Stabilized landfill leachate treatment by coagulation-flocculation coupled with UV-based sulfate radical oxidation process

Ecotoxicological risk assessment on coagulation-flocculation in water/wastewater treatment: a systematic review

It is undeniable that removal efficiency is the main factor in coagulation-flocculation (C-F) process for wastewater treatment. However, as far as environmental safety is concerned, the ecotoxicological aspect of the C-F process needs to be examined further. In this study, a systematic review was performed based on publications related to the toxicity research in C-F technology for wastewater treatment. Through a series of screening steps, available toxicity studies were categorized into four themes, namely acute toxicity, phytotoxicity, cytotoxicity, and genotoxicity, which comprised 48 articles. A compilation of the methodologies executed for each theme was also outlined. The findings show that conventional metallic coagulants (e.g., alum, iron chloride, and iron sulfate) were less toxic when tested on test species such as Daphnia magna (water flea), Lattuca sativa (lettuce), and animal cells compared to synthetic polymers. Natural coagulants such as chitosan or Moringa oleifera were less toxic compared to metallic coagulants; however, inconsistent results were observed. Moreover, an advanced C-F (electrocoagulation) as well as integration between C-F and Fenton, adsorption, and photocatalytic does not significantly change the toxicological profile of the system. It was found that diverse coagulants and flocculants, species sensitivity, complexity in toxicity testing, and dynamic environmental conditions were some key challenges faced in this field. Finally, it was expected that advances in technology, interdisciplinary collaboration, and a growing awareness of environmental sustainability will drive efforts to develop more effective and eco-friendly coagulants and flocculants, improve toxicity testing methodologies, and enhance the overall efficiency and safety of water and wastewater treatment processes.

Coagulation in combination with anaerobic digestion for enhancement of resource recovery from faecal sludge

Poorly managed faecal sludge (FS) poses significant challenges to public health and the environment. Anaerobic digestion (AD) of FS provides an effective method for energy recovery while reducing FS associated threats. Recognizing the critical role of the dewatering process before AD, this study investigates the synergistic application of chemical coagulation and mesophilic AD for synthetic FS treatment. FeCl3, AlCl3, Fe2(SO4)3, poly ferric sulfate (PFS) and poly aluminium ferric chloride (PAFC) were utilized at varying dosages to examine their impact on FS properties and subsequent biogas production from the dewatered FS. It was found that coagulation enhances sedimentation efficiencies and dewaterability through mechanisms such as charge neutralization, charge patching and bridging, thereby improving the FS feasibility for AD. Notably, polymer coagulant PFS showed good performance in balancing pollutant removal and methane recovery, contributing to facilitating the hydrolysis and acidogenesis microorganisms involved in the AD process. Optimal dosage was identified at 150 mg/g TS (1.7 g/L FS), achieving prominent removal efficiencies for total COD (67%), turbidity (85%), and total phosphorus (60%), while simultaneously enhancing AD performance with specific CH4 production reaching 517 ml CH₄/g VS or 24.8 ml CH₄/g AD wet feedstock compared to 309 ml CH₄/g VS or 2.7 ml CH₄/g AD wet feedstock in untreated FS.

Treatment of landfill leachate by coagulation: A review

Landfill leachate is a seriously polluted and hazardous liquid, which contains a high concentration of refractory organics, ammonia nitrogen, heavy metals, inorganic salts, and various suspended solids. The favorable disposal of landfill leachate has always been a hot and challenging issue in wastewater treatment. As one of the best available technologies for landfill leachate disposal, coagulation has been studied extensively. However, there is an absence of a systematic review regarding coagulation in landfill leachate treatment. In this paper, a review focusing on the characteristics, mechanisms, and application of coagulation in landfill leachate treatment was provided. Different coagulants and factors influencing the coagulation effect were synthetically summarized. The performance of coagulation coupled with other processes and their complementary advantages were elucidated. Additionally, the economic analysis conducted in this study suggests the cost-effectiveness of the coagulation process. Based on previous studies, challenges and perspectives met by landfill leachate coagulation treatment were also put forward. Overall, this review will provide a reference for the coagulation treatment of landfill leachate and promote the development of efficient and eco-friendly leachate treatment technology.

UV/persulfate processes for the removal of total organic carbon from coagulation-treated industrial wastewaters

Sulfate radical-based oxidation processes were investigated to understand the relationship between persulfate (PS) consumption and total organic carbon (TOC) removal from industrial wastewater under various PS concentrations. First, the degradation and mineralization of Bisphenol A (BPA) (initial concentration: 11 mg/L) were investigated in ultraviolet (UV)/PS systems. Complete degradation was achieved within 30 min of UV irradiation, and 41%-72% TOC removal was achieved at PS concentrations of 200 and 400 mg/L. The consumed concentration of S2O82- and generated concentration of SO42- increased gradually to similar levels. The ratio of the PS consumption to TOC removal based on the mass concentration (mg/L) was 14.5 and 23.2 at 180 min for 200 and 400 mg/L of S2O82-, respectively. Three types of coagulation-treated industrial wastewater from metal-processing, food-processing, and adhesive-producing plants were obtained, and TOC removal was analyzed using the same UV/PS systems (initial TOC concentration: 100 mg/L). The TOC removal rates ranged from 16.9% to 94.4% after 180 min of UV irradiation at PS concentrations of 1,000, 2,000, 4,000, and 8,000 mg S2O82-/L. Despite the higher TOC removal at higher PS concentrations, the PS activation efficiency decreased significantly as the PS concentration increased. Only approximately 30%-40% activation efficiency was achieved at a PS concentration of 8,000 mg/L. In this study, the ratio of PS consumption to TOC removal ranged from 20.6 to 43.9.

Sequential treatment of landfill leachate by electrocoagulation/aeration, PMS/ZVI/UV and electro-Fenton: Performance, biodegradability and toxicity studies

This study presents a systematic study on sequential treatment of highly resistant landfill leachate by electrocoagulation (EC)/aeration, sulfate radical advanced oxidation process (SR-AOP) and electro-Fenton (EF). In case of SR-AOP, peroxymonosulfate (PMS) catalyzed by zero valent iron (ZVI) and ultraviolet irradiation (UV) system was developed. Treatment process was optimized in respect to COD removal. Analysis of results revealed that sequential application of EC/aeration, PMS/ZVI/UV, and EF processes provide an extraordinary performance and meet the environmental regulations. The source of iron for EF process was provided from previous process reducing the cost of sequential process. Separately, EC/aeration (inlet COD = 4040 mg/L), PMS/ZVI/UV (inlet COD = 1560 mg/L), and EF (inlet COD = 471 mg/L) removed 61, 69 and 82% of COD respectively. Overall, sequential processes of EC/aeration, PMS/ZVI/UV and EF could remove the COD, TOC and ammonia of the landfill leachate around 98%, 93% and 94%, respectively. The comparison of different sequences of following processes indicated that current configuration (EC/aeration-PMS/ZVI/UV-EF) could meet the discharge standards. Furthermore, humification degree was significantly improved after oxidative processes. Biodegradability study was also performed by means of BOD/COD, average oxidation state (AOS), and Zahn-Wellens test, and the best results associated with these indices were obtained 0.56, 2.37, and over 98%, respectively. Phytotoxicity of leachate was remarkably reduced and the final effluent can be considered as a non-phytotoxic wastewater.

Effect of the association of coagulation/flocculation, hydrodynamic cavitation, ozonation and activated carbon in landfill leachate treatment system

Mature landfill wastewater is a complex effluent due to its low biodegradability and high organic matter content. Currently, mature leachate is treated on-site or transported to wastewater treatment plants (WWTPs). Many WWTPs do not have the capacity to receive mature leachate due to its high organic load leading to an increase in the cost of transportation to treatment plants more adapted to this type of wastewater and the possibility of environmental impacts. Many techniques are used in the treatment of mature leachates, such as coagulation/flocculation, biological reactors, membranes, and advanced oxidative processes. However, the isolated application of these techniques does not achieve efficiency to meet environmental standards. In this regard, this work developed a compact system that combines coagulation and flocculation (1st Stage), hydrodynamic cavitation and ozonation (2nd Stage), and activated carbon polishing (3rd Stage) for the treatment of mature landfill leachate. The synergetic combination of physicochemical and advanced oxidative processes showed a chemical oxygen demand (COD) removal efficiency of over 90% in less than three hours of treatment using the bioflocculant PGα21Ca. Also, the almost absolute removal of apparent color and turbidity was achieved. The remaining CODs of the treated mature leachate were lower when compared to typical domestic sewage of large capitals (COD ~ 600 mg L^-1), which allows the interconnection of the sanitary landfill to the urban sewage collection network after treatment in this proposed system. The results obtained with the compact system can help in the design of landfill leachate treatment plants, as well as in the treatment of urban and industrial effluents which contains different compounds of emerging concern and persistence in the environment.

Molecular-level transformation of refractory organic matter during flocculation-ultraviolet/peroxymonosulfate treatment of MBR-treated landfill leachate

Refractory organic matter in membrane bioreactor effluent resulting from landfill leachate treatment has a complex composition. This paper identified the transformation mechanism of organic matter in a flocculation-ultraviolet (UV)/peroxymonosulfate (PMS) system at the molecular level using electrospray ionization coupled with Fourier transform ion cyclotron resonance mass spectrometry. The results showed that the flocculation system was able to remove a large amount of dissolved organic matter (DOM) with high oxidation and unsaturation/saturation. UV radiation displayed a relatively strong reactivity for DOM with an electron-rich structure, which it can transform into DOM with lower aromaticity through photolysis and photosensitivity, although the effectiveness of the transformation was poor. In comparison, due to the action of reactive oxygen species, the UV/PMS system can enable reactions such as demethylation, dehydrogenation, decarboxylation, dehydroxylation, ring cleavage, and decarbonylation. It can remove approximately 60% quantity of the total DOM and produce DOM featuring a higher degree of oxidation and saturation than that of the UV system alone. The results showed that the UV/PMS system was a complementary of flocculation in DOM removal from the membrane bioreactor effluent, while the system also resulted in a large number of sulfuric compounds; thus, requiring further evaluation of its ecological effects.

Combined organic coagulants and photocatalytic processes for winery wastewater treatment

Due to the consumers demand for quality wines, washing and disinfection operations are necessary in wine productions, leading to the generation of large volumes of winery wastewater (WW) with a high organic content which has the potential to cause irreversible environmental impacts. The aim and novelty of this work is the production of natural organic coagulants (NOCs) to be applied in coagulation-flocculation-decantation (CFD) process. To complement this treatment process, it is also aimed the performed a photo-Fenton process, combining hydrogen peroxide (H₂O₂) and potassium persulfate (KPS). The Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM) showed that NOCs are carbon-based materials with adsorption capacity. Under the best operational conditions, NOCs achieved a turbidity removal between 86.2 and 98.9%, a total suspended solids (TSS) removal ranging between 85.0 and 94.9% and a dissolved organic carbon (DOC) removal ranging between 14.1 and 44.9%. To degrade the DOC present in the WW, different advanced oxidation processes (AOPs) were tested. Results showed that KPS-photo-Fenton, under the best operational conditions [Fe²⁺] = 2.5 mM, [KPS] = 1.0 mM, pH = 3.0, radiation UV-C mercury lamp (254 nm), agitation 350 rpm, temperature 298 K, reaction time 240 min achieved a DOC removal of 91.2 and 96.8%, with a H₂O₂ consumption of 156.9 and 199.0 mM, respectively for red and white WW. With application of combined CFD-KPS-photo-Fenton process, it was observed an increase of DOC removal with lower H₂O₂ consumptions. The energy consumption of the photosystem was evaluated by application of electric energy per mass (E_EM). The application of KPS-photo-Fenton process achieved an E_EM of 0.308 and 0.0309 kWh/g/L DOC, with a cost of 2.05 and 2.59 €/g/L DOC respectively for red and white WW. The combination of CFD-KPS-photo-Fenton decreased significantly the costs of treatment and the treated wastewater achieved the Portuguese legal values for wastewater discharge. This work shows that NOCs are a promising technology that can be an alternative to traditional metal salts, the combination of sulfate radicals with hydroxyl radicals can achieve high DOC removal and the combination of CFD with KPS-photo-Fenton process can decrease the operational costs.

Advanced oxidation process based on hydroxyl and sulfate radicals to degrade refractory organic pollutants in landfill leachate

As a special type of wastewater produced in the landfill, leachate is mainly composed of organic pollutants, inorganic salts, ammonia nitrogen and heavy metals, and featured by high pollutants concentration, complex composition and large fluctuations in water quality and volume. Biological, chemical and physical methods have been proposed to treat landfill leachate, but much attention has been paid to the advanced oxidation processes (AOPs), due to their high adaptability and organic degradation efficiency. This paper summarizes the recent findings on the AOPs based on hydroxyl radical (OH) (e.g., ozonation and catalyzed ozone oxidations, Fenton and Fenton-like oxidations) and sulfate radical (SO₄^-) (e.g., activated and catalyzed persulfate oxidations), especially the production routes of free radicals and mechanisms of action. When dealing with some special landfill leachates, it is difficult for a single advanced oxidation technology to achieve the expected results, but the synergistic combination with biological or physical methods can produce satisfactory outcomes. Therefore, this paper has summarized the application of these combined treatment technologies on landfill leachate.

Food By-Product Valorization by Using Plant-Based Coagulants Combined with AOPs for Agro-Industrial Wastewater Treatment

Re-using and adding value to by-products is one of the current focuses of the agri-food industry, following the Sustainable Development Goals of United Nations. In this work, the by-products of four plants, namely chestnut burr, acorn peel, olive leaf, and grape stem were used as coagulants to treat elderberry wastewater (EW), a problematic liquid effluent. EW pre-treatment using these natural coagulants showed promising results after pH and coagulant dosage optimization. However, the decrease in total organic carbon (TOC) was not significant, due to the addition of the plant-based natural coagulants which contain carbon content. After this pre-treatment, the photo-Fenton advanced oxidation process was selected, after preliminary assays, to improve the global performance of the EW treatment. Photo-Fenton was also optimized for the parameters of pH, H₂O₂, Fe²⁺, and irradiance power, and the best conditions were applied to the EW treatment. Under the best operational conditions defined in the parametric study, the combined results of coagulation–flocculation–decantation (CFD) and photo-Fenton for chestnut burr, acorn peel, olive leaf, and grape stem were, respectively, 90.2, 89.5, 91.5, and 88.7% for TOC removal; 88.7, 82.0, 90.2 and 93.1%, respectively, for turbidity removal; and finally, 40.6, 42.2, 45.3, and 39.1%, respectively, for TSS removal. As a final remark, it is possible to suggest that plant-based coagulants, combined with photo-Fenton, can be a promising strategy for EW treatment that simultaneously enables valorization by adding value back to food by-products.

Novel strategy for controlling colloidal instability during the flocculation pretreatment of landfill leachate

Flocculation is an economical and effective pretreatment technology for landfill leachate. An iron salt flocculant is often used in landfill leachate pretreatment, but the flocs that are formed are affected by the operation sequence, which subsquently influences flocculation. This study selected three representative landfill leachates (i.e., mature landfill leachate (MLL), biologically treated landfill leachate (BTL), and nanofiltration concentrate leachate (NFCL)). The effect of different operation modes on the removal of organic matter from landfill leachate by flocculation was studied, and a strategy to control colloidal instability is put forward. The results revealed that adjusting the pH value to 9 using NaOH changes the zeta potential of leachate when the leachate and sludge are not separated, which affects electric neutralization in flocculation and colloidal stability. Furthermore, a part of the collected organic matter is released to the leachate again, leading to a decrease in the flocculation pretreatment effect. In this improved flocculation process, the leachate and sludge are first separated, and the pH value of the system is then adjusted to 9. The effect of OH^- on electric neutralization is avoided and the remaining Fe³⁺ can further remove organic matter from leachates. Finally, the UV₂₅₄ removal efficiencies of MLL, BTL, and NFCL increased by 20.38%, 28.67%, and 22.67%, respectively. In a full-scale application, i.e., an NFCL treatment facility, the UV₂₅₄ removal efficiency during long-term operation reached 87.50%. Therefore, the colloid instability control strategy this study proposes can provide theoretical and engineering references for the flocculation pretreatment of landfill leachate.

Occurrence of organic micropollutants in municipal landfill leachate and its effective treatment by advanced oxidation processes

Landfilling is the most prominently adopted disposal technique for managing municipal solid waste across the globe. However, the main drawback associated with this method is the generation of leachate from the landfill site. Leachate, a highly concentrated liquid consisting of both organic and inorganic components arises environmental issues as it contaminates the nearby aquifers. Landfill leachate treatment by conventional methods is not preferred as the treatment methods are not much effective to remove these pollutants. Advanced oxidation processes (AOPs) based on both hydroxyl and sulfate radicals could be a promising method to remove the micropollutants completely or convert them to non-toxic compounds. The current review focuses on the occurrence of micropollutants in landfill leachate, their detection methods and removal from landfill leachate using AOPs. Pharmaceuticals and personal care products occur in the range of 10^-1 to more than 100 μg L^-1 whereas phthalates were found below the detectable limit to 384 μg L^-1, pesticides in the order of 10^-1 μg L^-1 and polyaromatic hydrocarbons occur in concentration from 10^-2 to 114.7 μg L^-1. Solid-phase extraction is the most preferred method for extracting micropollutants from leachate and liquid chromatography (LC) - mass spectrophotometer (MS) for detecting the micropollutants. Limited studies have been focused on AOPs as a potential method for the degradation of micropollutants in landfill leachate. The potential of Fenton based techniques, electrochemical AOPs and ozonation are investigated for the removal of micropollutants from leachate whereas the applicability of photocatalysis for the removal of a wide variety of micropollutants from leachate needs in-depth studies.

Physical-chemical pre-treatment of sanitary landfill raw leachate by direct ascending filtration

Several environmental problems in Brazil are caused by the accelerated urban and industrial growth and by the multiplicity of urban waste generated. Waste disposal in landfills is still common practice in Brazil. This work was conducted in sand filters and activated carbon column, proposing an alternative for the physical-chemical treatment of leachate as a pre-treatment to preserve the biological process. The results showed reductions of up to 74% for COD, 47% for BOD5, 93% for color, 90% for ammonia and an increase from 0.3 to 0.9 in the BOD5/COD ratio. Although the results obtained do not fall within the limits of the legislation, the results for ammonia concentration was reduced by 33.25% and 85.37% after filtration and activated carbon column treatment respectively. The use of activated carbon columns resulted in an excellent performance in the reduction of heavy metals in the leachate. The performance demonstrated a removal of 60-96%. Limitations were found in the length of the filtration races, as a limiting factor in the process. The results show the potential of using direct upward filtration with sand and activated carbon filters for the treatment of landfill leachate.

Combined landfill leachate treatment methods: an overview

Landfill leachate is commonly heavily contaminated and consists of high amount of organic compounds, inorganic salts, toxic gases, halogenated hydrocarbons, and heavy metals that exerts a serious threat to public health and the environment. Thus, it requires treatments before direct release into receiving waters. Selecting the efficient method for leachate treatment is still a major challenge. While physicochemical treatment methods such as coagulation-flocculation, adsorption, membrane filtration, ozonation, air stripping, and advanced oxidation processes (AOP) are appropriate for mature leachate, young leachate requires biological treatments including membrane bioreactor (MBR), activated sludge (AS), upflow anaerobic sludge blanket (UASB), and rotational biological contactor (RBC). Recently, the integration of biological processes and physicochemical methods has been demonstrated to be very efficient. It is found that combined coagulation-flocculation/nanofiltration and activated sludge/reverse osmosis are more efficacious than other integrated physicochemical methods and combined physicochemical/biological methods, respectively.

Landfill leachate treatment by persulphate related advanced oxidation technologies

Landfill leachate is produced from garbage decomposition with highly toxic and bio-refractory compounds, which poses serious harm to environmental security and human health. Thus, it is urgent to treat landfill leachate properly. Persulfate (PS) oxidation has attracted extensive attentions in terms of fast reaction speed, non-selectivity to target pollutants and thorough oxidation. In recent years, PS oxidation has been widely adopted for landfill leachate purification. However, the related results have been rarely summarized. In this review, the treatment of landfill leachate by PS oxidation system is discussed systematically including oxidants, activation modes and oxidation mechanisms. In addition, the current situation of PS oxidation system and other coupled systems for landfill leachate treatment is also summarized. Finally, the challenges and future research directions of landfill leachate treatment based on PS oxidation process are proposed. Meaningfully, this review will provide valuable references for the development of landfill leachate treatment process, promoting the application of advanced oxidation technology in landfill leachate treatment.

Effective treatment of high-salinity landfill leachate using ultraviolet/ultrasonication/ peroxymonosulfate system

Landfill leachate, as a complex medium with a high concentration of organic and mineral materials, is a serious problem for the environment. In the current study, the saline landfill leachate of Bushehr coastal city (Iran) was treated using ultraviolet/ultrasonic waves/peroxymonosulfate system. The initial TOC and TDS of the studied leachate was 915 mg/L and 7390 mg/L, respectively. The system had the maximum efficiency at conditions of pH 3, peroxymonosulfate (PMS) of 4 mM, and reaction time of 150 min. Based on the findings, the initial ratio of BOD₅/COD (0.66) was reduced to 0.38 using the developed system. After treatment of the landfill leachate at the optimal condition, the values of COD, BOD₅, and UV₂₅₄ were reached to 983 mg/L, 348 mg/L, and 10.16 cm^-1, respectively. The concentration of all studied elements (except Pb, As, and Ca) increased after purification. According to the GC-mass spectrometry, the molecular weight and concentration of organic matter in raw leachate were higher than that of the treated one. The studied system had an energy consumption value of 86 kW·h/m³ for the treatment of landfill leachate. The results confirm the effectiveness of the ultraviolet/ultrasonic waves/PMS system for the treatment of high saline landfill leachate.

Landfill leachate treatment through the combination of genetically engineered bacteria Rhodococcus erythropolis expressing Nirs and AMO and membrane filtration processes

This study developed a process of genetically engineered bacteria Rhodococcus erythropolis expressing Nirs and AMO combined with membrane bioreactor (MBR), nanofiltration (NF) and reverse osmosis (RO) membrane (pRho-NA-MNR) for advanced treatment of landfill leachate. Results demonstrated that pRho-NA-MNR presented higher removal rate of chemical oxygen demand (COD), biological oxygen demand (BOD), ammonia nitrogen (N-NH₄), total nitrogen (TN) and total organic carbon (TOC) than activated sludge (AS-MNR) system. Administration of pRho-NA increased nitrification by converting N-NH₄ to nitrite (N-NO₂) and Nitrate (N-NO₃), and promoting denitrification by converting N-NO₂ to nitrogen (N₂) in the landfill leachate treatment, promoted the pH control, increased sludge activity and effluent yield, shortened phase length adaptation under alternating aerobic-anoxic conditions. pRho-NA increased the nitration and denitrifying rate in the aerobic and anaerobic stage in the system by increasing Cyt cd1 and Cyt c expression in the activated sludge. Nitrogen removal by nitrification and denitrification was positively correlated to the concentration of Nirs and AMO expression. Treatment with pRho-NA promoted pollutant removal efficiency of membrane bioreactor, nanofiltration and reverse osmosis membrane processes in landfill leachate. In conclusion, data suggest that pRho-NA-MNR facilitates the formation of granular sludge and enhances comparable removal of nitrogen and organic compounds, indicating the practice of this process should be considered in landfill leachate treatment system.

Interactions among low-molecular-weight organics, heavy metals, and Fe(III) during coagulation of landfill leachate nanofiltration concentrate

The generation of landfill leachate nanofiltration concentrate (LLNC) has been a dilemma for leachate treatment plants because it contains large amounts of refractory organics with low molecular weight (LMWO), as well as heavy metals (HMs), and is difficult to handle. The coagulation removal of LMWOs is a significant challenge, as is the removal of HMs bonded to LMWOs. In this study, coagulation through the dosing of FeCl₃ was used to remove LMWOs and HMs from LLNC. The results interestingly demonstrated that the removal rates of dissolved organic carbon (DOC), Cr, Ni, and As reached up to 84.1% ± 3.9%, 91.0 ± 1.1%, 73.1 ± 2.2%, and 96.9 ± 1.5%, respectively. The partition of LMWO components, as well as the interactions among the LMWOs, HMs, and Fe(III) were investigated to determine the mechanism behind the LMWO and HM removal. LMWOs with a high degree of humification, including humic and fulvic acid-like components, were preferentially removed through aggregation and electrostatic attraction originating from the specialistic adsorption of Fe₂(OH)₂⁴⁺ and Fe₃(OH)₄⁵⁺. In addition to being removed, a portion of these two components was dissociated into aromatic protein I, aromatic protein II, and soluble microbial by-product-like materials due to an acid effect and the formation of inner-sphere complexes. A redundancy analysis revealed that As, Cr, and Ni are mainly removed through the electrostatic attraction of Fe(III), bonding to humic substances and hydrophilic organics, respectively. The outcomes provide a new understanding on the coagulation removal of LMWOs and HMs.

Recent advances in municipal landfill leachate: A review focusing on its characteristics, treatment, and toxicity assessment

Nowadays, sanitary landfilling is the most common approach to eliminate municipal solid waste, but a major drawback is the generation of heavily polluted leachates. These leachates must be appropriately treated before being discharged into the environment. Generally, the leachate characteristics such as COD, BOD/COD ratio, and landfill age are necessary determinants for selection of suitable treatment technologies. Rapid, sensitive and cost-effective bioassays are required to evaluate the toxicity of leachate before and after the treatment. This review summarizes extensive studies on leachate treatment methods and leachate toxicity assessment. It is found that individual biological or physical-chemical treatment is unable to meet strict effluent guidelines, whereas a combination of biological and physical-chemical treatments can achieve satisfactory removal efficiencies of both COD and ammonia nitrogen. In order to assess the toxic effects of leachate on different trophic organisms, we need to develop an appropriate matrix of bioassays based on their sensitivity to various toxicants and a multispecies approach using organisms representing different trophic levels. In this regard, a reduction in toxicity of the treated leachate will contribute to assessing the effectiveness of a specific remediation strategy.

Effective removal by coagulation of contaminants in concentrated leachate from municipal solid waste incineration power plants

Municipal solid waste (MSW) incineration is widely used in China. Concentrated leachate, containing high concentrations of pollutants, is an important type of secondary pollution produced in MSW incineration power plants and requires proper treatment. In this study, various coagulants were used to treat concentrated leachate from a nanofiltration (NF) membrane that treated leachate from an MSW incineration plant. The optimal coagulation condition was determined in this study. Under the optimal condition, removals of chemical oxygen demand, light absorbing substances (at 254 nm), total nitrogen, color and turbidity were 68.42%, 69.01%, 44.14%, 92.31% and 87.44%, respectively. Much of the refractory organic matter with relatively high molecular weight, aromaticity and humification degree was removed, and effluent had a lower molecular weight than raw NF concentrated leachate. Study also found that some parts of high molecular weight compounds from NF CL were removed by coagulation process, but the change of distribution of molecular weight was not outstanding. The NF concentrated leachate, both before and after coagulation, contained a large amount of chloride. Hence, a follow-up study should be conducted to find an effective additional processing that can remove organic matter using the high concentration of chloride in the NF concentrated leachate coagulation effluent. This study provides a theoretical basis for the treatment of concentrated leachate from MSW incineration power plants.

Physico-chemical processes

The review scans research articles published in 2018 on physico-chemical processes for water and wastewater treatment. The paper includes eight sections, that is, membrane technology, granular filtration, flotation, adsorption, coagulation/flocculation, capacitive deionization, ion exchange, and oxidation. The membrane technology section further divides into six parts, including microfiltration, ultrafiltration, nanofiltration, reverse osmosis/forward osmosis, and membrane distillation. PRACTITIONER POINTS: Totally 266 articles on water and wastewater treatment have been scanned; The review is sectioned into 8 major parts;  Membrane technology has drawn the widest attention from the research community.

Treatments for color removal from wastewater: State of the art

It is evident from many recent papers that release of colored wastewater into the environment is source of pollution and this is a problem that particularly affect textile, dyeing and food industries. The review: (i) presents an analysis of various mechanisms involved in the different processes for color removal; (ii) describes conveniences and disadvantages that may exist in adopting one type of treatment in spite of another; (iii) reports the results of approximately 180 experimental tests. Both examples of treatments already widely applied to the real scale and still in the experimental phase are reported. This work focuses on different types of chemical/physical, chemical, electrochemical and biological processes applied in the field of color removal from industrial wastewater. Common chemical/physical treatments such as coagulation/flocculation, adsorption and membrane filtration as well as chemical-type processes are discussed, both those that exploit the traditional oxidizing chemical agents such as Ozone, H₂O₂ and reactive based on chlorine and those based on the principle of advanced chemical oxidation. In particular, both Hydroxyl radical based Advanced Oxidation Processes (AOPs) and Sulfate radical based AOPs are reported. The most commonly used Electrochemical processes for the removal of color are also presented as well as biological treatments. Based on more than 200 papers, this review provides important information on the use, effectiveness, advantages and downsides of the various treatments aimed at removing the color from the wastewater with a look at the technologies still under development.

Improved landfill leachate quality using ozone, UV solar radiation, hydrogen peroxide, persulfate and adsorption processes

Advanced oxidation processes based on ozonation, UV solar radiation, hydrogen peroxide, and persulfate were tested for the complete treatment of a specific landfill leachate. As a post-treatment of the advanced oxidation process, an additional adsorption process was carried out using a natural zeolite. Application of the UV_solar/O₃/H₂O₂ process required 140 min of irradiation and the consumption of 0.67 g/L H₂O₂ to eliminate 56% and 17% of colour and chemical oxygen demand (COD), respectively. When adding persulfate to the system (UV_solar/O₃/H₂O₂/S₂O₈^-2), colour and COD were reduced by 29% and 77%, respectively, with a 0.2 g/L concentration of S₂O₈^-2 requiring 250 min of irradiation time. In an experimental run with landfill leachate, adsorption post-treatment with a natural zeolite resulted in 36%, 99%, and 18% total reductions in COD, ammonium, and chloride, respectively. In another experimental run, adsorption with a zeolite was used as a pre-treatment for the advanced oxidation process (UV_solar/O₃/H₂O₂ and UV_solar/O₃/H₂O₂/S₂O₈^-2). The results were similar to those for adsorption post-treatment, with 30%, 90%, and 20% total reductions in COD, ammonium, and chloride, respectively. Despite improvements, some measured parameters of treated landfill leachate still exceeded Chilean regulations for water quality. Furthermore, Lactuca sativa seeds did not germinate after irrigation with 100% treated landfill leachate or dilutions above 3%. Finally, EC₅₀ values were enhanced during treatment, going from 0.002% for raw landfill leachate to 1.179% after the adsorption process.

Sequential coagulation/flocculation and microwave-persulfate processes for landfill leachate treatment: Assessment of bio-toxicity, effect of pretreatment and cost-analysis

The possibility of landfill leachate treatment in a coupled microwave-persulfate (MW-PS) system with and without pretreatment, i.e. coagulation-flocculation (C-F) was investigated. The C-F pretreatment with alum and FeCl₃ has reduced the turbidity from 90 NTU to 43 NTU and 10 NTU, respectively, at the optimized coagulant dosage. Moreover, 73% COD and 86% color removal was observed in C-F pretreatment with FeCl₃. The application of MW-PS system (at 10 g/L of PS dosage) for pretreated leachate (FeCl₃ dosage 1 g/L and pH 5.5) has produced a final COD removal of 89%. Similarly, alum pretreatment (dosage 1.6 g/L, pH 8.2) coupled with MW-PS system has achieved a total COD removal of 62%. In MW-PS system, the ratio of initial PS dosage to initial COD ratio has shown significant effect on leachate treatment. However, slightly lesser ammonia removal was observed in MW-PS (93%) compared to MW alone (97%) owing to reduction in pH of the system. The comparison of bio-toxicity (i.e. inhibition to aliivibrio fischeri) of treated samples from MW-PS and MW alone after pretreatment, i.e. 12.1 mg/L and 6.8 mg/L of equivalent ZnSO₄ toxicity, indicated that MW-PS treated sample were found to be more toxic than MW alone treatment and raw leachate (7.6 mg/L and 7.2 mg/L of equivalent ZnSO₄ toxicity, respectively) due to sulfate ion. This indicates that C-F followed by MW alone would be an ideal option for leachate treatment. The cost and energy estimation of MW and MW coupled systems well supported the above findings.

Potential Use of Dimocarpus longan Seeds as a Flocculant in Landfill Leachate Treatment

Landfill leachate is a highly polluted and generated from water infiltration through solid waste produced domestically and industrially. In this study, a coagulation–flocculation process using a combination of Polyaluminium chloride (PACl) as a coagulant and Dimocarpus longan seed powder (LSP) as coagulant aid was used in treating landfill leachate. LSP has been tested as the main coagulant and as coagulant aid with PACl. As the main coagulant, the optimum dosage and pH for PACl were 5 g/L and 6, respectively, with removal efficiencies of 67.44%, 99.47%, and 98% for COD, SS, and color, respectively. For LSP as the main coagulant, results show that LSP is not effective where the removal efficiencies obtained for COD, SS, and color were 39.40%, 22.20%, and 28.30%, respectively, with the optimum dosage of 2 g/L and pH 4. The maximum removal efficiencies of COD, SS, and color were 69.19%, 99.50%, and 98.80%, respectively, when LSP was used as coagulant aid with PACl. Results show that using LSP as coagulant aid was found to be more effective in the removal of COD, SS, and color with less PACl dosage. The PACl dosage was decreased from 5 to 2.75 g/L when LSP was used as a coagulant aid. Cost estimation for using PACl alone and using LSP as the coagulant aid showed a reduction in the cost of approximately 40% of the cost of using PACl alone. Overall, this study confirmed the efficiency of LSP to be used as a natural coagulant aid in leachate treatment.