Effect of FeCl3 concentration in chemically enhanced primary treatment on the performance of a conventional wastewater treatment plant. A case study

The effect of coagulant dosage in a chemically enhanced primary treatment (CEPT) on the performance of a conventional wastewater treatment plant (WWTP) has been investigated. Lab-scale experiments simulations were carried out in order to evaluate the effect of coagulant addition on the primary settling performance. In these experiments, FeCl3 was used as coagulant. Later, the WWTP was theoretically simulated using a commercial software (WEST®) to evaluate the effect of coagulation/flocculation on the global system, based on the results obtained at lab-scale. According to these results, the CEPT modifies the organic matter balance in the WWTP, decreasing the contribution of readily (SS) and slowly (XS) biodegradable fractions of COD to the aerobic biological process up to 27.3% and 80.8%, respectively, for a dosage of FeCl3 of 24 mg L-1. Consequently, total suspended solids in the aerobic reactor and the secondary purged sludge decreased up to 33% and 13%, respectively. However, the influence on effluent quality was negligible. On the contrary, suspended solids concentration in the sludge to be treated by anaerobic digestion increased, mainly regarding the Ss and Xs fractions, which caused an 8.1% increase in biogas production potential, with approximately 60% of CH4 concentration.

Response Surface Methodology (RSM) Approach to Optimization of Coagulation-Flocculation of Aquaculture Wastewater Treatment Using Chitosan from Carapace of Giant Freshwater Prawn Macrobrachium rosenbergii

The major sources of waste from aquaculture operations emanates from fish or shellfish processing and wastewater generation. A simple technique called coagulation/flocculation utilizes biowaste from aquaculture to produce chitosan coagulant for wastewater treatment. A chemical method was applied in the present study for chitin and chitosan extraction from carapace of Macrobrachium rosenbergii and subsequent application for removal of turbidity and salinity from shrimp aquaculture wastewater. Box-Behnken in RSM was used to determine the optimum operating conditions of chitosan dosage, pH, and settling time, after which quadratic models were developed and validated. Results show that 80 g of raw powder carapace yielded chitin and chitosan of 23.79% and 20.21%, respectively. The low moisture (0.38%) and ash (12.58%) content were an indication of good quality chitosan, while other properties such as water-binding capacity (WBC), fat-binding capacity (FBC), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscope (SEM) confirmed the structure and the α-group, as well as the rough morphology of chitosan. In addition, the high solubility (71.23%) and DDA (85.20%) suggested good coagulant potentials. It was recorded in this study that 87.67% turbidity was successfully removed at 20 mg/L of chitosan dosage and 6.25 pH after 30 min settling time, while 21.43% salinity was removed at 5 mg/L of chitosan dosage, 7.5 pH, and 30 min settling time. Therefore, the process conditions adopted in this study yielded chitosan of good quality, suitable as biopolymer coagulant for aquaculture wastewater treatment.

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 4 L. 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 chemical oxygen demand (COD) (2200 mg/L), the optimized conditions gave a good reduction in % color and % COD, that is, 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 field emission scanning electron microscopy (FESEM)/energy dispersive X-ray analysis (EDAX), UV-visible diffuse reflectance spectroscopy (UV-vis DRS), and X-ray diffraction (XRD) 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 among 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. PRACTITIONER POINTS: Industrial waste products were used to fabricate inert support that promoted the idea of circular economy/waste management. Iron from the waste used to execute photo-Fenton process along with forming Fe-TiO₂ complex to make it visibly active composite. Enhanced production of OH radicals facilitated removal of stout color and COD from the real pulp and paper industry wastewater in just 90 min. Coagulation/flocculation followed by dual technique proved to be the best approach out of three different approaches applied. Composite showed excellent durability even after 50 recycles.

Influence of bionanoparticles to treat a slaughterhouse wastewater

Treatment of effluents from animal slaughterhouse industries is indispensable, standing out coagulation/flocculation/sedimentation processes. Bionanoparticles (BioNPs) (nanoparticles (NPs) functionalized with Moringa extracts (MO)) were studied as an alternative natural coagulant that would contribute to the microbial load reduction, without increasing the treated effluent toxicity. MO extracts were prepared with different salts, and then, in a kinetics study, different NPs mass and coagulant dosages were evaluated. In the best-defined conditions, microbial load, toxicity tests for the bioindicator Lactuca sativa, and NPs reuse evaluation were performed. Removals of 96.14% turbidity and 43.63% UV254nm were achieved when using 500 mg L-1 of BioNPs containing 60 mg of NPs for every 20 mL of MO extract prepared with 0.1 M CaCl2. The BioNPs with an external magnetic field also decreased the sedimentation time from 140 to 10 min compared to MO, and the process efficiency did not expressively decrease after reusing the recovered NPs. Through toxicity tests, BioNPs were not considered to leave residuals toxic to the Lactuca sativa in the treated effluent. Besides, the microbial load reduction was 97.33% for heterotrophic microorganisms and total mesophiles and 99.25% for moulds/yeasts. Therefore, a satisfactory primary treatment was achieved, contributing to the sustainability of industries.

Evaluation of the effect of different treatment methods on sugarcane vinasse remediation

Sugarcane vinasse is a by-product obtained during ethanol production in sugar-ethanol plants. For each 1 L of ethanol produced approximately 11 L of vinasse are generated. As this residue is obtained in high amounts, it is used as fertilizer in sugarcane crops. However, despite being rich in nutrients, sugarcane vinasse is approximately one hundred times more polluting than domestic sewage, making it an environmental problem. Thus, the aim of the present study was to propose a treatment sequence for sugarcane vinasse and evaluate the possibility of energetic use of the generated sludge in the coagulation/flocculation stage. pH, conductivity, turbidity and decreases in UV/Vis absorption spectra were determined for each treatment step. In addition, the upper calorific value of the generated sludge was also determined, while ash (adsorption treatment) and catalyst (heterogeneous photocatalysis) characterizations were also carried out. At the end of the treatment, initial vinasse turbidity was reduced by 100% and pH and conductivity values were stabilized. The sludge presented a higher calorific value of approximately 3,000 kcal kg^-1 and the ash and catalyst displayed favorable characteristics to be applied to the sugarcane vinasse treatment stages.

Potential of the Moringa oleifera saline extract for the treatment of dairy wastewater: application of the response surface methodology

In this work, the coagulation/flocculation/sedimentation treatment of dairy wastewater samples was investigated through serial factorial designs utilizing the saline extract obtained from Moringa oleifera (Moringa) as a coagulant. The sedimentation time (ST), pH, Moringa coagulant (MC) dose and concentration of CaCl₂ have been evaluated through the response surface methodology in order to obtain the ideal turbidity removal (TR) conditions. The empirical quadratic model, in conjunction with the desirability function, demonstrated that it is possible to obtain TRs of 98.35% using a coagulant dose, concentration of CaCl₂ and pH of 280 mg L^-1, 0.8 mol L^-1 and 9, respectively. The saline extract from Moringa presented its best efficiency at an alkaline pH, which influenced the reduction of the ST to a value of 25 min. It was verified that the increase in the solubility of the proteins in the Moringa stimulated the reduction of the coagulant content in the reaction medium, and it is related to the use of calcium chloride as an extracting agent of these proteins. The MC proved to be an excellent alternative for the dairy wastewater treatment, compared to the traditional coagulants.

Removal of bisphenol A and 2,4-Di-tert-butylphenol from landfill leachate using plant- based coagulant

Landfill leachate contain persistent organic pollutants (POPs), namely, bisphenol A (BPA) and 2,4-Di-tert-butylphenol, which exceed the permissible limits. Thus, such landfill leachate must be treated before it is released into natural water courses. This article reports on investigations about the removal efficiency of POPs such as BPA and 2,4-Di-tert-butylphenol from leachate using locust bean gum (LBG) in comparison with alum. The vital experimental variables (pH, coagulant dosage and stirring speed) were optimised by applying response surface methodology equipped with the Box-Behnken design to reduce the POPs from leachate. An empirical quadratic polynomial model could accurately model the surface response with R² values of 0.928 and 0.954 to reduce BPA and 2,4-Di-tert-butylphenol, respectively. Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) were performed on treated flocs for further understanding. FTIR analysis revealed that the bridging of pollutant particles could be due to the explicit adsorption and bridging via hydrogen bonding of a coagulation mechanism. SEM micrographs indicated that the flocs produced by LBG have a rough cloudy surface and numerous micro-pores compared with alum, which enabled the capture and removal of POPs from leachate. Results showed that the reduction efficiencies for BPA and 2,4-Di-tert-butylphenol at pH 7.5 were 76% and 84% at LBG dosage of 500 mg·L^-1 and 400 mg·L^-1, respectively. Coagulant dosage and pH variation have a significant effect on POPs reduction in leachate. Coagulation/flocculation using LBG could be applied for POPs reduction in leachate as a pre-treatment prior to advanced treatments.

Physical-chemical treatment of rainwater runoff in recovery and recycling companies: lab-scale investigation

Scrap material recovery and recycling companies are producing wastewater in which common pollutants (such as COD, nutrients and suspended solids), toxic metals, polyaromatic hydrocarbons (PAH) and polychlorinated biphenyls (PCB) frequently can exceed the discharge limits. Lab-scale optimisation of different possible physical-chemical treatment techniques was performed on the wastewater originating from three different companies in view of further testing at pilot-scale testing and implementation at full-scale. The lab-scale tests demonstrate that sedimentation or hydrocyclone treatment as stand-alone technique cannot be used for proper treatment of this type of wastewater. Dual bed filtration or coagulation/flocculation proved to be more promising with removal efficiencies of about 71-95% (dual bed filtration) and 61-97% (coagulation/flocculation) for the above-mentioned pollutants (metals, PAH and PCB).

Integration of traditional systems and advanced oxidation process technologies for the industrial treatment of olive mill wastewaters

A complete industrial treatment system (involving the integration of coagulation/flocculation and Fenton processes) to depurate real wastewaters coming from two-phase olive oil production mills has been studied. The experimental results indicated that at the end of this combined strategy, involving a primary physical separation stage followed by Fenton's chemical oxidation, chemical oxygen demand (COD) is reduced up to 90% and total polyphenols' concentration is decreased up to 92%. The treated stream biodegradability (BOD5/COD) reached 0.52 and the Total Suspended Solids (TSSs) and Total Dissolved Solids (TDSs) decreased up to 95% and 69%, respectively. Fenton's procedure was optimized bearing in mind the pH adjustment step, different procedures for hydrogen peroxide addition and the use of coagulants instead of the chemical precipitation (by raising pH) to promote iron sludge settling. Our results demonstrated that pH (3.0 ± 0.1) control during the oxidation reaction improves the oxidation efficiency. Moreover, the final NaOH addition is essential to a better sludge formation and consequent precipitation of the residual iron removing also some organic matter.

Physical-chemical treatment of rainwater runoff in recovery and recycling companies: Pilot-scale optimization

Pilot-scale optimisation of different possible physical-chemical water treatment techniques was performed on the wastewater originating from three different recovery and recycling companies in order to select a (combination of) technique(s) for further full-scale implementation. This implementation is necessary to reduce the concentration of both common pollutants (such as COD, nutrients and suspended solids) and potentially toxic metals, polyaromatic hydrocarbons and poly-chlorinated biphenyls frequently below the discharge limits. The pilot-scale tests (at 250 L h(-1) scale) demonstrate that sand anthracite filtration or coagulation/flocculation are interesting as first treatment techniques with removal efficiencies of about 19% to 66% (sand anthracite filtration), respectively 18% to 60% (coagulation/flocculation) for the above mentioned pollutants (metals, polyaromatic hydrocarbons and poly chlorinated biphenyls). If a second treatment step is required, the implementation of an activated carbon filter is recommended (about 46% to 86% additional removal is obtained).