| Abstract | U proteklih nekoliko desetljeća glavni izvor onečišćenja vodnih, ali i kopnenih ekosustava teškim metalima su industrija, rudarenje i poljoprivreda te sve više stanovnika ima problem s nedostatkom vode i njenom kakvoćom. Ispuštanje neobrađenih industrijskih te sanitarnih voda uzrokuje dugoročne posljedice na okoliš i sva živa bića te je pročišćavanje otpadnih voda ključno za očuvanje okoliša i zdravlja ljudi. Uklanjanje teških metala iz otpadnih voda provodi se brojnim metodama, a uz kemijsko taloženje adsorpcija je vrlo učinkovita i često primjenjivana metoda. Međutim, cijena aktivnog ugljena kao vrlo učinkovitog adsorbensa je visoka pa se istražuju novi ekonomičniji sorbensi, a obrada voda sve češće provodi kombinacijom više metoda. U ovome radu ispitano je dvostupanjsko uklanjanje cinka iz vodene otopine koncentracije 500 mg Zn/L kemijskim taloženjem uz neutralizaciju različitim taložnim sredstvima u pH području 7,0-7,5; 8,0-8,5 te 9,0-9,5, a potom sorpcijom na biosorbensima. Kemijskim taloženjem cinka uz neutralizaciju dokazana je značajna ovisnost o pH vode te je već u prvom stupnju obrade pri pH=9,0-9,5 koncentracija cinka smanjena na vrijednost ispod maksimalno dopuštene (2 mg/L) za sva ispitana taložna sredstva, s izvrsnom učinkovitošću ≥ 99,85%. Efluenti dobiveni kemijskim taloženjem uz neutralizaciju do pH=7,0-7,5 te pH=8,0-8,5 s koncentracijom cinka ˃ 2 mg/L podvrgnuti su drugom stupnju obrade sorpcijom na košticama maslina, trešanja i višanja. Postignuta je ostatna koncentracija cinka < 2 mg/L za sve ispitane biosorbense u efluentima nakon kemijskog taloženja do pH=8,0-8,5, dok za najniže pH područje nije postignuta. Ovim istraživanjem je dokazano da se onečišćena voda sa sadržajem cinka od 500 mg/L može uspješno pročistiti već u jednom stupnju obrade metodom kemijskog taloženja uz neutralizaciju do pH=9,0-9,5 bilo kojim od ispitanih taložnih sredstava. Također je moguće uspješno ukloniti cink dvostupanjskom obradom, najprije kemijskim taloženjem uz neutralizaciju do pH=8,0-8,5; a potom sorpcijom na biosorbensima. Koji način u praksi odabrati, ovisit će o potrošnji i cijeni taložnog sredstva kao i o troškovima i načinima zbrinjavanja nastalog otpada u obliku mulja cinkova hidroksida te cinkom zasićenih biosorbenasa. |
| Abstract (english) | In the past few decades, the main source of heavy metal pollution of aquatic and terrestrial ecosystems is industry, mining and agriculture, and there is a growing problem with the lack of water and its quality. The discharge of untreated industrial and sanitary water causes long-term consequences, and the treatment of wastewater is essential for the preservation of the environment and human health. The removal of heavy metals from wastewater is carried out by numerous methods, and in addition to chemical precipitation, adsorption is a very effective and often used method. However, the price of activated carbon as a highly effective adsorbent is high, so new, more economical sorbents are being researched, and water treatment is increasingly being carried out using a combination of several methods. In this bachelor thesis, the two-stage treatment of zinc-contaminated water containing 500 mg Zn/L was performed, firstly by chemical precipitation with neutralization by different precipitating agents up to pH ranges of 7.0-7.5; 8.0-8.5 and 9.0-9.5, and then by sorption onto biosorbents. Chemical precipitation of zinc proved a significant dependence on water pH, and already in the first stage of treatment at pH=9.0-9.5, the zinc concentration was reduced to a value below the maximum allowed (2 mg/L) for all tested precipitating agents, with excellent efficiency ≥ 99.85%. Effluents obtained by chemical precipitation with neutralization to pH=7.0-7.5 and pH=8.0-8.5 with a concentration of zinc ˃ 2 mg/L were subjected to the second stage of treatment by sorption on the olives, cherries and sour cherries pits. A residual zinc concentration < 2 mg/L was achieved for all tested biosorbents only in effluents after chemical precipitation up to pH=8.0-8.5. This research has proven that contaminated water containing 500 mg Zn/L can be successfully purified in just one treatment stage using the chemical precipitation method with neutralization to pH=9.0-9.5, by any of the tested precipitating agents. It is also possible to successfully remove zinc by two-stage treatment, first by chemical precipitation with neutralization to pH=8.0-8.5; and then by sorption on biosorbents. Which method will be used in practice depends on the consumption and price of the precipitating agent, as well as on the costs and methods of disposal of the generated waste in the form of zinc hydroxide sludge and zinc-saturated biosorbents. |
