Browsing by Author "Stephenson, Tom"
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Item Open Access Advanced reactor technology for wastewater treatment.(Cranfield University, 2015-04) Hassard, Francis; Stephenson, Tom; Cartmell, EliseElevated stringency regarding discharges and an aging asset base represent challenges to modern wastewater treatment. This requires upgrade of existing wastewater assets for low energy nutrient removal for minimal cost. Advanced rotating biofilm reactors can be used as a pre-treatment, high organic loading rate (OLR), low hydraulic residence time (HRT) treatment facilitating upgrade of existing wastewater treatment plant (WWTP). The threshold for stable nitrification in rotating biological contactors (RBCs) was assumed to be 15 g.BOD₅.m⁻²d⁻¹ however media modifications have shown that this value can be elevated to ~35 g.sCOD.m⁻²d⁻¹ (73.5 g.BOD₅.m⁻²d⁻¹ ) in rotating biofilm reactors (RBR). Mesh media was compared to two different reticulated foam media, the mesh media had similar porosities but elevated performance compared to the foam media. Elevated OLR resulted in lower volumetric bacterial viability suggesting inhibition at >100 g.sCOD.m⁻²d⁻¹. Comparison of four different mesh media suggested that high porosity mesh media is best for performance and to prevent pore clogging. Bacterial specific activity increased with OLR, but performance at very high OLR decreased. Biofilm reactors can be operated in a ‘hybrid’ configuration where settled bacterial solids can be recycled into the biofilm reactor to improve performance by reducing the effective biofilm OLR. Studies at full scale revealed that extracellular enzyme activity was higher in biofilms compared to suspended growth bacteria. Hybrid upgrade of existing wastewater treatment works resulted in 52 and 40% increase in removal rate of COD and NH₄-N respectively. Comparing different solids type for hybrid reactors utilising activated sludge flocs had the greatest performance benefit compared to HS and FE respectively for sCOD and NH₄-N removal. Incorporating a solids feed in hybrid reactors improved nitrification and organics removal at lower loading. However the solids in the recycle feed reduced denitrification at very high OLR suggesting flocs inhibit denitrification. Hybrid RBRs have 4.8 fold increase in protein EEA compared to single pass reactors under similar conditions. Recycling bacterial solids reduces the effective OLR on the biofilm and confers significant performance benefits. Upfront RBRs provide suitable upgrade for existing WWTP.Item 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, AnaThe 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/ADItem Open Access Bacteriophages - potential for application in wastewater treatment processes.(Elsevier Science B.V., Amsterdam., 2005-03-01T00:00:00Z) Withey, S.; Cartmell, Elise; Avery, L. M.; Stephenson, TomBacteriophages are viruses that infect and lyse bacteria. Interest in the ability of phages to control bacterial populations has extended from medical applications into the fields of agriculture, aquaculture and the food industry. Here, the potential application of phage techniques in wastewater treatment systems to improve effluent and sludge emissions into the environment is discussed. Phage-mediated bacterial mortality has the potential to influence treatment performance by controlling the abundance of key functional groups. Phage treatments have the potential to control environmental wastewater process problems such as: foaming in activated sludge plants; sludge dewaterability and digestibility; pathogenic bacteria; and to reduce competition between nuisance bacteria and functionally important microbial populations. Successful application of phage therapy to wastewater treatment does though require a fuller understanding of wastewater microbial community dynamics and interactions. Strategies to counter host specificity and host cell resistance must also be developed, as should safety considerations regarding pathogen emergence through transduction.Item Open Access Bioaugmentation for the improvement of nitrification in wastewater treatment(Cranfield University, 1993-07) Stephenson, Dianne; Stephenson, TomThe literature relating to nitrification in wastewater treatment and bioaugmentation as a method to enhance wastewater treatment processes is reviewed. The use of a commercially available bioaugmentation product (based on a Nitrosomonas culture), which claimed to enhance nitrification in biological wastewater treatment was investigated.The product was tested in full scale trials, in shake flask experiments and its efficacy modelled using a simple activated sludge simulation. At full scale trickling filter plants a bioaugmentation product designed to enhance BOO removal was also tested. This product increased BOO removal by up to 7% in the recovery period following low temperature. The Nitrosomonas culture improved percentage ammonia removal by nearly 10% in trickling filters even at low temperatures of 6.5°C. A maximum improvement of 20% occurred at one trickling filter site at higher temperatures. At activated sludge sites the Njtrosomonas culture improved the nitrifying ability of the activated sludge, as assessed by the laboratory standard method, and at one site noticeably improved percentage ammonia removal during periods of high dosing. At one site the maximum improvement was an increase of 22% in percentage ammonia removal during high dosing. However the operational parameters, loads, hydraulic retention time, mixed liquor suspended solids, sludge age and temperature had a great effect on nitrification. If better process control was applied at one of the works the plant would have had little trouble nitrifying i.e. lower loads, higher HRT, MLSS and sludge age during low temperatures. Sludge wastage regimes contributed greatly to the failure to nitrify. It was found that the activity of the Nitrosomonas culture increased with temperature and acclimatisation and decreased on inoculation into activated sludge. The product facilitated nitrification when inoculated into non-nitrifying activated sludge. Ammonia removal increased with size of inoculum. The simple dynamic model described showed the development of a Njtrosomonas population from inoculation with the Nitrosomonas culture. The model showed that the effectiveness of a bioaugmentation product in activated sludge would depend on the amount of nitrifiers returned to the aeration basin more than other operational factors. The model predicted full nitrification at one of the full scale sites within three days. Bioaugmentation did enhance nitrification at full scale works. However, dosage rates required for improvement meant that conventional methods such as better process control or retrofitting would be economically more feasible.Item Open Access Biological treatment of coke making wastewater.(2017-04) Raper, Eleanor; Soares, Ana; Stephenson, TomProduction 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.Item Open Access Biomass characteristics, aeration and oxygen transfer in membrane bioreactors: their interrelations explained by a review of aerobic biological processes(Springer, 2005-11) Germain, Eve; Stephenson, TomMembrane bioreactor (MBR) is a promising alternative to conventional wastewater treatment methods. However this process is still under-used due to its high running costs. Its main power requirement comes from aeration, which is used to supply dissolved oxygen to the micro-organisms and to maintain the solids in suspension. In addition, in submerged MBRs, aeration is used for membrane cleaning. A complex matrix links the biomass characteristics, the aeration and the oxygen transfer. These parameters can impact on each other and/or delete one another effect. In order to understand the phenomena occurring in MBRs, similar aerobic biological processes, such as fermentation, mineral industry and slurry, were investigated. This review discusses the interrelations of the biomass characteristics (solids concentration, particle size and viscosity), the aeration intensity and the oxygen transfer in MBRs.Item Open Access Biomass effects on membrane bioreactor operations(Cranfield University, 2004-10) Germain, E. A. M.; Stephenson, TomDiverse operating parameters were investigated for their effects on biomass characteristics, membrane fouling and aeration efficiency in submerged membrane bioreactors (MBRS). The characteristics of the solid phase of the biomass were affected by the biomass state (unstabilised, stabilising and stabilised) and by the SRT and HRT, whereas the characteristics of the liquid phase appeared to be more dependent on inuent composition and strength. Under operating conditions at constant SRT and HRT, the biomass characteristics reached their stabilised state aer 1.0±0.3 SRT. The impact of membrane aeration, permeate flux and biomass characteristics was determined for biomass at unstabilised state and at stabilised state. A transitional permeate flux was observed between 16.5 and 22 l.m`2.h`l, below which no significant fouling was observed regardless of the permeate flux, membrane airflow velocity and biomass characteristics. Above transitional flux, membrane fouling increased and was affected by the permeate flux, the membrane aeration velocity and parameters either characterising the liquid or the solid phase of the biomass depending on the carbohydrate concentration of the liquid phase. A comparison of ne and coarse bubble aeration efficiency for biomass at unstabilised state and at several airflow rates established that ne bubble aeration was more efficient in tem of oxygen transfer rate, but led to similar values to coarse bubble aeration for ot-factor. The effects of airflow rate and biomass characteristics on oxygen transfer coefficient and ot-factor were determined for biomass coming from pilot and full scale submerged MBRS treating municipal and industrial wastewaters. Solids concentrations (correlated to viscosity), COD concentration of the liquid phase, carbohydrate concentration of the EPS and volumetric airflow rate were found to affect the aeration efficiency parameters. A transitional solids concentration existed around 15 g.L", above which low or no oxygen transfer occurred.Item Open Access Biomass effects on oxygen transfer in membrane bioreactors.(Elsevier, 2007-03) Germain, Eve; Nelles, F.; Drews, A.; Pearce, P.; Kraume, M.; Reid, E.; Judd, Simon J.; Stephenson, TomTen biomass samples from both municipal and industrial pilot and full scale submerged membrane bioreactors (MBRs) with mixed liquor suspended solids concentrations (MLSS) ranging from 7.2 to 30.2 g L−1 were studied at six air-flow rates (0.7, 1.3, 2.3, 3, 4.4 and 6 m3 m−3 h−1). Statistical analyses were applied to identify the relative impacts of the various bulk biomass characteristics on oxygen transfer. Of the biomass characteristics studied, only solids concentration (correlated with viscosity), the carbohydrate fraction of the EPS (EPSc) and the chemical oxygen demand (COD) concentration of the SMP (SMPCOD) were found to affect the oxygen transfer parameters kLa20 (the oxygen transfer coefficient) and α-factor. The relative influence on kLa20 was MLSS>aeration>EPSc>SMPCOD and on α-factor was MLSS>SMPCOD>EPSc>aeration. Both kLa20 and α-factor increased with increasing aeration and EPSc and decreased with increasing MLSS and SMPCOD. MLSS was found to be the main parameter controlling the oxygen transfer.Item Open Access Biomodule - a combined structured and granulat media BAF(School of Water Sciences, Cranfield University, 1999-03-03) Williams, T. R.; Stephenson, TomBiological aerated filters operate as fixed film systems in which micro-organisms grow on a submerged fixed structured or granular inert support media within an aerated reactor (Stephenson et al., 1993). Periodic backwashing of the filter is required as the media bed gradually clogs due to the growth of biomass and retention of solids. The advantage of the BAF process is the small footprint it occupies relative to comparable processes such as activated sludge and trickling filters. The small footprint is due to the fact that the fixed film of biomass on the support material (media) leads to a high concentration of active bacteria per unit volume of the media and thereby to relatively small reactors. Another advantage is the retention of suspended solids that eliminate the need for final sedimentation tanks (Hagedorn et al., 1994). For the same degree of treatment, biofilters require approximately three times less aeration volume than activated sludge units, and twenty times less than trickling filters (Smith et al., 1992). In summary BAF systems are used for providing a treatment method for reducing the amount of organic carbonaceous material (BOD/COD), suspended solids and ammonia in wastewater.Item Open Access Biosolids recycling impact on biofilm extracellular enzyme activity and performance of hybrid rotating biological reactors(Elsevier, 2019-11-30) Hassard, Francis; Biddle, Jeremy; Cartmell, Elise; Coulon, Frederic; Stephenson, TomBiological processes for wastewater treatment is limited by extracellular enzyme activity (EEA) of the biofilm on polymeric substrates. The efficiency of biodegradation / biosorption mechanisms causing EEA and organic load removal in biofilms remains unknown. Our hypothesis was that the limiting step of biological process can be overcome by biostimulation and/or bioaugmentation of the return sludge in hybrid biofilm reactors, which leads to competition between suspended and attached bacteria and lower effective substrate to microrganism ratio. Therefore, we considered more active biosolids to perform best at enhancing reactor removal rate. To test this, the efficacy of recycling distinct bio-solids types considered to have different bacterial activity such as final effluent (FE), humus solids (HS) and recycle activated sludge (RAS) on performance improvements of rotating biofilm reactors (RBRs). These bio-solids were investigated under high organic loading rates (OLR) and solids loading rates (SLR) using pilot scale reactors receiving real municipal wastewaters. Controlled overloading of RBRs revealed that EEA improved with increasing OLR/SLR. High SLR (>3.3 kg Total Suspended Solids m−2 d−1) delayed and decreased the reduction of organic and inorganic removal rates in the biological processes which commonly occurs under high OLRs. This effect was more pronounced in the highest activity solids (RAS > HS > FE) suggesting the activity and function of bio-solids was critical to improve performance of RBRs. High OLR and SLR induced efficient denitrification and organics removal within the biofilm reactor at residence times of <5 min. Recycling active solids permitted EEA despite overloading which was critical to the performance of the RBRs.Item 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, AnaMicrobial 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.Item Open Access Chemical Inhibitors for Biomass Yield Reduction in Activated Sludge(Cranfield University, 1999) Mayhew, Maxine Eleanor; Stephenson, TomIncreasing legislation and rising treatment and disposal costs have promoted optimisation of the activated sludge process to encompass reduction of waste biomass. Manipulation of process control such as increasing sludge age and decreasing food to microorganism ratio can lower waste sludge production, but capital works as well as increased operating costs in the form of power requirement for oxygen supply may be required. The need for a cost effective method of biomass reduction without capital expenditure has prompted research into methods beyond process control. The use of chemicals capable of disrupting microorganism metabolic pathways can theoretically allow continuation of catabolic (degradative) paths whilst halting some or all of the anabolic (growth) pathways. This project explored the use of metabolic inhibitors (uncouplers, tricarboxylic acid cycle inhibitors and antibiotics) to reduce the yield of the activated sludge process. Initial respirometric studies identified many chemicals capable of interacting with the activated sludge microorganisms. Increased oxygen uptake rate was taken as an indication of a good uncoupler, and tests highlighted 4 chemicals with significant potential for achieving biomass reduction (trypan blue, rotenone, 2,4 DNP and 4 NP). These chemicals were then tested at a laboratory scale and at bench scale in both batch and continuous simulations. Simulations were carried out using activated sludge and settled sewage feed to obtain as realistic conditions as possible. In batch tests, trypan blue, rotenone and 2,4 DNP successfully reduced mixed liquor suspended solids accumulation with little effect on COD removal compared to controls. In continuous simulations, 2,4 DNP and 4 NP both lowered yield with respect to their relative controls. Rotenone addition did not result in lowered yield. In all cases, any yield reduction was not at the expense of process efficiency in terms of COD and BOD removal. At pilot scale, 2,4 DNP almost halved the observed yield compared to the control whilst having no significant effect on BOD, COD or ammonia removal, nitrite and nitrate production, SVI or CST. Addition of chemical uncouplers had little effect on the species diversity of the activated sludge though a reduction in the floc size was observed in treated samples. Selection of a suitable chemical can result in reduced yield without detrimental effect to process efficiency in the activated sludge process. An increase in oxygen consumption occurred which has an associated cost implication, but this was not found to be significant compared to the savings made by reducing the yield.Item Open Access A comparison of floating and sunken media biological aerated filters (BAF)(1997-03) Mann, Allan; Stephenson, TomThe aim of this experimental work was to directly compare the performance of two types of media support in pilot scale biological aerated filter (BAF) reactors. The two media types were identical in shape and size except one was sunken with a relative density of 1.05 and the other floating with a relative density of 0.92 and made of polypropylene. Empty bed tracer studies were initially undertaken to ascertain the hydraulic characteristics of the media types under different process conditions. Almost ideal plug-flow was seen without aeration but with aeration some mixing and by-passing was seen which increased with higher aeration rates. Aerator design and positioning had little effect on the flow and that the sunken media would perform best in downflow and the floating media in upflow during biological treatment. Two methods of start-up were employed during unsteady state analysis, activated sludge seeding and the use of the process liquid (settled domestic sewage) at the operational flowrate. Both methods showed a similar total start-up time of 28 d. At steady state the floating media removed 78% suspended solids (SS) and 75% soluble chemical oxygen demand (sCOD) compared to 66% and 68% respectively in the sunken media. At high flowrates and during shock loadings of up to 1.5 times the nominal flowrate the floating media again showed a better performance than the sunken media. With increasing shock loadings the recovery time increased with a corresponding decrease in solids and soluble COD removal rates. At the maximum SS loading of 1.397 kg m'3 d'1 ( 1.403 kg m"3 d'1 sCOD) only 35% (30% sCOD) removal was seen in the sunken media compared to 60% (40% sCOD) in the floating media. The steady state results were used to produce an empirical model relating effluent soluble COD to influent COD and reactor height. Assuming plug flow the profiles showed a first order rate of reaction. A first order empirical model was then established based on that used for trickling filters, which produced constants dependent on the media type. During tertiary treatment low ammonia loadings of 0.2 kg m'3 d"1 restricted autotrophic growth and led to preferential growth of heterotrophic bacteria. At ammonia loadings of up to 1.16 kg m'3 d"1 nitrification was rapid. Below 5 °C nitrification was minimal but almost full nitrification was achieved at approximately 10 °C. Though backwashing was carried out only on a weekly basis, overwashing appeared to have caused a gradual reduction in treatment efficiency. During nitrification the sunken media was more efficient at ammonia removal than the floating media, indicating that the autotrophic bacteria prefer the more open structure of the sunken media. Reactor profiles indicated a zero to half order reaction.Item Open Access Consequences of pH change on wastewater depth filtration using a multimedia filter(Elsevier, 2017-10-21) Ncube, Philani; Pidou, Marc; Stephenson, Tom; Jefferson, Bruce; Jarvis, PeterDifferent media materials in a multimedia filter have the potential to trap particles of different characteristics dependent on the media-suspension particle interactions. However, the removal of particles from wastewater secondary effluent using granular media filtration is relatively poorly understood because of the complexity of the wastewater matrix. Often the wastewater treatment process is liable to undergo pH changes due to removal or addition of chemicals in the treatment chain or from biological instability which in turn may alter the wastewater characteristics. Wastewater contains a mixture of organic and inorganic components, dissolved or particulate which may influence the aggregation and deposition of suspension solids during depth filtration. Changes in wastewater pH has the potential to change the wastewater matrix and media surface properties hence affecting aggregation and deposition in wastewater filtration. This study investigated how pH change affects wastewater filtration by monitoring zeta potential, aggregation and deposition of solids. The wastewater and filter media were also characterised over a range of pH from 1 to 13. Aggregation and deposition of wastewater solids was found to be most efficient near neutral pH. This was not concurrent with the conditions of lowest net charge in the system.Item Open Access Design and evaluation pf a small package sewage treatment system(Cranfield University, 2003-06) Daude, D.; Stephenson, TomThe aim was to develop and subsequently evaluate a small package sewage treatment system that combined the commercial demands of the market with current and future environmental legislation in the UK. Questionnaires sent to key customers confirmed results from an initial literature review that non-process related features such as installation, plant price, aesthetic impact, maintenance requirement and operation have a similar impact on the final purchase decision than the achievable effluent quality. Conventional submerged aerated filter (SAF) technology was chosen for its simple operation over more advanced treatment technologies like sequencing batch reactors (SBR) and membrane bioreactors (MBR). The combination of SAF technology and jet aeration allowed the use of an exceptionally shallow tank structure. Two settlement stages for primary treatment and final clarification completed the new unitank design. Following successful clean water and field trials of a prototype unit, the new design was finalised, set-up for production and launched into the market. A second trial plant was permanently installed at a rural cottage in Cranfield, UK, with the objectives to validate and further improve the performance of the new design. Despite high variations in influent conditions, the trial unit produced a good effluent quality with average effluent BOD s , COD and SS levels of 16 mg rI, 100 mg rI and 30 mg rI respectively, thereby achieving overall removal efficiencies of 95.3%, 86.2% and 88.5% respectively. However, effluent ammonia nitrogen (~-N) levels were found to be inconsistent varying from as low as 9 mg rI to over 60 mg rI. Similar findings were revealed from other plants in the field serving domestic and non-domestic applications. The compact and exceptionally shallow tank structure combined with a competitive retail price met the commercial needs of the target market, which resulted in increased sales turnover and market share.Item Open Access Development of a novel lightweight media for Biological Aerated Filters (BAFS)(School of Water Sciences, Cranfield University, 1999-03-03) Moore, R.; Quarmby, Joanne; Stephenson, TomClay has been foamed and extruded using novel technology, to produce a lightweight media called StarLight C. Altering the production process parameters allows control of the media diameter, density, strength, and surface roughness. In its application as a Biological Aerated Filter (BAF) media, a low density may be advantageous since this will reduce the minimum fluidisation velocity (Vmf) of the media. Consequently a lower liquid velocity will be required during filter backwashing, which could reduce the operating costs and increase the productivity of the reactor. This paper reports the performance of StarLight C and standard expanded clay (media A) as media in pilot scale BAFs treating settled sewage with hydraulic residence times between 58 and 96 minutes. The BAFs were backwashed every 24 hours at a liquid flow rate corresponding to 40% of the Vmf of the media. The BAF using StarLight C required approximately half the volume of backwash water needed by the BAF filled with media A. To optimise the performance of BAFs further the filter run time should be maximised. This requires the media size and voidage to be maximised without compromising filtration efficiency.Item Open Access Development of a novel medium to improve the performance of Biological Aerated Filters (BAFs)(1999-10) Moore, Rebecca Ellen; Stephenson, Tom; Quarmby, Joanne; Millier, P.A foamed clay, StarLight C, was selected as a potential BAF medium after qualifying as a filter medium according to the BEWA standard tests, and showing the propensity to collect a biofilm. At loading rates > 10 kg COD/ m3 working volume/ d, two pilot- scale downflow BAFs running in parallel and containing either StarLight C or medium A (a standard expanded clay) achieved a mean of 87% suspended solids removal and 75% soluble COD removal. Both reactors were backwashed daily for ten minutes at a liquid flow rate corresponding to 40% of the minimum fluidisation velocity (Vmf) of the media. The approximate experimental Vmf of StarLight C was 120 m/h compared to 215 m/h for medium A. Therefore, the BAF using StarLight C exhibited between 11 and 19 % increased productivity at liquid velocities from 1.4 to 2.4 m/h. Lowering the Vmf of a BAF medium should also reduce the operating and capital costs of the process. According to representatives of the wastewater treatment companies, high operating costs are the major disadvantage of the BAF process. Increasing the feed bentonite concentration from 35 g/1 to 56 g/1 produced a StarLight C variant with improved crush resistance and a lower attrition rate. Meanwhile, a larger extruder nozzle was used to increase the particle size of the medium. Pilot-scale trials showed that the maximum run times were extended by between 8 and 31 hours when using the larger variant (2.5-4.5 mm diameter) compared to the smaller (1.5-3.5 mm diameter). Observing logarithmic head loss development and the cessation of suspended solids removal in the lower region of the reactor, suggested that the smaller StarLight C was an inefficient filter medium. Using an environmental scanning electron microscope, hydrated biofilms were observed growing on StarLight C’s surface. The highly variable biofilm distribution and structure is not accounted for by current biofilm and mechanistic process models. A first-order empirical model described the removal of soluble COD in the top section of the reactors containing medium A, small StarLight C and large StarLight C. The first-order constants were dependant on the liquid velocity and at 1.4 m/h were 61 d"1, 45 d'1 and 33 d"1 respectively.Item Open Access Development of a recitculating plastic media Biological Aerated Filter (REBAF)(School of Water Sciences, Cranfield University, 1996-06-12) Stephenson, TomTrue biological aerated filters (BAFs) combine two unit operations in one reactor: aerobic biological treatment and subsequent biomass separation from the effluent (Stephenson et al., 1993). The submerged media used as support for the microbial biofilms are usually granular in nature and are therefore able to also act as depth filtration media. Therefore BAFs should provide a small footprint alternative to traditional aerobic processes. Indeed, Dillon and Thomas (1990) noted that a "good quality effluent" was possible up to a loading of 4.1 kgBOD/m3/d (9.1 kgCOD/m3/d); with an automated backwash programme influent BOD5 was reduced by between 90.3 % and 97.6 %. Pujol et al. (1992) found an effluent standard of 90 mgCOD/I difficult to achieve for loading rates above 6.0 kgCOD/m3/d. Stensel et al., 1988) achieved 88 % removal of ammonia at a loading rate of 1.6 kgBOD/m3/d and modern BAFs can achieve simultaneous carbonaceous BOD and ammonia removal at loading rates of 2.5 kgBOD/m3/d (Rogalla and Payraudeau, 1987). Despite the impressive loadings rates possible, BAFs require large volumes of water for backwashing on a regular basis to prevent blockage of the media. Therefore these processes require large volume tanks to hold effluent for backwashing and mudwells for collection of the backwash water. In addition, large pumps and pipework systems are needed to achieve the required backwash flowrates. In depth filters, this problem can be overcome by using continuous filtration systems, e.g. Dynasand (Kramer and Wouters, 1993). These incorporate a media recycle and wash system which allows uninterrupted treatment to occur. In Dynasand, the liquid flow is upwards and the media flow downward. The sand is removed from the base of the reactors, cleaned and then transported to the top of the bed. Thus the water exiting the filter always see a clean polishing layer of sand. The sand is removed by means of an airlift pump at the base of the reactor. Moving bed systems have been tested on sewage as an alternative to sedimentation (Mixon, 1973). It is possible that the advantages of the moving bed principle could be combined with BAF technology to reduce or eliminate the need for expensive backwashing facilities. Such a system would not be the same as moving bed biofilm reactors described by Rusten (1984) and Hem et al. (1994) which require separate secondary sedimentation tanks. The current paper reports on an investigation into operating a plastic media BAF with media recirculation in order to eliminate backwashing.Item Open Access Dinitrogen oxide production by a mixed culture of nitrifying bacteria during ammonia shock loading and aeration failure(Springer, 2002-12-01T00:00:00Z) Burgess, Joanna E.; Colliver, Bettina B.; Stuetz, Richard M.; Stephenson, TomA number of experiments was conducted in order to establish if N2O in the exhaust gas from an aerobic consortium of nitrifiers could be used as an indicator for monitoring the nitrification process. Laboratory-scale experiments with an activated sludge system showed a strong correlation between ammonia shock loads and both the concentration of N2O and the rate of increase of N2O in the exhaust gas for shock loads less than 1.60 mg ammonical nitrogen (NH3-N) per g total suspended solids (TSS). For greater ammonia shock loads, correlation was found between build-up of nitrite in the aeration tank and the concentration of N2O in the exhaust gas from the tank. When subjecting the system to aeration failure, a similar pattern was seen, with a correlation between nitrite build-up in the aeration tank and increases in the concentration of N2O in the exhaust gas. The results from this work suggest that the changes in N2O concentration in the exhaust gas from a nitrifying process may be a useful parameter for monitoring such processes.Item Open Access Disinfection of grey water(Cranfield University, 2007-10) Winward, Gideon Paul; Stephenson, TomThe reuse of grey water, for applications such as toilet flushing and irrigation, represents a potential sustainable solution to water shortages experienced by regions worldwide. Although reused grey water is not intended for potable use, the potential for transmission of waterborne pathogens by aerosol inhalation, topical contact, or indirect ingestion is a key concern for grey water reuse. This thesis explores the pathogen content of grey water and investigates pathogen removal through treatment and disinfection processes. The impacts of organic and particulate material in grey water on the efficacy of disinfection processes are investigated in depth. Grey water can potentially harbour a range of pathogenic microorganisms, with opportunistic bacterial pathogens in grey water indicating a particular risk of grey water reuse for the vulnerable members of society. The disinfection of grey water is therefore critical prior to reuse. Particulate material in grey water limits the efficacy of disinfection by chlorine, ultraviolet light, and origanum essential oil, by shielding microorganisms from the applied disinfectant. Microbial resistance to the disinfectants was linked to the particle size distribution of the grey water, with increasing particle size offering greater protection to associated microorganisms. Additional organic material was shown to reduce the applied disinfectant but no impact on microorganism resistance to disinfection was observed when a constant disinfectant dose was maintained. Treatment of grey water, targeting the removal of large particulate material, improves the efficacy of grey water disinfection, allowing compliance with stringent microbiological standards for urban water reuse.