Review of experimental biodegradation data on pharmaceuticals and comparison with predictive BIOWIN models.

In this study the experimental data on the biodegradation of 16 pharmaceuticals in activated sludge were reviewed and also the theoretical biodegradation of these pharmaceuticals was calculated using BIOWIN models. The main aim was to show the similarities or discrepancies between the two. Experimental data were critically reviewed considering biodegradation rates, biodegradation mechanisms and biosorption of pharmaceuticals. For some pharmaceuticals, theoretical BIOWIN estimations and experimental findings deviated from each other. For example, if only BIOWIN estimations are considered, clarithromycin, azithromycin and ofloxacin would be defined as refractory. However, in experimental studies, they appeared to be not completely refractory. One of the reasons is that in most cases pharmaceuticals could be used as secondary substrates in the presence of sufficient bulk organic matter. In addition, all experimental studies indicate that at long Solids Retention Times (SRTs), nitrification activity becomes enhanced and the enzyme AMO leads to the cometabolic elimination of many pharmaceuticals. BIOWIN models prove to be very helpful for having an initial idea about biodegradability of pharmaceuticals. However, in order to estimate the biodegradability under real conditions, the models can be extended to include the different removal mechanisms reported in this study.

Exposure of activated sludge to nanosilver and silver ion: Inhibitory effects and binding to the fractions of extracellular polymeric substances.

The main aim of the study was to determine the inhibitory effects of Ag(+) and AgNP (commercial and synthesized) on activated sludge by using respirometry. Along with this aim, also the changes taking place in extracellular polymeric substances (EPS) were studied. Additionally, the binding of Ag(+) or AgNP to the different fractions in EPS was assessed using voltammetry. Synthesized AgNP led to an obvious inhibition whereas commercial AgNP had no effect on activated sludge. For Ag(+) and AgNP, IC50 values were found between 2.3-3.0mg/L and 3.2-11.1mg/L, respectively. Thus, AgNP was less inhibitory than silver ion, since the release of free silver from AgNP was very small. The protein and carbohydrate content of EPS generally increased when Ag(+) was added. Both tightly- and loosely bound fractions in EPS could bind Ag(+) and AgNP. Silver binding capacity of EPS was seen to depend on the molecular weight of proteins.

Extracellular polymeric substances (EPS) and surface properties of activated sludges: effect of organic carbon sources.

The study aims to clarify how the type of organic substrate in a wastewater affects the production and composition of extracellular polymeric substances (EPS) and hydrophobicity and surface charge of activated sludges. For this purpose, three activated sludge reactors were operated in parallel with feeds composed of the organics (i) peptone, glucose, and acetate and (ii) peptone and (iii) glucose. EPS extracted from sludges were fractionated into very loosely bound, loosely bound, and tightly bound fractions and analyzed for protein and polysaccharide. Also, molecular weight distribution of proteins was determined by using high-pressure size exclusion chromatography (HPSEC). Regardless of the type of organic substrate, in each sludge, tightly bound EPS (TB-EPS) prevailed. The type of organic substrate affected the relative proportion of protein and polysaccharide and had an impact on hydrophobicity and surface charge. The sludge fed with peptone was distinctly more hydrophobic and had a lower negative surface charge than others. HPSEC fingerprints revealed that the variety and size of proteins were dependent on the type of feed. HPSEC also pointed to a shift of high molecular weight (MW) proteins from TB-EPS to others. In addition, results of a parallel study examining the inhibitory effect of Ag(+) on three sludges were interpreted along with feed composition, EPS, and surface measurements. The response of each sludge to toxic Ag(+) ion seemed to change with the type of feed.

Inhibition of respiration and distribution of Cd, Pb, Hg, Ag and Cr species in a nitrifying sludge.

The study investigated the inhibitory effects of the heavy metals Cd, Pb, Hg, Ag and Cr (as Cr(3+) and Cr(6+)) on a nitrifying sludge. The aim was to assess the IC(50) concentrations leading to 50% inhibition. The method is based on respiration of nitrifying sludge in the presence of these metals. Both O(2) consumption and CO(2) production were taken into account. The order of the inhibitory effect was Ag>Hg>Cd>Cr(3+)=Cr(6+). Metal speciation was calculated in terms of free metal, inorganic metal complexes and bound metal. Pb largely precipitated and 50% inhibition was never reached. Ag was always in the form of the free ion or labile complexes. Hg had apparently a lower toxicity than Ag, since most of it was initially highly complexed with ammonia. Cd was present in the form of free ion and complexes which caused inhibition although a large part of them were precipitated. The inhibitory effects of trivalent chromium (Cr(3+)) and hexavalent chromium (Cr(6+)) were similar. The latter was present in the form of the anion CrO(4)(2-) and was not taken up by biomass. The study highlighted that IC(50) values alone do not have an explanatory power of inhibition unless speciation is also considered.

Adsorption and cometabolic bioregeneration in activated carbon treatment of 2-nitrophenol.

The extent of cometabolic bioregeneration of activated carbons loaded with 2-nitrophenol was investigated in lab-scale batch activated sludge reactors. Bioregeneration was quantified by measuring the deterioration in adsorption capacity of a fresh activated carbon after a pre-loading and a subsequent bioregeneration sequence. Activated carbons loaded with 2-nitrophenol could be partially bioregenerated cometabolically in the presence of phenol as the growth substrate. The occurrence of exoenzymatic bioregeneration was also possible during cometabolic bioregeneration of thermally activated carbon. However, cometabolic bioregeneration of chemically activated carbon was higher in accordance with higher desorbability. Rather than biodegradation, desorption was the rate-limiting step in bi-solute bioregeneration of phenol and 2-nitrophenol. The absence of oxidative coupling reactions leads to sufficient reversible adsorption, which eventually makes 2-nitrophenol an ideal compound in terms of bioregenerability.

Cometabolic bioregeneration of activated carbons loaded with 2-chlorophenol.

Thermally and chemically activated carbons were used to investigate the extent of cometabolic bioregeneration in laboratory scale activated sludge reactors. Bioregeneration was determined and quantified by measuring the substrate and chloride concentrations, oxygen uptake rates, and deterioration in adsorption capacities. Activated carbons loaded with 2-chlorophenol could be partially bioregenerated in the presence of phenol as the growth substrate. The occurrence of exoenzymatic bioregeneration was also possible during cometabolic bioregeneration of thermally activated carbons. However, cometabolic bioregeneration of chemically activated carbons was much superior compared with thermally activated carbons. In cometabolic bioregeneration of activated carbons loaded with 2-chlorophenol, biodegradation, rather than desorption, was the rate-limiting step. Environmental Scanning Electron Microscopy analyses showed that groups of cocci-shaped phenol-oxidizers were attached to the outer surface or internal cavities of activated carbon as a fingerprint of bioregeneration.

Effect of continuous Cd feeding on the performance of a nitrification reactor.

The inhibitory effect of Cd on nitrification was investigated in a continuous-flow system with enriched nitrifying bacteria. The maximum specific ammonium utilization rate and the half-saturation constant were found as 671 mg NH(4)-N/g VSS day and 0.48 mg/l, respectively. In the case of continuous Cd input at 1 and 2.5 mg/l, nitrification was inhibited by 30% and 47%, respectively. Inhibition ranged from 20% to 40% and no further increase in inhibition was exhibited in new runs except at 10 mg/l influent Cd. At 10 mg/l influent Cd, specific ammonium utilization and nitrate production rates were inhibited by 90%. On the contrary, a serious nitrite accumulation was not observed during this period. When Cd feeding was stopped, recovery from inhibition was observed after 37 day which was seen by the improvement in ammonium utilization and nitrate production rates. A shift in microbial population from the initial Nitrosomonas sp. to the Cd-tolerant Nitrosospira sp. was observed in the recovery period from severe Cd inhibition. After the domination of Nitrosospira species, redosing at 10 mg/l and then at 15 mg/l did not affect the performance as before.

Monitoring of population shifts in an enriched nitrifying system under gradually increased cadmium loading.

The changes in nitrifying bacterial population under cadmium loading were monitored and evaluated in a laboratory scale continuous-flow enriched nitrification system. For this purpose, the following molecular microbiological methods were used: slot-blot hybridization, denaturing gradient gel electrophoresis (DGGE), real-time PCR followed by melting curve analysis, cloning and sequence analysis. The initial cadmium concentration was incrementally increased from 1 to 10mg/l which led to a drop in ammonia removal efficiency from 99 to 10%. Inhibition was recovered when cadmium loading was stopped. During the second application of cadmium, nitrifying population became more tolerant. Even at 15mg/l Cd, only a minor inhibition was observed. To investigate the variations in ammonia and nitrite oxidizing bacteria populations in a period of 483 days, ammonia monooxygenase (amoA) and 16S rRNA genes-based molecular techniques were used. An obvious shift was experienced in the diversity of ammonia oxidizers after the first application of 10mg/l Cd. Metal-tolerant ammonia oxidizing species became dominant and the microbial diversity sharply shifted from Nitrosomonas and Nitrosococcus sp. to Nitrosospira sp. which were observed to tolerate higher cadmium loadings. This result indicated that the extent of nitrification inhibition was not only related to the metal concentration and quantity of microorganisms but also depended on the type of species.

Importance of cadmium speciation in nitrification inhibition.

In this study, the influence of Cd speciation on nitrification inhibition was investigated in batch suspended growth activated sludge systems which contain biomass enriched in terms of nitrifiers. For this purpose, parallel measurements of specific oxygen uptake rates (SOUR), ammonium utilization rates [Formula: see text] and Cd uptake were carried out. Cd speciation was adjusted with a strong complexing agent, ethylenediaminetetraacetic acid (EDTA). Free and biosorbed Cd concentrations were theoretically determined by using the MINEQL+ program and the Cd adsorption constant, whereas labile Cd was determined by voltammetric measurements. The presence of EDTA decreased nitrification inhibition by lowering the available Cd species and by preventing biosorption of Cd. Almost complete recovery from inhibition was attained by EDTA addition to nitrifying bacteria which were inhibited by Cd for a certain time. These results suggested that the sites sensitive to Cd were rather located on the surface of bacterial cell than inside. Nitrification inhibition depended on equilibrium concentrations of free (Cd2+), labile (Cd(volt)) and biosorbed Cd (Cd(volt)) and did not correlate with the total Cd. The measurement of labile metal by voltammetry in inhibition studies is a promising approach since it is easy to apply in practice.

Adsorption, desorption and bioregeneration in the treatment of 2-chlorophenol with activated carbon.

This study aims to clarify the effect of activated carbon type on the extent of adsorbability, desorbability, and bioregenerability in the treatment of 2-chlorophenol. Four different activated carbon types; thermally activated and chemically activated powdered carbons (PAC), and their granular countertypes (GAC) with similar physical characteristics were used. Thermally activated carbons adsorbed 2-chlorophenol much better than chemically activated ones. However, adsorption was more reversible in the case of chemically activated ones. The use of powdered and granular activated carbon countertypes resulted in comparable adsorption and desorption characteristics. For each activated carbon type, 2-chlorophenol exhibited higher adsorbability and lower desorbability than phenol. Biodegradation of 2-chlorophenol took place very slowly when it was used as the sole carbon source in acclimated and non-acclimated activated sludges. Bioregeneration occurred only via desorption due to an initial concentration gradient and no further desorption took place due to low biodegradability. Bioregeneration of activated carbon loaded with 2-chlorophenol was not a suitable option when 2-chlorophenol was the only carbon source. It is suggested to remove 2-chlorophenol via adsorption onto activated carbon rather than applying biological treatment. Also in such cases, the use of thermally activated carbons with higher adsorption and lower desorption capacities is recommended rather than chemically activated carbons.

Kinetic analysis of the inhibitory effect of trichloroethylene (TCE) on nitrification in cometabolic degradation.

In this study, the inhibitory effect of TCE on nitrification process was investigated with an enriched nitrifier culture. TCE was found to be a competitive inhibitor of ammonia oxidation and the inhibition constant (K(I)) was determined as 666-802 microg/l. The TCE affinity for the AMO enzyme was significantly higher than ammonium. The effect of TCE on ammonium utilization was evaluated with linearized plots of Monod equation (e.g., Lineweaver-Burk, Hanes-Woolf and Eadie-Hofstee plots) and non-linear least square regression (NLSR). No significant differences were found among these data evaluation methods in terms of kinetic parameters obtained.

Cometabolic degradation of TCE in enriched nitrifying batch systems.

The aim of this study was to evaluate the effect of the trace pollutant trichloroethylene (TCE) on the nitrification process and to assess its cometabolic degradation. Nitrification was accomplished in batch suspended growth systems containing an enriched nitrifier culture. The presence of TCE resulted in both the inhibition of specific oxygen uptake rate (SOUR) and specific ammonium utilization rate (qNH(4)-N). In both SOUR and qNH(4)-N a 50% decrease was observed in a TCE concentration range of 1000-2000 ppb. TCE was cometabolically degraded by this enriched nitrifier culture. The cometabolic degradation of TCE was found to be dependent on initial TCE concentration. The results may be applicable in the treatment of TCE containing industrial wastewaters and contaminated groundwaters and soils.