PAHs and toxicity removals under aerobic conditions in petrochemical industry

Çevre Koruma Ajansı (EPA) tarafından öncelikli kirleticiler listesinde belirtilen 15 adet poliaromatik hidrokarbonun (PAH) petrokimya endüstrisi atıksularının aerobik sürekli karıştırmalı bir tank reaktörde (SKTR) arıtma verimliliğinin ve toksisitenin giderilmesi amaçlanmıştır. Ramnolipit biyosürfaktanının aerobik biyolojik arıtma verimi ile bazı kimyasal oksijen ihtiyacı (KOİ) bileşenlerinin giderim verimine etkileri incelenmiştir. Aerobik SKTR sistemler 25 günlük çamur yaşında ve 5 günlük hidrolik bekleme sürelerinde işletilmiştir. Petrokimya endüstrisinden alınan atıksuyun ramnolipit (15mg/L) ilaveli SKTR reaktörde toplam PAH konsantrasyonu 65.36 ng/mL olup arıtılmış çıkış suyunda ise toplam PAH konsantrasyonu 8.76 ng/mL ve toplam PAH giderim verimi %87 olarak bulunmuştur. 3 benzen halkalı PAH’larda %74 ile % 99 arasında, 4 benzen halkalı PAH’larda (BaA hariç) %71 ile %79 arasında, 5 benzen halkalı PAH’larda %54 ile %74 ve 6 benzen halkalı PAH’larda ise %84 ile %87 arasında değişen giderim verimleri elde edilmiştir. Ramnolipit ilavesi inert KOİ giderim verimini %0’dan %60’a yükseltirken, yavaş ayrışabilen KOİ ve kolay ayrışabilen KOİ giderme verimlerini de sırası ile %2’den %74 ve %78’den %91’e çıkarmıştır. Vibrio fischeri akut toksisite testinde organizmanın %50’sinin etkilendiği konsantrasyon (EC50) değerleri tespit edilmiştir. Giriş atıksuyunda sırası ile PAH ve KOİ baz alınarak hesaplanan EC50 değerleri 50.65 ng/mL ve 820 mg/L iken çıkış atıksuyunda 5.25 ng/mL ve 68.5 mg/L’ye azalmış olup PAH ve KOİ bazlı akut toksisite giderim verimleri sırasıyla %90 ve %92 olarak tespit edilmiştir. Anahtar Kelimeler: Aerobik, aktif çamur sistemi, poloaromatik hidrokarbon (PAH), petrokimya, ramnolipit, toksisite.Petrochemical industry wastewaters are the most important source of the persistent organic compounds PAHs which are toxic, mutagenic and carcinogenic substances. Due to their high toxicity and wide distribution in the environment, including air, water, soils, and sediments, some PAHs have been listed as priority pollutants by the United States Environmental Protection Agency (U.S. EPA). The determination and monitoring of PAHs in environmental samples is necessary and important to human health. Wastewater treatment plants, especially those serving both urban and industrial areas, consistently receive complex mixtures and a wide variety of organic pollutants. Activated sludge system is the most widely used biological wastewater treatment process to treat petrochemical industry wastewaters in Turkey. However, the removal efficiencies of PAHs are low, in the conventional aerobic activated sludge reactor system treating this wastewater in Izmir. In the laboratory studies, an aerobic completely stirred tank reactor (CSTR) was used for the biodegradation of PAHs in the wastewater taken from the influent of aerobic activated sludge tank of the petrochemical industry wastewater treatment plant in Izmir. The removal efficiencies of acenaphthene (ACT), fluorene (FLN), phenanthrene (PHE), anthracene (ANT), carbazole (CRB), fluoranthene (FL), pyrene (PY), benz [a] anthracene (BaA), chrysene (CHR), benz [b] fluoranthene (BbF), benzo [k] fluoranthene (BkF), benzo [a] pyrene (BaP), indeno [1,2,3-cd] pyrene (IcdP), dibenz [a,h] anthracene (DahA), benzo [g,h,i] perylene (BghiP) were determined in wastewater. The present study was primarily motivated to investigate the potential application of a biosurfactant (rhamnolipid) in order to increase the biodegradability of a raw wastewater taken from a petrochemical industry treatment plant. 15 mg/L rhamnolipid was useful to enhance the biodegradation performances of 15 PAHs. The yield of 3 ring PAHs removal was almost 92% and 99% for ANT and ACT PAHs, respectively. The administration of 15 mg/L rhamnolipid increased the PAHs removals from 72%, 78% and 80% up to 80%, 92% and 99%, respectively, for CRB, ANT and ACT PAHs. Removals of 4 ring PAHs (FL, PY, and CHR) were significantly higher in the presence of 15 mg/L rhamnolipid (71%, 60% and 79%, respectively) in comparison to rhamnolipid free conditions (69%, 60% and 65%). Treatment with rhamnolipid (15 mg/L) caused a significant increase of 5 and 6 ring PAHs degradation. The PAHs removal efficiencies increased from 45%, 67% and 57% up to 54%, 73% and 86% for BkF, BaP and DahA. PAHs treatment with rhamnolipid slightly increases the PHE BaA and BbF, PAHs removals. PAH treatment with rhamnolipid was beneficial for the degradation of all ring PAHs with a total PAHs removal yield of 87% in comparison to 74% in the rhamnolipid free case. Aerobic degradation in the CSTR process was very efficient for all ring PAHs removal. The total COD removals were around 88% in the CSTR reactor containing 15 mg/L rhamnolipid. The soluble COD removal efficiencies were 93% and 80% in rhamnolipid added and non-added CSTR reactors, respectively. The readily and slowly degradable COD concentrations were determined as 1025 and 500 mg/L in the influent of petrochemical industry wastewater, respectively, in the CSTR reactor containing 15 mg/L rhamnolipid. The readily and slowly degradable COD were removed with treatment efficiencies of 91% and 74%, respectively. These indices were removed with removal efficiencies of 78% and 2% in the CSTR reactor without rhamnolipid. The non-degraded inert COD concentrations were measured as 170 mg/L in the influent of the raw petrochemical industry wastewater, while the inert COD concentrations decreased to 68 mg/L in the effluent of CSTR reactor resulting in an inert COD removal efficiency of 60% in the CSTR reactor containing 15 mg/L rhamnolipid. The inert COD concentrations increased from 50 and 170 mg/L to 65 and 232 mg/L in the effluent of the control and without rhamnolipid reactors, respectively. However, the inert COD concentrations decreased in the aerobic reactor containing rhamnolipid as aforementioned. The removal in metabolic product COD was also, 99% in the reactor with rhamnolipid while this parameter increased in the control and in the rhamnolipid free reactors. The effective PAHs concentration affecting the half of Vibrio fischeri organism (EC50 value) reduced from 50.65 ng/mL to 5.25 ng/mL at the end of the aerobic treatment at a SRT of 25 days. The EC50 value for COD reduced from 820 mg/L to 68.5 mg/L after aerobic treatment. Toxicity removals originated from PAHs and COD were 90% and 92%, respectively. Keywords: Aerobic, activated sludge system, polycyclic aromatic hydrocarbon (PAHs), petrochemical, rhamnolipid, toxicity