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In this paper the effect of ultrasound and electrocoagulation on the removal of manganese from synthetic wastewater was investigated. It was shown that 20 kHz ultrasound alone is not very efficient for manganese removal, but it enhances the efficiency of electrocoagulation. It was also shown that settling has a great effect on the electrocoagulation process because it stabilizes the flocs. A total of four laboratory-scale experiments were conducted, and the optimal experiment included 10 minutes of ultrasound and 10 minutes of electrocoagulation with iron electrodes. Under these conditions, 89.0 % of the manganese was removed with an operating cost of 0.13 EUR/mg Mn. Adding the cost of replacing the immersed ultrasonic probe, the total operating cost increased 3000-fold, making the immersed ultrasonic probe method unviable for large-scale application.

Water conditioning is a method of removing altering minerals, chemicals and contaminants from a water source and it is carried out on facilities equipped with the corresponding electro-mechanical equipment. Although efficient, conventional processes typically use several complex devices connected to a single functional unit, which are often expensive to maintain and occupy large areas. Therefore, the aim of this paper is to present the electrocoagulation (EC) method as an alternative to conventional water conditioning processes. The examples of previous studies of the EC process application is presented in this paper. The focus of the paper is to investigate the influence of the certain operational parameters such as pH, temperature, electrode material, etc., on the efficiency of pollutant removal such as Escherichia coli and elevated concentrations of iron, arsenic, manganese, ammonia and others. Further, an economic analysis is made, which, from an economic point of view, shows when it is feasible to use the EC in the conditioning process. Furthermore, a case study of electrocoagulation process for Total Nitrogen (TN) removal is presented. According to results, 69.7 % of TN was removed with aluminum electrodes after 240 minutes. For this case, total operating costs were 7.60 €/m3.

Abstract:The efficiency of the electrocoagulation (EC) process for the removal of total N (TN) is analyzed using a pilot device (reactor) with stainless-steel electrodes. Additionally, a three-dimensional (3D) numerical model for TN removal via the EC process is developed. The effects of the flow rate through the reactor and the initial NaCl concentration were the focus of the research. The concentrations of TN, nitrate (NO3-N), dissolved O, Fe (Fe 2+ /Fe 3+ ), and chloride (Cl -), as well as the water temperature and pH, were measured in the EC reactor. By using the 3D numerical model, spatially continuous velocity fields and the TN concentration were determined. The results of this study show that the TN removal efficiency is dependent primarily on the initial concentration of NaCl and secondarily on the flow rate through the reactor. The initial TN concentration is reduced by 35% after 240 min of reactor operation when the flow rate is set as 0.15 L/s and the initial NaCl concentration is 2 g/L, while the current density is maintained at 150 A/m 2 . The NO3-N concentrations and pH are reduced by 5% with respect to the initial values.Keywords: electrocoagulation; pilot device; numerical model; ammonia MODELIRANJE DINAMIKE UKUPNOG DUŠIKA PRI RADU ELEKTROKOAGULACIJSKOG UREĐAJA S INOKS ELEKTRODAMASažetak: Analizirana je učinkovitost elektrokoagulacijskog (EC) pilot uređaja s inoks elektrodama u postupku pročišćavanja vode opterećene povišenom koncentracijom ukupnog dušika. Dodatno je uspostavljen i 3D numerički model strujanja i pronosa. U provedbi analiza na pilot-uređaju variran je protok kroz reaktor sa inoks elektrodama te inicijalna koncentracija NaCl. U komori EC uređaja praćene su i promjene koncentracija ukupnog dušika (TN), nitrata (NO3-N), otopljenog kisika (DO), željeza (Fe 2+ /Fe 3+ ) i klorida (Cl -), te promjene temperature vode i pH. Primjenom 3D numeričkog modela, definirana su polja strujanja i koncentracije ukupnog dušika u procesu pronosa. Rezultati provedenog istraživanja pokazali su da je učinkovitost procesa pročišćavanja primarno ovisna o inicijalnoj koncentraciji NaCl, a sekundarno i o protoku kroz reaktor. Pri protoku kroz reaktor Q = 0.15 l/s, uz primjenu gustoće jakosti struje 150 A/m 2 i inicijalnu koncentraciju NaCl od 2 g/l, nakon 240 minuta rada elektrode postignuto je smanjenje inicijalne koncentracije TN od 35 %. Koncentracija nitrata (NO3-N) i pH smanjuju se na skali od 5 % u odnosu na početne vrijednosti.

Wastewater containing oil is becoming a growing problem worldwide due to increasing quantities and existing pollution. The pollutants contained in these effluents, when released into the environment, affect surface and groundwater pollution, endanger human life and health, and pollute the atmosphere. Their sustainable treatment should be cost-effective and meet all requirements to prevent the pollutants from being transferred to the environment or to humans. This study gives a brief overview of some conventional and modern technologies that have been proven in practice for the treatment of oily wastewater. Due to the high concentrations of chemical oxygen demand (COD) and total hydrocarbons (mineral oils) in oily wastewater its treatment is complex, and to achieve optimum treatment conditions and efficiency a combination of different technologies is required. This paper focuses on hybrid electrochemical process combining the electro-Fenton process (EF) using stainless steel (SS), and electrocoagulation (EC) with iron (Fe) and aluminum (Al) electrodes. The influence of the two different types of pretreatment, i.e., pretreatment of the raw wastewater on the overall efficiency of oily wastewater treatment using a hybrid treatment process, which is a combination of AOP and EC, is investigated. Two type of pretreatment were tested, with primary sedimentation and pretreatment of the mixture of raw wastewater and previously generated electrochemical sludge with primary sedimentation. During the applied treatment processes, the concentration of COD, mineral oils, and other elements in the raw and treated wastewater (As, Ca, Cd, Cr, Cu, Ni, Pb, Sn, Zn) and in the generated sludge (K, Ca, Fe, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, As, Br, Rb, Sr, Y, Zr, Pb, Th) were determined. By combining the primary sedimentation of the raw wastewater with the EF/EC process, a mineral oil removal efficiency of 72% (1.1 mg/L) and COD of 89% (170 mg/L) was achieved. Using primary sedimentation of a mixture of raw wastewater with previously generated sludge as pretreatment and followed by EF/EC treatment, a higher efficiency for mineral oils of 94% (7.6 mg/L) and COD of 98% (43 mg/L) was achieved.