ارزيابي عملكرد سيستم تصفيه پساب واحد توليد اكريلونيتريل بوتادين استايرن (ABS)

Evaluation of operating performance of ABS wastewater treatment system

اين مطالعه به منظور ارزيابي عملكرد سيستم تصفيه پساب واحد توليد رزين اكريلونيتريل بوتادين استايرن (ABS) انجام شده است. سيستم تصفيه شامل 3 آشغالگير ريز، يك حوض دانه‌گير، يك حوض متعادل‌ساز، سيستم شناورسازي با هواي محلول (DAF)، يك واحد بيولوژيكي لجن فعال و واحد زلال‌ساز ميباشد. اين سيستم پيش‌تصفيه به منظور كاهش مواد جامد معلق و COD پساب واحد ABS قبل از ورود به واحد تصفيه مركزي شركت پتروشيمي طراحي شده است. نمونه‌هاي تركيبي متناسب با دبي در 4 نوبت در طي 6 ماه برداشته شده و پارامترهاي BOD5, COD ,TSS، اكريلونيتريل، اكريلاميد، اكريليك اسيد، سيانيد و آمونياك مطابق با روش‌هاي استاندارد اندازه‌گيري شده‌اند. ساختار جمعيت ميكروبي سيستم لجن فعال نيز مورد بررسي قرار گرفته است. تحت بار سطحي m3/m2.h 2.76 اعمال شده به سيستم DAF، راندمان حذف COD و SS به ترتيب 24 و 43 درصد به دست آمد. در مقادير بار آلي 0.79اعمال شده به سيستم لجن فعال، راندمان حذف COD و BOD5 به ترتيب 59 و 68 درصد بوده است. در مجموع، راندمان حذف COD، BOD5 و TSS در كل سيستم پيش‌تصفيه به ترتيب 90،80 و88 بوده است. به‌علاوه، راندمان حذف اكريلونيتريل در سيستم 91 درصد بوده كه 26 درصد حذف در واحد بيولوژيكي رخ داده است. در ميان باكتري‌هاي جداسازي شده از لجن فعال، جنس‌هاي Alcaligenes، Pseudomonas، Bacillus و Moraxella به عنوان باكتري‌هاي نيتريفاير هتروترف شناسايي شده‌اند.

The treatment of wastewater generated from acrylonitrile butadiene styrene (ABS) resin manufacturing industry have a great importance due to its high chemical oxygen demand (COD) and some other toxic substances. Activated carbon adsorption, chemical oxidation and biodegradation are the most conventional methods to the treatment of ABS effluents. Among them, the biological treatment as an environmentally friendly technology is highly regarded in the bio treatment and biotransformation of the toxic compounds of ABS wastewater to the intermediate and final compounds such as CO2 and water. This study was conducted to evaluate the performance of an activated sludge system for pretreating ABS manufacturing effluents. The wastewater pretreatment plant is consisted of 3 fine screens, a grit chamber, an equalization basin, dissolved air floatation (DAF) system, an activated sludge reactor and a final clarifier. This system was operated to reduce the TSS and COD values in the effluent in order to obtain to interior discharge permits to the central wastewater treatment utility operated by Tabriz petrochemical complex. Four runs weighed average sling was conducted during 6 months according to the standard methods of the examination of water and wastewater. The parameters including COD, BOD5, TSS, TDS, sulfate, total kjeldahl nitrogen (TKN), ammoniaN, nitrateN, alkalinity, cyanide, phosphate and pH were measured in wastewater sles according to the standard methods. The concentrations of acrylonitrile, acrylamide and acrylic acid in wastewater sles were determined using gas chromatography (GC) equipped with flame ionization detector (FID) with capillary column. Microbial structure of activated sludge was also evaluated using R2A, PCA and Nutrient Agar culture media as well the biochemical standard tests. According to the results, at surface loading rate of 2.76 m3/m2.h applied to DAF, the COD and TSS removal efficiencies of 24 and 43% were obtained, respectively. The ratio of BOD5/COD in the influent was 0.57 indicated the moderate biodegradability of ABS wastewater. In addition, the COD and BOD5 removal efficiencies in biological reactor were 59 and 68% respectively, at the organic loading rates (OLR) of 0.79 ± 0.06 kgCOD/m3.d. Totally, the COD, BOD5 and TSS removal efficiencies in the pretreatment system were 80, 90 and 88%, respectively. In addition, at the acrylonitrile loading rates of 0.067 ± 0.008 kg ACN/ m3.d, the removal efficiency of acrylonitrile was 91% which 26% of that has occurred in the biological reactor. Also, the removal efficiency of cyanide was 97% which only 4% of that has occurred in the biological reactor. Twenty bacterial strains were isolated and identified from the activated sludge sles. Among the isolated bacterial strains, four strains include Alcaligenes sp. Pseudomonas sp. Bacillus sp. and Moraxella sp. were identified as heterotrophic nitrifiers. Based on the results, the nitrifier bacteria have played an important role in the degradation of acrylonitrile in the biological activated sludge system. The results of parameters analysis, performance evaluation and microbial assessment revealed the satisfactory performance of COD removal as well nitrification. However, it seems that a significant portion of the volatile organic compounds (VOCs) are removed from the influent wastewater by stripping.