U. Hübner

Influence of wastewater particles on ozone degradation of trace organic contaminants.

In this Article, we demonstrate the influence of effluent particles (in the range of <50 μm) on ozone degradation of trace organic contaminants (TrOCs) and effluent-quality parameters. Secondary effluent was filtered through different pore-size filters and ozonated at various ozone doses. Degradation of both ozone-reactive and ozone-refractory contaminants improved following ozonation of effluent filtered with smaller pore size filters, indicating that particles in this range may adversely affect ozonation. The inhibitory effect of particles was attributed to their reaction with ozone, reducing available ozone and HO(•) radicals. In addition, increasing filtration level decreased the effluents (instantaneous) ozone demand and increased removal of effluent UV absorbance (UVA254), further establishing that ozone reacts with effluent particles, in competition with dissolved matter. Moreover, ozone was shown to react with particles even during the first seconds of the process, suggesting a high rate of some ozone-particle reactions, comparable to ozone reaction with highly reactive dissolved organic matter moieties. Particle image analysis revealed that particle formation/aggregation and particle disintegration occurs simultaneously during wastewater (WW) ozonation. Our study implies that particles could affect the efficiency of WW ozonation, by increasing the effluents ozone demand and decreasing contaminant degradation.

Evaluation of the prediction of trace organic compound removal during ozonation of secondary effluents using tracer substances and second order rate kinetics

The application of the R(CT)-concept for predicting the removal of trace organic compounds (TrOCs) in organic rich WWTP effluents is often problematic due to the fast ozone depletion with instantaneous ozone demand in the range of typically applied ozone dosages. In this study, the determination of OH-radical and ozone exposure from second order rate kinetics with two internal tracer substances was evaluated as alternative approach for these waters. Results from batch and semi-batch experiments showed a linear correlation of OH-radical exposure with ozone consumption, characterized by its slope indicating the formation efficiency of OH-radicals and a lag ozone consumption without significant formation of OH-radicals. Evaluation of data from the project PILOTOX on ozonation of secondary effluent confirmed reasonable prediction of ozone resistant compound removal from relative residual concentration of an internal tracer substance. In contrast, predicting the reduction of TrOCs by direct reactions with ozone from internal tracers was not feasible. Similar removal efficiencies for fast reacting compounds with different rate constants from k(O3) = 10(4) M(-1) s(-1) to k(O3) = 10(6) M(-1) s(-1) were observed indicating a limitation of the reaction by mass transfer. This effect was observed at low ozone dosages in semi-batch and pilot experiments as well as in batch experiments, where mass transfer from gas to liquid phase is not limiting. It is assumed that consumption of low ozone dosages is faster than sample homogenization in the batch reactors used. Thus, prediction of compound removal by direct reaction with ozone always needs to consider reactor design and geometry.

Evaluation of advanced oxidation processes for water and wastewater treatment – A critical review

This study provides an overview of established processes as well as recent progress in emerging technologies for advanced oxidation processes (AOPs). In addition to a discussion of major reaction mechanisms and formation of by-products, data on energy efficiency were collected in an extensive analysis of studies reported in the peer-reviewed literature enabling a critical comparison of various established and emerging AOPs based on electrical energy per order (EEO) values. Despite strong variations within reviewed EEO values, significant differences could be observed between three groups of AOPs: (1) O3 (often considered as AOP-like process), O3/H2O2, O3/UV, UV/H2O2, UV/persulfate, UV/chlorine, and electron beam represent median EEO values of <1 kWh/m3, while median energy consumption by (2) photo-Fenton, plasma, and electrolytic AOPs were significantly higher (EEO values in the range of 1-100 kWh/m3). (3) UV-based photocatalysis, ultrasound, and microwave-based AOPs are characterized by median values of >100 kWh/m3 and were therefore considered as not (yet) energy efficient AOPs. Specific evaluation of 147 data points for the UV/H2O2 process revealed strong effects of operational conditions on reported EEO values. Besides water type and quality, a major influence was observed for process capacity (lab-vs. pilot-vs. full-scale applications) and, in case of UV-based processes, of the lamp type. However, due to the contribution of other factors, correlation of EEO values with specific water quality parameters such as UV absorbance and dissolved organic carbon were not substantial. Also, correlations between EEO and compound reactivity with OH-radicals were not significant (photolytically active compounds were not considered). Based on these findings, recommendations regarding the use of the EEO concept, including the upscaling of laboratory results, were derived.

Determination of oxidant exposure during ozonation of secondary effluent to predict contaminant removal.

The use of kinetic models to predict oxidation performance in wastewater is limited due to fast ozone depletion during the first milliseconds of the reaction. This paper introduces the Quench Flow Module (QFM), a bench-scale experimental technique developed to measure the first 5-500 milliseconds of ozone depletion for accurate determination of ozone exposure in wastewater-ozonation processes. Calculated ozone exposure in QFM experiments was up to 24% lower than in standard batch experiments, strongly depending on the initial sampling point for measurement in batch experiments. However, oxidation rates of slowly- and moderately-reacting trace organic compounds (TrOCs) were accurately predicted from batch experiments based on integration of ozone depletion and removal of an ozone-resistant probe compound to calculate oxidant exposures. An alternative concept, where ozone and hydroxyl radical exposures are back-calculated from the removal of two probe compounds, was tested as well. Although the QFM was suggested to be an efficient mixing reactor, ozone exposure ranged over three orders of magnitude when different probe compounds reacting moderately with ozone were used for the calculation. These effects were beyond uncertainty ranges for apparent second order rate constants and consistently observed with different ozone-injection techniques, i.e. QFM, batch experiments, bubble columns and venturi injection. This indicates that previously suggested mixing effects are not responsible for the difference and other still unknown factors might be relevant. Results furthermore suggest that ozone exposure calculations from the relative residual concentration of a probe compound are not a promising option for evaluation of ozonation of secondary effluents.

UV/H2O2 process stability and pilot-scale validation for trace organic chemical removal from wastewater treatment plant effluents

This study investigated the removal of 15 trace organic chemicals (TOrCs) occurring at ambient concentrations from municipal wastewater treatment plant effluent by advanced oxidation using UV/H2O2 at pilot-scale. Pseudo first-order rate constants (kobs) for photolytic as well as combined oxidative and photolytic degradation observed at pilot-scale were validated with results from a bench-scale collimated beam device. No significant difference was determined between pilot- and lab-scale performance. During continuous pilot-scale operation at constant UV fluence of 800 mJ/cm2 and H2O2 dosage of 10 mg/L, the removal of various TOrCs was investigated. The average observed removal for photo-susceptible (kUV>10-3 cm2/mJ; like diclofenac, iopromide and sulfamethoxazole), moderately photo-susceptible (10-4<kUV<10-3 cm2/mJ; like climbazole, tramadol, sotalol, citalopram, benzotriazole, venlafaxine and metoprolol), and most photo-resistant (kUV<10-4 cm2/mJ; like primidone, carbamazepine and gabapentin) compounds was 90%, 49% and 37% including outliers, respectively. The poorly reactive compound TCEP was not significantly eliminated during pilot-scale experiments. Additionally, based on removal kinetics of photo-resistant TOrCs, continuous pilot-scale operation revealed high variations of OH-radical exposure determined from removal kinetics of photo-resistant TOrCs, primarily due to nitrite concentration fluctuations in the feed water. Furthermore, a correlation between OH-radical exposure and scavenging capacity could be determined and verified by mechanistic modeling using UV fluence, H2O2 dosage, and standard water quality parameters (i.e., DOC, NO3-, NO2- and HCO3-) as model input data. This correlation revealed the possibility of OH-radical exposure prediction by water matrix parameters and proved its applicability for pilot-scale operations.

Sequential biofiltration – A novel approach for enhanced biological removal of trace organic chemicals from wastewater treatment plant effluent

Recent studies revealed the benefits of oligotrophic and oxic conditions for the biological removal of many trace organic chemicals (TOrCs) during soil-aquifer treatment. These findings indicate an unused tuning potential that might also be applicable in engineered biofiltration systems with drastically reduced hydraulic retention times for an enhanced mitigation of TOrCs during wastewater treatment. This study introduces the novel approach of sequential biofiltration (SBF) for the advanced treatment of secondary effluent using two granular media filters operated in series with an intermediate aeration step aiming for oxic and oligotrophic conditions in the second filter stage. Results from the experiments conducted at pilot-scale confirm a reduced substrate availability and predominantly oxic conditions in the second filter stage of the SBF setup. An increased removal of several TOrCs was observed in an SBF system as compared to a conventional single-stage biofiltration unit operated at the same overall empty bed contact time (EBCT). Short-term tests with varying EBCTs in the first filter stage revealed a high degree of system robustness of TOrC mitigation when confronted with sudden hydraulic load variations. Higher removal of several TOrCs at increased EBCTs in the second filter stage indicates that EBCT might play a crucial role for the degradation of certain compounds.

Evaluation of the short-term fate and transport of chemicals of emerging concern during soil-aquifer treatment using select transformation products as intrinsic redox-sensitive tracers

In this study, known products from oxic transformation of the X-ray contrast medium iopromide were introduced for the first time as intrinsic tracer for in situ characterization of the transition zone between oxic and suboxic conditions during the initial phase of soil-aquifer treatment (SAT). Two wet-dry cycles of a full-scale infiltration basin were monitored to characterize hydraulic retention times, redox conditions, removal of bulk organic parameters and the fate of chemicals of emerging concern (CECs). Tracer tests at the site showed an average hydraulic retention time of <20h before collection in drainage pipes located approximately 1.5m below surface. Dissolved oxygen at different depth rapidly depleted and only increased towards the end of the flooding event. Transformation of iopromide and all known intermediates to persistent transformation products (TPs) usually occurring during oxic biodegradation was very limited in samples from suction cups immediately underneath the basin. But transformation was complete in samples collected from the drainage outlet indicating that dissolved oxygen had been introduced to the system before sample collection in the combined drainage outlet. Similar to iopromide and its TPs, removal of several CECs (diclofenac, bezafibrate, mecoprop, TCEP) was inefficient after 90cm infiltration (<35%) but significantly enhanced in the combined drainage outlet (>80%). These results highlight that the analysis of iopromide along with its intermediates and persistent TPs can serve as a promising probing tool to determine overall efficiency of CEC biodegradation and to identify potential in situ oxygen limitations.

Tertiary treatment of Berlin WWTP effluents with ferrate (Fe(VI))

New and higher standards in the EU water framework directive necessitate advanced treatment of secondary effluents for reduction of trace organic compounds (TrOCs) and nutrients before the discharge into receiving surface waters. Due to its dual function as oxidant and coagulant, ferrate is considered as a promising alternative for tertiary treatment. The oxidation of selected TrOCs and simultaneous flocculation of phosphates by ferrate was tested in batch experiments with secondary effluent from Berlin Ruhleben. The concentrations of carbamazepine (CBZ) and diclofenac were reduced by >90% with ferrate dosages of 6 mg/L as Fe. CBZ was transformed to 1-(2-benzaldehyde)-4-hydro-(1H,3H)-quinazoline-2-one, which is known as the major product from the reaction of CBZ with ozone. In contrast to ozonation, no further transformation of this product was observed. The concentration of ibuprofen was not reduced by ferrate treatment. For efficient removal of 60-100 μg/L phosphate-P to values <20 μg/L, ferrate dosages of 3-4 mg/L as Fe were sufficient.

Removal of Residual Dissolved Ozone with Manganese Dioxide for Process Control with UV254

ABSTRACT Ozonation is one of the most promising options to remove organic micropollutants (OMP) from wastewater treatment plant effluents. For an economic operation and in order to avoid formation of bromate, the ozone dose has to be adjusted in real-time due to the strongly varying effluent quality. The reduction of UV absorption at 254 nm (∆UV254) is a useful surrogate parameter for OMP removals. Unfortunately dissolved ozone also absorbs UV at 254 nm and therefore might disturb a ∆UV254-based process control. A fixed bed of manganese dioxide granules was found to efficiently remove residual ozone.

Removal of trace organic chemicals in wastewater effluent by UV/H2O2 and UV/PDS

In this study, we comparatively investigated the degradation of 12 trace organic chemicals (TOrCs) during UV/H2O2 and UV/peroxydisulfate (PDS) processes. Second-order rate constants for the reactions of iopromide, phenytoin, caffeine, benzotriazole, and primidone with sulfate radical (SO4•-) were determined for the first time. Experiments were conducted in buffered pure water and wastewater effluent with spiked TOrCs. UV/PDS degraded all TOrCs more efficiently than UV/H2O2 in buffered pure water due to the higher yield of SO4•- than that of hydroxyl radical (•OH) at the same initial molar dose of PDS and H2O2, respectively. UV/PDS showed higher selectivity toward TOrCs removal than UV/H2O2 in wastewater effluent. Compounds with electron-rich moieties, such as diclofenac, venlafaxine, and metoprolol, were eliminated faster in UV/PDS whereas UV/H2O2 was more efficient in degrading compounds with lower reactivity to SO4•-. The fluence-based rate constants ( [Formula: see text] ) of TOrCs in wastewater effluent linearly increased as a function of initial H2O2 dose during UV/H2O2, possibly due to the constant scavenging impact of the wastewater matrix on •OH. However, exponential increase of kobs-UV/PDS with increasing PDS dose was observed for most compounds during UV/PDS, suggesting the decreasing scavenging effect of the water matrix (electron-rich site of effluent organic matter (EfOM)) after initial depletion of SO4•- at low PDS dose. Fulvic and humic-like fluorophores appeared to be more persistent during UV/H2O2 compared to aromatic protein and soluble microbial product-like fluorophores. In contrast, UV/PDS efficiently degraded all identified fluorophores and showed less selectivity toward the fluorescent EfOM components. Removal pattern of TOrCs during pilot-scale UV/PDS was consistent with lab-scale experiments, however, overall removal rates were lower due to the presence of higher concentration of EfOM and nitrite.