Elektrokoagülasyonlu biyodizel atık suyu ile biyofilm tabakasında Chlorella Vulgaris üretimi ve atık suyun arıtımı
Production of Chlorella Vulgaris in biofilm layer with electrocoagulation biodisel wastewater and treatment of wastewater
Yazar: BÜŞRA ÇELİK
Danışman: PROF. DR. İSMAİL AYHAN ŞENGİL
Sakarya Üniversitesi / Fen Bilimleri Enstitüsü / Çevre Mühendisliği Ana Bilim Dalı
Derece: Yüksek Lisans, 2023
Konu: Çevre Mühendisliği = Environmental Engineering
Dizin: Atık su arıtma = Waste water treatment ; Biyofilmler = Biofilms ; Biyolojik arıtma = Biological treatment ; Elektrokoagülasyon = Electrocoagulation ; Endüstriyel atık su = Industrial waste water

Özet:
Nüfus artışı ve sanayinin gelişimi ile birlikte artan yakıt tüketimi alternatif biyoyakıt kaynaklarına olan ilgiyi arttırmıştır. Biyodizel yenilenebilir alternatif bir enerji kaynağıdır. Bitkisel yağlardan veya hayvansal yağlardan biyodizel üretilebilir. Transesterifikasyon yöntemi biyodizel üretiminde yaygın olarak kullanılmaktadır. Bu tezde kullanılan biyodizel atık suları laboratuvar ölçeğinde transesterifikasyon yöntemi ile elde edilen atık sulardır. Biyodizel üretiminden çıkan atık sular yüksek oranda organik madde içerir. Ayrıca biyodizel atık suları yüksek KOİ konsantrasyonu içerir. Bu nedenle ilk olarak elektrokagülasyon ile ön arıtımı yapılmıştır. 
Son yıllarda atık suların arıtılmasında mikroalgler kullanılmaktadır. Chlorella Vulgaris atık su arıtımında en çok tercih edilen alg türüdür. Deneylerde kullanılan Chlorella Vulgaris Sakarya Üniversitesi Çevre Mühendisliği Laboratuvarı'nda üretilmiştir. Bu tez çalışmasında elektrokoagülasyon ile ön arıtımdan geçirilen biyodizel atık suyu Chlorella Vulgaris mikroalglerinin biyofilm tabakası oluşturması için kullanılmıştır. Chlorella Vulgaris biyofilm tabakasının oluşturulması sırasında sisteme besin maddeleri ilavesi gerekmektedir. Mikroalglerin gelişimi için ortamda karbon, azot ve fosfor bulunmalıdır. Mikroalglerin yapısına katılan azot ve fosfor eksikliğinde yeterli alg gelişimi görülemez. Biyodizel atık suyunda yeterli miktarda karbon vardır. Atık suya azot ve fosfor eklenmiştir. Azot kaynağı olarak NaNO3, fosfor kaynağı olarak K2HPO4 eklenmiştir. 
Farklı N/P oranlarının biyofilm oluşum miktarı, mikroalglerin azot ve fosfatı kullanım miktarı ve dolayısıyla atık sudan azot, fosfat giderimi ve KOİ giderimi üzerindeki etkileri değerlendirildi. Çalışma 16:1 ve 20:1 N/P oranlarında yürütülmüştür. Chlorella Vulgaris'in gelişim dönemleri esas alınarak 6 gün boyunca atık su arıtma ve alg büyüme parametreleri ölçülmüştür. 16:1 N/P oranında 2,579 gram biyofilm oluşurken, 20:1 N/P oranında 3,963 gram biyofilm oluşmuştur. 20:1 N/P oranında biyofilm oluşumu daha yüksektir. Sonuçlara göre 6 günlük biyofilmde 16:1 N/P oranında yapılan deneysel çalışmada KOİ %80,02, PO43- %66,66, NH4+ %100, NO3- %74,25 ve NO2- %21,98 giderim verimi tespit edilmiştir. 20:1 N/P oranında yapılan deneysel çalışmada KOİ %69,69, PO43- %81,33, NH4+ %100, NO3- %70,67 ve NO2- %38,23 giderim verimi tespit edilmiştir. 
Bulgularımıza göre Chlorella Vulgaris'in biyodizel atık suyunda biyofilm oluşturabildiği, atık sudan yüksek miktarda nütrient giderimi sağlayabildiği ve atık suyu arıtabildiği görülmüştür.

Abstract:
The increase in population in the world, the development of the industry and the increasing energy need in parallel with these have increased the use of fossil fuels. Crude oil prices increased due to the depletion of oil reserves. Biodiesel is a renewable alternative energy source. Biodiesel can be produced from waste vegetable oils. Transesterification method is widely used in biodiesel production. 
Biodiesel wastewater used in this thesis is resulting wastewaters from transesterification method in laboratory scale. 200 ml of methanol per 1 L of oil and 4,9 g of KOH was added. KOH is the catalyst. Stirred to dissolve the catalyst in methanol. The oil was heated to 40 degrees. The alcohol-catalyst mixture was added to the oil. The temperature was set at 55-60 degrees.The mixture was stirred for 1 hour. Then, the mixture was left to stand for 12. Two phases occurred. 
Ester and glycerin were separated. Ester was washed.The resulting wastewater from the biodiesel have high ratio of organic materials. In addition wastewater from the biodiesel processing industry contains high concentrations of COD. 
Accordingly electrocoagulation process was applied as the first treatment for wastewater. Electrocoagulation is very effective in the treatment of oily wastewater. Electrodes made of iron plates are bipolar connected. Effective the electrode area was designed as 144 cm2. 4 pieces of electrodes its dimensions are equal and are 6x12x0,15 cm. The distance between the electrodes is 7,5 mm. The voltage value of the power supply is between 0-30 V and the current value is between 0-5 A. As a result of the electrocoagulation process, the COD removal efficiency was found to be 94%.
Algae are the oldest microorganisms with photosynthetic structure. Algae are ubiquitous single to multi cellular chlorophyll containing organisms. They are divided into macroalgae and microalgae. In recent years, microalgaes are used for purification of wastewater. The use of algae as a wastewater treatment method and the development of algae in wastewater have been emphasized and many studies have been carried out. 
Microalgae are used in biological wastewater treatment.Wastewater treatment with the microalgae-based system is effective in removing inorganic compounds such as ammonium, nitrate, nitrite, phosphate and COD wastewater through their uptake mechanism. The uptake nitrate and phosphate by microalgae cells for growth can reduce the nitrogen and phosphorus content in wastewater.
There are some parameters necessary for the growth of microalgae. These parameters are nutrients, light, temperature, pH and trace elements. Microalgae contain carbon, nitrogen and phosphorus in their structures. Chlorella Vulgaris is the most prefer algae in wastewater treatment. Chlorella is in the green algae group.  Chlorella Vulgaris grows fast. 
Chlorella Vulgaris to be used to experiment were produced in the laboratory of the Department of Environmental Engineering at Sakarya University. Chlorella Vulgaris microalgae culture was developed in BG11 medium. BG11 was added to the algae medium twice a week.  In this thesis, biodiesel wastewater, which was passed through pre-treatment by electrocoagulation, was used to produce biofilm layer by using microalgae of Chlorella Vulgaris. 
Biofilms are communities of microorganisms that grow on surfaces. Growing algal biofilms as a nutrient removal option for wastewater treatment provide nutrient treatment technology. When algal biofilms are utilized for wastewater treatment nutrient addition may be required to optimize the molar stoichiometric ratios of carbon, nitrogen, and phosphorus necessary for growth.
Carbon, phosphorus and nitrogen must be present in the medium for the growth of microalgae. Inorganic phosphorus present in wastewater plays a big role in microalgae energy metabolism and growth. Uptake of inorganic phosphates place across the plasma membrane of microalgae cells. Nitrogen affects the structure of algae. Organic nitrogen is found in the structure of enzymes, peptides, proteins, chlorophylls, ADP and ATP. 
There is sufficient amount of carbon in biodiesel wastewater. Nitrogen and phosphorus were added to the wastewater.  The nitrogen required for the microalgae was obtained from sodium nitrate. Potassium hydrogen phosphate was used as the source of phosphorus. 
250 ml of algae was added to 250 ml of biodiesel wastewater and the microalgae were pre-adapted to the wastewater. Erlenmeyer flasks were shaken at a light intensity of 100 μmol photon/m2-s in a continuous bright environment. This process continued for two days. By hand shaking 2-3 times, the algae mass was prevented from collapsing to the bottom.
The plate was covered with cotton fabric and a cotton surface was obtained. The plate was placed in the reactor at an inclination of 45°. Equal amount of wastewater was given to the system through 4 holes from the cylindrical apparatus. Microalgae were passed through the reactor for 2 days. Microalgae adhered to the cotton surface.Then, wastewater was circulated. The circulation of the wastewater was done with a peristaltic pump.
With the peristaltic pump, the water circulation rate treatments on our surfaces were kept the same throughout the study and the structure of the formed biofilm layers was maintained. 
On the basis of the developmental periods of Chlorella Vulgaris wastewater treatment and algal growth parameters were measured during 6 day. Biofilm layer formed during operation in the reactor PO43-, NH4+, NO3-, NO2- and COD removal efficiencies of wastewater passed over examined.
2,579 grams of biofilm was formed at a 16:1 N/P ratio. According to the results of daily analyzes, it was observed that the initial phosphate concentration in the wastewater decreased from 15 mg/L to 5 mg/L. 
At the end of the 6th day of the study, the phosphate removal efficiency was 66,66%. The initial concentration of ammonium nitrogen in the wastewater is 2 mg/L. 
The ammonium nitrogen was depleted by the 4th day.
According to the results of daily analyzes, it was observed that the nitrate nitrogen concentration decreased from 101 mg/L to 26 mg/L on the day the experiment ended. During the study period, nitrate nitrogen removal showed a linear increase. Nitrate removal efficiency was 74,25% at the end of the 6th day. It was observed that the initial nitrite nitrogen concentration decreased from 141 mg/L to 110 mg/L.The nitrite nitrogen removal in wastewater is limited to 21,98%.
According to the results of daily analyzes, it was observed that the initial COD concentration decreased from 17300 mg/L to 3456 mg/L at the end of the study. COD removal in wastewater was 80,02%.
3,963 grams of biofilm was formed at a 20:1 N/P ratio. The amount of biofilm formation is higher at 20:1 N/P ratio.
According to the results of daily analyzes, it was observed that the initial phosphate concentration in the wastewater decreased from 15 mg/L to 2.8 mg/L at the end of the 6th day. At the end of the 6th day, phosphate removal was 81,33%. The ammonium nitrogen in the wastewater was depleted after the 2nd day.
It was observed that the initial nitrate nitrogen concentration decreased from 208 mg/L to 61 mg/L at the end of the day when the experimental study was ended. During the study, the amount of nitrate nitrogen removal showed a linear increase. At the end of the 6th day of the study, nitrate nitrogen removal was 70,67%. 
It was determined that the initial nitrite nitrogen concentration decreased from 170 mg/L to 105 mg/L at the end of the 6th day. Nitrite nitrogen removal is limited to 38,23%.
It was observed that the COD concentration decreased from 17389 mg/L to 5269 mg/L at the end of the experimental study. COD removal in wastewater was 69,69%.
It has been reported that microalgae use ammonium as their primary nitrogen source. In both experiments, the initial ammonium nitrogen concentration was low and the ammonium nitrogen was depleted during the experiment. Chlorella Vulgaris may have had to use nitrate nitrogen and nitrite nitrogen, which are forms of nitrogen.
In our experiment, it was observed that the thickening increased over time and then stabilized in the developing biofilm. Another reason could be the low light availability arising from self-shading at high algal density.
Chlorella Vulgaris can form biofilm in biodiesel wastewater and at the same time high nutrient removal from wastewater is provided.
As a result of these studies, it is seen that Chlorella Vulgaris, which has adapted to different industrial wastewaters, is quite successful in nutrient removal and COD removal.