Cranfield Conferences and Symposia
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Browsing Cranfield Conferences and Symposia by Publisher "School of Water Sciences, Cranfield University"
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Item Open Access BAF's get media attention(School of Water Sciences, Cranfield University, 1999-03-03) Smith, Alan J.; Edwards, Wayne; Hardy, Peter; Kent, TanyaThe Biological Aerated Filter is an accepted wastewater treatment option that has the advantage of treatment and solids separation in a single, compact reactor. Choosing the correct support media for the attached biomass is critical in the design and operation of the process to achieve the required effluent quality. This paper considers the physical properties of granular media, such as density, shape, size and surface structure in relation to biomass attachment and treatment efficiency. A pilot evaluation of downflow granular media BAF columns filled with media of different particle sizes, operated over a range of hydraulic and volumetric loading rates, is reported. Nitrification on the smallest 2-4 mm media was found to be inhibited at loading rates above 0.5 kg NH4-N and 2.5 kg BOD / m3media/d due to the greater hetrotrophic growth and enhanced wash requirement.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 Colne Bridge (Huddersfield) WWTW - Biopur plant process design and performance(School of Water Sciences, Cranfield University, 1999-03-03) Holmes, J.; Dutt, S.The complexity of the Huddersfield works and the issues addressed by the scheme design engineers are highlighted, including the need for a robust nitrification process due to the high levels of nitrification inhibition in the plant feed. Issues influencing the Biopur process selection are discussed and a detailed description of the Biopur process design is given, together with details on process commissioning and performance testing. Finally the plant performance to date is summarised together with a list of issues for consideration on future plants.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 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 Experiences with Biological Aerated Filters for treatment of settles sewage and dairy effluent(School of Water Sciences, Cranfield University, 1996-06-12) Rundle, HowardTwo plants are described which are designed for partial (or roughing) treatment of settled sewage, and settled sewage with dairy waste, and some of the lessons learned from these are described. These plants are ColOX units which is a trade name for a BAF using sunken mineral medium, normally operated in upflow mode.Item Open Access Industrial applications of Biological Aerated Filters(School of Water Sciences, Cranfield University, 1999-03-03) Rundle, Howard; Chen, Jeffrey J.; McCarty, DonBiological aerated filters (BAF's) are compact wastewater treatment reactors capable of achieving biological oxidation and solids removal in a single reactor. The basic principle of operation is that biomass grows on the surface of a submerged medium. Air is injected at or near the base of the medium. The effluent to be treated flows either upward or downward through the bed. Biological oxidation occurs during passage through the bed and suspended solids are retained within the bed. These solids are removed periodically by backwashing. The use of BAF technology is well known for treatment of municipal sewage. The application of this technology to industrial effluents is less well documented. In this paper the application of the TETRA ColOXTM BAF to treatment of effluents arising from paper making, from steel making, from plastics manufacture and from the electronics industry is described.Item Open Access Modelling Biological Aerated Filters for wastewater treatment(School of Water Sciences, Cranfield University, 1996-06-12) Mann, Allan T.; Stephenson, Tom1. Biological aerated filters (BAFs) are submerged three-phase fixed media reactors for wastewater treatment. A major characteristic of BAF reactors is the use of granular media which allows solids separation as well as secondary or tertiary biological treatment in one unit. The aim of this work was to design a simple empirical model relating influent soluble chemical oxygen demand (sCOD) to effluent sCOD and reactor height, verify experimentally the suitability of this model and ascertain the relationship between model constants and reactor performance. The theoretical model was based on that designed for trickling filters as both fixed-film processes show a similar plug flow pattern. 2. Two reactors were set-up to run in parallel treating settled domestic sewage using media identical in size and shape except one was less dense than water (relative density 0.92) and the other denser than water (relative density 1.05). The reactors were run upflow with liquid flowrates of 0.2 to 0.5 I mire' and an air : liquid ratio of 10 : 1. After 4 weeks from start-up steady-state was reached. From this point, samples were taken at different heights along the reactors at timed intervals and profiles of sCOD removal against reactor height were produced. This analysis was repeated for a number of different flowrates and organic loadings (0.57 to 1.40 kg sCOD c1-1). The resulting data was then used with the empirical model, which was based on a first order reaction, to calculate the values of k* (overall process constant) and n (media factor). A much higher value of k* was found for the floating media (100) compared with the value found for the sunken media (33). This indicated the greater efficiency of sCOD removal in the floating media. The values of the media constants were similar showing the similarity in the media shape and size.Item Open Access A new generation of Aerated Filter(School of Water Sciences, Cranfield University, 1999-03-03) Martin, J.The use of the activated sludge process is a very well known technology. It is and has been used very widely in full scale plants from its first development at the Davyhulme works in Manchester. However this process becomes very difficult to upgrade or to extend in order to ensure compliance with either more stringent discharge consent conditions or to achieve the same quality of discharge where increasing flows are the problem. This problem of upgrading or extension to existing works led OTV almost twenty years ago to develop the bio-filter process. This process consists of essentially biological filters operating either in the down flow or up flow mode, the main benefits of this system being they are compact in their space requirements, together with their ability to combine both filtration and aerobic/anaerobic bio degradation. They are used for the removal of suspended solids, COD, BOD, ammonia (and nitrate) either in the secondary or the tertiary treatment stage, plus with the use of a precipitating chemical, they can also be used for the removal of phosphates.Item Open Access Operating performance and future development of the BioBead (TM) system(School of Water Sciences, Cranfield University, 1996-06-12) Cantwell, A. D. C.This paper reports on the performance of the BiobeadTM version of the Biological Aerated Flooded Filter Process over the last few years. More than twenty of these units have been installed in the U.K. and the operating experience has enabled further development steps to be made, the range of application to be widened and the design methods associated with the technology to be refined. Operating problems have arisen when the design load is less than that found upon commissioning. For the BAFF system because of the short retention times within the media bed it is essential that excess dissolved oxygen is present at all times. Diurnal peaks in load must be allowed for in design. A related problem is that of septic influent. Septicity has a profound influence on the development flora and fauna in any biological system and so it is preferable that septicity is corrected outside of the BAFF system. Similarly intermittent saline intrusion will reduce performance, although to a lesser extent than that found on Activated Sludge processes. The final problem with BAFF's is that of media quality which is exclusively a quality control problem. The major engineering change introduced to the Biobead system is the aeration system which is now a simple sparge tube immersed in the media. This increases the allowable air rates and is particularly helpful in designing for larger than normal diurnal variation. Similarly, the air scour system now used an array of simple drop tubes. The performance of the media has been further improved by the use of charge neutralising additives to the plastic formulation together with broadening the range of source materials able to produce the textured surface finish. Modules of any size can be produced by assemblies of smaller modules of proven engineering performance.Item Open Access Operational trials of different propriety lamella and BAF systems(School of Water Sciences, Cranfield University, 1996-06-12) Budge, F.; Gorrie, D.Halcrow Scotland were appointed by Grampian Regional Council (now North of Scotland Water Authority) in April 1993 to carry out the Aberdeen Wastewater Treatment Feasibility Study. The study started with a verification of the flows and polluting loads generated within the catchment followed by a review of the treatment technologies available. The purpose of examining the available technologies was to ascertain the land areas required. Different technologies had different land requirements, and it was important to evaluate this for the site selection stage. Inevitably, conventional activated sludge treatment processes required the greater land take, but it was the only proven technology as far as the client was concerned. Other treatment processes, loosely termed "small footprint", could be accommodated within a much smaller area. The most promising of these processes was Biological Aerated Flooded Filters (BAFF), but at that time there were very few plants operating in the UK and none in Scotland. Halcrow recommended that the client establish pilot plant trials of the BAFF process. For minimal land take lamella plate separators would be required in the primary treatment stage and it was decided to include this compact settlement process (with or without chemical assistance) in the pilot plant trials.Item Open Access Optimising and trouble shooting Biological Aerated Filters(School of Water Sciences, Cranfield University, 1996) Smith, A. J.; Brignal, W. B.Legislation requiring the first time treatment of coastal wastewater discharges and the uprating of existing treatment plant to meet tighter quality standards has led to the introduction of the Biological Aerated Filter (BAF) as an alternative to conventional treatment options. Correct process design will ensure the required effluent quality standards are met, however, with the rationalisation of operating practises currently under way in most UK water service companies it is equally important to understand the operating limits of the process and agree an appropriate hardware specification that suits the needs and competencies of the operator. The generic Biological Aerated Filter comprise an aerated reactor containing submerged inert media supporting the growth of an attached biomass, through which the wastewater flows. No secondary clarification is required and excess biomass is removed by washing the media bed. Similar submerged, attached growth reactors which are not washed and do require secondary solids removal are known as Submerged Aerated Filters (SAF).Item Open Access Recent application and developments of the Biobead system(School of Water Sciences, Cranfield University, 1999-03-03) Cantwell, A. D. C.; Mosey, F. E.This paper describes the background of recent engineering changes to the BiobeadTM system. In particular known design pitfalls are described. The development of technically improved aeration and flow distribution methods are outlined. The extension of the system to combined C & N removal is outlined together with some recent experimental data which shows higher than expected de-nitrification performance. The benefits of a pre-filtration before the aerated part of the media bed is apparent particularly when removal of industrially derived COD is required to reach UWWT directives standards. This method also allows tertiary treatment of high influent solids whilst maintaining Ammonia removal.Item Open Access Recent experience and developments using the Biopur BAF process(School of Water Sciences, Cranfield University, 1996-06-12) Clarke, S.Biological processes have been used to treat waste waters for many years in order to improve public health, remove offensive odours and to reduce pollution in the receiving watercourse. In the 1980's public concern led to UK and European legislation to further improve the treatment required of sewage prior to passing to a watercourse. This legislation is now embodied in the UK Bathing Water Directive and the Urban Waste Water Treatment Directive. This has lead to the improvement of sewerage and the reduction of the number of sewage discharges, as more sewers are now being fed to sewage treatment works. Sewage works have therefore often become overloaded and now require to be upgraded in order to meet these legislative requirements. In some cases completely new sewage treatment works have been required. Development of sewage treatment works is often in already built up areas where land can be often restricted. This combination of a sizeable market with technical constraints such as available land, odour control requirements and noise restriction has encouraged major innovation and development of sewage treatment processes to provide cost effective solutions using new technology. One such innovative process is the Biological Aerated Filter (BAF) of which many systems are now available on the market and well over 100 plants are currently operated worldwide, treating both industrial and domestic waste water for carbonaceous pollutant, ammonia or complete nitrogen removal. One innovative system that is now proving popular for treating wastewaters is the Sulzer Biopur biological aerated filter. This uses a submerged structured packing rather than the more common granular forms, which leads to a number of advantages for operating companies. This paper presents a brief description of the Biopur BAF process, its key operating features, and three case studies using the Biopur process for wastewater treatment in the UK.