2nd Symposium on Biological Aerated Filters (BAF2) - 1996
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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 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.Item Open Access Aeration optimisation of Biolgical Aerated Filters(of Water Sciences, Cranfield University, 1996-06-12) Pearce, Peter A.Aeration costs account for a large proportion of the total running costs of biological aerated filters (BAFs) which are in themselves an energy intensive form of treatment process. Optimisation of oxygenation efficiency is therefore an obvious goal as small improvements in operating efficiency will yield significant savings in energy consumption. This paper will deal with the oxygen transfer characteristics of a downflow BAF using mineral media. Clean water and operational performance are compared over a range of hydraulic and organic loadings and a range of air flow rates. Alternative aeration devices and aeration procedures were also evaluated but will only be discussed in summary in this paper.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 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 Poole waste water treatment BAF plant(of Water Sciences, Cranfield University, 1996-06-12) Brewer, Peter1. The town of Poole in south east Dorset has undergone substantial development during the 1980's. Wessex Water recognised the pressure on the water services in this region and commissioned a strategy study for this region. This resulted in a proposal to extend each sewage treatment works in that area up to a standard required by the receiving watercourse. 2. The 2 main river catchments are the River Stour and River Avon. The latter flows into Christchurch harbour in the east, whilst the Stour flows into Poole Harbour. Poole WWTW discharges directly into Holes Bay in the upper reaches of Poole Harbour.This tidal estuary is of national importance in environmental terms, whilst being extensively used for recreation. 3. Consultations with the National Rivers Authority (now the Environmental Agency) led to a discharge standard of 20 mg/I BOD; 30 mg/I SS;10 mg/I Amm N on a 95 percentile basis being accepted for design of the extensions. Indications are that in the long term nutrient removal and disinfection may well become a necessity. The EA has plans to conduct extensive surveys of Poole Harbour in the next few years. 4. The extensions to Poole VWVTVV will raise the treatment capacity from a population equivalent of 129,000 to some 151,000. Dry weather flow will be 46,700 m3/d, and flow to full treatment will be 17,700 m3/d at the 12 year planning horizon. These extensions now provide a treatment plant with some 48% increase in hydraulic capacity, whilst producing a fully nitrified effluent. 5. The existing treatment plant consists of essentially two separate plants, known as eastern and western, both activated sludge plants. The site is quite close to the historical town centre, and growth in the town over the last half century has extended well beyond the works site. Consequently, the works is now completely surrounded by development fro housing to light industry. Indeed, we now have the benefit of a major supermarket on our southern boundary, some 20m from the inlet pumping station!Item Open Access Experiences with BIOFOR reactors at Veas, Norway(of Water Sciences, Cranfield University, 1996-06-12) Sagberg, Paul; Grundness Berg, KirstiBoth the local situation in the inner Oslofiord and the political decisions of the countries surrounding the North Sea called for further treatment. Through 1989 and 1990, VEAS put bits and pieces of known technology together to compose a process for nitrogen and phosphorus removal to be installed in the area of the existing sedimentation tanks, only extended in depth. In addition, the process should reduce the amount of sludge considerably. A working hypothesis was presented in 1990 and later named "The VEAS Concept" by prof. H. Odegaard, Techn. Univ. of Trondheim. The status for the development is described in more detail by Sagberg et al. (1995). Figure 1. show the state of the VEAS Concept by end of 1994. Further adjustments has later been made and new will be.Introductory tests were run by VEAS with RBC from Klargester, Mechana and Envirex, with submerged Munthers media, with the Kaldnes moving bed media and with the upflow BIOFOR system from Degremont. After international pre-qualification, call for turn key tenders, which were rejected, and finally licence negotiations, the BIOFOR system was selected for full scale application.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 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 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).