Chemical Oxygen Demand Removal Performance Research Articles

A mechanistic mathematical model for the treatment of synthetic oil-field wastewater (produced water) by electrocoagulation process using aluminium electrodes.

Produced water (PW) is the largest by-product that comes out of the oil wells during oil and gas (O&G) field exploration. PW contains high-salt concentration along with other organic and inorganic components; therefore, PW must be treated before disposal. Electrocoagulation (EC) is an effective treatment method to remove pollutants from PW which has been the focus of many experimental studies; however, a mathematical model specifically for PW treatment by EC has not been developed yet. In this work, a comprehensive mathematical model has been developed to elucidate the role of EC operating parameters on the PW treatment performance and determine the mechanism for COD (Chemical Oxygen Demand) removal. The present model considers and identifies the dominant Al-hydroxy complex species and their contribution to the COD removal from synthetic PW samples by estimating their rate constants and comparing their magnitudes and investigates multi-scale modelling of the EC reactor. The influence of working parameters such as current density, initial pH, interelectrode distance, mixing speed and solution volume of PW on Al coagulant production and COD removal was investigated and modelled. The study estimates the rate constants of the reactions taking place for COD removal by EC process and by comparing their magnitudes identifies the dominant reactions and coagulant species involved in the process. The mathematical model prediction of COD removal fits well with the experimental data at 10mAcm-2, 15mAcm-2 and 20mAcm-2 current density with R2 value of 0.96, 0.97 and 0.92, respectively and for dissolved Al concentration R2 value of 0.96, 0.99, and 0.97, respectively. The simulated results reproduced a good fit at initial pH of 6.1, 7.3 and 8.6 with R2 value of 0.92, 0.96 and 0.98, respectively for COD removal. The mathematical model and the experimental results showed the role of dominant Al-hydroxy complex species such as , , , and in controlling the COD removal process. Under different operating conditions considered in the study, the model also predicted the COD removal performance of the EC reactors at different reactor volumes with R2 value of 0.96 for higher solution volume and larger reactor. The model presented and rate constants determined in the study will provide a theoretical basis for designing, scaling up and operating the EC reactor for oil-field PW treatment.

Sludge-derived iron-carbon material enhancing the removal of refractory organics in landfill leachate: Characteristics optimization, removal mechanism, and molecular-level investigation

Mature landfill leachate is a refractory organic wastewater, and needs physical and chemical pretreatments contemporaneously, e.g. iron-carbon micro-electrolysis (IC-ME). In this study, a novel iron-carbon (Fe-C) material was synthesized from waste activated sludge to be utilized in IC-ME for landfill leachate treatment. The pyrolysis temperature, mass ratio of iron to carbon, and solid-liquid ratio in leachate treatment were optimized as 900 °C with 1.59 and 34.7 g/L. Under these optimal conditions, the chemical oxygen demand (COD) removal efficiency reached 79.44 %, which was 2.6 times higher than that of commercial Fe-C material (30.1%). This excellent COD removal performance was indicated to a better mesoporous structure, and uniform distribution of zero-valent iron in novel Fe-C material derived from sludge. The contribution order of COD removal in IC-ME treatment for landfill leachate was proven as coagulation, adsorption, and redox effects by a contrast experiment. The removal of COD includes synthetic organic compounds, e.g. carcinogens, pharmaceuticals and personal care products. The contents of CHO, CHON, and CHOS compounds of dissolved organic matter (DOM) in the leachate were decreased, and both the molecular weight and unsaturation of lipids, lignin, and tannic acids concentration were also reduced. Some newly generated small molecular DOM in the treated leachate further confirmed the existence of the redox effect to degrade DOM in leachate. The total cost of sludge-derived Fe-C material was only USD$ 152.8/t, which could save 76% of total compared with that of commercial Fe-C materials. This study expands the prominent source of Fe-C materials with excellent performance, and deepens the understanding of its application for leachate treatment.

Overevaluation of Electro-oxidation for Chemical Oxygen Demand Removal Using a Boron-Doped Diamond Anode: The Roles of Various Electrogenerated Oxychlorides and Countermeasure

Electrochemical oxidation using a boron-doped diamond (BDD) anode has been extensively investigated in various wastewater treatments, where the electrogenerated oxychlorides (ClOx–, x = 1 to 4) from Cl– oxidation have been well illustrated. However, the false chemical oxygen demand (COD) reduction induced by ClOx– adulteration has been almost completely overlooked when evaluating the electrochemical wastewater treatment performance. In this study, it was revealed that all the ClOx– species except ClO4– served as strong oxidants in lieu of dichromate to degrade organic matter under digestion conditions during the COD test procedure. To eliminate the interference of ClOx– mixtures on the assessment of electrochemical COD removal performance, the modified sulfite-based reduction method was developed for the electrochemical case to remove ClOx– mixtures from the BDD-treated water samples before the COD test. It was demonstrated that the unadulterated COD removal performance of the BDD-based electrochemical system used for both synthetic and real wastewater treatments could be obtained after sulfite-based reduction of the electrogenerated ClOx– mixtures within 30 min in a sealed reaction chamber with the molar [sulfite]ini/[ClOx–]ini ratio of 1–3, where the reactants were isochronously depleted without producing oxidative radicals (SO4•– and •OH). Due to extreme lack of oxygen in the sealed ClOx–-sulfite system, radical propagation reactions were terminated and ClOx– constituents (ClO3–, ClO2–, and ClO–) were reduced by sulfite stoichiometrically via the oxygen transfer process with Cl– and SO42– as the final products. This new sulfite-based protocol could be regarded as a robust and adulteration-proof countermeasure for evaluating the real COD removal performance of an electrochemical system.

The Material Flow and Stability Performance of the Anaerobic Digestion of Pig Manure after (Hyper)-Thermophilic Hydrolysis Is Introduced: A Comparison with a Single-Stage Process

Slow hydrolysis persistently affects the anaerobic digestion of animal manure. Thermophilic and hyper-thermophilic treatments introduced into a two-stage anaerobic process treating pig manure were investigated, with a single-stage mesophilic process as a control. The results from the 100-day experiment showed the thermophilic-mesophilic system had the highest removal efficiency of volatile solids at 60.8%, 18% higher than the single-stage process. The thermophilic and hyper-thermophilic hydrolysis reactors contributed 23.5% and 21.7% solubilization of chemical oxygen demand (COD), respectively. The hydrolysis efficiency achieved in the single process was 49.7%, which was lower than the hydrolysis in the two-stage processes. Approximately 60% of COD was distributed in the solid fraction in the first stage, and more than half of the particle COD continued to hydrolyze in the subsequent second stage. The mass balance of COD and volatile solids removal performance illustrated the advantages of the temperature-phased process. Comparatively, the three mesophilic reactors all had strong stability.

Application of Sequential Combination of Electro-Coagulation/Electro-Oxidation and Adsorption for the Treatment of Hemodialysis Wastewater for Possible Reuse

Reusing hemodialysis wastewater (HWW) is more difficult due to its higher conductivity (salinity) and the need for an iterative RO or adsorption process. It can therefore be challenging and technologically laborious. In this context, this study aimed to investigate the possibility of treating HWW by combining electro-coagulation (EC) and electro-oxidation (EO) processes and adsorption as the best technologies to achieve efficient removal of dissolved micropollutants. In this work, the application of electro-coagulation/electro-oxidation processes using, respectively, aluminum and platinum electrodes combined with adsorption onto active carbon to treat HWW was studied. In the EC process, high removal of phosphate ions and chemical oxygen demand (COD) was observed. In the EO process, the COD removal performance, total nitrogen, and Mg were significant and reached 100, 83, and 89%, respectively, after 100 min of treatment. The estimated energies required to treat HWW by EC and/or EO were approximately 0.7 kWh/m3 and 0.05 kWh/m3, respectively. While the EO and EC processes used for COD removal from HWW showed almost similar performances, the EO process seems to consume less energy. Therefore, electrochemical removal of HWW can be successfully performed using the EO process and activated carbon (AC) for the complete removal of COD and the mineralization of pharmaceutical residues. The experimental results showed that the coupling of the three processes (EC–EO–AC) provides treated water that can be reused in agriculture due to its less sodium absorption ratio (SAR) value and might be an alternative method of wastewater treatment responding to the concept of green dialysis.

Floating Wetlands for Sustainable Drainage Wastewater Treatment

The preservation of water resources in modern urbanized society is a major concern. In this study, a floating constructed wetland (FWT) pilot plant was designed and constructed for the treatment of a polluted wastewater drain. A series of experiments were run continuously for a year in pilot-scale FWTs in a semi-arid area located in Egypt’s Delta. Four aquatic plant species (Eichhornia, Ceratophyllum, Pistia stratiotes, and Nymphaea lotus) were used to assess the performance of FWTs for pollutant removals, such as biochemical oxygen demand (BOD), chemical oxygen demand (COD), total suspended solids (TSS), total nitrogen (TN), total phosphorus (TP), electrical conductivity (EC), and total dissolved solids (TDS), from drainage wastewater to reuse the treated effluent in irrigation practices. The FWT systems were fed drainage tainted water on a weekly basis, and the concentrations and removal efficiency were assessed in the experiments. The average reduction in BOD, COD, TSS, TDS, TN, EC, and TP were 76–86%, 61–80%, 87–95%, 36.6–44.1%, 70–97%, 37–44%, and 83–96%, respectively. ANOVA with Post-HOC t-tests show that the Eichhornia, Pistia stratiotes, and Nymphaea lotus have the highest BOD and COD removal performance, whereas Pistia stratiotes and Nymphaea lotus have the highest TN and TP removal performance. In all cases, the Nymphaea lotus performed well in terms of pollutant removal. In addition, a design procedure for a FWT systems is presented. For wastewater treatment, FWT systems have proven to be a low-cost, long-term option.

Change the original microbial community structure in the hydrolysis acidification tank to enhance the COD removal performance of oily wastewater.

The hydrolysis acidification tank mainly relies on microorganisms to treat oily sewage, but in many cases the chemical oxygen demand (COD) of the effluent from the hydrolysis acidification tank does not decrease or even increase. In this work, about 50 L of oily wastewater is treated in a facultative anaerobic hydrolysis acidification tank with a temperature of 29 °C, pH 6, high-throughput sequencing technology analyzes found that after long-term operation of the hydrolysis and acidification tank, the dominant bacterial Pseudomonas accounted for only 2.87%, at this time, the effluent COD of the hydrolysis and acidification tank was 450 mg/L. Pseudomonas stutzeri LH-42 a strain screened in the laboratory, was domesticated and colonized in the hydrolysis acidification tank. High-throughput sequencing and bioinformatics analysis showed that the proportion of Pseudomonas in the hydrolysis acidification tank reached 5.89%, the effluent COD of the hydrolysis and acidification tank was 200 mg/L. The above results indicate the importance of the proportion of Pseudomonas in the hydrolysis and acidification tank for the COD degradation of oily wastewater.

Remediation of extracted water from El-Burullus drains sediments using chemical oxidation

The efficiency of treatment was eliminated based on residual concentration of ammonia-nitrogen (NH4-N) and chemical oxygen demand (COD). Removal percentage of ammonia in case of using H2O2 increased in a concentration of 30%. the removal of organic pollutants recorded high efficiency of removal in 14.28 and 10.71% for east El-Burullus and Damru drains, respectively. KMnO4 gave better results which, the maximum ammonia removal was 66.59 % for 0.2 g/L of KMnO4 in Hokx site, whereas COD removal was 34.48 % at 0.1of KMnO4 in Hokx site. Acidic conditions (pH 3) demonstrated conducive to the removal of all factors for both oxidants with the exclusion of COD removal in Burullus east that displayed a high removal at pH 5. The reduction of NH4-N at pH 3 for both KMnO4 and H2O2, with 76.74%, 93.76%, 92.03 % for Burullus east, Damro and Hokx sites, respectively. whereas the higher percentage removal in COD was 23.07% and 8.97% for both Damro and Hokx sites at PH 3, while in Burullus east was 22.22% at pH 5. Furthermore, Fe2+/H2O2 (Fenton’s reagent) was run in the batch process with various doss. Under the optimal parameters, the removal efficiency of COD was achieved 58. 69 % and 12.60 % for both Burullus east and Damro, respectively at Fe2+ =0.4 g/L, pH= 3 and contact time of 120 min. The NH4-N and COD removal performance of KMnO4 was well compared with H2O2. Finally, remediation needn’t extra pH adjustment which it is simple operation and low capital cost.

Yeast and bacteria co-culture-based lipid production through bioremediation of palm oil mill effluent: a statistical optimization

In the present study, a co-culture of yeast (Lipomyces starkeyi) and bacterium (Bacillus cereus) was used to optimize lipid accumulation capability and simultaneous treatment of wastewater using palm oil mill effluent (POME) as a carbon source. The influence of process parameters (i.e., inoculum composition, pH, temperature, and time) on the lipid accumulation and the chemical oxygen demand (COD) removal were optimized using design of experiments (DoE) as a statistical tool. The DoE results suggested that the maximum lipid accumulation of 2.95 g/L and COD removal efficiency of 86.54% could be obtained while the inoculum composition, pH, temperature, and incubation time were 50:50, 6.50, 32.5 ??C, and 90 h, respectively. The predicted results were very close to the experimental results (<???5% deviation); hence, the proposed model could be useful to predict the lipid accumulation and COD removal performance of a yeast and bacteria co-culture.

Anaerobic-aerobic processes for the treatment of textile dyeing wastewater containing three commercial reactive azo dyes: Effect of number of stages and bioreactor type

In this study, the effect of number of stages and bioreactor type on the removal performance of a sequential anaerobic–aerobic process employing activated sludge for the treatment of a simulated textile dyeing wastewater containing three commercial reactive azo dyes was considered. Two stage processes performed better than one stage ones, both in terms of overall organic and color removal, as well as the higher contribution of anaerobic stage to the overall removal performance, thereby making them a more energy efficient option. The employment of a moving bed sequencing batch biofilm reactor, which uses both suspended and attached biomass, for the implementation of the anaerobic stage of the process, was compared with a sequencing batch reactor that only employs suspended biomass. The results showed that, although there was no meaningful difference in biomass concentration between the two bioreactors, the latter reactor had better performance in terms of chemical oxygen demand (COD) removal efficiency and rate and color removal rate. Further exploratory tests revealed a difference between the roles of suspended and attached bacterial populations, with the former yielding better color removal whilst the latter had better COD removal performance. The sequential anaerobic–aerobic process, employing an aerobic membrane bioreactor in the aerobic stage resulted in COD and color removal of 77.1 ± 7.9% and 79.9 ± 1.5%, respectively. The incomplete COD and color removal was attributed to the presence of soluble microbial products in the effluent and the autoxidation of dye reduction metabolites, respectively. Also, aerobic partial mineralization of the dye reduction metabolites, was experimentally observed.

Study of a coupled adsorption/electro-oxidation process as a tertiary treatment for tequila industry wastewater.

Vinasse wastewater from tequila industry that has been conventionally treated is usually characterized by a chemical oxygen demand (COD) above 150mgL-1, which is the maximum content permitted for discharge by Mexican Regulation. In order to increase the wastewater quality, different processes were applied, and from the experimental results, the advantages and limitations were analyzed. In this way, although Fenton experiments showed acceptable COD removal efficiencies (79-90%), operation as well as cost limit its adoption as a viable technology. Therefore, additional experiments explored electro-Fenton (EF) as well as adsorption coupled to EF in a tubular reactor. The corresponding data revealed that there was no additional increase in COD removal performance probably due to the low oxygen solubility in the electrolytic solution and the high pH that prevents the existence of Fe2+ ions necessary for the Fenton mixture. In view of these results, when an activated carbon (AC) filter was coupled to polarization at current densities between 0.5 and 2mAcm-2, removal efficiencies from 71 to 81%, corresponding to final COD of 78 to 33mgL-1, were achieved. Also, the adsorbent surface was continuously regenerated, promoting a more efficient adsorption and a longer service life for the AC filter. In this case, by using a current density of 0.5mAcm-2, COD was reduced to sufficiently small values for discharge into natural water bodies, maintaining low energy consumption and therefore acceptable operation costs.

Co-enhanced activated sludge system by static magnetic field and two halotolerant yeasts for azo dye treatment.

The effect of static magnetic field (SMF) on azo dye Acid Red B (ARB) decolorization by the co-culture of activated sludge (AS) and two halotolerant yeasts Candida tropicalis A1 and Pichia occidentalis A2 was investigated. Microbial community structure of the co-cultures before and after treatment with SMFs of different intensity was analyzed through high-throughput sequencing and quantitative real-time polymerase chain reaction. The results showed that ARB decolorization efficiency by the defined co-culture was 1.25-fold to 1.51-fold elevated by 24.6-305.0mT SMF. The best ARB decolorization and chemical oxygen demand (COD) removal performances by the co-culture were both achieved with 95.0mT SMF. By contrast, biomass multiplication and sedimentation property of AS systems were not significantly influenced by SMF. Higher activities of intracellular key enzymes were determined (with 95.0mT SMF) as responsible for better decolorization and COD removal performances. Bacteria belonging to Prolixibacter, Corynebacterium, Pelagibacterium, Demequina, and Sphingobacterium which might be responsible for azo dye decolorization and aromatic compounds biodegradation were significantly enriched only in presence of SMF. Fungal genera Candida and Pichia were also significantly enriched by 41.4-305.0mT SMF, which might be responsible for higher treatment efficiency. PRACTITIONER POINTS: Dye degradation was enhanced by combination of static magnetic field and yeasts. Improvement of enzyme activity was responsible for better treatment performance. Putative azo-degrading-related bacteria and fungi were selectively enriched. High relative abundance of Candida and Pichia ensured high decolorization effects. Potentially effective improvement of bioprocesses for treating hypersaline wastewater.

Treatment of Textile Wastewater by CAS, MBR, and MBBR: A Comparative Study from Technical, Economic, and Environmental Perspectives

In this study, three different biological methods—a conventional activated sludge (CAS) system, membrane bioreactor (MBR), and moving bed biofilm reactor (MBBR)—were investigated to treat textile wastewater from a local industry. The results showed that technically, MBR was the most efficient technology, of which the chemical oxygen demand (COD), total suspended solids (TSS), and color removal efficiency were 91%, 99.4%, and 80%, respectively, with a hydraulic retention time (HRT) of 1.3 days. MBBR, on the other hand, had a similar COD removal performance compared with CAS (82% vs. 83%) with halved HRT (1 day vs. 2 days) and 73% of TSS removed, while CAS had 66%. Economically, MBBR was a more attractive option for an industrial-scale plant since it saved 68.4% of the capital expenditures (CAPEX) and had the same operational expenditures (OPEX) as MBR. The MBBR system also had lower environmental impacts compared with CAS and MBR processes in the life cycle assessment (LCA) study, since it reduced the consumption of electricity and decolorizing agent with respect to CAS. According to the results of economic and LCA analyses, the water treated by the MBBR system was reused to make new dyeings because water reuse in the textile industry, which is a large water consumer, could achieve environmental and economic benefits. The quality of new dyed fabrics was within the acceptable limits of the textile industry.

Ensuring sustainability of conventional aerobic wastewater treatment system via bio-augmentation of aerobic bacterial consortium: An enhanced biological phosphorus removal approach

Enhanced biological phosphorus removal (EBPR) is an inevitable need of sustainable waste water treatment systems (WWTS). In this regard, this study aimed to investigate the potential of an aerobic continuously stirred tank reactor (CSTR), enriched with selected bacterial consortium, for enhanced phosphorus removal. The CSTR biomass was bioaugmented through addition of 12 distinct phosphorus accumulating and solubilizing strains. The medium and high strength synthetic waste water, having the phosphorus concentration in the range of 1.4–40 mg/L, was fed to the CSTR throughout this study. With respect to medium strength feed, total phosphorus (TP) removal efficiency reached up to 90% at an influent concentration of 20 mg/L, followed by a declining trend of removal efficiency as 62 and 30%, at the TP concentration of 30 and 40 mg/L, respectively. Contrary, the EBPR activity was observed to be inhibiting (lesser accumulation of phosphorus in biomass) at lower influent TP value of 10 mg/L, when the CSTR was operated with high strength waste water. Further, ammonical nitrogen and chemical oxygen demand removal performance of the system was observed to be independent of influent TP concentration. Detailed experimental investigations revealed that the inoculated bacterial consortium favored the transformation and storage of influent TP into intracellular storage of polyphosphate (poly-P). Overall, the results indicated that the sustainability of existing WWTS can be ensured through bioaugmentation of non-EBPR sludge to aerobically cultivated EBPR performing sludge.

Treatment of typical antibiotics in constructed wetlands integrated with microbial fuel cells: Roles of plant and circuit operation mode

This study evaluated the removal efficiencies of sulfamethoxazole (SMX), tetracycline (TC) and their common co-existing contaminants, i.e., chemical oxygen demand (COD) and nitrogen in constructed wetlands integrated with microbial fuel cells (MFC-CWs), as affected by plant, circuit operation mode and influent antibiotic loads. The results demonstrated that MFC-CWs with plant and circuit connection exhibited the best performance in SMX and TC removal. The removal percentages for SMX and TC were 99.70–100% and 99.66–99.85% at HRT of 1 d, respectively, in MFC-CWs with plant and circuit connection when the influent SMX and TC concentrations were 5–100 μg L−1 and 5–50 μg L−1. The removal efficiencies of both SMX and TC were mainly enhanced by the circuit connection, compared to the plants. The presence of plant and circuit connection also accelerated the accumulation of SMX and TC in electrode layers, and the residues of both antibiotics in the anode layer were higher than in the cathode layer. Besides, closed-circuit MFC-CWs showed better COD removal performance than open-circuit MFC-CWs, irrespective of the increasing influent COD and antibiotic concentrations. The NH4+-N removal in MFC-CWs was mainly promoted by the presence of plants and decreased with increasing influent antibiotic concentrations. Additionally, the bioelectricity generation of planted MFC-CWs was better than in unplanted systems. The coulombic efficiencies in both planted and unplanted MFC-CWs decreased with increasing influent antibiotic concentrations. In summary, MFC-CWs with plant and circuit connection have potential for the treatment of wastewater containing SMX and TC.

Long-term effect of different Cu(II) concentrations on the performance, microbial enzymatic activity and microbial community of sequencing batch reactor

The performance, microbial community and enzymatic activity of sequencing batch reactors (SBRs) were investigated under 75-day exposure of different Cu(II) concentrations. Cu(II) at 0–5 mg/L had no distinct impact on the chemical oxygen demand (COD) and nitrogen removal, oxygen-uptake rate (OUR), nitrification and denitrification rate, and microbial enzymatic activity. The inhibitory effects of Cu(II) at 10 and 30 mg/L on the nitrogen removal rate, OUR, and microbial enzymatic activity of SBR increased with an increment in operation time due to the Cu(II) biotoxicity and the Cu(II) accumulation in activated sludge. The changes of microbial reactive oxygen species production, lactate dehydrogenase release, catalase activity and superoxide dismutase activity demonstrated that Cu(II) at 10 and 30 mg/L broke the equilibrium between the oxidation and antioxidation processes in microbial cells and also damaged the cytomembrance integrity, which could affect the COD and nitrogen removal performance and change normal microbial cell morphology. The Cu(II) in the influent could be removed by the microbial absorption and accumulated in the activated sludge under long-term exposure. The microbial community displayed some distinct changes from 0 to 30 mg/L Cu(II). In contrast with 0 mg/L Cu(II), Nitrosomonas, Nitrospira and some denitrifying bacteria obviously decreased in relative abundance under long-term exposure of 10 and 30 mg/L Cu(II).

Optimization and simulation of a carbon-based flow-through composite anode configuration to enhance power generation and improve effluent quality simultaneously for microbial fuel cells

As a viable wastewater treatment and energy recovery technology, microbial fuel cell (MFC) requires more research with regard to the simultaneous achievement of high-quality effluent and high power generation. In this study, a novel flow-through carbon-based composite anode configuration is proposed, which combines the carbon cloth of two-dimensional anode with wooden granular activated carbon of three-dimensional anode. The proposed configuration enhances the performance of power production and chemical oxygen demand degradation by promoting the mass transfer, reducing internal resistance and increasing bioburden. Microbial fuel cell with the composite anode exhibited the highest maximum power density (1300 ± 50 mW m−2) and the highest chemical oxygen demand removal rate constant (0.155 ± 0.007 h−1) compared with the microbial fuel cell using the carbon cloth anode (1136 ± 46 mW m−2 and 0.072 ± 0.008 h−1) or the wooden granular activated carbon anode (1045 ± 32 mW m−2 and 0.129 ± 0.009 h−1). Meanwhile, at a lower chemical oxygen demand concentration (about 48 mg L−1), the microbial fuel cell with the composite anode maintained a current density of 2.4 A m−2, which is 18% higher than the wooden granular activated carbon anode (2.04 A m−2) and 400% higher than the carbon cloth anode (0.48 A m−2). The cyclic voltammetry and electrochemical impedance spectroscopy tests confirmed that the composite anodes displayed better electrochemical performance. Improving the flow rate and reducing the external resistance could effectively enhance the power production and chemical oxygen demand removal performance of microbial fuel cells, while the computational fluid dynamics simulation intuitively demonstrated the positive effect of the composite anode on chemical oxygen demand degradation. These results suggest that the flow-through composite anode provides a feasible strategy to simultaneously enhance the power generation and improve the effluent quality.

Evaluation of Pilot-Scale Constructed Wetlands with Phragmites karka for Phytoremediation of Municipal Wastewater and Biomass Production in Ethiopia

A pilot horizontal subsurface flow constructed wetland (HSSFCW) was constructed, covered with geomembrane, and packed with gravel as substrate. Phragmites karka was planted in one cell and the other cell was left unplanted. The experiment was carried out over a 3-year period at two hydraulic loading rates (HLRs): 0.025 m/d and 0.05 m/d. The aim of the study was to evaluate the phytoremediation and biomass production potential of Phragmites karka for municipal wastewater treatment to remove chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP). The highest average COD, TN, and TP removal performances attained were 94.1%, 97.3%, and 89.9%, respectively, at HLR of 0.025 m/d, and 90.4%, 86.8%, and 88.5%, respectively, at HLR of 0.05 m/d. COD, TN, and TP removal performances were considerably higher in the planted HSSFCW than in the unplanted (p < 0.05). The study found: a progressive increase in plant density, from 3 ± 1 to 113 ± 43 shoots per m2; an increase in plant height (erect), from 8 to 365 cm; and growth of the running stem of P. karka (stolon) to 16 m after 16 months. The maximum nutrient content and nutrient accumulation of the above-ground biomass of P. karka recorded were 78.7 gN/kg DW and 21.6 gP/kg DW, and 2014.7 gN/m2 and 550.4 gP/m2 throughout the experimental period. The findings from the experiments showed the successful performance of the HSSFCW cell planted with P. karka for the treatment of municipal wastewater. P. karka demonstrated high biomass production and high nutrient removal performance. We conclude that scaling up this pilot HSSFCW has great potential for treating municipal wastewater in Ethiopia and other low-income countries with similar climatic conditions.

Effects of Hydraulic Retention Time and Solid Retention Time of POME on COD Removal Efficiency

The aim of this paper is to report on the effects of Hydraulic Retention Time (HRT) and Sludge Retention Time (SRT) on the removal of Chemical Oxygen Demand (COD) from palm oil mill effluent (POME). In this study, an upflow anaerobic reactor was used to evaluate the effects of HRT at 6, 8 10, 12 and 15 days. In order to measure the effects of SRT, the 10, 15 and 20 days aged sludge were used. The differences in COD value of POME and effluent at inlet and outlet of the anaerobic reactor were used to measure the effects of HRT and SRT. The experiments were conducted at 35oC for a length of 60 days, and input-output data of COD were used to achieve the research objectives. The estimated results show that the COD removal was optimum at 12 days of HRT and the estimated COD removal performance was at 40.4 percent. It was also found that COD removal was optimum at 20 days of SRT and the estimated COD removal performance was at 34.1 percent. The study concluded that anaerobic reactor is an effective method to remove COD from POME. This study recommends future researches which aim to increase COD removal to level that is economically and environmentally sustainable.

Effect of Green synthesized iron nanoparticles by Azardirachta Indica in different proportions on antibacterial activity

Green synthesis of iron nanoparticles has accumulated an ultimate interest over the last few years to their distinctive properties, applicable in various fields of science and technology. In the present study, synthesis of iron nanoparticles using Azadirachta Indica leaf extract is performed. Different proportions of precursor (ferrous sulphate) to leaf extract were prepared by varying the volume quantity of leaf extract from 1:1 to 1:5. Their morphology, structure and size distribution is confirmed by Scanning Electron Microscope along with X-ray energy dispersive spectroscopy and Fourier Transform Infrared spectroscopy analysis. Presence of accountable polyphenols such as total phenolic content by Folin-Ciocalteau(FC) method (20 mg per gram of leaf extract) and gallic acid(0.280 mg/g), caffeic acid(0.278 mg/g) &catechin(0.532 mg/g) for synthesis conciliation and were quantified by High Performance Liquid Chromatography. Its performance is evaluated on treatment of petrochemical refinery waste water to assess Chemical Oxygen Demand(COD) and nitrate removal for different proportions. The performance of COD removal (77%) and nitrate removal(74%) for 1:5 on 5th day is observed to be efficient. To further study this effect, size of FeNPs formed and concentration of polyphenols were taken into consideration. Antibacterial activity of synthesized iron nanoparticles from AI leaf extract on bacteria (Escherichia Coli, Pseudomonas Aeruginosa, and Staphylococcus Aureus) is accomplished by well diffusion method. Size of FeNPs achieved for 1:2 ratio was 98–200 nm and for all proportions varying between 120 and 600 nm due to agglomeration enhanced bacterial decay. It was portrayed that there was an increase in the inhibition zone as the proportions increased from 1:2 to 1:5. Hence for the contact time of 48 h, 1:5 found to be effective in inhibiting more number of bacterial cells compared to other proportions.