Bu çalışmada, bir tekstil atıksuyunun elektrokoagülasyon (EC) ile arıtılmasının sonuçları ortaya konmuştur. Demir ve alüminyum elektrotlar, monopolar paralel, monopolar seri ve bipolar seri bağlantı şekli ile kullanılmıştır. Arıtma verimliliğinin ölçülmesinde KOİ ve türbidite giderimleri dikkate alınmıştır. KOİ gideriminde, her iki elektrot materyalinde asidik ortam daha uygun olup; demir elektrot için, Bipolar Seri (BP-S) bağlantı şekli etkili olurken, alüminyum elektrotlarda ise her üç bağlantı şekli için birbirine yakın sonuçlar elde edilmiştir. Türbidite gideriminde; optimum pH’nın elektrot materyaline bağlı olduğu, alüminyum elektrotlar için asidik ortamın, demir elektrotlar için ise nötral ortamın daha uygun olduğu tespit edilmiştir. Genel olarak, yüksek akım yoğunluklarının yüksek KOİ ve türbidite giderme verimleri sağladığı görülmüştür. Düşük akım yoğunluğunda (30 A.m-2) demir elektrotlarda sadece Monopolar Paralel (MP-P) sistemden verim alınmıştır. Alüminyum elektrotlarda ise; KOİ giderimi bağlantı şekline göre değişirken, türbidite giderimi bağlantı şeklinden oldukça bağımsızdır. Diğer yandan, EC prosesi alüminyum elektrotlarla daha hızlı ilerlediğinden; her üç bağlantı için de 5 dakikalık bir süre etkili olurken, demir elektrotlarda ise; seri bağlantı sistemleriyle en az 10 dakikalık bir işlem süresine ihtiyaç duyulmakta, MP-P bağlantı şekli ise daha fazla işlem süresi gerektirmektedir. Ekonomik analizde, bir tekstil fabrikasının 1000 m3.gün-1 debide atıksuyunun EC ile arıtılmasının işletme giderleri hesaplanmıştır. Sonuç olarak, bu çalışmada EC prosesinin, kimyasal koagülasyona göre daha az materyal tüketen ve daha az çamur üreten, daha hızlı ve daha ekonomik bir proses olduğu belirlenmiştir. Anahtar kelimeler: Ekonomik analiz, elektrokoagülasyon, elektrot malzemesi, KOİ, tekstil atıksuları, türbidite.Electrocoagulation (EC) is an effective method for wastewater treatment. This paper presents the results of the treatment of a textile wastewater by EC process. Two electrode materials, aluminium and iron, were connected in three modes namely, monopolar-parallel (MP-P), monopolar-serial (MP-S), and bipolar-serial (BP-S). In MP-P mode; anodes and cathodes are in parallel connection, the current is divided between all the electrodes in relation to the resistance of the individual cells. Hence, a lower potential difference is required in parallel connection, when compared with serial connections. In MP-S configuration; each pair of sacrificial electrodes is internally connected with each other, because the cell voltages sum up, a higher potential difference is required for a given current. Otherwise, in BP-S connection; there is no electrical connection between inner electrodes, only the outer electrodes are connected to the power supply. Outer electrodes are monopolar and inner ones are bipolar. This connection mode has simple setup with and has less maintenance cost during operation. The effects of wastewater pH, current density and operating time are presented separately for two sacrificial electrode materials, Fe and Al, and three electrode connection modes mentioned above. COD and turbidity removals were selected as performance criteria. The following conclusions may be drawn from the experimental results; acidic medium is preferable for a high COD removal for both electrode materials; iron electrode performs clearly better with BP-S mode, while the performance of aluminium is not strongly dependent on connection mode. For a high turbidity removal, the optimum pH depends on the electrode material; aluminium electrode connected in BP-S mode performs better in acidic medium, while the poor filterability of the flocs dictates pH 7 to be more suitable for the iron electrode connected in MP-S mode. High current density is generally favorable for high COD and turbidity removals in the case of iron; at low current density, MP-P mode performs better, while at high current densities, the three modes perform equally well. In the aluminium case, the effect is more pronounced on COD removal and it depends strongly on the connection mode, but it has nearly a negligible effect on the turbidity removal which also unaffected by the connection mode. In the case of aluminium, steady removal efficiencies are reached within 5 min for all three systems, while for iron electrode, serial connection systems, BP-S and MP-S reach steady values in 10 min, while MP-P needs longer operating time. For a complete technical analysis, it is worth to compare EC with conventional chemical coagulation, in regard with removal efficiencies and various important aspects. For this purpose, jar-tests were performed at laboratory scale in order to determine the adequate coagulant dosage. After choosing the best amount, same experiments have been performed to determine optimum pH value for each coagulant. Experimental conditions, removal efficiencies and some other pertinent data of electrocoagulation and chemical coagulation process variations are shown in text. At first sight, it is clearly seen that EC is faster, consumes less material and produces less sludge than chemical coagulation for similar COD and turbidity removal levels. The process using aluminium electrodes connected in MP-S mode seems to be the best choice. Meanwhile, an economic analysis is, of course, needed for a final selection. In economic analysis; the total operation cost was calculated using various experimental dataset such as; energy consumption, sacrificial electrode material, chemicals and sludge amounts per m3 of wastewater for a textile plant with 1000 m3.day-1 of wastewater. Iron is preferred as a low cost one for electrocogulation. On the other hand, FeCl3 is the preferable salt in view of its techno-economic performance for CC. Finally, when EC and CC are compared both technically and economically, the following results may be drawn; the COD removal performance of CC is 10% higher than EC, the turbidity removal is nearly the same, but in 60% longer retention time. With the same initial pH, the final pH is 7.9 in EC, but 2.9 in CC. The final acidic and chloride bearing medium is an important drawback of CC, causing severe corrosion problems which may necessitate high-cost building materials. From this point, Fe2(SO4)3.7H2O may be used despite of its higher operating cost. High coagulant consumption in CC means high chloride concentration in the effluent. Finally, and more importantly, the operating cost of CC is 3.2 times as high as the operating cost of EC. Keywords: COD, economic analysis, electrocoagulation, electrode material, textile wastewaters, turbidity
