Wolfgang Gernjak

Photo-Fenton treatment of water containing natural phenolic pollutants

Phenolic compounds are known to be present in high concentrations in various types of agro-industrial wastes. As they are highly biorecalcitrant, the possibility of treatment by advanced oxidation processes should be investigated. In this work, six model phenolic compounds (vanillin, protocatechuic acid, syringic acid, p-coumaric acid, gallic acid and L-tyrosine) were chosen for a demonstration of degradation by photo-Fenton reaction, under artificial light in laboratory experiments in Vienna and under sunlight in pilot-plant experiments at the Plataforma Solar de Almería in Spain. All compounds were completely mineralised. No non-degradable intermediates were produced, either in experiments with single substances or in a more complex matrix of a mixture of phenolic compounds. The expected selectivity of the photo-Fenton reaction for aromatic compounds was proven by comparison of the decrease in total organic carbon with the removal of total phenolic content.

Decontamination industrial pharmaceutical wastewater by combining solar photo-Fenton and biological treatment

Characterization and treatment of a real pharmaceutical wastewater containing 775 mg dissolved organic carbon per liter by a solar photo-Fenton/biotreatment were studied. There were also many inorganic compounds present in the matrix. The most important chemical in this wastewater was nalidixic acid (45 mg/L), an antibiotic pertaining to the quinolone group. A Zahn-Wellens test demonstrated that the real bulk organic content of the wastewater was biodegradable, but only after long biomass adaptation; however, the nalidixic acid concentration remained constant, showing that it cannot be biodegraded. An alternative is chemical oxidation (photo-Fenton process) first to enhance biodegradability, followed by a biological treatment (Immobilized Biomass Reactor--IBR). In this case, two studies of photo-Fenton treatment of the real wastewater were performed, one with an excess of H2O2 (kinetic study) and another with controlled H2O2 dosing (biodegradability and toxicity studies). In the kinetic study, nalidixic acid completely disappeared after 190 min. In the other experiment with controlled H2O2, nalidixic acid degradation was complete at 66 mM of H2O2 consumed. Biodegradability and toxicity bioassays showed that photo-Fenton should be performed until total degradation of nalidixic acid before coupling a biological treatment. Analysis of the average oxidation state (AOS) demonstrated the formation of more oxidized intermediates. With this information, the photo-Fenton treatment time (190 min) and H2O2 dose (66 mM) necessary for adequate biodegradability of the wastewater could be determined. An IBR operated in batch mode was able to reduce the remaining DOC to less than 35 mg/L. Ammonium consumption and NO3- generation demonstrated that nitrification was also attained in the IBR. Overall DOC degradation efficiency of the combined photo-Fenton and biological treatment was over 95%, of which 33% correspond to the solar photochemical process and 62% to the biological treatment.

Effect of water-matrix composition on Trimethoprim solar photodegradation kinetics and pathways.

Direct photolysis and solar TiO(2) photocatalysis of Trimethoprim (TMP) in different water matrices (demineralised and simulated seawater) have been studied. Direct photolysis yielded a similar, slow TMP degradation rate in both water matrices, and the formation of very stable photo-transformation products. Dissolved organic carbon decreased slightly after prolonged irradiation. The main intermediate identified was a ketone derivative (trimethoxybenzoylpyrimidine), which was proved to be a photosensitizer of TMP degradation. During TiO(2) photocatalysis, TMP was completely eliminated in both water matrices at a similar rate, however, the mineralization rate was appreciably reduced in seawater, which can be explained by the presence of inorganic species acting as hydroxyl radical scavengers, and directly affecting photocatalytic efficiency. Identification of intermediates showed differences between the two processes but hydroxylation, demethylation and cleavage of the original drug molecule were observed in both.

Sewage pollution in urban stormwater runoff as evident from the widespread presence of multiple microbial and chemical source tracking markers.

The concurrence of human sewage contamination in urban stormwater runoff (n=23) from six urban catchments across Australia was assessed by using both microbial source tracking (MST) and chemical source tracking (CST) markers. Out of 23 stormwater samples human adenovirus (HAv), human polyomavirus (HPv) and the sewage-associated markers; Methanobrevibacter smithii nifH and Bacteroides HF183 were detected in 91%, 56%, 43% and 96% of samples, respectively. Similarly, CST markers paracetamol (87%), salicylic acid (78%) acesulfame (96%) and caffeine (91%) were frequently detected. Twenty one samples (91%) were positive for six to eight sewage related MST and CST markers and remaining two samples were positive for five and four markers, respectively. A very good consensus (>91%) observed between the concurrence of the HF183, HAv, acesulfame and caffeine suggests good predictability of the presence of HAv in samples positive for one of the three markers. High prevalence of HAv (91%) also suggests that other enteric viruses may also be present in the stormwater samples which may pose significant health risks. This study underscores the benefits of employing a set of MST and CST markers which could include monitoring for HF183, adenovirus, caffeine and paracetamol to accurately detect human sewage contamination along with credible information on the presence of human enteric viruses, which could be used for more reliable public health risk assessments. Based on the results obtained in this study, it is recommended that some degree of treatment of captured stormwater would be required if it were to be used for non-potable purposes.

Reducing sewer corrosion through integrated urban water management

Sourcing corrosive sewer sulfides Sewer systems are corroding at an alarming rate, costing governments billions of dollars to replace. Differences among water treatment systems make it difficult to track down the source of corrosive sulfide responsible for this damage. Pikaar et al. performed an extensive industry survey and sampling campaign across Australia (see the Perspective by Rauch and Kleidorfer). Aluminum sulfate added as a coagulant during drinking water treatment was the primary culprit in corroding sewer systems. Modifying this common treatment strategy to include sulfate-free coagulants could dramatically reduce sewer corrosion across the globe. Science, this issue p. 812; see also p. 734 Decreasing sulfate added during drinking water treatment can prevent corrosion of sewers caused by wastewater. [Also see Perspective by Rauch and Kleidorfer] Sewer systems are among the most critical infrastructure assets for modern urban societies and provide essential human health protection. Sulfide-induced concrete sewer corrosion costs billions of dollars annually and has been identified as a main cause of global sewer deterioration. We performed a 2-year sampling campaign in South East Queensland (Australia), an extensive industry survey across Australia, and a comprehensive model-based scenario analysis of the various sources of sulfide. Aluminum sulfate addition during drinking water production contributes substantially to the sulfate load in sewage and indirectly serves as the primary source of sulfide. This unintended consequence of urban water management structures could be avoided by switching to sulfate-free coagulants, with no or only marginal additional expenses compared with the large potential savings in sewer corrosion costs.

Factors affecting the formation of disinfection by-products during chlorination and chloramination of secondary effluent for the production of high quality recycled water

During the production of high quality recycled water by reverse osmosis membrane filtration secondary effluent must be disinfected to limit biofouling on the membrane surface. Advanced Water Treatment Plants in South East Queensland, Australia use disinfectant contact times ranging from 30 min up to 24 h. Disinfectants such as chlorine and chloramines react with effluent organic matter to generate disinfection by-products (DBPs) which could be potentially hazardous to human health if the water is destined for supplementing public water supplies. In this context, secondary effluents are of concern because of their high total organic carbon content which can act as DBP precursors. Also, effluent organic matter may form different DBPs to those formed from natural organic matter during conventional drinking water treatment, either in quantity, identity or simply in the abundance of different DBPs relative to each other. It cannot be assumed per se with certainty that DBP formation will be affected in the same way by operational changes as in drinking water production. Response surface modelling has been employed in this study at the bench scale to investigate the effect of reaction time (0-24 h), pH (5.5-8.5), temperature (23-35 °C), disinfection strategy (chlorine vs chloramines used prior to membrane treatment) and the interaction between these different parameters on DBP formation during disinfection of secondary effluent. The concentration of halogenated DBPs formed during the first 24 h of reaction with the different disinfectants followed the order chlorination >> in line-formed monochloramine > pre-formed monochloramine. Contact time with chlorine was the major influencing factor on DBP formation during chlorination, except for the bromine-containing trihalomethanes and dibromoacetonitrile for which pH was more significant. Chlorination at high pH led to an increased formation of chloral hydrate, trichloronitromethane, dibromoacetonitrile and the four trihalomethanes while the opposite effect was observed for the other targeted DBPs. Temperature was identified as the least influencing parameter compared to pH and reaction time for all DBPs in all the disinfection strategies, except for the formation of chloral hydrate where pH and temperature had a similar significance and bromoform that was similarly affected by temperature and reaction time. Chloramines employed at pH 8.5 reduced the concentration of all studied DBPs compared to pH 5.5. Furthermore, reaction time was the most significant factor for trichloronitromethane, chloroform, trichloroacetonitrile, dichloroacetonitrile and bromochloroacetonitrile formation while pH was the most influencing factor affecting the formation of the remaining DBPs.

Fate of N-nitrosodimethylamine, trihalomethane and haloacetic acid precursors in tertiary treatment including biofiltration

The presence of disinfection by-products (DBPs) such as trihalomethanes (THMs), haloacetic acids (HAAs) and N-nitrosamines in water is of great concern due to their adverse effects on human health. In this work, the removal of N-nitrosodimethylamine (NDMA), total THM and five HAA precursors from secondary effluent by biological activated carbon (BAC) is investigated at full and pilot scale. In the pilot plant two filter media, sand and granular activated carbon, are tested. In addition, we evaluate the influence of ozonation prior to BAC filtration on its performance. Among the bulk of NDMA precursors, the fate of four pharmaceuticals containing a dimethylamino moiety in the chemical structure are individually investigated. Both NDMA formation potential and each of the studied pharmaceuticals are dramatically reduced by the BAC even in the absence of main ozonation prior to the filtration. The low removal of NDMA precursors at the sand filtration in comparison to the removal of NDMA precursors at the BAC suggests that adsorption may play an important role on the removal of NDMA precursors by BAC. Contrary, the precursors for THM and HAA formation are reduced in both sand filtration and BAC indicating that the precursors for the formation of these DBPs are to some extent biodegradable.

Understanding the operational parameters affecting NDMA formation at Advanced Water Treatment Plants

N-nitrosodimethylamine (NDMA) can be formed when secondary effluents are disinfected by chloramines. By means of bench scale experiments this paper investigates operational parameters than can help Advanced Water Treatment Plants (AWTPs) to reduce the formation of NDMA during the production of high quality recycled water. The formation of NDMA was monitored during a contact time of 24h using dimethylamine as NDMA model precursor and secondary effluent from wastewater treatment plants. The three chloramine disinfection strategies tested were pre-formed and in-line formed monochloramine, and pre-formed dichloramine. Although the latter is not employed on purpose in full-scale applications, it has been suggested as the main contributing chemical generating NDMA during chloramination. After 24h, the NDMA formation decreased in both matrices tested in the order: pre-formed dichloramine>in-line formed monochloramine≫pre-formed monochloramine. The most important parameter to consider for the inhibition of NDMA formation was the length of contact time between disinfectant and wastewater. Formation of NDMA was initially inhibited for up to 6h with concentrations consistently <10 ng/L during these early stages of disinfection, regardless of the disinfection strategy. The reduction of the contact time was implemented in Bundamba AWTP (Queensland, Australia), where NDMA concentrations were reduced by a factor of 20 by optimizing the disinfection strategy.

Reductive electrochemical remediation of emerging and regulated disinfection byproducts

Long-term exposure to low concentrations of disinfection byproducts (DBPs) in drinking water has been associated with increased human-health risks of bladder cancer and adverse reproductive outcomes. In this study, we investigated electrochemical reduction utilizing a resin-impregnated graphite cathode for the degradation of 17 DBPs (i.e. halomethanes, haloacetonitriles, halopropanones, chloral hydrate and trichloronitromethane) at low μg L(-1) concentration levels. The reduction experiments were potentiostatically controlled at cathode potentials -700, -800 and -900 mV vs Standard Hydrogen Electrode (SHE) during 24 h. At the lowest potential applied (i.e. -900 mV vs SHE), the disappearance of DBPs from the solution after 24 h of reduction was >70%, except for chloroform (32%), 1,1-dichloropropanone (48%), and chloral hydrate (31%). Due to the participation of several removal mechanisms (e.g. electrochemical reduction, adsorption, volatilization and/or hydrolysis) it was not possible to distinguish the removal efficiencies of electrochemical reduction of individual compounds. Adsorption of the more hydrophilic DBPs (i.e. haloacetonitriles, chloral hydrate, and 1,1-dichloropropanone) onto the electrode seems to be affected by the cathode polarization, as the removals observed in the open circuit experiments were significantly higher than the ones obtained in electrochemical reduction under the same conditions. The overall efficiency of reduction was estimated based on the analyses of the released Cl(-), Br(-) and I(-) ions. Nearly complete C-I bond cleavage was achieved at all three potentials applied, and from the theoretically predicted release of I(-) ions, calculated based on the removed DBPs, 86 ± 9 to 92 ± 1% was measured in the catholyte solution at -700 to -900 mV vs SHE. Debromination efficiencies obtained were 74 ± 3, 79 ± 6 and 68 ± 4% at -700, -800 and -900 mV vs SHE, while for C-Cl bond cleavage the obtained values were 69 ± 1, 72 ± 1 and 76 ± 4%, respectively. Nevertheless, dechlorination efficiencies are to be considered as approximate, since an increase in Cl(-) concentration was observed in the open circuit experiments due to the hydrolysis of some of the chlorine-containing DBPs. Although the Coulombic efficiencies for DPBs dehalogenation were only 1.9 ± 0.3 (-900 mV vs SHE) -4.1 ± 0.2% (-700 mV vs SHE), relatively low energy consumption of the process was observed, estimated at 72 ± 2 Wh m(-3) at -900 mV vs SHE for the concentration range of DBPs in this study (i.e. 65.3-129.7 μg L(-1)). The study demonstrated that reductive electrochemical treatment has the potential to be a modern remediation technology for the removal of low concentrations of halogenated DBPs in water.

Toxicity characterization of urban stormwater with bioanalytical tools.

Stormwater harvesting has become an attractive alternative strategy to address the rising demand for urban water supply due to limited water sources and population growth. Nevertheless, urban stormwater is also a major source of surface water pollution. Runoff from different urban catchments with source contributions from anthropogenic activities and various land uses causes variable contaminant profiles, thus posing a challenging task for environmental monitoring and risk assessment. A thorough understanding of raw stormwater quality is essential to develop appropriate treatment facilities for potential indirect potable reuse of stormwater. While some of the key chemical components have previously been characterized, only scarce data are available on stormwater toxicity. We benchmarked stormwater samples from urban, residential and industrial sites across various Australian capital cities against samples from the entire water cycle, from sewage to drinking water. Six biological endpoints, targeting groups of chemicals with modes of toxic action of particular relevance for human and environmental health, were investigated: non-specific toxicity (Microtox and combined algae test), the specific modes of action of phytotoxicity (combined algae test), dioxin-like activity (AhR-CAFLUX), and estrogenicity (E-SCREEN), as well as reactive toxicity encompassing genotoxicity (umuC) and oxidative stress (AREc32). Non-specific toxicity was highly variable across sites. The baseline toxicity equivalent concentrations of the most polluted samples were similar to secondary treated effluent from wastewater treatment plants. Phytotoxicity results correlated well with the measured herbicide concentrations at all sites. High estrogenicity was found in two sampling events and could be related to sewage overflow. Genotoxicity, dioxin-like activity, and oxidative stress response were evident in only three of the samples where the stormwater drain was beside a heavy traffic road, confirming that road runoff is the potential source of contaminants, while the bioanalytical equivalent concentrations (BEQ) of these samples were similar to those of raw sewage. This study demonstrates the benefit of bioanalytical tools for screening-level stormwater quality assessment, forming the basis for the evaluation of future stormwater treatment and reuse schemes.