INVESTIGATION ON TEXTILE INDUSTRY WASTEWATER REUSE: FROM METHODOLOGY DEFINITION TO FULL SCALE DEMONSTRATION OF SPECIFIC BAT

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1 INVESTIGATION ON TEXTILE INDUSTRY WASTEWATER REUSE: FROM METHODOLOGY DEFINITION TO FULL SCALE DEMONSTRATION OF SPECIFIC BAT Loredana De Florio, Andrea Giordano, Davide Mattioli ENEA PROT IDR UNIT Water Resources Management, via Martiri di Montesole, 4, Bologna, Italy ABSTRACT With the objective of assessing ways of reducing water consumption in the textile sector, optimization of water use schemes within the factory and reuse options were investigated in the framework of a multicriteria integrated methodology set up in the European funded R&D project Towef0 (Toward Effluent Zero), EVK1 CT The conclusions drawn put the basis for the analysis of the sector needs hindering the implementation of good environmental practices. In order to scale up the results of the Towef0 project. The methodology allows the implementation of measures which proved their potential in reducing environmental impact of industrial activities. A full scale application is going on in a textile SME, to stand as guideline target for the overall sector. Keywords Water reuse, textile wastewater, BAT. INTRODUCTION Industrial activities, although essential for the economy growth and the consumers needs, have a deep environmental impact and, in intensive water demanding sectors, they generate one of the main route of pure water depletion. Textile finishing industry consumes large amounts of primary water (average value of 160 m3/t of finished textile) which is normally discharged as waste after required treatments in on-site facilities or in centralised municipal plants (Mattioli, 2002). According to the IPPC European Directive 96/91/CE, Best Available Techniques (BATs) should be identified and implemented by big companies (IPPC production threshold: 10 t/day) in order to prevent and control pollution with measures integrated in the production lines, instead of taking actions for the pollution abatement. Wastewater reuse, although recognised as a fundamental issue to avoid fresh water consumption and reduce discharges, requires technical measures to be applied on large scale. With this purpose a methodology for the integrated implementation of water reuse strategies is described in this paper. METHODOLOGY DESCRIPTION To support the implementation of sustainable water reuse in textile finishing processes, a specific methodology has been elaborated within the EU research project TOWEF0 (TOWards EFfluent zero) (Mattioli et al., 2005) and applied for textile SMEs. In order to identify an optimal solution for the minimisation of environmental impacts of the industrial activity and maximum recovery of resources, several tools were integrated in the methodology and adapted to the specific application. The

2 development and adaptation of the tools was carried out on 10 textile companies (5 in Italy and 5 in Belgium), selected taking into account the criteria of good environmental performance and significant representation of the European textile finishing industry. The methodology is a four steps analysis process: 1. Complete data collection to be carried out in the company. In order to identify relevant processes and to collect data from textile industries, a specific procedure was used consisting of an audit inside the company, with the involvement of the company management. It leads to a document called "Process Identification and Data Collection Sheet", referred to as "PIDACS". 2. Analysis of all (or at least the most important) process effluents to identify and characterise all their possible destinations (direct reuse, reuse after on site treatment, discharge to WWTP after on site preliminary treatment, direct discharge to WWTP or alternative disposal). Essential for the analysis is the characterisation (Bisschops, 2003) of the effluents treatability for reuse and this objective was achieved by performing membrane treatment tests on several process effluents selected by focusing on the most important effluent streams in the textile finishing industries. Seven effluent processes were selected from pre-treatment operations, seven among dyeing operations and three from printing operations (both effluents from the whole operation and from the rinsing phase only were sampled for testing): Polyester double scouring PDS; Polyester scouring PS; Polyester scouring rinsing PSR; Polyester disperse dyeing PDD; Polyester disperse dyeing rinsing PDDR; Polyester printed wash PPW; Polyester disperse print PDP; Silk HT scouring SS; Silk HT scouring rinsing SSR; Silk polymer charge SPC; Silk yarn dark reactive dyeing SRD; Silk acid dyeing rinsing SADR; Viscose reactive printed wash VRPW; Viscose direct dyeing rinsing VDDR; Polyamide acid dyeing PAD; Cotton reactive dyeing CRD; Cotton bleaching line CBL. All the streams tested were characterized through a chemical screening (Table 1), showing a high variability in the organic carbon content (TOC) as well as in colour (measured by the absorbance value at 3 different wave length) and salinity (evaluated by the conductivity). Pilot scale plant Membranatest (Osmonics) used for tests (scheme reported in Figure 1) was composed of: feed storage tank (50L); pre-filter in polypropylene fiber; feeding pump (500 kpa) and additional pump for NF and RO (2000 kpa); vessel (30.5 cm length, 4.6 cm diameter) for spiral wound polymeric membranes (MF, UF, NF or RO); flow control valves, manometers and flowmeter. Effluent ph Conductivity [µs cm-1] Turbidity [NTU] Abs λ = 426 nm [cm-1] Abs λ = 558 nm [cm-1] Abs λ = 660 nm [cm-1] TSS [mg l-1] [mg l-1] PS PDS SS SPC CBL PDD PPW PDP PAD VRPW SRD ,

3 CRD , PSR SSR PDDR SADR VDDR Table 1: Effluents characteristics Feed Permeate Concentrate 1 Feed tank 2 Cartridge pre-filter 3 Centrifugal feeding pump Additional pump Membrane vessel Heat exchange Figure 1: Scheme of the pilot scale plant To evaluate the reusability specific tests have to be performed using the permeate of the membrane filtration for carrying out lab scale textile pretreatment and dyeing processes. The reuse tests were made both on yarn and fabric, assessing: degree of whiteness, degumming efficiency, charge efficiency in pre-treatment operations (scouring, bleaching, degumming, polymer charge) and colour difference, colour fastness to washing, colour fastness to rubbing for dyeing operations. Assessment was performed in comparison with a reference test carried out with fresh process water. To evaluate WWTP treatability of the effluents toxicity and biodegradability need to be assessed. Actually, textile wastewater disposal involves treatment in an aerobic biological stage, in most cases together with municipal wastewater. Activated sludge process is sensitive to several toxic compounds, in particular the biological nitrification process within BNR WWTP (Wastewater Treatment Plant operating for Biological Nutrient Removal) is a critical step. The main reason is the lower growth rate of the autotrophic nitrifying biomass, which is strongly dependent on temperature, substrate concentration, dissolved oxygen concentration and ph. Due to the low growth rate of nitrifiers and on their higher sensitivity to toxicants, toxic compounds in the raw wastewater may completely prevent nitrification for a long period. Even if nitrification is not a main concern in the WWTP, the protection of the activated sludge is of essential importance. Therefore, measuring wastewaters inhibition on nitrifying biomass is an effective way to obtain useful indications on the

4 potential inhibitory effect on biological activity and, therefore, on the biological treatability of the effluent. A recently developed methodology for the assessment of the inhibitory effect on nitrifying biomass was applied to several textile effluents from productive processes. Results were combined with biodegradability values measured by conventional methods (i.e BOD5/COD), allowing for a more detailed wastewater characterisation. 3. Elaboration of all the data gained resulting in the definition of optimised water reuse scenarios. On the basis of the results of phase 2 water reuse networks can be designed. Water reuse scenarios were based on membrane filtration technology for effluents reclamation and the removal efficiencies expected for this water regeneration were obtained from the treatment tests results. Specific tools may be used to analyse water reuse networks, and to carry out sensitivity analysis which enables to pinpoint streams and processes where relaxation of contaminant concentration will lead to important reductions in water usage. Costs and benefits of the reuse scenarios were evaluated and compared with the initial situation. The water saving, compared to the initial situation, was calculated. 4. Comparison of the scenarios by LCA to support the decision making leading to the implementation. Life Cycle Assessment can be applied to evaluate water reuse scenarios. Alternative water management scenarios implementing water reuse were analysed: the first, named Innovative scenario, using UF and NF technologies onto selected process effluent streams (mainly rinsing water); the second, named Effluent zero scenario, using UF and RO onto all process effluents. A LCA software, with a web-based interface to end-users, was specifically designed in the project to conduct Life Cycle Assessments in the textile industry. RESULTS AND DISCUSSION The set up of the above described methodology produced several interesting results. In the following the main outcome of step 2 is reported. Membrane treatment tests generated a wide range of operational data resulting in a general evaluation of feasibility both technical and economical. Pilot scale tests, here briefly reported, permitted to scale up facilities requirements, capital and O&M costs. This is a way of choosing which effluents can be diverted and treated for reuse at affordable costs and companies can be involved on the base of reliable evaluations. In fact, effluent reduction target should to be pursued without affecting the competitiveness of the companies and becoming a strengthening point where regulatory policies would push toward a different approach to the valuable resources management. Therefore special attentions was paid on the evaluation of operative costs related to the flux performances. According to the different characteristics of the effluents, the following treatment configurations were tested on pilot scale using: UF (on 12 effluents), NF (on 5 rinsing effluents), NF after UF pre-treatment (on 12 effluents), RO after UF pre-treatment (on 4 effluents). Data gained with the treatment tests Tests aimed at simulating on pilot scale the real operation mode and were carried out as follows: First Characterization (1stC) test, flow rate was measured feeding and circulating of deionised water. Characterization was performed at different pressure

5 conditions and temperatures. The flow rate values were normalised at 25 C for comparison. Complete re-circulation (R) test with real effluents, performed by continuously recycling permeate and concentrate in the feeding tank for 1 hour, assuring an almost constant concentration of the feed. Measurements of flow rate and temperature were carried out at fixed intervals and samples for analytical screening of the permeate quality were collected at the beginning and at the end of each trial. Concentration effect (CE) test with real effluents, performed by continuously re-circulating the concentrate in the feeding tank while the permeate is discharged.. These conditions bring to a growing concentration in the feeding tank during the test. Measurements of flow rate and temperature were carried out at regular intervals, each corresponding to 20% of the original feed volume treated, and simultaneously samples were collected (corresponding to 0%, 20%, 40%, 60%, 80% of volume treated) for analytical screening. Second Characterization (2ndC) test with deionised water performed as the 1stC test at the end of the CE test. In Figure 2, the typical representation of the flux data obtained by each trial (i.e. each effluent) is given. Q (L h -1 m -2 ) st Characterization Complete Recirculation CE concentration 0% CE concentration 20% CE concentration 40% CE concentration 60% CE concentration 80% 2nd Characterization Figure 2: Typical trend of flow rates registered during each trial Treatment tests results, specific for every single effluents, were used for the scaling up of the facilities allowing costs evaluation (both capital and O&M costs) for different plant size (ranging from 10,000 to 250,000 m3/y). The calculated cost for

6 the UF + NF treatment of a cubic meter of effluent, in the scenario of 50,000 m3/year, ranges between 0.67 /m3 for PAD and 1.04 /m3 for SPC; in the same scenario UF + RO treatment would cost between 1.4 /m3 and 3.21 /m3. Definitely more affordable the costs for direct NF applied on rinsing effluents ranging from 0.57 /m3 to 0.63 /m3. Characteristics of the permeates for reuse purposes It was assessed that the only treatment of UF does not normally assure a quality of the permeates suitable for reuse as feed stream for all the industrial processes, despite the relevant removals obtained (Table 2). Effluent % abat % abat % abat Colour Cond. Abs λ = Abs λ = Abs λ = 426nm 558nm 660nm PDS PS PDD PPW SS SPC 49 n.a.* n.a.* n.a.* 5 SRD VRPW PAD PDP 93 n.a.* n.a.* n.a.* 3 CRD CBL *not applicable, due to too low values in the influent Table 2: Main features during UF trials: percentage abatements of organic content, colour, conductivity (average values during the concentration effect test) NF cut-off resulted to be the best solution between the need of having high flow rates (consequently reducing treatment costs) and good quality permeates. The colour is almost completely removed (Table 3) in all effluents and residual values never affect the reusability. The salinity abatement is variable and in some dyeing operation, with high salinity due mainly to mono-valent salts (i.e. reactive dyeing of silk and cotton) the removal was low not allowing the reuse. The removal of organic matter is high, typically 80-90%, nevertheless effluents with a high organic content (> mg l-1) gave permeates normally non reusable. The treatment configuration UF + NF seems in most cases technically and economically feasible. Effluent % abat % abat % abat Colour Cond. Abs λ = Abs λ = Abs λ = 426nm 558nm 660nm PDS PS PDD

7 PPW SS SPC 92 n.a.* n.a.* n.a.* 54 SDR VRPW PAD PDP 94 n.a.* n.a.* n.a.* 58 CRD CBL *not applicable, due to too low values in the influent Table 3: Main features during NF trials following UF: percentage abatements of organic content, colour, conductivity (average values during complete recirculation test) Direct NF treatment was possible only on very diluted effluents obtained from rinsing operations (De Florio, 2005). The percentages of removals obtained (Table 4) in these cases are lower but sufficient to allow the production of a permeate reusable in any process. In all other cases an UF pre-treatment was necessary. Effluent % abat % abat % abat Colour Cond. Abs λ = Abs λ = Abs λ = 426nm 558nm 660nm PSR n.a.* n.a.* n.a.* n.a.* 69 SSR SADR PDDR n.a.* n.a.* n.a.* n.a.* 69 VDDR n.a.* *not applicable, due to too low values in the influent Table 4: Main features during direct NF trials: percentage abatements of organic content, colour, conductivity (average values during complete recirculation test) RO treatment of the effluent tested always requires an UF pre-treatment and despite the very high removal of contaminants (Table 5), it resulted to be scarcely promising due to the very low fluxes. Effluent % abat % abat % abat Colour Cond. Abs λ = Abs λ = Abs λ = 426nm 558nm 660nm PDS PS PDD PPW Table 5: Main features during RO trials following UF: percentage abatements of organic content, colour, conductivity (average values during complete recirculation test) The NF permeates quality evaluation, based on the analytical screening of the samples during the tests, was obtained for comparison with the threshold value for

8 acceptability as primary water and confirmed by the reuse test on lab-scale. In textile processes in which little or no salt (NaCl) is dosed, the quality of the treated (pretreatment/dyeing) textile material was as good as the reference. Effluents containing a high content of NaCl results in a permeate with a comparable concentration and, since NaCl regulates the speed and the depth of reactive and direct dyeing of cotton, a higher concentration has a significant effect on the colour of the dyed cotton. As a conclusion, the permeate can be reused for pre-treatment and/or dyeing of some of the most used textile raw materials, i.e. polyester (PES), polyamide (PA), silk, viscose. The presence of salt (NaCl) however hampers the reusability for the dyeing of cotton. Final effluents treatability in WWTP Results of effluents treatability, classified according to the degree of inhibition as EC50 (concentration producing a 50% nitrification inhibition); showed a wide range of EC50 ranging from 20 ml gvss-1 (83 ml l-1) to values above 100 ml gvss-1 (300 ml l-1). Taking into account biodegradability and toxicity evaluations, most of the studied effluents confirmed a good treatability in traditional biological wastewater treatment plant. CONCLUSIONS Reuse option proved possible, as confirmed by the existing literature on treatability of textile wastewater, nevertheless water recycling is seldom in use and it cannot be considered as an available non-conventional source of industrial water. According to both technical and economical criteria, a specific selection of the effluents to be treated is the key element to foresee a reliable implementation of reuse: Towef0 results gave a methodological approach to design schemes for the purpose and elaborated a cost-analysis for the treatment of segregated effluents. A full application of the methodology is now being carried out in the demonstrative project BATTLE (BAT for water reuse in TextiLE SMEs), focused on demonstrating on large scale the feasibility of wastewater reuse. In a printing and dyeing SME, the methodology application will lead to the design of a demonstrative treatment plant will be built-up supported by a prototype Expert System (E. S.) to comply with the extreme variability of the production processes. REFERENCES Bisschops, I. and Spanjers, H. (2003). Literature review on textile wastewater characterisation. Environ. Technol., 24, De Florio L., Giordano A., Mattioli D. (2005). Nanofiltration of low-contaminated textile rinsing effluents for on-site treatment and reuse Desalination 181, European Commission (2003) Integrated Pollution Prevention and Control (IPPC) Reference Document on Best Available Techniques for the Textile Industry. Mattioli, D., Malpei, F., Bortone, G. and Rozzi, A. (2002) Water minimisation and reuse in the textile industry. In: Water Recycling and resource recovery in industry. IWA Publishing, London, Chapter 27 pp Mattioli D., De Florio L., Giordano A., Tarantini M. and Scalbi S., Aguado M., Bianchi R., Bergna G., Witters H., Genné I., Schiettecatte W., Spanjers H., Bisschops I., Hanke G., Loos R., Ligthart J., Osset P., Vayn C., De Vreese I. (2005) Efficient use of water in the textile finishing industry E-WAter Official Publication of the European Water Association (EWA)

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