Display omitted
•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.
•Treating textile dyeing effluents by SBR coupled with waste sludge adsorption.•Metal hydroxide sludge: a good adsorbent for a direct textile dye.•Good adsorption capacities were found with the ...low-cost adsorbent.•Adsorbent performance considerably reduced by auxiliary products.•Color removal complies with discharge limits.
Color removal from textile wastewaters, at a low-cost and consistent technology, is even today a challenge. Simultaneous biological treatment and adsorption is a known alternative to the treatment of wastewaters containing biodegradable and non-biodegradable contaminants. The present work aims at evaluating the treatability of a simulated textile wastewater by simultaneously combining biological treatment and adsorption in a SBR (sequencing batch reactor), but using a low-cost adsorbent, instead of a commercial one. The selected adsorbent was a metal hydroxide sludge (WS) from an electroplating industry. Direct Blue 85 dye (DB) was used in the preparation of the synthetic wastewater. Firstly, adsorption kinetics and equilibrium were studied, in respect to many factors (temperature, pH, WS dosage and presence of salts and dyeing auxiliary chemicals in the aqueous media). At 25°C and pH 4, 7 and 10, maximum DB adsorption capacities in aqueous solution were 600, 339 and 98.7mg/g, respectively. These values are quite considerable, compared to other reported in literature, but proved to be significantly reduced by the presence of dyeing auxiliary chemicals in the wastewater. The simulated textile wastewater treatment in SBR led to BOD5 removals of 53–79%, but color removal was rather limited (10–18%). The performance was significantly enhanced by the addition of WS, with BOD5 removals above 91% and average color removals of 60–69%.
Display omitted
•Review of literature on phosphate uptake from water through adsorption.•Comparative assessment of advantages and disadvantages of different adsorbents.•Desorption is discussed as a ...strategy to recover phosphate and reuse adsorbents.•Direct use of loaded adsorbent as a fertilizer is considered.
The need to control eutrophication in water bodies and the risk of supply shortage of phosphate rock have motivated the search for treatment techniques able to sequester and recover P from wastewaters. Current techniques can recover phosphate from highly loaded aqueous media, but it is increasingly important to develop economically attractive solutions for low concentration effluents. Adsorption can be highly selective and efficient for phosphate uptake and recovery from water and wastewater, which can act as secondary sources of phosphorus. This review gathers the data reported in the literature about phosphate removal from water through adsorption and subsequent recovery through desorption or direct use of the phosphorus-loaded adsorbent as a fertilizer. Metal (e.g. Al, Ca, Ce, Fe, La, Mg, Mn, Zn, Zr) hydroxides/oxides provide excellent adsorption capacities of phosphate, in addition to other advantages such as fast kinetics and good selectivity. These compounds have been incorporated into zeolites, mesoporous silica, activated carbon, biochar, and bio-derived materials, to enhance their adsorption capacities. Significant advances have been made in engineered materials, including magnetic and granular adsorbents. Literature reports other valuable attempts to upscale the process including pilot-scale experiments, application in fixed-bed columns and to real wastewaters. Further studies are necessary to overcome some limitations still observed. Future work should give more attention to phosphorus recovery from the eluates and to the direct use of P-loaded adsorbents.
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
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.
Display omitted
•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.
Display omitted
•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.
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.
Biosorption is an emerging technique for water treatment utilizing abundantly available biomaterials (especially agricultural wastes). Among several agricultural wastes studied as biosorbents for ...water treatment, coconut has been of great importance as various parts of this tree (e.g. coir, shell, etc.) have been extensively studied as biosorbents for the removal of diverse type of pollutants from water. Coconut-based agricultural wastes have gained wide attention as effective biosorbents due to low-cost and significant adsorption potential for the removal of various aquatic pollutants. In this review, an extensive list of coconut-based biosorbents from vast literature has been compiled and their adsorption capacities for various aquatic pollutants as available in the literature are presented. Available abundantly, high biosorption capacity, cost-effectiveness and renewability are the important factors making these materials as economical alternatives for water treatment and waste remediation. This paper presents a state of the art review of coconut-based biosorbents used for water pollution control, highlighting and discussing key advancement on the preparation of novel adsorbents utilizing coconut wastes, its major challenges together with the future prospective. It is evident from the literature survey that coconut-based biosorbents have shown good potential for the removal of various aquatic pollutants. However, still there is a need to find out the practical utility of such developed adsorbents on commercial scale, leading to the superior improvement of pollution control and environmental preservation.
The current study has proved the technical feasibility of including electrochemical advanced oxidation processes (EAOPs) in a multistage strategy for the remediation of a sanitary landfill leachate ...that embraced: (i) first biological treatment to remove the biodegradable organic fraction, oxidize ammonium and reduce alkalinity, (ii) coagulation of the bio-treated leachate to precipitate humic acids and particles, followed by separation of the clarified effluent, and (iii) oxidation of the resulting effluent by an EAOP to degrade the recalcitrant organic matter and increase its biodegradability so that a second biological process for removal of biodegradable organics and nitrogen content could be applied. The influence of current density on an UVA photoelectro-Fenton (PEF) process was firstly assessed. The oxidation ability of various EAOPs such as electro-Fenton (EF) with two distinct initial total dissolved iron concentrations (TDI0), PEF and solar PEF (SPEF) was further evaluated and these processes were compared with their analogous chemical ones. A detailed assessment of the two first treatment stages was made and the biodegradability enhancement during the SPEF process was determined by a Zahn–Wellens test to define the ideal organics oxidation state to stop the EAOP and apply the second biological treatment. The best current density was 200 mA cm−2 for a PEF process using a BDD anode, TDI0 of 60 mg L−1, pH 2.8 and 20 °C. The relative oxidation ability of EAOPs increased in the order EF with 12 mg TDI0 L−1 < EF with 60 mg TDI0 L−1 < PEF with 60 mg TDI0 L−1 ≤ SPEF with 60 mg TDI0 L−1, using the abovementioned conditions. While EF process was much superior to the Fenton one, the superiority of PEF over photo-Fenton was less evident and SPEF attained similar degradation to solar photo-Fenton. To provide a final dissolved organic carbon (DOC) of 163 mg L−1 to fulfill the discharge limits into the environment after a second biological process, 6.2 kJ L−1 UV energy and 36 kWh m−3 electrical energy were consumed using SPEF with a BDD anode at 200 mA cm−2, 60 mg TDI0 L−1, pH 2.8 and 20 °C.
Display omitted
•First study of EAOPs with H2O2 electrogeneration for landfill leachate treatment.•Multistage treatment strategy: bio-process/coagulation/EAOP/bio-process.•EAOPs used for recalcitrant organics degradation and biodegradability enhancement.•Efficiency of EAOPs in the order EF < PEF ≤ SPEF.•Consumption of 6.2 kJ L−1 UV energy and 36 kWh m−3 electrical energy using SPEF.
PDF
