Journal of Environmental Engineering

A floating breakwater can significantly reduce the wave invasion of marine structures and provide a safe construction environment and service environment for wave attenuation protection for marine structures. With the development and utilization of marine resources, the application of floating breakwaters in engineering is becoming more and more important; research on integrated systems of a floating breakwater and wave-energy converter (WEC) is also valuable. However, existing research has not yet systematically improved the influencing factors of wave attenuation performance of floating breakwaters and the summary of the wave attenuation mechanism; there are few summaries about the integration of floating breakwaters and wave-energy converters. Therefore, the research progress on the wave attenuation performance and wave-energy integration of floating breakwaters is reviewed and summarized. Firstly, according to the structural shape, floating breakwaters are divided into three types: box type, floating cylinder type, and other types. Secondly, the wave attenuation performance of three types of breakwaters and the research progress of floating breakwater-WEC integrated devices are discussed and reviewed. Finally, the problems to be solved in the study of various breakwaters and the key directions for future research are summarized. This review is helpful to deepen the cognition and understanding of wave attenuation performance of floating breakwater and floating breakwater-WEC integration devices, which can provide reference for the optimization research and engineering application of floating breakwaters.

Per- and polyfluoroalkyl substances (PFAS) have been widely used in consumer products, and some inevitably end up as municipal solid waste. Significant knowledge gaps associated with the fate and release of PFAS from postconsumer products in solid waste management processes exist that limit our current ability to develop appropriate end-of-life management strategies for PFAS. The objectives of this paper are to summarize the current knowledge associated with the fate and release of PFAS from postconsumer products from commonly used waste management processes (including landfilling, recycling, composting, and incineration) and to use that information to identify knowledge gaps and potential exposure pathways for humans and the environment. The current results indicate that landfills are major sinks of PFAS because most PFAS-containing consumer products are landfilled, and PFAS was extensively reported in landfill leachate. More information is needed regarding the total influx of PFAS into landfills as well as landfill gas emissions. Recycling and composting also present potential exposure pathways. The reprocessing of carpet and paper packaging was reported to cause direct exposure to onsite workers through PFAS volatilization and dust emissions. Recycling can cause the circularity of PFAS in the new product and subsequent release throughout its lifespan. Composted food packaging was found to contain PFAS and could cause contamination during the land application of compost. The incineration of waste provides near-complete destruction ($\sim 99\%$) of PFAS. However, some low-temperature regions within the furnace may still result in products of incomplete combustion, such as short-chain perfluoroalkyl acids and other stable fluorinated compounds, which may be released in incinerator ash. More information is needed regarding the mechanisms of PFAS thermal destruction. Case studies of PFAS product categories indicated that carpet and cosmetics might contribute to the release of more soluble and volatile PFAS, such as perfluoroalkyl acids and fluorotelomer alcohols during landfilling in leachate and gas. The fate of specific PFAS during waste management aligns well with their physical/chemical properties, such as solubility and volatility.

Aair quality issues and respiratory diseases have become issues of particular concern since the outbreak of the COVID-19 pandemic. The indoor air quality of crowded places such as underground metro stations has received growing attention from passengers and staff, thus requiring both qualitative and quantitative assessment. However, the traditional fuzzy comprehensive evaluation is ineffective in this respect. Therefore, this paper proposed the method of optimal combination weight and improved fuzzy comprehensive evaluation to assess the air quality. First, subjective weights were calculated with the multiple-input weighted precedence chart and analytic hierarchy process; objective weights were computed using the entropy weight and exceedance multiple methods. Second, the moment estimation theory was introduced for the optimal combination of these weights. Results show that the optimal combination weighting method achieves the minimum relative deviation. Moreover, in the traditional fuzzy comprehensive evaluation, the air quality is generally classified based on the maximum membership, and the evaluation is inapplicable when the validity ($K_0$) is less than 0.5. Therefore, the concept of confidence was introduced herein for improvement. Finally, the optimal combination weight and improved fuzzy comprehensive evaluation is proved to be the most reasonable in comparison with the traditional fuzzy comprehensive evaluation and indoor air quality index. This study not only suggests a good method to assess the indoor air quality of metro stations but also provides references for decision makers.

Feed water pretreatment commonly is required for low-pressure membrane technologies employed in drinking water treatment applications to reduce membrane fouling and create stable operating conditions. Comparatively few studies have investigated coagulation–flocculation–dissolved air flotation (CF-DAF) pretreatment for drinking water applications, and none have compared CF-DAF, coagulation–flocculation–sedimentation (CF-S), and in-line coagulation (CF-IN) pretreatments using the same water. This study compared these three pretreatments for the filtration of a high dissolved organic carbon (DOC), high hydrophobic (HPO) surface water using a hydrophilic polyvinylidene fluoride (h-PVDF) ultrafiltration (UF) fiber. Multiday filtration tests were carried out using an automated bench-scale testing system operated in an outside-in configuration. CF-S and CF-DAF were found to be equally effective at mitigating membrane fouling, although CF-DAF pretreated water had a lower residual DOC and the greatest removal of ${\mathrm{UV}}_{254}$ absorbent organics. Compared with CF-DAF and CF-S, CF-IN pretreatment resulted in higher levels of total and irreversible fouling regardless of the applied coagulant dose. For all the pretreatments studied, irreversible membrane fouling was found to be strongly dependent on both the hydrophobicity of the feed water [in terms of specific UV absorbance (SUVA)] and the concentration of the 5–10-kDa DOC fraction, suggesting that the HPO humic organics were the principal foulant for this membrane–water combination. CF-IN pretreatment performance also was strongly impacted by the feed water zeta potential, suggesting that the characteristics of the formed flocculant particles are critical to the fouling behavior of the hybrid CF-IN-UF system.

The influence of aeration diffuser system design on electricity usage, effluent water quality, and life-cycle cost in biological wastewater treatment was investigated. A plant-wide model was implemented, and simulations were carried out with different process configurations and aeration systems. Model-aided design of new aeration diffuser systems could significantly decrease electricity usage and life-cycle cost while at the same time avoiding negative effects on the treatment performance. The optimum distribution of diffuser systems in tanks in series was found to be influenced by process configuration, volumetric loading rate, temperature, and the internal recirculation flow rate. Compared with a conventional design approach, increasing the number of diffusers, up to a critical point, led to higher energy efficiency and lower life-cycle cost. This was despite an increasing limitation of the minimum airflow rate, leading to dissolved oxygen levels significantly exceeding control targets. Aeration systems optimized by simulations were found to, independently of process configuration, exhibit 20% lower electricity usage and 16%–18% lower life-cycle costs compared with systems designed based on a more conventional approach typically applied in practice.

Abstract

Even though chlorination is a widely used disinfection technique, it has several disadvantages, such as formation of chlorates during prolonged storage, requirement for skilled supervision during operations, risk of leakage, and related accidents during transport and storage. Electrochlorination (EC) is one of the novel technologies generating in-situ chlorine, thereby limiting most of the disadvantages of conventional chlorination treatment for water disinfection. The correlation between the various influencing parameters for EC, which is important for achieving the optimal conditions for in-situ chlorine generation, is still unclear. The major objective of the present study is to provide a detailed correlation analysis between the parameters influencing the EC process based on the extensive experimental data generated from the developed lab-scale setup for electrochlorination using graphite electrodes and titanium electrodes separately. The present study also examined the rate of loss of the electrode materials to check the longevity of electrodes. The experimental results generated were used for comparative analysis of the EC process for maximum in-situ chlorine generation. A detailed principal component analysis (PCA) was performed for the data generated during experimentation to understand the correlation between the influencing parameters for optimum in-situ chlorine generation. The optimum conditions for maximum in-situ chlorine generation obtained from the experiments were 10 V electric voltage, 60 min electrolysis time, 4 cm distance between electrodes, and $3.5\mathrm{g}/\mathrm{L}$ electrolyte concentration, with maximum chlorine generation of $15.95\mathrm{mg}/\mathrm{L}$ obtained for titanium electrodes using NaCl electrolytes for the developed lab setup. The results of PCA established the correlation between the influencing parameters and concluded that the most significant parameter influencing chlorine generation was electrolyte concentration and electrochlorination time, and electric potential was moderately influential, whereas distance between electrodes was least influential. The rate of material loss was $15.3\mathrm{mg}/\min$ for titanium electrodes and $24\mathrm{mg}/\min$ for graphite electrodes, indicating titanium electrodes are more durable than graphite electrodes during a prolonged EC process. The applicability of the generated chlorine stock solution was also examined for drinking water sample disinfection and found to be effective.

Practical Applications

Sustainable Development Goal 6 discusses the need for the provision of pathogen-free drinking water to each and every region of countries. Remote and rural areas that are deprived of disinfected drinking water can benefit from low-cost and easy maintenance of electrochlorination system. An electrochlorination system limits the disadvantages of conventional chlorination. The chlorine generated through an electrochlorination system was found effective in water disinfection. For optimized working of a electrochlorination unit, the influencing parameters for in-situ chlorine generation and their interdependence should be understood. The present study discusses the correlation between these influencing parameters for optimum in-situ chlorine generation during the electrochlorination process. The study will be helpful in understanding the optimum conditions for chlorine generation using the electrochlorination process for various electrodes and electrolyte combinations.

Abstract

Colloidal fouling on a brackish water reverse osmosis (BWRO) membrane was simulated by a lab-scale plate-and-frame module in the presence and absence of air micro-nano bubbles (AMNBs). Synthetic feed water samples with the same physical and chemical properties, but various concentrations of colloidal silica (50, 100, 200, and $300\mathrm{mg}/\mathrm{L}$), were used for experiments. The results illustrate that colloidal fouling caused a severe decrease in permeate flux (24%–56%) and salt rejection (1.25% to 4.18%) in the absence of AMNBs. This reduction in membrane performance was attributed to the high hydraulic resistance and the cake-enhanced osmotic pressure (CEOP) of a fouled gel layer that were intensified with increase in the colloidal concentration. On the other hand, presence of AMNBs decreased the deposition rate of colloidal particles significantly and increased the porosity of fouling layer. Thus, an improvement in the membrane permeate flux (21%–40%) and salt rejection (1.2%–2.6%) were seen in the different concentrations of colloidal particles. The SEM images also confirmed the formation of loose fouling layers which were easily removed from the membrane surface by a clean-in-place (CIP) process. This research introduces AMNBs technology as an effective in-line method to control the adverse effects of colloidal fouling in reverse osmosis (RO) systems.

Practical Applications

RO is a well-known process in the field of water and wastewater treatment. RO membranes have the ability to remove all pollutants, undesirable ions, and micro-organisms from the liquid phase that leads to their accumulation on the membrane surface. This phenomenon is called membrane fouling. Colloidal particles are one of the major fouling agents that are found in all water resources which has a direct adverse effect on the efficiency of RO systems. Various technics (based on the filtration process) are used to remove the colloidal particles in pretreatment stage of RO systems. In this research, the micro-nano bubbles (MNBs) technology was used to control the colloidal fouling in RO process. The results showed the presence of MNBs in feed water of RO could decrease the fouling of the membrane surface and improve the quality and quantity of produced water. Also, the energy consumption of this technology can be restored easily by the improvement in the quantity of the produced water. Thus, the MNBs technology could control the colloidal fouling of RO membranes with no adverse environmental effects.

To explore the treatment performance of a biological aerated filter (BAF) for exogenous pollutants in low-temperature landscape water, a laboratory and pilot system were constructed in urban rivers in the alpine region of northern China, and the key influencing factors such as pH, hydraulic load, air–water ratio, and temperature were studied. The results showed that the operation parameters of the BAF need to be controlled to achieve good nitrogen removal effect. Based on the hazard identification of ammonia nitrogen in landscape water effluent, the critical control points of the BAF process were determined, and corresponding control strategies were formulated. By adjusting operation parameters and other measures, hazards can be identified and overcome with reasonable accuracy. Therefore, the effluent ammonia nitrogen and concentration can be kept within the limits of the law. Double-layer aerated organisms can operate stably at normal temperature, in a transition period, and at low temperature period. The average removal rate of ammonia nitrogen in the three periods can reach 83.29%, 68.53%, and 56.55%, respectively, and the effluent quality can meet the requirements of landscape water during operation.

A pipe-in-pipe (PIP) system is an important engineering structure in the petroleum industry. Under the excitation of ocean fluids, the PIP system produces vortex-induced vibration (VIV), which can affect the oil recovery efficiency of large offshore drilling platforms and cause various engineering accidents. In this work, a fluid–structure coupled vibration model of the PIP system excited by a vortex-induced force is established based on an Euler–Bernoulli double-beam model and a wake oscillator model. The harmonic balance method is used to solve the coupled vibration model. Influences of the connection layer stiffness, tension, mass ratio, phase angle, and frequency ratio on displacements of the PIP system are studied. It is shown from numerical results that displacements of inner and outer pipes increase with the slenderness ratio. Displacements of inner and outer pipes decrease with the connection layer stiffness, but the frequency ratio and traveling wave velocity increase with it. In addition, the frequency ratio of the PIP system exhibits a multivalued characteristic, which is the characteristic of a nonlinear system. A small stiffness of the connection layer can induce unstable vibrations. Displacements of inner and outer pipes decrease with the tension, but the frequency ratio increases with it. The collision time of the inner and outer pipes gradually increases with the tension. The pipe displacements decrease with the mass ratio.

The present case study evaluates the treatment efficiency (R%) of vertical flow constructed wetlands (VFCW) with different design considerations for the efficient treatment of domestic wastewater. Four modified VFCW’s were constructed at the pilot scale to study their overall performance with domestic wastewater as the source. Since traditional VFCWs are responsible for increases in nitrates, this study also focuses on the removal of nitrates. These different VFCW’s were termed two stage (TS), two stage-charcoal (TSC), mixed flow (MF), and double stage (DS) VFCWs. The inlet chemical oxygen demand (COD), ${\mathrm{NH}}_3\text{-}\mathrm{N}$, ${\mathrm{NO}}_3\text{-}\mathrm{N}$, ${\mathrm{NO}}_2\text{-}\mathrm{N}$, TN, total organic carbon (TOC), and ortho-P ranged from 300–900, 30–50, 25–50, 30–40, 15–50, 30–120 and $10–15\mathrm{mg}/\mathrm{L}$, respectively, with a pH around 7 and high total coliforms (T-C). The MFCW and DS-VFCW were found to be the most effective in treating almost all the parameters with the highest R% ($>90$). The TS-VFCW showed better treatment of carbon rather than nitrogen compounds (like ${\mathrm{NO}}_3\text{-}\mathrm{N}$). The TSC-VFCW showed better treatment when the system was new, as decreases in R% were observed over time. Statistical analysis with one and paired-sample T-tests were conducted to support similar findings with significance values $<0.05$. The findings from both tests showed that DS-VFCW was the better system compared to the other two for COD, TOC, ${\mathrm{NO}}_2\text{-}\mathrm{N}$, and ortho-P showing $\mathrm{p}=0.000$; whereas, MFCW was the better system to treat pollutants like TN and ${\mathrm{NO}}_3\text{-}\mathrm{N}$. The MFCW and DS-VFCW were both shown to effectively treat ${\mathrm{NH}}_3\text{-}\mathrm{N}$ and T-C.

Nonthermal plasma (NTP) is a promising technology for the decomposition of chlorobenzene (CB), but many conditions will affect the performance of NTP. The effects of gas temperature, relative humidity, oxygen content, sulfur dioxide (${\mathrm{SO}}_2$), and nitric oxide (NO) on the removal of CB in dielectric barrier discharge (DBD) were studied in this study. The results showed that the gas temperature with the highest CB removal rate was 50°C at 14 kV and 200°C at 18 kV. With the addition of water vapor, the removal efficiency of CB first increased and then decreased, reaching the highest (52.94%) when the relative humidity was 20% at 14 kV. The presence of oxygen inhibited the degradation of CB. At 14 kV, when the oxygen concentration increased from 0% to 25%, the degradation efficiency of CB decreased from 71.93% to 32.54%. In the discharge process, the addition of ${\mathrm{SO}}_2$ promoted the removal of CB, while NO inhibited under the same conditions. The addition of ${\mathrm{SO}}_2$ and NO did not change the specific energy density. For ozone (${\mathrm{O}}_3$), the addition of water molecules, ${\mathrm{SO}}_2$, and NO inhibited the formation of ${\mathrm{O}}_3$. It is of great significance to study the influence of relevant gas conditions on the degradation of CB by NTP technology, so as to provide a reference for industrial application.

Abstract

Effective methods for the recovery and reuse of phosphorus are needed for sustainable agriculture. In this study, magnesium-amended corn cob chars prepared with brucite and sea bittern and calcium silicate hydrate (CSH) synthesized with hydrated lime and rice husk ash were tested for phosphorus recovery from a model animal wastewater at pH 8.0. After phosphorus uptake from the model wastewater, the two Mg-chars had a phosphorus concentration of $182–198\mathrm{mg}\mathrm{P}/\mathrm{g}$, and CSH had a phosphorus concentration of $46\mathrm{mg}\mathrm{P}/\mathrm{g}$. In continuous-flow column release studies, in which these materials were mixed with sand after phosphorus uptake, Mg-chars released over 80% of the recovered phosphorus within five pore volumes at pH 5.5, 7.0, and 8.5. Post-P-exposure CSH, on the other hand, required 335 pore volumes to release 90% of the recovered phosphorus at pH 8.5. The more rapid release at pH 5.5 and 7.0 compared to pH 8.5 for the spent Mg-chars is attributed to the greater solubility of magnesium phosphate minerals at lower pH values. When goethite or kaolinite was added to the sand columns containing spent Mg-char, the rate and extent of phosphorus release slowed significantly, especially for goethite versus kaolinite, and especially at pH 5.5. and 7.0 versus pH 8.5 for both minerals. This trend is attributed to the greater electrostatic driving force for the adsorption of phosphate to the mineral surface below the mineral point of zero charge (${\mathrm{pH}}_{\mathrm{pzc}}$).

Practical Applications

Identifying ways to conserve and reuse phosphorus are important for several reasons: global reserves of phosphorus minerals are limited, phosphorus is essential for food production, anticipated population growth will require increasingly intensive food production in the coming decades, and uncontrolled release of phosphorus to the environment causes environmental degradation. For these reasons, novel materials were prepared from agricultural wastes and other low-cost materials and used to recover phosphorus from model animal wastewater. Then, the phosphorus-loaded treatment materials were added to soil columns to understand how they would release phosphorus when applied to crops as fertilizers. After exposure to the model wastewater, treatment materials made from magnesium-amended corn cobs had concentrations of phosphorus similar to commercial fertilizers and were also effective at phosphorus release, especially at low to neutral pH. Together, the results demonstrate the promise of these treatment materials for recovering phosphorus from concentrated wastewater and subsequent use as fertilizers to meet the challenges of sustainable food production. The treatment materials also have the potential for lower environmental impacts and reduced costs compared to commercial fertilizers.

Abstract

The instability of colloidal gas aphrons (CGAs) in aquifers is one of the major obstacles influencing the remediation efficiency of CGAs-flushing. In this study, hydrophobic $\mathrm{nano}\text{-}{\mathrm{SiO}}_2$ ($\mathrm{HN}\text{-}{\mathrm{SiO}}_2$) was utilized to enhance the stability of CGAs. The batch experiments were carried out to investigate the effect of hydrogeochemical conditions on the stability of $\mathrm{HN}\text{-}{\mathrm{SiO}}_2$ stabilized CGAs in aquifers, such as ions, pH, and nitrobenzene (NB); 2-D tank experiments designed with various injection velocities and medium particle sizes were conducted to determine the factors influencing the migration of CGAs in the aquifer; and 1-D column experiments were established to evaluate the remediation efficiency of $\mathrm{HN}\text{-}{\mathrm{SiO}}_2$ stabilized CGAs flushing for NB removal. The results indicated that $\mathrm{HN}\text{-}{\mathrm{SiO}}_2$ had a favorable effect on the stability of CGAs, which enhanced the half-life of CGAs from 328 to 1,050 s. $\mathrm{HN}\text{-}{\mathrm{SiO}}_2$ particles formed a shell film on the gas-liquid interface of CGAs to slow down the gas escape and drainage velocity. The stability of CGAs decreased while $\mathrm{pH}<6$ or $\mathrm{pH}>8$, whereas this was enhanced with the addition of 0.1 wt.% NaCl. The 2-D tank experiments demonstrated that the $\mathrm{HN}\text{-}{\mathrm{SiO}}_2$ stabilized CGAs had better stability when they flowed in aquifers compared to sodium dodecyl sulfate (SDS) CGAs. The fine medium and high injection velocity facilitated CGAs forming the larger radius remediation area. The injection pressure was inversely proportional to the medium grain sizes, whereas directly proportional to the injection velocities. In addition, column experiments demonstrated the remediation efficiency of $\mathrm{HN}\text{-}{\mathrm{SiO}}_2$ stabilized CGAs (81.7%) flushing for NB removal was higher than that of SDS CGAs (61.4%) flushing. Therefore, in comparison with SDS CGAs, $\mathrm{HN}\text{-}{\mathrm{SiO}}_2$ stabilized CGAs were more efficient reagents for NB removal. CGAs-flushing technique using $\mathrm{HN}\text{-}{\mathrm{SiO}}_2$ stabilized CGAs is feasible to remedy the contaminated aquifers.

Practical Applications

The contamination caused by dense nonaqueous phase liquids in aquifers has a great threat to ecosystems and human health. Colloidal gas aphron (CGA) flushing has been proposed as an effective remediation technology for dense nonaqueous liquids contaminated aquifers. However, the instability of colloidal gas aphrons in aquifers is one of the major obstacles influencing remediation efficiency. In this work, the hydrophobic $\mathrm{nano}\text{-}{\mathrm{SiO}}_2$ was used to improve its stability. Besides, the migration of colloidal gas aphron generated with sodium dodecyl sulfate (SDS) and $\mathrm{SDS}/{\mathrm{SiO}}_2$ was investigated, and the remediation efficiency for nitrobenzene removal of $\mathrm{SDS}/{\mathrm{SiO}}_2$ colloidal gas aphrons flushing was evaluated. ${\mathrm{SiO}}_2$ had a favorable effect on the stability of colloidal gas aphrons, enhancing the half-life of colloidal gas aphrons from 328 to 1,050 s, and the enhancement effect was more evident with the increasing ${\mathrm{SiO}}_2$ concentration. The tank experiment results indicated that $\mathrm{SDS}/{\mathrm{SiO}}_2$ colloidal gas aphron had fine migration performance and wide applicability in aquifer environments. In addition, column experiments demonstrated the remediation efficiency of hydrophobic $\mathrm{nano}\text{-}{\mathrm{SiO}}_2$ stabilized colloidal gas aphrons flushing for nitrobenzene removal was higher than that of SDS colloidal gas aphrons flushing. Therefore, the colloidal gas aphron flushing technique using $\mathrm{SDS}/{\mathrm{SiO}}_2$ colloidal gas aphrons is feasible to remedy the contaminated aquifers.

Abstract

Lecythis minor is a tree commonly known as Monkey pot tree. Its fruits are composed of urn-shaped epicarps, which are bulky ligneous capsules of slow degradation. Activated carbon monoliths were prepared from this fruit epicarp (bioresidue, the source of lignocellulosic matter) by chemical activation with ${\mathrm{H}}_3{\mathrm{PO}}_4$. The activation conditions were optimized using a central composite design, considering parameters of temperature, time, and chemical ratio as variables, and iodine and methylene blue number ($IN$ and MBN), along with yield ($Y$), as responses. The best conditions for activation were 532°C ($T$), 1.5 h ($t$), and 1.5-g ${\mathrm{H}}_3{\mathrm{PO}}_4/1\text{-}\mathrm{g}$ raw matter (chemical ratio, CR), with response values of 996 mg $\mathrm{I}/1\text{-}\mathrm{g}$ activated carbon (AC) ($IN$), 361-mg $\mathrm{MB}/1\text{-}\mathrm{g}$ AC (MBN), and 42% ($Y$). Likewise, the physicochemical/surface characterization of the activated carbon Lecythis minor (ACLM) allowed establishing that it developed micro- and mesopores ($V_{micro}=0.72{\mathrm{cm}}^3/\mathrm{g}$; $V_{meso}=0.87{\mathrm{cm}}^3/\mathrm{g}$), as well as ultra-microporosity, a BET surface area of $\mathrm{2,164}{\mathrm{m}}^2/\mathrm{g}$, and a total pore volume of $1.7{\mathrm{cm}}^3/\mathrm{g}$; also, the removal percentages of the emerging contaminants diclofenac and cephalexin in water were above 96%. It is concluded that fruit epicarp of L. minor is a natural-origin resource to produce AC monoliths, with satisfactory yield, desirable surface development, and high thermal stability, capable of adsorption and removal of pharmaceutical products, and other emergent contaminants from water bodies.

Practical Applications

The development of activated carbons from agricultural residues, following processes that maximize their potential as adsorbents, has great potential for the removal of pollutants in water bodies. The above takes into account that in tropical countries there are residues that are totally wasted and that can be investigated by researchers following the methods listed in this work. The pollutants that can be adsorbed vary; for example, chemical residues and medicines that are excreted from the body or that are not properly disposed, dyes, or any other residue that, due to its dimensional characteristics, is complex to capture with other techniques for cleaning water bodies (e.g., mechanical means or filters). The solution to the removal of emerging pollutants is within everyone’s reach.

Abstract

Perfluoroalkyl and polyfluoroalkyl substances (PFAS) are a large class of ubiquitous and persistent environmental contaminants. Due to the extremely stable carbon-fluorine bonds, PFAS are difficult to destruct. Increasing research efforts are focusing on PFAS defluorination, and one of the key challenges is tracking down the breakdown products and achieving a reasonable mass balance. In this study, we demonstrate one vital but often overlooked aspect of PFAS destruction studies, using perfluorooctanesulfonic acid (PFOS) destruction with acoustic cavitation as a case. This study showed that PFOS–container interactions can significantly impact the destruction efficiency and provided an example whereby these interactions may be prevented using surface coating. A showcase of mass balance for PFAS defluorination using acoustic cavitation was also investigated by employing targeted analysis [liquid chromatography-mass spectrometry (LC-MS)] and complementary untargeted analysis (total organofluorine measurement). This study demonstrated the necessity for a thorough consideration of all aspects in PFAS destruction experiments and the necessity of early adoption of total organofluorine measurements.

Practical Applications

This case study provides a working example of mass balance challenges regarding the handling and destruction of PFAS compounds. In this study, we demonstrate that destruction efficiency decreased by over 50% due to interactions between the reactor and PFOS, as measured by recovering unreacted PFOS from the walls of the vessel with a solvent rinse. When the container interactions were addressed, destruction efficiency doubled. If these interactions are not considered, PFAS destruction efficiency may be overestimated and could lead to unexpected residual PFAS when applied in a treatment system. Not accounting for this residual PFAS could result in PFAS releases from destruction and treatment systems, presenting possible public health concerns. Furthermore, this study represents an early use of total organofluorine (TOF) measurements to validate destruction performance. This research can be used to inform the design of PFAS destruction reactors, improve destruction efficiency, and outlines an approach to reporting mass balances in PFAS destruction schemes.

During the leather tanning process, chromium (Cr) can interact with different macromolecular organics to generate mixed ligand complexes. The removal of organochromium complexes is one of the main difficulties in the treatment of tannery wastewater. In this study, a gelatin-gallic ac-id-Cr(III) (G-GA-Cr) mixed ligand complex was used to examine the effects of ultrasonic on chromium destabilization and removal from the dissolved complexes. To investigate organic destruction and chromium liberation, alkali precipitation or chelating precipitation assisted with ultrasound were conducted, respectively. The findings demonstrate that ultrasonic-assisted alkali precipitation and chelating precipitation, respectively, removed over 50% and 93% of Cr from the complexes. According to the data, ultrasonication weakened the bonds that bound macromolecular ligands together, and depolymerization took place to the point where Cr could interact directly with hydroxide ions or chelating agents. In addition, by applying ultrasonic-assisted chelating precipitation, the chromium concentration could meet the discharge standard and the amount of precipitation was also noticeably decreased.

A three-dimensional coupled hydrodynamic and water quality model (Deflt3D-WAQ) was applied to evaluate the ability of a computational simulation to reproduce seasonal water quality conditions over a seven-month period in a wastewater stabilization pond located in eastern Ontario, Canada. Trends in effluent nutrient concentrations, pH, and dissolved oxygen were visually reproduced, and root-mean square errors, in comparison with weekly observations (alkalinity, $43{\mathrm{gHCO}}_3{\mathrm{m}}^{-3}$; dissolved oxygen, $4.0{\mathrm{gm}}^{-3}$; ${\mathrm{NO}}_3$, $2.2\mathrm{gN}{\mathrm{m}}^{-3}$; ${\mathrm{PO}}_4$, $0.10\mathrm{gP}{\mathrm{m}}^{-3}$; ${\mathrm{NH}}_4$, $0.14\mathrm{gN}{\mathrm{m}}^{-3}$; pH, 0.65), were consistent with literature values. Three phytoplankton groups (green algae, diatoms, and flagellates) were also simulated. The calibrated model was extended to investigate the effects of changes in pond design on treatment efficiency, including removing the baffle, increasing the pond depth, increasing wind sheltering, and relocating the influent pipe from the pond bottom to the surface. Increasing the pond depth and wind sheltering reduced vertical mixing, sequestering nutrients near the sediments and improving effluent water quality. Removing the baffle had no impact on removal efficiency, and relocating the inlet to the surface reduced pond efficiency. Three-dimensional biogeochemical models thus provide a virtual process-based means for testing pond prototype design.