Intermittent aeration strategy for azo dye biodegradation: A suitable alternative to conventional biological treatments?

Most solutions for biological treatment of azo dyes are based on conventional anaerobic-aerobic processes, but transition to full scale demands technology simplification and cost reductions. We suggest a new approach, in which aeration is intermittently supplied for simultaneous removal of color and toxic metabolites in a single compartment. Effects of aeration strategy and glucose concentration on decolorization and organic matter removal were assessed using factorial design (32) and response surface analysis. Bioreactors were inoculated with microorganisms previously acclimated to Direct Black 22 (DB22), which was the azo compound used in this study. Assays performed with synthetic textile wastewater showed that long-term decolorization was not impaired at a moderate level of aeration (4 hourly-cycles per day). Aerated batches presented lower color removal velocities, but these negative impacts were offset by increasing initial glucose concentration. Higher degrees of mineralization of the azo compound and higher organic matter removals were achieved in intermittently aerated experiments, which led to lower toxicity to Daphnia magna. Biomolecular analysis revealed that the microbial community structure was strongly associated with operational efficiency parameters. These findings suggest intermittent aeration can be implemented to accomplish enhanced azo dye biodegradation.

Carbon-nitrogen removal in a structured-bed reactor (SBRRIA) treating sewage: Operating conditions and metabolic perspectives.

The present study evaluated the efficiency of a structured-bed reactor subjected to recirculation and intermittent aeration (SBRRIA) to promote nitrogen and carbon removal from domestic sewage. The intermittent aeration and the recycling rate of 3 keeps the desired mixing degree inside the SBRRIA. Four different operational conditions were tested by varying the hydraulic retention time (HRT) from 12 to 8 h and aerated and non-aerated periods (A/NA) from 2 h/1 h and 3 h/1 h. At the THD of 8 h and A/NA of 2 h/1 h there was a decrease in the nitrification process (77.5%) due to the increase of organic matter availability, affecting the total-N removal performance. However, by increasing the aerated period from 2 h to 3 h, the nitrification efficiency rose to 91.1%, reaching a total-N removal efficiency of 79%. The system reached a maximum total-N loading removed of 0.117 kgN.m-3.d-1 by applying an HRT of 8 h and an intermittent aeration cycle of 3 h, aerated and 1 h non-aerated. The simultaneous nitrification and denitrification (SND) process was related to a complex interplay among microorganisms affiliated mostly to Acidovorax sp., Comamonas sp., Dechloromonas sp., Hydrogenophaga sp., Mycobacterium sp., Rhodobacter sp., and Steroidobacter sp.

Influence of COD/N ratio and carbon source on nitrogen removal in a structured-bed reactor subjected to recirculation and intermittent aeration (SBRRIA).

This study aimed to evaluate the influence of COD/N ratio and carbon source on simultaneous nitrogen and carbon removal processes. A continuous up-flow structured-bed reactor subjected to recirculation and intermittent aeration (SBRRIA) was operated with hydraulic retention time (HRT) of 11.2 ± 0.6 h. The carbon sources were meat peptone and sucrose. The COD/N ratio varied by maintaining the organic loading rate fixed at 1.07 kg COD m(-3) d(-1) and changing the total-N concentration. The COD/N ratios tested were 9.7 ± 1 (sucrose); 7.6 ± 1 (meat peptone); 2.9 ± 1 (meat peptone) and 2.9 ± 0.4 (sucrose). COD removal efficiencies remained above 90% in all experimental phases. At lower COD/N ratios, NH4(+)-N oxidation efficiencies were higher than 90%. An autotrophic metabolism by anammox process was observed in Phases III and IV, which was responsible for 35% and 27% of total-N loading removal rates, respectively. Therefore, the system achieved total nitrogen removal efficiencies of 84.6 ± 10.1 and 81.5 ± 5.3%, under low availability of organic electron donors.

Nitrogen and carbon removal from synthetic wastewater in a vertical structured-bed reactor under intermittent aeration.

The removal of nitrogen and organic matter using a single reactor has been a common focus of investigation, and reactors operated in batch mode and under intermittent aeration have attracted special attention. This study aimed to evaluate the application of a new reactor configuration consisting of a fixed-bed reactor that was operated under conditions of continuous feeding and intermittent aeration. The reactor was built using acrylic, with a working volume of 6.1L. The fixed bed used for biomass support was composed of polyurethane foam cylinders vertically oriented inside the reaction zone. The reactor was operated under intermittent aeration (2h aerated and 1h non-aerated) and a recirculation ratio Q(r)/Q=5. Three different operating conditions (Phase I, Phase II, and Phase III) corresponding to hydraulic retention times (HRT) of 12h, 8h, and 10h, respectively, were tested. In Phase I, the system achieved total nitrogen (TN) and chemical oxygen demand (COD) removal efficiencies of 82% and 89%, respectively. At HRTs of 8 h and 10 h, the reactor was unstable with respect to TN removal, and the average resultant removal efficiencies were 49% and 45%, respectively. However, COD removal efficiencies remained high with mean values of 85% and 88% for Phases II and III, respectively. Based on these results, it can be concluded that this new reactor configuration constitutes an alternative method for effective removal of organic matter and nitrogen from wastewater.

Performance of a horizontal-flow anaerobic immobilized biomass (HAIB) reactor and dynamics of the microbial community during degradation of pentachlorophenol (PCP).

The anaerobic biological treatment of pentachlorophenol (PCP) and methanol as the main carbon source was investigated in a horizontal-flow anaerobic immobilized biomass (HAIB) reactor at 30+/-1 degrees C, during a 220-day trial period. The reactor biomass was developed as an attached biofilm on polyurethane foam particles, with 24h of hydraulic retention time. The PCP concentrations, which ranged from 2.0 to 13.0 mg/L, were controlled by adding synthetic substrate. The HAIB reactor reduced 97% of COD and removed 99% of PCP. The microbial biofilm communities of the HAIB reactor amended with PCP, without previous acclimatization, were characterized by polymerase chain reaction (PCR) and amplified ribosomal DNA restriction analysis (ARDRA) with specific Archaea oligonucleotide primers. The ARDRA technique provided an adequate analysis of the community, revealing the profile of the selected population along the reactor. The biomass activities in the HAIB reactor at the end of the experiments indicated the development of PCP degraders and the maintenance of the population of methanogenic Archaea, ensuring the high efficiency of the system treating PCP with added methanol as the cosubstrate. The use of the simplified ARDRA method enabled us to monitor the microbial population with the addition of high concentrations of toxic compounds and highlighting a selection of microorganisms in the biofilm.

Granules characteristics in the vertical profile of a full-scale upflow anaerobic sludge blanket reactor treating poultry slaughterhouse wastewater.

The performance and the granules characteristics of a 450 m(3) -UASB reactor operating for 1228 days, treating poultry slaughterhouse wastewater with an average COD reduction of 85% was examined. Granules were sampled in three different positions along the vertical central line of the reactor, revealing variations in the concentration of volatile total solids. Although the reactor had been in operation for an extended period of time, granule sizes of 0.5-1.5 mm appeared to predominate. The hollow core was well defined for granules with sizes ranging from 2 to 3 mm in all the sampling ports. The granules exhibited no layered microbial distribution and were packed with different morphotype cells intertwined randomly throughout the cross-section. Methanogenic Archaea predominated in the granules taken from every sampling port along the reactor. The results indicated that the characterization of the granules is a useful tool for the adoption of operational strategies toward optimization of UASB reactors.

Gas chromatographic methods for monitoring of wastewater chlorophenol degradation in anaerobic reactors.

Wastewater samples from an anaerobic reactor were extracted with hexane and derivatized with diazomethane (method 1) and with acetic anidride (method 2). Gas chromatography with electron-capture detection (ECD) was employed for separating the parent compound and intermediates trichlorophenols (TCP) and dichlorophenols (DCP) which originated from the penta chlorophenol (PCP) degradation process. The relations between concentrations of PCP, TCP and DCP areas were linear in the range of concentrations of 0.2 to 8 mg/L and 0.025 mg/L to 5 mg/L for methods 1 and 2, respectively. The repeatability of the extraction methods was satisfactory, with variation coefficients lower than 11%. For method 1, at the fortification level of 0.2 mg/L, recovery of PCP, TCP, and DCP was 112%, 74% and 45%, respectively. For method 2, the corresponding recovery values at the fortification level of 0.1 mg/L were 91%, 93% and 103%, respectively. Storage of the frozen samples did not alter their PCP determination properties. The chromatographic methods adapted for chlorophenol determination in wastewater were suitable with relatively simple manipulation techniques. The obtained results were reproducible and allowed identification of intermediates formed during the PCP degradation process.