Electrochemical treatment of wastewater from the process of surface protection of metals

U radu je ispitana mogućnost primjene elektrokemijskih metoda (elektroredukcije, elektrokoagulacije, indirektne anodne oksidacije) korištenjem željezovog i aluminijevog seta elektroda sa ili bez dodatka elektrolita za obradu otpadne vode koja nastaje u procesu površinske zaštite metala. Otpadna voda je karakterizirana visokim vrijednostima cinka (2029 mg dm-3) i željeza (78,4 mg dm-3) te povišenim vrijednostima Cr(VI) (5,4 mg dm-3) i kemijske potrošnje kisika (820 mg dm-3) koje premašuju granične vrijednosti za ispust u okoliš za 1014, 39, 56, odnosno 6,6 puta. U svrhu optimizacije procesa u radu je ispitan utjecaj vrste elektroda (željezo, aluminij), kontaktnog vremena (5-30 minuta), mase elektrolita (0,5-1,5 g NaCl) te jakosti struje (20-50 A) na stupanj uklanjanja navedena četiri pokazatelja. Između dvije testirane elektrode, željezova se pokazala značajno efikasnijom u uklanjanju svih mjerenih pokazatelja, a naročito Cr(VI) i KPK. Statistički značajno bolji rezultati u uklanjanju KPK za obje elektrode su postignuti dodatkom elektrolita te porastom jakosti struje s 20 na 40 A. Najveći udio anorganskog onečišćenja se ukloni u prvih 5 minuta obrade. Najbolji rezultati su postignuti kombinacijom dviju elektroda uz dodatak klorida kao elektrolita. Nakon 15 minuta elektroredukcije/elektrokoagulacije/indirektne anodne oksidacije pomoću željezovih elektroda, 15 minuta elektrokoagulacije pomoću aluminijevih elektroda te 20 minuta koagulacije/flokulacije i oksidacije zrakom uklonjeno je 99,79% Cr(VI), 99,97% Fe, 98,23% Ni, 99,23% Cu, 99,999% Zn, 98,00% Pb i 86,46% KPK a svi mjereni pokazatelji su zadovoljavali uvjete za ispust u okoliš, dok su se izlazne koncentracije teških metala kretale od 0,009 do 0,023 mg dm-3.The paper investigated a possibility of implementing electrochemical methods (electroreduction, electrocoagulation, indirect anodic oxidation) by using iron and aluminium electrode sets, with or without the addition of electrolytes for treatment of wastewater generated in the process of surface protection of metals. The wastewater is characterized by high values of zinc (2029 mg dm-3) and iron (78.4 mg dm-3) as well as increased values of Cr(VI) (5.4 mg dm-3) and chemical oxygen demand (820 mg dm-3) that exceed limit values for discharge into the environment by 1014, 39, 56 and 6.6 times, respectively. In order to optimize the process, the paper investigated the impact of electrode type (iron, aluminium), contact time (5-30 minutes), electrolyte mass (0.5-1.5 g NaCl) and amperage (20-50 A) on the removal level of the stated four indicators. Of the two tested electrode types, iron electrodes proved to be significantly more efficient in the removal of all measured indicators, in particular Cr(VI) and COD. A statistically significant improvement of the results in COD removal for both electrode types was achieved by the addition of electrolytes and increased amperage from 20 to 40 A. The majority of inorganic pollution is removed in the first 5 minutes of treatment. The best results are achieved by a combination of the two electrode types, with the addition of chloride as an electrolyte. After 15 minutes of electroreduction / electrocoagulation / indirect anodic oxidation by iron electrodes, 15 minutes of electrocoagulation by aluminium electrodes and 20 minutes of coagulation / flocculation and oxidation by air, 99.79% Cr(VI), 99.97% Fe, 98.23% Ni, 99.23% Cu, 99.999% Zn, 98.00% Pb and 86.46% COD were removed. All measured indicators complied with the conditions for discharge into the environment whereas all output concentrations of heavy metals ranged from 0.009 to 0.023 mg dm-3

Treatment of Acidic Mine Effluents and Wastewater from Ship Cleaning Facilities by Application of Red Mud

U radu je prikazan postupak obrade kiselog efluenta nastalog u toku eksploatacije i prerade bakrene rude kompleksa Borskih rudnika (Bor- Krivelj-Cerovo) pomoću crvenog mulja - otpadnog produkta iz procesa proizvodnje glinice u bivšoj tvornici glinice iz Obrovca te primjena nastalog otpadnog mulja za pročišćavanje otpadnih voda iz prališta brodova. Izvršena je karakterizacija otpadnih voda i crvenog mulja te su utvrđeni optimalni uvjeti uklanjanja ključnih pokazatelja iz otpadnih voda. Rudnička otpadna voda je karakterizirana niskom pH vrijednošću (3,21), visokom koncentracijom sulfata (10830 mg dm-3), visokim vrijednostima željeza (921 mg dm-3), mangana (107 mg dm-3), bakra (92 mg dm-3) i cinka (59 mg dm-3), dok su u otpadnoj vodi iz prališta brodova ključna onečišćivala bakar (34 mg dm-3), cink (59 mg dm-3) i boja (11470 PtCo). Obzirom na visok neutralizacijski i sorpcijski kapacitet crvenog mulja, njegovo miješanje s rudničkom otpadnom vodom u optimalnim omjerima dovodi do neutralizacije oba otpadna produkta te uklanjanja teških metala iz otpadne vode ispod graničnih vrijednosti. Pri optimalnim uvjetima uklanjanja (pH = 8; kontaktno vrijeme = 15 minuta) uklonjeno je više od 99,9% Cr, Mn, Fe, Cu i Zn te 65,5% sulfata. Preostali otpadni mulj je moguće ponovo upotrijebiti za pročišćavanje otpadnih voda iz prališta brodova visoko opterećenih bojama protiv obraštaja, a s jednom dozom mulja je moguće izvršiti pet ciklusa pročišćavanja s učinkovitošću uklanjanja ključnih pokazatelja preko 99%.The paper presents a procedure for treating acidic effluent generated during the exploitation and proce¬ssing of copper ore at the Bor mining complex (Bor-Krivelj-Cerovo) by application of red mud, a waste by-product of the alumina production process at the now-defunct alumina plant in Obrovac, and the application of the generated waste mud to treating wastewater from ship cleaning facilities. The characterisation of wastewater and red mud was carried out, resulting in the determination of optimal conditions for the removal of key indicators from wastewater. The acidic mine wastewater is characterised by a low pH value (3.21), high sulfate concentration (10,830 mg dm-3), high values of iron (921 mg dm-3), manganese (107 mg dm-3), copper (92 mg dm-3) and zinc (59 mg dm-3), whereas the key polluters in the wastewater from ship cleaning facilities include copper (34 mg dm-3), zinc (59 mg dm-3) and paint (11470 PtCo). Considering a high neutralisation and adsorption capacity of red mud, its mixing with mine drainage wastewater in op¬timal ratios leads to the neutralisation of both waste by-products and the removal of heavy metals from wastewater to below their limit values. Under the optimal removal conditions (pH = 8; contact time = 15 minutes), more than 99.9% of Cr, Mn, Fe, Cu and Zn as well as 65.5% of sulfates were removed. The remaining waste mud can be reused in the treatment of wastewater from ship cleaning facilities which has a high load of anti-fouling paint. A single mud dosage is sufficient for five treatment cycles and has a key indicator removal efficiency rate of over 99%

Electrochemical treatment of wastewater from potato chips production

U radu je prikazan novi kombinirani pristup u obradi otpadne vode koja nastaje u procesu prerade krumpira u čips kombinacijom elektrokemijskih metoda i ozoniranja. Otpadna voda je karakterizirana visokim vrijednostima ukupne suspendirane tvari (1517 mg dm-3), kemijske potrošnje kisika (2240 mg dm-3) te biokemijske potrošnje kisika (1780 mg dm-3) koje premašuju granične vrijednosti za ispust u okoliš za 43, 18 odnosno 71 puta. U svrhu optimizacije procesa u radu je ispitan utjecaj vrste elektroda (nehrđajući čelik, željezo, aluminij), kontaktnog vremena (5-30 minuta) te jakosti struje (30-100 A) na stupanj uklanjanja navedena tri parametra. Iako se aluminijev set elektroda pokazao najefikasnijim za uklanjanje navedenih pokazatelja, značajno bolji rezultati su dobiveni kombinacijom sve tri vrste elektroda uz istovremeno ozoniranje. Nakon 10 minuta elektrokoagulacije/elektroksidacije pomoću elektroda od nehrđajućeg čelika, 5 minuta elektrokoagulacije/ozoniranja pomoću željezovih elektroda, 15 elektrokoagulacije/ozoniranja pomoću aluminijevih elektroda te 15 minuta ozoniranja uklonjeno je 100% boje, mutnoće i UST, 94,5% KPK te 98,9% BPK5 a svi mjereni pokazatelji su zadovoljavali uvjete za ispust u okoliš.The paper presents a new approach which combines electrochemical methods and ozonation to wastewater treatment from potato processing in potato chips production. This wastewater is characterized by high values of total suspended solids (1517 mg dm-3), chemical oxygen demand (2240 mg dm-3) and biochemical oxygen demand (1780 mg dm-3) that exceed the limit values for discharges into the environment by 43.18 and 71 times, respectively. For the purpose of optimisation of this process, the paper investigated the impact of different electrode types (stainless steel, iron, aluminium), contact time (5-30 minutes) and amperage (30-100 A) on the degree of removal of these three parameters. Although the aluminium electrode set proved the most effective for the removal of these indicators, significantly better results were obtained by a combination of all three electrode types with simultaneous ozonation. After 10 minutes of electrocoagulation / electrooxidation with stainless steel electrodes, 5 minutes of electrocoagulation / ozonation with iron electrodes, 15 minutes of electrocoagulation / ozonation with aluminium electrodes and 15 minutes of ozonation, 100% colour, turbidity and TSS, 94.5% COD and 98. 9% BOD5 were removed, and all measured indicators met the requirements for discharges into the environment

Thermal/electrochemical processing of slaughterhouse wastewater

U radu je prikazana obrada klaoničkih otpadnih voda kombinacijom termičke predobrade i glavne elektrokemijske obrade uz simultano ozoniranje. Ispitana je učinkovitost uklanjanja karakterističnih pokazatelja te količina generiranog mulja obzirom na vrstu elektroda (nehrđajući čelik, željezo, aluminij), vrijeme obrade (5-30 minuta) i jakost struje (50-100 A). Otpadna voda je karakterizirana vrlo neugodnim mirisom, visokim vrijednostima boje (17400 CoPt), mutnoće (4230 NTU) ukupne suspendirane tvari (1730 mg dm-3), kemijske potrošnje kisika (3720 mg dm-3) te biokemijske potrošnje kisika (1870 mg dm-3) te povišenim vrijednostima amonija (128 mg dm-3) i fosfata (93 mg dm-3). Termičkom predobradom je uklonjeno 98,23% mutnoće, 89,94% boje, 75,14% ukupne suspendirane tvari (UST), 49,73% BPK5 i 36,29% KPK. Set elektroda od nehrđajućeg čelika se pokazao najučinkovitijim u uklanjanju organskih pokazatelja i amonija, a rezultirao je i najmanjim volumenom otpadnog mulja, dok su aluminijeve elektrode najučinkovitije u uklanjanju boje, ali uz najveću produkciju mulja. Najbolji rezultati su dobiveni kombinacijom sve tri vrste elektroda uz istovremeno ozoniranje uz kontaktno vrijeme 20 minuta, jakost struje od 70 A i napon od 10 V. Nakon elektrokoagulacije/elektroksidacije pomoću elektroda od nehrđajućeg čelika, elektrokoagulacije/ozoniranja pomoću željezovih elektroda, elektrokoagulacije/ozoniranja pomoću aluminijevih elektroda te završnog ozoniranja uklonjeno je 100% boje, mutnoće i UST, 99,77% KPK te 99,25% BPK5, 99,98% fosfata, 99,80% amonija i 43,86% ukupne otopljene tvari, a svi mjereni pokazatelji su zadovoljavali uvjete za ispust u okoliš.The paper presents slaughterhouse wastewater treatment implemented as a combination of thermal pre-treatment and main electrochemical treatment, with a simultaneous ozonation. The efficiency of the characteristic indicator removal and the quantity of generated sludge according to electrode types (stainless steel, iron and aluminium), treatment time (5-30 minutes) and amperage (50-100 A) was tested. The wastewater is characterized by a very unpleasant odour, high colouring value (17400 CoPt), turbidity (4230 NTU), total suspended solids (1730 mg dm-3), chemical oxygen demand (3720 mg dm-3) and biochemical oxygen demand (1870 mg dm-3) as well as increased values of ammonium (128 mg dm-3) and phosphates (93 mg dm-3). Thermal pre-treatment removed 98.23% turbidity, 89.94% colour, 75.14% total suspended solids (TSS), 49.73% BOD5 and 36.29% COD. A stainless steel electrode set proved to be the most efficient in the removal of organic indicators and ammonium and the lowest sludge volume, whereas aluminium electrodes were the most efficient in colour removal, although with the highest sludge production. The best results were achieved by a combination of all three electrode types, with a simultaneous ozonation of 20-minute contact time, amperage of 70 A and voltage of 10 V. Following the electrocoagulation / electrooxidation by stainless steel electrodes, electrocoagulation / ozonation by iron electrodes and electrocoagulation / ozonation with aluminium electrodes and the final ozonation, 100% colour, turbidity and TSS were removed as well as 99.77% COD and 99.25% BOD5, 99.98% phosphates, 99.80% ammonium and 43.86% total dissolved solids. All measured indicators complied with the conditions for discharge into the environment