Membrane bioreactor for advanced wastewater treatment and reuse

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

2. Qualitative: Textile wastewater contains slowly- or non-biodegradable organic substances Quantitative: High water consumption Textile wastewater characteristics produces Impacts on water resources 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. 2 Million of cubic meters of industrial water consumption in Prato (2002) Number of industries with high water demands in Prato Industrial activities and water supply in Prato The industrial district of Prato area extends over 700 Km2 with about 45.000 workers engaged and 8.000 medium and small textile activities

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. Effluent characteristics from the textile industries (Barclay and Buckley, 2000) Process Composition Nature Sizing Starch, waxes, carboxymethylcellulose, polyvinyl alcohol High in BOD and COD Desizing Starch, glucose, carboxymethylcellulose, polyvinyl alcohol, fats and waxes High in BOD and COD, suspended and dissolved solids. Scouring Caustic soda, waxes, grease, soda ash, sodium silicate, fibres, surfactants, sodium phosphate Dark coloured, high pH, high COD, dissolved solids Bleaching Hypoclorite, chlorine, caustic soda, hydrogen peroxide, acids, surfactants, sodium phosphate Alcaline, suspended solids Mercerising Caustic soda High pH, low COD, high dissolved solids. Dyeing Various dyes, mordants, reducing agents, acetic acid, soap Strongly coloured, high COD, dissolved solids, low suspended, solids, heavy metals. Printing Pastes, stanch, gums, oil, mordants, acids, soaps Highly coloured, high COD, oily appearance, suspended solids Finishing Inorganic salts, toxic compounds Slightly alkaline, low BOD

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. Study area 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.

8. 3 Bisenzio river Intake basin II Macrolotto area Wastewater from Prato draining system I Macrolotto area RWP WWTP Ombrone river Evolution of industrial aqueduct of Prato 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 m3/h(more than 3 million m3/year) 2) Surface water from Bisenzio river- about 60 m3/h (0,5 million m3/year) Center of the city of Prato • 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 • 1990 • Accomplishments • Refining Water Plant (RWP) • Distribution system for 30 industries located in First Macrolotto area

9. MBR Pilot Plant Permeate • 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 m3/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 Equalization Preliminary treatments Primary sedimentation Biological oxidation Secondary sedimentation Clariflocculation Ozonation Effluent

10. Variable Mean Max Min STD Q (m3/d) 119.200 130.700 31.930 108.894 COD (mg/L) 686 1.263 167 241 TSS (mg/L) 228 1.060 52 145 N-total (mg/L) 18,4 27,2 8,2 4,6 MBAS (mg/l) 5,9 9,6 0,0 0,9 Non-ionic surfactants (mg/l) 31,5 44,2 9,2 5,4 Absorbance at 420 nm 0,302 0,489 0,02 0,069

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. The pilot plant (plate and frame) • The module consists of 4 elements in series (each one made up of 7 membranes) for a total filtering surface of about 3 m2. • 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 m3/h, which turns into a cross-flow velocity of 2,1 m/s. Pin=1,8 – 2,5 bar  Pout1,0 – 1,7 bar

13. Results and discussion

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. Permeate flow The trend of permeate flow extracted from the pilot plant was comprised between 35 and 65 l/h m2, considerably lower than the 100 l/h m2 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

16. COD Monitoring 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.

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. Range Mean Absorbance values a 420 nm Color monitoring 0,322 • Inlet 0,153 - 0,504 0,075 • Permeate 0,041 - 0,119

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

20. Color monitoring Clariflocculation outlet Ozone effluent MBR effluent Abs. a 420 nm 0,090 0,074 0,070

21. Membrane removal Adsorbtion and biodegradation Color inlet Color permeate Color monitoring

22. 2 • assenza di macrostruttura del fiocco di fango • presenza di batteri dispersi • ridotta presenza di microfauna 1 1 – Traditional activated sludge 400x 200x 2 – Activated sludge disintegrated by boiling WWTP Sludge MBR Sludge 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

23. Inlet Permeate Secondary Effluent Ozone outlet MBAS Average 5,3 0,4 0,58 0,35 STD 0,45 0,06 0,08 0,06 Max 6,2 0,52 0,75 0,51 Min 4,2 0,25 0,41 0,25 Non-ionic surfactants Average 34,1 0,26 1,22 0,97 STD 3,9 0,21 0,30 0,21 Max 40,8 0,98 2,05 1,23 Min 26,4 0,09 0,57 0,62 Surfactants monitoring 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.

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 m3/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.