Application of membrane separation processes for textile wastewater treatment

Tekstilna je industrija karakteristična po visokoj potrošnji vode i kemikalija, a otpadna voda iz proizvodnog procesa pripada kategoriji najjače onečišćenih otpadnih voda. Temelj istraživanja ovog doktorskog rada bio je ispitivanje mogućnosti obrade otpadne vode tekstilne industrije iz procesa mercerizacije i bojenja polimernim i keramičkim membranama odabranih veličina pora u svrhu ponovnog korištenja vode, smanjenja opterećenja i količine otpadne vode. Izvršena je selekcija membranskih procesa, tj. vrsta membrana za postizanje zadanih ciljeva. Na laboratorijskoj skali testirane su performanse membranskih sustava s PE membranom sa šupljikavim vlakna, polietersulfonskom (PES) cijevnom i ravnom membranom, te keramičkim membranama s otpadnim vodama iz procesa mercerizacije i bojanja tekstila. Optimirani su radni parametri: promjena brzine strujanja ulaznog toka, fluks permeata i temperatura kako bi se postiglo minimalno blokiranje membrana, produžila njihova stabilnost i radni vijek. Također je ispitana mogućnost povrata permeabilnosti membrana odabirom različitih uvjeta čišćenja membrana te sredstava za čišćenje (pranje), njihovu koncentraciju, i temperaturu pranja. Pokusima s otpadnom vodom prethodilo je određivanje permeabilnost ispitanih membrana, njihova karakterizacija s otopinama polietilenglikola (PEG) i polietilenoksida (PEO), dok je blokiranje membrana procijenjeno po Hermijinom modelu. Utvrđena su odstupanja između deklariranih vrijednosti granične molarne mase (MWCO) od strane proizvođača, te onih dobivenih eksperimentom; granična molarna masa za stupanj separacije od 90% je viša kod ispitanih membrana u odnosu na karakteristike proizvođača. Ispitane keramičke membrane pokazuju tendenciju blokiranja pora i kod separacije PEG i PEO otopina veličine molekula manjih od deklarirane veličine pora membranskog materijala. Usporedbom eksperimentalno dobivenih performansi membrana s otpadnom vodom iz procesa mercerizacije najviši stupanj separacije suspendiranih i organskih tvari postignut je s 1 000 g mol^-1 keramičkom membranom. Najviši stupanj separacije suspendiranih i organskih tvari, te boje pri obradi otpadne vode iz procesa bojenja postignut je s PES ravnom membranom. Pri obradi otpadne vode iz procesa mercerizacije utrošak energije za keramičke membrane je viši za membrane s manjim porama pri proizvodnji istog volumena permeata. Najviši utrošak energije je zabilježen pri obradi otpadne vode iz bojenja keramičkom membranom, a najniži PE membranom. Utrošak energije prikazan je i s obzirom na učinkovitost uklanjanja ukupnih suspendiranih tvari (TSS) i ukupnih organskih tvari (TOC).The textile industry is characterized by high consumption of water and chemicals and textile wastewaters are rated as the most polluting among all industrial sectors. The purpose of this dissertation research is the assessment of possibilities in treatment of textile wastewater gained from the process of mercerization and dye processing with polymer and ceramic membranes with selected pore size with a purpose to reuse the water, reduce pollution load and the amount of wastewater. A selection of the membrane process, i.e., types of membranes to achieve these objectives was conducted. Performance of these membrane systems was tested on a laboratory scale with hollow fibre PE membrane, polyethersulpfone (PES) tubular membrane, flat sheet membrane and ceramic membranes using wastewater from the process of mercerization and dyeing textiles. Operating parameters were optimized: cross flow velocity of the input stream, the permeate flux and temperature in order to achieve minimum membrane fouling, their stability and extended service life. Membrane permeability recovery was also examined by selecting different cleaning conditions and chemicals, their concentration, and cleaning temperature. Membrane permeability and their characterization was conducted with polyethylene glycol (PEG) and polyethylene oxide (PEO), while blocking the membranes was assessed by Hermia’s model. Deviations from the declared value molecular weight cut-off (MWCO) by the manufacturer, and those gained by experiment were obtained; limit of molecular weight for the degree of separation of 90% was higher in the examined membrane in relation to the characteristics of the manufacturer. Tested ceramic membranes have a tendency to membrane fouling and during separation of molecules smaller than the declared pore size of the membrane material. For mercerization wastewater the highest separation efficiency for suspended and organic compounds was achieved with 1 000 g mol^-1 ceramic membrane. The highest separation efficiency for suspended and organic substances, and colour from dyeing process wastewater was achieved with PES flat sheet membrane. Energy consumption for mercerization wastewater experiments using ceramic membranes is higher for membranes with smaller pores for the production of the same volume of permeate. The highest energy consumption for treatment of dyeing wastewater was obtained with the 1 000 g mol^-1 ceramic membrane, and the lowest with PE membrane. Energy consumption was also expressed by efficiency of removing total organic carbon (TOC) and total suspended solids (TSS)