Physiologic impact of 2-chlorophenol on denitrification process in mixture with different electron sources.

The aim of this study was to evaluate the physiologic behavior of sludge in the absence and presence of 2-chlorophenol (2-CP) with different electron donors (phenol, glucose, and acetate) during denitrification process. In batch assays with phenol in the presence of 2-CP, a significant decrease of phenol consumption efficiencies (E phenol) up to 99% was observed regarding the cultures without 2-CP. However, in most of the cases, nitrate consumption efficiencies ( E NO 3 - ), and yields of nitrogen gas ( Y N 2 ) and bicarbonate ( Y HCO 3 - ) were high, showing that the denitrifying respiratory process successfully occurred with phenol and 2-CP. The specific consumption rates of nitrate ( q NO 3 - ) and phenol (q phenol) decreased up to 6.0 and 32.3 times, respectively. In assays with glucose in the presence of 2-CP, the denitrifying performance was not significantly altered in terms of efficiencies and product yields; however, q NO 3 - was up to 1.6 times smaller than that obtained without 2-CP whereas q glucose was increased up to 1.17 times. In assays with acetate plus 2-CP, the E NO 3 - , E acetate, and Y N 2 values remained high but 2-CP caused a decrease in Y HCO 3 - . Moreover, q NO 3 - and q acetate increased up to 1.4 and 2.0 times, respectively. These results show that the negative or positive effects of 2-CP on denitrification process depend on the type and concentration of electron source. The obtained physiologic and kinetic information might be useful to define strategies to maintain successful denitrification processes in wastewater treatment bioreactors fed with 2-CP.

Heterogeneous photo-Fenton process using iron-modified regional clays as catalysts: photonic and quantum efficiencies.

A regional raw clay was used as the starting material to prepare iron-pillared clays with different iron contents. The catalytic activity of these materials was tested in the heterogeneous photo-Fenton process, applied to the degradation of 2-chlorophenol chosen as the model pollutant. Different catalyst loads between 0.2 and 1.0 g L-1 and pH values between 3.0 and 7.0 were studied. The local volumetric rate of photon absorption (LVRPA) in the reactor was evaluated solving the radiative transfer equation applying the discrete ordinate method and using the optical properties of the catalyst suspensions. The photonic and quantum efficiencies of the 2-chlorophenol degradation depend on both the catalyst load and the iron content of the catalyst. The higher values for these parameters, 0.080 mol Einstein-1 and 0.152 mol Einstein-1, respectively, were obtained with 1.0 g L-1 of the catalyst with the higher iron content (17.6%). For the mineralization process, photonic and quantum efficiencies depend mainly on the catalyst load. Therefore, it was possible to employ a natural and cheap resource from the region to obtain pillared clay-based catalysts to degrade organic pollutants in water.

Decrease of inhibitory effect of 2-chlorophenol on nitrification in sequencing batch reactors.

The metabolic and kinetic behaviour of a nitrification process in the presence of 2-chlorophenol (2-CP) was evaluated in two sequencing batch reactors (SBR1, SBR2) inoculated with nitrifying sludge previously exposed to phenolic compounds. The SBR1 was inoculated with sludge previously exposed to 2-CP, while the SBR2 was inoculated with sludge previously exposed to p-cresol. An inhibitory effect of 20 mg 2-CP-C/L on both nitrification processes was observed, as specific rates decreased according to a control assay in the absence of 2-CP. However, the inhibitory effect decreased throughout the cycles. At the end of cycle 6, a stable nitrifying process was observed with the sludge previously exposed to 2-CP (SBR1), as an ammonium consumption efficiency and a nitrate production yield close to 99.6 ± 0.3% and 0.99 ± 0.02 were respectively achieved. Despite a complete ammonium consumption being achieved with the sludge previously exposed to p-cresol (SBR2), partial nitrification was observed as nitrate production yield accounted for 0.28 ± 0.08 and nitrite was accumulated within the culture. Nevertheless, both nitrifying sludges had the ability to completely consume 2-CP. The use of SBR systems with nitrifying sludge previously exposed to 2-CP resulted in a better nitrification performance, thus it may be a good alternative for achieving a stable nitrifying respiratory process where complete and simultaneous ammonium and 2-CP consumption can be acquired.

2-Chlorophenol consumption by cometabolism in nitrifying SBR reactors.

Cometabolic consumption of 2-chlorophenol (2-CP) by a nitrifying sludge was evaluated in two SBR reactors fed with 60 mg 2-CP-C/L and different initial ammonium concentrations (100, 200, 300, 400, and 500 mg NH4+-N/L). Irrespectively to the increase in ammonium concentration and throughout the operational cycles, the sludge achieved a complete nitrification in 14 days, accounting for ammonium consumption efficiencies close to 99% and nitrate production yields between 0.93 and 0.99. The sludge was able to completely consume 2-CP within 7 days. The increase in ammonium concentration provoked an increment in the specific rates of both ammonium (qNH4+-N) and 2-CP (q2-CP-C) consumption up to 5.2 and 3.1 times, respectively. The cometabolic effect of the increase in ammonium concentration on 2-CP consumption was supported by a direct and significant relationship between the qNH4+-N and q2-CP-C (r = 0.83). Moreover, batch assays conducted with ammonium, 2-CP, allylthiourea as specific inhibitor of the ammonium monooxygenase (AMO) enzyme, and the sludge inoculated into the reactors, resulted in a decrease of 34% in q2-CP-C, evidencing the participation of the AMO in the consumption of 2-CP. When the same assays were carried out with the sludge obtained from the SBR reactors after 13 operating cycles, a higher participation of the AMO in 2-CP consumption was noticed with a decrease of 53% in q2-CP-C. According to these results, the use of nitrifying sludge and high ammonium concentrations in SBR systems can be a suitable alternative for increasing the cometabolic consumption of recalcitrant compounds like 2-CP.

Bacterial community structure within an activated sludge reactor added with phenolic compounds.

Biodegradation of phenolic compounds in bioreactors is well documented, but the changes in the bacterial populations dynamics during degradation were not that often. A glass bubble column used as reactor was inoculated with activated sludge, spiked with 2-chlorophenol, phenol and m-cresol after 28 days and maintained for an additional 56 days, while the 16S rRNA gene from metagenomic DNA was monitored. Proteobacteria (68.1%) dominated the inoculum, but the bacterial composition changed rapidly. The relative abundance of Bacteroidetes and Firmicutes decreased from 4.8 and 9.4 to <0.1 and 0.2% respectively, while that of Actinobacteria and TM7 increased from 4.8 and 2.0 to 19.2 and 16.1% respectively. Phenol application increased the relative abundance of Proteobacteria to 94.2% (mostly Brevundimonas 17.6%), while that of Bacteroidetes remained low (1.2%) until day 42. It then increased to 47.3% (mostly Leadbetterella 46.9%) at day 84. It was found that addition of phenolic compounds did not affect the relative abundance of the Alphaproteobacteria initially, but it decreased slowly while that of the Bacteroidetes increased towards the end.

Mineralization of 2-chlorophenol by sequential electrochemical reductive dechlorination and biological processes.

In this work, a novel approach was applied to obtain the mineralization of 2-chlorophenol (2-CP) in an electrochemical-biological combined system where an electrocatalytic dehydrogenation process (reductive dechlorination) was coupled to a biological denitrification process. Reductive dechlorination of 2-CP was conducted in an ECCOCEL-type reactor on a Pd-Ni/Ti electrode at a potential of -0.40V vs Ag/AgCl(s)/KCl(sat), achieving 100 percent transformation of 2-CP into phenol. The electrochemically pretreated effluent was fed to a rotating cylinder denitrifying bioreactor where the totality of phenol was mineralized by denitrification, obtaining CO2 and N2 as the end products. The total time required for 2-CP mineralization in the combined electrochemical-biological process was 7.5h. This value is close to those previously reported for electrochemical and advanced oxidation processes but in this case, an efficient process was obtained without accumulation of by-products or generation of excessive energy costs due to the selective electrochemical pretreatment. This study showed that the use of electrochemical reductive pretreatment combined with biological processes could be a promising technology for the removal of recalcitrant molecules, such as chlorophenols, from wastewaters by more efficient, rapid, and environmentally friendly processes.