Environmental optimization of continuous flow ozonation for urban wastewater reclamation

Unlocking energy potential: Decarbonizing water reclamation plants with salinity gradient energy recovery

Climate change, together with the ecological droughts suffered by a large part of the European Union's territory, calls for joint environmental solutions. In this regard, water reclamation is a promising way to alleviate the pressure on existing water resources. However, reuse strategies are penalized by the extra energy consumed in urban wastewater treatment plants (UWWTPs), facilities mainly powered by fossil fuels. The opportunity to integrate renewable sources of energy into the energy-intensive UWWTPs holds great promise towards decarbonization of the sector. In this context, the energy harvested from a Salinity Gradient (SGE) has attracted great interest in the last decade. This work aims at the analysis of opportunity of implementing integrated processes for water reclamation and SGE recovery in the coastal EU UWWTPs. According to the selection criteria, a total of 281 potential sites located across eighteen coastal countries of the EU have been inventoried attending to the current state of the art. The water reclamation potential has been estimated at 3.7 million m3/day. As a consequence, the environmental burdens of the reclamation process could result in the reduction of 1.5·105 t CO2/year. The Mediterranean region, highly affected by hydrological drought, has proved to be a hot spot for water reclamation, with the highest number of plants inventoried in the study and a predicted potential for SGE harvesting of 60 Wh/m3 of reclaimed water. These results highlight a niche of opportunities to encourage water reclamation, avoid water bodies' degradability due to effluent discharge and the further decarbonization of reclamation processes.

Removal of Micropollutants by Ozone-Based Processes

Micropollutants and emerging substances pose a serious problem to environmental sustainability and remediation, due to their widespread use and applications in everyday life. This group of chemicals is diverse but with common toxic and harmful properties. Their concentration in the environment is often very low; however, due to their recalcitrant nature, they are persistent in air, water, and soil. From an engineering point of view, the challenge is not straightforward. It is difficult to remove these contaminants from complex mixtures of substances by conventional methods used in wastewater and drinking water treatment. Ozonation and ozone-based AOPs are accepted processes of degradation of resistant substances or at least enhancement of their biodegradability. The aim of this review paper is to present research trends aimed at solving problems in the research and application of ozone-based processes in the removal of micropollutants from wastewater, thus preventing leakage of harmful substances into surface water, soil, and groundwater and facilitating the reuse of wastewater. Priority substances, micropollutants and emerging pollutants, as well as processes and technologies for their transformation and elimination, are briefly specified. Results obtained by the authors in solving research projects that were aimed at eliminating selected micropollutants by ozonation and ozone-based AOPs are also presented. This review focuses on selected alkylphenols, petroleum substances, and organochlorine pesticides.

Mitigation of antibiotic resistance in a pilot-scale system treating wastewater from high-speed railway trains

Wastewater from high-speed railway trains represents a mobile reservoir of microorganisms with antibiotic resistance. It harbors abundant and diverse antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs). This study investigated the removal of ARB and ARGs in a pilot-scale reactor, which consisted of an anaerobic/anoxic/oxic process, anaerobic/anoxic/aerobic process, and ozone-based disinfection to treat 1 m³/day wastewater from an electric multiple unit high-speed train. Further, the high prevalence of two mobile genetic elements (intI1 and Tn916/615) and five ARGs (tetA, tetG, qnrA, qnrS, bla_NDM-1, and ermF) was investigated using quantitative PCR. Significant positive correlations between ARGs (tetA, bla_NDM-1, and qnrA) and intI1 were identified (R² of 0.94, 0.85, and 0.70, respectively, P < 0.01). Biological treatment could significantly reduce Tn916/1545 (2.57 logs reduction) and Enterococci (2.56 logs reduction of colony forming unit (CFU)/mL), but the qnrS abundance increased (1.19 logs increase). Ozonation disinfection could further significantly decrease ARGs and Enterococci in wastewater, with a reduction of 1.67-2.49 logs and 3.16 logs CFU/mL, respectively. Moreover, food-related bacteria families which may contain opportunistic or parasitic pathogens (e.g., Moraxellaceae, Carnobacteriaceae, and Ruminococcaceae) were detected frequently. Enterococci filtered in this study shows multi-antibiotic resistance. Our study highlights the significance to mitigate antibiotic resistance from wastewater generated from high-speed railway trains, as a mobile source.

Monitoring, sources, receptors, and control measures for three European Union watch list substances of emerging concern in receiving waters - A 20year systematic review

Pollution of European receiving waters with contaminants of emerging concern (CECs), such as with 17-beta-estradiol (a natural estrogenic hormone, E2), along with pharmaceutically-active compounds diclofenac (an anti-inflammatory drug, DCL) and 17-alpha-ethynylestradiol (a synthetic estrogenic hormone, EE2)) is a ubiquitous phenomenon. These three CECs were added to the EU watch list of emerging substances to be monitoring in 2013, which was updated in 2015 to comprise 10 substances/groups of substances in the field of water policy. A systematic literature review was conducted of 3952 potentially relevant articles over period 1995 to 2015 that produced a new EU-wide database consisting of 1268 publications on DCL, E2 and EE2. European surface water concentrations of DCL are typically reported below the proposed annual average environmental quality standard (AA EQS) of 100ng/l, but that exceedances frequently occur. E2 and EE2 surface water concentrations are typically below 50ng/l and 10ng/l respectively, but these values greatly exceed the proposed AA EQS values for these compounds (0.04 and 0.035ng/l respectively). However, levels of these CECs are frequently reported to be disproportionately high in EU receiving waters, particularly in effluents at control points that require urgent attention. Overall it was found that DCL and EE2 enter European aquatic environment mainly following human consumption and excretion of therapeutic drugs, and by incomplete removal from influent at urban wastewater treatment plants (WWTPs). E2 is a natural hormone excreted by humans which also experiences incomplete removal during WWTPs treatment. Current conventional analytical chemistry methods are sufficiently sensitive for the detection and quantification of DCL but not for E2 and EE2, thus alternative, ultra-trace, time-integrated monitoring techniques such as passive sampling are needed to inform water quality for these estrogens. DCL appears resistant to conventional wastewater treatment while E2 and EE2 have high removal efficiencies that occur through biodegradation or sorption to organic matter. There is a pressing need to determine fate and behaviour of these CECs in European receiving waters such as using GIS-modelling of river basins as this will identify pressure points for informing priority decision making and alleviation strategies for upgrade of WWTPs and for hospital effluents with advanced treatment technologies. More monitoring data for these CECs in receiving waters is urgently needed for EU legislation and effective risk management.

Occurrence and removal of organic micropollutants: An overview of the watch list of EU Decision 2015/495

Although there are no legal discharge limits for micropollutants into the environment, some regulations have been published in the last few years. Recently, a watch list of substances for European Union-wide monitoring was reported in the Decision 2015/495/EU of 20 March 2015. Besides the substances previously recommended to be included by the Directive 39/2013/EU, namely two pharmaceuticals (diclofenac and the synthetic hormone 17-alpha-ethinylestradiol (EE2)) and a natural hormone (17-beta-estradiol (E2)), the first watch list of 10 substances/groups of substances also refers three macrolide antibiotics (azithromycin, clarithromycin and erythromycin), other natural hormone (estrone (E1)), some pesticides (methiocarb, oxadiazon, imidacloprid, thiacloprid, thiamethoxam, clothianidin, acetamiprid and triallate), a UV filter (2-ethylhexyl-4-methoxycinnamate) and an antioxidant (2,6-di-tert-butyl-4-methylphenol) commonly used as food additive. Since little is known about the removal of most of the substances included in the Decision 2015/495/EU, particularly regarding realistic concentrations in aqueous environmental samples, this review aims to: (i) overview the European policy in the water field; (ii) briefly describe the most commonly used conventional and advanced treatment processes to remove micropollutants; (iii) summarize the relevant data published in the last decade, regarding occurrence and removal in aqueous matrices of the 10 substances/groups of substances that were recently included in the first watch list for European Union monitoring (Decision 2015/495/EU); and (iv) highlight the lack of reports concerning some substances of the watch list, the study of un-spiked aquatic matrices and the assessment of transformation by-products.

Life cycle assessment as development and decision support tool for wastewater resource recovery technology

Life cycle assessment (LCA) has been increasingly used in the field of wastewater treatment where the focus has been to identify environmental trade-offs of current technologies. In a novel approach, we use LCA to support early stage research and development of a biochemical system for wastewater resource recovery. The freshwater and nutrient content of wastewater are recognized as potential valuable resources that can be recovered for beneficial reuse. Both recovery and reuse are intended to address existing environmental concerns, for example, water scarcity and use of non-renewable phosphorus. However, the resource recovery may come at the cost of unintended environmental impacts. One promising recovery system, referred to as TRENS, consists of an enhanced biological phosphorus removal and recovery system (EBP2R) connected to a photobioreactor. Based on a simulation of a full-scale nutrient and water recovery system in its potential operating environment, we assess the potential environmental impacts of such a system using the EASETECH model. In the simulation, recovered water and nutrients are used in scenarios of agricultural irrigation-fertilization and aquifer recharge. In these scenarios, TRENS reduces global warming up to 15% and marine eutrophication impacts up to 9% compared to conventional treatment. This is due to the recovery and reuse of nutrient resources, primarily nitrogen. The key environmental concerns obtained through the LCA are linked to increased human toxicity impacts from the chosen end use of wastewater recovery products. The toxicity impacts are from both heavy metals release associated with land application of recovered nutrients and production of AlCl3, which is required for advanced wastewater treatment prior to aquifer recharge. Perturbation analysis of the LCA pinpointed nutrient substitution and heavy metals content of algae biofertilizer as critical areas for further research if the performance of nutrient recovery systems such as TRENS is to be better characterized. Our study provides valuable feedback to the TRENS developers and identifies the importance of system expansion to include impacts outside the immediate nutrient recovery system itself. The study also show for the first time the successful evaluation of urban-to-agricultural water systems in EASETECH.

Ozonation and ultrafiltration for the treatment of olive mill wastewaters: effect of key operating conditions and integration schemes

With the objective of reaching suitable techniques for olive mill wastewater treatment, ozonation and ultrafiltration were studied individually and combined. A continuous reactor was run for the treatment of a phenolic mixture mimicking an actual olive mill wastewater (OMW) by ozonation. The effect of the main operating parameters was analysed (pH, liquid flow rate and ozone inlet concentration). The increase of pH and ozone dose improved ozonation efficiency. As expected, the highest residence time led to higher steady-state degradation (35 % of chemical oxygen demand (COD) abatement). Even if the rise on ozone inlet gas concentration was able to remove COD in a higher extent, it should be taken into consideration that with the lowest oxidant load (15 g O3/m(3)), the maximum steady-state biochemical oxygen demand (BOD5)/COD ratio was reached which would reduce the process costs. These operating conditions (pH 9, 1 mL/min of liquid flow rate and 15 g O3/m(3)) were applied to an actual OMW leading to 80 % of phenolic content abatement and 12 % of COD removal at the steady state. Regarding ultrafiltration, it was concluded that the best total phenolic content (TPh) and COD abatement results (55 and 15 %) are attained for pH 9 and using a transmembrane pressure drop of 1 bar. Among the integration schemes that were tested, ultrafiltration followed by ozonation was able to reach 93 and 20 % of TPh and COD depletion, respectively. Moreover, this sequence led to an effluent with a BOD5/COD ratio of about 0.55 which means that it likely can be posteriorly refined in a municipal wastewater treatment plant.

High-resolution MS and MS(n) investigation of ozone oxidation products from phenazone-type pharmaceuticals and metabolites

Phenazone-type pharmaceuticals, such as aminopyrine, metamizole, phenazone and propyphenazone, are widely used analgesics that have been detected in wastewater treatment plant effluents in μg L(-1) concentrations. Acetamido antipyrine (AAA) and formyl aminoantipyrine (FAA) - the main metabolites of aminopyrine and metamizole - have also been detected in sub μg L(-1) concentrations in environmental water bodies and in resources used to produce drinking water, suggesting their highly persistent character. In this study phenazone, propyphenazone, AAA and FAA were treated with ozone under laboratory conditions and 17 degradation products were identified by an elucidation approach based on high-resolution mass spectrometry (LTQ Orbitrap). Typical oxidation of carbon-carbon double bonds by ozone was observed among other mechanisms of ring opening. It was demonstrated that reactivity of these compounds with ozone is high (rate constants kO3 ranging from 6.5×10(4) to 2.4×10(6) M(-1) s(-1)). The toxicity of the degradation products from ozonation was estimated by quantitative structure-activity relationships (QSAR). It was shown that, when the carbon-carbon double bond is partially oxidized to an epoxy, the toxicity towards fish and daphnids is higher than that of the parent compound. By further oxidizing the molecules, a common degradation product - 1-acetyl-1-methyl-2-phenylhydrazide (AMPH) - was also found to be more toxic than its parent compounds, which is of concern since this compound has previously been reported in environmental waters.

Potential contribution of inorganic ions to whole effluent acute toxicity and genotoxicity during sewage tertiary treatment

Two acute toxicity tests (luminescent bacteria assay and cladoceran assay) and one genotoxicity test (broad bean assay) were used to evaluate whole effluent toxicity during the standard anion exchange resin-based pilot-scale sewage tertiary treatment that stably achieved significant dissolved organic carbon and inorganic ions reduction. The effect of six representative inorganic ions (i.e., Cl(-), SO4(2-), NO3(-)-N, NO2(-)-N, NH4(+)-N and PO4(3-)-P) on the acute toxicity and genotoxicity was further investigated. Significant whole effluent genotoxicity reduction was observed as an ∼ 57% micronucleated cell frequency reduction and ∼ 46% mitotic index increment during the pilot-scale periods, which should be attributed to significant organic removal since no significant (p ≥ 0.116) increase in genotoxicity was observed with the increase in these ionic concentrations. However, no significant (p ≥ 0.14) reductions were observed for whole effluent acute toxicity using two acute toxicity assays during the pilot-scale periods, and these inorganic ions, especially NH4(+)-N, contributed considerably to the acute toxicity. Based on Pearson correlation coefficients, whole effluent acute toxicity showed significant positive (p < 0.001, r ≥ 0.758) correlations with the NH4(+)-N concentration. Two optimal models were finally developed using step-wise multiple linear regression to predict the whole effluent acute toxicity via NH4(+)-N concentrations.

Continuous ozonation treatment of ofloxacin: transformation products, water matrix effect and aquatic toxicity

The continuous ozonation of the antibiotic ofloxacin (OFX) has been performed using a synthetic water matrix and in a sewage treatment plant (STP) effluent. The aim was to study the effect of the water matrix on the ozonation with particular emphasis on the aquatic toxicity of treated water. OFX was completely removed in both water matrices, although the amount of ozone consumed for its depletion was strongly matrix-dependent. The extent of mineralization was limited and a number of intermediate transformation products (TPs) appeared, twelve of which could be identified. OFX reaction pathway includes the degradation of piperazinyl and quinolone moieties. The further oxidation of TPs gave rise to the formation and accumulation of carboxylic acids, aldehydes, nitrogen-containing organic compounds and inorganic ions. Aquatic toxicity of treated mixtures was assessed using four standard species: the bacteria Vibrio fischeri and Pseudomonas putida as target organisms and the algae Pseudokirchneriella subcapitata and the protozoan Tetrahymena thermophila as non-target organisms. OFX was toxic for the bacteria and the microalgae at the spiked concentration in untreated water. However, the continuous ozonation at the upper operational limit removed its toxic effects. T. thermophila was not affected by OFX, but was sensitive to STP effluent.

Energy efficiency for the removal of non-polar pollutants during ultraviolet irradiation, visible light photocatalysis and ozonation of a wastewater effluent

This study aims to assess the removal of a set of non-polar pollutants in biologically treated wastewater using ozonation, ultraviolet (UV 254 nm low pressure mercury lamp) and visible light (Xe-arc lamp) irradiation as well as visible light photocatalysis using Ce-doped TiO2. The compounds tracked include UV filters, synthetic musks, herbicides, insecticides, antiseptics and polyaromatic hydrocarbons. Raw wastewater and treated samples were analyzed using stir-bar sorptive extraction coupled with comprehensive two-dimensional gas chromatography (SBSE-CG × GC-TOF-MS). Ozone treatment could remove most pollutants with a global efficiency of over 95% for 209 μM ozone dosage. UV irradiation reduced the total concentration of the sixteen pollutants tested by an average of 63% with high removal of the sunscreen 2-ethylhexyl trans-4-methoxycinnamate (EHMC), the synthetic musk 7-acetyl-1,1,3,4,4,6-hexamethyltetrahydronaphthalene (tonalide, AHTN) and several herbicides. Visible light Ce-TiO2 photocatalysis reached ~70% overall removal with particularly high efficiency for synthetic musks. In terms of power usage efficiency expressed as nmol kJ(-1), the results showed that ozonation was by far the most efficient process, ten-fold over Xe/Ce-TiO2 visible light photocatalysis, the latter being in turn considerably more efficient than UV irradiation. In all cases the efficiency decreased along the treatments due to the lower reaction rate at lower pollutant concentration. The use of photocatalysis greatly improved the efficiency of visible light irradiation. The collector area per order decreased from 9.14 ± 5.11 m(2) m(-3) order(-1) for visible light irradiation to 0.16 ± 0.03 m(2) m(-3) order(-1) for Ce-TiO2 photocatalysis. The toxicity of treated wastewater was assessed using the green alga Pseudokirchneriella subcapitata. Ozonation reduced the toxicity of treated wastewater, while UV irradiation and visible light photocatalysis limited by 20-25% the algal growth due to the accumulation of reaction by-products. Three transformation products were identified and tracked along the treatments.

Influence of planting patterns on fluoroquinolone residues in the soil of an intensive vegetable cultivation area in northern China

Recent studies have demonstrated the persistence of antibiotics in soil, especially in areas of vegetable cultivation. However, there are very few studies of the influence of planting regimes on the levels of antibiotic pollution. This work introduces geographical-detector models to investigate the relationship between planting patterns (vegetable planting model, manure type and quantity, planting age, greenhouse area, and topographic elevation) and residual fluoroquinolones (FQs) in soil in a pilot project in Shouguang County, Shandong Province (the largest vegetable-producing area in China). The results led to the following findings. 1. The vegetable planting model is the major determinant of the spatial stratification of FQ in the soil. For example, the "cucumber-cucumber" model (growing cucumbers after cucumbers) has a three-fold power of determinant compared to the "pepper-melon" model (growing melons after peppers). 2. Planting age (years with continuous vegetable cultivation) does not necessarily affect the spatial distribution of FQ owing to their relatively short degradation period. 3. Interactions between risk factors were more significant than the individual factors for FQ pollution. In particular, the interaction between the vegetable planting model and amount of manure resulted in the highest pollution level. The findings of the present study make it possible to introduce effective and practical measures to alleviate pollution of soils by FQ in the study area. Adjustment of the vegetable cultivation models and application of chicken manure (less than 6 kg/m(2) manure annually with a more dry than fresh manure) could be an effective and flexible approach to alleviate FQ pollution.