Red mud (an aluminium industry waste) has received wide attention as an effective adsorbent for water pollution control, showing significant adsorption potential for the removal of various aquatic ...pollutants. In this review, an extensive list of red‐mud‐based adsorbents has been compiled and their adsorption capacities (maximum uptake value of the adsorbent for the pollutant or adsorbate being removed) for various aquatic pollutants (metal ions, dyes, phenolic compounds, inorganic anions) are presented. The review provides a summary of recent information obtained using batch studies and deals with the adsorption mechanisms involved. It is evident from the literature survey that red mud has been found to be efficient for the removal of various aquatic pollutants, especially arsenic and phosphate. However, there is still a need to investigate the practical utility of these adsorbents on a commercial scale.
Different advanced oxidation processes (AOPs) were applied to the treatment of a real cotton-textile dyeing wastewater as a pre-oxidation step to enhance the biodegradability of the recalcitrant ...compounds, which can be further oxidized using a biological process. Tests were conducted on a lab-scale prototype using artificial solar radiation and at pilot scale with compound parabolic collectors using natural solar radiation. The cotton-textile dyeing wastewater presents a lilac color, with a maximum absorbance peak at 641 nm, alkaline pH (pH = 8.2), moderate organic content (DOC = 152 mg C L⁻¹, COD = 684 mg O₂ L⁻¹) and low-moderate biodegradability (40 % after 28 days in Zahn–Wellens test). All the tested processes contributed to an effective decolorization and mineralization, but the most efficient process was the solar-photo-Fenton with an optimum catalyst concentration of 60 mg Fe²⁺ L⁻¹, leading to 98.5 % decolorization and 85.5 % mineralization after less than 0.1 and 5.8 kJUV L⁻¹, respectively. In order to achieve a final wastewater with a COD below 250 mg O₂ L⁻¹ (discharge limit into water bodies imposed by the Portuguese Legislation-Portaria no. 423/97 of 25 June 1997), considering the combination of a solar-photo-Fenton reaction with a biological process, the phototreatment energy required is 0.5 kJUV L⁻¹, consuming 7.5 mM hydrogen peroxide, resulting in 58.4 % of mineralization Formula: see text
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•Oil and grease is a widespread pollutant of several types and sources.•Review of state-of-the-art technologies for oil and grease removal.•Sorption is an emerging technology with ...high efficiency and low cost.•Review of natural and synthetic sorbents for oil and grease removal.•Comparison of advantages and disadvantages of oil and grease removal technologies.
Oil and grease (O&G) is a class of pollutants with very low affinity to water. Their removal from wastewaters is often challenging and involves the combination of different treatment technologies, according to the specifications for the treated water and the O&G substances involved. O&G can be classified according to its type and source and this influences the choice of the treatment process.
This paper presents a review of the state-of-the-art technology on O&G removal. Treatment usually involves several steps, including primary, secondary and tertiary treatment. Gravity separators accomplish removal of free oil as a primary treatment. Secondary treatments include chemical, electrical and physical methods which target emulsified oil, such as, coagulation/flocculation, dissolved air flotation, electro-coagulation/flotation, and membrane separation. Tighter membranes and advanced oxidation processes can refine treatment in a tertiary step.
Many of these treatments present, however, disadvantages such as production of hazardous sludge or high energy requirements. In this context, sorption as a secondary treatment is gaining focus in the literature, especially using natural organic sorbents. These present the advantages of lower cost and biodegradability, and may enable the recovery or recycling of sorbed O&G. Additionally, some of them may be reused up to a limited number of working cycles. Several kinds of sorbents and mechanisms for oil sorption and recovery are reviewed in this article.
Cow bone char was investigated as sorbent for the defluoridation of aqueous solutions. The cow bone char was characterized in terms of its morphology, chemical composition, and functional groups ...present on the bone char surface using different analytical techniques: SEM, EDS, N
2
-BET method, and FTIR. Batch equilibrium studies were performed for the bone chars prepared using different procedures. The highest sorption capacities for fluoride were obtained for the acid washed (
q
= 6.2 ± 0.5 mg/g) and Al-doped (
q
= 6.4 ± 0.3 mg/g) bone chars. Langmuir and Freundlich models fitted well the equilibrium sorption data. Fluoride removal rate in batch system is fast in the first 5 h, decreasing after this time until achieving equilibrium due to pore diffusion. The presence of carbonate and bicarbonate ions in the aqueous solution contributes to a decrease of the fluoride sorption capacity of the bone char by 79 and 31 %, respectively. Regeneration of the F-loaded bone char using 0.5 M NaOH solution leads to a sorption capacity for fluoride of 3.1 mg/g in the second loading cycle. Fluoride breakthrough curve obtained in a fixed-bed column presents an asymmetrical
S
-shaped form, with a slow approach of
C
/
C
0
→ 1.0 due to pore diffusion phenomena. Considering the guideline value for drinking water of 1.5 mg F
−
/L, as recommended by World Health Organization, the service cycle for fluoride removal was of 71.0 h (F
−
feed
∼ 9 mg/L; flow rate = 1 mL/min;
m
sorbent
= 12.6 g). A mass transfer model considering the pore diffusion was able to satisfactorily describe the experimental data obtained in batch and continuous systems.
This study aims to investigate the applicability of a hybrid electrochemical sensor composed of cork and graphite (Gr) for detecting caffeine in aqueous solutions. Raw cork (RAC) and regranulated ...cork (RGC, obtained by thermal treatment of RAC with steam at 380 °C) were tested as modifiers. The results clearly showed that the cork-graphite sensors, GrRAC and GrRGC, exhibited a linear response over a wide range of caffeine concentration (5-1000 µM), with R
of 0.99 and 0.98, respectively. The limits of detection (LOD), estimated at 2.9 and 6.1 µM for GrRAC and GrRGC, suggest greater sensitivity and reproducibility than the unmodified conventional graphite sensor. The low-cost cork-graphite sensors were successfully applied in the determination of caffeine in soft drinks and pharmaceutical formulations, presenting well-defined current signals when analyzing real samples. When comparing electrochemical determinations and high performance liquid chromatography measurements, no significant differences were observed (mean accuracy 3.0%), highlighting the potential use of these sensors to determine caffeine in different samples.
Nitrogen Removal from Landfill Leachate by Microalgae Pereira, Sérgio F L; Gonçalves, Ana L; Moreira, Francisca C ...
International journal of molecular sciences,
11/2016, Letnik:
17, Številka:
11
Journal Article
Recenzirano
Odprti dostop
Landfill leachates result from the degradation of solid residues in sanitary landfills, thus presenting a high variability in terms of composition. Normally, these effluents are characterized by high ...ammoniacal-nitrogen (N-NH₄⁺) concentrations, high chemical oxygen demands and low phosphorus concentrations. The development of effective treatment strategies becomes difficult, posing a serious problem to the environment. Phycoremediation appears to be a suitable alternative for the treatment of landfill leachates. In this study, the potential of
for biomass production and nutrients (mainly nitrogen and phosphorus) removal from different compositions of a landfill leachate was evaluated. Since microalgae also require phosphorus for their growth, different loads of this nutrient were evaluated, giving the following N:P ratios: 12:1, 23:1 and 35:1. The results have shown that
was able to grow in the different leachate compositions assessed. However, microalgal growth was higher in the cultures presenting the lowest N-NH₄⁺ concentration. In terms of nutrients uptake, an effective removal of N-NH₄⁺ and phosphorus was observed in all the experiments, especially in those supplied with phosphorus. Nevertheless, N-NO₃
removal was considered almost negligible. These promising results constitute important findings in the development of a bioremediation technology for the treatment of landfill leachates.
This study focuses on the degradation of pharmaceuticals from a municipal wastewater after secondary treatment by applying various advanced oxidation processes (AOPs) and electrochemical AOPs (EAOPs) ...like UVC, H2O2/UVC, anodic oxidation (AO), AO with electrogenerated H2O2 (AO-H2O2), AO-H2O2/UVC and photoelectro-Fenton (PEF) using either UVC radiation (PEF-UVC) or UVA radiation (PEF-UVA). The municipal wastewater after secondary treatment was spiked with 5.0 mg L−1 of trimethoprim (TMP) antibiotic. The efficiency of processes to remove TMP followed the order UVC < AO-H2O2 < PEF-UVA << AO ≈ PEF-UVC < AO-H2O2/UVC < PEF-UVA (pH = 2.8) < H2O2/UVC ≈ PEF-UVC (pH = 2.8), using neutral pH, except when identified. While the UVC radiation alone led to a very low TMP removal, the H2O2/UVC process promoted a very high TMP degradation due to the production of hydroxyl radicals (OH) by H2O2 cleavage. In the AO-H2O2/UVC process, the electrogeneration of H2O2 can avoid the risks associated with the transportation, storage and manipulation of this oxidant and, furthermore, OH at the anode surface are also formed. Nevertheless, low contents of H2O2 were detected mainly at the beginning of the reaction, leading to a lower initial reaction rate when compared with the H2O2/UVC system. In the PEF-UVC, the addition of iron at neutral pH led to the visible formation of insoluble iron oxides that can filter the light. At pH 2.8, the iron remained dissolved, thereby promoting the Fenton's reaction and increasing the organics removal. The UVA-driven processes showed limited efficiency when compared with those using UVC light. For all processes with H2O2 electrogeneration, the active chlorine species can be scavenged by the H2O2, diminishing the efficiency of the processes. This can explain the lower efficiency of AO-H2O2 when compared with AO. Moreover, the degradation of the MWWTP effluent spiked with 18 pharmaceuticals in μg L−1 during AO process was assessed as well as the influence of the following operational variables on the process efficiency: (i) H2O2 concentration on H2O2/UVC, (ii) current density on AO, AO-H2O2, AO-H2O2/UVC, PEF-UVC and PEF-UVA, and (iii) pH on PEF-UVA.
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•First study on AO-H2O2, AO-H2O2/UVC, PEF-UVC and PEF-UVA to degrade a MWWTP effluent.•Unprecedented comparison of chemical and electrochemical advanced oxidation processes.•Trimethoprim removal: PEF-UVC ≈ H2O2/UVC > PEF-UVA > AO-H2O2/UVC > AO > AO-H2O2 > UVC.•Assessment of pharmaceuticals removal at mg L−1 and μg L−1 levels.•Assessment of the effect of H2O2 content, current density and pH on various processes.
Apart from a high biodegradable fraction consisting of organic acids, sugars and alcohols, winery wastewaters exhibit a recalcitrant fraction containing high-molecular-weight compounds as ...polyphenols, tannins and lignins. In this context, a winery wastewater was firstly subjected to a biological oxidation to mineralize the biodegradable fraction and afterwards an electrochemical advanced oxidation process (EAOP) was applied in order to mineralize the refractory molecules or transform them into simpler ones that can be further biodegraded. The biological oxidation led to above 97% removals of dissolved organic carbon (DOC), chemical oxygen demand (COD) and 5-day biochemical oxygen demand (BOD5), but was inefficient on the degradation of a bioresistant fraction corresponding to 130 mg L−1 of DOC, 380 mg O2 L−1 of COD and 8.2 mg caffeic acid equivalent L−1 of total dissolved polyphenols. Various EAOPs such as anodic oxidation with electrogenerated H2O2 (AO-H2O2), electro-Fenton (EF), UVA photoelectro-Fenton (PEF) and solar PEF (SPEF) were then applied to the recalcitrant effluent fraction using a 2.2 L lab-scale flow plant containing an electrochemical cell equipped with a boron-doped diamond (BDD) anode and a carbon-PTFE air-diffusion cathode and coupled to a photoreactor with compound parabolic collectors (CPCs). The influence of initial Fe2+ concentration and current density on the PEF process was evaluated. The relative oxidative ability of EAOPs increased in the order AO-H2O2 < EF < PEF ≤ SPEF. The SPEF process using an initial Fe2+ concentration of 35 mg L−1, current density of 25 mA cm−2, pH of 2.8 and 25 °C reached removals of 86% on DOC and 68% on COD after 240 min, regarding the biologically treated effluent, along with energy consumptions of 45 kWh (kg DOC)−1 and 5.1 kWh m−3. After this coupled treatment, color, odor, COD, BOD5, NH4+, NO3− and SO42− parameters complied with the legislation targets and, in addition, a total dissolved polyphenols content of 0.35 mg caffeic acid equivalent L−1 was found. Respirometry tests revealed low biodegradability enhancement along the SPEF process.
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•First study on EAOPs for winery wastewater remediation.•Biodegradable fraction of the winery effluent removed by initial biological oxidation.•Order of EAOPs efficiency on the recalcitrant fraction reduction: AO-H2O2 < EF < PEF ≤ SPEF.•Up to 86% DOC, 68% COD and 89% BOD5 removals with 5.1 kWh m−3 cost for SPEF process.•Color, odor, COD, BOD5, NH4+, NO3− and SO42− in agreement with legislation at the end.
Literature describes a kinetic mineralization profile for most of acrylic-textile dyeing wastewaters using a photo-Fenton reaction characterized by a slow degradation process and high reactants ...consumption. This work tries to elucidate that the slow decay on DOC concentration is associated with the formation of stable complexes between Fe3+ and textile auxiliary products, limiting the photoreduction of Fe3+. This work also evaluates the enhancement of a solar photo-Fenton reaction through the use of different ferric-organic ligands applied to the treatment of a simulated acrylic-textile dyeing wastewater, as a pre-oxidation step to enhance its biodegradability. The photo-Fenton reaction was negatively affected by two dyeing auxiliary products: i) Sera® Tard A-AS, a surfactant mainly composed of alkyl dimethyl benzyl ammonium chloride and ii) Sera® Sperse M-IW, a dispersing agent composed of polyglycol solvents. The catalytic activity of the organic ligands toward the ferrous-catalysed system followed this order: Fe(III)-Oxalate > Fe(III)-Citrate > Fe(III)-EDDS, and all were better than the traditional photo-Fenton reaction. Different design parameters such as iron concentration, pH, temperature, flow conditions, UV irradiance and H2O2 addition strategy and dose were evaluated. The ferrioxalate induced photo-Fenton process presented the best results, achieving 87% mineralization after 9.3 kJUV L−1 and allowing to work until near neutral pH values. As expected, the biodegradability of the textile wastewater was significantly enhanced during the photo-Fenton treatment, achieving a value of 73%, consuming 32.4 mM of H2O2 and 5.7 kJUV L−1.
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•Fe3+ formed stable complexes with the organic pollutants of the textile wastewater.•The photo-Fenton reaction was enhanced through the use of ferric-organic ligands.•The PF with Fe(III)-oxalate or citrate showed similar mineralization profiles.•The best iron concentration must be selected taking into account the UV irradiance.•The PF efficiency depends on the photoreactor hydrodynamic conditions.
A solar photo-Fenton process combined with a biological nitrification and denitrification system is proposed for the decontamination of a landfill leachate in a pilot plant using photocatalytic ...(4.16 m
2 of Compound Parabolic Collectors – CPCs) and biological systems (immobilized biomass reactor). The optimum iron concentration for the photo-Fenton reaction of the leachate is 60 mg Fe
2+ L
−1. The organic carbon degradation follows a first-order reaction kinetics (
k = 0.020 L kJ
UV
−1,
r
0 = 12.5 mg kJ
UV
−1) with a H
2O
2 consumption rate of 3.0 mmol H
2O
2 kJ
UV
−1. Complete removal of ammonium, nitrates and nitrites of the photo-pre-treated leachate was achieved by biological denitrification and nitrification, after previous neutralization/sedimentation of iron sludge (40 mL of iron sludge per liter of photo-treated leachate after 3 h of sedimentation). The optimum C/N ratio obtained for the denitrification reaction was 2.8 mg CH
3OH per mg N–NO
3
−, consuming 7.9 g/8.2 mL of commercial methanol per liter of leachate. The maximum nitrification rate obtained was 68 mg N–NH
4
+ per day, consuming 33 mmol (1.3 g) of NaOH per liter during nitrification and 27.5 mmol of H
2SO
4 per liter during denitrification. The optimal phototreatment energy estimated to reach a biodegradable effluent, considering Zahn–Wellens, respirometry and biological oxidation tests, at pilot plant scale, is 29.2 kJ
UV L
−1 (3.3 h of photo-Fenton at a constant solar UV power of 30 W m
−2), consuming 90 mM of H
2O
2 when used in excess, which means almost 57% mineralization of the leachate, 57% reduction of polyphenols concentration and 86% reduction of aromatic content.
► The solar photo-Fenton process was found to be very efficient in the treatment of leachates, enhancing the biodegradability of the leachate and making possible a subsequent treatment by a biological oxidation process. ► Solar energy is an important natural resource and using it in advanced oxidation processes is probably one of the best ways to make the detoxification of leachates from sanitary landfills economically attractive. ► Biological nitrogen removal was achieved by a by two-step process: aerobic nitrification of ammonia to nitrite and then to nitrate followed by anoxic denitrification of nitrate to nitrite, nitric oxide, nitrous oxide and nitrogen gas using an external carbon source.
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