Volumetric Organic Loading Rate Research Articles

Effects of ciprofloxacin on biogas production and microbial community composition in anaerobic digestion of swine wastewater in ASBR type reactor

ABSTRACT In swine farming, antibiotics are often used to reduce disease and promote animal growth. Part of these compounds is not absorbed by the swine body, being excreted and later reaching the treatment systems, soil, and nearby waterbodies. This research sought to investigate the influence of adding ciprofloxacin (CIP) on the anaerobic digestion of swine wastewater. For that, a bench-scale anaerobic sequential batch reactor (ASBR) was used, with 5 L of working volume in six different phases, with volumetric organic loading rate (VOLR) and CIP dosage variation. According to the results, the optimal VOLR for the reactor was 0.60 ± 0.11 gSV L−1 d−1, resulting in biogas productivity of 0.51 ± 0.03 Lbiogas L−1 d−1. After initial stability, adding substrate with 0.5 mgCIP L−1 resulted in an abrupt drop of 82% in the productivity from the 7th to 11th day of addition, coinciding with volatile acids accumulation. Afterward, the reactor recovered and reached apparent stability, with productivity similar to the previous step without the drug. For 2.5 mgCIP L−1 in the substrate, the biogas productivity at equilibrium was 11.8% lower than in the phases with the same VOLR and 0.0 and 0.5 mgCIP L−1. Organic matter removals near 80% were achieved for both dosages. The 16S rRNA metagenomic analyses showed an increase in the relative abundance of most of the phyla found, indicating that the dosages used allowed the acclimatization of microorganisms and possibly the compound biodegradation.

Integrated selection of PHA-storing biomass and nitrogen removal via nitrite from sludge reject water: a mathematical model

ABSTRACT One of the most recent innovations to promote a circular economy during wastewater treatment is the production of biopolymers. It has recently been demonstrated that it is possible to integrate the production of biopolymers in the form of polyhydroxyalkanoates (PHA) with nitrogen removal via nitrite during the treatment of sludge reject water. In the present study, simulation of a new process for bioresource recovery was conducted by an appropriate modification of the Activated Sludge Model 3. The process consists of the integrated nitrogen removal via nitrite from sludge reject water and the selection of PHA-storing biomass by inducing a feast and famine regime under aerobic and anoxic conditions. According to the results, it is anticipated that simulation data matched very satisfactorily with the experimental data and confirmed the main experimental observation, showing that during the famine period the PHA depletion was almost complete due to the availability of nitrite as the electron acceptor. Simulation results indicate that the selection of the volumetric organic loading rate and of the relative duration of the aerobic feast/anoxic famine duration is critical in order to allow for the effective denitritation of the internally stored PHA during the famine phase.

Sequencing Batch Reactor Performance Evaluation on Orthophosphates and COD Removal from Brewery Wastewater

The discharge of industrial effluent constituting high orthophosphates and organic pollutants in water receiving bodies compromises freshwater quality and perpetuates eutrophication. In this study, an anaerobic–aerobic sequencing batch reactor (SBR) under activated sludge was investigated for orthophosphates and chemical oxygen demand (COD) removal from brewery wastewater. Raw brewery wastewater samples were collected on a daily basis for a period of 4 weeks. The findings of the study are reported based on overall removal efficiencies recording 69% for orthophosphates and 54% for total COD for a sludge retention time (SRT) of 7 days and hydraulic retention time of 18 h at mesophilic temperature conditions of ±25 °C. Moreover, the SBR system showed stability on orthophosphate removal at a SRT ranging from 3 to 7 days with a variation in organic volumetric loading rate ranging from 1.14 to 4.83 kg COD/m3.day. The anaerobic reaction period was experimentally found to be 4 h with the aerobic phase lasting for 14 h. The SBR system demonstrated feasibility on orthophosphates and COD removal with variation in organic loading rate.

Recovery of methane dissolved in the effluent of a novel upflow anaerobic hybrid reactor (UAHB) submitted to temperature variation

ABSTRACT Recent studies point out losses of 30–40% of the produced methane in the effluent of anaerobic reactors treating sewage, reducing the renewable energy potential and the environmental footprint. A novel bench-scale upflow anaerobic hybrid (UAHB) reactor combining a sludge blanket at the bottom and a filter media at the top, both with three-phase separators, was proposed to evaluate the recovery of dissolved methane. UAHB was operated with volumetric organic loading rate of 1.24 kg COD m−3 d−1 and hydraulic retention time of 8 h for 218 days to evaluate the influence of temperature (18°C, 23°C, and 28°C) in the methane dissolved in the effluent and collected from three-phase separators. Chemical oxygen demand (COD) and total suspended solids (TSS) removals efficiencies remained constant during the operation and equal to 90 and 95%, respectively, related to the activity of biomass retained in the filter media. Temperature increase influenced more the methane production in the sludge blanket rather than in the upper bed. The volume of recovered methane increased about 20% with the installation of the support media and the upper three-phase separator (3PHS). The loss of methane dissolved in the effluent was strongly influenced by the temperature, and higher with the decrease of this parameter. Non-statistically significant correlations were observed between the temperature and the methane production in the upper bed (p-value = 0.0943) and total (p-value = 0.0930). Thus, it can be concluded that the evaluated temperatures did not influence the global efficiency and the total methane yield of the UAHB reactor.

Effect of hydraulic shock loads on the performance of GRABBR & UASB reactor (Dept.C)

The granular bed baffled reactor (GRABBR) and die upflow anaerobic sludge blanket (UASB) are considered as the novel types of the high rate anacrobic reactors with distinct advantages over other types of anacrobic reactors. The GRABBR is an anaerobic reactor characterized by its granular sludge bed like the UASB and compartmentalized like the ABR. This thesis describes the performance of both of the reactors when receiving unpredictable hydraulic shock loads. Shock loads were created by rapidly increasing volumetric organic loading rates from 3 to 60 kg COD m-3 d-1, along with decreasing the hydraulic retention time from 20 hrs to l hr. Synthetic wastewater containing glucose as the main organic compound was used in this study. The GRABBR and the VASB reactor achieved chemical oxygen demand (COD) removal of 58% - 89% and 51% - 82% respectively with high methane production. Both of the reactors appeared to possess high tolerance to rapid hydraulic changes with fast recovery time. Marked phase separation between different micro-organisms occurred in the GRABBR at high organic loading rates, with acidogenesis and methanogenesis being the respective dominant activities in the upstream and downstream compartments of the reactor. Granular biomass possessed good settling characteristics, which encourage high biomass relention within the system.

Anaerobic co-digestion of industrial waste landfill leachate and glycerin in a continuous anaerobic bioreactor with a fixed-structured bed (ABFSB): Effects of volumetric organic loading rate and alkaline supplementation

Anaerobic co-digestion from industrial waste landfill (IWL) leachate and glycerin was evaluated in a continuous anaerobic bioreactor with fixed-structured bed (ABFSB) under mesophilic conditions (30 ± 1 °C). The ABFSB reactor had a useful volume of 4.77 L. The support medium consisted of polyurethane (PU) foam arranged in an orderly manner. The substrate used corresponded to a mixture of 95% IWL leachate and 5% glycerin (v/v) and the inoculum consisted of flocculent anaerobic sludge. The ABFSB reactor was operated in two phases – the 1st phase (between the 49th and the 439th days of operation): started after the inoculum adaptation and the effect of the increase in the organic loading rate (OLR) was evaluated (2; 3.5; 7.1 and 11.6 gCOD L−1 d−1); the 2nd phase (between the 440th and 471st days of operation): the effect of the reduction in alkalinity supplementation via sodium bicarbonate (NaHCO3) was evaluated (0.56; 0.42; 0.28; 0.14 gNaHCO3 gCODinfluent−1 and non-supplementation). The OLR of 7.1 gCOD L−1 d−1 was the condition that presented the best results in the 1st phase for the parameters: maximum methane flow rate (MFR) (7.61 LNCH4 d−1), methane yield (MY) (0.30 LNCH4 gCODremoved−1), volumetric methane production rate (VMPR) (2.79 LNCH4 L−1 d−1), COD removal efficiencies (ERTCOD) and soluble COD (ERSCOD) higher than 90%. In the 2nd phase, the reactor was operated with an OLR of 7.1 gCOD L−1 d−1 and a hydraulic retention time (HRT) of 35.22 h and CODinfluent of 10.68 g L−1. The minimum alkalinity supplementation required was 0.28 gNaHCO3gCODinfluent−1, a condition in which the reactor showed stability and satisfactory performance for the parameters: MFR (9.48 LNCH4 d−1), MY (0.33 LNCH4 gCODremoved−1) and VMPR (3.18 LNCH4 L−1 d−1). It was concluded that the ABFSB reactor proved to be stable in the IWL leachate co-digestion and glycerin, when the alkalinity supplementation, effectively necessary, was met.

Upgrading of anaerobic digestion of tequila vinasse by using an innovative two-stage system with dominant lactate-type fermentation in acidogenesis

A novel two-stage anaerobic digestion (AD) process was examined to continuously treat tequila vinasse (TV), the liquid waste from the tequila industry, for a period of 176 days at different volumetric organic loading rates (OLRs) ranging from 2.5 to 12.5 g COD/L/d in the methanogenic stage. The novelty of this configuration relies on promoting a dominant lactate-type fermentation in the acidogenic stage as a strategy to enhance the overall performance of the process, as it leads to a lower loss of substrate in acidogenesis and is thermodynamically advantageous in methanogenesis. The results showed, however, that the soluble end products found in the acidogenic stage included not only lactate (6.3 ± 0.8 g/L) and acetate (0.7 ± 0.1 g/L) but also propionate (3.8 ± 0.6 g/L) and butyrate (2.5 ± 0.6 g/L). Despite this fact, the methanogenic unit was able to handle an OLR as high as 10.1 g COD/L/d, where it showed the highest productivity of 3.2 NL CH4/L/d with a biogas methane content of 83%, suggesting that lactate might promote syntrophic degradation processes. A methane yield of 0.33 NL CH4/g CODremoved or 15.5 NL CH4/LTV and a total COD removal efficiency close to 94% were achieved. In the two-stage process, the production of hydrogen and methane accounted for 1% and 85%, respectively, of the total energy content of the TV, which together yielded 544.5 kJ/LTV or 15.34 kJ/g VSadded. Taken together, the outstanding results obtained prove the potential application of the lactate-type fermentation to upgrade the AD of TV.

Aerobic granular sludge formation in a sequencing batch reactor treating agro-industrial digestate

ABSTRACT Most of nitrogen emissions can be ascribed to agro-industrial activities. Since digestate produced by fermentation of agro-industrial residues can be difficult to dispose of due to its high ammonium content, advanced technical- and cost-effective technologies must be developed and applied in order to significantly reduce its impact on the environment. In this study, aerobic granules were successfully cultivated in a granular sludge sequencing batch reactor (GSBR) fed with the ammonium-rich (approx. 2500 mg L−1) effluent of a 3-stage anaerobic digester treating agro-industrial residues. The peculiar characteristics of such wastewater required a 2-step operating strategy aimed at the selection of nitrifying biomass (Step 1) and the formation of aerobic granular sludge (Step 2). During Step 1, nitrifying biomass selection was achieved by properly regulating the cycle length: removal rates progressively increased from 42 to 109 mgN L−1d−1, and a corresponding increase in specific removal rates from 8 to 24 mgN gVSS −1d−1 was also observed. During Step 2, the increase in selective pressures (i.e. minimum settling velocity and volumetric organic loading rate) led to the formation of compact (average diameter, 1.02 ± 0.43 mm) and well-settling granules (SVI5, 28.6 ± 3.8 mL gTSS −1), which were able to remove up to 89 ± 2% of organic matter (as COD), 79 ± 3% of and 59 ± 4% of nitrogen (as a sum of , and ). The 2-step operating strategy played a key role in biomass selection and subsequent granule formation and maintenance in the GSBR, and may be successfully adopted for the treatment of different ammonium-rich wastewaters.

Performance and working mechanism of a novel anaerobic self-flotation reactor for treating wastewater with high suspended solids.

The new design of internal flotation components and the use of biogas were employed to develop a novel anaerobic self-flotation (ASF) reactor. Compared with the upflow anaerobic sludge blanket (UASB) reactor, the removal efficiencies of total chemical oxygen demand (COD) and suspended solids (SS) of the ASF reactor were higher than 90% under high SS concentration and high volumetric organic loading rate (OLR). The biogas flotation, sludge bed retention, and effluent washout accounted for 60%, 30%, and 10% of SS mass, respectively, proving that the biogas flotation was the main mechanism of SS removal in the ASF reactor. Extracellular polymer substance, mainly consisting of polysaccharide (PS) and protein (PN), was found to promote the SS removal by biogas flotation via the scum formation at the ratio of 294.12 g-VS/g-PS and 103.09 g-VS/g-PN. The EPS yield was determined as 2.3 ± 0.6 g-PS/g-COD and 11.5 ± 2.6 g-PN/g-COD at the OLR of 60 kg/(m3 day). The biogas production was revealed to enhance the SS removal by providing flotation driving force and by decreasing the scum density. A model was established to describe the quantitative relationship between flotation scum and OLR. This work would shed light on the high SS wastewater treatment challenge of high-rate anaerobic processes by using biogas flotation.

Effect of hydraulic retention time on electricity generation using a solid plain-graphite plate microbial fuel cell anoxic/oxic process for treating pharmaceutical sewage

Treatment efficiency and electricity generation were evaluated using a solid plain-graphite plate microbial fuel cell (MFC) anoxic/oxic (A/O) process that treated pharmaceutical sewage using different hydraulic retention times (HRT). Short HRTs increased the volumetric organic loading rate, thereby reducing the MFC performance due to rapid depletion of the substrate (carbon/nitrogen source). The COD removal efficiency decreased from 96.28% at a HRT of 8 h to 90.67% at a HRT of 5 h. The removal efficiency of total nitrogen was reduced from 74.16% at a HRT of 8 h to 53.42% at a HRT of 5 h. A shorter HRT decreased the efficiency in treatment of the pharmaceutical products (PPs), which included acetaminophen, ibuprofen and sulfamethoxazole in an aerobic reactor because these antibiotic compounds inhibited the microbial activity of the aerobic activated sludge in the MFC A/O system. The average power density and coulombic efficiency values were 162.74 mW m−2 and 7.09% at a HRT of 8 h and 29.12 mW m−2 and 2.23% at a HRT of 5 h, respectively. The dominant bacterial species including Hydrogenophaga spp., Rubrivivax spp. and Leptothrix spp., which seem to be involved in PP biodegradation; these were identified in the MFC A/O system under all HRT conditions for the first time using next generation sequencing. Bacterial nanowires were involved in accelerating the transfer of electrons and served as mediators in the SPGRP biofilm. In conclusion, a SPGRP MFC A/O system at a HRT of 8 h gave better removal of COD, T-N and PPs, as well as generated more electricity.

Evaluación de una planta piloto para el tratamiento de aguas residuales ordinarias por medio de un filtro percolador con relleno de esponjas colgantes de flujo descendente (DHS) como postratamiento de un efluente de sedimentador primario

La investigación consistió en evaluar un filtro percolador con material de relleno de espuma de poliuretano para el postratamiento de un efluente de sedimentador primario. A esta tecnología se le conoce como DHS por sus siglas en inglés para Downflow Hanging Sponge. El tren de tratamiento se completó con un sedimentador secundario (SS) a la salida del DHS. El sistema DHS + SS se monitoreó por más de un año (entrada al DHS y salida del SS), haciendo variar el tiempo de retención hidráulica y revisando las eficiencias de remoción de materia orgánica en términos de la DBO, DQO y los SST. El sistema presentó su mejor desempeño para un tiempo de retención hidráulica de 2,8 horas, equivalente a una carga orgánica volumétrica de entre 0,60 a 0,80 kgDBO/m3-d. Para esa condición se cumplió con los límites de DBO y DQO del DE-33601-S-MINAE en el 100% de los casos, aunque se incumplió en un 25% del tiempo para el parámetro de SST. Se presume que el sistema presentó problemas a nivel del sedimentador secundario, generando un arrastre de lodos que afectó el resultado de SST en el efluente final. Se recomienda ampliar la escala de la prueba con el reactor DHS, usando una planta de tratamiento de escala real y mejorando sustancialmente el sistema de distribución de agua a la entrada y el sedimentador secundario.

Down-flow fixed-structured bed reactor: An innovative reactor configuration applied to acid mine drainage treatment and metal recovery

A down-flow fixed-structured bed reactor (DFSBR) was operated for 277 days treating a mixture of synthetic substrates simulating an iron-rich acid mine drainage (AMD) and the soluble fraction of a sugarcane vinasse. The synthetic sugarcane vinasse was used as electron donor for biological sulfate-reduction, resulting in influent chemical oxygen demand (COD) close to 4000 mg L−1 and volumetric organic loading rate of 4.8 g L−1d−1. The influent sulfate concentration was kept close to 2000 mg L−1 (volumetric sulfate loading rate of 2.5 g L−1d−1) while a gradual increase of iron concentration (2–400 mg L−1) was applied. COD removal efficiencies were higher than 93% and the sulfate removal efficiencies were close to 100%. With the highest iron concentration (400 mg L−1) applied, the DFSBR achieved 95% of iron removal efficiency. The precipitate collected at the reactor bottom showed increasing concentrations of fixed suspended solids (FSS), as well as an increasing proportion of iron, indicating the possibility of metal recovery from the system. The association between sulfidogenic and methanogenic processes also enables energy recovery from the methane-rich biogas produced.

Effect of Parameters on Anaerobic Digestion EGSB Reactor for Producing Biogas

The effect of hydraulic and organic loading rate on the anaerobic digest EGSB (Expanded Granular Sludge Blanket) reactor for producing methane gas from starch wastewater was studied. The results show that, when the hydraulic loading rate of reactor is in the range of 1 - 4m/h and the influent concentration of CODCr is in the range of 5000 - 10000mg/L, the EGSB reactor can operate stably. Under the volumetric organic loading rate of 30 kg/ (m3•d), the removal rate of COD is over 80%. The granular sludge in the reactor has good settleability, the proportion of granular sludge in the bottom of reactor with particle diameter larger than 1.5mm accounted for more than 75%.

Effect of volumetric organic loading rate (OLR) on H2 and CH4 production by two-stage anaerobic co-digestion of food waste and brown water

Two-stage anaerobic digestion system consisting of two continuously stirred tank reactors (CSTRs) operating at mesophillic conditions (37°C) were studied. The aim of this study is to determine optimum Hydraulic Retention Time (HRT) of the two-stage anaerobic digester system for hydrogen and methane production. This paper also discusses the effect of OLR with change in HRT on the system. Four different HRTs of 48, 24, 12, 8h were monitored for acidogenic reactor, which provided OLR of 17.7, 34.8, 70.8, 106gVS/L·d respectively. Two HRTs of 15days and 20days were studied with OLR of 1.24 and 1.76gVS/L·d respectively in methanogenic reactor. Hydrogen production at higher OLR and shorter HRT seemed favorable 106gVS/L·d (8h) in acidogenic reactor system. In methanogenic reactor system HRT of 20day with OLR of 1.24gVS/L·d was found optimum in terms of methane production and organic removal. The result of this study illustrated the optimum HRT of 8h and 20days in acidogenic stage and methanogenic stage for maximum hydrogen and methane production.

EVALUATION OF AN INNOVATIVE ANAEROBIC BIOREACTOR WITH FIXED-STRUCTURED BED (ABFSB) FOR BREWERY WASTEWATER TREATMENT

The aim of this study was to evaluate the application of the anaerobic bioreactor with fixed-structured bed (ABFSB) for brewery wastewater treatment with high volumetric organic loading rate (VOLR) and its comparison with a traditional packed-fixed bed bioreactor. Two different biomass support materials were tested, including polyurethane (PU) and polypropylene (PP) for both configurations. The best global efficiency was reached by the structured-fixed bed reactor with polyurethane as biomass support (SB PU). For a VOLR of 14.0 kg CODt m-3 d-1 (HRT of 8 h) and 20.3 kg CODt m-3 d-1(HRT of 12 h), the SB PU reached the average CODt removal efficiencies (ECOD) of 81% and 71%, respectively. The results show that ABFSB is a promising technology for high organic matter and solids concentration wastewater treatment, but the type of the biomass support had a big impact on the reactors performance.

Aerobic granulation with petrochemical wastewater in a sequencing batch reactor under different operating conditions

The aim of this study was to define the best operating conditions for the successful start-up of a granular sludge sequencing batch reactor (GSBR) treating petrochemical wastewater (PW) produced by the integrated gasification combined cycle and characterized by high -N concentration (up to 630 mg/L). Two different start-up strategies were applied during Phases A and B, using different shear forces, inoculum source and pH. The GSBR was fed with a mixture of synthetic medium and real wastewater, and a readily degradable growth substrate (i.e. sodium acetate) was supplied in order to maintain the volumetric organic loading rate at 3 g COD/L d: the share of PW in the influent was gradually increased, depending on the observed reactor performance. In Phase A, aerobic granules irreversibly deteriorated when the share of PW in the influent was increased to 30%. Conversely, a faster and more stable granulation was observed during Phase B, likely due to the higher superficial gas velocity applied (i.e. harsher conditions) and the different sludge used as inoculum (already acclimated to toxic substances): under such conditions, the synthetic medium was completely replaced by the PW. The observed total organic carbon removal efficiencies were similar in Phases A and B (92 ± 6–94 ± 2%, respectively), while -N removal efficiency was higher during Phase B (up to 78% when PW% was 100%). The inoculum with acclimated sludge and the harsher selective pressure (Phase B) were proved to speed up the formation of compact and well settling granules, more resistant to the increase of PW share in the influent.

A simple kinetic modeling approach for aerobic stabilization of real waste activated sludge

The objective of this study is to propose a procedure to simplify the modeling of aerobic stabilization process. In order to achieve this, the activated sludge models no. 1 (ASM1) and no. 3 (ASM3) were evaluated based on uncomplicated chemical oxygen demand and volatile suspended solid data gathered from batch aerobic digesters. The aerobic digestion period of real waste activated sludge was modeled and then the modeling results were validated at different volumetric organic loading rates. The uniqueness of given model parameters were confirmed by sensitivity analyses. According to experimental results, at the end of 30days, the maximum volatile suspended solid removal rate was as 51.50%. The model simulations indicated the viability of both models, with regression coefficients of >0.978 without requiring the addition of any process or component to the original model structures contrary to those suggested by prior studies. According to sensitivity analyses used to determine the identifiability of estimated model parameters, the active biomass fraction, production rate of microbial products, endogenous decay rate and heterotrophic yield coefficient are the most sensitive and identifiable parameters in both models. As a result of modeling, the endogenous decay process was determined to be the main microbial mechanism involved in aerobic digestion, while the hydrolysis of particulate organic matter and removal of storage products were found as insignificant mechanisms during aerobic digestion process. Additionally, the modeling studies indicated the importance of the organic loading to achieve satisfactory organic removal since microbial kinetic rates were decreased under a threshold level of organic loading.

Biofouling Aspects and Critical Flux Evaluation in an Intermittently Aerated and Fed Submerged Membrane Bioreactor

Nowadays, much attention is being paid to environmental issues since legislation has become stricter. Membrane bioreactors (MBR) are non-conventional treatment systems that gain ground in wastewater processing. In this study, the operation of a 24 L submerged membrane bioreactor, treating municipal wastewater, was investigated under different organic loading rates and high mixed liquor suspended solids concentrations (up to 13 g/L). The system, consisting of a hollow fibre membrane for ultrafiltration (0.1 μm pore-size), was operated under intermittent aeration (30 min/30 min aeration - on & off) and periodic feeding at the beginning of the anoxic phase, while effluent was discarded at the end of the aerobic phase. The transmembrane pressure and operation processes were monitored and controlled by a programmable logic controller (PLC). Complete suspended solids removal was achieved throughout the entire operation and BOD and COD average removal values higher than 97 % and 93 % were determined. Moreover, TKN and NH4 +-N mean removal efficiencies were estimated to be higher than 77 % and 91 %, respectively, regardless of the increase in the organic loading rate and biomass concentration. No membrane fouling was observed since the submerged membrane bioreactor was operated below the critical flux. A 2nd order equation considering fouling and sieving phenomena was found to mathematically express critical flux. It is concluded that the MBR system could effectively operate without membrane fouling for a long period of time, even at high volumetric organic loading rates and high biosolids concentrations.

Performance and Characteristics of Aerobic Granular Sludge Degrading 2,4,6‐Trichlorophenol at Different Volumetric Organic Loading Rates

Aerobic granular sludge represents a promising option for the treatment of wastewater contaminated by 2,4,6‐trichlorophenol (2,4,6‐TCP). Nevertheless, the need for high volumetric organic loading rates (vOLR) still constitutes a practical drawback, since the supply of an external carbon source for the treatment of low‐strength industrial wastewater would imply significant costs at full‐scale. This study investigates the possibility to sustain 2,4,6‐TCP degrading aerobic granules with low vOLR, preserving long‐term process performance. Sodium acetate was used as external carbon source for aerobic granules degrading 2,4,6‐TCP (20 mg/L), and its concentration in the influent was progressively reduced from 1000 to 420 mg/L. The effects on process performance, granule properties and microbial population dynamics were investigated: complete 2,4,6‐TCP removal was maintained, specific removal rates increased from 2.2 ± 0.5 to 4.3 ± 0.4 mg 2,4,6‐TCP/g VSS per hour (mg2,4,6‐TCP/gVSS · h) and a shift of granule diameter toward smallest size fractions occurred. Moreover, the qualitative evaluation of polyhydroxyalkanoates (PHA) inclusions in microbial cells suggested their active role in 2,4,6‐TCP degradation. The results showed that for low‐strength wastewater containing toxic substances like 2,4,6‐TCP, high concentrations of the external carbon source are required during the process start‐up, but not in the long‐term operation, thus reducing the operating costs significantly without compromising process performance: this represents an important step toward process scale‐up.

Robustness of ANAMMOX granule sludge bed reactor: Effect and mechanism of organic matter interference

The organic matter together with ammonium has become a major concern in the applications of ANaerobic AMMonium OXidation (ANAMMOX) process because of its possible adverse influences. The robustness of ANAMMOX against organic matter interference was found by accident in the ANAMMOX Granule Sludge Bed (GSB) reactor. Under inorganic conditions, Autotrophic ANAMMOX Granular Sludge (AGS) was cultivated, in which ANAMMOX accounted for 89.7% of the total nitrite removal. The bioreactor based on AGS showed an intriguing resistance to organic matter interference, with a stable volumetric nitrogen removal rate (NRR) for a surprisingly long time (|ΔNRR|≤10% for 33 days). Under organic conditions, however, AGS gradually shifted to mixotrophic ANAMMOX granular sludge (MGS), in which ANAMMOX accounted for 51.9% of the total nitrite removal. The bioreactor based on MGS was sensitive to organic matter interference, with a decrease by 20.9% in NRR when the volumetric organic loading rate was 7.5kg COD/(m3d). Beneath the threshold COD/NO2−-N ratio of 1.71, ANAMMOX played its dominant role in MGS (contributed to 68.9% of the total nitrite removal). While above the threshold ratio, ANAMMOX was dramatically inhibited (contributed to less than 34.1% of the total nitrite removal), but it did not disappear completely as expected. The discovery of ANAMMOX robustness in AGS is significant for the development of new ANAMMOX process suitable for the treatment of ammonium-containing wastewaters with coexistence of organic matter.