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This paper reviewed systematically the odor production and emissions in wastewater systems including sewer and wastewater treatment plants (WWTP). The subjective and objective characterization of wastewater odor was briefly discussed while the recent literature data of the measured concentrations of various odor compounds is collated with their odor description, threshold value, and human health limits. The extensive compiled data provide a full range of spatial and temporal variations. It was found that hydrogen sulfide, organic sulfur compounds, and aldehydes are the key odorants in sewer emissions. The odor emission from different treatment units of a WWTP are distinct from each other. The primary treatment odor is similar to that from the sewer with high level of hydrogen sulfide. In contrast, the odor from sludge handling units are characterized with high organic compounds and very low level of hydrogen sulfide. Odor from both sewer and WWTP are affected by the operation and environmental conditions. Typical diurnal and seasonal pattern can be observed due to the hydraulic patterns. A prioritization framework is proposed to rank the complicated odorants in wastewater emissions for the design and optimization of treatment and control measures. [ABSTRACT FROM PUBLISHER]

This study was conducted to evaluate the relationship between the flora and the changes in the microbial communities during tomato paste wastewater treatment. The bio-analytical techniques like Polymerase chain reaction denaturing gradient gel electrophoresis (PCR-DGGE), adenosine-triphosphate (ATP) analysis, and testing of mixed liquid and suspended solids (MLSS) were simultaneously conducted to analyze the dynamics of the microbial communities during tomato paste wastewater treatment process. The study suggests that the combined approaches of PCR-DGGE, ATP, and MLSS provided a simple and accurate method to evaluate the changes in microbial activity, microbial structure, and population size with the shift in contaminants in different treatment processes. The study also demonstrates that the structure and quantity of a microbial community are influenced by MLSS during the wastewater treatment process, which consequently determines the overall functionality of the system. [ABSTRACT FROM AUTHOR]

Wastewater treatment is a huge industry worldwide. Despite the massive capital and operating costs, only a relatively small amount of R&D investment is made. This might have been related to the limited demands in terms of effluent quality in the past, but today's environmental awareness requires much stricter effluent standards to be achieved. This in turn should give sufficient incentives, together with the possible large cost savings, to increase the R&D activities in this field. There are certainly significant knowledge gaps to be filled and substantial benefits could be gained from this. A range of knowledge gaps are identified in this paper, extending from the role of intermediates in nutrient removal over parameter estimation in modelling and simulation to understanding the microbial metabolic pathways at a genetic and enzymatic level. These gaps are opportunities and challenges for all researchers and professionals in this field. Addressing them will help substantially in the continuing development of wastewater treatment technologies. The complexity of biological wastewater treatment processes requires a broad range of tools and expertise to address the knowledge gaps. Novel process analysis tools are critically important to investigate biological treatment processes in future. They will come from different expertise areas and will need to be used in close integration to gain maximal benefits from the efforts. These tools will likely include respirometry, novel chemical analyses, microsensors, gene-based identification, microbial physiology techniques and integrated modelling and simulation. Examples of the application of such techniques are provided to demonstrate the way these techniques may be used in future. In the next few years, there is likely an exciting and highly interactive period of research and development for the wastewater industry. [ABSTRACT FROM AUTHOR]

Abstract: Hydrogen sulfide generation is a major issue in sewer management. A novel method based on electrochemical sulfide oxidation was recently shown to be highly effective for sulfide removal from synthetic and real sewage. Here, we compare the performance of five different mixed metal oxide (MMO) coated titanium electrode materials for the electrochemical removal of sulfide from domestic wastewater. All electrode materials performed similarly in terms of sulfide removal, removing 78±5%, 77±1%, 85±4%, 84±1%, and 83±2% at a current density of 10mA/cm2 using Ta/Ir, Ru/Ir, Pt/Ir, SnO2 and PbO2, respectively. Elevated chloride concentrations, often observed in coastal areas, did not entail any significant difference in performance. Independent of the electrode material used, sulfide oxidation by in situ generated oxygen was the predominant reaction mechanism. Passivation of the electrode surface by deposition of elemental sulfur did not occur. However, scaling was observed in the cathode compartment. This study shows that all the MMO coated titanium electrode materials studied are suitable anodic materials for sulfide removal from wastewater. Ta/Ir and Pt/Ir coated titanium electrodes seem the most suitable electrodes since they possess the lowest overpotential for oxygen evolution, are stable at low chloride concentration and are already used in full scale applications. [Copyright &y& Elsevier]

Nitrospira and Nitrobacter are nitrite-oxidising bacteria commonly identified in nitrogen removal wastewater treatment plants. Little is known about the growth parameters of Nitrospira or the effects of environmental conditions or inhibitory compounds on Nitrospira activity. These bacterial properties were investigated using an enriched Nitrospira culture and an enriched Nitrobacter culture or Nitrobacter literature values. Compared to Nitrobacter, Nitrospira was found to have a comparable optimal pH range (8.0–8.3); similar normalised activity–temperature relationship (0.44e0.055(T–15)) for temperatures between 15 and 30°C and a similar oxygen half-saturation constant, K O (0.54±0.14mgL−1). The major differences identified were that Nitrospira had a lower nitrite half-saturation constant, K S (0.9±0.07mgNO2-NL−1); lower inhibition threshold concentrations for free ammonia (between 0.04 and 0.08mgNH3-NL−1) and free nitrous acid (less than 0.03mgHNO2-NL−1) and a higher yield (0.15±0.04gVSSg N−1). Therefore, Nitrospira is more likely to dominate nitrite oxidation under conditions with low ammonium and nitrite concentrations, which would provide an advantage to them due to their lower K S value while avoiding any free ammonia or free nitrous acid inhibition. [Copyright &y& Elsevier]

• Electrochemical Fe-dosing decreases TSS, COD, dissolved S2−, and P concentrations. • Electrochemical Fe-dosing also decreases H 2 S and CO 2 contents in biogas. • Electrochemical Fe-dosing can mitigate organic fouling of membrane filtration. • The in-situ electrochemical Fe-dosing can generate more benefits than the ex-situ. • Electrochemically generated iron is cost-effective compared to use of iron chemicals. Although iron salts such as iron(III) chloride (FeCl 3) have widespread application in wastewater treatment, safety concerns limit their use, due to the corrosive nature of concentrated solutions. This study demonstrates that local, electrochemical generation of iron is a viable alternative to the use of iron salts. Three laboratory systems with anaerobic membrane processes were set up to treat real wastewater; two systems used the production of either in-situ or ex-situ electrochemical iron (as Fe2+ and Fe2+(Fe3+) 2 O 4 , respectively), while the other system served as a control. These systems were operated for over one year to assess the impact of electrochemically produced iron on system performance. The results showed that dosing of electrochemical iron significantly reduced sulfide concentration in effluent and hydrogen sulfide content in biogas, and mitigated organics-based membrane fouling, all of which are critical issues inherently related to sustainability of anaerobic wastewater treatment. The electrochemical iron strategy can generate multiple benefits for wastewater management including increased removal efficiencies for total and volatile suspended solids, chemical oxygen demand and phosphorus. The rate of methane production also increased with electrochemically produced iron. Economic analysis revealed the viability of electrochemical iron with total cost reduced by one quarter to a third compared with using FeCl 3. These benefits indicate that electrochemical iron dosing can greatly enhance the overall operation and performance of anaerobic membrane processes, and this particularly facilitates wastewater management in a decentralized scenario. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: To better understand granule growth and breakage processes in aerobic granular sludge systems, the particle size of aerobic granules was tracked over 50 days of wastewater treatment within four sequencing batch reactors fed with abattoir wastewater. These experiments tested a novel hypothesis stating that granules equilibrate to a certain stable granule size (the critical size) which is determined by the influence of process conditions on the relative rates of granule growth and granule breakage or attrition. For granules that are larger than the critical size, granule breakage and attrition outweighs granule growth, and causes an overall reduction in granule size. For granules at the critical size, the overall growth and size reduction processes are balanced, and granule size is stable. For granules that are smaller than the critical size, granule growth outweighs granule breakage and attrition, and causes an overall increase in granule size. The experimental reactors were seeded with mature granules that were either small, medium, or large sized, these having respective median granule sizes of 425 μm, 900 μm and 1125 μm. An additional reactor was seeded with a mixture of the sized granules to represent the original source of the granular sludge. The experimental results were analysed together with results of a previous granule formation study that used mixed seeding of granules and floccular sludge. The analysis supported the critical size hypothesis and showed that granules in the reactors did equilibrate towards a common critical size of around 600–800 μm. Accordingly, it is expected that aerobic granular reactors at steady-state operation are likely to have granule size distributions around a characteristic critical size. Additionally, the results support that maintaining a quantity of granules above a particular size is important for granule formation during start-up and for process stability of aerobic granule systems. Hence, biomass washout needs to be carefully managed to optimize granule formation during the reactor start-up. [Copyright &y& Elsevier]

Abstract: Chemical phosphorus (P) removal during aerobic wastewater treatment induced by iron salt addition in sewer systems for sulfide control is investigated. Aerobic batch tests with activated sludge fed with wastewater containing iron sulfide precipitates showed that iron sulfide was rapidly reoxidised in aerobic conditions, resulting in phosphate precipitation. The amount of P removed was proportional to the amount of iron salts added, and for the sludge used, ratios of 0.44 and 0.37 mgP/mgFe were obtained for ferric and ferrous dosages, respectively. The hydraulic retention time (HRT) of iron sulfide in sewers was found to have a crucial impact on the settling of iron sulfide precipitates during primary settling, with a shorter HRT resulting in a higher concentration of iron sulfide in the primary effluent and thus enabling higher P removal. A mathematical model was developed to describe iron sulfide oxidation in aerated activated sludge and the subsequent iron phosphate precipitation. The model was used to optimise FeCl3 dosing in a real wastewater collection and treatment system. Simulation studies revealed that, by moving FeCl3 dosing from the WWTP, which is the current practice, to a sewer location upstream of the plant, both sulfide control and phosphate removal could be achieved with the current ferric salt consumption. This work highlights the importance of integrated management of sewer networks and wastewater treatment plants. [Copyright &y& Elsevier]

Abstract: Methane formation and emission in sewer systems has not received as much attention as hydrogen sulphide formation. Through field measurements from two rising mains, with an average sewage temperature of 28.4 and 26.6°C, respectively, at the time of sampling, this study shows that a significant amount of methane can be produced in sewer systems, and that this production is positively correlated with the hydraulic retention time of wastewater in these systems. The experimental results from a laboratory-scale sewer system fed with real sewage with a temperature of approximately 21°C confirmed these field observations and further revealed that methanogenesis and sulphate reduction occur simultaneously in sewers, with methane production contributing considerably more to the loss of soluble COD in sewers than sulphate reduction. The production of methane in sewers at levels revealed by this study is a serious environmental concern as it potentially results in greenhouse emissions that is comparable to that caused by the energy consumption for the treatment of the same wastewater. Further, methane production in sewers influences sulphide production and its management due to the competition between methanogens and sulphate-reducing bacteria for potentially the same electron donors. The potential interactions between sulphate-reducing and methanogenic bacteria in sewer networks are discussed. [Copyright &y& Elsevier]

• First real wastewater demonstration for n-DAMO processes. • High nitrogen removal achieved in both mainstream and sidestream treatment. • Methane-based MBfR coupling anammox with n-DAMO is versatile and robust. • Substantial roles of n-DAMO being confirmed by batch tests and microbial analysis. Nitrite/nitrate-dependent anaerobic methane oxidation (n-DAMO) processes have been proven effective for nitrogen removal from synthetic wastewater. However, the demonstration using real wastewater has not been achieved yet. To this end, this study investigated the versatile applications of n-DAMO process in real wastewater treatment for the first time. Two methane-based membrane biofilm reactors (MBfRs) were employed to combine anammox and n-DAMO microorganisms, targeting nitrogen removal in mainstream (i.e., domestic sewage) and sidestream (i.e., anaerobic digestion liquor), respectively. Considering various technologies in sewage treatment, three different technical routes, including nitritation + methane-based MBfR, partial nitritation + methane-based MBfR and partial nitritation + anammox + methane-based MBfR, were investigated comprehensively, all producing effluent quality with total nitrogen (TN) at 5 mg N/L or less. Regarding the sidestream treatment, the methane-based MBfR also removed up to 96% TN from the partially nitrified anaerobic digestion liquor at a practically useful rate of 0.5 kg N/m3/d. Microbial communities revealed by 16S rRNA gene amplicon sequencing indicated the dominance of n-DAMO archaea in both reactors, along with the existence of anammox bacteria and n-DAMO bacteria. As the first demonstration of n-DAMO process in real wastewater, this study comprehensively confirmed the applicability of using methane as carbon source to remove nitrogen from both mainstream and sidestream wastewater, supporting their adoption by industries in practice. [Display omitted] [ABSTRACT FROM AUTHOR]

The use of coagulants and flocculants in the water and wastewater industry is predicted to increase further in the coming years. Alum is the most widely used coagulant, however, the use of ferric chloride (FeCl 3) is gaining popularity. Drinking water production that uses FeCl 3 as coagulant produces waste sludge rich in iron. We hypothesised that the iron-rich drinking water sludge (DWS) can potentially be used in the urban wastewater system to reduce dissolved sulfide in sewer systems, aid phosphate removal in wastewater treatment and reduce hydrogen sulfide in the anaerobic digester biogas. This hypothesis was investigated using two laboratory-scale urban wastewater systems, one as an experimental system and the other as a control, each comprising sewer reactors, a sequencing batch reactor (SBR) for wastewater treatment, sludge thickeners and anaerobic digestion reactors. Both were fed with domestic wastewater. The experimental system received in-sewer DWS-dosing at 10 mgFe L−1 while the control had none. The sulfide concentration in the experimental sewer effluent decreased by 3.5 ± 0.2 mgS L−1 as compared with the control, while the phosphate concentration decreased by 3.6 ± 0.3 mgP L−1 after biological wastewater treatment in the experimental SBR. The dissolved sulfide concentration in the experimental anaerobic digester also decreased by 15.9 ± 0.9 mgS L−1 following the DWS-dosing to the sewer reactors. The DWS-doing also enhanced the settleability of the mixed liquor suspended sludge (MLSS) (SVI decreased from 193.2 ± 22.2 to 108.0 ± 7.7 ml g−1), and the dewaterability of the anaerobically digested sludge (the cake solids concentration increased from 15.7 ± 0.3% to 19.1 ± 1.8%). The introduction of DWS into the experimental system significantly increased the COD and TSS concentrations in the wastewater, and consequently the MLSS concentration in the SBR, however, this did not affect normal operation. The results demonstrated that iron-rich waste sludge from drinking water production can be used in the urban wastewater system achieving multiple benefits. Therefore, an integrated approach to urban water and wastewater management should be considered to maximise the benefits of iron use in the system. Image 1 • Fe-rich DWS dosed to sewers effectively decreases dissolved sulfides in sewers. • Fe-rich DWS dosed to sewers aids in P removal during wastewater treatment. • Fe-rich DWS dosed to sewers decreases sulfides in the AD sludge. • Fe-rich DWS dosed to sewers improves settleability and dewaterability of sludge. • Fe-rich DWS-dosing elevates MLSS in the WWTP. [ABSTRACT FROM AUTHOR]

Free nitrous acid (FNA), the protonated form of nitrite, has historically been an unwanted substance in wastewater systems due to its inhibition on a wide range of microorganisms. However, in recent years, advanced understanding of FNA inhibitory and biocidal effects on microorganisms has led to the development of a series of FNA-based applications that improve wastewater management practices. FNA has been used in sewer systems to control sewer corrosion and odor; in wastewater treatment to achieve carbon and energy efficient nitrogen removal; in sludge management to improve the sludge reduction and energy recovery; in membrane systems to address membrane fouling; and in wastewater algae systems to facilitate algae harvesting. This paper aims to comprehensively and critically review the current status of FNA-based applications in improving wastewater management. The underlying mechanisms of FNA inhibitory and biocidal effects are also reviewed and discussed. Knowledge gaps and current limitations of the FNA-based applications are identified; and perspectives on the development of FNA-based applications are discussed. We conclude that the FNA-based technologies have great potential for enhancing the performance of wastewater systems; however, further development and demonstration at larger scales are still required for their wider applications. Image 1 • Underlying mechanisms of FNA inhibitory and biocidal effects are reviewed. • FNA is used to control sewer corrosion and odor, and membrane fouling. • FNA improves wastewater treatment, sludge management and algae harvesting. • Knowledge gaps and current limitations of the FNA-based applications are identified. • Perspectives on the development of FNA-based applications are discussed. [ABSTRACT FROM AUTHOR]