copper, the ammonium removal rate decreased as the copper concentration increased and that of the MLSS decreased. This was attributed to the enhanced sorption of copper to heterotrophs at high MLSS concentrations. The relative % inhibition was plotted against free Cu2+ ions, which showed a close relationship. In the tests on copper and phenol mixtures, the mixture effects turned out overestimated by the calculation based on the additional chemical concentrations. In most Cu-phenol mixture tests, the presence of phenol as a complexation ligand caused a reduction of the inhibition rate to nitrifiers over the entire exposure range. Consequently, the prediction of nitrification inhibition in mixture environments, such as wastewater treatment plants, is influenced by the presence of a number of parameters that affect the activity of nitrifiers and, therefore, chemical speciation should be taken into consideration.

Performance evaluation of pilot scale sulfur-oxidizing denitrification for treatment of metal plating wastewater

A full-scale and two pilot-scale upflow sulfur-oxidizing denitrification (SOD) columns were evaluated using metal plating wastewater as feed. The sludge was autotrophically enriched, and inoculated in the SOD columns attached to the effluent line of three metal plating wastewater treatment facilities. The effects of activated carbon and aeration were also studied, and found effective for the removal of suspended solids and ammonia, respectively. The results showed that the constituents, such as the total nitrogen, nitrates, nitrites, ammonia, chemical oxygen demand (COD), and heavy metals, were effectively removed. The pH was observed to be maintained at 7-8 due to the alkalinity supplied by the sulfur-calcium carbonate (SC) pellet. The denitrification efficiency and start-up period were observed to be affected by the influent quality. Chromium, iron, nickel, copper, and zinc--the major heavy metal components of the influent--were effectively reduced at certain concentrations. Other metal ions were also detected and reduced to undetectable concentrations, but no trends in the comparison with denitrification were observed. From the results it can be concluded that SOD is effective for the removal of nitrogen, particularly nitrates, without a drastic pH change, and can effectively remove minute concentrations of heavy metals and COD in metal plating wastewaters.

Assessing wastewater toxicity to activated sludge: recent research and developments

Toxicants in municipal sewage treatment plant (STP) influent wastewater may inhibit the biological activity of the activated sludge and cause treatment plant process upsets. Such process upsets may be avoided if influent wastewater is monitored for toxicity and protective actions are taken when toxicity is detected. A comprehensive review of the methods that can be used for assessing wastewater toxicity to biological treatment systems was conducted several years ago and the resultant report was published in 2000 by Water Environment Research Foundation (WERF). The WERF report also specified the criteria for influent wastewater toxicity monitoring methods and suggested research needs to be addressed. A significant amount of effort was made since the publication of the WERF report to develop new assays or devices and to improve existing ones. In this manuscript, recent research and developments in methods for assessing wastewater toxicity to activated sludge were reviewed. The literature indicates that bioluminescence- and respirometry-based methods received much attention in recent research. A comparison of the new/improved methods with the criteria described in the WERF report reveals that none of these methods has been shown to meet all the specified criteria. The present review also indicates that research efforts since 2000 have not fully taken into account the criteria for influent wastewater toxicity monitoring methods and have not addressed the research needs proposed in the WERF report.