Percent Chemical Oxygen Demand Research Articles

Comparative analysis of feed-forward neural network and second-order polynomial regression in textile wastewater treatment efficiency

<abstract><p>This study refines a single-layer Feed-Forward Neural Network (FFNN) for the treatment of textile dye wastewater, concentrating on percentage decolorization (%DEC) and percentage chemical oxygen demand (%COD) reduction. The optimized neural network configuration comprises four input and one output neuron, fine-tuned based on the mean squared error (MSE). The training phase demonstrates a consistent MSE decline, reaching its lowest at epoch 209 for %DEC and epoch 34 for %COD, with corresponding MSEs of $1.799 \times 10^{-5}$ and $ 1.4 \times 10^{-3} $, respectively. The maximum absolute errors for %DEC and %COD were found to be $ 4.0787 $ and $ 2.4486 $, while the mean absolute errors were $ 0.4821 $ and $ 0.7256 $, respectively. In contrast to second-degree polynomial regression, the FFNN model exhibits enhanced predictive accuracy, as indicated by higher $ R^2 $ values of $ 0.99363 $ for %DEC and $ 0.99716 $ for %COD, and reduced error metrics.</p></abstract>

Design of a compact wastewater treatment and isolation of microbial consortia for nutrient reduction of plastic recycling wastewater

The wastewater generated during the plastic recycling is an aspect that is often overlooked in the process. This wastewater contains pollutants that can affect the environment and human health. To address this problem, a study was conducted to design and evaluate the performance of an anoxic-oxic (AO) system and an anoxic-oxic-oxic (AO2) system in treating plastic recycling wastewater. Additionally, the study collected wastewater from a plastic recycling company and activated sludge from a sewage treatment plant to test the viability of biological treatment for treating plastic recycling wastewater. The results showed that both systems were effective at reducing chemical oxygen demand (COD), with the AO system having a higher percent COD removal (98.13%) than the AO2 system (85.33%). Also, there were 18 unique colonies isolated from the wastewater and activated sludge. Overall, the study concludes that biological treatment can be used to treat plastic recycling wastewater, and the design of upscaled system is crucial to fully solve the wastewater problem.

Optimisation of chemical oxygen demand removal from animal house wastewater using central composite design

In the developing world, most animal farmhouses dispose of their wastewater without treatment and that creates conditions for the spread of diseases. To discourage this practice, there is the need to provide relatively simpler wastewater treatment options. Thus, this research work sought to optimise the chemical oxygen demand (COD) removal efficiency of a simple anaerobic digester by determining the optimum concentrations of rhamnolipid biosurfactant and potassium phosphate buffer needed to make the anaerobic digester remove COD efficiently. The central composite design was used for the optimization study. In the one factor at a time experiment, increasing the concentration of the potassium phosphate buffer from 1.07 g/l K2HPO4 + 0.53 g/l KH2PO4 to 1.37 g/l K2HPO4 + 0.83 g/l KH2PO4 increased the COD removal efficiency of the anaerobic digester from 19.3 to 24.7%. Also, increasing the concentration of rhamnolipid from 80 to 320 mg/l increased the efficiency of the digester from 24.2 to 26%. The percentage COD removal was highly improved (> 85%) in the optimisation study when both rhamnolipid and buffer were combined at high levels (+ 1). The model built from the central composite design reflected a good fit of the data obtained with R2 of 82.5% and a p value of 0.000. This study therefore demonstrated that a simple anaerobic digester can be used to remove COD in wastewater by optimising the concentrations of rhamnolipid and potassium phosphate buffers in the treatment system.

Determination of optimum coagulant dosage in the treatment of abattoir wastewater, using calcium hydroxide as coagulant

This research was carried out to evaluate the effective and efficient treatment of abattoir wastewater using calcium hydroxide coagulant. Samples were collected from an abattoir unit in Ikpoba-Okha Local Government Area, Benin City, Edo State. The raw samples were characterized to determine: Dissolved oxygen (DO), chemical oxygen demand (COD), biochemical oxygen demand (BOD), temperature (T), pH, electrical conductivity (EC), turbidity, total dissolved solids (TDS), total suspended solids (TSS), total alkalinity (Alk), chloride, total Kjeldhal nitrogen (TN), hardness, potassium, phosphorous and total bacteria count (TBC). Thereafter, the samples were treated with several doses of calcium hydroxide coagulant (2g, 4g, 6g, 8g, 10g, 12g, 14g, and 16g). Results obtained were used to determine the optimum coagulant dosage in a plot of percentage COD against masses of coagulants used. From the optimum dose obtained (12g Ca(OH)2), a batch treatment was carried out. The treated wastewater was further characterized to ascertain compositional changes. Result revealed increase in oxygen and substantial reduction in chemical oxygen demand, total nitrogen, phosphorus and turbidity. Biochemical oxygen demand and total solids were also reduced. The treated effluent could be discharged into the environment without fear of pollution and may be reused for agricultural purposes.

Performance analysis of a half-batch multi-cell three-dimensional electrode reactor for drilling wastewater: COD removal, energy consumption and hydrodynamic characteristic

Although a three-dimensional electrode system (3DES) has made remarkable achievements in improving the property of electrodes and investigating pollutant degradation mechanism, the design of an electrochemical reactor for application in drilling wastewater has not been reported yet. In this study, a novel half-batch multi-cell 3DES reactor was constructed by us to degrade organic compounds from drilling wastewater. The separate effect of electrolysis time, current density, the configuration of granular activated carbon (GAC) electrodes, aeration rate and volumetric recirculation flow on chemical oxygen demand (COD) removal and energy consumption of the half-batch reactor were analyzed, and further optimization via response surface methodology (RSM). Results showed that the optimal operation conditions for the reactor included electrolysis time of 100 min, a current density of 9.2 mA/cm2, GAC electrode vertical configuration, an aeration rate of 2.67 L/min and a volumetric recirculation flow of 100 mL/min. Under these conditions, the maximum percentage COD removal was found to be 97.39% with an energy consumption of 77.89 kWh(kg COD)-1. The residence time distribution (RTD) method was carried out in continuous flow pattern to investigate the hydrodynamic characteristics of the reactor. Results showed that flow rate was the most dominant factor for the flow pattern of the reactor, followed by the aeration rate and current density. The low dispersion number and the percentage of dead volume are 0.214 and 3.87% when the flow rate of 100 mL/min, respectively, which indicates that there is an intermediate flow pattern existing in between plug-flow ideal and complete mixing flow, furthermore, it is close to the plug-flow ideal.

Sonocatalytic Tannery Effluent Degradation—Response Surface Methodology and Particle Swarm Optimization Embedded Artificial Neural Network Modeling Approach

AbstractExperimental studies are performed on the degradation of tannery effluent using an advanced oxidation process combined with sonication. A probe sonicator is used to enhance the advanced oxidation process in the presence of titanium di‐oxide (TiO2) catalyst. The effect of initial chemical oxygen demand (COD), ultrasound power intensity, probe diameter, and sonication time are studied. Box‐Behnken experimental design is used to study the effect of the process variables on percent COD reduction. 73.6% COD reduction is observed for the optimized condition of 825.71 mg L−1 initial COD of effluent, 542.58 W ultrasound power, 47.4 min of sonication time, and 18 mm probe diameter. The energy requirement calculated for the optimized condition is 2964.21 kWh m−3. The results of the response surface methodology (RSM) model are compared with a hybrid artificial neural network (ANN) model with particle swarm optimization (PSO). The ANN‐PSO model with a 4‐11‐1 architecture consisting of 15 swarm particles results in the coefficient of determination (R2) value of 0.989 and the mean square error value of 3.88 thereby, predicting the experimental results better than the response surface methodology (RSM) model. An attempt to elucidate the mechanism of degradation by sonication is made by gas chromatography‐mass spectrometry and Fourier transform infrared spectroscopy.

MoS2/WO3 heterojunction with the intensified photocatalytic performance for decomposition of organic pollutants under the broad array of solar light

Heterojunction photocatalysts have emerged as a stronger candidate for the decomposition of noxious pollutants in contrast to the single-component system. Herein, the binary composites of MoS2/WO3 (MSW) of the different weight ratios were synthesized by the hydrothermal method. Various analytical techniques were performed to investigate the structural, optical (band gap value is 2.5 eV), morphological as well as surface chemical composition of the as-prepared catalysts. A mean pore volume of 6.024 cm3/g, favourable surface area of 26 m2/g, and a pore diameter of 32.31 nm were all validated by surface area analyses. The creation of strong interfacial contact between MoS2 and WO3 caused the charges to be separated for a long time. The degradation of rhodamine B dye (Rh B) and colorless thiamethoxam (TM) under the influence of solar light was used to test the photocatalytic performance of the as-prepared catalyst. The maximum degradation efficiency of 90.20%, and 92.60% with the rate constant of 0.020 min−1, and 0.01858 min−1 was achieved for the photocatalytic degradation of TM, and Rh B, respectively using optimum ratio (1:3 MSW) in 120 min. The photocatalyst's effectiveness was further tested by reusability experiments (5 runs) and the characterization results afterwards indicated the intactness of crystalline planes that is responsible for high efficacy. The percent chemical oxygen demand (% COD) removal of ∼66.6 and 57.14% was attained for Rh B and TM, respectively while percent total organic carbon (% TOC) removal for these pollutants was around 49.5 and 76.48%, respectively after 120 min. The % COD and TOC removal of the real industrial waste water (WW) was analyzed to be 80 and 78.9%, respectively. The scavenger studies were performed to discover the primary reactive species. The gas chromatography-mass spectrometry (GC–MS) study was also carried out to investigate the intermediates and products formed in the photodegradation process of TM. The photocatalytic decomposition mechanism of the organic pollutants via MSW photocatalyst was finally proposed.

Comparative Anaerobic Co-Digestion Effects of Some Agricultural Biomass on Their Digestates Biochemical Properties

The huge agro-industrial biomass wastes had engendered the need for appropriate treatment technology, which could be deployed to sustainably manage and convert them to useful by-products. Consequently, the comparative anaerobic co-digestion effects of some agricultural biomass on their digestates biochemical properties were conducted. Twelve (12) replicates slurries from four mixing ratios of maize cob, poultry droppings and cow dung (1:0, 1:0, 1:0 and 1:1:1) as treatments TA, TB, TC and TD respectively, were separately digested in 13.6L locally fabricated batch-digester reactors, for eight weeks. Proximate and amino acids constituents were evaluated by standard procedure prior to and at post anaerobic digestion (AD). The biogas yields followed the sequence of TD (2200.7ml/kg) > TB (2197.9ml/kg) >TC (2079.0ml/kg) > TA (1713.2ml/kg), showing co-substrate effects. Proximate assay depicted a decrease in crude lipid across the treatments, with TC (86.82%) and TD (64.66%) as highest and lowest values. Crude fiber and nitrogen free extract had similar observation, apart from TB and TC with increased values. Percentage moisture and percentage ash contents increased across treatments. Carbon - Nitrogen ratio reduction (C/N Reduction) was in the range of 12.94 -85.79%. The Percentage chemical oxygen demand reduction (CODR), followed the order of TA (46.81%) > TB (34.15) >TC (25.81%) >TD (8.00%). There was increased histidine, glycine, cystine, methionine, total nonessential amino acids (TNEAA) and total aromatic amino acids (TArAA), with decrease in aspartic acids and serine. Percentage arginine, threonine, glutamic acid, proline, alanine, isoleucine, tyrosine, total amino acids (TAA) and total essential amino acid (TEAA) decreased only in TB. While, only TA had Percentage increased lysine (25.00%), valine (40.98%) and TArAA (6.13%), with phenylalanine unaffected (0.00%), Percentage leucine of TB (60.14%) and TD (23.08%) were reduced after AD. The process had revealed the alternative waste management, energy options, and useful industrial by-products for agro-allied industries.

Electrochemical technique for paper mill effluent degradation using concentric aluminum tube electrodes (CATE).

In this study, Taguchi experimental design was used to the optimize operating parameters for the degradation of paper mill effluent using electrochemical (EC) process with two-dimensional concentric aluminum tube electrodes (CATE). For this purpose, four significant experimental factors were used in four levels pH (6-9), electrolysis time (10-40min), voltage (6-12V)and surface area (357-624cm2). The process parameters were optimized, through performing L16 orthogonal array of Taguchi technique, for the removal of chemical oxygen demand (COD) and turbidity. The percent COD and turbidity reductions were transferred into an accurate S/N ratio for a largervalue is the better (LBT) response. The study presents a unique method of finding optimum combination of process parameters to illustrate their effect on the turbidity and COD reduction. The treatment conditions for the maximum elimination of the pollutants were second level of pH (7), third level of ET (30min), fourth level of voltage (12V) and second level of surface area (446cm2). The confirmation experiment results were within the confidence intervals (CI) indicating an acceptable agreement between predicted and observed values. Based on the p-values, the electrolysis time and voltages were found to be the most significant factors for both COD and turbidity reduction. The findings of research indicated, that the Taguchi method can be used successfully for the treatment of paper industry effluent by electrochemical technique.

Reduction of COD from real graywater by electro-coagulation using Fe electrode: Optimization through box-behnken design

The treatment of graywater has attained priority to engineers as these wastewater have the ability to be reused for non-potable purposes. In the present study, the use of batch-scale electro-coagulation (EC) is proposed for real graywater treatment using Iron (Fe) electrodes. The optimization and modelling has been carried out by using response surface methodology (RSM). The impact of pH, applied voltage and electrolysis time on EC performance was evaluated by calculating the reduction of chemical oxygen demand (COD). The optimum pH, applied voltage and electrolysis time were 8.67, 13.78 V and 60 mins respectively. Under these optimum conditions, the percentage COD removal and energy consumption was 70.09% and 0.04782 kWh/ kg COD removed respectively. The accuracy and reliability of the data predicted and calculated has been verified by ANOVA tool.

Photocatalytic Decolorization and Biocidal Applications of Nonmetal Doped TiO2: Isotherm, Kinetic Modeling and In Silico Molecular Docking Studies.

Textile dyes and microbial contamination of surface water bodies have been recognized as emerging quality concerns around the globe. The simultaneous resolve of such impurities can pave the route for an amicable technological solution. This study reports the photocatalytic performance and the biocidal potential of nitrogen-doped TiO2 against reactive black 5 (RB5), a double azo dye and E. coli. Molecular docking was performed to identify and quantify the interactions of the TiO2 with β-lactamase enzyme and to predict the biocidal mechanism. The sol-gel technique was employed for the synthesis of different mol% nitrogen-doped TiO2. The synthesized photocatalysts were characterized using thermal gravimetric analysis (TGA), scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Brunauer–Emmett–Teller (BET) and diffuse reflectance spectroscopy (DRS). The effects of different synthesis and reaction parameters were studied. RB5 dye degradation was monitored by tracking shifts in the absorption spectrum and percent chemical oxygen demand (COD) removal. The best nanomaterial depicted 5.57 nm crystallite size, 49.54 m2 g−1 specific surface area, 11–40 nm particle size with spherical morphologies, and uniform distribution. The RB5 decolorization data fits well with the pseudo-first-order kinetic model, and the maximum monolayer coverage capacity for the Langmuir adsorption model was found to be 40 mg g−1 with Kads of 0.113 mg−1. The LH model yielded a higher coefficient KC (1.15 mg L−1 h−1) compared to the adsorption constant KLH (0.3084 L mg−1). 90% COD removal was achieved in 60 min of irradiation, confirmed by the disappearance of spectral peaks. The best-optimized photocatalysts showed a noticeable biocidal potential against human pathogenic strain E. coli in 150 min. The biocidal mechanism of best-optimized photocatalyst was predicted by molecular docking simulation against E. coli β-lactamase enzyme. The docking score (−7.6 kcal mol−1) and the binding interaction with the active site residues (Lys315, Thr316, and Glu272) of β-lactamase further confirmed that inhibition of β-lactamase could be a most probable mechanism of biocidal activity.

Treatment of petroleum wastewater using synthesised haematite (α-Fe2O3) photocatalyst and optimisation with response surface methodology

ABSTRACT Haematite (α-Fe2O3) photocatalyst (HPC) has been synthesised by a modified solution combustion method. The prepared catalyst was characterised with a Scanning Electron Microscopy (SEM) and X-ray Diffractometer (XRD). Catalyst characterisation confirmed its composition and phase, but it also showed a slight lack in uniformity and crystallinity due to uncontrolled combustion caused by the modifications made to the preparation procedure. The photocatalyst was tested for the removal of pollutants present in the petroleum refinery wastewater (PRW) under UV-A lamp solar irradiation. A central composite design (CCD) with response surface methodology (RSM) was employed for optimisation of the model. The PRW treatment achieved a marked improvement in biodegradability, raising the biological oxygen demand (BOD)/chemical oxygen demand (COD) ratio from 0.074 to 0.604 in 90 min and percentage COD removal was 90.85% at a catalyst concentration of 5 g/L, pH 7.5 and hydrogen peroxide (H2O2)/COD ratio of 1 mg/mg. RSM optimisation predicted a maximum theoretical BOD/COD ratio of 0.661 and percentage COD removal of 94.73% at a catalyst concentration of 1.494 g/L, pH 7.5 and hydrogen peroxide (H2O2)/COD ratio of 1 mg/mg.

Assessment of algae-based wastewater treatment in hot climate region: Treatment performance and kinetics

This study evaluated the use of microalgae for wastewater treatment in hot climate regions. The growth rates of C. vulgaris (C.v.) and N. oleoabundans (N.o.) at 36 °C were studied in primary effluent (PE), secondary effluent (SE) and centrate (CEN) and their performance in removing soluble chemical oxygen demand (CODs), inorganic nitrogen and total dissolved phosphorus were determined. A comprehensive kinetics model was developed to predict algae growth and treatment efficiencies under the studied conditions. Significant differences between the growth patterns and rates of C.v. and N.o. were observed in different wastewater samples. C.v. showed the highest growth rate in CEN followed by PE and SE. N.o. showed the highest growth rate in PE followed by SE and CEN. The percentage CODs removals (%CODs) for C.v. were 51%, 55% and 80%, and for N.o. were 63%, 47% and 72% in PE, SE, and CEN, respectively. Ammonia removal efficiencies (70%–84%) were very similar for C.v. and N.o. in different wastewaters. Phosphorus removal by C.v. and N.o. was high in PE (> 84%), moderate in CEN (>22%) and limited in SE (<15%). Growth rates of C.v. and N.o and percent removals of CODs, ammonia, nitrate and total dissolved phosphorus at 36 °C were compared to those at 20 °C.The kinetics of algal strains, validated using experimental data, accurately reproduced the growth profile and evolution of organic matter and nutrients, permitting process optimization and scale-up. The results of the study showed that microalgae can be successfully cultivated in a wide range of wastewaters at 36 °C and can achieve natural treatment of wastewaters in hot climate regions by removing organic carbon, nitrogen, and phosphorus.

ASSESSMENT OF BIODEGRADATION EFFECTS OF AGRO-WASTES (POULTRY DROPPINGS AND COW DUNG) ON SOME PHYSICO-CHEMICAL PROPERTIES OF THEIR EFFLUENTS

Purpose: The biodegradation effects of agro-wastes (poultry droppings and cow dung) on some physico-chemical properties of the effluents were assessed. Methodology: Triplicate slurries (1:3 w/v) of five ratios of poultry droppings and cow dung: (0:1, 1:3, 1:1, 3:1 and 1:0 as treatments A, B, C, D and E) were separately fed into 13.6L locally constructed digesters, under strict anaerobic condition. They were kept for eight weeks retention period. Separate fractions of the undigested and digested treatments were subjected to standard assay procedures to determine their C, N, heavy contents, chemical oxygen demand (COD). The average weekly temperature and the pH before and after digestion of the media were measured. Findings: The cumulative biogas yield was in the order of treatment C (2961.0ml) &gt;D(2241.7ml) &gt; E(2197.9ml) &gt; A(2079.0ml) &gt; B(2031.1ml), based on the following mixing ratios 1:1&gt;3:1&gt;0:1&gt;1:0&gt;1:3. The gas production was affected by weekly temperature variation, which peaked at the mesophilic range (40.5±0.3 ̶ 44.1±0.3OC). The resultant pH of the digestates was in the order of 1:3 &gt; 3:1 &gt; 1:1 &gt; 0:1 &gt; 1:0. There was a general reduction in heavy metal contents for all treatment digestates, except Cu, with 200.00, 35.82 and 7.34% as %increases in treatments A, E and C respectively. All treatments indicated reduction in C:N ratios, ranging from 7.93 ̶ 13.02, in the order of 3:1&gt;1:1&gt;1:3&gt;0:1&gt;1:0. Similarly, there was decrease in COD contents for all treatments due to AD. Consequently, the percentage COD reduction (%CODR) was in the order of treatment D(53.70%) &gt; E(34.15%) &gt; C(29.63%) &gt; A(25.81%) &gt; B(19.23%). Unique contribution to theory, practice and policy: The biodegradation process had provided an effective means of alternative energy production, agricultural waste management initiative, which would ensure bioremediation, sustainable public health and environmental management

Reduction of Chemical Oxygen Demand (COD) Effluent of Plastic Recycling Processing Plant using LD Slag

In wastewater plastic recycling processing plant, commonly contain high chemical oxygen demand (COD) concentration. Coagulation-flocculation, adsorption and foam fractionation are the examples of treatment processes that can reduce COD concentration in wastewater. Steel slag can be used as an alternative to remove COD concentration of wastewater adsorption process. Linz-Donawitz (LD) slag can be obtained from steel manufacturing plant. LD slag also contains alkali oxides, porous characteristic, large surface area and contain an easy solid-liquid separation. This research is to study the percentage reduction of COD in wastewater using LD slag as adsorbent. This research will investigate the effect of particle size, dosage amount and contact time between LD slag and COD reduction. From the experiment, the highest percentage COD removal for particle size is 0.2mm, the dosage amount is 6 gram and the contact time is at 60 min. Comparison of COD removal by using coagulation -flocculation, adsorption using activated carbon and adsorption using LD slag processes was done. LD slag can reduce 2% higher of COD compared to activated carbon. LD slag should be invested more in wastewater treatment process.

Application of Electrocoagulation Methods to Reduce BOD and COD Content in The Soft Drink Industry’s Wastewater with Addition Bittern

Wastewater from the soft drink industry must be treated before release to reservoir. One of many treatments of wastewater is electrocoagulation method. Five litres of wastewater was agitated using a magnetic stirrer with the addition of bitterns in a tank electrochemical device. It was started by 100 rpm of agitation for 3 minutes and then the agitation was decreased to 50 rpm for the certain time. The filtrate was separated and analysed Chemical Oxygen Demand (COD) and BOD. Percent of COD removal tends to increase with the length of the electrocoagulation process and vice versa for BOD. Different things occur in percent COD and BOD removal, where the best percent removal is obtained at 0.5% bitter addition. The highest percentage of COD removal reached 98.31% at 6 hours and the highest percent of BOD removal reached 95.00% within 2 hours.

Enhancement in the photo-electrocatalytic activity of SnO2-Sb2O4 mixed metal oxide anode by nano-WO3 modification: Application to trypan blue dye degradation

The SnO2-Sb2O4 (MMO) and SnO2-Sb2O4-WO3 (MMO-WO3) electrodes were prepared by electrodeposition followed by dip coating and characterized by scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and X-ray diffraction (XRD) analysis. The electrochemical (EC) and photoelectrochemical (PEC) degradation studies were carried out on trypan blue (TB) dye. These studies revealed that the characteristics and performance of MMO electrode improved significantly on nano-WO3 modification. The oxygen evolution potential (OEP) increased from 2.07V (vs Ag/AgCl) to 2.21V and the accelerated service life increased by 1.7 times. 88 and 93% color removal was achieved on electrolysis for 240min using MMO electrode; whereas, 100% color removal was achieved within 120min by both EC and PEC using MMO-WO3. The percentage chemical oxygen demand (COD) removal achieved using MMO electrode by EC and PEC were only 60 and 63% respectively; whereas, it increased to 78 and 84% with MMO-WO3 electrode. A probable pathway for TB degradation was proposed on the basis of liquid chromatography–mass spectrometry (LC–MS) analysis and quantum chemical calculations were performed on TB molecule to corroborate the proposed degradation pathway.

Evaluation and disposability study of actual textile wastewater treatment by electro-oxidation method using Ti/RuO2 anode

Abstract Electro-oxidation (EO) treatment performance for actual textile wastewater using RuO 2 coated Ti electrode (Ti/RuO 2 ) was studied, and effects of EO process parameters like pH, current (i) and electrolysis time (t) on percentage chemical oxygen demand removal (S 1 ), percentage color removal (S 2 ) and energy consumed (S 3 ) were investigated. Box Behnken Design was used for experimental design and data analysis. Furthermore, pollutants oxidation method involved, direct and/or indirect oxidation, was also investigated. Safe disposability of treated wastewater was examined through spectrophotometric and GC–MS analysis by identifying eliminated organic compounds and transformation products in treated effluent. Moreover, operating cost (electrode and electricity cost) analysis was also performed to evaluate the economic feasibility of the process. At the optimum condition, the actual values of S 1 , S 2 and S 3 were found to be 80.0%, 97.25% and 0.679 Wh, respectively. Kinetic study showed faster COD removal than color, revealing rate constant and R 2 values for S 1 and S 2 to be 0.025 min −1 and 0.015 min −1 ; 0.988 and 0.986, respectively. GC–MS analysis of the EO treated wastewater revealed that most of the organics were completely eliminated during EO process. The presence of chlorinated organic compounds and other transformation products with the already present compounds in untreated textile wastewater was also detected.

Co-digestion of Livestock Wastes for Biogas Production

Co-digestion of cow dung, poultry dropping and pig manure was carried out in batch digesters at mesophilic temperature for twenty-eight days to determine the biogas generating potentials. The wastes were also digested individually for the same period and under the same conditions. The physicochemical and bacteriological characteristics were determined using standard techniques. The range of PH, temperature, percentage moisture content, percentage chemical oxygen demand, percentage carbon content, and the bacterial loads of the wastes slurries before digestion were 6.4- 6.8, 28.0℃ - 29.0℃, 80.0 - 80.2, 9.2 - 11.0, 32.0-46.0 and 3.7 x 106cfu/ml -6.2 x 106 cfu/ml respectively and 6.6-7.5, 27.6℃ -28.5℃, 80.2-91.6, 7.0-9.4, 35.0-58.0 and 1.6 x 106 cfu/ml-5.2 x 106 cfu/ml respectively at the end of digestion. The biogas yield from the digestion of the cow dung, poultry dropping and pig manure individually were 185ml, 220ml and 170ml respectively while the co-digestion of the substrates yielded more biogas. The cumulative biogas yield from the digestion was 2780ml. The slurry containing 48g: 144g: 48g of cow dung, poultry dropping and pig manure gave the highest biogas yield. This study showed that though the digestion of a single livestock waste can yield some biogas, co-digestion of such wastes has the potential to generate more biogas.

Flow optimization and performance evaluation of bioreactors for municipal solid waste treatment

ABSTRACTPerformance evaluation of the anaerobic digestion of the organic fraction of municipal solid waste (OFMSW) was conducted in a laboratory scale test rig consisting of an upflow bioreactor with central substrate dispenser (UBCSD), an upflow anaerobic sludge blanket reactor (UASB) and a continuous stirred tank reactor (CSTR). An influent chemical oxygen demand (COD) concentration of 120,320 mg/l was utilized at steady state conditions. Hydraulic retention time (HRT) of 0–10 days were investigated throughout the experiment at a mesophilic temperature of 37 °C. Two kg of cow rumen content was used as inoculum (to improve microbial activities) and mixed with the organic waste at the initial stage before the reactors were loaded and allowed to run continuously for the stipulated range of HRT. During operation, substrate flow was observed to be more effective in the UBCSD than in the other reactors due to the action of the central substrate dispenser (CSD). The results obtained show the realization of a biogas production lag phase,, less than 24 hours. Cumulative biogas production for UBCSD, UASB and CSTR were 52915, 23550 and 28980 ml while their percentage COD reductions were calculated to be 95.2, 79.0 and 80.8% respectively. Modified Gompertz and Fenton's first order kinetic models were employed in the study for the analysis of the kinetic parameters. The values of the first order kinetic constant (k) of COD obtained for the reactors were 0.2857, 0.147 and 0.1708 respectively. UBCSD proved to be more efficient than the UASB and CSTR in terms of biogas production and COD reduction.