High Influent Concentrations Research Articles

Saline wastewater treatment with purple phototrophic bacteria

Biological removal of organics, nitrogen and from saline wastewaters is adversely impacted by high salinity, which can be a major concern for treatment of industrial or domestic saline wastewater. In anaerobic treatment systems, sulfidogensis, especially when treating sulfate-rich saline wastewaters (e.g. seawater has 930 mgSO4-S L−1, or 2800 mg L−1 as SO42−) can cause additional biological, operational, and safety issues, due to H2S toxicity. Here, the use of anaerobic purple phototrophic bacteria (PPB) is tested as mediator to treat high salinity domestic wastewater (NaCl), and marine wastewater (Red Sea Salt - high sulfate, potassium, etc.) in a continuous anaerobic infra-red photo bioreactor, operated over 372d. Saline adapted PPB simultaneously removed COD, nitrogen and phosphorus with biomass yields of 0.8 gCOD gCOD−1. Batch activity tests found a broad optimum peak for saline adapted PPB between 30 and 70 mS cm−1, and 50% reduced activity at 140 mS cm−1 (3.5x seawater). For marine wastewater, high sulfate influent concentrations (770 mgSO4-S L−1) did not result in substantial H2S production (<1.6 mgS L−1) over 80 d. When irradiation was removed, sulfide rapidly rose to >90 mgS L−1 and the process failed. The results indicate rapid adaptation to high-salt conditions (both NaCl and marine), and the capacity for PPB to form a combined wastewater treatment/resource recovery process, particularly for salty industrial wastewater.

Performance and bacterial community composition of volcanic scoria particles (VSP) in a biological aerated filter (BAF) for micro-polluted source water treatment.

A laboratory-scale biological aerated filter (BAF), using volcanic scoria particles (VSP), was used for treating micro-polluted source water. The system reached a steady-state stage and performed better at removing pollutants. In steady-state stage, the effluent ammonia ( ) and chemical oxygen demand (COD) were consistently maintained below 0.3 and 3mg/L, respectively. Both the and COD removal efficiencies decreased with shorter hydraulic retention time (HRT). The effluent and COD exceeded health standards at 15min of HRT. Although performance was relatively poor for VSP-BAF at low temperature, the removal still achieved the drinking water quality standard. The influences of influent and COD concentration changes were similar to that of temperature. A better performance was observed in removal under higher influent concentrations. In contrast, the effluent COD was more than 3mg/L when the influent COD concentrations increased to about 9mg/L. The phylogenetic and cluster analyses indicated that the effect of HRT on bacteria community structure was higher than that of temperature, while the ammonia-oxidizing bacteria (AOB) are sensitive to temperature. The main phyla identified in total bacteria communities were Proteobacteria, Bacteroidetes, Firmicutes, and Nitrospirae. The main AOB were Nitrosomonadales and an uncultured ammonia-oxidizing bacterium. PRACTITIONER POINTS: The BAF using VSP obtained a good performance for treating micro-polluted source water. The influence of HRT on the system was more significant than that of temperature. The system is resistant to concentration shocks while is unable to withstand the COD increasing. The effect of HRT on bacteria community structure was significantly higher than that of temperature.

Occurrence and potential environmental risk of surfactants and their transformation products discharged by wastewater treatment plants

Seven-day composite effluent samples from a German monitoring campaign including 33 conventional wastewater treatment plants (WWTP) were analyzed for linear alkylbenzene sulfonates (LAS) and alkyl ethoxysulfates (AES) and were screened by wide-scope suspect screening for 1564 surfactants and their transformation products (TPs) by UHPLC-ESI-QTOF-MS. Corresponding seven-day composite influent samples of selected WWTPs showed high influent concentrations as well as very high removal rates for LAS and AES. However, average total LAS and AES effluent concentrations were still 14.4 μg/L and 0.57 μg/L, respectively. The LAS-byproducts di-alkyl tetralin sulfonates (DATSs), the TPs sulfophenyl alkyl carboxylic acids (SPACs) and sulfo-tetralin alkyl carboxylic acids (STACs) reached maximum effluent concentrations of 19 μg/L, 17 μg/L and 5.3 μg/L, respectively. In many cases the sum of the concentration of all LAS-related byproducts and TPs surpassed the concentration of the precursors. High concentrations of up to 7.4 μg/L were found for 41 polyethylenoglycol homologs. Quantified surfactants and their TPs and by-products together accounted for concentrations up to 82 μg/L in WWTP effluents. To determine the risk of individual surfactants and their mixtures, single homologs were grouped by a “weighted carbon number approach” to derive normalized Predicted No-Effect Concentrations (PNEC), based on experimental ecotoxicity data from existing risk assessments, complemented by suitable Quantitative Structure-Activity Relationships (QSAR) predictions. Predicted Environmental Concentrations (PEC) were derived by dividing effluent concentrations of surfactants by local dilution factors. Risks for all analyzed surfactants were below the commonly accepted PEC/PNEC ratio of 1 for single compounds, while contributions to mixture toxicity effects from background levels of LAS and DATS cannot be excluded. Maximum LAS concentrations exceeded half of its PNEC, which may trigger country-wide screening to investigate potential environmental risks.

Evaluating Antibiotic Resistance Gene Correlations with Antibiotic Exposure Conditions in Anaerobic Membrane Bioreactors

Anaerobic membrane bioreactors (AnMBRs) are an emerging technology with potential to improve energy efficiency and effluent reuse in mainstream wastewater treatment. However, their contribution to the proliferation of contaminants of emerging concern, such as antibiotic resistance genes (ARGs), remains largely unknown. The purpose of this study was to determine the effect of select influent antibiotics at varying concentrations on the presence and abundance of ARGs in an AnMBR system and its effluent. Quantification of targeted ARGs revealed distinct profiles in biomass and effluent, with genes conferring resistance to different antibiotic classes dominating in biomass (macrolides) and effluent (sulfonamides). Effluent sul1 gene abundance was strongly correlated with abundance of intl1, signifying the potential importance of mobile genetic elements in ARG release from AnMBR systems. The addition of specific antibiotics also affected normalized abundances of their related ARGs, exemplifying the potential impact of selective pressures at both low (10 μg/L) and high (250 μg/L) influent antibiotic concentrations.

Enhancing biodegradation of toxic industrial wastewaters in a continuous two-phase partitioning bioreactor operated with effluent recycle

In this study, we propose the application of a Continuous Two-Phase Partitioning Bioreactor (C-TPPB) operated with the tubing effluent recycle to enhance the biodegradation of toxic substrates in industrial wastewaters under severe loading conditions. Stepwise increasing influent concentrations (from 200 to 900 mg L−1) of 2,4-dichlorophenol (2,4-DCP) were fed to a C-TPPB operated with Hytrel G3548 tubing to simulate phenolic wastewater. Practically complete 2,4-DCP removal has been achieved during the entire experimental period, but the increased load reduced biodegradation efficiency. At influent concentration of 700 mg L−1, the first effluent recycle (recycle /influent flow rate ratio = 0.3) was applied: biodegradation efficiency doubled from 40 to 80% and was maintained until influent concentrations of 800 mg L−1. Higher influent concentrations caused a decrease in 2,4-DCP biodegradation, so the effluent recycle ratio was increased to 0.5 at 900 mg L−1 and, also in this case, the bioreactor showed a fast recovery (∼ 24 h) of the biodegradation efficiency at 80%. Mass transfer data analysis showed that the effluent recycle resulted in an increase of the mass transfer coefficient. This positive effect, joined with the reduction of the influent concentrations, demonstrated the feasibility of recycle application in enhancing the C-TPPB performance.

Sustainable bioremadiation of Cd(II) in fixed bed column using green adsorbents: Application of Kinetic models and GA-ANN technique

Abstract This paper is continuation of our earlier paper in batch studies (Nag et al., 2018) and aims to deliver efficient and affordable solution for Cd(II) remotion from their wastewater of small to medium scale industries operating in India and worldwide. Three biowaste materials, jackfruit, mango and rubber leaves are used for Cd(II) bioremediation from synthetic wastewater in continuous down flow in packed bed columns. The influence of influent concentration (20–80 mg L−1), flow rate (10–25 ml min−1) and bed depth (3–9 cm) on Cd(II) removal has been examined at pH 6. Rise in bed height favoured the adsorption process whereas the decrease in bio-sorption efficiency was recorded at high influent flow rate and concentration. 98.26% Cd(II) was removed at breakthrough by jackfruit leaves at a flow rate of 10 ml min − 1 when the influent concentration was 20 mg L−1 and 5 cm bed height. Different kinetic models were evaluated for their comparative applicability. Applicability of hybrid artificial intelligence GA-ANN was attempted as a tool for simulation and optimization of Cd(II) removal efficiency prediction as a function of influent variables. The network performed appreciably well in terms of cross-correlation coefficient (R) value (between 0.997 to 0.999) and minimization of errors.

Continuous removal of the model pharmaceutical chloroquine from water using melanin-covered Escherichia coli in a membrane bioreactor.

Environmental release and accumulation of pharmaceuticals and personal care products is a global concern in view of increased awareness of ecotoxicological effects. Adsorbent properties make the biopolymer melanin an interesting alternative to remove micropollutants from water. Recently, tyrosinase-surface-displaying Escherichia coli was shown to be an interesting self-replicating production system for melanin-covered cells for batch-wise absorption of the model pharmaceutical chloroquine. This work explores the suitability of these melanin-covered E. coli for the continuous removal of pharmaceuticals from wastewater. A continuous-flow membrane bioreactor containing melanized E. coli cells was used for adsorption of chloroquine from the influent until saturation and subsequent regeneration. At a low loading of cells (10 g/L) and high influent concentration of chloroquine (0.1 mM), chloroquine adsorbed until saturation after 26 ± 2 treated reactor volumes (39 ± 3 L). The average effluent concentration during the first 20 h was 0.0018 mM, corresponding to 98.2% removal. Up to 140 ± 6 mg chloroquine bound per gram of cells following mixed homo- and heterogeneous adsorption kinetics. In situ low-pH regeneration released all chloroquine without apparent capacity loss over three consecutive cycles. This shows the potential of melanized cells for treatment of conventional wastewater or highly concentrated upstream sources such as hospitals or manufacturing sites.

Impact of food-to-microorganisms ratio on the stability of aerobic granular sludge treating high-strength organic wastewater

This work investigated the long-term stability of aerobic granular sludge treating high-strength organic wastewater in a semi-pilot scale sequential batch reactor (SBR). The reactor was operated for 316 days under different operational conditions. It was found that the F/M ratio is an important parameter affecting granules formation and stability. Three selection mechanisms were investigated: (1) cultivation and maturation at moderately high influent COD concentration (2500 mg/L) followed by increase in influent COD concentration to 7500 mg/L; (2) stressed cultivation and operation at high influent COD concentration of 4500 mg/L; and (3) alternate feed loading strategy (variable influent COD concentration across the daily schedule of cycles at 50%, 75%, and 100% of the peak concentration of 5000 mg/L). It was found that adopting high OLR at the reactor start-up accelerated the formation of granules. However, the overgrowth of biomass under high organics concentration negatively affected the stability of granules and led to disintegration due to the presence of methanogens in the granule core. Cultivation at high organics concentration resulted in a rapid loss of microbial diversity and reactor failure. Under alternate feed loading, adequate selection of microbial community was maintained and resulted in stable reactor performance. Moreover, a strong correlation between F/M ratio and the granules settling ability was observed. When F/M ratio exceeded 1.5 gCOD/gSS.d, granules showed poor settleability and under very high sludge loading rates (above 2.5), sludge bulking occurred and led to washout of sludge due to the strong selection pressure of short settling time. Operating the reactor at F/M ratio of 0.5–1.4 gCOD/gSS.d appears to favor stable long-term granule stability.

Enhanced PHA Production with Mixed Cultures Using a Robust and Simple Controller

This work proposes the use of feedback control tools to enhance the production of bacterial polyhydroxyalkanoates (PHA) in an aerobic bioreactor fed with volatile fatty acids (VFA), by regulating the dissolved oxygen (DO) concentration at an optimal reference value and using the airflow signal behaviour to decide when to stop the reaction. The proposed method uses a standard proportional-integral (PI) controller to regulate the DO at a reference value by modifying the airflow, and this latter signal as an indicator to stop the reaction. Experiments were carried out in a batch aerobic bioreactor inoculated with enriched PHA-producing biomass from another bioreactor to determine the optimal DO reference value for PHA production and to compare the proposed operational scheme with the usual strategy that uses a constant airflow. The proposed method allows operation at a DO set-point that is optimal for PHA production and is able to identify the total degradation of substrate by a simple algorithm. It can cope with high VFA influent concentrations and inhibition because of PHA accumulation, by adapting the reaction time on-line. The PHA productivity rate was enhanced and the air consumption was decreased when compared with the usual operation strategy for this type of system. The method is able to identify the end of the reaction using the online measured airflow signal, enhances PHA production, improves the substrate rate and saves air consumption.

Simultaneous anaerobic oxidation/partial nitrification–denitrification for cost-effective and efficient removal of organic carbon and nitrogen from highly polluted streams

ABSTRACTLaboratory bench-scale anoxic/aerobic reactors with complete mix and continuous flow conditions were operated with high-strength synthetic wastewater to achieve simultaneous COD and nitrogen removal. High concentrations of organic carbon and nitrogen can be found in slaughterhouse, dairy, and food processing wastewaters, and also in some landfill leachates. Therefore, the goal of this study is to find a simple, efficient, reliable, cost-effective, and general solution for organic carbon and ammonia removal from streams with high influent concentrations of more than 5000 mg/L COD and 250 mg/L NH3–N. The highest COD (97%) and NH3–N (91%) removal efficiencies were obtained with initial COD and ammonia concentrations of 5211 mg/L and 262.8 mg/L NH3–N with volumetric loading rates of 11.26 kg COD/m3 d and 0.57 kg NH3–N/m3 d for COD and ammonia, respectively. Anaerobic oxidation is the main COD removal pathway in a simultaneous anaerobic oxidation/partial nitrification–denitrification (SAO/PND) system, and nitrogen removal significantly occurs via bacterial assimilation and partial nitrification–denitrification pathways. There are several advantages for this proposed SAO/PND system from a practical point of view, such as feasibility of simultaneous COD and nitrogen removal in a single reactor; simple operation; flexibility and practicality of this system as a general solution and cost effectiveness.

Study on the Enhanced Operation of Self-Ventilation-Based Coupling System for Domestic Wastewater Treatment

In this study, a new coupling system of biological filter bed and subsurface-flow constructed wetland based on the self-ventilation network was proposed, and the comparative pollutant removal efficiency at low and high influent concentration of the pilot coupling system with different substrates configurations were investigated. The study found that: The comparison system (b) had better removal rates than that of the original system (a), and the removal rate when treating low influent concentration was 74.10%, 94.14%, 73.57% and 69.53%, while in high influent concentration case was 81.30%, 90.28%, 88.57% and 75.36% for CODCr , NH4+ -N, TN and TP, respectively. The removal of the above main water indexes of the comparison system (b) promoted by 11.00%, 11.55%, 2.69% and 8.09% respectively in low influent concentration case and 4.20%, 9.20%, 7.66% and 13.61% respectively in high influent concentration case when comparing to the original system (a), which showed that the optimized configuration of various kinds of substrates was significant and was more beneficial to the degradation and removal of pollutants. The adsorption and interception function of substrates in the constructed wetland was the main way of phosphorus removal. The function of self-ventilation ensured the amount of DO in the coupling system, making the phosphorus removal was less affected comparing to structure of traditional wetland.

Role of Ammonia-Oxidizing Archaea in Ammonia Removal of Wetland Under Low-Temperature Condition

Ammonia-oxidizing archaea (AOA) have aroused great attention since it can supplement nitrogen cycle and show extensive existence relative to its bacterial counterpart, ammonia-oxidizing bacteria (AOB). This study compared the abundance and community compositions of AOA and AOB between natural and constructed wetlands under low temperature. More complex community structures were obtained in the constructed wetland, which may be ascribed to the differences in available nutrient contents. Nitrosospira-like organisms predominated AOB communities in both wetlands. Nitrososphaera cluster dominated the AOA community in the constructed wetland, while both Nitrososphaera and Nitrosopumilus clusters were dominant in the natural wetland. AOA dominated over AOB in both the natural and constructed wetlands, and AOA to AOB ratio ranged from 1.47 to 8.13. The natural wetland showed higher nitrification potential at low temperature, mainly due to its higher AOA to AOB ratio. This also explained why a better ammonia treatment performance was observed in the natural wetland even when it had high influent concentrations. The present results provided some new insights to ammonia removal in the wetlands under low temperature.

Comparing young landfill leachate treatment efficiency and process stability using aerobic granular sludge and suspended growth activated sludge

The treatment of young landfill leachate was investigated using two 3L sequencing batch reactors (SBR) with different biomass: aerobic granular sludge (GSBR) and the suspended growth activated sludge (ASBR). According to the nature of aerobic granular sludge, high settling velocities were expected in the GSBR and it was confirmed with 60ml/gVSS of 5-min sludge volume index (SVI5). However, the activated sludge required 30min for the ASBR to achieve a SVI of 42ml/gVSS. Compared to the ASBR, the GSBR was also more efficient in nitrogen and carbon removal. During the steady period of the experiment, 99% of total ammonium nitrogen (TAN) was removed through nitritation and nitrification in the GSBR with an average influent TAN concentration of 498mg/L. With high influent TAN concentration, the GSBR could achieve a full nitrification efficiency of 56±12% without accumulating nitrite. On the contrary, complete nitrification was not achieved in the ASBR as it was exposed to high concentrations of free ammonia (FA) and free nitrous acid (FNA), 16 and 0.2mg/L respectively. Partial nitrification (nitritation) with the efficiency of 77±10% was observed in the ASBR. The GSBR also presented higher efficiency in denitrification compared to the ASBR. 23% denitrification was observed in the GSBR during the anaerobic phase. Moreover, higher chemical oxygen demand (COD) removal efficiency was observed in GSBR than ASBR. Phosphorus removal efficiency was almost identical in both reactors. Overall, compared with the activated sludge, the aerobic granular sludge showed the best nutrients removal performance and higher tolerance to toxic compounds in young landfill leachate.

Adsorption performance of coconut shell activated carbon for the removal of chlorate from chlor-alkali brine stream.

Activated carbon from coconut shell was used to investigate the adsorption of chlorate from a chlor-alkali plant's brine stream. The effect of pH, flowrate, chlorate and chloride concentration on the breakthrough curves were studied in small-scale column trials. The results obtained show enhanced adsorption at low flowrates, higher chlorate concentrations, and at a pH of 10. These studies show that introducing an activated carbon adsorption column just before the saturator would remove sufficient quantities of chlorate to allow more of the chlor-alkali plant's brine stream to be reused. From column dynamic studies, the Thomas model showed close approximation when the chlorate in the effluent was higher than breakthrough concentrations and there was close correlation at high influent concentration. The qo (maximum adsorption capacity) values were close to those obtained experimentally, indicating close representation of the breakthrough curve by the Thomas model.

Nutrient removal of a floating plant system receiving low- pollution wastewater: Effects of plant species and influent concentration

Plant floating bed was adopted in this study to compare the purification effect of four plant species (Oenanthe javanica, Ipomoea aquatica, Hydrocotyle vulgaris, and Iris sibirica) receiving high and low treated domestic sewage. The experiment was conducted for eight months during the low temperature season. The results indicated that the average removal rates of TN and NH4+-N in I. aquatica floating bed were relatively high both under high and low influent concentration during the first stage of the experiment. During the second stage, H. vulgaris showed the best performance for nitrogen treatment, and the average removal rates of TN were 70.7% and 87.7% under high and low influent concentration, while the average removal rates of NH4+-N were as high as 98.9% and 98.9%, accordingly. Moreover, H. vulgaris contributed most for plant assimilation to nitrogen removal among different plant floating systems. It was also found that the existence of hydrophytes effectively controlled the rise of water pH value and algae growth and reproduction, which helped to improve the aquatic environment. The results provide engineering parameters for the future design of an ecological remediation technology for low-pollution wastewater purification.

Microbial dynamics of the extreme-thermophilic (70 °C) mixed culture for hydrogen production in a chemostat

Most studies of mixed culture fermentation for hydrogen production focus on the metabolite distribution under different operational conditions. While, the corresponding microbial dynamics research is limited. The aim of this work was to reveal the microbial community dynamics of extreme-thermophilic mixed culture enriched in a chemostat for hydrogen production with the combining molecular tools of denaturing gradient gel electrophoresis (DGGE), Illumina Miseq high-throughput sequencing platform, and 16S rRNA clone library sequencing. The analyzed results showed that the genera of Caldanaerobius, Caldicellulosiruptor and/or Thermoanaerobacter dominated the bacteria. While archaea were not detected even by Illumina Miseq high-throughput sequencing. The effects of hydrogen partial pressure or pH increasing from 5.5 to 7.0 on the microbial communities were not notably, and genera of Caldicellulosiruptor and Thermoanaerobacter were the dominants. High hydrogen yield in this chemostat was attributed to the enrichment of Caldicellulosiruptor. While Caldanaerobius dominated the bacteria communities as pH decreased to 4.5. Caldanaerobius and Thermoanaerobacter dominated at high influent glucose concentrations. Thereby, it clearly indicated that the microbial dynamics shall be considered when analyzing the extreme-thermophilic mixed culture fermentation in the future.

Floating constructed wetland for the treatment of polluted river water: A pilot scale study on seasonal variation and shock load

This paper reports the performance of a pilot scale floating constructed wetland (FCW), employed for the treatment of polluted water collected from Buriganga river in Bangladesh. The FCW system included a tank for accommodating collected water and a floating mat with media, to support the growth of two macrophyte species Phragmites australis and Canna indica. Mean mass removal rates of 0.66, 0.76, 0.08, 0.51, 2.49g/m2d were achieved for ammoniacal nitrogen (NH4-N), total inorganic nitrogen (TIN), phosphorus (P), biochemical oxygen demand (BOD), chemical oxygen demand (COD), respectively by the FCW. Nitrogen removal was via nitrification-denitrification processes, whereas filtration–sedimentation appeared to influence phosphorus removal. The system achieved substantial Escherichia coli mortality rates, through protozoa predation and oxidation processes. Higher influent concentrations during dry period allowed greater removal of nutrients and E. coli. Hydraulic shock-loading experiment revealed critical interdependency between hanging roots maturity, input hydraulic, and pollutant loadings for maintaining stable performances.

Characterization of microbial compositions in a thermophilic chemostat of mixed culture fermentation.

The microbial community compositions of a chemostat enriched in a thermophilic (55°C) mixed culture fermentation (MCF) for hydrogen production under different operational conditions were revealed in this work by integrating denaturing gradient gel electrophoresis (DGGE), Illumina Miseq high-throughput sequencing, and 16S rRNA clone library sequencing. The results showed that the community structure of the enriched cultures was relatively simple. Clones close to the genera of Thermoanaerobacter and/or Bacillus mainly dominated the bacteria. And homoacetogens and archaea were washed out and not detected even by Illumina Miseq high-throughput sequencing which supported the benefit for hydrogen production. On the other hand, the results revealed that the metabolic shift was clearly associated with the change of dominated bacterial groups. The effects of hydrogen partial pressure (PH2) and pH from 4.0 to 5.5 on the microbial compositions were not notable and Thermoanaerobacter was dominant, thus, the metabolites were also not changed. While Bacillus, Thermoanaerobacter and Propionispora hippei dominated the bacteria communities at neutral pH, or Bacillus and Thermoanaerobacter dominated at high influent glucose concentrations, consequently the main metabolites shifted to acetate, ethanol, propionate, or lactate. Thereby, the effect of microbial composition on the metabolite distribution and shift shall be considered when modeling thermophilic MCF in the future.

Influence of Organic Load on Biohydrogen Production in an AnSBBR Treating Glucose-Based Wastewater.

An anaerobic sequencing batch reactor with immobilized biomass (AnSBBR) was applied to the production of biohydrogen treating a glucose-based wastewater. The influence of the applied volumetric organic load was studied by varying the concentration of influent at 3600 and 5250mg chemical oxygen demand (COD) L(-1) and cycle lengths of 4, 3, and 2h resulting in volumetric organic loads of 10.5 to 31.1g CODL(-1). The results revealed system stability in the production of biohydrogen and substrate consumption. The best performance was an organic removal (COD) of 24% and carbohydrate removal (glucose) of 99%. Volumetric and specific molar productivity were 60.9molH2 m(-3)day(-1) and 5.8molH2 kg SVT(-1)day(-1) (biogas containing 40% H2 and no CH4) at 20.0g CODL(-1)day(-1) (5250mg CODL(-1) and 3h). The yield between produced hydrogen and removed organic matter in terms of carbohydrates was 0.94molH2 Mol GLU(-1) (biogas containing 52% H2 and no CH4) at 10.5g CODL(-1)day(-1) (3600mg CODL(-1) and 4h), corresponding to 23 and 47% of the theoretical values of the acetic and butyric acid metabolic routes, respectively. Metabolites present at significant amounts were ethanol, acetic acid, and butyric acid. The conditions with higher influent concentration and intermediate cycle length, and the condition with lower influent concentration and longer cycle showed the best results in terms of productivity and yield, respectively. This indicates that the best productivity tends to occur at higher organic loads, as this parameter involves the biogas production, and the best yield tends to occur at lower and/or intermediate organic loads, as this parameter also involves substrate consumption.

Optimization of three-stage Anammox system removing nitrogen from landfill leachate

Advanced nitrogen removal had been realized from mature landfill leachate via three-stage anaerobic ammonium oxidation (Anammox) system during the previous study. However, the Anammox system was influenced by factors such as influent nitrite and organic concentrations and needed to be optimized. To optimize the Anammox system, this study investigated Anammox Sequence Batch Reactor (ASBR) with different feeding modes and influent organic concentrations. The results showed that with influent ammonia and nitrite concentrations of 250±20 and 320±20mg/L, respectively, a continuous feeding mode reduced the adverse effect of high influent nitrite concentration on Anammox. A small amount of organics improved rather than inhibited nitrogen removal. However, as influent COD increased (from 600±50 to 800±50mg/L), Anammox was gradually inhibited. Influent organics concentration should be kept below 800mg/L, which facilitated Anammox.