Application of UV-rays in removal of polycyclic aromatic hydrocarbons from treated wastewater

Combining sequential extraction and 3D fluorescence to investigate the behavior of antibiotic and polycyclic aromatic hydrocarbons during solar drying of sewage sludge

Solar drying and liming are commonly used for sludge treatment, but little is known about their efficiency on antibiotics and Polycyclic Aromatic Hydrocarbons (PAHs) removal. This study aimed to investigate the removal of antibiotics and PAHs during solar drying of Limed Sludge (LS) and Non-Limed Sludge (NLS). Thus, organic matter fractionation and 3D fluorescence were used to assess the accessibility and the complexity of organic matter. 2 experiments have been conducted using LS and NLS for 45 days of drying in a pilot scale tunnel. Physicochemical results indicated significant decrease of water content (90%) for both sludge samples within 15 days of drying. For both treatments, the removal of total organic carbon and total nitrogen was low and similar for both treatments. Through this study, it has been confirmed that liming and drying contributed to a strong modification of the organic matter quality with an increase of its accessibility. On the other hand, drying alone increased the less accessible compartments, while the presence of lime affected the interconnexion between the organic matter pools. 3D fluorescence confirmed the obtained results and indicated that LS leads to obtaining more simple molecules in the most accessible compartments, while NLS leads to obtaining more complex molecules in the less accessible compartments. In addition, solar radiations and leaching may contribute to the significant removal (p < 0.01) of roxithromycin, benzo(a)anthracene, chrysene, benzo[k]fluoranthene, benzo[a]pyrene, and benzo(g, h, i) perylene in the presence of lime. Furthermore, the evolution of organic matter pools in terms of accessibility and complexity may drive the bioavailability of these pollutants, leading to their significant removal.

Biosorption of LMW PAHs on activated sludge aerobic granules under varying BOD loading rate conditions

Polycyclic aromatic hydrocarbons belong to the main priority substances for the aquatic environment. One of the emission sources of these compounds to environment is wastewater discharged from conventional wastewater treatment systems, which are not designed to cope with this type of pollution. Thus, due to the widely discussed properties of aerobic granular activated sludge in the literature - a conducted study has proven its ability to remove LMW PAHs (naphthalene (Nap), acenaphthylene (Acy), acenaphthene (Ace), fluorene (Flu), phenanthrene (Phe) and anthracene (Ant)) from wastewater by biosorption process at varying loadings of organic compounds expressed as BOD (kg/kg·d) on the activated sludge mass. The maximum biosorption of Nap was 605 µg/kg_d.m., Acy equals to 134 µg/kg_d.m., Ace equals to 355 µg/kg_d.m. Flu equals to 104 µg/kg_d.m. Phe equal to 204 µg/kg_d.m. and Ant equal to 173 µg/kg_d.m. The study showed that the BOD loading rate is one of the factors affecting the biosorption process of LMW PAHs. However, as the amount of adsorbed LMW PAHs increased, the condition of aerobic granular activated sludge deteriorated, which was evidenced by gradual increase in the values of technological parameters of activated sludge (SVI, HRT, SRT) and a smaller increase in activated sludge dry mass.

Review on polycyclic aromatic hydrocarbons (PAHs) migration from wastewater

Rapidly increasing global population and increased civilization has increased burden on potable water resources and results in larger volumes of wastewater. Physical wastewater management techniques has advanced for domestic usage and commercial effluent new conceptions about imminent wastewater treatment have been acclaimed for highly carcinogenic polycyclic aromatic hydrocarbon (PAH) compounds. The present review study emphasis on the assessment of several accessible PAHs treatment methods used in wastewater management. The elementary principles, contextual remediation mechanisms and recent development in PAHs removal practices have also been precisely explained. The comprehensive information regarding sources, dispersal, classification, physicochemical properties, PAHs toxicity for humans and aquatics life, conventional treatment procedures, and advanced oxidation processes specified can assist us to identify the PAHs problem and their intensity. The performance evaluation of different removal techniques are discussed in details and found that highest PAHs' reduction for 5-or 6-ring (99%,) while 3-ring (79% reduction) with oxidant dose of 1.64 mL/L using titanium catalyst. In case of MWTPs, with secondary techniques, the average removal efficiency found in the range of 81.1-92.9% while for AOPs are 32-99.3%. Here, overall yield through AOPs most suitable if process used with some catalyst enhanced the yield as well and suitable for high ring as well as low ring PAHs. Among various processes, advanced oxidation and catalytic oxidation processes are the most valuable and promising techniques for PAHs removal. Based on the given evidences, the AOPs coupled with catalysts have been decided as the most competent design for wastewater PAHs treatment.

Photolysis of a mixture of anthracene and benzo[a]pyrene at ultra-trace levels in natural water with disinfection purposes

The photodegradation of anthracene (AN) and benzo[a]pyrene (BaP), two priority polycyclic aromatic hydrocarbons (PAHs), was examined at ultra-trace levels in surface water to elucidate their behaviour under several irradiance values and types of radiation. The emitting flux and the spectrum of the lamps were found to develop a crucial role in AN and BaP degradation since removal efficiencies of the target contaminants higher than 99% were found after 15 min of irradiation under an ultraviolet C (UVC) irradiance of 0.63 mW/cm², corresponding to a fluence of 560.25 mJ/cm². On the other hand, although ultraviolet A (UVA) lamps exhibited a higher irradiance compared to that of UVC lamps, they were not efficient for degrading the target PAHs. The removal kinetic studies corroborated these findings, being the AN elimination rate in surface water higher than that in deionized water at optimal operating conditions. Disinfection potential was also measured. A rapid microbial load inactivation, in terms of total coliforms naturally contained in the water matrix studied, was evidenced within 15 min of treatment for the fluence referred. However, after 24 hr in the dark, a regrowth was observed. Additionally, photolysis products more toxic than the parent compounds were found, which were not removed even by extending the treatment time. In this regard, it can be concluded that the individual action of UVC light for removing AN and BaP with disinfection purposes is not an efficient treatment; therefore, the use of radiation in combination with other kinds of treatments is required.

Profile of polycyclic aromatic hydrocarbons in digested sewage sludge

One of the methods of sludge disposal in cities is its use as an amendment in adjoining agricultural soil. Contaminants in sludge can, however, nullify the benefits. Polycyclic aromatic hydrocarbons (PAHs) are a class of persistent organic pollutants, if present, can pose health risks by virtue of their carcinogenic potential and persistence in soil. The present study deals with profile analysis of PAHs in digested sewage sludge of a megacity, Delhi. Mean concentration of the sum of 16 PAHs in the sludge from 5 sewage treatment plants (STPs) was 20.67 ± 4.14 mg/kg, dry weight (dw). Carcinogenic PAHs represented ∼47% of the total PAHs. Benzo[g,h,i]perylene recorded the highest mean concentration followed by dibenzo[a,h]anthracene. Low molecular weight PAHs and high molecular weight PAHs contributed 19% and 81% to total PAHs content respectively. Principal component analysis identified the major sources of PAHs in sludge as coal and natural gas combustion. Wood combustion, oil and oil derivatives are the other identified sources. The observed PAH levels in sludge from selected STPs of Delhi were found to violate the limit values proposed by the European Union and the US legislation for application in agriculture.

Comprehensive review of polycyclic aromatic hydrocarbons in water sources, their effects and treatments

Polycyclic aromatic hydrocarbons (PAHs) are principally derived from the incomplete combustion of fossil fuels. This study investigated the occurrence of PAHs in aquatic environments around the world, their effects on the environment and humans, and methods for their removal. Polycyclic aromatic hydrocarbons have a great negative impact on the humans and environment, and can even cause cancer in humans. Use of good methods and equipment are essential to monitoring PAHs, and GC/MS and HPLC are usually used for their analysis in aqueous solutions. In aquatic environments, the PAHs concentrations range widely from 0.03 ng/L (seawater; Southeastern Japan Sea, Japan) to 8,310,000 ng/L (Domestic Wastewater Treatment Plant, Siloam, South Africa). Moreover, bioaccumulation of ∑16PAHs in fish has been reported to range from 11.2 ng/L (Cynoscion guatucupa, South Africa) to 4207.5 ng/L (Saurida undosquamis, Egypt). Several biological, physical and chemical and biological techniques have been reported to treat water contaminated by PAHs, but adsorption and combined treatment methods have shown better removal performance, with some methods removing up to 99.99% of PAHs.

Evaluation of the UV/H2O2 system for treating natural water with a mixture of anthracene and benzo[a]pyrene at ultra-trace levels

The presence of polycyclic aromatic hydrocarbons, such as anthracene (AN) and benzo[a]pyrene (BaP), in water has become a problem of great concern due to the detrimental health effects caused to humans and living beings. In this work, the efficiency of the UV/H₂O₂ system for degrading the target compounds at ultra-trace levels in surface water has been evaluated. For this purpose, a previous optimization step using a face-centered central composite experimental design has been conducted, considering the effect of the UV-C irradiance and the initial concentration of H₂O₂. It was evidenced that under optimal operating conditions (11 mg L^-1 H₂O₂ and 0.63 mW cm^-2 irradiance), AN and BaP removal percentages were higher than 99.8%. Additionally, 69.3% of the organic matter, in terms of total organic carbon, was mineralized without the production of transformation by-products more harmful than the parent compounds. These findings demonstrate the oxidation capacity of the examined system in a natural matrix for degrading micropollutants that cannot be converted through conventional treatment processes. Consequently, new horizons are opened for the effective use of the UV/H₂O₂ system for drinking water production, providing the accomplishment of other regulated parameters related to water quality.

Process simulation and dynamic control for marine oily wastewater treatment using UV irradiation

UV irradiation and advanced oxidation processes have been recently regarded as promising solutions in removing polycyclic aromatic hydrocarbons (PAHs) from marine oily wastewater. However, such treatment methods are generally not sufficiently understood in terms of reaction mechanisms, process simulation and process control. These deficiencies can drastically hinder their application in shipping and offshore petroleum industries which produce bilge/ballast water and produced water as the main streams of marine oily wastewater. In this study, the factorial design of experiment was carried out to investigate the degradation mechanism of a typical PAH, namely naphthalene, under UV irradiation in seawater. Based on the experimental results, a three-layer feed-forward artificial neural network simulation model was developed to simulate the treatment process and to forecast the removal performance. A simulation-based dynamic mixed integer nonlinear programming (SDMINP) approach was then proposed to intelligently control the treatment process by integrating the developed simulation model, genetic algorithm and multi-stage programming. The applicability and effectiveness of the developed approach were further tested though a case study. The experimental results showed that the influences of fluence rate and temperature on the removal of naphthalene were greater than those of salinity and initial concentration. The developed simulation model could well predict the UV-induced removal process under varying conditions. The case study suggested that the SDMINP approach, with the aid of the multi-stage control strategy, was able to significantly reduce treatment cost when comparing to the traditional single-stage process optimization. The developed approach and its concept/framework have high potential of applicability in other environmental fields where a treatment process is involved and experimentation and modeling are used for process simulation and control.

Naphthalene degradation in seawater by UV irradiation: the effects of fluence rate, salinity, temperature and initial concentration

A large amount of oil pollution at sea is produced by the operational discharge of oily wastewater. The removal of polycyclic aromatic hydrocarbons (PAHs) from such sources using UV irradiation has become attractive, yet the photolysis mechanism in seawater has remained unclear. This study examines the photodegradation kinetics of naphthalene in natural seawater through a full factorial design of experiments (DOE). The effects of fluence rate, salinity, temperature and initial concentration are investigated. Results show that fluence rate, temperature and the interaction between temperature and initial concentration are the most influential factors. An increase in fluence rate can linearly promote the photodegradation process. Salinity increasingly impedes the removal of naphthalene because of the existence of free-radical scavengers and photon competitors. The results will help understand the photolysis mechanism of PAHs and develop more effective methods for treating oily seawater generated from offshore industries.

Removal of polycyclic aromatic hydrocarbons in aqueous environment by chemical treatments: a review

Due to their carcinogenic, mutagenic and teratogenic potential, the removal of polycyclic aromatic hydrocarbons (PAHs) from aqueous environment using physical, biological and chemical processes has been studied by several researchers. This paper reviews the current state of knowledge concerning PAHs including their physico-chemical properties, input sources, occurrence, adverse effects and conventional and alternative chemical processes applied for their removal from water. The mechanisms and reactions involved in each treatment method are reported, and the effects of various variables on the PAH degradation rate as well as the extent of degradation are also discussed. Extensive literature analysis has shown that an effective way to perform the conversion and mineralization of this type of substances is the application of advanced oxidation processes (AOPs). Furthermore, combined processes, particularly AOPs coupled with biological treatments, seem to be one of the best solutions for the treatment of effluents containing PAHs.