Prečišćavanje otpadne vode iz procesa proizvodnje pšeničnog skroba mikro-I ultrafiltracijom

Abstract

<p>U radu su ispitane mogućnosti preči&scaron;ćavanja otpadne vode iz industrije p&scaron;eničnog skroba mikro- i ultrafiltracijom. Napojnu sme&scaron;u za mikroi ultrafiltraciju je predstavljala otpadna voda industrije p&scaron;eničnog skroba, koja je pre membranske filtracije podvrgavana taloženju u trajanju od 2, 3 i 4 sata, a potom dekantaciji, pri čemu se dobija napojna sme&scaron;a sa različitim sadržajem suve materije. Eksperimentalna<br />ispitivanja su izvedena na keramičkim membranama sa otvorima pora od 200 nm (oblast mikrofiltracije) i 2,5 nm (oblast ultrafiltracije), bez i sa primenom statičkog me&scaron;ača kao promotora turbulencije. Tokom recirkulacije i koncentrovanja napojne sme&scaron;e praćen je uticaj nezavisno promenljivih (transmembranskog pritiska, protoka,<br />sadržaja suve materije otpadne vode) na fluks permeata, na sadržaj suve materije permeata, na hemijsku potro&scaron;nju kiseonika permeata i retentata, i na suspendovane materije u permeatu retentatu. Ispitan je uticaj statičkog me&scaron;ača na prljanje IV membrane, na potro&scaron;nju energije, i urađena je ekonomska analiza ugradnje mikrofiltracionog postrojenja za preči&scaron;ćavanje otpadne vode. Eksperimentalni rezultati su jasno pokazali da se najveća vrednost fluksa permeata (24 lm-2h-1) pri<br />mikrofiltraciji nakon postizanja stacionarnog stanja (nakon 30 minuta filtracije) bez upotrebe statičkog me&scaron;ača je postignuta na 3 bara i pri protoku od 150 lh-1, i to kada se otpadna voda pre mikrofiltracije taloži 4 časa. Nakon 4 sata mikrofiltracije beleži se pad fluksa permeata, i to za oko 40% u odnosu na uslove nakon 30 minuta mikrofiltracije. Kada se koristi statički me&scaron;ač, fluks permeata beleži veće vrednosti i to za 40% nego pri uslovima bez me&scaron;ača, zbog povećanja turbulencije tokom protcanja napojne sme&scaron;e i smanjivanja koncentracione polarizacije. Prilikom otimizacije uslova separacije otpadne vode mikrofiltracijom najveći uticaj na fluks permeata u uslovima bez i sa statičkim me&scaron;ačem, ima protok otpadne vode kao napojne sme&scaron;e. Kori&scaron;ćenjem membrane od 200 nm suva materija otpadne vode<br />se smanjuje u proseku za 53% (sa početnog 9.500 mgl-1 u napojnoj sme&scaron;i), hemijska potro&scaron;nja kiseonika u proseku za 66% (sa početnog 21.000 mgO₂l-1 u napojnoj sme&scaron;i) a suspendovane materije za čak 94% (sa 8.100mgl-1 u napojnoj<br />sme&scaron;i). Pri uslovima ultrafiltracije, maksimalne vrednosti fluksa permeata bez i sa me&scaron;ačem mogu se dobiti pri niskom protoku od 50 lh-1, održavajući transmembranski pritisak u intervalu od 1,5 do 2,5 bara. U uslovima ultrafiltracije, takođe dolazi do izražaja veoma pozitivan efekat statičkog me&scaron;ača, s obzirom na to da je fluks permeata pri upotrebi me&scaron;ača dvostruko veći (32 lm-2h-1) u odnosu na<br />uslove bez me&scaron;ača (16 lm-2h-1). Kori&scaron;ćenjem membrane od 2,5 nm sadržaj suve materije otpadne vode se smanjuje prosečno za 67%, hemijske potro&scaron;nje kiseonika za 88%, a suspendovane materije za 95%. Pri upotrebi me&scaron;ača dolazi do smanjenja otpora polarizacionog sloja maksimalno do 80-90%. Kod membrane sa otvorom pora 200 nm je prisutno nepovratno prljanje u većoj meri, s obzirom da su čestice i<br />V jedinjenja prisutni u otpadnoj vodi dosta veći od prečnika otvora pora membrane za ultrafiltraciju, te ne dolazi do utiskivanja čestica u pore, kao ni do stvaranja značajnog polarizacionog sloja.</p>

<p>The objective of this PhD work was to investigate the possibilities of treatment of wastewater from the wheat starch industry by micro- and ultrafiltration. Prior to the membrane filtration, the feeding mixture was subjected to settling during 2, 3 and 4<br />hours and then decanted, yielding thus mixtures with the different content of dry matter. Experiments were carried out using ceramic membranes with pore sizes of 200 nm (range of microfiltration) and 2.5 nm (range of ultrafiltration), with and without application of a static mixer as a promoter of turbulence. In the course of the recircultating and concentrating of the feeding mixture, the effect of independent variables (transmembrane pressure, flow rate, dry matter content) on the content of dry matter in the permeate, chemical oxygen demand (COD) of the permeate and retentate, as well as on the contents of suspended matter in the permeate and retentate was monitored regularly. Also, it was examined the effect of the static mixer on the fouling of the membrane, energy consumption and an economic analysis was made of constructing of a microfiltration plant for treatment of examined wastewater. Experimental results clearly showed that the highest value of the permeate flux (24 lm- 2h-1) in the microfiltration after attaining a stationary state (after 30 min of filtration) without the use of static mixer was achieved at 3 bar and at a flow rate of 150 lh-1 in the case when the wastewater prior to the microfiltration was left to settle for 4 hours. After 4 hours, a drop of the permeate flux was observed by about 40%<br />compared to the conditions after 30 min of microfiltration. When static mixer was used, the values of the permeate flux were higher by 40% than under the conditions without the mixer, which is a consequence of the increased turbulence during the flow of the feeding mixture and decrease in the concentration polarization. In the optimization of the wastewater treatment by microfiltration a highest effect on the permeate flux under the conditions with and without static mixer had the flow rate of the wastewater as the feeding mixture. When use was made of the 200 nm membrane, dry matter content in the wastewater decreased in average by 53% (from the initial 9.500 mgl-1 in the feeding mixture), COD in average by 66% (from the initial 21.000 mgO₂l-1 in the feeding mixture), while the content of suspended matter decreased even by 94% (from 8.100 mgl-1 in the feeding mixture). Under the conditions of ultrafiltration, maximum values of permeate flux with and without mixer<br />could be obtained at a very small flow rate of 50 lh-1 while keeping the transmembrane pressure in the range from 1.5 to 2.5 bar. Under the conditions of<br />microfiltration there was a very pronounced favorable effect of the mixer, as the permeate flux was then twice higher (32 lm-2h-1) compared to the conditions without the mixer (16 lm-2h-1). When the 2.5 nm membrane was used, the content of dry<br />matter was reduced in average by 67%, COD by 88%, and suspended matter by 95%. The use of the mixer resulted in a decrease in the resistance of the polarization layer maximally by 80-90%. When the membrane with the pores of 200 nm was used, there occurred irreversible fouling to a greater extent, since the particulates and compound particles present in the wastewater were of a diameter that was larger than the pores size of the ultrafiltration membrane, so that neither clogging nor formation of a significant concentration polarization were taking place.</p>