CERES :: Browsing by Author "Soares, Ana"

Browsing by Author "Soares, Ana"

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Open Access
Ammonia recovery from brines originating from a municipal wastewater ion exchange process and valorization of recovered nitrogen into microbial protein
(Elsevier, 2021-06-18) Guida, Samuela; Van Peteghem, Lotte; Luqmani, Ben; Sakarika, Myrsini; McLeod, Andrew; McAdam, Ewan J.; Jefferson, Bruce; Rabaey, Korneel; Soares, Ana
A hollow fibre membrane contactor (HFMC), and two vacuum thermal stripping processes, a rotary evaporator (VTS) and multi-component system (MVTS) were compared for their ability to recover ammonia (NH3) from ion exchange (IEX) regeneration brines. The IEX was a 10 m3/day demonstration scale plant fed with secondary municipal wastewater. The 10% potassium chloride regeneration brine was used multiple times leading to ammonium (NH4+-N) saturation (up to 890 mg N/L). When treating the saturated IEX brine, the highest NH3 mass transfer coefficient for the HFMC, MVTS and VTS were 0.6, 0.7 and 0.1 h−1, respectively, compared to values between 1.7 and 3.5 h−1, when treating a synthetic solution. The highest NH3 recovery was obtained with the HFMC (99.8%) and the ammonium sulphate produced was characterised for impurities, presenting high quality. Concentrated ammonium (NH4+-N) solutions (0.5–3.1 g N/L) were obtained from the MVTS and VTS processes. To further valorise the recovered NH4+-N solution produced from the MVTS process, this was used as a substrate for microbial protein (MP) production. Limited differences were observed for production rate (specific growth rate 0.092–0.40 h−1), protein yield (0.021–0.18 g protein/g acetate-CODconsumed) and protein content (0.073–0.87 g protein/g cell dry weight) between recovered and commercial nitrogen (N) sources, indicating that recovered N from IEX can serve as a substrate for MP production. This study demonstrates a comprehensive N management solution for wastewater applications, leading to a range recovered products. These combined technologies can contribute to the local economy, whilst delivering to the ambitious NET-ZERO and circular economy targets.
Open Access
Ammonia removal from thermal hydrolysis dewatering liquors via three different deammonification technologies
(Elsevier, 2020-10-06) Ochs, Pascal; Martin, Benjamin D.; Germain, Eve; Stephenson, Tom; van Loosdrecht, Mark C. M.; Soares, Ana
The benefits of deammonification to remove nitrogen from sidestreams, i.e., sludge dewatering liquors, in municipal wastewater treatment plants are well accepted. The ammonia removal from dewatering liquors originated from thermal hydrolysis/anaerobic digestion (THP/AD) are deemed challenging. Many different commercial technologies have been applied to remove ammonia from sidestreams, varying in reactor design, biomass growth form and instrumentation and control strategy. Four technologies were tested (a deammonification suspended sludge sequencing batch reactor (S-SBR), a deammonification moving bed biofilm reactor (MEDIA), a deammonification granular sludge sequencing batch reactor (G-SBR), and a nitrification suspended sludge sequencing batch reactor (N-SBR)). All technologies relied on distinct control strategies that actuated on the feed flow leading to a range of different ammonia loading rates. Periods of poor performance were displayed by all technologies and related to imbalances in the chain of deammonification reactions subsequently effecting both load and removal. The S-SBR was most robust, not presenting these imbalances. The S-SBR and G-SBR presented the highest nitrogen removal rates (NRR) of 0.58 and 0.56 kg N m−3 d−1, respectively. The MEDIA and the N-SBR presented an NRR of 0.17 and 0.07 kg N m−3 d−1, respectively. This study demonstrated stable ammonia removal from THP/AD dewatering liquors and did not observe toxicity in the nitrogen removal technologies tested. It was identified that instrumentation and control strategy was the main contributor that enabled higher stability and NRR. Overall, this study provides support in selecting a suitable biological nitrogen removal technology for the treatment of sludge dewatering liquors from THP/AD
Open Access
Ammonium and phosphorus removal and recovery from wastewater through the ion exchange process.
(2020-07) Guida, Samuela; Soares, Ana; Jefferson, Bruce
Challenges to implement circular economy principles in the wastewater cycle are connected to the need of reducing nutrients (ammonium as NH₄⁺-N, and phosphorus as PO₄-P) in treated effluent whilst enabling their recovery in an environmentally sustainable way. Conventional biology-based technologies fail to address these challenges by having high greenhouse gases footprint and offering limited possibilities for nutrient recovery. The aim of this work was to underline the mechanisms of removal and recovery of NH₄⁺-N and PO₄-P from wastewater through the ion exchange (IEX) process in order to optimise the removal efficiency and maximise the recovery from IEX regenerant brines (sodium hydroxide and potassium chloride), when working at demonstration scale over an extended period of time. The IEX process was tested in a 10 m³/day demonstration plant for 2.5 years using Zeolite-N and a hybrid anion exchanger (HAIX) for the removal of NH₄⁺-N and PO₄-P at empty bed contact times of 10 and 5 min, respectively. The operation at demonstration scale confirmed the resilience and consistency of the IEX process and the possibility to maintain high effluent quality (<0.3 mg PO₄-P/L and <1 mg NH₄⁺-N/L) despite changes in influent concentration (i.e. <0.006-26 mg NH₄⁺-N/L) and extended operational period (up to 63 consecutive adsorption/regeneration cycles with HAIX). Additionally, the regenerant brines were reused multiple times and nutrients could be recovered as high purity ammonium sulphate and hydroxyapatite using a hollow fibre membrane contactor for ammonium recovery and simple precipitation with calcium hydroxide and filtration for phosphorus recovery. The results obtained from this work additionally highlighted the need of an automated system to start the regeneration when the desired effluent quality is reached, the need of a nearly solids-free influent and high mechanical strength media to avoid media packing and losses. This work significantly moved the IEX process higher in the technology readiness level (from level 5 to level 7) for mainstream wastewater treatment with the advantages of simple operation, consistency, resilience and lower environmental impact (-25% cumulative energy demand, - 66% global warming potential, -62% marine eutrophication potential) compared to traditional biological processes.
Open Access
Anaerobic membrane bioreactors in upflow anaerobic sludge blanket configuration for energy neutral sewage treatment.
(2018-03) Wang, Kanming; McAdam, Ewan; Soares, Ana
Anaerobic membrane bioreactors (AnMBRs) are emerging as a promising technology to offer the prospect to achieve energy neutral sewage treatment. The key challenges limiting full-scale application of AnMBR for municipal wastewater treatment are high operational cost of energy demand for fouling control and high capital cost of membrane investments. This thesis explores a novel pseudo dead-end gas sparging regime for membrane fouling control, enabling a high sustainable flux (15 L m ¯² h¯¹) with low energy demand (0.14 kWh m⁻³ ) in upflow anaerobic sludge blanket (UASB) configured AnMBR, sufficient to achieve energy neutral sewage treatment. However, this strategy is only possible within low solids environment, emphasising the importance of solids management in the UASB reactor. Solids accumulated in the sludge blanket enhances UASB treatment efficiency during the steady-state operation, indicating to control the sludge blanket at a threshold between the sludge blanket development and steady-state period. The granular inoculum has good stability which exerts a positive influence on reactor stability and sustained permeability, whilst the flocculent inoculum enables to deliver similar sustained membrane operation provided the sludge blanket is controlled. Low temperatures (average temperature of 10 °C) cause the instability of UASB reactor especially for the one with flocculent inoculum biomass. It is therefore proposed to keep relatively high upflow velocity (Vup) of 0.8-0.9 m h⁻¹ in the UASB reactor for granular AnMBR to promote the stratification of particular and granular material, whilst reducing Vup to 0.4 m h⁻¹ for flocculent AnMBR to minimise solids washout and sustain membrane operation at low temperatures. The potential for permeability recovery following peak flow (diurnal peaks and storm water flows) has been investigated and evidenced, suggesting that membrane surface area for AnMBR can be specified based on average flow, providing a considerable (67 %) capital cost reduction compared with the design based on peak flows (three times of average flow). Importantly, this thesis promotes UASB configured AnMBR as a highly reliable and more economically viable technology, facilitating to achieve the energy neutral sewage treatment at ambient temperature.
Open Access
Bioconversion of carbon dioxide in anaerobic digesters for on-site carbon capture and biogas enhancement - A review
(Taylor & Francis, 2017-12-11) Bajón Fernández, Yadira; Soares, Ana; Koch, K.; Vale, P.; Cartmell, Elise
Energy consumption of the water sector presents an increasing energy demand, contrary to GHG mitigation aims. As a result, research aimed at capturing emitted CO2 and at developing treatment technologies with a low energy demand and increased renewable energy production has increased, leading to a surge in implementation of anaerobic digestion (AD). Valorization of the biogenic CO2 emitted with biogas AD (estimated at over 1 MtCO2 per annum for the UK water and organic waste sectors), presents an opportunity to further reduce carbon footprint and support energy supply decarburization. This paper reviews bioconversion of CO2 into CH4 in ADs (without addition of H2) as a means to valorize CO2 emissions. The review has concluded this to be a promising solution to reduce carbon footprint and uplift renewable energy production. However, in order to increase readiness for implementation (1) the mechanisms of CO2 utilization need to be elucidated, including the sources of additional H2 needed, (2) studies need to report more thoroughly the conditions of CO2 injection and (3) trials where ADs are integrated with gas to liquid mass transfer technologies need to be performed.
Open Access
Biological carbon dioxide utilisation in food waste anaerobic digesters
(Elsevier, 2015-06-09) Bajón Fernández, Yadira; Green, K.; Schuler, K.; Soares, Ana; Vale, P.; Alibardi, Luca; Cartmell, Elise
Carbon dioxide (CO2) enrichment of anaerobic digesters (AD) was previously identified as a potential on-site carbon revalorisation strategy. This study addresses the lack of studies investigating this concept in up-scaled units and the need to understand the mechanisms of exogenous CO2 utilisation. Two pilot-scale ADs treating food waste were monitored for 225 days, with the test unit being periodically injected with CO2 using a bubble column. The test AD maintained a CH4 production rate of 0.56 ± 0.13 m3 CH4·(kg VSfed d)−1 and a CH4 concentration in biogas of 68% even when dissolved CO2 levels were increased by a 3 fold over the control unit. An additional uptake of 0.55 kg of exogenous CO2 was achieved in the test AD during the trial period. A 2.5 fold increase in hydrogen (H2) concentration was observed and attributed to CO2 dissolution and to an alteration of the acidogenesis and acetogenesis pathways. A hypothesis for conversion of exogenous CO2 has been proposed, which requires validation by microbial community analysis.
Open Access
Biological treatment of coke making wastewater.
(2017-04) Raper, Eleanor; Soares, Ana; Stephenson, Tom
Production of coke for steel manufacturing produces a wastewater containing total nitrogen (TN) (up to 600 mg/L) alongside toxic compounds phenol (60 - 400 mg/L), thiocyanate (SCN-) (100 - 400 mg/L), polycyclic aromatic hydrocarbons (PAHs) (Ʃ6PAHs:179±35 µg/L) and trace metals. Emission limits introduced by the Industrial Emissions Directive (IED) in 2016 require treated coke effluent to contain <50 mg/L TN, <4 mg/L SCN-, <0.5 mg/L phenol and <50 µg/L Ʃ6PAHs which cannot be consistently met by the conventional activated sludge process (ASP). Treatment process modifications were investigated to ensure compliance. Activated carbon addition to the ASP (400 mg/L) increased Ʃ6PAHs removal by 20% enabling emission compliance whilst increasing nickel, chromium and cadmium removal. The addition of 0.5 g/L of a commercial bioaugmentation product increased dissolved Ʃ6PAHs removal by 51%. Biostimulation (addition of micronutrients/alkalinity) enabled SCN-and phenol emission compliance. Survival of supplemented exogenous bacteria in a simulated river water discharge was investigated for the first time showing limited survivability. Thiocyanate degradation mechanisms were poorly understood but were important to ascertain, especially as SCN-degradation produces ammonia increasing TN loading. Control of influent ammonia and phenol concentration was important enabling SCN-degradation under anoxic and aerobic conditions. Deoxyribonucleic acid sequencing of the mixed culture identified a new species of Thiobacillus which had metabolic similarities to T. thioparus and T. denitrificans. Nitrification was limited (41%) confirming the importance of intrinsic alkalinity availability in the wastewater, however, sodium carbonate addition (300 mg/L as CaCO₃) increased efficiencies to 96%. An anoxic-aerobic ASP was investigated for TN removal enabling an effluent TN <50 mg/L when the soluble chemical oxygen demand (sCOD):TN ratio was maintained above 5.7. Acetic acid was identified as a suitable source of carbon addition to maintain this ratio. An anoxic-aerobic ASP combined with AC and bioaugmentation can ensure compliance with the IED.
Open Access
Campus source to sink wastewater surveillance of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2)
(Elsevier, 2024-05-06) Folkes, Miles; Castro-Gutierrez, V. M.; Lundy, Lian; Bajón-Fernández, Y.; Soares, Ana; Jeffrey, Paul; Hassard, Francis
Wastewater-based surveillance (WBS) offers an aggregate, and cost-effective approach for tracking infectious disease outbreak prevalence within communities, that provides data on community health complementary to individual clinical testing. This study reports on a 16-month WBS initiative on a university campus in England, UK, assessing the presence of SARS-CoV-2 in sewers from large buildings, downstream sewer locations, raw wastewater, partially treated and treated effluents. Key findings include the detection of the Alpha (B.1.1.7) variant in wastewater, with 70 % of confirmed campus cases correlating with positive wastewater samples. Notably, ammonium nitrogen (NH4-N) levels showed a positive correlation (ρ = 0.543, p < 0.01) with virus levels at the large building scale, a relationship not observed at the sewer or wastewater treatment works (WWTW) levels due to dilution. The WWTW was compliant to wastewater standards, but the secondary treatment processes were not efficient for virus removal as SARS-CoV-2 was consistently detected in treated discharges. Tools developed through WBS can also be used to enhance traditional environmental monitoring of aquatic systems. This study provides a detailed source-to-sink evaluation, emphasizing the critical need for the widespread application and improvement of WBS. It showcases WBS utility and reinforces the ongoing challenges posed by viruses to receiving water quality.
Open Access
Carbon capture and biogas enhancement by carbon dioxide enrichment of anaerobic digesters treating sewage sludge or food waste
(Elsevier Science B.V., Amsterdam., 2014-05-01T00:00:00Z) Bajón Fernández, Yadira; Soares, Ana; Villa, Raffaella; Vale, P.; Cartmell, Elise
The increasing concentration of carbon dioxide (CO2) in the atmosphere and the stringent greenhouse gases (GHG) reduction targets, require the development of CO2 sequestration technologies applicable for the waste and wastewater sector. This study addressed the reduction of CO2 emissions and enhancement of biogas production associated with CO2 enrichment of anaerobic digesters (ADs). The benefits of CO2 enrichment were examined by injecting CO2 at 0, 0.3, 0.6 and 0.9M fractions into batch ADs treating food waste or sewage sludge. Daily specific methane (CH4) production increased 11-16% for food waste and 96-138% for sewage sludge over the first 24h. Potential CO2 reductions of 8-34% for sewage sludge and 3-11% for food waste were estimated. The capacity of ADs to utilise additional CO2 was demonstrated, which could provide a potential solution for onsite sequestration of CO2 streams while enhancing renewable energy production.
Open Access
Carbon dioxide utilisation in anaerobic digesters as an on-site carbon revalorisation strategy
(Cranfield University, 2014-11) Bajón Fernández, Yadira; Cartmell, Elise; Soares, Ana; Vale, Peter
The increasing carbon footprint of the water and organic waste sectors has led to water utilities to voluntarily include carbon mitigation approaches within their strategic plans and to an increase in research aimed at mitigating carbon dioxide (CO2) emissions. Injection of CO2 in anaerobic digesters (ADs) for its bioconversion into methane (CH4) has been identified as a potential solution. However, previous literature provided limited knowledge of the carbon benefits obtainable and presented conflicting information regarding the mechanisms of CO2 utilisation. This thesis investigated the potential of injecting exogenous CO2 into ADs for its bioconversion into CH4 to reduce CO2 emissions from water and organic waste facilities. Batch laboratory scale and continuous pilot-scale ADs enriched with CO2 were operated. A substrate dependant response to exogenous CO2 was reported for the first time and potential CO2 savings of up to 34% and 11% were estimated for sewage sludge and food waste batch ADs, respectively, injected with CO2 before the digestion process. Higher benefits in CH4 production were observed in sewage sludge ADs than in food waste units. An up to 2.4 fold increase in CH4 production during the 24 hours following saturation with CO2 was obtained in sewage sludge units, while benefit was limited to 1.16 fold in food waste ADs. Microbial community analyses were performed to elucidate CO2 fate mechanisms. An increase of up to 80% in the activity of Methanosaetaceae (obligate acetoclastic methanogen) was observed in sewage sludge ADs periodically enriched with CO2. Methanosaetaceae was scarce (4.3±1.7%) in food waste units, which was attributed to an inhibitory concentration of ammonia (4 gL-1 NH4-N). Based on Archaea analyses and on monitoring hydrogen (H2) and volatile fatty acids (VFA) speciation dynamics in a pilot-scale AD, it was proposed that exogenous CO2 is reduced by homoacetogenesis (Wood-Ljungdahl mechanism) and the acetate generated by this route is converted to CH4 by acetoclastic methanogenesis. Gas to liquid mass transfer was identified as limiting of the amount of dissolved CO2 loaded to an AD and the complex rheology of anaerobically digested media as detrimental for transfer performance. An increase of apparent viscosity (μa) from 130 to 340 cPo (typical variability of sewage sludge) reduced gas transfer efficiency (GTE) by 6 percentage points. The use of bubble columns was identified as suitable for further scaled-up units. Injection of CO2 could be performed in the digestate recirculation loop of single phase ADs or in the first phase of two phase ADs (TPADs), with CO2 sourced from off-gas of biogas upgrading technologies. It has been demonstrated that bioconversion of CO2 in ADs can reduce carbon footprint and increase CH4 production, with the possibility of becoming an on-site carbon revalorisation strategy.
Open Access
Characterisation of thiocyanate degradation in a mixed culture activated sludge process treating coke wastewater
(Elsevier, 2019-05-22) Raper, Eleanor; Stephenson, Tom; Fisher, Raymond; Anderson, David R.; Soares, Ana
Microbial degradation of thiocyanate (SCN−) has been reported to suffer from instability highlighting the need for improved understanding of underlying mechanisms and boundaries. Respirometry, batch tests and DNA sequencing analysis were used to improve understanding of a mixed culture treating coke wastewater rich in SCN−. An uncultured species of Thiobacillus was the most abundant species (26%) and displayed similar metabolic capabilities to Thiobacillus denitrificans and Thiobacillus thioparus. Thiocyanate was hydrolysed/oxidised to NH4+-N, HCO3− and SO42−. Nevertheless, at 360–2100 mg SCN−/L a breakdown in the degradation pathway was observed. Respirometry tests demonstrated that NH4+-N was inhibitory to SCN− degradation (IC50: 316 mg/L). Likewise, phenol (180 mg/L) and hydroxylamine (0.25–16 mg/L) reduced SCN− degradation by 41% and ca. 7%, respectively. The understanding of the SCN− degradation pathways can enable stable treatment efficiencies and compliance with effluent of <4 mg SCN/L, required by the Industrial Emissions Directive.
Open Access
Cloth filters as alternative to the conventional membranes for solids removal from UASB effluents.
(Cranfield University, 2018-12) Campitelli, Antonio; Jefferson, Bruce; Soares, Ana; Alibardi, Luca
Anaerobic Membrane Bioreactors (anMBR) represent one of the most promising technology to achieve energy neutral or positive wastewater treatment with a high effluent quality. Despite this potential, its implementation is still restricted by the high costs of the ultrafiltration membrane. This thesis investigated the feasibility of using a cloth filter as an alternative to the conventional membranes for solids removal from an Upflow Anaerobic Sludge Blanket (UASB) effluent. The advantages of the cloth filter are the low cost of the material, simpler operation and maintenance procedures. However, solids removal efficiencies are lower than those of the ultrafiltration membrane. The removal efficiency depends on the pore size of the cloth and on the influent particle and solid profile load characterisation. The aim of this study is to assess the efficacy of cloth filters to treat UASB effluent. Effective solids separation was possible with the cloths tested with optimal performance achieved for the 1 and 10 µm non-woven cloths operated under low cross flow or dead end conditions. In these cases, solids removal efficiencies up to 67% were possible whilst maintaining a flux of 1000 LMH. In relation to the UASB operation, the sludge blanket height in the UASB was seen to correlate to the suspended solids removal and resulted in a progressively higher median particle size exiting the reactor. Further, incorporation of the separation in the recycle line deteriorated performance a little indicating that the cloth filters would be best configured post the recycle line.
Open Access
Comparable membrane permeability can be achieved in granular and flocculent anaerobic membrane bioreactor for sewage treatment through better sludge blanket control
(Elsevier, 2019-02-05) Wang, Kanming; Soares, Ana; Jefferson, Bruce; McAdam, Ewan
MBR, to establish the impact of biomass selection on sustaining membrane permeability for sewage treatment. When operated as an UASB (10 °C), similarly poor organics removal was observed for both inocula, which was overcome by membrane integration, producing solids-free permeate and consistently low CODt (34–39 mg L−1) and BOD5 (10–13 mg L−1), sufficient to meet discharge standards. At an average sewage temperature of 22 °C, membrane permeabilities in granular (G-AnMBR) and flocculent (F-AnMBR) systems were comparable. However, at lower temperature (10 °C), significant fouling was observed in F-AnMBR at a flux of 7.5 L m−2 h−1. The permeability decline was ascribed to a decreased particle settling velocity which induced washout of smaller particles into the membrane tank, subsequently increasing the colloidal concentration due to the floc erosion induced by gas sparging. This was confirmed by halving UASB upflow velocity in the F-AnMBR, which reduced pCOD and colloidal load by 31–36% onto the membrane, permitting comparable permeability to G-AnMBR. The UASB configured AnMBR promoted low solids loading onto the membrane, enabling pseudo dead-end gas sparging to be used which reduced specific energy demand. Analysis of the dead-end filtration cycle attributed the primary resistance (85–88%) to the development of a concentrated but less compact cake. Importantly, this study evidences comparable permeabilities in G-AnMBR and F-AnMBR through controlling solids retention, and specifying filtration cycle length to minimise solids deposition, such that low energy membrane operation can be achieved (<0.122 kW h m−3).
Open Access
Comparison between disintegrated and fermented sewage sludge for production of a carbon source suitable for biological nutrient removal
(Elsevier Science B.V., Amsterdam., 2010-03-15T00:00:00Z) Soares, Ana; Kampas, Pantelis; Maillard, Sarah; Wood, Elizabeth; Brigg, Jon; Tillotson, Martin; Parsons, Simon A.; Cartmell, Elise
There is a need to investigate processes that enable sludge re-use while enhancing sewage treatment efficiency. Mechanically disintegrated thickened surplus activated sludge (SAS) and fermented primary sludge were compared for their capacity to produce a carbon source suitable for BNR by completing nutrient removal predictive tests. Mechanically disintegration of SAS using a deflaker enhanced volatile fatty acids (VFAs) content from 92 to 374 mg l−1 (4.1-fold increase). In comparison, primary sludge fermentation increased the VFAs content from 3.5 g l−1 to a final concentration of 8.7 g l−1 (2.5-fold increase). The carbon source obtained from disintegration and fermentation treatments improved phosphate (PO4-P) release and denitrification by up to 0.04 mg NO3-N g−1 VSS min−1 and 0.031 mg PO4-P g−1 VSS min−1, respectively, in comparison to acetate (0.023 mg NO3-N g−1 VSS min−1and 0.010 mg PO4-P g−1 VSS min−1). Overall, both types of sludge were suitable for BNR but disintegrated SAS displayed lower carbon to nutrient ratios of 8 for SCOD:PO4-P and 9 for SCOD:NO3-N. On the other hand, SAS increased the concentration of PO4-P in the settled sewage by a further 0.97 g PO4-P kg−1 SCOD indicating its potential negative impact towards nutrient recyc
Open Access
Comparison of fouling between aerobic and anaerobic MBR treating municipal wastewater
(IWA Publishing, 2018-11-26) Wang, K. M.; Martin Garcia, N.; Soares, Ana; Jefferson, Bruce; McAdam, Ewan
The key driver for anaerobic membrane bioreactors (AnMBR) for municipal wastewater treatment is enabling the transition to energy neutral wastewater treatment. However, municipal wastewater delivers a comparatively constrained methane yield, which means energy conservation must be prioritised to achieve the proposed energy neutral ambition. A critical focus on membrane fouling is therefore warranted, as membrane operation represents the primary energy demand in MBRs. This review seeks to quantify the characteristics of the prevailing AnMBR biological suspension and to ascertain whether knowledge transfer exists between fouling characteristics in aerobic and anaerobic MBRs for municipal applications. Analysis of literature data revealed that the level of extractable extracellular polymeric substrate is slightly higher in aerobic MBRs than in anaerobic MBRs. However, AnMBR comprises considerably higher soluble microbial product concentrations, which have been widely reported to increase fouling propensity in aerobic systems. More distinct is the difference in the colloidal and fine solids fraction (between 1 and 10–15 μm), which is likely to dominate fouling in anaerobic systems and limit knowledge transfer from aerobic MBRs. Literature data on energy production was compared to that employed for membrane operation, and evidences that despite the challenging character of the particle matrix, energy neutral operation is achievable for AnMBR applied to municipal wastewater treatment.
Open Access
Conductance based sensing and analysis of soluble phosphates in wastewater
(Elsevier Science B.V., Amsterdam., 2014-02-15T00:00:00Z) Warwick, C.; Guerreiro, Antonio R.; Gomez-Caballero, Alberto; Wood, Elizabeth; Kitson, James; Robinson, James; Soares, Ana
The current standard method used for measuring soluble phosphate in environmental water samples is based on a colourimetric approach, developed in the early 1960s. In order to provide an alternative, label free sensing solution, a molecularly imprinted polymer (MIP) was designed to function as a phosphate receptor. A combination of functional monomer (N-allylthiourea), cross-linker and monomer/template ratios were optimised in order to maximise the binding capacity for phosphate. When produced in membrane format, the MIP's ability to produce a reversible change in conductance in the presence of phosphate was explored for fabrication of a sensor which was able to selectively detect the presence of phosphate compared to sulphate, nitrate and chloride. In wastewater samples the sensor had a limit of detection of 0.16 mg P/l, and a linear range between 0.66 and 8 mg P/l. This is below the minimum monitoring level (1 mg P/l) as required by current legislation for wastewater discharges, making the sensor as developed promising for direct quantification of phosphate in environmental monitoring applications.
Open Access
Demonstration of anaerobic membrane bioreactors for resource recovery in wastewater treatment applications.
(Cranfield University, 2023-08) Paissoni, Eleonora; Soares, Ana; Jefferson, Bruce
Pilot-scale studies on anaerobic membrane bioreactors (AnMBRs) for municipal wastewater treatment at low temperature (<20°C) showed promising results, however, their application at larger scale is still relatively unknown. This study investigated the scalability of an AnMBR, comprising an upflow anaerobic sludge blanket (UASB) reactor and an external ultrafiltration membrane tank, operating AnMBRs both at pilot- and demonstration-scale and identifying how sludge physical and microbiological properties, membrane design and variations in influent temperature, chemical oxygen demand (COD) and sulphate (SO₄) influence the successful scale-up of the technology. At pilot-scale, the source and adaptation of the inoculum and the orientation and arrangement of the membrane fibres did not affect the performance of the reactors. However, the use of horizontal hollow fibres led to lower gas sparging energy consumption compared to a vertical module. The membrane improved removal efficiencies (from 49-57% to 88-92% COD removal), solids hydrolysed (from 0.82-0.86 g/(L∙d) to 1.57-1.87 g/(L∙d)) and methane production (from 2.3-2.7 L/d to 5.3-5.7 L/d). Methanogenesis percentages were linearly correlated to hydrolysis, which in turn was affected by temperature and inversely correlated to the Sauter mean diameter of the sludge particles. Higher substrate affinities were found at the operational temperature of the reactors (15-20°C), while hydrolytic enzyme activities in UASB reactors and AnMBRs were higher at 37°C. Methane was mainly dissolved in the effluent (70-90%), implying the need for a recovery process to improve the net energy balance. At demonstration-scale, low COD:SO4 ratio caused competition between sulphate-reducing bacteria and methanogens, leading to a decrease in methane yield. This study proved that AnMBRs are a suitable technology to treat municipal wastewater, however site- specific control strategies to manage fouling and sulphate and appropriate post- treatments are necessary to ensure the successful application of the process at full-scale in temperate climates and the recovery of useful resources from wastewater.
Open Access
Demonstration of ion exchange technology for phosphorus removal and recovery from municipal wastewater
(Elsevier, 2021-04-20) Guida, Samuela; Rubertelli, Giorgia; Jefferson, Bruce; Soares, Ana
Orthophosphate (PO4-P) removal and recovery from municipal wastewater were investigated in a 10 m3/day hybrid anion exchanger (HAIX) demonstration plant. To date, HAIX resins have been investigated for PO4-P removal at laboratory scale with promising results but there is a need to investigate the application of the technology at larger scale, over extended operation whilst establishing an efficient regenerant management solution. The HAIX removed an average of 6 mg PO4-P /L to >0.3 mg PO4-P/L, within 430 bed volumes, with a capacity of 4.1 mg PO4-P/g resin. To manage the regenerant (NaOH 2%) efficiently, this was reused up to 8 times, reaching 785 mg PO4-P/L, but the adsorption capacity was compromised, and it decreased to 1.5 mg PO4-P/g resin. By adding calcium hydroxide to the saturated NaOH, 95% of the PO4-P was recovered as hydroxyapatite, and at the same time the regeneration effectiveness was re-established, as <0.3 mg PO4-P/L was reached again in the effluent. The treated NaOH was reused as regenerant solution, ensuring high effluent quality of <0.2 mg PO4-P/L. This study confirmed the capability of HAIX technology to remove and recover PO4-P from wastewater offering a solution which ensures both a high effluent quality and a circular economy approach.
Open Access
Development and calibration of a new mathematical model for the description of an ion-exchange process for ammonia removal in the presence of competing ions
(Elsevier, 2021-10-20) Lizarralde, Izaro; Guida, Samuela; Canellas, Judit; Jefferson, Bruce; Grau, P.; Soares, Ana
Ammonia ion removal and recovery via an ion-exchange process using zeolites is a promising alternative to traditional biological treatments. The analysis of its efficiency is not straightforward as it depends on various factors, such as the cation exchange capacity of the zeolite, amount of zeolite available, initial ammonia concentration, contact time, ammonia speciation depending on pH or the presence of competing ions. Mathematical modelling and simulation tools are very useful to analyse the effect of different operational conditions on the efficiency and optimal operation of the process. This paper experimentally analyses the effect that the presence of competing ions has on the efficiency of ammonia removal. This experimental work has shown a reduction of around 21% of ammonia removal efficiency in the presence of competing ions. The main contribution of this paper is the development new mathematical model able to describe the ion-exchange process in the presence of competing ions. The mathematical model developed is able to analyse the performance of the IEX process under different empty bed contact times, influent loads, pH and concentrations of competing ions. The capability of the model to reproduce real data has been proven comparing the experimental and simulation results. Finally, an exploration by simulation has been undertaken to show the potential of the mathematical model developed.
Open Access
Dissolved methane recovery from anaerobic effluents using hollow fibre membrane contactors
(Elsevier, 2015-12) Cookney, Joanna; McLeod, Andrew J.; Mathioudakis, Vasileios; Ncube, Philani; Soares, Ana; Jefferson, Bruce; McAdam, Ewan J.
Hollow fibre membrane contactor (HFMC) systems have been studied for the desorption of dissolved methane from both analogue and real anaerobic effluents to ascertain process boundary conditions for separation. When using analogue effluents to establish baseline conditions, up to 98.9% methane removal was demonstrated. Elevated organic concentrations have been previously shown to promote micropore wetting. Consequently, for anaerobic effluent from an upflow anaerobic sludge blanket reactor, which was characterised by a high organic concentration, a nonporous HFMC was selected. Interestingly, mass transfer data from real effluent exceeded that produced with the analogue effluent and was ostensibly due to methane supersaturation of the anaerobic effluent which increased the concentration gradient yielding enhanced mass transfer. However, at high liquid velocities a palpable decline in removal efficiency was noted for the nonporous HFMC which was ascribed to the low permeability of the nonporous polymer provoking membrane controlled mass transfer. For anaerobic effluent from an anaerobic membrane bioreactor (MBR), a microporous HFMC was used as the permeate comprised only a low organic solute concentration. Mass transfer data compared similarly to that of an analogue which suggests that the low organic concentration in anaerobic MBR permeate does not promote pore wetting in microporous HFMC. Importantly, scale-up modelling of the mass transfer data evidenced that whilst dissolved methane is in dilute form, the revenue generated from the recovered methane is sufficient to offset operational and investment costs of a single stage recovery process, however, the economic return is diminished if discharge is to a closed conduit as this requires a multi-stage array to achieve the required dissolved methane consent of 0.14 mg l−1.