Application of response surface methodology (RSM) for optimisation of COD, NH3-N and 2,4-DCP removal from recycled paper wastewater in a pilot-scale granular activated carbon sequencing batch biofilm reactor (GAC-SBBR)

Evaluation of combined thermo-chemical processes for the treatment of landfill leachate using virgin and recovered FeCl3 coagulants

Sludge resulting from treatment of municipal waste landfill leachate contains suitable cationic substances such as Fe-based recovered coagulants which, if not recovered, can cause environmental problems. The present study aimed to maximise coagulant recoverability and investigate its potential reuse for the treatment of municipal waste landfill leachate. The study focused on establishing (i) the effect of mineral acids on leaching of Fe, (ii) the % of maximum recovery of Fe coagulant, (iii) the impact of ultrasound on recovery, and (iv) effectiveness of recovered coagulant when reused in coagulation-flocculation treatment of landfill leachate. Sulfuric acid outran hydrochloric acid in performance, with the acid leaching process leading to the recovery of 70.12% of Fe (acid concentration = 3.80 M, solid-to-liquid ratio = 8%, and heating time = 5 h). Subsequently, a developed acid leaching process was tested, which results showed that the highest rate of Fe recovery occurred without ultrasound treatment, meaning the use of it could reduce the recovery rate due to the increase in the iron (III) oxide-hydroxide [Fe(OH)3] sedimentation. Comparative experiments were undertaken with the recovered and virgin coagulants. These revealed that Fe-based recovered coagulant led to the 60.21% and 91.40% removal of COD and total suspended solid respectively, while the values of the COD and total suspended solid removal with the virgin FeCl3 were 7.66% and 6.42% lower than that of Fe under optimal conditions (dosage = 9.38 g/L, pH = 8.94, settling time = 52.9 min). The present study established that Fe recovered could be exploited as an eco-friendly coagulant to replace FeCl3 in the landfill leachate treatment.

Greywater treatment in SBR-SND reactor - optimization of hydraulic retention time, volumetric exchange ratio and sludge retention time

In this study, simultaneous nitrification and denitrification-sequencing batch reactor (SND-SBR) process was investigated to treat greywater. The effect of three process parameters, including hydraulic retention time (HRT), volumetric exchange ratio (VER) and sludge retention time (SRT), was optimised using a 23 full factorial design. The statistic model was developed for two response variables, i.e. chemical oxygen demand (COD) and ammonia (NH3-N) removal. The optimum conditions were 6.8 h HRT (anaerobic/aerobic/anoxic: 1.77 h/2.77 h/2.27 h), 0.7 VER and 7.94 d SRT, which resulted in 93.9% COD and 84.6% NH3-N removal efficiency. SRT was the most significant factor, followed by HRT and VER for COD and NH3-N removal. The interaction effect of VER and SRT was significant in COD removal. On the other hand, the interaction effects of HRT-VER and HRT-SRT were significant in NH3-N removal. The removal efficiencies of 89.6 ± 1.1% and 83.7 ± 2.3% were observed for TKN and TN, respectively, in the optimised SND-SBR system. NH3-N removal was obtained via nitrate pathway in the SND-SBR system. The PO43--P removal of 74.2 ± 3.4% was obtained via aerobic phosphorus uptake and post anoxic denitrification at the optimal condition. To enhance PO43--P removal, adsorption (using corn cob adsorbent) was integrated with SBR by adding the optimum adsorbent dose (0.5 g/L). The PO43--P removal efficiency in the SBR-adsorption system was found to be 80 ± 1.5%. The biodegradation of emerging contaminants (ECs) was also carried out in the SND-SBR system, and the results showed removal rate of 58.9 ± 2.3% benzophenone-3 (BP) and 80.1 ± 2.2% anionic surfactant (AS).

Convex optimization for maximizing the degradation efficiency of chloroquine in a flow-by electrochemical reactor

The degradation efficiency of chloroquine phosphate (CQ), an anti-COVID-19 drug, was investigated in a flow-by electrochemical reactor (FBER) provided with two boron-doped diamond (BDD) electrodes (as cathode and anode) under batch recirculation mode. A central composite rotatable design (CCRD) was run down to model and assess the influence of initial pH in an interval of 3.71 to 11.28, the current density in an interval of 34.32 to 185.68 mA cm-2, and liquid volumetric flow rate in an interval of 0.58 to 1.42 L min-1, and conduct the convex optimization to obtain the maximum degradation efficiency. Experimental results were modeled through a second-order polynomial equation having a determination coefficient (R2) of 0.9705 with a variance coefficient of 1.1%. Optimal operating conditions found (initial pH of 5.38, current density (j) of 34.4 mA cm-2, and liquid flow rate (Q) of 1.42 L min-1) led to a global maximum degradation efficiency, COD removal efficiency, and mineralization efficiency of 89.3, 51.6 and 53.1%, respectively, with an energy consumption of 0.041 kWh L-1 within 9 h of treatment. Additionally, a pseudo-zero-order kinetic model was demonstrated to fit the experimental data and the calculated pseudo-zero-order kinetic constant (kapp) was 13.14 mg L-1 h-1 (2.54 × 10-5 mol dm-3 h-1). Furthermore, the total operating cost was of 0.47 US$ L-1. Finally, this research could be helpful for the treatment of wastewater containing an anti-COVID-19 drug such as CQ.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10008-023-05452-7.

Electrocoagulation treatment of raw palm oil mill effluent: Optimization process using high current application

In the electrocoagulation wastewater treatment process, extremely polluted water treatment requires an effective technique, and using high current is one of those. This study aims to optimize electrocoagulation parameters such as operation time, electrodes gap and the initial pH by applying high current intensity to treat palm oil mill effluent (POME) via Box-Behnken design (BBD) method. Chemical oxygen demand (COD), biological oxygen demand (BOD), and suspended solids (SS) were used as the response variables in the quadratic polynomial model. Most of the selected models in the analysis of variance (ANOVA) have shown significant results. A high connection between the parameters and dependent variables was surprisingly discovered in this study which the obtained value of R² for removal percentage of COD, BOD and SS were 0.9975, 0.9984 and 0.9979 respectively. Optimal removal was achieved at 19.07 A of current intensity (equivalent to 542 mA/cm² of current density), 44.97 min of treatment time, 8.60 mm of inter-electrode distance and 4.37 of pH value, resulted in 97.21%, 99.26% and 99.00% of COD, BOD and SS removal respectively. This optimized scheme of operating parameters combination offers an alternate choice for enhancing the treatment efficiency of POME and also can be a benchmark for other researchers to treat highly polluted wastewater.

Bioremediation of greywater using a novel bacterial-fungal consortium: optimization and validation of the operating parameters in vitro

In the present study, removal of pollutants in greywater was investigated using a novel bacterial-fungal consortium. Response surface methodology was used for the optimization of process variables like pH, temperature, inoculum size, and Carbon/Nitrogen (C/N ratio) for degradation of pollutants. Experiments were based on Box Behnken statistical design and the results show a good fit with the quadratic model, coefficient of determination (R²) value of 0.9499. The reliability of the model was established by various statistical parameters like lack of fit, pure error, and residual sum of squares. The optimized conditions for maximum reduction in chemical oxygen demand, oil & grease and sulphate were found to be 78.7%, 82.6% and 89.7%, respectively after 96 h of incubation of the reaction mixture at pH 7; temperature 35°C; inoculum size 150 µl and C/N ratio of 1:2. Our results clearly demonstrate that the developed novel bacterial-fungal consortium can be a cost-effective, safe, and environment-friendly alternative for remediation of greywater.

Effect of carrier particle size on enrichment and shift in nitrifier community behaviors for treating increased strength wastewater

In activated sludge systems, adding carriers can improve nitrifier enrichment. Different attachment area induced by different particle sizes of carriers may result in different nitrifier community. This research investigated the effect of different particle sizes of coal ash on nitrifier enrichment treating increased strength wastewater. Results indicated efficient nitrifying coal ash was obtained with smaller coal ash. The ammonia removal rates reached over 98%, which outclassed that in negative control (63.28%), and no nitrite accumulated in these systems under high nitrogen concentration of 1123.35 mg N/L. The high-throughput sequencing assays indicated carriers changed the microbial community structure significantly, thus facilitated the nitrification capacity. Increase abundance of nitrifier has a negative correlation with particle size of carriers. Nitrosomonas became the biggest beneficiary, which maximum composed 50.29% in fillers system and only 13.69% in negative control, whereas the number of Nitrobacter (less than 3.04%) became much lower than ammonia-oxidizing bacteria (AOB). However, the shift of microbial structures, large number of Dokdonella for instance, may guarantee the complete nitrification in systems with smaller carriers. Batch experiments showed a high dissolved oxygen (DO) concentration (4 mg/L) and slightly alkaline condition (pH 8.0) had a positive effect on nitrifying coal ash. PRACTITIONER POINTS: The increase size of nitrifier has a negative correlation with particle size of coal ash. The smaller coal ash reduces the adverse effect of high nitrogen on nitrification. The ammonia removal rate reached 99.82% with influent of 1123.35 mg NH 4 + - N /L in the smallest carriers system.

Multi-Strain Tropical Bacillus spp. as a Potential Probiotic Biocontrol Agent for Large-Scale Enhancement of Mariculture Water Quality

Aquaculture is suffering from long-term water eutrophication in intensive models, whereas the knowledge of multi-strain/specie for improving water quality is extremely limited. Herein, we aimed to develop multi-strain tropical Bacillus spp. as a potential probiotic biocontrol agent for large-scale enhancement of mariculture water quality. Given the practical application, the optimum multi-strain tropical Bacillus spp. (B. flexus QG-3, B. flexus NS-4, and B. licheniformis XCG-6 with the proportion 5: 5: 4) as a probiotic biocontrol agent was screened and obtained, which effectively improved water quality by removing chemical oxygen demand (COD), ammonia-nitrogen, and nitrate and significantly inhibited Vibrio spp. even at relatively low bacterial concentrations (10⁴ CFU/ml) in artificial feed wastewater and large-scale shrimp aquaculture ponds. More importantly, we found that the initial proportion of these three Bacillus sp. strains of multi-strain tropical Bacillus spp. markedly affected the final purification effects, whereas the initial concentration of that only influenced the purification rates at the early stage (0–48 h) instead of final purification effects. We reason that this multi-strain tropical Bacillus spp. as a good probiotic biocontrol agent could perform multiple actions, such as COD-degrading, nitrifying, denitrifying, and antagonistic actions, for large-scale enhancement of tropical aquaculture water. Additionally, the multi-strain tropical Bacillus spp. was safe for shrimp and could be stored for at least 240 days in spore form at room temperature. This multi-strain probiotic biocontrol agent may facilitate its adoption for further marine recirculating aquaculture system development and large-scale commercial application.

Combination of Coagulation-Flocculation-Decantation and Ozonation Processes for Winery Wastewater Treatment

This research assessed a novel treatment process of winery wastewater, through the application of a chemical-based process aiming to decrease the high organic carbon content, which represents a difficulty for wastewater treatment plants and a public health problem. Firstly, a coagulation–flocculation–decantation process (CFD process) was optimized by a simplex lattice design. Afterwards, the efficiency of a UV-C/ferrous iron/ozone system was assessed for organic carbon removal in winery wastewater. This system was applied alone and in combination with the CFD process (as a pre- and post-treatment). The coagulation–flocculation–decantation process, with a mixture of 0.48 g/L potassium caseinate and 0.52 g/L bentonite at pH 4.0, achieved 98.3, 97.6, and 87.8% removals of turbidity, total suspended solids, and total polyphenols, respectively. For the ozonation process, the required pH and ferrous iron concentration (Fe²⁺) were crucial variables in treatment optimization. With the application of the best operational conditions (pH = 4.0, [Fe²⁺] = 1.0 mM), the UV-C/ferrous iron/ozone system achieved 63.2% total organic carbon (TOC) removal and an energy consumption of 1843 kWh∙m⁻³∙order⁻¹. The combination of CFD and ozonation processes increased the TOC removal to 66.1 and 65.5%, respectively, for the ozone/ferrous iron/UV-C/CFD and CFD/ozone/ferrous iron/UV-C systems. In addition, the germination index of several seeds was assessed and excellent values (>80%) were observed, which revealed the reduction in phytotoxicity. In conclusion, the combination of CFD and UV-C/ferrous iron/ozone processes is efficient for WW treatment.

Electrochemical Mineralization of Ibuprofen on BDD Electrodes in an Electrochemical Flow Reactor: Numerical Optimization Approach

Statistical analysis was applied to optimize the electrochemical mineralization of ibuprofen with two boron-doped diamond (BDD) electrodes in a continuous electrochemical flow reactor under recirculation batch mode. A central composite rotatable (CCR) experimental design was used to analyze the effect of initial pH (2.95–13.04), current intensity (2.66–4.34 A), and volumetric flow rate (0.16–1.84 L/min) and further optimized by response surface methodology (RSM) to obtain the maximum mineralization efficiency and the minimum specific energy consumption. A 91.6% mineralization efficiency (EM) of ibuprofen with a specific energy consumption (EC) of 4.36 KW h/g TOC within 7 h of treatment was achieved using the optimized operating parameters (pH0 = 12.29, I = 3.26 A, and Q of 1 L/min). Experimental results of RSM were fitted via a third-degree polynomial regression equation having the performance index determination coefficients (R2) of 0.8658 and 0.8468 for the EM and EC, respectively. The reduced root-mean-square error (RMSE) was 0.1038 and 0.1918 for EM and EC, respectively. This indicates an efficient predictive performance to optimize the operating parameters of the electrochemical flow reactor with desirability of 0.9999993. Besides, it was concluded that the optimized conditions allow to achieve a high percentage of ibuprofen mineralization (91.6%) and a cost of 0.002 USD $/L. Therefore, the assessed process is efficient for wastewater remediation.”

Statistical Optimization by the Response Surface Methodology of Direct Recycled Aluminum-Alumina Metal Matrix Composite (MMC-AlR) Employing the Metal Forming Process

In this study, the response surface methodology (RSM) and desirability function (DF) were utilized to optimize the recycling conditions of aluminum (AA6061) chips, in the presence of particulate alumina (Al2O3), to obtain a metal matrix composite of recycled aluminum (MMC-AlR) using hot press forging processes. The effects of temperature (430–530 °C) and holding time (60–120 min) were investigated. The introduction of 2.0 wt. % of Al2O3 to the aluminum matrix was based on preliminary research and some pilot tests. This study employed the 2k factorial design of experiments that should satisfy the operating temperatures (T) of 430 °C and 530 °C with holding times (t) of 60 min and 120 min. The central composite design (CCD) was utilized for RSM with the axial and center point to evaluate the responses to the ultimate tensile strength (UTS), elongation to failure (ETF), and microhardness (MH). Based on RSM, with the desirability of 97.6%, the significant parameters T = 530 °C and t = 120 min were suggested to yield an optimized composite performance with UTS = 317.99 MPa, ETF = 20.45%, and MH = 86.656 HV. Three confirmation runs were performed based on the suggested optimum parameters, and the error revealed was less than 25%. The mathematical models suggested by RSM could adequately describe the MMC-AlR responses of the factors being investigated.

Coupling of thermophilic biofilm-based systems and ozonation for enhanced organics removal from high-temperature pulping wastewater: Performance, microbial communities, and pollutant transformations

This study focused on the establishment of thermophilic biofilm-based systems (TBSs) coupled with ozonation for treatment of high-temperature pulping wastewater. The effects of the inoculum, sludge growth mode, and temperature were investigated. These factors played roles in the organics removal performance and microbial communities of pulping wastewater treatment systems. At 50 °C, the TBS inoculated with optimal inoculum achieved 59.12% and 37.96% reductions in COD and chromaticity, which were superior to the reductions achieved by other systems. In this TBS, thermophilic lignocellulolytic microorganisms (Chloroflexus, Meiothermus, norank_f_Caldilineaceae, and Roseiflexus) and carbohydrate-fermenting bacteria (norank_f_Anaerolineaceae) were predominant. Their relative abundances were 25.55% and 10.42%, respectively. For enhanced removal of COD and chromaticity, an integrated system consisting of a primary TBS, ozonation, and a secondary TBS was proposed. The total COD and chromaticity removal efficiencies increased to 90.48% and 87.89%, respectively. BOD₅/COD increased from 0.20 to 0.40, and shifts of lignin-like and humic acid-like substances were observed during ozonation with the primary TBS effluent.

Microbial Decolorization of Triazo Dye, Direct Blue 71: An Optimization Approach Using Response Surface Methodology (RSM) and Artificial Neural Network (ANN)

The release of wastewater from textile dyeing industrial sectors is a huge concern with regard to pollution as the treatment of these waters is truly a challenging process. Hence, this study investigates the triazo bond Direct Blue 71 (DB71) dye decolorization and degradation dye by a mixed bacterial culture in the deficiency source of carbon and nitrogen. The metagenomics analysis found that the microbial community consists of a major bacterial group of Acinetobacter (30%), Comamonas (11%), Aeromonadaceae (10%), Pseudomonas (10%), Flavobacterium (8%), Porphyromonadaceae (6%), and Enterobacteriaceae (4%). The richest phylum includes Proteobacteria (78.61%), followed by Bacteroidetes (14.48%) and Firmicutes (3.08%). The decolorization process optimization was effectively done by using response surface methodology (RSM) and artificial neural network (ANN). The experimental variables of dye concentration, yeast extract, and pH show a significant effect on DB71 dye decolorization percentage. Over a comparative scale, the ANN model has higher prediction and accuracy in the fitness compared to the RSM model proven by approximated R ² and AAD values. The results acquired signify an efficient decolorization of DB71 dye by a mixed bacterial culture.

Application of response surface methodology (RSM) for optimizing coagulation process of paper recycling wastewater using Ocimum basilicum

The wastewater produced in a pulp and paper industry is one of the most polluted industrial wastewaters, and therefore its treatment requires complex processes. One of the simple and feasible processes in pulp and paper wastewater treatment is coagulation and flocculation. Overusing a chemical coagulant can produce a large volume of sludge and increase costs and health concerns. Therefore, the use of natural and plant-based coagulants has been recently attracted the attention of researchers. One of the advantages of using Ocimum basilicum as a coagulant is a reduction in the amount of chemical coagulant required. In this study, the effect of basil mucilage has been investigated as a plant-based coagulant together with alum for treatment of paper recycling wastewater. Response surface methodology (RSM) was used to optimize the process of chemical coagulation based on a central composite rotatable design (CCRD). Quadratic models for colour reduction and TSS removal with coefficients of determination of R²> 96 were obtained using the analysis of variance. Under optimal conditions, removal efficiencies of colour and total suspended solids (TSS) were 85% and 82%, respectively.

Parametric optimization of domestic wastewater treatment in an activated sludge sequencing batch reactor using response surface methodology

In this work, the parametric optimization of real domestic wastewater treated in an activated sludge sequencing batch reactor (SBR) was performed by means of the response surface methodology (RSM). The influences of influent organic matter concentration as chemical oxygen demand (COD_inf), biomass concentration (X_s) and aeration time (t) on the COD, organic matter removal efficiency as COD (η) and sludge volume index (SVI) were determined to evaluate the performance of activated sludge SBR. The results showed that organic matter efficiency and maximum SVI were obtained at a t of 12 h, 300 mg L^-1 of COD_inf and 2000 mg L^-1 of X_s. The SBR-activated sludge exhibited a η of 73% and an SVI of 119 mL g^-1. Both values indicated a very good performance. Furthermore, the COD of the effluent under these conditions complied with Mexican regulations for wastewater discharged into water bodies.

Durability and performance of loofah sponge as carrier for wastewater treatment with high ammonium

Loofah sponge (LS) was used as carrier for high ammonia wastewater treatment with a sequencing batch biofilm reactor (SBBR), aimed at evaluating its nitrogen removal performance and durability to changeable pH and microbial corrosion. The results indicate that the average removal for COD, NH 4 + -N and total nitrogen (TN) accounted for more than 80%, 90%, and 70%, respectively, in 203 days. After SBBR operation for 108 days, the average weight loss of the loofah sponge was 49.1%. Yet, the main structure of utilized loofah sponge remained unaffected (proved by scanning electron microscopy). Moreover, based on attenuated total reflection-infrared spectroscopy (ATR-IR) and X-ray diffraction (XRD) measurements, cellulose, and hemicelluloses in the loofah sponge were reduced significantly obviously causing the proportion of lignin to increase. During the 108th to 203 days, the removal efficiencies of COD (81.6 ± 7.05%), NH 4 + -N (79.4 ± 8.82%), and TN (79.9 ± 2.85%) remained at a high level. PRACTITIONER POINTS: Loofah sponge had good durability to high ammonia and changeable pH. Lignin was the protective material of loofah sponge for resisting pH fluctuation and microbial corrosion. SBBR maintained a steady nitrogen removal performance with a low COD/N ratio.

Optimization of saline wastewater treatment using electrochemical oxidation process: Prediction by RSM method

Response surface methodology (RSM) was applied to find the optimum parameters for COD and TOC removal from saline wastewaters using electrochemical oxidation process. The independent variables considered were reaction time, pH, salt concentration, and voltage. Optimization of parameters was performed by analysis of variance (ANOVA). Quadratic regression equation was suggested as a model for prediction of chemical oxygen demand (COD) and total organic carbon (TOC) removal efficiency. The results indicated that the COD and TOC removal efficiencies at the optimal conditions of pH 7.69, reaction time of 30.71 min, salt content of 30. 94 g/L and voltage of 7.41 V were 91.78% and 68.49%, respectively. In terms of COD and TOC removal efficiency, the coefficients of determination were found to be 0.95 and 0.94, respectively. This study suggests that electro-oxidation is an effective process in decreasing COD and TOC from saline wastewaters. Further, RSM was a suitable technique for optimization of the variables involved in COD and TOC removal through electro-oxidation process.

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The findings demonstrate that response surface methodology is a good tool for the optimization of parameters of the experimental data.

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A quadratic model was suggested as a good model for COD and TOC removal prediction.

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The findings proved good agreement between the experimental data and the predicted equation.

Multiresponse Optimization and Environmental Analysis in Direct Recycling Hot Press Forging of Aluminum AA6061

Ecological manageability in manufacturing these days is a dire and exceptional issue and the principle concerns are identified with increasingly proficient utilization of energy and materials. Recycling can save a large amount greenhouse gas emissions, particularly in the case of aluminum. The parameter on the innovative technique on the direct recycling was investigated by employing design of experiments, via hot press forging process (DR-HPF). Thus, reutilizing of aluminum chips AA6061 with full factorial 3² design of experiment comprising a variety of working temperature and holding time were employed. Central composite design (CCD) was applied to outline the experiments towards evaluating the influences of the hot press forging parameters to the three responses; ultimate tensile strength (UTS), elongation to failure (ETF), and global warming potential (GWP). In conjunction with this, the environmental impacts associated with DR-HPF process are evaluated alongside the resultant conventional recycling (CR) by using re-melting route as indication. Experimental measurements, literature analysis and industrial data were merged to acquire the analysis of aluminum recycling life cycle. Clear conclusions were successfully drawn through the attained results on the outlook proposed by solid state direct recycling for the purpose of reducing the environmental effects by taking material and energy conservation as one of the most essential impacting factor. The global warming potential of a DR-HPF route gives a significant environmental impact where it is reduced up to 69.2% in comparison to the conventional (melting) routes.

Different bioreactors for treating secondary effluent from recycled paper mill

Secondary effluent from paper mill was characterized by poor biodegradability and containing recalcitrant compounds. In this study, four bioreactors, including a sequencing batch biofilm reactor (SBBR), a stirred-tank reactor (STR) and two submerged aeration reactors (SAR) were used to treat secondary effluent from a recycled paper mill respectively. The results indicated that chemical oxygen demand (COD) was increased by SAR2 treatment and COD removal efficiency for SBBR, SAR1 and STR was 39.7%, 15.7% and 30.9% respectively. It is suggested that recalcitrant compounds were removed by SBBR, SAR1 and STR respectively. Total nitrogen (TN) and total phosphorus (TP) of wastewater were increased by treatments of each bioreactor, which suggested that endogenous respiration of biomass occurred during the treatment. Microbial analysis of sludge from different bioreactors suggested that the removal of recalcitrant compounds in SBBR and STR might be related to the presence of unique microorganisms in each reactor.

Sulfamethoxazole removal in membrane-photocatalytic reactor system - experimentation and modelling

In this study, the efficacy of membrane-photocatalytic reactor (MPR) in sulfamethoxazole (SMX) removal was explored at a fixed initial SMX concentration, i.e. 100 mg/L. A supported catalyst, i.e. TiO₂ on granular activated carbon (GAC-TiO₂), was used for MPR experiments. The SMX removal efficiency of the MPR was investigated under a range of hydraulic retention time (i.e. HRT from 51 to 152.5 min) and TiO₂ catalyst dosage (55-50 mg/L). A maximum SMX removal efficiency of 83.6% was observed under 220 mg/L catalyst dosage and 80 min HRT. The increase in catalyst dosage from 55 to 550 mg/L has increased the transmembrane pressure of the reactor from 9.8 to 22.2 kPa. A multiple non-linear regression model was developed based on the experimental data and its significance was analyzed using two-way ANOVA. Based on the model, the optimal HRT and catalyst dosage for complete SMX removal (100%) were found out. The comparison of photocatalytic degradation experiments with sorption experiments conducted earlier revealed that SMX removal in the MPR was mainly by photocatalytic degradation and not by adsorption onto GAC-TiO₂ catalyst. However, the performance of MPR in removing other emerging pollutants from real-time wastewaters could be explored before its field-scale application.

Performance of full-scale coagulation-flocculation/DAF as a pre-treatment technology for biodegradability enhancement of high strength wastepaper-recycling wastewater

Paper mill wastewater leads to a serious damage on the environment owing to the high content of organic matters, suspended solids, toxic substances, and lignin. Hence, exploring new treatment technologies is the passion of environmental engineers to minimize the effluent impact on the environment and cleaner production aspects. This research focused on the performance of full-scale coagulation-fluctuation/DAF system for pre-treatment of high strength wastepaper-recycling wastewater and its effect on biodegradability improvement. To optimize unit performance, optimum coagulant and flocculant doses were firstly determined by jar test without prior change and adjustment of pH in lab-scale experiments. The optimum dosages were obtained by 1500 mg L^-1 polyaluminum chloride (PACl) as coagulant coupled with 40 mg L^-1 cationic polyacrylamide (C-PAM) as flocculant. Percentage removals of 39 ± 10, 6.8 ± 3.6, 31.0 ± 6.7, 24.0 ± 3.8, and 33.0 ± 20.0 were achieved for COD, sCOD, BOD₅, sBOD₅, and color, respectively. The average BOD₅ to COD ratio after pre-treatment increased from 0.44 to 0.5, whereas the ratio of sBOD₅/sCOD dropped from 0.65 to 0.53. A superior effectiveness in reduction of TSS (98.1%) and VSS (98.4%) was also achieved. The results show that the application process is able to prevent malfunction operation in the following bioreactors which is obtainable through bio-treatability enhancement of pre-treated wastewater and reducing the risks of clogging and sludge washout. Attached growth processes are suggested to be applied in the further anaerobic/aerobic processes because of high proportion of soluble fraction of COD in the effluent to avoid poor floc formation and dispersed growth problems.

Simultaneous wastewater treatment and biogas production using integrated anaerobic baffled reactor granular activated carbon from baker's yeast wastewater

In this study, simultaneous degradation of organic matter and color removal from food processing industries wastewater using an integrated anaerobic baffled reactor granular activated carbon (IABRGAC) was investigated. Theretofore, effective parameters such as hydraulic retention time (HRT) and granular activated carbon (GAC) filling ratio were studied. The bioreactor was operated at 3, 4 and 5 d of HRT and GAC filling ratio of 20%, 35% and 50%. To analyze and optimize the independent operating variables, response surface methodology was applied. Operating condition was optimized for HRT (4 d) and GAC filling ratio (50%). Better COD (94.6%) and BOD (93.7%) removal efficiency occurred with loading COD of 15,000 mg/L, with diminished wastewater color around 54% and turbidity to 54 NTU. In addition, methane production, methane yielding rate (Y_m) and specific methanogenic activity (SMA) test in an integrated system were investigated. The system IABRGAC was able to generate a volumetric rate about 0.31 and 0.44 L/g COD_removed d at the experimental condition. The Y_m was between 0.31 and 0.44 L/g COD_removed.d and SMA was between 0.13 and 0.38 g COD/g volatile suspended solid. Based on results it can be concluded that the IABRGAC to be a successful pretreatment for highstrength wastewater before discharging the final effluent to sewerage and aerobic treating processes.

Optimization of rotational speed and hydraulic retention time of a rotational sponge reactor for sewage treatment

A rotational sponge (RS) reactor was proposed as an alternative sewage treatment process. Prior to the application of an RS reactor for sewage treatment, this study evaluated reactor performance with regard to organic removal, nitrification, and nitrogen removal and sought to optimize the rotational speed and hydraulic retention time (HRT) of the system. RS reactor obtained highest COD removal, nitrification, and nitrogen removal efficiencies of 91%, 97%, and 65%, respectively. For the optimization, response surface methodology (RSM) was employed and optimum conditions of rotational speed and HRT were 18 rounds per hour and 4.8 h, respectively. COD removal, nitrification, and nitrogen removal efficiencies at the optimum conditions were 85%, 85%, and 65%, respectively. Corresponding removal rates at optimum conditions were 1.6 kg-COD m^-3d^-1, 0.3 kg-NH₄⁺-N m^-3d^-1, and 0.12 kg-N m^-3d^-1. Microbial community analysis revealed an abundance of nitrifying and denitrifying bacteria in the reactor, which contributed to nitrification and nitrogen removal.

Response surface modeling of reductions in uropathogenic Escherichia coli biofilms on silicone by cranberry extract, caprylic acid, and thymol

A response surface methodology was used to build a model to predict reductions in uropathogenic Escherichia coli biofilms in response to three compounds: cranberry extract [CB] at 3.0-9.0%, and caprylic acid [CAR] and thymol [TM] at 0.01%-0.05%. The predictive model for microbial reduction had a high regression coefficient (R² = 0.9988), and the accuracy of the model was verified (R² = 0.9527). Values of CAR, TM, and the quadratic term CAR² were the most significant (P < 0.0001) for bacterial reduction. Interactions between CB and CAR, and TM and CB, also affected bacterial reduction. The optimum conditions (a 5.8 log₁₀ reduction) determined by ridge analysis were 8.3% CB +0.04% CAR +0.04% TM at 37 °C for 1 min. The model could be used to predict the most cost-efficient amounts of antimicrobial agents for anti-urinary tract infection products such as catheter lock solution and antimicrobial coatings for catheters.

Statistical optimization of the phytoremediation of arsenic by Ludwigia octovalvis- in a pilot reed bed using response surface methodology (RSM) versus an artificial neural network (ANN)

In this study, the removal of arsenic (As) by plant, Ludwigia octovalvis, in a pilot reed bed was optimized. A Box-Behnken design was employed including a comparative analysis of both Response Surface Methodology (RSM) and an Artificial Neural Network (ANN) for the prediction of maximum arsenic removal. The predicted optimum condition using the desirability function of both models was 39 mg kg^-1 for the arsenic concentration in soil, an elapsed time of 42 days (the sampling day) and an aeration rate of 0.22 L/min, with the predicted values of arsenic removal by RSM and ANN being 72.6% and 71.4%, respectively. The validation of the predicted optimum point showed an actual arsenic removal of 70.6%. This was achieved with the deviation between the validation value and the predicted values being within 3.49% (RSM) and 1.87% (ANN). The performance evaluation of the RSM and ANN models showed that ANN performs better than RSM with a higher R² (0.97) close to 1.0 and very small Average Absolute Deviation (AAD) (0.02) and Root Mean Square Error (RMSE) (0.004) values close to zero. Both models were appropriate for the optimization of arsenic removal with ANN demonstrating significantly higher predictive and fitting ability than RSM.

Optimization of paper mill industry wastewater treatment by electrocoagulation and electro-Fenton processes using response surface methodology

This study deals with chemical oxygen demand (COD), phenol and Ca⁺² removal from paper mill industry wastewater by electrocoagulation (EC) and electro-Fenton (EF) processes. A response surface methodology (RSM) approach was employed to evaluate the effects and interactions of the process variables and to optimize the performance of both processes. Significant quadratic polynomial models were obtained (R² = 0.959, R² = 0.993 and R² = 0.969 for COD, phenol and Ca⁺² removal, respectively, for EC and R² = 0.936, R² = 0.934 and R² = 0.890 for COD, phenol and Ca⁺² removal, respectively). Numerical optimization based on desirability function was employed; in a 27.55 min trial, 34.7% of COD removal was achieved at pH 9 and current density 96 mA/cm² for EC, whereas in a 30 min trial, 74.31% of COD removal was achieved at pH 2 and current density 96 mA/cm² and H₂O₂/COD molar ratio 2.0 for EF. The operating costs were calculated to be 6.44 €/m³ for EC and 7.02 €/m³ for EF depending on energy and electrode consumption at optimum conditions. The results indicate that the RSM is suitable for the design and optimization of both of the processes. However, EF process was a more effective technology for paper mill industry wastewater treatment as compared with EC.

Application of high rate integrated anaerobic-aerobic/biogranular activated carbon sequencing batch reactor (IAnA-BioGACSBR) for treating strong municipal landfill leachate

The aim of the present study is to evaluate the application of high rate integrated anaerobic-aerobic/biogranular activated carbon sequencing batch reactor (IAnA-BioGACSBR) to treat raw strong leachate from open dumping of municipal solid waste. The influence of two important and effective independent variables, COD concentrations and volumetric filling rate with GAC, onto the leachate treatment were investigated. Three responses such as TKN, BOD and COD were considered for evaluating the interaction of parameters. The results showed that maximum BOD₅ removal of 98.9% in anaerobic zone and 99% in aerobic zone was obtained at the highest values of COD (~30000 mg/L) and filling ratio (~50%). The highest values of COD removal efficiency were found to be 98.54% and 98%, at COD rate of 10000 mg/L and GAC of 35%, respectively. The highest removal values of TKN was 77.2% and 78.9% in anaerobic and aerobic zone, respectively. Under optimal conditions, compared with the SBR and the GAC-SBR performances, results reveal that the application of the GAC-SBR has shown better effluent characteristics. Based on the results, it can be asserted that the application of the high rate IAnA-BioGACSBR for the treatment of biodegradable landfill leachate was more effective.

Application of response surface methodology to optimize the fabrication of ZnCl2-activated carbon from sugarcane bagasse for the removal of Cu2

The present study focused on the application of response surface methodology to optimize the fabrication of activated carbon (AC) from sugarcane bagasse for adsorption of Cu²⁺ ion. The AC was synthesized via chemical activation with ZnCl₂ as the activating agent. The central composite design based experiments were performed to assess the individual and interactive effect of influential parameters, including activation temperature, ZnCl₂ impregnation ratio and activation time on the AC yield and removal of Cu²⁺ ion from the aqueous environment. The statistically significant, well-fitting quadratic regression models were successfully developed as confirmed by high F- and low P-values (<0.0001), high correlation coefficients and lack-of-fit tests. Accordingly, the optimum AC yield and removal efficiency of Cu²⁺ were predicted, respectively, as 48.8% and 92.7% which were approximate to the actual values. By applying the predicted optimal parameters, the AC shows a surprisingly high surface area of around 1,500 m²/g accompanied by large pore volume and narrow micropore size at low fabrication temperature.

Optimizing COD removal from greywater by photoelectro-persulfate process using Box-Behnken design: assessment of effluent quality and electrical energy consumption

Greywater (GW) is a potential source for water reuse in various applications. However, GW treatment is still a vital issue in water reuse in cases of environmental standards and risk to public health. This study investigates optimization and modeling of a hybrid process for COD removal from GW. Persulfate (PS) was simultaneously activated by electrogenerated ferrous ion (EC) and UV to generate sulfate radical. Photoelectro-persulfate (PEPS) was optimized by Box-Behnken design and the effects of four variables (pH, PS dosage, current density, and electrolysis time) were evaluated on COD removal. The results and several coefficients showed that the obtained model was acceptable for predicting the COD removal. Moreover, under optimum conditions (pH = 6.9, PS = 8.8 mM, current density = 2.0 mA/cm(2), and 49.3 min electrolysis time), BOD5, turbidity, TSS, phosphate, and UV254 were effectively removed and COD and BOD5 values reached to discharge standards. Different configurations of the processes were assessed for COD removal. The order of COD removal efficiency followed: PS < Fe(II) < UV/PS ≤ Fe(II)/PS < Fe(II)/PS/UV < electrocoagulation ≤ electrocoagulation/UV < electro-PS < PEPS. The monitoring PS concentration during 60 min reaction time in the aforesaid processes indicated that PEPS could remarkably activate PS. The solution pH was also monitored and related results revealed that the presence of PS during the 10 min first time decreased pH value while production of hydroxide ion at cathode increased pH significantly. Finally, the contribution of electrochemical process in the electrical energy consumption was far less than that of photolysis process in hybrid PEPS process.

Ozonation optimization and modeling for treating diesel-contaminated water

The effect of ozonation on treatment of diesel-contaminated water was investigated on a laboratory scale. Factorial design and response surface methodology (RSM) were used to evaluate and optimize the effects of pH, ozone flow rate, and contact time on the treatment process. A Box-Behnken design was successfully applied for modeling and optimizing the removal of total petroleum hydrocarbons (TPHs). The results showed that ozonation is an efficient technique for removing diesel from aqueous solution. The determination coefficient (R(2)) was found to be 0.9437, indicating that the proposed model was capable of predicting the removal of TPHs by ozonation. The optimum values of experimental initial pH, degree of O3, and reaction time were 7.0, 1.5, and 35 min, respectively, which could contribute to approximately 60% of TPH removal. This result is in good agreement with the predicted value of 57.28%.

Degradation of 2,4-dichlorophenol from aqueous using UV activated persulfate: kinetic and toxicity investigation

2,4-DCP is a high-toxicity phenol compound, which is difficult to remove, harmful to the health of people and seriously influences the aquatic ecosystems.

Application of response surface methodology for investigation of membrane fouling behaviours in microalgal membrane bioreactor: the effect of aeration rate and biomass concentration

This study was performed to investigate membrane fouling phenomena and to optimize fouling parameters in a submerged membrane bioreactor.

Review on recent developments on pulp and paper mill wastewater treatment

Economic benefits of the pulp and paper industry have led it to be one of the most important industrial sections in the world. Nevertheless, in recent years, pulp and paper mills are facing challenges with the energy efficiency mechanisms and management of the resulting pollutants, considering the environmental feedbacks and ongoing legal requirements. This study reviews and discusses the recent developments of affordable methods dealing with pulp and paper mill wastewaters. To this end, the current state of the various processes used for pulp and paper production from virgin or recovered fibers has been briefly reviewed. Also, the relevant contaminants have been investigated, considering the used raw materials and applied techniques as the subject for further discussion about the relevant suitable wastewater treatment methods. The results of the present study indicated that adopting the integrated methods, alongside a combination of biological (e.g., anaerobic digestion) and physicochemical (e.g., novel Fenton reactions) treatment methods, can be environmentally and economically preferable to minimize environmental contaminants and energy recycling.