Anaerobic treatment of soapstock splitting wastewater

Abstract

In the developing world, the needs of the people are also increasing due to the rapidly increasing population. Nutrition comes at the beginning of these needs. In order to meet the increasing nutritional need on a global scale, edible oil production continues every day. Edible oil can generally be made of vegetable origin or animal origin. However, a very large part of the oil produced worldwide consists of vegetable oils produced from oilseeds. Many different kinds of oilseeds are grown in many different countries around the world. In order to obtain vegetable oils from oil seeds, an extraction process must be carried out. And, undesirable substances in the raw vegetable oil as a result of the extraction process must be removed by a couple of processes. Substances in raw vegetable oil that must be removed are generally free fatty acids, vitamins, antioxidants, alcohol, waxy substances, etc. Refining is carried out in order to remove such unwanted substances from the raw oil. In the neutralization step of the refining process, an alkaline environment is created by caustic and thus soapy waxy substances are formed. In this way, the free fatty acids in the raw oil are removed and converted into this soapy by-product called soapstock. Soapstock contains oil due to its structure and for this reason, it is a valuable by-product. The soapstock splitting method with sulfuric acid is applied for the production of acid oil. In this process, sulfuric acid and soapstock are brought together in a high-temperature boiler and the acid oil is recovered as the upper phase. Also, the remaining phase is wastewater. In this thesis, the performance of anaerobic treatment of carbon removal from soapstock splitting wastewater was investigated. For this purpose, a wastewater sample was obtained from the soapstock recycling facility of an edible oil production factory in the Marmara Region of Turkey. Detailed characterization of wastewater was carried out. Sludge from an anaerobic digester of a yeast production industry, digestate, and fresh manure was used as inoculum. Anaerobic reactors were designed as a semi-batch continuous system and operated in a constant temperature room under mesophilic conditions (37°C). The reactors were generally operated to examine the effect of different pH values and different inoculum, different volumetric loading rates, FeCl3 dosages. In the first part of the experimental study, different pH and inoculums were setup to observe best COD removal efficiencies. In the second experimental set, the reactors were operated at the pH where good efficiency was observed in the first experimental setup, and with the inoculum which was also observed with good efficiency. In this set of experiments, the effect of VLR on COD removal efficiency was investigated. Also, the effect of mixing on the removal efficiency was tested. In the third experimental setup, the amount of FeCl3 added in order to prevent the inhibition caused by the H2S gas formed in the anaerobic environment due to the high sulfate content of the soapstock wastewater was investigated simultaneously with the increasing in VLR. In order to investigate the effect of high daily FeCl3 amount on the efficiency of anaerobic reactors, a fourth experimental reactor was set. In this part, the experiment was carried out by adding three different FeCl3 dosages to different reactors. TS, VS, SS, VSS, sCOD, tCOD, pH, Conductivity, Color, TP, TKN, Ammonia, and Acidity parameters were determined according to standard methods. Sulphate and ion concentrations were measured using an IC device (Dionex, ICS-3000, USA). pH was measured using Thermo-Orion 720 A+ model pH meter and conductivity was measured using a Hach-sensION5 model device. The total COD value of the raw wastewater is approximately 28100 mg/L, and the soluble COD value is 25500 mg/L on average. TS in wastewater is 76500 mg/L on average, of which approximately 45500 mg/L is volatile. In addition, SS in the wastewater is approximately 500 mg/L and VSS is 385 mg/L. Wastewater has a pH of 0.2 and conductivity of 103 mS/cm. The color parameter of the wastewater sample is 3495 PtCo. Wastewater's TP and TKN are 41 mg/L and 2000 mg/L, respectively. In addition, ammonia is 300 mg/L. There is a total acidity of 39150 mg CaCO3/L in wastewater and 26200 mgCaCO3/L of this is mineral acidity. SO42- concentration of the wastewater is 68000 mg/L. The pH values of the different inoculum sludges are 8.58 for the sample from the anaerobic digester of the yeast production industry, 8.30 for the digestate, and 8.25 for the fresh manure, respectively. The TS ratio of the inoculum from the anaerobic digester of the yeast production industry is 10 % and the VS ratio is 0.3 %. Digestate has a TS rate of 13 % and a VS rate of 7 %. On the other hand, the TS ratio of fresh manure is 11 % and the VS ratio is 9 %. Mixed sludge was found to be the best inoculum observed for COD removal in anaerobic reactors. It was also observed that reactors at pH 7 had better COD removal than pH 5. In the optimization study carried out in the first experimental setup, the COD removal efficiency of the reactor group operated with mixed sludge at pH 7 was 67 % and the COD reduced to 8416 mg/L. In the second experimental setup, in the reactors operated at pH 7 and in which mixed sludge was added as inoculum, the highest COD removal (72 %) was realized when the volumetric loading ratio was 4. And, COD reduced to 7288 mg/L. At the end of this period, the COD/SO42- ratio was 0.27. In the third experimental set, when the volumetric loading ratio was 4, the reactor group containing 0.70 g FeCl3 had the highest removal rate with 73 % in terms of COD removal, and the COD reduced to 7009 mg/L. The COD/SO42- ratio was 0.33 for reactors with a FeCl3 dose of 0.7 g/day. In the fourth experimental setup, when the volumetric loading ratio was 4, the reactor group dosed with 0.70 g FeCl3 was the most efficient in terms of COD removal. The COD and SO42- removal efficiencies for this reactor group are 74 % and 73 %, respectively. The COD was 6774 mg/L, and the COD/SO42- ratio was 0.36. The efficiency of the reactor with 0.70 g/day FeCl3 dose was higher than the other reactors in both the periods of volumetric loading rate 2 and 4. Despite having the same initial volumetric loading (volume loading: 2) and the same FeCl3 dosages, lower yield (70 %) were obtained from the reactors in experimental setup 3 and the COD was reduced to 7716 mg/L. To sum up, the COD was reduced to 6774 mg/L in semi-batch continuous reactors using mixed sludge as inoculum by dosing 0.70 g/L/day FeCl3 while VLR was 4 at pH 7, under mesophilic conditions (37°C). 74 % carbon removal at COD/SO42- ratio of 0.36 was a significant achievement under these operating conditions. Considering the 200 mg/L of COD discharge to the receiving water bodies of this wastewater, there is a need of additional steps to satisfied these limits.