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Ca. Accumulibacter was the predominant microorganism (relative FISH bio-abundance of 67 ± 5%) in a lab-scale sequential batch reactor that accomplished enhanced biological phosphorus removal (EBPR) while using glucose and acetate as the carbon sources (1:1 COD-based ratio). Both organic compounds were completely anaerobically consumed. The reactor's performance in terms of P/C ratio, phosphorous release and uptake, and overall kinetic and stoichiometric parameters were on the high end of the reported spectrum for EBPR systems (100:9.3 net mg phosphate removal per mg COD consumed when using glucose and acetate in a 1:1 ratio). The batch tests showed that, to the best of our knowledge, this is the first time a reactor enriched with Ca. Accumulibacter can putatively utilize glucose as the sole carbon source to biologically remove phosphate (COD:P (mg/mg) removal ratio of 100:6.3 when using only glucose). Thus, this research proposes that Ca. Accumulibacter directly anaerobically stored the fed glucose primarily as glycogen by utilizing the ATP provided via the hydrolysis of poly-P and secondarily as PHA by balancing its ATP utilization (glycogen generation) and formation (PHA storage). Alternative hypotheses are also discussed. The reported findings could challenge the conventional theories of glucose assimilation by Ca. Accumulibacter, and can be of significance for the biological removal of phosphorus from wastewaters with high contents of fermentable compounds or low VFAs.

Various business models for fecal sludge emptying and transport have been developed to address challenges and their advantages have been documented; however, their evaluation has not been investigated. This study developed an evaluation framework, which was tested in informal settlements in Kampala for sustainable business models of fecal sludge emptying and transport. Through key informant interviews and stakeholder consultations, service delivery challenges from informal settlements in Kampala were identified and included in the framework, which were: high cost of emptying services, spillages, access to facilities, high operational costs and social stigma. The evaluation framework adopted six service criteria: Financial, Institutional, Environmental, Technological, Social and Scalability; these were further defined by fifteen service sub-criteria. The criteria were tested separately on eight business models—for mechanized (cesspool) and semi-mechanized (gulper) technologies. The key output of the evaluation framework (business model scorecard) revealed that two models (scheduled desludging and call center) for cesspool technology and three models (mobile transfer stations, scheduled desludging and call center) for gulper technology have high potential for service improvement in informal settlements. Scheduled desludging and mobile transfer stations can effectively optimize emptying services and subsequently reduce emptying charges, whereas the call center is critical for bridging service delivery.

The aerobic granular sludge (AGS) process is an effective wastewater treatment technology for organic matter and nutrient removal that has been introduced in the market rapidly. Until now, limited information is available on AGS regarding the removal of bacterial and viral pathogenic organisms present in sewage. This study focussed on determining the relation between reactor operational conditions (plug flow feeding, turbulent aeration and settling) and physical and biological mechanisms on removing two faecal surrogates, Escherichia coli and MS2 bacteriophages. Two AGS laboratory-scale systems were separately fed with influent spiked with 1.0 × 106 CFU/100 mL of E. coli and 1.3 × 108 PFU/100 mL of MS2 bacteriophages and followed during the different operational phases. The reactors contained only granular sludge and no flocculent sludge. Both systems showed reductions in the liquid phase of 0.3 Log10 during anaerobic feeding caused by a dilution factor and attachment of the organisms on the granules. Higher removal efficiencies were achieved during aeration, approximately 1 Log10 for E. coli and 0.6 Log10 for the MS2 bacteriophages caused mainly by predation. The 18S sequencing analysis revealed high operational taxonomic units (OTUs) of free-living protozoa genera Rhogostoma and Telotrochidium concerning the whole eukaryotic community. Attached ciliates propagated after the addition of the E. coli, an active contribution of the genera Epistylis, Vorticella, and Pseudovorticella was found when the reactor reached stability. In contrast, no significant growth of predators occurred when spiking the system with MS2 bacteriophages, indicating a low contribution of protozoa on the phage removal. Settling did not contribute to the removal of the studied bacterial and viral surrogates. M.L. Barrios-Hernández acknowledges the Technological Institute of Costa Rica for providing the fellowship (Grant Number 007-2014-M) to pursue her PhD programme (2016-2020) at IHE-Delft, the Netherlands. K. Mora-Cabrera acknowledges the Generalitat Valenciana (GRISOLIAP/2017/173) and the European Social Funds (BEFPI/2019/065) for their financial support.

In this study, the impact of applied solids retention time (SRT) on the biological performance of an anaerobic membrane bioreactor (AnMBR) treating synthetic dairy wastewater with high lipid content was assessed. Two side-stream AnMBR systems were operated at an SRT of 20 and 40 days (R20 and R40, respectively), equipped with an inside-out tubular membrane operated in cross-flow mode under full-scale operational conditions, i.e. crossflow velocity, transmembrane pressure, membrane flux. Successful operation was achieved and removal efficiencies of both reactors were up to 99% applying an organic loading rate (OLR) of 4.7 g COD L−1 d−1. No precipitation of lipids was observed throughout the operational period, keeping the lipids available for the anaerobic degradation. Long chain fatty acid (LCFA) accumulation was very modest and amounted 148 and 115 mg LCFA-COD per gram of volatile suspended solids (VSS) for R20 and R40, respectively. At an SRT of 40 days, a slightly better biological conversion was obtained. Periodically performed specific methanogenic activity (SMA) tests showed stabilization of the SMA for R40 sludge, whereas for R20 sludge the SMA continued to decrease. This study revealed a more stable reactor performance operating the AnMBR at an SRT of 40 days compared to 20 days.

A majority of the world's population use onsite sanitation systems, which store or treat excreta close to where it is generated. Sludge from these systems needs to be managed through a series of stages, known as the sanitation value chain. There is a huge diversity of service providers, not only within each part of the chain, but also along the chain bridging the different components. These service providers are linked not only by the flow of materials, but also by the transfer of money. Therefore for this system to be considered financially sustainable all services from the toilet to reuse or disposal need to be considered. A tool has been developed (eSOSView™) to simulate, evaluate, and optimise the financial flows along and within the sanitation value chain. In this paper eSOSView™ was tested, validated (using existing data), and piloted (including data collection). This paper demonstrates how eSOSView ™ can be used to evaluate different financial flow models, to assess financial sustainability in different parts of the sanitation value chain and optimise the financial sustainability along the sanitation value chain.

Photo-activated sludge (PAS) systems are an emerging wastewater treatment technology where microalgae provide oxygen to bacteria without the need for external aeration. There is limited knowledge on the optimal conditions for enhanced biological phosphorus removal (EBPR) in systems containing a mixture of polyphosphate accumulating organisms (PAOs) and microalgae. This research aimed to study the effects of substrate composition and light intensity on the performance of a laboratory-scale EBPR-PAS system. Initially, a model-based design was developed to study the effect of organic carbon (COD), inorganic carbon (HCO3) and ammonium-nitrogen (NH4-N) in nitrification deprived conditions on phosphorus (P) removal. Based on the mathematical model, two different synthetic wastewater compositions (COD:HCO3:NH4-N: 10:20:1 and 10:10:4) were examined at a light intensity of 350 µmol m−2 sec−1. Add to this, the performance of the system was also investigated at light intensities: 87.5, 175, and 262.5 µmol m−2 sec−1 for short terms. Results showed that wastewater having a high level of HCO3 and low level of NH4-N (ratio of 10:20:1) favored only microalgal growth, and had poor P removal due to a shortage of NH4-N for PAOs growth. However, lowering the HCO3 level and increasing the NH4-N level (ratio of 10:10:4) balanced PAOs and microalgae symbiosis, and had a positive influence on P removal. Under this mode of operation, the system was able to operate without external aeration and achieved a net P removal of 10.33 ±1.45 mg L−1 at an influent COD of 100 mg L−1. No significant variation was observed in the reactor performance for different light intensities, indicating the EBPR-PAS system can be operated at low light intensities with a positive influence on P removal.

An eSOS (emergency Sanitation Operation System) Smart Toilet experimental prototype, aimed at improving the provision of safe sanitation in emergency settings, was field tested in a temporary settlement in Tacloban City, Philippines. The design, usage, and user acceptance of the toilet were all evaluated. Quantitative and qualitative data were collected through interviews and questionnaires, supported by the research-team's observations. The survey results indicated that 98% of users (both first-time users and those who tried it a few times) intended to use the toilet again. There were more features that the users liked than disliked. The in-built water supply and user-operated smart toilet features were liked, but the bad smell was disliked. User-operated smart features were an important factor in user acceptance although they were not the main incentives. Key recommendations are to improve the toilet's design to address the odor and cleanliness issues, make handwashing more convenient, and lower the height of the toilet bowl.

Populations of “Candidatus Accumulibacter”, a known polyphosphate-accumulating organism, within clade IC have been proposed to perform anoxic P-uptake activity in enhanced biological phosphorus removal (EBPR) systems using nitrate as electron acceptor. However, no consensus has been reached on the ability of “Ca. Accumulibacter” members of clade IC to reduce nitrate to nitrite. Discrepancies might relate to the diverse operational conditions which could trigger the expression of the Nap and/or Nar enzyme and/or to the accuracy in clade classification. This study aimed to assess whether and how certain operational conditions could lead to the enrichment and enhance the denitrification capacity of “Ca. Accumulibacter” within clade IC. To study the potential induction of the denitrifying enzyme, an EBPR culture was enriched under anaerobic–anoxic–oxic (A2O) conditions that, based on fluorescence in situ hybridization and ppk gene sequencing, was composed of around 97% (on a biovolume basis) of affiliates of “Ca. Accumulibacter” clade IC. The influence of the medium composition, sludge retention time (SRT), polyphosphate content of the biomass (poly-P), nitrate dosing approach, and minimal aerobic SRT on potential nitrate reduction were studied. Despite the different studied conditions applied, only a negligible anoxic P-uptake rate was observed, equivalent to maximum 13% of the aerobic P-uptake rate. An increase in the anoxic SRT at the expenses of the aerobic SRT resulted in deterioration of P-removal with limited aerobic P-uptake and insufficient acetate uptake in the anaerobic phase. A near-complete genome (completeness = 100%, contamination = 0.187%) was extracted from the metagenome of the EBPR biomass for the here-proposed “Ca. Accumulibacter delftensis” clade IC. According to full-genome-based phylogenetic analysis, this lineage was distant from the canonical “Ca. Accumulibacter phosphatis”, with closest neighbor “Ca. Accumulibacter sp. UW-LDO-IC” within clade IC. This was cross-validated with taxonomic classification of the ppk1 gene sequences. The genome-centric metagenomic analysis highlighted the presence of genes for assimilatory nitrate reductase (nas) and periplasmic nitrate reductase (nap) but no gene for respiratory nitrate reductases (nar). This suggests that “Ca. Accumulibacter delftensis” clade IC was not capable to generate the required energy (ATP) from nitrate under strict anaerobic-anoxic conditions to support an anoxic EBPR metabolism. Definitely, this study stresses the incongruence in denitrification abilities of “Ca. Accumulibacter” clades and reflects the true intra-clade diversity, which requires a thorough investigation within this lineage.

Emergency sanitation technologies make up some of the most significant gaps in the water, sanitation and hygiene sector. Major initiatives to address identified gaps may be characterised as donor-funded, top-down processes driven by international or European-based non-governmental organisations. However, local organisations also innovate. To better understand how local organisations innovate for emergency sanitation, the paper presents a case study of an Indonesian NGO who had developed a toilet for use in emergencies. The NGO developed the toilet by modifying an existing non-emergency toilet. The process was unstructured and informal. When testing ideas, for instance, the NGO used their own methods rather than referring to testing protocols recognised by the industry. The NGO surveyed end users, but the respondents did not come from post-disaster settings. Compared to designs developed through international initiatives, the NGO's design deviated somewhat from internationally recognised standards, for instance, the size of the latrine slab. The paper also discusses differences between the way local and international organisations develop emergency sanitation products. Each approach has advantages and disadvantages in terms of methodology and access to resources and expertise. Therefore, there are potential benefits to the different organisations working more closely.

Activated sludge systems have been applied for 100 years now. Over the course of the years, researchers have developed various models to describe activated sludge processes. The main aim has been to gain a better understanding of the conditions that favour the conversions of carbon, nitrogen and phosphorus present in wastewater, and associated oxygen consumption and sludge production. The current paper presents a reflection on the historical developments, state-of-the-art of activated sludge modelling and future trends. Over the years, many wastewater research groups have benefitted greatly from the development of activated sludge models (ASMs). On one hand, modelling has been expanded through the development of novel theoretical concepts and their application in new fields. On the other hand, models have been used for practical projects. Although, scientists are still searching for the ideal model, one can say that ASMs are developed to the extent that they can be applied in practice with confidence. New developments are expected to be seen regarding plant-wide modelling, integration with other models at the (urban) system level, organizational and computational infrastructure, and interface and communication with various stakeholders and users.

The aim of this study was to evaluate the effectiveness of the novel aerobic granular sludge (AGS) wastewater treatment technology in removing faecal indicator organisms (FIOs) compared to the conventional activated sludge (CAS) treatment system. The work was carried out at two full-scale wastewater treatment plants (WWTP) in the Netherlands, Vroomshoop and Garmerwolde. Both treatment plants have a CAS and AGS system operated in parallel. The parallel treatment lines are provided with the same influent wastewater. The concentrations of the measured FIOs in the influent of the two WWTPs were comparable with reported literature values as follows: F-specific RNA bacteriophages at 106 PFU/100 mL, and Escherichia coli (E. coli), Enterococci, and Thermotolerant coliforms (TtC) at 105 to 106 CFU/100 mL. Although both systems (CAS and AGS) are different in terms of design, operation, and microbial community, both systems showed similar FIOs removal efficiency. At the Vroomshoop WWTP, Log10 removals for F-specific RNA bacteriophages of 1.4 ± 0.5 and 1.3 ± 0.6 were obtained for the AGS and CAS systems, while at the Garmerwolde WWTP, Log10 removals for F-specific RNA bacteriophages of 1.9 ± 0.7 and 2.1 ± 0.7 were found for the AGS and CAS systems. Correspondingly, E. coli, Enterococci, and TtC Log10 removals of 1.7 ± 0.7 and 1.1 ± 0.7 were achieved for the AGS and CAS systems at Vroomshoop WWTP. For Garmerwolde WWTP Log10 removals of 2.3 ± 0.8 and 1.9 ± 0.7 for the AGS and CAS systems were found, respectively. The measured difference in removal rates between the plants was not significant. Physicochemical water quality parameters, such as the concentrations of organic matter, nutrients, and total suspended solids (TSS) were also determined. Overall, it was not possible to establish a direct correlation between the physicochemical parameters and the removal of FIOs for any of the treatment systems (CAS and AGS). Only the removal of TSS could be positively correlated to the E. coli removal for the AGS technology at the evaluated WWTPs., Graphical abstract Image 1, Highlights • No difference in removal efficiencies (α = 5%) of FIOs was found for the studied AGS and CAS systems. • 1.3 to 2.1 Log10 removals for F-specific RNA bacteriophages were found for the CAS and AGS systems. • 1.1 to 2.3 Log10 removals for E. coli, Enterococci, and TtC were obtained for the AGS and CAS systems. • The two stage CAS performed better than the carrousel CAS in removing F-specific RNA bacteriophages. • A positive correlation was found between the TSS and E. coli removal, and COD and TtC removal in the AGS systems.

The direct use of seawater as secondary quality water for toilet flushing can function as a free unlimited magnesium source for phosphorus recovery from urine through chemical precipitation. This research assessed the precipitation of phosphorus present in urine in the form of struvite as a result of mixing with seawater. Taking into account the different feces and urine collection systems available, seawater was mixed with (a) non-hydrolyzed urine to mimic water-flush urinals and (b) hydrolyzed urine to mimic water-free urinals. Different seawater-to-urine mixing ratios were analyzed taking into account the water volume commonly used by conventional toilets, urinals and urine-diverting toilets. Up to 99% phosphorus removal was observed at seawater-to-urine ratios below 3.3:1.0 (as the ones reached by water-less and water-saving urinals). Above this ratio the hydrolysis process in non-hydrolyzed urine is inhibited. Phosphorus removal occurred through the formation and precipitation of struvite; less struvite crystals were observed at Ca/PO4-P ratios higher than 0.8. Seawater can be used as a source of ions for phosphorus recovery from urine; water-free urinals, diverting toilets and water-flush urinals operating with seawater-to-urine ratio lower than 3.3:1.0 (like water-saving systems) can provide better conditions for phosphate precipitation using seawater as magnesium source.

The overall performance of the Anjana wastewater treatment plant (WWTP) located in Surat, India, was assessed by coupling the Activated Sludge Model No. 3 (ASM3) and the Anaerobic Digestion Model No. 1 (ADM1). Guidelines developed by the Dutch Foundation for Applied Water Research (STOWA) were successfully applied for the determination of wastewater characteristics. Concerning the fractionation of primary and secondary sludge, the approach proved to be adequate for the application of ADM1. A satisfactory description of the performance of the plant was obtained in terms of effluent quality, biogas generation and sludge production. This was achieved through coupling ASM3 with ADM1 and adjusting four default values (the growth of autotrophic bacteria from 1 to 0.46 day−1, influent fraction of unbiodegradable particulate chemical oxygen demand (COD) to 0.14 gCOD/gCOD, and the anaerobic disintegration factors for soluble and particulate unbiodegradable COD in ADM1 to 0.01 and 0.29 gCOD/gCOD, respectively). The model was applied to optimise the plant performance and to assess the potential influence of the return of high strength reject effluents through the implementation of an ADM1-ASM3 interface. This study underlines the feasibility, advantages and benefits of mathematical modelling as a reliable tool for process optimisation, plant upgrade and resource recovery in developing countries.

Although simultaneous P-removal and nitrate reduction has been observed in laboratory studies as well as full-scale plants, there are contradictory reports on the ability of PAO I to efficiently use nitrate as electron acceptor. Such discrepancy could be due to other microbial groups performing partial denitrification from nitrate to nitrite. The denitrification capacities of two different cultures, a highly enriched PAO I and a PAO I-GAO cultures were assessed through batch activity tests conducted before and after acclimatization to nitrate. Negligible anoxic phosphate uptake coupled with a reduction of nitrate was observed in the highly enriched PAO I culture. On the opposite, the PAO I-GAO culture showed a higher anoxic phosphate uptake activity. Both cultures exhibited good anoxic phosphate uptake activity with nitrite (8.7 ± 0.3 and 9.6 ± 1.8 mgPO4-P/gVSS.h in the PAO I and PAO I-GAO cultures, respectively). These findings suggest that other microbial populations, such as GAOs, were responsible to reduce nitrate to nitrite in this EBPR system, and that PAO I used the nitrite generated for anoxic phosphate uptake. Moreover, the simultaneous denitrification and phosphate removal process using nitrite as electron acceptor may be a more sustainable process as can: i) reduce the carbon consumption, ii) reduce oxygen demand of WWTP, and iii) due to a lower growth yield contribute to a lower sludge production.

Phosphate accumulating organisms (PAO) are assumed to use nitrate as external electron acceptor, allowing an efficient integration of simultaneous nitrogen and phosphate removal with minimal organic carbon (COD) requirements. However, contradicting findings appear in literature regarding the denitrification capacities of PAO due to the lack of clade specific highly enriched PAO cultures. Whereas some studies suggest that only PAO clade I may be capable of using nitrate as external electron acceptor for anoxic P-uptake, other studies indicate that PAO clade II may be responsible for anoxic P-removal. In the present study, a highly enriched PAO clade IC culture (>99% according to FISH) was cultivated in an SBR operated under Anaerobic/Oxic conditions and subsequently exposed to Anaerobic/Anoxic/Oxic conditions using nitrate as electron acceptor. Before and after acclimatization to the presence of nitrate, the aerobic and anoxic (nitrate and nitrite) activities of the PAO I culture were assessed through the execution of batch tests using either acetate or propionate as electron donor. In the presence of nitrate, significant P-uptake by PAO I was not observed before or after acclimatization. Using nitrite as electron acceptor, limited nitrite removal rates were observed before acclimatization with lower rates in the acetate fed reactor without P-uptake and slightly higher in the propionate fed reactor with a marginal anoxic P-uptake. Only after acclimatization to nitrate, simultaneous P and nitrite removal was observed. This study suggests that PAO clade IC is not capable of using nitrate as external electron acceptor for anoxic P-removal. The elucidation of the metabolic capacities for individual PAO clades helps in better understanding and optimization of the relation between microbial ecology and process performance in enhanced biological phosphate removal processes.

The influence of different carbon sources (acetate to propionate ratios), temperature and pH levels on the competition between polyphosphate- and glycogen-accumulating organisms (PAO and GAO, respectively) was evaluated using a metabolic model that incorporated the carbon source, temperature and pH dependences of these microorganisms. The model satisfactorily described the bacterial activity of PAO (Accumulibacter) and GAO (Competibacter and Alphaproteobacteria-GAO) laboratory-enriched cultures cultivated on propionate (HPr) and acetate (HAc) at standard conditions (20 degrees C and pH 7.0). Using the calibrated model, the effects of different influent HAc to HPr ratios (100-0, 75-25, 50-50 and 0-100%), temperatures (10, 20 and 30 degrees C) and pH levels (6.0, 7.0 and 7.5) on the competition among Accumulibacter, Competibacter and Alphaproteobacteria-GAO were evaluated. The main aim was to assess which conditions were favorable for the existence of PAO and, therefore, beneficial for the biological phosphorus removal process in sewage treatment plants. At low temperature (10 degrees C), PAO were the dominant microorganisms regardless of the used influent carbon source or pH. At moderate temperature (20 degrees C), PAO dominated the competition when HAc and HPr were simultaneously supplied (75-25 and 50-50% HAc to HPr ratios). However, the use of either HAc or HPr as sole carbon source at 20 degrees C was not favorable for PAO unless a high pH was used (7.5). Meanwhile, at higher temperature (30 degrees C), GAO tended to be the dominant microorganisms. Nevertheless, the combined presence of acetate and propionate in the influent (75-25 and 50-50% HAc to HPr ratios) as well as a high pH (7.5) appear to be potential factors to favor the metabolism of PAO over GAO at higher sewage temperature (30 degrees C).

The Activated Sludge Model No. 3 (ASM3) and Dutch calibration guidelines (STOWA) were evaluated in the modelling of an activated sludge system treating effluents from a large oil refinery. The plant was designed to remove suspended solids, organic matter and nitrogen from wastewater at an average water temperature of 34 degrees C. The plant consists of three tanks in series; the first two tanks operate in on-off aeration mode with pure oxygen for N-removal, whilst extra methanol is added for the denitrification, and the third tank is maintained as constantly aerobic. Calibration was performed based on a simplified influent characterisation and extra batch experiments (nitrification and denitrification). With the adjustment of only four parameters the model proved capable of describing the performance of the plant concerning both the liquid phase and the biomass. The model was further used to analyse possible modifications in the plant layout and optimize operational conditions in order to reduce operating costs. Modelling results indicated reduction in methanol dosage by implementing an idle time between aerobic and anoxic phases. In this way, surplus methanol was prevented from entering during the aerobic period. Moreover, simulations showed that the most cost-effective option regarding the denitrification process was a combined pre-post-denitrification scheme, without the need for enlarging existing basins. It can be concluded that although ASM3 and STOWA guidelines were originally developed for domestic wastewater application at a temperature range of 10 to 20 degrees C, they proved well capable of describing the performance of an oil refinery wastewater treatment plant operating at 34 degrees C. Moreover, the plant model proved useful for optimization of the plant performance regarding operational costs.

The anaerobic acetate (HAc) uptake stoichiometry of phosphorus-accumulating organisms (PAO) in enhanced biological phosphorus removal (EBPR) systems has been an extensive subject of study due to the highly variable reported stoichiometric values (e.g. anaerobic P-release/HAc-uptake ratios ranging from 0.01 up to 0.93 P-mol/C-mol). Often, such differences have been explained by the different applied operating conditions (e.g. pH) or occurrence of glycogen-accumulating organisms (GAO). The present study investigated the ability of biomass highly enriched with specific PAO clades (‘Candidatus Accumulibacter phosphatis’ Clade I and II, hereafter PAO I and PAO II) to adopt a GAO metabolism. Based on long-term experiments, when Poly-P is not stoichiometrically limiting for the anaerobic VFA uptake, PAO I performed the typical PAO metabolism (with a P/HAc ratio of 0.64 P-mol/C-mol); whereas PAO II performed a mixed PAO-GAO metabolism (showing a P/HAc ratio of 0.22 P-mol/C-mol). In short-term batch tests, both PAO I and II gradually shifted their metabolism to a GAO metabolism when the Poly-P content decreased, but the HAc-uptake rate of PAO I was 4 times lower than that of PAO II, indicating that PAO II has a strong competitive advantage over PAO I when Poly-P is stoichiometrically limiting the VFA uptake. Thus, metabolic flexibility of PAO clades as well as their intrinsic differences are additional factors leading to the controversial anaerobic stoichiometry and kinetic rates observed in previous studies. From a practical perspective, the dominant type of PAO prevailing in full-scale EBPR systems may affect the P-release processes for biological or combined biological and chemical P-removal and recovery and consequently the process performance.

To assess the feasibility of the Anammox process as a cost-effective post-treatment step for anaerobic sewage treatment, the simultaneous effects of organic carbon source, chemical oxygen demand (COD)/N ratio, and temperature on autotrophic nitrogen removal was studied. In batch experiments, three operating conditions were evaluated at 14, 22 and 30 °C, and at COD/N ratios of 2 and 6. For each operating condition, containing 32 ± 2 mg NH4+-N/L and 25 ± 2 mg NO2−-N/L, three different substrate combinations were tested to simulate the presence of readily biodegradable and slowly biodegradable organic matter (RBCOD and SBCOD, respectively): (i) acetate (RBCOD); (ii) starch (SBCOD); and (iii) acetate + starch. The observed stoichiometric NO2−-N/NH4+-N conversion ratios were in the range of 1.19–1.43, and the single or simultaneous presence of acetate and starch did not affect the Anammox metabolism. High Anammox nitrogen removal was observed at 22 °C (77–84%) and 30 °C (73–79%), whereas there was no nitrogen removal at 14 °C; the Anammox activity was strongly influenced by temperature, in spite of the COD source and COD/N ratios applied. These results suggest that the Anammox process could be applied as a nitrogen removal post-treatment for anaerobic sewage systems in warm climates.

In this study the following was evaluated: (a) application of a complex activated sludge model on a full-scale plant (Phostrip ® -like process), (b) influent and sludge characterization procedures for bio-P modeling, (c) the use of batch tests for model evaluation and (d) different alternative BPR process configurations (A/O, UCT and BCFS ® ). An integrated model for aerobic and denitrifying biological phosphorus removal (Delft bio-P model) replaced the module for P removal of ASM No. 2 and was combined with retained equations for COD and N conversion of the ASM No 2. This combined model proved well capable of describing the wastewater treatment plant (wwtp) Haarlem Waarderpolder with adjustment of only three (out of the sixty) default parameters. Some of batch tests were satisfactorily described by the model too. Batch tests proved as a useful tool for sludge characterization and model validation. The standard Dutch procedure for influent and sludge characterization proved satisfactory for the model construction. Modeling of alternative BPR process configuration showed that good P removal was achieved by all three alternative process configurations, by the latest one with comparatively lowest construction and operational costs (lower building costs and no acetate addition). Valuable experience from practical application of the model was obtained; study indicated where the model should be improved; the plant operation and treatment processes were better understood and plant performance was further optimized.

This paper describes the impact of long-term (weeks) temperature changes on stoichiometry and kinetics of the anaerobic and aerobic phases of the biological phosphorus removal process. Steady state conversion of relevant compounds for biological phosphorus removal was studied at 20, 30, 20, 10 and 5°C, following chronological order. Integrated in the process study, two methods (electron-microscopy and dry denaturing gradient gel electrophoresis) were applied to investigate the complexity of the bacterial community of biological phosphorus removing sludge cultivated at different temperatures. The coefficient for metabolic conversions obtained from long-term temperature tests was similar to the temperature coefficient observed in short-term (hours) tests ( θ =1.085 versus θ =1.078, respectively).Temperature had a moderate impact on the aerobic P-uptake process rate ( θ =1.031) during long-term tests. However, a strong temperature effect on other metabolic processes of the aerobic phase, such as polyhydroxyalkanoate consumption ( θ =1.163), oxygen uptake ( θ =1.090) and growth ( θ >1.110), was observed. Different temperature coefficients were obtained for the aerobic phase from long-term and short-term tests, probably due to a change in population structure. This change was also visible from molecular ecological studies. The different temperature coefficient found for P-uptake compared to the other metabolic processes of the aerobic phase underlines that, in complex processes such as BPR, it is dangerous to draw conclusions from easily observable parameters (like phosphate) only. Such consideration can easily lead to underestimation of the temperature dependency of other metabolic processes of the aerobic phase of BPR.

Glycogen plays an important role in biological phosphorus removal from wastewaters. Existing measurement techniques often overestimate the glycogen content of the biomass due to the presence of glucose and/or other carbohydrates than glycogen in the cell material. As an alternative to conventional methods a bioassay for glycogen determination in biological phosphorus removal systems was developed. The bioassay is based on the strict stoichiometric coupling between anaerobic acetate uptake and glycogen consumption. In other words, the glycogen concentration of the sludge was determined indirectly by measuring the maximal total acetate uptake by the activated sludge in anaerobic batch tests. The bioassay was successfully tested for the determination of glycogen content of the sludge taken from the lab-scale, acetate-fed, anaerobic-aerobic-settling sequencing batch reactor operating at pH 7±0.1 and temperature of 20°C. This determination of glycogen requires that glycogen (not poly-P) is the limiting factor for anaerobic acetate uptake. A method to verify this assumption based on the effect of pH on phosphate/acetate ratio is proposed and used. The bioassay is easy to apply and gives a direct measure of the glycogen content of bio-P bacteria, but its reliability still needs to be verified at full-scale biological P-removal plants.

It has been reported that deterioration of biological phosphorus removal (BPR) efficiency at some wastewater treatment plants (WWTPs) regularly occurred after heavy rainfall or weekends. The deterioration has been attributed to low plant loading that took place during such events. However, it is hypothesized in this study that the cause of such deterioration may have been the excessive aeration that took place at some of those plants due to inadequate control of aeration system during weekends and rainfall periods. In order to prove this hypothesis, the influence of excessive aeration (aeration during starvation conditions) on BPR processes was studied using a laboratory anaerobic-aerobic-settling sequencing batch reactor (SBR). It was clearly demonstrated that the phosphorus uptake stops due to a gradual depletion of poly-hydroxy-butyrate (PHB) in an over-aerated process. If organic substrate is introduced to the system, phosphorus release is immediately at its maximal rate. However, the released phosphorus cannot be taken-up fully again because the PHB content limits the uptake rate. Consequently, incomplete phosphorus uptake leads to temporary reduction of BPR efficiency. This causal effect can explain the deterioration of BPR efficiency after heavy rainfall or weekends. Since excessive aeration clearly negatively affects the BPR processes, the aeration should be properly controlled at sewage treatment plants. Some other findings of this study deserve to be mentioned. • • It was confirmed that the presence of acetate under aerobic conditions provokes phosphorus release. This may also contribute to deterioration of the BPR efficiency. • • The aerobic phosphate uptake was found to depend not only on the PHB but also on polyphosphate (poly-P) content of the cells. • • A maximal poly-P (0.18 g-P/g-VSS) and minimal PHB content of the cells (2.11 mg-COD/g-VSS) were observed in the enriched sludge during excessive aeration experiments. • • It was shown that, under aerobic starvation conditions, glycogen can not replace PHB for phosphate uptake and is only used for maintenance. During this period, no oxygen consumption due to decay processes has been observed. © 1998 Elsevier Science Ltd. All rights reserved

Hong Kong has practiced seawater toilet flushing since 1958, saving 750,000 m3 of freshwater every day. A high sulfate-to-COD ratio (>1.25 mg SO 4 2 − /mg COD) in the saline sewage resulting from this practice has enabled us to develop the S ulfate reduction, A utotrophic denitrification and N itrification I ntegrated (SANI®) process with minimal sludge production and oxygen demand. Recently, the SANI® process has been expanded to include Enhanced Biological Phosphorus Removal (EBPR) in an alternating anaerobic/limited-oxygen (LOS-EBPR) aerobic sequencing batch reactor (SBR). This paper presents further development – an anaerobic/anoxic denitrifying sulfur cycle-associated EBPR, named as DS-EBPR, bioprocess in an alternating anaerobic/anoxic SBR for simultaneous removal of organics, nitrogen and phosphorus. The 211 day SBR operation confirmed the sulfur cycle-associated biological phosphorus uptake utilizing nitrate as electron acceptor. This new bioprocess cannot only reduce operation time but also enhance volumetric loading of SBR compared with the LOS-EBPR. The DS-EBPR process performed well at high temperatures of 30 °C and a high salinity of 20% seawater. A synergistic relationship may exist between sulfur cycle and biological phosphorus removal as the optimal ratio of P-release to SO 4 2 − -reduction is close to 1.0 mg P/mg S. There were no conventional PAOs in the sludge.

A full-scale sewage treatment plant designed for biological phosphorus removal may experience short- or long-term shortage in potassium of the influent. In this study, using an anaerobic-aerobic sequenced batch reactor system, inoculation sludge from laboratory-, pilot- and full-scale phosphorus removal plants was exposed to different potassium-phosphorus ratios in the influent. By simulating the conditions which may occur in practice, it was shown that potassium is an essential factor in biological phosphorus removal processes. When the system was exposed to severe shortage of potassium in the influent: (a) phosphorus removal was absent, (b) polyphosphate concentration in the biomass decreased exponentially due to sludge wasting and (c) the anaerobic phosphorus release and the related acetate uptake was only affected after several days of potassium absence, likely due to insufficient content of polyphosphate in the biomass to allow full acetate uptake under anaerobic conditions. In contrast, the system achieved complete phosphorus removal when potassium was present in excess amounts.

Recent research suggests future alterations in rainfall patterns due to climate variability, affecting public safety and health in urban areas. Urban growth, one of the main drivers of change in the current century, will also affect these conditions. Traditional drainage approaches using grey infrastructure offer low adaptation to an uncertain future. New methodologies of stormwater management focus on decentralized approaches in a long-term planning framework, including the use of Green Infrastructure (GI). This work presents a novel methodology to select, evaluate, and place different green-grey practices (or measures) for retrofitting urban drainage systems. The methodology uses a hydrodynamic model and multi-objective optimization to design solutions at a watershed level. The method proposed in this study was applied in a highly urbanized watershed to evaluate the effect of these measures on Combined Sewer Overflows (CSO) quantity. This approach produced promising results and may become a useful tool for planning and decision making of drainage systems.

Hong Kong has practiced seawater toilet flushing since 1958, saving 750,000 m 3 freshwater every day. A high sulfate-to-COD ratio (>1.25 mg SO 4 /mg COD) in the saline sewage resulting from this practice has enabled us to develop the S ulfate reduction A utotrophic denitrification and Nitrification I ntegrated (SANI ® ) process with minimal sludge production. This study seeks to expand the SANI process into an enhanced biological phosphorus removal (EBPR) process. A sulfur cycle associated EBPR was explored in an alternating anaerobic/oxygen-limited aerobic sequencing batch reactor with acetate fed as sole electron donor and sulfate as sulfur source at a total organic carbon to sulfur ratio of 1.1–3.1 (mg C/mg S). Phosphate uptake and polyphosphate formation was observed in this reactor that sustained high phosphate removal (20 mg P/L removed with 320 mg COD/L). This new EBPR process was supported by six observations: 1) anaerobic phosphate release associated with acetate uptake, poly-phosphate hydrolysis, poly-hydroxyalkanoate (PHA) (and poly-S 2− /S 0 ) formation and an “aerobic” phosphate uptake associated with PHA (and poly-S 2− /S 0 ) degradation, and polyphosphate formation; 2) a high P/VSS ratio (>0.16 mg P/mg VSS) and an associated low VSS/TSS ratio (0.75) characteristic of conventional PAOs; 3) a lack of P-release and P-uptake with formaldehyde inactivation and autoclaved sterilized biomass; 4) an absence of chemical precipitated P crystals as determined by XRD analysis; 5) a sludge P of more than 90% polyphosphate as determined by sequential P extraction; and 6) microscopically, observed PHA, poly-P and S globules in the biomass.

There are current concerns about the presence of persistent chemicals in recharge water used in soil aquifer treatment systems. Triclocarban (TCC) has been reported as a persistent, high production volume chemical with the potential to bioaccumulate in the environment. It is also known to have adverse effects such as toxicity and suspected endocrine disruption. This study was carried out to study the fate of TCC in soil aquifer treatment (SAT) through laboratory simulations in a soil column. The system performance was evaluated with regards to TCC influent concentration, sand (column) depth, and residence time. Results obtained confirmed the ability of SAT to reduce TCC concentrations in wastewater. Sorption and biodegradation were responsible for TCC removal, the latter mechanism however being unsustainable. The removal efficiency was found to be dependent on concentration and decreased over time and increased with column depth. Within the duration of the experimental run, TCC negatively impacted on treatment performance through a reduction in COD removals observed in the column.

Enhanced biological phosphorus removal (EBPR) from wastewater relies on the enrichment of activated sludge with phosphorus-accumulating organisms (PAOs). The presence and proliferation of glycogen-accumulating organisms (GAOs), which compete for substrate with PAOs, may be detrimental for EBPR systems, leading to deterioration and, in extreme cases, failure of the process. Therefore, from both process evaluation and modeling perspectives, the estimation of PAO and GAO populations in activated sludge systems is a relevant issue. A simple method for the quantification of PAO and GAO population fractions in activated sludge systems is presented in this paper. To develop such a method, the activity observed in anaerobic batch tests executed with different PAO/GAO ratios, by mixing highly enriched PAO and GAO cultures, was studied. Strong correlations between PAO/GAO population ratios and biomass activity were observed (R2 > 0.97). This served as a basis for the proposal of a simple and practical method to quantify the PAO and GAO populations in activated sludge systems, based on commonly measured and reliable analytical parameters (i.e., mixed liquor suspended solids, acetate, and orthophosphate) without requiring molecular techniques. This method relies on the estimation of the total active biomass population under anaerobic conditions (PAO plus GAO populations), by measuring the maximum acetate uptake rate in the presence of excess acetate. Later, the PAO and GAO populations present in the activated sludge system can be estimated, by taking into account the PAO/GAO ratio calculated on the basis of the anaerobic phosphorus release-to-acetate consumed ratio. The proposed method was evaluated using activated sludge from municipal wastewater treatment plants. The results from the quantification performed following the proposed method were compared with direct population estimations carried out with fluorescence in situ hybridization analysis (determining Candidatus Accumulibacter Phosphatis as PAO and Candidatus Competibacter Phosphatis as GAO). The method showed to be potentially suitable to estimate the PAO and GAO populations regarding the total PAO-GAO biomass. It could be used, not only to evaluate the performance of EBPR systems, but also in the calibration of potential activated sludge mathematical models, regarding the PAO-GAO coexistence.

This article assesses how a small island state can choose the best option in the process of private sector involvement. It reviews the decision process to involve or not the private sector in water and sanitation supply and in which way. Nine criteria are used to make the choice. A careful weighing process is necessary, taking the history into account, looking at the special institutional situation in the country and involving the stakeholders, and even then there is no guarantee of success! An existing public utility may be better placed to look after the modernisation and extension of the water and sanitation system than a new private firm.

This paper presents results of a novel application of coupling the Activated Sludge Model No. 3 (ASM3) and the Anaerobic Digestion Model No.1 (ADM1) to assess a tropical wastewater treatment plant in a developing country (Surat, India). In general, the coupled model was very capable of predicting current plant operation. The model proved to be a useful tool in investigating various scenarios for optimising treatment performance under present conditions and examination of upgrade options to meet stricter and upcoming effluent discharge criteria regarding N removal. It appears that use of plant-wide modelling of wastewater treatment plants is a promising approach towards addressing often complex interactions within the plant itself. It can also create an enabling environment for the implementations of the novel side processes for treatment of nutrient-rich, side-streams (reject water) from sludge treatment.

The influence of operating and environmental conditions on the microbial populations of the enhanced biological phosphorus removal (EBPR) process at seven full-scale municipal activated sludge wastewater treatment plants (WWTPs) in The Netherlands was studied. Data from the selected WWTPs concerning process configuration, operating and environmental conditions were compiled. The EBPR activity from each plant was determined by execution of anaerobic-anoxic-aerobic batch tests using fresh activated sludge. Fractions of Accumulibacter as potential phosphorus accumulating organisms (PAO), and Competibacter, Defluviicoccus-related microorganisms and Sphingomonas as potential glycogen accumulating organisms (GAO) were quantified using fluorescence in situ hybridization (FISH). The relationships among plant process configurations, operating parameters, environmental conditions, EBPR activity and microbial populations fractions were evaluated using a statistical approach. A well-defined and operated denitrification stage and a higher mixed liquor pH value in the anaerobic stage were positively correlated with the occurrence of Accumulibacter. A well-defined denitrification stage also stimulated the development of denitrifying PAO (DPAO). A positive correlation was observed between Competibacter fractions and organic matter concentrations in the influent. Nevertheless, Competibacter did not cause a major effect on the EBPR performance. The observed Competibacter fractions were not in the range that would have led to EBPR deterioration. Likely, the low average sewerage temperature (12+/-2 degrees C) limited their proliferation. Defluviicoccus-related microorganisms were seen only in negligible fractions in a few plants (

In biological nitrogen removal processes, nitrite can be formed and accumulated through both nitrification and denitrification. Despite the fact that, in practice, biological phosphate removal (BPR) is often combined with biological nitrogen removal, there are only a few publications reporting the effect of nitrite on BPR. In this study, phosphate-accumulating organisms (PAO) were cultivated in an anaerobic–anoxic–aerobic sequencing batch reactor (SBR). The effect of nitrite on the enrichment of the sludge with PAO, the phosphate uptake rates and the sludge respiration was investigated. The results indicate that (1) presence of nitrite inhibits both aerobic and anoxic (denitrifying) phosphate uptake, (2) aerobic phosphate uptake was more affected than anoxic phosphate uptake, (3) presence of nitrite could be one of the factors enhancing the presence of glycogen accumulating organisms (GAO)—competitors to PAO for substrate in the anaerobic phase, and (4) it is required to monitor and control nitrite accumulation in a full-scale wastewater treatment plants.

This paper describes several techniques and methods for sludge characterization which are recently developed and used in our ongoing research on biological phosphorus removal (BPR): (i) chemical measurement of the poly-hydroxy-alkanoate (PHA) content of the biomass, (ii) bioassay for glycogen determination in BPR systems, (iii) determination of the fraction of denitrifying phosphorus accumulating organisms (DPAOs) in P-removing sludge, (iv) determination of the aerobic and anoxic ATP/NADH2 ratio (δ value) in BPR systems, and (v) determination of the glycogen accumulating organisms (GAOs) / phosphorus accumulating organisms (PAOs) ratio in activated sludge.

Glycogen plays an important role in biological phosphorus removal from wastewaters. Existing measurement techniques often overestimate the glycogen content of the biomass due to the presence of glucose and/or other carbohydrates than glycogen in the cell material. As an alternative to conventional methods a bioassay for glycogen determination in biological phosphorus removal systems was developed. The bioassay is based on the strict stoichiometric coupling between anaerobic acetate uptake and glycogen consumption. In other words, the glycogen concentration of the sludge was determined indirectly by measuring the maximal total acetate uptake by the activated sludge in anaerobic batch tests. The bioassay was successfully tested for the determination of glycogen content of the sludge taken from the lab-scale, acetate-fed, anaerobic-aerobic-settling sequencing batch reactor operating at pH 7±0.1 and temperature of 20°C. This determination of glycogen requires that glycogen (not poly-P) is the limiting factor for anaerobic acetate uptake. A method to verify this assumption based on the effect of pH on phosphate/acetate ratio is proposed and used. The bioassay is easy to apply and gives a direct measure of the glycogen content of bio-P bacteria, but its reliability still needs to be verified at full-scale biological P-removal plants.