Endogenous Decay Research Articles

Autotrophic Fixed-Film Systems Treating High Strength Ammonia Wastewater.

The aim of the study was enrichment of nitrifying bacteria and to investigate the potential of autotrophic fixed-film and hybrid bioreactors to treat high strength ammonia wastewater (up to 1,000 mg N/L). Two types of fixed-film systems [moving bed biofilm reactor (MBBR) and BioCordTM] in two different configurations [sequencing batch reactor (SBR) and a continuous stirred tank reactor (CSTR)] were operated for 306 days. The laboratory-scale bioreactors were seeded with activated sludge from a municipal wastewater treatment plant and fed synthetic wastewater with no organics. Strategies for acclimation included biomass reseeding (during bioreactor start-up), and gradual increase in the influent ammonia concentration [from 130 to 1,000 mg N/L (10% every 5 days)]. Stable ammonia removal was observed up to 750 mg N/L from 45 to 145 days in the MBBR SBR (94–100%) and CSTR (72–100%), and BioCordTM SBR (96–100%) and CSTR (92–100%). Ammonia removal declined to 87% ± 6, in all bioreactors treating 1,000 mg N/L (on day 185). Following long-term operation at 1,000 mg N/L (on day 306), ammonia removal was 93–94% in both the MBBR SBR and BioCordTM CSTR; whereas, ammonia removal was relatively lower in MBBR CSTR (20–35%) and BioCordTM SBR (45–54%). Acclimation to increasing concentrations of ammonia led to the enrichment of nitrifying (Nitrosomonas, Nitrospira, and Nitrobacter) and denitrifying (Comamonas, OLB8, and Rhodanobacter) bacteria [16S rRNA gene sequencing (Illumina)] in all bioreactors. In the hybrid bioreactor, the nitrifying and denitrifying bacteria were relatively more abundant in flocs and biofilms, respectively. The presence of dead cells (in biofilms) suggests that in the absence of an organic substrate, endogenous decay is a likely contributor of nutrients for denitrifying bacteria. The nitrite accumulation and abundance of denitrifying bacteria indicate partial denitrification in fixed-film bioreactors operated under limited carbon conditions. Further studies are required to assess the contribution of organic material produced in autotrophic biofilms (by endogenous decay and soluble microbial products) to the overall treatment process. Furthermore, the possibility of sustaining autotrophic nitrogen in high strength waste-streams in the presence of organic substrates warrants further investigation.

Investigation of sludge solubilization and phosphorous release in anaerobic side-stream reactor with a low pressure swirling jet hydrodynamic cavitation treatment

In this study, the feasibility of a novel hydrodynamic cavitation (HC) system was evaluated to speed up the biological sludge reduction mechanisms of the anaerobic side-stream reactor (ASSR) process. In the first part of the research, HC was performed on ASSR sludge by using a low pressure swirling jet cavitation system, named Ecowirl – EW 25. The effects of the Ecowirl – EW 25 system, in terms of sludge solubilisation, disintegration degree and microbial activity, were investigated considering two different injection plates, respectively, with two and four injection slots and four different treatment times, from 10 to 80 minutes. The best results were achieved after 80 min of HC treatment, using the plate with two injection slots and with a specific supplied energy (SE) equal to 12670 kJ kg TSS-1. Respirometric tests showed an increase in the readily biodegradable COD through the HC treatment of sludge. Moreover, low endogenous decay rates (bH) were measured on the ASSR sludge for SE lower than 6340 kJ kg TSS-1 revealing that the sludge solubilization was due to a modification in the floc structure rather than a decrease in the biomass viability. In the second part of the research, the solubilized sludge, after HC treatment, was used as carbon substrate for the biological activity of bacteria into the ASSR, such as total phosphate accumulating organisms (TPAOs). Results revealed that the phosphorous releasing and uptake rate, obtained using the HC treated sludge as carbon source, were comparable with those obtained with the addition of a ready biodegradable carbon source such as acetate.

Impacts of dissolved oxygen control on different greenhouse gas emission sources in wastewater treatment process

Activated sludge wastewater treatment plant (WWTP) has been recognized as one of the main contributors of greenhouse gas (GHG). Several technologies have attempted to control GHG in WWTP but have resulted in limited impacts and caused secondary pollution. Recently, often calculating total GHG as an evaluation indicator, the GHG emissions from different GHG sources have rarely been investigated. In this study, focusing on the automation of WWTP process, an alternative solution is proposed to explore the effects of control implement on GHG reduction. Firstly, simulating with the influent data of 14-days stormy weather, based on the recognized benchmark simulation model No 1 (BSM1) that accounts for the reaction kinetics and material balances of microorganism, the on-site GHG emission models of four sub-processes in WWTP, including CO2 from endogenous decay, biochemical oxygen demand removal, nitrification, and N2O from denitrification, are developed, and the off-site CO2 and CH4 emissions caused by the sludge disposal, CO2 from energy for aeration, pumping and chemical usage, are also estimated. The simulation results show that the overall averaged GHG of 844.01 kg CO2-eq/h are emitted, where 25.83% emits from the on-site sub-processes and 74.17% discharges from the off-site sources. Subsequently, the traditional proportional-integral (PI) control strategy is applied to control the concentrations of dissolved oxygen (DO) in three aerated tanks. With the control actions, the DO-PI control systems manage to reduce the GHG emissions by 15.53 kg CO2-eq/h averagely, and the GHG reduction mainly comes from the sources of aeration and nitrification, which are reduced by 11.67 kg CO2-eq/h and 4.64 kg CO2-eq/h, respectively. But, there are few influences on the other sources. Summarily, the impacts of DO-PI control on the GHG emissions from different sources of WWTP are investigated, revealing that the automatic control system can be a practical and viable approach to achieve the GHG reduction in WWTP, which caters to the sustainable development of WWTP.

A Toxic RNA Catalyzes the Cellular Synthesis of Its Own Inhibitor, Shunting It to Endogenous Decay Pathways

Myotonic dystrophy type 2 (DM2) is a genetically defined disease caused by a toxic expanded repeat of r(CCUG) [r(CCUG)exp], harbored in intron 1 of CCHC-type zinc-finger nucleic acid binding protein (CNBP) pre-mRNA. This r(CCUG)exp causes toxicity via a gain-of-function mechanism, resulting in three pathological hallmarks: aggregation into nuclear foci; sequestration of muscleblind-like-1 (MBNL1) protein, leading to splicing defects; and retention of CNBP intron 1. We studied two types of small molecules with different modes of action, ones that simply bind and ones that are templated by r(CCUG)exp in cells, i.e., the RNA synthesizes its own drug. Indeed, our studies completed in DM2 patient-derived fibroblasts showed that the compounds disrupt the r(CCUG)exp-MBNL1 complex, reduce intron retention, subjecting the liberated intronic r(CCUG)exp to native decay pathways, and rescue other DM2-associated cellular defects. Importantly, this study shows that small molecules can modulate RNA biology by shunting toxic transcripts toward native decay pathways.

Foaming control and determination of biokinetic coefficients in membrane bioreactor system under various organic loading rate and sludge retention time

This work aims to control foaming in a submerged membrane bioreactor (SMBR) by optimizing the organic loading rate (OLR) and sludge retention time (SRT) values to decrease the extracellular polymeric substance (EPS) production used for the pharmaceutical wastewater treatment. Four lab-scale SMBRs were operated for a period of more than 8 months to determine the biokinetic coefficients and optimize the SMBR systems operation under the SRT of 5, 10, 15, 20, 25 days and OLRs of 0.03-0.32 gCOD/L.day. The investigation revealed that the lowest foaming quantity was at an organic loading rate of 0.32 gCOD/L.day and a sludge retention time of 15 days related to few protein concentration of EPS. The results also showed that the foaming quality at the OLR of 0.03 gCOD/L.day was higher compared to the greater OLRs in all SRTs. It was found that the yield (Y), the endogenous decay coefficient (kd), the maximum specific growth rate (μmax), and the saturation constant (Ks) of four SMBRs were in the range of 0.073-0.310 mg/mg, 0.985-3.119 day−1, 1.249-3.672 day−1, and 2.63-106.671–232.55 mg/mg, 1–3.156 day mgCOD/L, respectively. Furthermore, the most appropriate operating condition to activated sludge among the SMBRs was the OLR of 0.1 gCOD/L.day and SRT of 15 days. Under these optimum conditions, a 92.8 % COD removal efficiency and 3.708 1/day μmax were achieved.

Kinetic study on nitrification of ammonium nitrogen-enriched synthetic wastewater using activated sludge.

Nitrification of ammonium nitrogen (NH4 +-N)-bearing synthetic wastewater was performed in a batch-activated sludge reactor by varying the initial ammonium nitrogen concentration up to 400 mg/L at a pH of 8.1 ± 0.2 and temperature of 36 ± 2 °C for developing the process kinetics using acclimatised biomass. Maximum ammonium nitrogen removal efficiency of 98.3% was achieved with initial ammonium nitrogen and mixed liquor suspended solids concentration of 235 mg/L and 2,180 mg/L, respectively, at 48 h batch period. Based on the experimental results, kinetic constants for ammonia nitrogen removal following Monod's approach were obtained as maximum substrate removal rate coefficient = 0.057 per day, yield coefficient = 0.336 mg volatile suspended solids/mg ammonium nitrogen, half velocity constant = 12.95 mg NH4 +-N/L and endogenous decay constant = 0.02 per day. Nitrification is a consecutive reaction with ammonium oxidation as the first step followed by nitrite oxidation. The overall rate of nitrite and nitrate formation was observed to be 1.44 per day and 0.34 per day, respectively.

Combination of the OSA process with thermal treatment at moderate temperature for excess sludge minimization

This study investigated the chance to couple the conventional Oxic Settling Anaerobic (OSA) process with a thermic treatment at moderate temperature (35 °C). The maximum excess sludge reduction rate (80%) was achieved when the plant was operated under 3 h of hydraulic retention time (HRT). Compared with the conventional OSA system, the thermic treatment enabled a further improvement in excess sludge minimization of 35%. The observed yield coefficient decreased from 0.25 gTSS gCOD−1 to 0.10 gTSS gCOD−1 when the temperature in the anaerobic reactor was increased to 35 °C, despite the lower HRT (3 h vs 6 h). Moreover, the thermic treatment enabled the decrease of filamentous bacteria, thereby improving the sludge settling properties. The thermic treatment enhanced the destruction of extracellular polymeric substances and the increase of endogenous decay rate (from 0.64 d−1 to 1.16 d−1) that reduced the biomass active fraction (from 22% to 4%).

Specific affinity and relative abundance of methanogens in acclimated anaerobic sludge treating low-strength wastewater.

Kinetic parameters affecting effluent water quality including half saturation constant (Ks), maximum specific growth rate (μmax), and specific affinity ([Formula: see text], defined as μmax/Ks) were investigated using three types of anaerobic sludge (raw anaerobic digestion sludge referred to as unacclimated sludge, unacclimated sludge after endogenous decay, and sludge acclimated to low-strength wastewater in an anaerobic membrane bioreactor (AnMBR) for 360 days). Long-term acclimation to low-strength wastewater resulted in sludge with high specific affinity (1.6 × 10-3 L/mg COD/day for acclimated sludge compared to 4.1 × 10-4 L/mg COD/day for unacclimated sludge). The μmax values for unacclimated sludge and acclimated sludge were 0.08 and 0.07 day-1, respectively. The Ks values for unacclimated sludge and acclimated sludge were 194 ± 81 mg COD/L and 45 ± 13 mg COD/L, respectively. Although the Ks of unacclimated sludge after endogenous decay increased to 772 ± 74 mg COD/L, μmax increased to 0.35 day-1 as well, resulting in no statistically significant difference of [Formula: see text] between the two types of unacclimated sludge. Overall, [Formula: see text] is a better indicator than μmax or Ks alone for determining effluent water quality, as effluent substrate concentration is approximately inversely proportional to the specific affinity. 16S rRNA sequencing data analysis indicated a high abundance (85.8% of total archaea) of Methanosaeta in the microbial community after long-term acclimation. High [Formula: see text] associated with the enrichment of Methanosaeta appears to ensure successful anaerobic treatment of low-strength wastewater.

Kinetic Model of Thermophilic Biohydrogen Production from POME

The study of fermentation kinetic parameters are crucial to understanding the environmental factors affect on biohydrogen production. Kinetic models for hydrogen production from anaerobic digestion of palm oil mill effluent (POME) by mixed culture were developed based on published work. The models accounted for substrate limitation, substrate inhibition, hydrogen production, and endogenous decay rate. Data from previous literature were used to compare four microbial growth kinetic models for hydrogen production in an ASBR system. The estimated values of the maximum specific growth rate (μm) were found to be 0.371 h-1. In this study, the parameters of Y, kd, and B0 calculated were 2.64 gVSS/gCOD, 0.053 h-1, and 0.133 L H2/gCOD, respectively. The model fitting was found to be in good agreement with the experimental and can be utilized for the optimization and design of the process.

Aerobic cometabolism of 1,4-dioxane by isobutane-utilizing microorganisms including Rhodococcus rhodochrous strain 21198 in aquifer microcosms: Experimental and modeling study

Aerobic cometabolism of the emerging contaminant 1,4-dioxane (1,4-D) by isobutane-utilizing microorganisms was assessed in pure culture and aquifer microcosm studies. The bacterium Rhodococcus rhodochrous strain ATCC 21198 transformed low, environmentally-relevant concentrations of 1,4-D when grown on isobutane. Microcosms were constructed with aquifer solids from Fort Carson, Colorado, a site contaminated with 1,4-D and trichloroethene (TCE). Multiple additions of isobutane and 1,4-D over 300 days were transformed in microcosms biostimulated with isobutane and microcosms bioaugmented with strain 21198. Results showed that, over time and with sufficient inorganic nutrients, biostimulation of native microorganisms with isobutane was just as effective as bioaugmentation with strain 21198 to achieve 1,4-D transformation in the microcosms. The presence of TCE at 0.2 mg/L did not inhibit 1,4-D transformation, though TCE itself was not readily transformed. An iterative process was used to determine kinetic parameter values to fit Michaelis-Menten/Monod models to experimental data for simultaneous isobutane utilization, biomass growth, and cometabolic transformation of 1,4-D. Parameter optimization resulted in good model fit to the data over multiple transformations of isobutane and 1,4-D in both short- and long-term experiments. Results suggest low concentrations of 1,4-D studied in the microcosms were cometabolically transformed according to a pseudo first-order rate of 0.37 L/mg TSS/day of 21198. Isobutane consumption was modeled with a maximum rate of 2.58 mg/mg TSS/day and a half saturation constant of 0.09 mg/L. 1,4-D transformation was competitively inhibited by the presence of isobutane and transformation rates were significantly reduced when inorganic nutrients were limiting. Simulations of the repeated additions found a first-order microbial endogenous decay coefficient of 0.03 day−1 fit the alternating periods of active transformation and stagnation between isobutane and 1,4-D additions over approximately one year. The model fitting process highlighted the importance of determining kinetic parameters from data representing low concentrations typically found in the environment.

KINETIC STUDY OF PALM OIL MILL EFFLUENT (POME) TREATMENT BY ACTIVATED SLUDGE

Kinetic parameter is a basis for design and optimization of activated sludge POME treatment. In fact, most of the kinetic parameter value used in design and optimization are default values taken from municipal wastewater. The kinetic parameters for POME treatment have not been thoroughlystudied and most of the system is using the Activated Sludge Models (ASM), either in modelling or design. Thus, the kinetic study of POME treatment by activated sludge system were carried out to obtain the kinetic parameters for the POME treatment plant design calculation.In this study, POME treatment was carriedout in batch studiesinto 14 L aeration tank with activated sludge for the biological oxidation process with optimum pH at 6.5 ± 0.1, MLVSS of 2000 ± 200 mg/Lfor HRT of 48 h and feeding with 650 ± 20 mg BOD3/L of anaerobic treated POME, while SRT was controlled at a range of 10 days to 20 days with interval of 2 days for the kinetic study experiment. From this kinetic study, the kinetic parameters for COD and BOD basis had been determined for maximum yields coefficient (Y), endogenous decay coefficient (kd), maximum specific substrate utilization rate (k) and half-velocity constant (Ks) at 0.2369 mg VSS/mg COD, 0.1060 day-1, 2.2717 day 1 and 758.7705 mg/L for COD basis whilst the kinetic parameters value for BOD basis were 0.6718 mg VSS/mg BOD3, 0.0658 day-1, 1.4136 day-1 and 556.1526 mg/L, respectively. Since the BOD is one of the discharge parameters in discharge regulatory, thus kinetic parameters for BOD basis will be used for the system design of POME treatment.

Translation affects mRNA stability in a codon-dependent manner in human cells

mRNA translation decodes nucleotide into amino acid sequences. However, translation has also been shown to affect mRNA stability depending on codon composition in model organisms, although universality of this mechanism remains unclear. Here, using three independent approaches to measure exogenous and endogenous mRNA decay, we define which codons are associated with stable or unstable mRNAs in human cells. We demonstrate that the regulatory information affecting mRNA stability is encoded in codons and not in nucleotides. Stabilizing codons tend to be associated with higher tRNA levels and higher charged/total tRNA ratios. While mRNAs enriched in destabilizing codons tend to possess shorter poly(A)-tails, the poly(A)-tail is not required for the codon-mediated mRNA stability. This mechanism depends on translation; however, the number of ribosome loads into a mRNA modulates the codon-mediated effects on gene expression. This work provides definitive evidence that translation strongly affects mRNA stability in a codon-dependent manner in human cells.

Determination and evaluation of kinetic parameters of activated sludge biomass from a sludge reduction system treating real sewage by respirometry testing

Oxic-settling-anoxic (OSA) process is one of the promising variants that produces lower amounts of sludge and has been applied to aerobic and nutrient removal systems. The only consequence on this modification is that supplementary research is advisable to fully understand the mechanism, which eventually leads to the development of a more realistic model. This study evaluated the characteristics of an OSA process as a sludge reduction system by calibration of kinetic coefficients of ASM1 model with some modifications. A series of respirometric tests were designed for the assessment of microbial kinetics and for further clarification of sludge reduction mechanism. The calibration results depicted that the decay rate is the most variable kinetic parameter depending on the system configuration. It was determined that this kinetic coefficient increased significantly after the system was modified into OSA configuration while other model parameters were almost kept constant. This may be referred to a change either in the microbial population or in the metabolism of the community. The active biomass ratio in the CAS reactor was found to be around 75%, while it was almost 2 times lower in the side-stream reactor. All results led to a conclusion that OSA process is encouraging endogenous decay and consequently lowers biomass viability in the reactor and achieves excess sludge reduction in the system. All experimental results confirmed that side-stream reactor accelerates decay rate of the community and causes the introduction of sludge with low viability to the main reactor.

Simulation of in situ biodegradation of 1,4-dioxane under metabolic and cometabolic conditions

Bioaugmentation is an option for aerobic remediation of groundwater contaminated with 1,4-dioxane. One approach uses microbes that cometabolize 1,4-dioxane following growth on a primary substrate (e.g., propane), whereas another uses microbes (e.g., Pseudonocardia dioxivorans CB1190) capable of using 1,4-dioxane as a sole substrate. The relative merits of these approaches are difficult to distinguish based on field data alone, and theoretical analyses of these processes have yet to be published. The objective of this study was to compare these remediation options using a transport model that incorporates advection, dispersion and biodegradation reactions described by multi-substrate Monod kinetics and co-inhibition effects. The transport model was coupled to an approximate steady-state air sparging simulation used to estimate gas (propane and oxygen) distribution at the field scale. The model was calibrated with field data for 1,4-dioxane and propane concentrations from a previously reported pilot study. The two remediation approaches were evaluated under different conditions that vary the initial concentration of 1,4-dioxane and the loading rates of oxygen, propane, and biomass. The metrics used to evaluate the remediation success were the time to reach an average 1,4-dioxane concentration of 1 μg L−1 and the percent of 1,4-dioxane biodegraded after 10 years of simulation. Results indicate that the initial concentration of 1,4-dioxane strongly influences which remediation approach is more effective. When initial concentrations were <10 mg L−1, propane-driven cometabolism led to faster remediation; whereas metabolic biodegradation was faster when initial concentrations were 10 mg L−1 or higher. Below 0.25 mg L−1, the viability of metabolic biodegradation improved, although cometabolism by propanotrophs still required less time to reach 1 μg L−1. Biomass injection rates had a strong effect on the rate of metabolism but not cometabolism because continuous input of primary substrate supported growth of propanotrophs. The performance of both cultures was negatively affected by a decrease in oxygen injection rate. The endogenous decay coefficient and the dispersion rate for biomass had a significant impact on cometabolic and metabolic biodegradation of 1,4-dioxane. The maximum specific rate for cometabolism of 1,4-dioxane, the dispersion rate for 1,4-dioxane, and effective porosity also had significant effects on the time to achieve remediation with propanotrophs.

Novel Cytonuclear Combinations Modify Arabidopsis thaliana Seed Physiology and Vigor.

Dormancy and germination vigor are complex traits of primary importance for adaptation and agriculture. Intraspecific variation in cytoplasmic genomes and cytonuclear interactions were previously reported to affect germination in Arabidopsis using novel cytonuclear combinations that disrupt co-adaptation between natural variants of nuclear and cytoplasmic genomes. However, specific aspects of dormancy and germination vigor were not thoroughly explored, nor the parental contributions to the genetic effects. Here, we specifically assessed dormancy, germination performance and longevity of seeds from Arabidopsis plants with natural and new genomic compositions. All three traits were modified by cytonuclear reshuffling. Both depth and release rate of dormancy could be modified by a changing of cytoplasm. Significant changes on dormancy and germination performance due to specific cytonuclear interacting combinations mainly occurred in opposite directions, consistent with the idea that a single physiological consequence of the new genetic combination affected both traits oppositely. However, this was not always the case. Interestingly, the ability of parental accessions to contribute to significant cytonuclear interactions modifying the germination phenotype was different depending on whether they provided the nuclear or cytoplasmic genetic compartment. The observed deleterious effects of novel cytonuclear combinations (in comparison with the nuclear parent) were consistent with a contribution of cytonuclear interactions to germination adaptive phenotypes. More surprisingly, we also observed favorable effects of novel cytonuclear combinations, suggesting suboptimal genetic combinations exist in natural populations for these traits. Reduced sensitivity to exogenous ABA and faster endogenous ABA decay during germination were observed in a novel cytonuclear combination that also exhibited enhanced longevity and better germination performance, compared to its natural nuclear parent. Taken together, our results strongly support that cytoplasmic genomes represent an additional resource of natural variation for breeding seed vigor traits.

Inhibiting transcription in cultured metazoan cells with actinomycin D to monitor mRNA turnover.

Decay of transcribed mRNA is a key determinant of steady state mRNA levels in cells. Global analysis of mRNA decay in cultured cells has revealed amazing heterogeneity in rates of decay under normal growth conditions, with calculated half-lives ranging from several minutes to many days. The factors that are responsible for this wide range of decay rates are largely unknown, although our knowledge of trans-acting RNA binding proteins and non-coding RNAs that can control decay rates is increasing. Many methods have been used to try to determine mRNA decay rates under various experimental conditions in cultured cells, and transcription inhibitors like actinomycin D have probably the longest history of any technique for this purpose. Despite this long history of use, the actinomycin D method has been criticized as prone to artifacts, and as ineffective for some promoters. With appropriate guidelines and controls, however, it can be a versatile, effective technique for measuring endogenous mRNA decay in cultured mammalian and insect cells, as well as the decay of exogenously-expressed transcripts. It can be used readily on a genome-wide level, and is remarkably cost-effective. In this short review, we will discuss our utilization of this approach in these cells; we hope that these methods will allow more investigators to apply this useful technique to study mRNA decay under the appropriate conditions.

Kinetic and microbial response of activated sludge community to acute and chronic exposure to tetracycline.

Current study aimed to discover both kinetic and microbial response of activated sludge biomass to continuous exposure to tetracycline, one of the most frequently detected antibiotics in wastewaters. Respirometric analysis and model evaluation of the oxygen utilization rate profiles generated at critical phases of the experimental period showed that, continuous exposure to tetracycline caused complete suppression of substrate storage aside from mild inhibition on the growth kinetics and it exerted a significant binding action with available organic carbon, leading to less oxygen consumption. Additionally, increase in endogenous decay rates by 1.5 fold was associated with maintenance energy dictated by the presence and production of antibiotic resistance genes, as demonstrated by resistance gene profile. High-throughput sequencing results showed that continuously exposure to tetracycline caused a significant shift in the community structure at species level so that tetracycline resistant bacteria like Arthrobacter sp and Diaphorobacter sp dominated the bacterial community.

Adaptation of granular sludge microbial communities to nitrate, sulfide, and/or p-cresol removal.

Effluents from petroleum refineries contain a toxic mixture of sulfide, nitrogen, and phenolic compounds that require adequate treatment for their removal. Biological denitrification processes are a cost-effective option for the treatment of these effluents, but the knowledge on the microbial interactions in simultaneous sulfide and phenol oxidation in denitrifying reactors is still very limited. In this work, microbial community structure and macrostructure of granular biomass were studied in three denitrifying reactors treating a mixture of inorganic (sulfide) and organic (p-cresol) electron donors for their simultaneous removal. The differences in the available substrates resulted in different community assemblies that supported high removal efficiencies, indicating the community adaptation capacity to the fluctuating compositions of industrial effluents. The three reactors were dominated by nitrate reducing and denitrifying bacteria where Thiobacillus spp. were the prevalent denitrifying organisms. The toxicity and lack of adequate substrates caused the endogenous decay of the biomass, leading to release of organic matter that maintained a diverse although not very abundant group of heterotrophs. The endogenous digestion of the granules caused the degradation of its macrostructure, which should be considered to further develop the denitrification process in sulfur-based granular reactors for treatment of industrial wastewater with toxic compounds.

Maximum growth and decay rates of autotrophic biomass to simulate nitrogen removal at 10°C with municipal activated sludge plants

The present study aims at determining most likely values for the maximum growth rate (µA, max) and the endogenous decay rate (bA) of nitrifiers for activated sludge processes treating municipal wastewater operated at low temperature (10°).The work used nitrification rate data measured on 10 full-scale plants and 2 pilot plants fed with domestic sewage. This set of data was combined with a modelling and a theoretical approach. The unified values (µA, max = 0.45·d-1 and bA = 0.13·d-1) were obtained at 10°C for the kinetic parameters of the autotrophic biomass in the SRT range 10 to 50 d. In addition, the factors affecting the expected nitrification rate (rv, nit) were established by a theoretical approach and confirmed by experimental results. For a given SRT, a linear relationship with the nitrogen volumetric loading rate was shown. The COD/TKN ratio of the influent on the nitrification rate was demonstrated. Finally, an operational tool for the verification of the nitrification rate in the design procedure of activated sludge processes is proposed.

Performance of Aerobic Granular Sludge in Treating Soy Sauce Wastewater at Different Hydraulic Retention Time

Aerobic granular sludge had shown its capability in treating soy sauce wastewater, but its reactor performance, granules properties and biokinetics in different hydraulic retention times (HRT) is still unknown. To ensure the reactor is performed in optimum condition, a judicially selection of HRT is important. The study was conducted in a high and slender column operated according to a sequential batch reactor (SBR) with a sequence of aerobic and anaerobic/anoxic reaction phases. Three different HRTs (8, 16, 24 h) and different anaerobic and aerobic reaction time were evaluated. In the study demonstrated the increase in HRT could reduce the organic loading rate (OLR) as well as biomass yield (Yobs, Y), endogenous decay rate (kd) and overall specific biomass growth rate (µoverall). It was observed a slight increase in the mixed liquor suspended solid (MLSS) and the granules mean size as the OLR decreased. Meanwhile, in the lowest HRT reactor, a narrow diameter range of aerobic granule from 3 to 100 µm was observed due to the development of small and dense granules. The HRT of 24h with aerobic and anaerobic/anoxic reaction time of 3.88 and 7.77h respectively is the SBR’s best performances due to the improvement of the aerobic granular physical properties.