Effect Of Chemical Oxygen Demand Research Articles

Simultaneous nitrification and denitrification pattern in aerated moving-bed sequencing batch reactor: Choosing appropriate SRT for different COD/N ratios

ABSTRACT The effect of chemical oxygen demand (COD)/N ratio and sludge retention time (SRT) on the simultaneous nitrification and denitrification (SND) process in an aerated moving-bed sequencing batch reactor (A-MBSBR), for treating synthetic municipal wastewater, was studied. Three lab-scale reactors with SRTs of 5, 10, and 15 days were operated under COD/N ratios of 10 (phase 1) and 20 (phase 2). The high correlation coefficients between nitrification and denitrification efficiencies in both phases demonstrated that the denitrification efficiency in A-MBSBRs was strongly affected by nitrification efficiency (nitrate concentration). A high COD/N ratio of 20 in phase 2 provided suitable conditions for the increase and dominance of the population of heterotrophic bacteria over autotrophic nitrifiers, which led to weak nitrification (29.6–39.1%) and consequently weak denitrification (15.8–27.9%) in all reactors. In phase 2, increasing SRT from 5 to 15 days was beneficial for both nitrification and denitrification reactions. Therefore, the optimal SND efficiency in phase 2 was expected to be achieved under SRTs higher than 15 days. Under the COD/N ratio of 10 in phase 1, a better balance between the population of heterotrophs and autotrophs resulted in higher nitrification and denitrification efficiencies (44.4–62.7% and 26.3–42.8%, respectively). In phase 1, the highest and the lowest nitrification and denitrification efficiencies were obtained at SRTs of 10 and 5 days, respectively.

Effects of chemical oxygen demand and chloramphenicol on attached microalgae growth: Physicochemical properties and microscopic mass transfer in biofilm

During the wastewater treatment and resource recovery process by attached microalgae, the chemical oxygen demand (COD) can cause biotic contamination in algal culture systems, which can be mitigated by adding an appropriate dosage of antibiotics. The transport of COD and additive antibiotic (chloramphenicol, CAP) in algal biofilms and their influence on algal physiology were studied. The results showed that COD (60 mg/L) affected key metabolic pathways, such as photosystem II and oxidative phosphorylation, improved biofilm autotrophic and heterotrophic metabolic intensities, increased nutrient demand, and promoted biomass accumulation by 55.9 %, which was the most suitable COD concentration for attached microalgae. CAP (5–10 mg/L) effectively stimulated photosynthetic pigment accumulation and nutrient utilization in pelagic microalgal cells. In conclusion, controlling the COD concentration (approximately 60 mg/L) in the medium and adding the appropriate CAP concentration (5–10 mg/L) are conducive to improving attached microalgal biomass production and resource recovery potential from wastewater.

The Impact of Environmental Regulation on Firm Performance: Evidence from the Pulp and Paper Industry in China

In areas with serious pollution problems, the government designates a special emission limit (SEL) for pollution control and environmental protection in China. This paper examines the effects of chemical oxygen demand (COD) SEL on firms' production activity and market performance in the pulp and paper industry in the Lake Tai area in China. Using firm-level data, we employ a difference-in-differences strategy and find that SEL has a negative impact on the production scale, profitability, and market size of the regulated firms, while showing no significant impact on firm exports. The heterogeneity tests suggest that the impact of SEL on production and market performance varies with firm ownership, firm size, and target market. The reallocation effect of production shifts extra production from exited firms to existing firms, which explains the expansion of production scale and market size for SOEs and large-sized regulated firms. Compared with the decline of production scale, the inventory alleviation effect reduces the negative impact of stricter environmental regulation on firm performance.

Salt-tolerant heterotrophic nitrification and aerobic denitrification (HNAD) bacterium enhancing a pilot-scale moving bed biofilm reactor (MBBR) treating mariculture wastewater treatment with different COD/TN ratios

Efficient nitrogen (N) removal from mariculture wastewater is one of the important measures to protect the marine ecological environment. A moving bed biofilm reactor (MBBR) inoculating heterotrophic nitrification and aerobic denitrification (HNAD) bacteria was set and the effects of chemical oxygen demand (COD) and total nitrogen (TN) (COD/TN) ratios on N removal performance, enzymatic activity, biofilm characteristics and microbial community were discussed. Results showed that a more stable N removal performance was obtained in the MBBR process inoculating HNAD bacteria under low COD/TN ratio compared with the conventional MBBR. The removal efficiency of nitrate nitrogen (NO3−-N) declined with COD/TN ratio decrease, and protein (PN) and polysaccharide (PS) concentration decreased from 284.3 and 37.1 mg (g VSS)−1 to 42.9 and 14.4 mg (g VSS)−1 with low ammonia monooxygenase (AMO), nitrite reductase (NIR) and nitrate reductase (NR) activities. Sequencing analysis revealed that strain Zobellella B307 became the dominant microorganism (the relatively abundance is 2.33–5.60 %), and its relatively abundance and the functional genes related to N metabolism reduced from 15.38 % to 9.66 % and 0.61 % to 0.55 % with COD/TN ratio decrease to explain the reason for the decrease of N removal efficiency. This study can provide a deep insight into N removal mechanism of the reactor inoculating HNAD bacteria under different COD/TN ratios.

Recovery of Acid and Alkaline from Industrial Saline Wastewater by Bipolar Membrane Electrodialysis under High-Chemical Oxygen Demand Concentration

Actual high saline wastewater containing concentrated organics and sodium chloride is a bioenergy and renewable resource. This study compared two different bipolar membrane electrodialysis membranes from two companies' stacks to recover HCl and NaOH from sodium chloride solution and actual chemical wastewater. The results demonstrated that the electrolysis rates were around 1.5 kg/m2h, the HCl and NaOH production rates were about 0.9 kg/m2h, energy consumption was in the range of 1.05-1.27 kWh/kg, and the economic benefits were above 1 yuan/h in BMED systems. From analyzing the performance of seven different BMED membrane stacks, the B2 stack was chosen for electrolyzing actual high salt wastewater to observe the effect of chemical oxygen demand on BMED systems, where electrolytic salt performance, HCl-NaOH alkali production rates, and energy consumption show linear dependence on time for 5000 mg/L chemical oxygen demand wastewater. It illustrated chemical oxygen demand can enhance energy consumption and reduce electrolytic salt performance and the acid and alkali production rates, due to improving the membrane area resistance. In this study, the effect of high COD saline wastewater on the performance of a BMED membrane stack was clarified and the mechanism was analyzed for its practical application in treating chemical high salt wastewater.

Technical and economic evaluation of the integration of membrane bioreactor and air-stripping/absorption processes in the treatment of landfill leachate.

A membrane bioreactor inoculated with commercial baker's yeast (Saccharomyces cerevisiae) (MBRy) integrated to an air-stripping/absorption (AS/AB) as pre-treatment (aiming ammonia recovery) or a post-treatment (polishment step) was assessed for the landfill leachate treatment. The effect of chemical oxygen demand (COD) and nitrogen (N) ratio (C:N) on the performance of the MBRy was also investigated. At high COD/N ratio, high organic matter removal in terms of COD (71±4%) and ammonia removal (97±3%) was observed. Lower COD/N ratio favored yeast growth in the mixed liquor even under adverse conditions. The results of ammonia removal and recovery, and economic analysis demonstrated that the best way to integrate the AS/BS processes is as pre-treatment of MBRy. The ammonia concentration in the AS/AB process feed was a key factor to achieve the market specification. Although pH and temperature adjustment were adequate to promote ammonia removal/recovery, the AS operation at high temperatures showed the highest ammonia removal rate (99%). Therefore, the integration of AS/AB with MBRy allows obtaining a permeate with a final concentration of 2902±374mg L-1 of COD and 9±7.5mg L-1 of ammonia. Although it was possible to reach the Brazilian discharge standard for ammonia (20mg L-1), it was not possible to reach the standard for COD, where the remaining fraction is recalcitrant organic matter, requiring the integration of a physico-chemical process. It should be noted that the proposed route allowed recovery 7kg of ammonia per m3 of treated leachate.

Effect of COD on methanotrophic growth and the anaerobic digestibility of its sludge as a further step for integration in WWTPS

Within wastewater treatment plants (WWTPs), the anaerobically produced biogas is often underutilized. Fortunately, methanotrophic based biotechnologies can be the remedy for on-site exploitation and recovery of unused biogas. In this regard, efforts have been placed on evaluating the suitably of methanotrophs to be deployed in WWTPs. Even so, the effect of chemical oxygen demand (COD) on methanotrophic activity and methanotrophic sludge digestibility have not been studied, which is the focus of the present study. A methanotrophic culture enriched from activated sludge was exposed to four different COD concentrations (0–540 mg/L) to evaluate the effect of COD on the culture activity in batch mode. It was attained that the presence of COD concentrations up to 540 mg/L has limited influence on methanotrophic activity. This finding was supported by the similar average methane uptake rate (between 2.48 and 2.53 mgCH4/hr) and consumption (61.4 ± 1.5%) observed under the different COD concentrations. On the other hand, methanotrophic sludge was digested in comparison to waste activated sludge (WAS) collected from a WWTP for more than 40 days to evaluate its digestibility. It was obtained that the methanotrophic sludge had a methane specific yield of approximately 1.72 times greater than WAS and had a higher solids destruction rate. This research is another step demonstrating the feasibility of methanotrophs integration in WWTP.

Effect of chemical oxygen demand load on the nitrification and microbial communities in activated sludge from an aerobic nitrifying reactor.

In this study, we explored the effect of chemical oxygen demand (COD) load on the nitrification and microbial communities in activated sludge isolated from an aerobic nitrifying tank. The activated sludge was cultured in three different COD groups: L-COD, 200 mg/L; M-COD, 1200 mg/L; H-COD, 4200 mg/L. The results indicated that the COD exerts a negligible effect on the nitrogen removal ability within the first 24 h. However, the nitrification rate decreased with culture time; the ammonium degradation rates were found to be 80.26%, 57.56%, and 43.43% at 72 h in the three COD groups, respectively. These values correspond to decreases of 19.40%, 41.83%, and 51.48%, respectively, in relation to those observed at 24 h. The activated sludge in the different COD groups exhibited similar community compositions after 24 h, as assessed by Illumina high-throughput sequencing, while a significant difference in the relative abundances of some organisms occurred after 48 and 72 h. Proteobacteria was the main phylum, with a relative abundance of >51.45%. The genera Aridibacter, Paracoccus, Nitrospira, and Nitrosomonas were suppressed by COD load over time. This study may contribute to our knowledge about the nitrification ability and microbial communities in activated sludge at different COD load levels.

Membrane distillation as post-treatment for anaerobic fluidized bed membrane bioreactor for organic and nitrogen removal

To observe feasibility of membrane distillation (MD) as post-treatment for anaerobic fluidized bed membrane bioreactor (AFMBR), removals of organic and total nitrogen were investigated by using the commercial polyvinylidene difluoride (PVDF) membrane for direct contact membrane distillation (DCMD) at various operational conditions. Test solutions for MD experiments were permeate produced by staged AFMBR (SAF-MBR), permeate from single AFMBR and synthetic wastewater fed to both reactors. Increasing in feed temperature improved permeate flux through PVDF membrane, but it decreased total nitrogen (TN) removal efficiency. Effect of chemical oxygen demand (COD) concentrations in feed solutions for DCMD on TN removal efficiency was almost negligible. However, the COD removal efficiency was lower at lower feed concentration in DCMD operation. At constant feed temperature, TN removal efficiency was improved by increasing a recirculation flow rate on PVDF membrane across DCMD system. Both organic and inorganic fouling were observed on PVDF membrane surface and pore matrix after conducting DCMD operation. The organic fouling on PVDF membrane consisted mainly of protein and fatty acids, supporting that the permeate produced by AFMBR should have potentials to foul the membrane applied in DCMD system as post-treatment.

Effects of temperature on white water treatment by the dominant bacteria

Abstract Three dominant bacteria including Virgibacillus pantothenticus, Bacillus cereus, and Bacillus subtilis were screened from an activated sludge domesticated via white water in the laboratory. The treatment effects of chemical oxygen demand (COD), electrical conductivity and cationic demand (CD) of the white water by three dominant bacteria were studied in different temperatures. The results showed that the optimum metabolic temperature of the three dominant bacteria was 30 °C with the tested range of 20 °C to 60 °C. The best treatment effect was tended to be stable at a hydraulic retention time of 14 h, COD removal rate was 67.69 %, 77 % and 75.38 %, the electrical conductivity decreased by 0.86 mS/cm, 0.86 mS/cm and 0.62 mS/cm and the CD decreased by 45.61 %, 73.68 % and 50 % for V. pantothenticus, B. cereus, and B. subtilis, respectively.

Treatment of centrifugal mother liquid of polyvinyl chloride by internal circulation aerobic biofilm reactor: Lab to plant scale system

Centrifugal mother liquid (CML) is a typical poorly biodegradable organic wastewater generated during the production of polyvinyl chloride (PVC). A method of treating PVC centrifugal mother liquid by a high efficiency internal circulation aerobic biofilm reactor (four reactors lined up together) is presented in this study. The optimized technique was tested and evaluated in a lab and in a plant scale system. The effect of chemical oxygen demand (COD) removal efficiency was studied under different hydraulic retention time (HRT): 40, 20, 17, 14 and 12 h, respectively. Considering the efficiency and removal rate, the best HRT was 14 h. At HRT of 14 h, the average volume loading was 0.326 kg COD/(m3∙d). During the product shift from TL-1000 to TL-800 (two kinds of PVC products with different polymerization degree), the treatment efficiency of the system was not affected. Compared with the plant scale system, the results showed that in the lab setup the removal rates of centrifugal mother liquid of TL-1000 (total organic carbon (TOC) = 70–75 mg/L) and TL-800 (TOC = 20 mg/L) were 90%–95% and 80%–90%, respectively. While in the plant scale system, the removal rates of centrifugal mother liquid of TL-1000 and TL-800 were 80%–90% and 65%–80% (effluent TOC 7.5–12 mg/L), respectively. Biofilm formation by the microbial reproduction as well as intensive filamentous bacteria settlements were observed.

High-rate anaerobic digestion of yogurt wastewater in a hybrid EGSB and fixed-bed reactor: Optimizing through response surface methodology

Abstract Dairy production industry is one of the most polluting industries since it generates large volumes of high-strength wastewater. In this research, we studied the interactive effects of chemical oxygen demand (COD), hydraulic retention time (HRT), and COD/nitrogen ratio (COD/N) on the performance of a hybrid expanded granular sludge bed (EGSB) and fixed-bed (FB) bioreactor treating yogurt effluent was studied. For this purpose, response surface methodology (RSM) was applied to predict the behaviors of the system in term of COD removal and biogas production rate (BPR). RSM showed that the best models for COD removal and biogas production rate were the cubic and quadratic models, respectively. The optimum region of the hybrid EGSB-FB reactor was acquired at influent COD of 11,200 mg/L, HRT of 27 h, and COD/N ratio of 51. These variables resulted in a 90% COD removal efficiency and a 180 mL/h BPR. COD/N ratio (relevant coefficient = 4.37) and influent COD (relevant coefficient = 29.99) resulted respectively as the most effective parameters on COD removal and BPR.

Partial nitrification-anammox (PNA) treating sewage with intermittent aeration mode: Effect of influent C/N ratios

The partial nitrification-anammox (PNA) process under intermittent aeration is feasible to treat low-strength ammonium wastewater, but the effect of chemical oxygen demand (COD) on mainstream anammox processes is not fully understood. In this study, PNA process was established for sewage treatment (average ammonium = 59.3 mg-N/L) in a sequencing batch reactor (SBR) with intermittent aeration mode. Influent organic carbon to nitrogen (C/N) ratios were gradually increased (1.1, 1.5, 2.0 and 2.5). With increasing C/N ratios, the total nitrogen (TN) removal efficiency increased steadily from 30.8% to 77.3%. When the C/N ratio increased from 1.1 to 2.0, the improvement of nitrogen removal was attributed to the increase of anammox bacteria, which exponentially increased at the C/N ratios from 1.1 to 1.5. Additionally, nitrate reduction using internal carbon was likely to combine with anammox reaction under intermittent aeration operation, which might further improve the nitrogen removal. Lastly, settleability and particle size of activated sludge were also improved with the elevated C/N ratios, which favored the enrichment of anammox bacteria and facilitated the combination of partial denitrification and anammox. When the C/N ratio was 2.5, TN removal efficiency still increased while the abundance and activity of anammox bacteria remained stable, indicating that influent organic carbon promoted denitrifying bacteria and inhibited anammox bacterial growth rate. Overall, this study demonstrates that influent COD has comprehensive effects on PNA systems and that the influent C/N ratios are suggested to adjust within optimal range to achieve long-term stability.

Simultaneous chemical oxygen demand removal, methane production and heavy metal precipitation in the biological treatment of landfill leachate using acid mine drainage as sulfate resource

Biological treatment played an important role in the treatment of landfill leachate. In the current study, acid mine drainage (AMD) was used as a source of sulfate to strengthen the anaerobic treatment of landfill leachate. Effects of chemical oxygen demand (COD) and SO42- mass concentration ratio on the decomposition of organic matter, methane production and sulfate reduction were investigated and the microbial community was analyzed using the high throughout methods. Results showed that high removal efficiency of COD, methane production and heavy metal removal was achieved when the initial COD/SO42- ratio (based on mass) was set at 3.0. The relative abundance of anaerobic hydrogen-producing bacteria (Candidatus Cloacamonas) in the experimental group with the addition of AMD was significantly increased compared to the control. Abundance of hydrogenotrophic methanogens of Methanosarcina and Methanomassiliicoccus was increased. Results confirmed that AMD could be used as sulfate resource to strengthen the biological treatment of landfill leachate.

Maximizing the accumulation of Poly-β-hydroxybutyrate (PHB) in low-carbon urban sewage

AbstractThis study investigated the influence of different factors in maximizing poly-β-hydroxybutyrate (PHB) accumulation in low-carbon urban sewage. The effects of chemical oxygen demand and total phosphorus (TP) concentrations on PHB accumulation were analyzed using an anaerobic/oxygen sequencing batch reactor. Both the anaerobic phase and the aeration phase were studied. The results showed that maximum PHB accumulations increased as the carbon source increased, growing from 5.45 to 27.51 mg/g, when the carbon source concentration increased from 140 to 400 mg/L, at the end of anaerobic phase. Maximum PHB accumulation decreased from 15.89 to 13.88 mg/g when exposed to influent carbon–phosphorus C/P, suggesting that carbon source is more influential and beneficial for PHB accumulation than TP. With an increase in pre-aeration time from 10 to 50 min, PHB accumulation rose from 21.12 to 31.96 mg/g; this is higher than 15.54 mg/g PHB accumulation without pre-aeration. When the pre-aeration time was fixed at...

Simultaneous nitrification and denitrification in a novel membrane bioelectrochemical reactor with low membrane fouling tendency.

Microbial fuel cells (MFCs) can use nitrate as a cathodic electron acceptor for electrochemical denitrification, yet there is little knowledge about how to apply them into current wastewater treatment process to achieve efficient nitrogen removal. In this study, two dual-chamber MFCs were integrated with an aerobic membrane bioreactor to construct a novel membrane bioelectrochemical reactor (MBER) for simultaneous nitrification and denitrification under specific aeration. The effects of chemical oxygen demand (COD) loading rate, COD/N ratio, hydraulic retention time (HRT), and external resistance on the system performance were investigated. High effluent quality was obtained in the MBER in terms of COD and ammonium. During the operation, denitrification simultaneously occurred with nitrification at the bio-cathode of the MBER, achieving a maximal nitrogen removal efficiency of 84.3%. A maximum power density of 1.8W/m3 and a current density of 8.5A/m3 were achieved with a coulombic efficiency of 12.1%. Furthermore, compared to the control system, the MBER exhibited lower membrane fouling tendency due to mixed liquor volatile suspended solids (MLVSSs) and extracellular polymeric substance (EPS) reductions, EPSp/EPSc ratio decrease, and particle size increase of the sludge. These results suggest that the MBER holds potential for efficient nitrogen removal, electricity production, and membrane fouling mitigation.

Effect of organic loading rate during anaerobic digestion of municipal solid waste

The effect of chemical oxygen demand (COD) and volatile solids (VS) on subsequent methane (CH4) production during anaerobic digestion (AD) of organic fraction of municipal solid waste (OFMSW) was studied in a laboratory-scale digester. The experiment was performed in 2L anaerobic digester under different experimental conditions using different input mass co-digested with inoculum and organic loading rate (OLR) for 27days at 38±2°C. Three digesters (digesters 1, 2 and 3) were operated at initial loading of 5.1, 10.4 and 15.2g/L CODS per batch which were reduced to 77.9% and 84.2%, respectively. Cumulative biogas productions were 9.3, 10.7 and 17.7L in which CH4 yields were 84.3, 101.0 and 168.4mL/gVS removal in digesters 1, 2, and 3, respectively. The observed COD removal was found to be influenced on variation in CH4 production. Co-efficient of determination (R2) was 0.67 and 0.74 in digesters 1 and 2, respectively.

Degradation of Linear Alkyl Benzene Using an Immobilized Nano TiO2 Photocatalytic Reactor: Process Analysis and Modeling

An immobilized nano TiO2 photocatalytic reactor under UVA (365 nm) irradiation was used for the degradation of linear alkyl benzene (LAB) in industrial wastewater. The performance of the photocatalysis was analyzed and modeled by response surface methodology. The effects of chemical oxygen demand (CODin), reaction time and initial pH on the COD removal efficiency, specific COD removal rate, biochemical oxygen demand (BOD)5/COD ratio, and final pH were determined. The enhancing effects of H2O2, O3, and O3/H2O2 on the performance of the photocatalysis process were also investigated. The maximum BOD5/COD ratio and COD removal efficiency for the photocatalytic reaction alone were found to be 0.45 and 37%, respectively, at an initial COD of 400 mg/L and pH 3, while the photocatalytic process induced by H2O2, O3, and O3/H2O2 showed maximum COD removal efficiencies of 50, 60, and 69%, respectively. The gas chromatography–mass spectrometry results also showed a noticeable reduction in the organic content of the wastewater during the process. As the photocatalytic process was found time independent due to the catalyst poisoning, the catalyst surface regeneration was carried out by sequence aeration and ozonation. As a result, the procedure could improve the process performance by about 12% increase in COD removal efficiency. The characterization of the prepared TiO2 photocatalyst was carried out by powder X‐ray diffraction, scanning electron microscopy, and atomic force microscopy.

Effects of Chemical Oxygen Demand, Nutrients and Salinity on Sulfate-Reducing Bacteria

Abstract As a result of seawater intrusion in sewer systems or due to seawater toilet flushing, domestic wastewater may contain significant amounts of sulfate, which might lead to sulfate reducing bacteria (SRB) activity. Because of the low biomass sludge-yield of SRB, application of SRB is beneficial for reduction of sludge treatment costs. Moreover, the produced sulfide helps to remove heavy metals from treated water. In this study, short-term (6 h) effect on sulfate reduction rate of chemical oxygen demand (COD), N, P, SO42−, and salinity variations, far beyond (10-fold) the regular concentrations in municipal wastewater, was investigated. Increased propionate levels (>1,000 mg COD/L) have shown to reduce sulfate reduction rate, while acetate up to 4,000 mg COD/L did not. Nitrate became inhibitory at levels higher than 500 mg N/L, due to formation of nitrite (<10 mg N/L). Higher concentrations of ammonium and phosphate did not lead to a change in the sulfate reduction rate. Increased salinity decreased...

Effect of organic matter to nitrogen ratio on membrane bioreactor performance

Effect of chemical oxygen demand (COD) to nitrogen (COD:N) ratio in feed on the performance of aerobic membrane bioreactor (MBR) for treating a synthetic high-strength industrial waste water containing glucose was studied for over 370 days. The widely recommended nutrients ratio (COD:N:P = 100:5:1) is not necessary for aerobic biological industrial waste water treatment. An increased COD:N ratio from 100:5 to 100:2.5 and 100:1.8 had a limited impact on COD removal efficiency and further led to a significant improvement in membrane performance, a reduced sludge yield, and improved effluent quality in terms of residual nutrients. An increased COD:N ratio will benefit the industrial waste water treatment using MBRs by reducing membrane fouling and sludge yield, saving chemical costs, and reducing secondary pollution by nutrients addition. Optimization of nutrients usage should be conducted for specific industrial waste water streams.