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1 Membrane bioreactor for advanced wastewater treatment and reuse Claudio Lubello Riccardo Gori Civil Engineering Department - University of Florence -

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Presentation on theme: "1 Membrane bioreactor for advanced wastewater treatment and reuse Claudio Lubello Riccardo Gori Civil Engineering Department - University of Florence -"— Presentation transcript:

1 1 Membrane bioreactor for advanced wastewater treatment and reuse Claudio Lubello Riccardo Gori Civil Engineering Department - University of Florence - Italy 4 th INTERNATIONAL SYMPOSIUM ON WASTEWATER RECLAMATION, RECYCLING AND REUSE 12-14 November 2003, Mexico City

2 2 Textile wastewater characteristics produces Impacts on water resources Quantitative: High water consumption Qualitative: Textile wastewater contains slowly- or non-biodegradable organic substances Necessity of wastewater reuse Limitations of wasterwater reuse This work is focused on the treatment of textile industry wastewater using Membrane Bio-reactor (MBR)

3 3 Industrial activities and water supply in Prato Number of industries with high water demands in Prato Million of cubic meters of industrial water consumption in Prato (2002) The industrial district of Prato area extends over 700 Km 2 with about 45.000 workers engaged and 8.000 medium and small textile activities 2

4 4 Textile industries carry out several fiber treatments using variable quantities of water from five to forty times the fiber weight. Consequently generate large volumes of wastewater to be disposed of. Such treatments include: Dyeing preliminary treatments (bleaching, desizing, mercerization); Textile ennobling treatments (from dyeing to post-dyeing treatments, such as those required to increase colorant fastness, in wet and dry conditions); Finishing, including operations such as fulling or impregnation with products giving special characteristics to fibers.

5 5 Effluent characteristics from the textile industries (Barclay and Buckley, 2000) ProcessCompositionNature SizingStarch, waxes, carboxymethylcellulose, polyvinyl alcohol High in BOD and COD DesizingStarch, glucose, carboxymethylcellulose, polyvinyl alcohol, fats and waxes High in BOD and COD, suspended and dissolved solids. ScouringCaustic soda, waxes, grease, soda ash, sodium silicate, fibres, surfactants, sodium phosphate Dark coloured, high pH, high COD, dissolved solids BleachingHypoclorite, chlorine, caustic soda, hydrogen peroxide, acids, surfactants, sodium phosphate Alcaline, suspended solids MercerisingCaustic sodaHigh pH, low COD, high dissolved solids. DyeingVarious dyes, mordants, reducing agents, acetic acid, soap Strongly coloured, high COD, dissolved solids, low suspended, solids, heavy metals. PrintingPastes, stanch, gums, oil, mordants, acids, soaps Highly coloured, high COD, oily appearance, suspended solids FinishingInorganic salts, toxic compoundsSlightly alkaline, low BOD

6 6 In this way, the effluent is enriched with compounds having high environmental impact and difficult to treat directly, through conventional biological processes. Priority pollutants are Dyes and Surfactants. Typical wastewater concentrations Dyes 10 – 50 mg/l; Surfactants 20 – 50 mg/l. Wastewater treatment problems Low biodegradability; Biomass interactions. Environmental impacts Alterations of gaseous exchanges; Light penetration reduction; Toxcity; Visual impact. Technical problems for wastewater reuse Foam Color

7 7 This study is part of a larger research framework whose target is to identify the most appropriate technologies to boost reuse of purified waters for industrial purposes, in the area of Prato, and in the well-watered Pistoia nursery district. Study area

8 8 1990 Accomplishments Refining Water Plant (RWP) Distribution system for 30 industries located in First Macrolotto area 1994 Accomplishments 2 pipelines to withdraw and return water from Bisenzio river Distribution system for 30 industries located near the centre of Prato’s city 1999 Accomplishments Distribution system for 35 industries located in Second Macrolotto area The water recycling system in Prato allows connected enterprises to use, as a water supply source in addition to groundwater: 1)Treated water from the Baciacavallo WWTP - about 400 m 3 /h (more than 3 million m 3 /year) 2) Surface water from Bisenzio river - about 60 m 3 /h (0,5 million m 3 /year) Bisenzio river Evolution of industrial aqueduct of Prato Center of the city of Prato II Macrolotto area Intake basin Ombrone river I Macrolotto area WWTP RWP Wastewater from Prato draining system 3

9 9 The Baciacavallo plant is the main wastewater treatment plant in the area of Prato, its capacity is of about 750.000 p.e. and has a maximum flow capacity of 6000 m 3 /h. The treated wastewater is partially reintroduced in the surface water system and partially (100 l/s) is further refined and reused to feed the industrial and fire-fighting waterworks of one of the main industrial areas in Prato. The pilot-scale plant is part of the treatment chain, and operates in parallel with the oxidation- nitrification treatment of the Baciacavallo plant, therefore, downstream the primary sedimentation. Wastewater Effluent Preliminary treatments Primary sedimentation Biological oxidation Secondary sedimentation Clariflocculation Ozonation Equalization MBR Pilot Plant Permeate

10 10 VariableMeanMaxMinSTD Q (m 3 /d)119.200 130.70031.930108.894 COD (mg/L)686 1.263167241 TSS (mg/L)228 1.06052145 N-total (mg/L)18,4 27,28,24,6 MBAS (mg/l)5,9 9,60,00,9 Non-ionic surfactants (mg/l) 31,5 44,29,25,4 Absorbance at 420 nm0,3020,4890,020,069

11 11 The biological reactor operates at constant level and the bio-mass is maintained in aerobic conditions via aeration, through 6 small bubble diffusers. The ultra-filtration module (Rhodia, UFP10) is of the external type, with plate and frame membranes, where a cross-flow type filtration is performed.

12 12 P in =1,8 – 2,5 bar P out 1,0 – 1,7 bar The module consists of 4 elements in series (each one made up of 7 membranes) for a total filtering surface of about 3 m 2. The membrane is of the organic type, made up of acrylonitrile copolymers, with a 3  m thickness and a pore cut-off of 40 KD (approximately, this corresponds to a pore average size of 0,02 – 0,03  m). The average module inlet flow rate is of 30 m 3 /h, which turns into a cross-flow velocity of 2,1 m/s. The pilot plant (plate and frame)

13 13 Results and discussion

14 14 Biomass development and characteristics The initial concentration of the biomass introduced in the bio-reactor was of 5 gTSS/l. Fluctuation in solid particle concentrations, together with inlet wastewater characteristics variability, led the pilot plant bio-mass to operate with extremely variable organic loads. After an initial start-up period, the bio-mass grew with a linear trend until it reached about 16 gTSS/l, in the space of 120 trial days.

15 15 The trend of permeate flow extracted from the pilot plant was comprised between 35 and 65 l/h m 2, considerably lower than the 100 l/h m 2 specified by the manufacturer. During the experimental period, on the basis of the previously described criteria, 4 chemical cleanings of the module were required, actually with a monthly frequency. The cleaning system proved to be efficient in restoring the flow conditions. However, the permeate flow descending trends were not regular and this can be explained on the basis of following phenomena: substantial fluctuation, even unexpected, of solid particle concentrations in the aerated mixture, due to sludge escape; change in the sludge viscosity and filterability characteristics Permeate flow

16 16 Tests conducted on COD fractionation, in its soluble and particulate components, provided a total COD average value of 869 mg/l, whose soluble component corresponded to 34.7%. Figure compares the COD trends, at the pilot plant outlet, from the Baciacavallo plant secondary settling and from the final ozone treatment. After about 2 weeks from start-up, a quick COD decrease at the outlet was observed; these values stabilized within 40 and 60 mg/l (mean value: 56,8 mg/l), in the third week, seldom exceeding the upper threshold. The removal efficiency, 93% on average, proved to be considerably higher with respect to that obtained only with biological treatment and secondary settling in the Baciacavallo plant. COD Monitoring

17 17 Nitrogen monitoring Nitrification process results were extremely satisfactory. With respect to the full scale plant, the nitrification process efficiency appeared considerably higher. The nitrification process proved to be complete since no nitrite accumulations were found in the oxidation tank (all values were below the 0.05 mg/l threshold).

18 18 Color monitoring Permeate 0,041 - 0,119 Inlet 0,153 - 0,504 0,322 0,075 Absorbance values a 420 nm RangeMean

19 19 Average removal MBR pilot plant WWTP (with ozone) 77,2 % 77,6 % Color monitoring

20 20 Clariflocculation outlet MBR effluent Ozone effluent 0,0900,0740,070 Abs. a 420 nm Color monitoring

21 21 Color monitoring Color inlet Membrane removalAdsorbtion and biodegradation Color permeate

22 22 Color monitoring Adosrption removal Nel caso dell’impianto pilota la capacità di adsorbimento è incrementata da: High biomass concentration High adsorption capability of MBR sludge MBR Sludge 200x WWTP Sludge 400x assenza di macrostruttura del fiocco di fango presenza di batteri dispersi ridotta presenza di microfauna 1 2 1 – Traditional activated sludge 2 – Activated sludge disintegrated by boiling

23 23 InletPermeateSecondary Effluent Ozone outlet MBAS Average5,30,4 0,58 0,35 STD0,450,06 0,08 0,06 Max6,20,52 0,75 0,51 Min4,20,25 0,41 0,25 Non-ionic surfactants Average34,10,26 1,22 0,97 STD3,90,21 0,30 0,21 Max40,80,98 2,05 1,23 Min26,40,09 0,57 0,62 As a general rule, the pilot plant proved to be efficient in surfactant removal from textile wastewater; however, with respect to removal efficiency obtained in the full scale plant, the MBR technology effect appeared different between anionic and non-ionic compounds. In the case of non-ionic surfactants, a considerable removal efficiency was found (higher than 99% on average). In this case, a significant removal increase was noticed, both with respect to the conventional activated sludge treatment and to the ozone treatment; the latter, as everyone knows, shows a lesser efficiency with respect to MBAS. Surfactants monitoring

24 24 Conclusions The pilot-scale plant demonstrated that the MBR treatment makes it possible to obtain high purification efficiency of textile wastewater. Extremely satisfactory results were obtained both on conventional parameters such as COD, suspended solids, ammonium, and on compounds typical of this type of wastewaters such as dyes and surfactants. In the case of dyes and surfactants, removal efficiency similar or higher than that obtained with the Baciacavallo plant complete chain, were reached. These results appear to be extremely important, but only a very limited literature is available on them. As regards treatment applicability, it is advisable to specify that the system adopted provides for the use of ‘plate and frame’ membranes with an external module. This system has high energy consumption and is suitable for small flow rates treatment (2000 – 3000 m 3 /d) with high pollutant concentrations. It would be therefore proper to experiment also alternate membrane typologies (for example, hollow fiber membranes) more suitable for high flow-rates treatment.

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