Modelovanje i optimizacija kontinualne biosorpcije jona teških metala iz vode

Abstract

U disertaciji je ispitana mogucnost korišcenja izluženih rezanaca šecerne repe za adsorpciju jona bakra u koloni sa nepokretnim slojem. Eksperimenti su izvedeni primenom Boks-Benkenovog eksperimentalnog dizajna na tri nivoa sa tri promenljive: koncentracija napojnog rastvora (50-150 mgL-1), masa adsorbenta (8-12 g) i pH napojnog rastvora (4,0-5,0). Dobijene prevojne krive su fitovane uobicajenim empirijskim modelima, Boart-Adamsovim i modelom doza-odziv. Na osnovu uocene asimetrije prevojne krive, predložen je novi matematicki model. Novi model predlaže prevojnu krivu koja se sastoji od dva dela, koji u zbiru daju kumulativnu krivu koja dosledno pokriva uocenu asimetriju. Uzimajuci u obzir najnižu prosecnu sumu kvadrata odstupanja, SSer (3,610-3) i najvišu prosecnu vrednost koeficijenta determinacije, R2 (0,9989), novi model je pokazao najbolje fitovanje eksperimentalnih podataka, u poreenju sa uobicajeno korišcenim modelima adsorpcije u koloni. RSM i ANN modelovanje je dalje korišceno za evaluaciju procesnih parametara i optimizaciju procesa. Najznacajnija nezavisno promenljiva velicina, koja ispoljava negativan uticaj na odabrani odziv (kriticno vreme), bila je koncentracija napojnog rastvora, dok je masa adsorbenta ispoljila slabiji i pozitivan uticaj na odziv. Optimizacijom procesa metodom ANN je utvreno da se najveca vrednost kriticnog vremena (341,4 min) postiže pri sledecim uslovima: C0=50 mgL-1, ma=12 g and pH 4,53, dok metoda RSM smatra pH vrednost faktorom koji nema znacaja po odziv u ispitivanom opsegu, i postiže maksimalno kriticno vreme od 314,8 min, pri istim ostalim uslovima kao i ANN. Iskorišceni adsorbent, zasicen jonima bakra, je zatim spaljen i dobijeni pepeo je iskorišcen kao punilo u proizvodnji gume. Proizvedena su cetiri uzorka gume sa razlicitim sadržajem pepela. Pracen je proces vulkanizacije gume, odreena su mehanicka svojstva gotovog proizvoda i izvreno je poreenje dobijenih rezultata izmeu uzoraka sa i bez dodatka pepela. Rezultati su pokazali da dodatak pepela u strukturu gume ne utice znacajno na njene mehanicke osobine. Meutim, povecanje sadržaja pepela u gumi dovodi do povecanja energije aktivacije procesa vulkanizacije, što se može smatrati unapreenjem procesa proizvodnje gume u slucaju proizvoda velikih dimenzija. Na kraju, ispitano je izluživanje bakra iz gotovih proizvoda od gume. Rezultti su pokazali da je kolicina bakra izluženog u vodu veoma niska, reda velicine 0,001%, što se može smatrati zanemarljivim.

The potential use of sugar beet shreds for copper ions removal from aqueous solution in a fixed-bed column was investigated. Experiments were performed using Box-Behnken experimental design on three levels and three variables: concentration of the inlet solution (50-150 mgL-1), adsorbent dosage (8-12 g) and pH of the inlet solution (4.0-5.0). The obtained breakthrough curves were fitted with two common empirical models, Bohart-Adams and dose-response. Observing the asymmetric shape of the breakthrough curves, the new mathematical model was proposed. The new model proposes the breakthrough curve composed of two parts, sum of which gives the asymmetrical S-shaped curve, accurately matching experimental data. Regarding the lowest average SSer (3.610-3) and highest average R2 (0.9989), new model exhibited the best fit comparing to the commonly used models. RSM and ANN modelling were employed for process variables evaluation and optimization. The most influential parameter exhibiting negative influence on target response (critical time) was concentration of the inlet solution, while the adsorbent dosage exhibited positive influence. Optimization procedure revealed that the highest critical time (341.4 min) was achieved at following conditions: C0=50 mgL-1, ma=12 g and pH 4.53 by ANN, while RSM considered pH as insignificant factor and obtained 314.8 min as the highest response. Discarded adsorbent, saturated with copper ions, was then incinerated and the obtained ash was used as a rubber filler. Four rubber samples containing different amounts of added ash were produced. The vulcanization process was monitored and mechanical properties was measured and compared with the samples with no ash added. The results revealed that addition of ash has no significant effect on the rubber mechanical properties. However, as the ash content increases, the activation energy of the vulcanization process increases too, which can be considered as an improvement in the cases of large-dimensioned rubber products production. Finally, the leaching of the copper from rubber products was investigated. Results showed that very small amount of copper, order of magnitude 0,001%, were leached from the rubber into the water, which can be considered as insignificant.