Richard M. Stuetz

Fluorescence as a potential monitoring tool for recycled water systems: a review.

A rapid, highly sensitive and selective detector is urgently required to detect contamination events in recycled water systems - for example, cross-connection events in dual reticulation pipes that recycle advanced treated sewage effluent - as existing technologies, including total organic carbon and conductivity monitoring, cannot always provide the sensitivity required. Fluorescence spectroscopy has been suggested as a potential monitoring tool given its high sensitivity and selectivity. A review of recent literature demonstrates that by monitoring the fluorescence of dissolved organic matter (DOM), the ratios of humic-like (Peak C) and protein-like (Peak T) fluorescence peaks can be used to identify trace sewage contamination in river waters and estuaries, a situation analogous to contamination detection in recycled water systems. Additionally, strong correlations have been shown between Peak T and biochemical oxygen demand (BOD) in rivers, which is indicative of water impacted by microbial activity and therefore of sewage impacted systems. Hence, this review concludes that the sensitive detection of contamination events in recycled water systems may be achieved by monitoring Peak T and/or Peak C fluorescence. However, in such systems, effluent is treated to a high standard resulting in much lower DOM concentrations and the impact of these advanced treatment processes on Peaks T and C fluorescence is largely unknown and requires investigation. This review has highlighted that further work is also required to determine (a) the stability and distinctiveness of recycled water fluorescence in relation to the treatment processes utilised, (b) the impact of matrix effects, particularly the impact of oxidation, (c) calibration issues for online monitoring, and (d) the advanced data analytical techniques required, if any, to improve detection of contamination events.

Fate of antibiotics during municipal water recycling treatment processes

Municipal water recycling processes are potential human and environmental exposure routes for low concentrations of persistent antibiotics. While the implications of such exposure scenarios are unknown, concerns have been raised regarding the possibility that continuous discharge of antibiotics to the environment may facilitate the development or proliferation of resistant strains of bacteria. As potable and non-potable water recycling schemes are continuously developed, it is imperative to improve our understanding of the fate of antibiotics during conventional and advanced wastewater treatment processes leading to high-quality water reclamation. This review collates existing knowledge with the aim of providing new insight to the influence of a wide range of treatment processes to the ultimate fate of antibiotics during conventional and advanced wastewater treatment. Although conventional biological wastewater treatment processes are effective for the removal of some antibiotics, many have been reported to occur at 10-1000 ng L(-1) concentrations in secondary treated effluents. These include beta-lactams, sulfonamides, trimethoprim, macrolides, fluoroquinolones, and tetracyclines. Tertiary and advanced treatment processes may be required to fully manage environmental and human exposure to these contaminants in water recycling schemes. The effectiveness of a range of processes including tertiary media filtration, ozonation, chlorination, UV irradiation, activated carbon adsorption, and NF/RO filtration has been reviewed and, where possible, semi-quantitative estimations of antibiotics removals have been provided.

Developments in odour control and waste gas treatment biotechnology: a review

Waste and wastewater treatment processes produce odours, which can cause a nuisance to adjacent populations and contribute significantly to atmospheric pollution. Sulphurous compounds are responsible for acid rain and mist; many organic compounds of industrial origin contribute to airborne public health concerns, as well as environmental problems. Waste gases from industry have traditionally been treated using physicochemical processes, such as scrubbing, adsorption, condensation, and oxidation, however, biological treatment of waste gases has gained support as an effective and economical option in the past few decades. One emergent technique for biological waste gas treatment is the use of existing activated sludge plants as bioscrubbers, thus treating the foul air generated by other process units of the wastewater treatment system on site, with no requirement for additional units or for interruption of wastewater treatment. Limited data are available regarding the performance of activated sludge diffusion of odorous air in spite of numerous positive reports from full-scale applications in North America. This review argues that the information available is insufficient for precise process design and optimization, and simultaneous activated sludge treatment of wastewater and airborne odours could be adopted worldwide.

Odour measurements for sewage treatment works.

Public concern over odours from sewage treatment works is increasing. More people are being exposed to odours, due to development around existing works or construction of new works. Increased awareness of both the environment and individual rights has meant people are now more likely to complain. Odour abatement and control is a major issue for sewage works operators. To control odours, they must first be measured. This is no easy task as response to odours is subjective. Our understanding of the sense of smell is incomplete, and there is no single measure that will directly relate to the likelihood of complaint. Odour measurement has often been regarded as an art as opposed to a science. Odour measurement techniques fall into two classes. Sensory measurements employ the human nose and measure the effects of the odour as perceived by an observer. Analytical measurements characterise odours in terms of their chemical composition and attempt to quantify the odorants present. Both methods are less than ideal--sensory measurements can be overly subjective and the interpretation of results requires care. Analytical measurements are complicated by the large number of odorants present, often at concentrations close to detection limits. Our incomplete understanding of odour perception makes linking analytical and sensory measurements difficult. This paper reviews the methods applied to sewage treatment works odour measurement. Sensory and analytical measurements are reviewed, along with a recent development, the electronic nose.

Organic matter fluorescence in municipal water recycling schemes: Toward a unified PARAFAC model

Organic matter (OM) is a ubiquitous constituent of natural waters quantifiable at very low levels using fluorescence spectroscopy. This technique has recognized potential in a range of applications where the ability to monitor water quality in real time is desirable, such as in water treatment systems. This study used PARAFAC to characterize a large (n=1479) and diverse excitation emission matrix (EEM) data set from six recycled water treatment plants in Australia, for which sources of variability included geography, season, treatment processes, pH and fluorometer settings. Five components were identified independently in four or more plants, none of which were generated during the treatment process nor were typically entirely removed. PARAFAC scores could be obtained from EEMs by simple regression. The results have important implications for online monitoring of OM fluorescence in treatment plants, affecting choices regarding experimental design, instrumentation and the optimal wavelengths for tracking fluorescent organic matter through the treatment process. While the multimodel comparisons provide a compelling demonstration of PARAFACs ability to distill chemical information from EEMs, deficiencies identified through this process have broad implications for interpreting and reusing (D)OM-PARAFAC models.

Monitoring techniques for odour abatement assessment

Odorous emissions from sewers and wastewater treatment plants are a complex mixture of volatile chemicals that can cause annoyance to local populations, resulting in complaints to wastewater operators. Due to the variability in hedonic tone and chemical character of odorous emissions, no analytical technique can be applied universally for the assessment of odour abatement performance. Recent developments in analytical methodologies, specifically gas chromatography, odour assessment approaches (odour wheels, the odour profile method and dynamic olfactometry), and more recently combined gas chromatography-sensory analysis, have contributed to improvements in our ability to assesses odorous emissions in terms of odorant concentration and composition. This review collates existing knowledge with the aim of providing new insight into the effectiveness of sensorial and characterisation approaches to improve our understanding of the fate of odorous emissions during odour abatement. While research in non-specific sensor array (e-nose) technology has resulted in progress in the field of continuous odour monitoring, more successful long term case-studies are still needed to overcome the early overoptimistic performance expectations. Knowledge gaps still remain with regards to the decomposition of thermally unstable volatile compounds (especially sulfur compounds), the inability to predict synergistic, antagonistic, or additive interactions among odorants in combined chemical/sensorial analysis techniques, and the long term stability of chemical sensors due to sensor drift, aging, temperature/relative humidity effects, and temporal variations. Future odour abatement monitoring will require the identification of key odorants to facilitate improved process selection, design and management.

Odor Assessment and Management in Wastewater Treatment Plants: A Review

The stricter environmental regulations, encroachment of residential areas on wastewater treatment plants (WWTPs), and increasing public expectations on privatized water companies have resulted in an increase in the number of public odor complaints during the last decades. Despite not being a direct cause of disease, long-term exposure to high-strength odorant emissions actually does negatively affect human health (e.g., causing nausea, headaches, respiratory problems). Therefore, the minimization and abatement of unpleasant odor emissions are becoming two of the major challenges for WWTP utilities worldwide. However, information regarding odor formation, sources, sampling, characterization, impact assessment, and control techniques is rather sparse in the literature. Therefore, there is a need for an integrated approach to odor assessment and management.

Novel filtration mode for fouling limitation in membrane bioreactors

A novel filtration mode is presented to reduce fouling propensity in membrane bioreactors (MBR). During this mode, an elevated high instantaneous flux (60Lm(-2)h(-1)) is initially applied for a short time (120s), followed by a longer filtration (290s) at lower flux (10.3Lm(-2)h(-1)) and a backwash in each filtration cycle. The mixed mode is expected to limit irreversible fouling as the reversible fouling created during the initial stage appears to protect the membrane. Hydraulic performance and the components of foulants were analyzed and compared with conventional continuous and backwash modes. It was found that the mixed mode featured lower trans-membrane pressure (TMP) after 24h of filtration when compared to other modes. The mixed mode was effective in preventing soluble microbial products (SMP) attaching directly onto the membrane surface, keeping the cake layer weakly compressed, and reducing the mixed liquor suspended solids (MLSS) accumulation on the membrane. This strategy reduced the resistances of both the cake layer and the gel layer. A factorial experimental design was carried out for eight runs with different conditions to identify the major operational parameters affecting the hydraulic performances. The results showed that the value of the flux in the initial high-flux period had the most effect on the performance of the mixed mode: high initial flux (60Lm(-2)h(-1)) led to improved performance.

Use of a chemical sensor array for detecting pollutants in domestic wastewater.

A chemical sensor array (consisting of 8 conducting polymers) was used to continuously monitor for the presence or absence of industrial pollutants in the headspace of wastewater generated from an on-line flow-cell. A domestic wastewater (Cranfield University sewage works) was dosed with diesel to stimulate the presence of an intermittent discharge in a wastewater influent. Response patterns between the sensors were used to detect for the presence of organic compounds in the wastewater. Correlations between the sensor response patterns or fingerprints were also analysed using principal component analysis. The results clearly demonstrate that a chemical sensor array can rapidly identify the presence of organic compounds (such as diesel) in a wastewater matrix and could be further developed to monitor for industrial pollutants at the inlet of a sewage works.

Dinitrogen oxide production by a mixed culture of nitrifying bacteria during ammonia shock loading and aeration failure.

A number of experiments was conducted in order to establish if N2O in the exhaust gas from an aerobic consortium of nitrifiers could be used as an indicator for monitoring the nitrification process. Laboratory-scale experiments with an activated sludge system showed a strong correlation between ammonia shock loads and both the concentration of N2O and the rate of increase of N2O in the exhaust gas for shock loads less than 1.60 mg ammonical nitrogen (NH3-N) per g total suspended solids (TSS). For greater ammonia shock loads, correlation was found between build-up of nitrite in the aeration tank and the concentration of N2O in the exhaust gas from the tank. When subjecting the system to aeration failure, a similar pattern was seen, with a correlation between nitrite build-up in the aeration tank and increases in the concentration of N2O in the exhaust gas. The results from this work suggest that the changes in N2O concentration in the exhaust gas from a nitrifying process may be a useful parameter for monitoring such processes.