Initial COD Concentration Research Articles

Sustainable treatment of combined industrial wastewater: synergistic phytoremediation with Eichhornia crassipes, Pistia stratiotes, and Arundo donax in biofilm wetlands

This study investigates the treatment of combined wastewater from Hattar Industrial Estate using Biofilm Wetlands (BW) planted with monoculture species: Eichhornia crassipes (EAC), Pistia stratiotes (WL), and Arundo donax (GR). Each species showed distinct capabilities in organic degradation, metal uptake, and pH stabilization. BW2, planted with EAC, achieved the highest total solids (TS) and total suspended solids (TSS) removal efficiencies of 66% and 65%, respectively. GR effectively reduced initial COD concentrations from 232 mg/L to 58.67 mg/L, while EAC and WL reached reductions to 72.78 mg/L and 70.67 mg/L, respectively. Overall, the plant efficiency ranking was EAC > GR > WL. These findings underscore the potential of these plant species in synergistic BW systems, highlighting their role as natural solutions for remediating complex industrial effluents. This research contributes to advancing eco-friendly wastewater treatment approaches, suggesting promising applications for sustainable practices in industrial contexts. RESEARCH HIGHLIGHTS This research assessed the effectiveness of phytoremediation using Eichhornia crassipes, Pistia stratiotes, and Arundo donax for removing pollutants i.e. heavy metals (Cd, Pb, Ni, K, Ca, Mg, Na, Fe, Hg) nitrates, phosphates and sulfates from combined industrial wastewater of Hattar Industrial Estate Pakistan. It highlighted the potential of selected plant species’ as natural treatment systems, providing crucial insights into their efficiency. Findings contribute to understanding nature-based solutions for complex industrial effluents.

Simultaneous removal of heavy metals and electricity generation from wastewater in constructed wetland-microbial fuel cells

Constructed wetlands (CWs) are environmentally friendly and cost-effective methods for wastewater treatment. Recently, there have been innumerable efforts to integrate CWs with microbial fuel cells (MFCs) to enhance the removal of pollutants while generating electricity. Constructed Wetland-Microbial Fuel Cells (CW-MFCs) are engineered systems incorporating physical, chemical, and biological processes for wastewater treatment. However, the application of CW-MFCs to remove multiple heavy metals from wastewater is still an active area of research. The present study explores for the first time the utilization of different types of CW-MFCs, including CW-MFC-planted, CW-MFC-unplanted, and CW-sand-filter for simultaneous removal of different concentrations of organic pollutants and multiple heavy metals such as zinc (Zn), cadmium (Cd), copper (Cu), and lead (Pb) from wastewater while generating electricity. The study employed nine CW-MFC microcosms, some of which were planted with Phragmites australis. The initial concentrations of Cu, Pb, Zn, and Cd were maintained at 2, 10, and 30 mg/l, respectively, while initial COD concentrations were 120, 500, and 1000 mg/l. Remarkably, the maximum removal rates achieved were 98.83 %, 95.74 %, 92.91 %, and 90.75 % for Cu, Pb, Zn, and Cd, respectively, and the maximum removal rate of COD was 97.96 % at 10 mg/l of Cu, Pb, Zn, Cd, and 500 mg/l of COD in CW-MFC-planted. The attained highest voltage, current, and power densities reached 687 mV, 4000 mA/m3, and 785.86 mW/m3, respectively, in CW-MFC-planted. This study demonstrates the significant impact of CW-MFC-planted systems on wastewater treatment and electricity generation.

Bentonite-Clay/CNT-Based Nano Adsorbent for Textile Wastewater Treatment: Optimization of Process Parameters

Dyes are the most carcinogenic organic compounds that are discarded by most of the textile industries without any prior treatment, which is harmful for the environment. This study aims to develop a bentonite-clay/carbon-nanotube (CNT)-based adsorbent to treat textile wastewater for water sustainability. The preliminary and post-characterization of adsorbent involves scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and Brunauer–Emmett–Teller (BET) and energy-dispersive X-ray (EDX) analysis to determine the changes in surface morphology, functional group, and surface area of the adsorbent. Linear and nonlinear isotherms and kinetic studies were performed to explore the sorption mechanism. The results show that the nonlinear form of the Langmuir isotherm best fits adsorption with a qmax of 550 mg/g. The adsorption followed the nonlinear pseudo-first-order kinetics, favoring chemisorption with R2 ≈ 1 and X2 = 0.22. Maximum dye removal (89.9%) was achieved under the optimum conditions of pH 3, an adsorbent dose of 100 mg, and a contact time of 120 min, with an initial COD concentration of 1140 mgL−1. This study has demonstrated the successful application of a bentonite-clay/CNT-based adsorbent on textile wastewater treatment.

Simultanous Electricity Production and Wastewater Ttreatment in a Microbial Fuel Cell Inoculeted with Anaerobic Sludge

In order to reduce the environmental pollution associated with the conventional energy sources and to achieve the increased global energy demand, alterative and renewable sustainable energy sources need to be developed. Microbial fuel cells (MFCs) represent a bio-electrochemical innovative technology for pollution control and a simultaneous sustainable energy production from biodegradable, reduced compounds. This study mainly considers the performance of continuous up flow dual-chambers MFC fueled with actual domestic wastewater and bio-catalyzed with anaerobic aged sludge obtained from an aged septic tank. The performance of MFCs was mainly evaluated in terms of COD reductions and electrical power output. Results revealed that the COD removal efficiency up to 89% was obtained for wastewaters having an average initial COD concentration of 350 mg/L. Stabilized power outputs were clearly observed achieving a maximum value of 170 mW/ m2.

Optimizing leachate treatment with titanium oxide-impregnated activated carbon (TiO2@ASC) in a fixed-bed column: characterization, modeling, and prediction study.

This research focused on the application of a fixed bed column filled with immobilized titanium oxide-loaded almond shell carbon (TiO2@ASC) for the treatment of leachate. The adsorption performance of synthesized TiO2@ASC in fixed bed column is analyzed using adsorption experiments and modeling study. The characteristics of synthesized materials are determined by several instrumental techniques like BET, XRD, FTIR, and FESEM-EDX. The flow rate, initial concentration of COD and NH3-N, and bed height were optimized to determine the effectiveness of leachate treatment. The linear bed depth service time (BDST) plots equations with a correlation coefficient of greater than 0.98 confirmed the model's accuracy for COD and NH3-N adsorption in column structure. The adsorption process was found to be well predicted by an artificial neural network (ANN) model with a root mean square error of 0.0172 and 0.0167 for COD and NH3-N reduction, respectively. The immobilized adsorbent was regenerated using HCl and was found to be reusable for up to three cycles, promoting material sustainability. This study is aimed to contribute towards SDG 6 and SDG11 by United Nations Sustainable Development Goals.

3D N-doped carbon derived from zeolitic imidazole framework as heterogeneous catalysts for decomposition of pulp and paper mill effluent: Optimization and kinetics study

Three specific catalysts, namely ZIF-67 (zeolitic imidazolate framework-67), Co@NCF (Co@Nitrogen-Doped Carbon Framework), and 3D NCF (Three-Dimensional Nitrogen-Doped Carbon Framework), were prepared and studied for pulp and paper mill effluent degradation using heterogeneous activation of peroxymonosulfate (PMS). Numerous characterizations, including scanning electron microscopy (SEM), X-ray diffraction (XRD), and N2 adsorption, were used to characterize the properties of three different catalysts. 3D NCF is remarkably effective at heterogeneous activation of PMS to generate sulfate radicals to degrade pulp and paper mill effluent (PPME) compared to the other as-prepared catalysts. The catalytic activity reveals a sequence of 3D NCF > Co@NCF > ZIF-67.3D NCF could degrade organic pollutants in 30 min at an initial COD concentration of 1146 mg/L of PPME, 0.2 g/L catalysts, 2 g/L PMS, and 50 °C. Consequently, it was observed that the degradation of PPME using 3D NCF followed first-order kinetics, with an activation energy of 40.54 kJ mol−1. Overall, 3D NCF/PMS system reveals promising performance for PPME removal.

Valorization of brewery waste slurry with glycerol as co‐substrate for hydrogen and butyrate production using dark fermentation

AbstractBACKGROUNDAmong the methods to produce hydrogen biologically, dark fermentation stands out mainly due to its low operating requirements. Organic wastes, such as brewing industry waste slurries and glycerol, can provide a cost‐effective feedstock with the additional potential of generating value‐added byproducts, while addressing a wastewater treatment issue.RESULTSThe hydrogen production potential in dark fermentation of a high‐strength brewery waste slurry was optimized with a selected seed sludge, initial COD concentration of 50–60 g L−1, pH 6.4 and fermentation time of 30 h. The main end product was butyric acid, accounting for over 50% of the carboxylic acids. The efficiency of the process on the basis of volume of H2 obtained per gram of COD converted into organic acids was 393 ± 5 and 430 ± 6 mL without and with glycerol, respectively, and the molar ratio of H2 per mole of substrate was 71% of the theoretical molar yield when the fermentation is dominated by butyrate as the end product.CONCLUSIONSA proposed brewery sludge treatment system comprising dark fermentation followed by anaerobic digestion is promising and can be more advantageous than anaerobic digestion alone with an increase of 18.5% in energy potential. Alternatively, with recovery of valuable butyrate, a reduction in 4.5 kg of CO2 emissions per cubic meter of sludge treated can be achieved, with a 27% net loss in energy potential. © 2023 The Authors. Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI).

The Electrochemical removal of Oil and COD from petroleum wastewater

Recently, COD and oil concentrations in the water have increased, as a result of reduced water volumes and increased industrial waste being dumped into the river. Increased concentrations of these pollutants lead to health and environmental problems. As the water treatment plants use the usual methods of water treatment and could not reduce the concentration of oil and COD to the limit set by the World Health Organization, so an effective way to treat these pollutants became absolutely necessary. In this study, electrochemical method was used to treat water contaminated with oil and COD, using aluminium and iron electrodes as positive electrode and cathode electrode. A coagulation cell with a volume of 2 litters was also used in the work. Several factors affecting the process of treating oil and carbon dioxide pollutants were studied, and these factors were as follows: Submerge depth, Number of electrodes, the distance between the electrodes. From the results, it was found that the optimum removal was 94.2% for oil, and 99.5% for COD. It was achieved when the number of electrodes was 4 aluminium and 4 irons, the distance between the electrodes was 2 cm, the depth was 12 cm, and the function variables were acidic equal to 7, time 50 min, and voltage 10.5 V. The concentration of sodium chloride is 0.5 g/l and the electrode material is aluminium as anode and cathode and the initial oil concentration is 95 mg per litter, initial COD concentration is 710 mg per litter and the consumption of energy was estimated to be 12 kwh/m³, the TSS was 73 mg/l. The results demonstrated that the electrochemical is a feasible technique for treatment of oily contaminated petroleum refinery wastewater.

Potential use of Foundry sand and Furnace blast sand for fabrication of visibly active composite to promote circular economy/waste-management for treating real agro-industrial wastewater.

A two-step process of coagulation/flocculation followed by a simultaneous dual process (photocatalysis + photo-Fenton) is developed to treat real pulp and paper (P and P) industry wastewater. The rigid stout color wastewater was treated using a sunlight-responsive and cost-effective Fe-TiO2 composite using recirculating photoreactor with a total working volume of 4L. The key point of this study is that the treatment is done in very less time (90 min) and it incorporates the idea of circular economy, as the composite is fabricated out of industrial rejects. The further intensification of the process was done by proper process optimization of both approaches. With an initial concentration of stout color (0.78 AU) and COD (2200 mg/L), the optimized conditions gave a good reduction in % color and % COD i.e. 64.1% and 41.8% (1280 mg/l) after coagulation/flocculation and 89.74% and 53.12% (600 mg/l) after dual respectively. The composite was characterized by using various techniques like FESEM/EDAX, UV-vis DRS, XRD, etc. to check the catalyst composition, complexes formed between Fe-TiO2, and the catalyst intactness in both fresh and 50 times recycled composite. A trapping study was also performed using various quenchers to confirm that OH• plays a major role in the present study amongst other radicals produced where 55-60% drop in color removal was seen. In order to foresee the commercial use of this study, the process' cost was also estimated.

Biodegradation and power production kinetics in microbial fuel cell during rice mill wastewater treatment

The influence of the initial substrate concentration of rice mill wastewater on substrate degradation rate and power production in a dual-chambered MFC was explored over a wide range of chemical oxygen demand (COD: 500–6000 mg/L) and lignin (77.5–930 mg/L) levels. Within a limited concentration range, increasing COD concentration increased degradation rates and electricity generation, but both processes were hindered at high substrate concentrations. A maximum power density of 4.3 W/m3 was attained in a MFC operated with an initial COD concentration of 2480 ± 17 mg/L which can be attributed to the low ohmic resistance (23.8 Ω) due to better solution conductivity. Different kinetic models were used to examine inhibition kinetics from an electrical perspective. The relationship between power density and COD concentration was best described by Han–Levenspiel model. The maximum power density, half-saturation constant, and critical inhibitory concentration were predicted to be 4.56 W/m3, 799.6 mg/L, and 7627 mg/L, respectively. A maximum lignin degradation rate of 0.063 ± 0.007 kg/m3∙d was achieved at a lignin concentration of 387.5 ± 2.8 mg/L which accounts for 83.17 ± 0.26 % removal efficiency, suggesting the possibility of lignin degradation in MFC even at higher concentrations. The detection of low molecular weight degradation by-products of lignin in the effluent sample further confirmed the ability of exoelectrogens to degrade lignin.

Decolorization of Boron-Based Wood Preservatives by Ozonation for Recycling: Optimization of Process Parameters

Preservation of sawn timber from rubber trees with a water-soluble mixture of boric acid and borax generates a large quantity of colored wood preservative solutions and carries toxic metals, especially boron. To save costs, millers commonly reuse the colored mixtures in successive preservation cycles but regularly add boric acid and borax to maintain boron levels. However, this strategy affects both the color and the economic value of the treated wood. This paper presents a new strategy to treat the colored mixture of waterborne preservative solutions using ozonation for recycling purposes. At optimum conditions which are determined by response surface methodology, very high color removal (96 - 97 %) is achieved from ozone treatment of the wood preservatives with an initial COD concentration of 2,250 ± 40 mg/L and solution pH of 3.59 ± 0.02 for 65 min reaction time. The effluent can be reused in successive preservation cycles without degrading the wood quality in terms of the color of the processed timber and boron penetration in the end grain as well as the sides of the wood. Ozone treatment shows to be a promising color removal technology for sawn rubberwood industry, aimed at the reuse of waterborne preservatives, resulting in direct environmental and economic benefits. HIGHLIGHTS Application of ozone (O3) can be a clean technology to treat the color of aqueous solutions for in-process recycling in sawn rubberwood industry Box-Behnken design and Response Surface Methodology applied to find the optimum conditions for color removal from the mixture of boric acid and borax Recycling the mixture of boric acid and borax in a subsequent wood preservation operation gave very promising results The reusability of boron-based wood preservative solutions after ozonation minimizes the occurrence of industrial chemical waste GRAPHICAL ABSTRACT

Advanced Wastewater Treatment by Using Entrapped nZVI into Alginate (Ag) Biopolymer: Adsorption Isotherm, Kinetic Models, and Statistical Analysis

Wastewater treatment by nanotechnology, specifically magnetic nanosorbent as nanoZero Valent Iron (nZVI), is a new technology for degradation of wide ranges of organic pollutants by the effect of free electrons as Advanced Oxidation Processes (AOPs) and adsorption processes. Due to their effectiveness, economic, and safety properties, this study prepared and characterized nZVI to be entrapped into natural alginate biopolymer (Ag/nZVI). The removal of wastewater chemical pollutants was tested by studying the variations of COD levels. The effect of operating conditions was studied at different pH, Ag/nZVI doses (g/L), contact time (min), stirring rate (rpm), and initial COD concentrations. Also, Adsorption isotherm, kinetic studies were conducted to estimate equilibrated reaction mechanisms. Linear regression analysis was tested to find the Response Surface Methodology (RSM) relations between variables and removal percentages. Nonlinear Feed-Forward backpropagation system was built for Artificial intelligence neural networks (ANNs) importance detections. Finally, this study approved effective COD removal percentages reached 76%. The maximum removal efficiency for initial COD concentration 400 mg/L was observed at pH 6, using wet dose 3g/L, 30min, and 150 rpm.

Treatment of printing ink wastewater using a continuous flow electrocoagulation reactor

Printing ink wastewater from printing facilities is difficult to treat because of its heavy pollutant load (chemical oxygen demand - COD, color and total suspended solids - TSS). In this study undiluted printing ink wastewater with high COD (i.e., 20,000 mgL−1) was treated using a highly efficient, continuous flow electrocoagulation reactor with aluminum electrodes. The parameters investigated were: initial COD concentration (4000, 10,000 and 20,000 mgL−1), current density (21, 42 and 83 mAcm−2), and inlet flow rate (6, 8 and 10 mLmin-1). All parameters showed great efficiency in terms of pollutant removal for diluted printing ink wastewater. For undiluted printing ink wastewater treatment, COD, color, and TSS removal were maximized at 6 mLmin-1 flow rate reaching 82%, 98%, and 85% COD, color, and TSS removal, respectively, by applying the lower tested current density 21 mAcm−2. COD, color and TSS removal increased with increasing current density. For undiluted printing ink wastewater and a flow rate of 8 mLmin-1, COD removal was between 42 and 88%, color reduction between 85 and 99%, and TSS reduction between 83 and 98% when the applied current was increased (from 21 to 83 mAcm−2). Lower pollutant removal was observed at the highest flow rate of 10 mLmin-1 for all current densities tested. Process cost calculations in terms of electrical energy, electrode material consumption and sludge disposal, showed that the use of continuous flow electrocoagulation reactor (with flow rate 6 mLmin-1, and at 21 mAcm−2) is an affordable and effective treatment method for printing ink wastewater streams with very high COD. Sludge characterization showed Al-silicate-rich sludge. Particle sizes increased after treatment and Cu and Ti were detected in the sludge. A post-treatment stage is necessary before discharging effluent into water bodies.

Electricity generation enhancement in microbial fuel cell via employing a new SPEEK based proton exchange membrane modified by goethite nanoparticles functionalized with tannic acid and sulfanilic acid

In this work, hydrophilic nanoparticles of goethite and its derivatives with functional groups of tannic acid and sulfanilic acid were prepared. The synthesized nanocomposites were embedded into sulfonated poly ether ether ketone (SPEEK) as base polymer of proton exchange membrane (PEM) for improvement of microbial fuel cell (MFC) performance. The SEM images, FTIR and AFM tests and contact angle measurements verified hydrophilic properties of the fabricated membranes. Proton exchangeability of the fabricated PEMs was examined in a two-chamber MFC under the same operating conditions (initial COD and biomass concentration of 3300 and 1500 mg/l, respectively). The MFC performance was assessed in terms of COD removal, coulombic efficiency, power density and current density. The best result was obtained from SPEEK nanocomposite membrane with goethite 0.5% wt. The proposed PEM showed significant improvement in terms of the maximum power density (73.7 mW/m 2 ) and current density (293 mA/m 2 ) compared to the bare membrane. A relatively high coulombic efficiency of 52.6% with COD removal of 97.6% was achieved. • Goethite NPs comparing to its derivatives with functional group of tannic acid and sulfanilic acid was a desirable modifier. • The optimal fabricated proton exchange membrane of SPEEK-goethite 0.5 %wt. showed an excellent performance in MFC. • The maximum power density and coulombic efficiency achieved for the optimal PEM were 73.7 mW/m2 and 52.6%, respectively. • Performance of the MFC operated with the selected PEM in terms of COD removal efficiency was 97.6%. • The reliability of the MFC was confirmed by testing its power to lighten red LED bulbs when four MFCs connected in series.

Modeling of continuous adsorption of greywater pollutants onto sawdust activated carbon bed integrated with sand column

The real greywater samples collected from the IIT Roorkee hostel have been treated using waste biomass-derived activated carbon in continuous operation. The synthesized ZnCl2 impregnated sawdust activated carbon (SAC) has been used to remove the COD, BOD, and TDS concentration from the greywater. The SAC characterization through FESEM-EDX, BET, and FTIR has been performed. The initial concentration of COD, BOD, and TDS in greywater was 670, 275, and 1819.52 mg/L, respectively. The sand column was used to retain the larger suspended solids and dissolved organic matter up to a certain concentration. Sand column effluent with the concentration of 412, 180, and 1116.8 mg/L for COD, BOD, and TDS respectively, was drawn to the adsorption column for studying the influence of flow rate (5, 10, and 15 mL/min) at 15 cm of bed height and the effect of bed height (10 and 20 cm) at 10 mL/min of flow rate. At optimum condition of 10 mL/min flow rate and 10 cm of bed height, the observed adsorption capacities are 3904.62, 1967.3, and 14,936.92 mg/g for the removal of COD, BOD, and TDS, respectively. Further, to comprehend the behavior of the breakthrough curves eight mathematical models, namely, Bohart-Adams, Thomas, Wolborska, Yoon-Nelson, Log Gompertz, Gompertz, Dose-Response, and Bed Depth Service Time (BDST), have been tested.

Variations of Net C/N Ratio with the Coulombic Efficiency in Dual-cathode MFC for the Simultaneous Removal of Organics and Nitrogen

The objective of this study was to suggest a method of determining the appropriate C/N ratio in a dual-cathode MFC that allowed to remove nitrogen and organics simultaneously with a single external resistance. The electrochemical characteristics and removal performances of MFC was analyzed based on the initial dose of organic matter and nitrogen. While ammonia was consistently removed regardless of the initial COD concentration, the amount of nitrate removal decreased as the C/N ratio decrease. Also, the coulombic efficiency (CE) decreased as the initial COD concentration increased. The C/N ratios based on the influent substrate concentration was revealed of 1.8~8.5 that had wider range than that of 3.36~7.57 which was calculated from substrate concentration removed during the reaction. The calculated C/N ratio considering the CE was a relatively consistent 3.16. The net C/N ratio was similar to the stoichiometric value of 2.86 g NO3- N/g COD, showing that the electrons transferred to the cathode were mostly used for denitrification. Electrons produced from the oxidation of organic matter for denitrification in the MFC exhibited greater loss at the anode compared to the cathode. Consequently, the amount of COD required for denitrification can be determined by considering the CE to the net C/N ratio.

Upflow Anaerobic Filter for the Treatment of Wastewater from a Natural Rubber Latex Concentration Unit

In this study, wastewater from a centrifuge rubber latex concentration unit was experimentally treated by an up-flow anaerobic filter (UAF) at variable hydraulic detention time to investigate the COD removal efficiency and the gas production rate. The UAF reactors were made of PVC pipe with an inside diameter of 9.5 cm, 180 cm in height, with a bed volume of 12.8 L, and filled with polyethylene media. The initial COD concentration of wastewater was in the range 4620 - 10400 mg.L-1. HRTs were controlled at 20 days, with the organic loading rate varying from 2.9 to 10.5 kg.day.m-3. The findings show that the COD removal efficiency of the system was in the range of 85% to 92% for the varying organic loading rates. In addition, the specific methane production rate varied from 8.2 to 14 L of CH4 produced/g of COD destroyed/day for the different organic loading rates.

Application of ABR/zeolite for TKN removal from compost leachate

Compost leachate is a strong wastewater with high organics, TKN, and ammonia nitrogen and anaerobic processes like the ones carried out in an ABR are of interest. ABR is highly efficient in removing COD but the TKN removal performance in this reactor has been reported to be low, and only some part of organic nitrogen is converted to ammonia in it. Ammonia has inhibitory effects on the acetogenic bacteria and the biogas production efficiency. In this work, a pilot scale of ABR with 8 compartments was used, and its last four compartments were filled with zeolite. Based on the EDS analysis, the zeolite used was clinoptilolite with an ammonium adsorption capacity equal to 1.02 meq/g. The bioreactor was operated at HRTs of 3, 4, and 5 days, the filling ratios of 10%, 20%, and 30%, and the initial COD concentrations of 10 000, 20 000, and 30 000 mg/L. The results showed that the maximum removal efficiency of TKN and organic nitrogen was, respectively, equal to 48% and 100%. Increasing the filling ratio in the reactor increased the removal efficiency of TKN and organic nitrogen but increasing OLR reduced the removal efficiency of the reactor. The initial TKN/ammonia ratio was 0.45, which was increased by elevating the filling ratio in the reactor, and in 30%, it reached 0.91. The results obtained also showed that zeolite had a great effect on the ABR performance; therefore, it could be used to treat a highly strong wastewater to suppress the anaerobic biological growth inhibitors like ammonia.

Estimation of N2O emissions from wastewater characteristics in constructed wetlands

Conventional wastewater treatment plants (WWTPs) contribute significantly to the nitrous oxide (N2O) emissions. On the other hand, the contribution of constructed wetlands (CWs) to N2O emissions is not clear. In this study, a literature review was initially conducted to study the factors that are correlated with N2O emissions from these systems. Afterwards, a statistical formula was developed using the metaregression method for estimating N2O emission factors (EFs) from CWs. This formula related EFs with influent wastewater characteristics (chemical oxygen demand-COD, total nitrogen-TN, COD/TN) and was applied to 56 small Greek settlements for predicting N2O emissions in an alternate scenario where CWs technology would be applied instead of conventional WWTPs. The estimated N2O EFs for the alternate scenario at these settlements ranged between 0.21% and 3.20% (as N2O/TN influent load), while the average value was equal to 0.94%. The specific N2O emission was estimated to 60.82 mg N2O per day and person equivalent. The application of different scenarios with wastewater of different strength showed that the lowest N2O EF in CWs is expected for wastewater with high initial COD and TN concentrations. To compare N2O emissions from CWs and conventional WWTPs, the Ordinary Least Squares multiple regression method was also applied to develop a general statistical equation that relates N2O EFs from conventional WWTPs with wastewater characteristics. According to the results, the estimated N2O emissions from the Greek settlements for conventional wastewater treatment are larger for 77% of the studied cases compared to the emissions found if CW technology had been applied instead.

Management and kinetics of methane production from anaerobic batch reactors treating PET bottle washing wastewater

The study evaluated the methanogenic potential of anaerobic sludge in Wastewater from the Washing of PET (Polyethylene terephthalate) bottles sent for Recycling (WWPR). The bioreactors were inoculated with sludge from an upflow anaerobic sludge blanket reactor treating poultry waste. The operation occurred under anaerobic conditions at 35 °C and 150 rpm for three bioreactors in triplicate with the initial COD concentration of 2000 mg L−1 (C1), 5000 mg L−1 (C2), and 10,000 mg L−1 (C3). The inhibition in the anaerobic biological treatment caused by high surfactant concentration impaired the wastewater biodegradation. COD removals were 67.8 ± 0.4% (C1), 67.6 ± 2.7% (C2), and 59.1 ± 2.9% (C3), indicating a process inhibition in the latter condition. The modified Gompertz model indicated a cumulative methane production of 290 mL for condition C1 with an adjustment coefficient of 99.11%. The methane potential for the production of electricity revealed a maximum annual production of 188,292 MWh. Annual thermal energy from condition C1 could produce 1.01 × 108 PET bottles. Therefore, the anaerobic treatment of WWPR is an alternative to wastewater management, avoiding greenhouse gases emission and potentiating the generation of electrical and thermal energy.