Browsing by Author "Quarmby, Joanne"

Now showing 1 - 5 of 5
  • Thumbnail Image
    ItemOpen 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, Tom
    Clay 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.
  • Thumbnail Image
    ItemOpen 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.
  • Thumbnail Image
    ItemOpen Access
    The effect of ultrasonic sludge pre-treatment on anaerobic digestion
    (1998-09-11) Scott, Joanna Ruth; Quarmby, Joanne
    As sewage sludge dumping at sea is banned from 31st December 1998, water companies are having to find alternative outlets for large volumes of sludge. This project looks at a method of improving the conventional sludge treatment process of anaerobic sludge digestion, by pre-treating sludge with ultrasound. Ultrasound produces cavitation, which breaks up sludge solids, making it easier for bacteria to utilise them. In theory, this leads to a greater reduction in volatile solids and an increase in the volume of methane produced. Sludge was thickened in a drum thickener and passed through a Nearfield Acoustical Processor (NAP-3606-HP-TC) ultrasound generator. Two different intensities were used, 5 amps and 16 amps. Sludge was then placed into the respective holding tanks of three 100 litre (1) capacity pilot scale digesters. Sludge treated at 5 amps was supplied to the first digester, sludge treated at 16 amps was supplied to the second digester, and the third digester received unsonicated sludge. Batch digestion tests, soluble chemical oxygen demand (sCOD) tests and capillary suction time (CST) tests were also carried out. No major differences in gas production or volatile solids reduction were found between the three pilot scale digesters, possibly because the effects of sonication were negated during the sludge storage stage, due to shearing by the mixing device. However, the batch tests, soluble COD tests and CST tests carried out all showed that sonication had a marked effect. The CST tests showed that sonication made sludge harder to dewater, before and after subsequent digestion. Future work should include a more detailed investigation into the effects of sonication on sludge dewaterability. This is because a pre-treatment process that produces a sludge that cannot be dewatered may not be economically viable, despite any advantages of the pre-treatment process.
  • Thumbnail Image
    ItemOpen Access
    The effects of media size on the performance of biological aerated filters
    (Elsevier, 2001-07) Moore, Rebecca; Quarmby, Joanne; Stephenson, Tom
    Biological aerated filters (BAFs) are an attractive process option, particularly when low land usage is required. They can combine BOD, solids and ammoniacal nitrogen removal and can be utilised at both secondary and tertiary stages of wastewater treatment. Media selection is critical in the design and operation of BAFs to achieve effluent quality requirements. Two size ranges, 1.5–3.5 and 2.5–4.5 mm, of a foamed clay called StarLight C were used in pilot-scale reactors. Both performed well as BAF media, with reactor loads up to 12 kg COD m−3 d and 4 kg suspended solids m−3 d (based on working volumes). The most consistent effluent was obtained using the smaller medium since, at flow rates above 0.4 l min−1, the BAF using the larger medium produced an effluent containing more than 20 mg l−1 of suspended solids for over 30 min after backwashing. Up to 70% longer run times, as determined by reaching a set head loss, were recorded for the BAF containing the larger rather than the smaller medium. Additionally, the development of pressure above the smaller medium filter bed tended to be logarithmic rather than linear. Reactor profiles indicated that suspended solids removal did not occur over the full 2.3 m depth of the columns. The BAF containing the smaller medium utilised a mean depth of 1.7±0.3 m, whereas a mean depth of 2.1±0.3 m was used by the larger medium BAF. Both the head loss development data and the suspended solids removal profiles indicated that the smaller medium BAF was underperforming as a filter.
  • Thumbnail Image
    ItemOpen Access
    Micronutrients for wastewater treatment
    (1999-09) Burgess, Joanna E.; Quarmby, Joanne; Stephenson, Tom
    The results of a postal survey strongly suggested that new developments in the optimisation of biological treatment processes would greatly increase the ability of wastewater-treating industries to adapt to Direct Toxicity Assessment (DTA). Trace metals (K, Fe, Mg, Cu, Ca, Mn, Al, Zn, Mo, Co) and vitamins (biotin, niacin, pyridoxine, lactoflavin, thiamine, pantothenic acid) were the micronutrients tested. Respirometry indicated that micronutrient addition could not ameliorate macronutrient deficiencies, but could significantly improve the degradation of hard chemical oxygen demand (COD) in the wastewater (up to 4.24kg COD/kg MLS S/d, i.e. 320% of the control) with no significant effect on the air requirement of the sludge. Complex interactions between trace metals that were dosed simultaneously were evident (e.g. Ca with other metals). Several positive effects led to the conclusion that micronutrients have the potential to optimise the process performance of activated sludge plants treating industrial wastewater. Porous pots were used to trial eight of the micronutrients. The retention of biomass in the pots was increased in all cases. Improvements in the degradation of COD (up to 260% of the control) were observed while biological oxygen demand (BOD) degradation was not affected. This implied the use of recalcitrant substrate components as a food source. Toxicity tests showed that the effluents from the experimental porous pots were less toxic than the control effluents. The effects of niacin addition in activated sludge treatment of industrial waste at pilot-scale were: improved sludge handling, increased COD, ammonia, SS and phosphorus removal. Mean test system COD removal efficiency was 123% of the control. The results of phosphorus and niacin dosing at pilotscale confirmed the trends observed in the porous pots. The results at all scales indicated that micronutrient addition could be a valuable tool for companies wishing to improve aerobic biological treatment of industrial wastewaters. Interviews were used to assess the potential value of micronutrient addition in responding to DTA. Several industrialists saw micronutrient addition as a route to successful adaptation.