Evsel atıksulardan biyolojik olarak besi maddesi giderimi

Abstract

Evsel atık s ulardan biyolojik olarak besi maddeleri Cazot ve fosfor) gideriminin incelendiği bu çalışma sekiz bölümden oluşmaktadır. Birinci bölümde, giriş, amaç ve kapsam bölümleri yeralmaktadı r. Giriş bölümünde, azot ve fosforun su kaynaklarına zararlı etkileri ve bunların giderilmesinin öneminden bahsedilmiştir. Amaç ve kapsam bölümünde hiyo- lojik olarak besi maddesi giderme esaslarından bahsedil miş, yapılan çalışma hakkında bilgi verilmiştir. İkinci bölümde, biyolojik olarak azot giderme metod- larından bahsedilmiştir. Nitrif ikasyon ve denitrif ikas- yon prosesi açıklanmış ve bu prosesleri etkileyen faktör ler incelenmiştir. Üçüncü bölümde, biyolojik olarak fosfor giderme metodları verilmiştir. Bu proseslerden A/0, phostrip ve Bardenpho proses tanıtılmış ve proses akım şemaları verilmişti r. Dördüncü bölümde, biyolojik olarak fosfor giderme me kanizması ve bu mekanizmayı etkileyen faktörler incelen miştir. Beşinci bölümde, azot ve fosforun birlikte giderildiği biyolojik arıtma sistemleri açıklanmıştır. Ohoredoks, A /O, UCT ve modifiye UCT proses tanıtılmış ve proses akım şemaları verilmiştir. Deneysel çalışmanın yeraldığı altıncı bölümde labora- tuvarda kurulmuş olan pilot sistem ve sistemin işletilme si anlatılmıştır. Analitik metodlardan, MLSS, MLVSS, nitrit, nitrat, TKN, Amonyak azotu, fosfor tayini standard methods <1987)'a göre anlatılmıştır. Yedinci bölümde, deneysel sonuçlar ve değerlendirme yapılmış, grafiklerle sistemin verimi verilmiştir. Bu grafiklere ve deney sonuçlarına bağlı olarak, anaerobik reaktöre asetik asit ve glikoz ilavesinin daha fazla fosfor açığa çıkmasına ve dolayısıyla fosfor giderme veriminin yüklenmesini sağladığı sonucuna varılmıştır. Sonuç ve önerilerin yeraldığı sekizinci bölümde, biyo lojik olarak azot ve fosfor giderme hakkında, bu çalışma ya bağlı olarak sonuçlar ve öneriler getirilmiştir.

Due to the effects of nitrogen and phosphorus compounds such as oxygen depletion, fish death eutrophication and hazards to public healt, it is important to remove them from the wastewaters. The source of nitrogen phosphorus in domestic wastes and synthetic detergents. The concentration of nitrogen and phosphorus in domestic wastewaters ranges from 20-85 mg/lt and 6-20 mg/lt depending on wastewater characteristics. Carbonecous matter is effectively removed in the conventional treatment plants, while the percent removal of nitrogen and phosphorus is notably low. So far many treatment technologies have been developed for nitrogen and phosphorus removal. These are mainly biological, physical and chemical methods. Chemical removal of phosphorus is achived by the addition of chemical such as iron salts, aluminum salts and lime. Chemical processes require large quantities of chemicals and generate large quatities of sludge containing lots of phosphorus. Processing and handling of such sludge requires high labor and maintenance costs. The physical process is very costly and is usually accomplished by ultrafiltration, reverse osmosis, and ion exchange-systems. Among these the biological treatment systems are the most economical. The biological nutrient removal systems are modifications of the activated sludge systems. While phosphorus removal systems consist of anaerobic and ae robic stages, nitrogen removal processes consist of an oxic and aerobic stages. In the systems in which nitro gen and phosphorus are removed together, consist of ana erobic, anoxic and aerobic stages. The biological phosphorus removal systems are A/0, Phostrip, Bardenpho. The phostrip process consist of biological and Chemical proceses. V 13. 1 The basis of the phosphorus removal mechanism is the release of phosphorus in the anaerobic stage and the uptake of phosphorus in the aerobic stage. In nitrogen removal, nitrification occurs in the aerobic stage. Nitrification is the biological oxidation of ammonia to nitrate with nitrite formation as an intermediate. The microorganisms involved are the autotrophic species Nitrosomonas and Nitrobacter. Denitrif ication is the conversion of nitrate nitrogen to more reduced forms such as Nz, N2O and NO. The process is brought about by a variety of facultative heterotrophs which can utilize nitrate instead of oxygen as the final electron acceptor. Denitrif ication occurs under the anoxic conditions. There are numeraus factors that have a significant performance of biological removal of nutrient removal systems. These are, temperature, PH, dissolved oxygen level, the solid retention time, sludge age, hydraulic retention time, organic loading etc. For nitrification processes, the recommended values of PH is the range of 7.5-8.5, temperature is the range of 5-30 C, dissolved oxygen concentration is above 2 mg/lt. For nitrification, the hydraulic retention time must be sufficient. This value is about 1 hour. Denitrif ication process depend on the absence of oxygen. The recommended value of PH is the range of 6.5-7.5. For phosphorus removal systems »anaerobic re retention time is very important. The purpose of the anaerobic stage is to provide fermentation products which will be utilized by poly-phosphate (poly-p) bacteria as carbon sources. Gerber and winter (1984) observed an increase in phosphate removal as the anaerobic retention time was increased. A longer anaerobic retention time than the customary 0.5 to 3h was recommended by their study to archieve high phosphorus removal efficiency. 1 >.: Maximum phosphate release is observed at pH 4 and maximum phophate uptake at pH 8 by Portgieter and Evans (1983). Influent COD and BOD effects on biological treatment systems have been studied by many scientists. Fukase et al (1985) suggested thet BOD loading rate and BOD to MLSS ratio have a significant effect on phoshorus release in the anaerobic unit and must be maintained below 2. 9 kg - BOD/kg-MLSS and 0.1 kg BOD/kg-MLSS, to achieve sufficient P-removal. The combined nitrogen and phosphorus removal systems are A2/0, phoredox processes, UCT and modified UCT process. In this study, the UCT process is used to investigate the performance of biological nutrient removal systems. Recently, bilogical systems the removal of nitrogen and phosphorus together have been developed. These are the modification of phosphorus removal systeems. To carry out the research investigation, a pilot system was conconstructed. The pilot plant system consisted of four identical reactors and a clarifier. Each reactor constructed of 4.5 mm plexiglass sheet, and each reactor was 13 cm diameter 30 cm high. The volume of each reactor was 2.5 liter and clarifier was 3.5 liter. Two pumps (ISMATEC Marks) were used to operate the system. The pilot plant was operated as a UCT process. All reactors were operated in series. The first reactor was operated anaerobically, the second reactor was operated as an anoxic reactor and the last two reactors were operated aerobically. There were three recycle lines within the pilot plant, sludge recycle from the underflow of clarifier to the anoxic unit, mixed liquor and nitrate recycle from the last aerobic reactor to the anoxic reeactor and the anoxic recyle from the anoxic unit to the anaerobic unit. The designed flow rate of the pilot plant system was 15 ml/min. The hydraulic retention times in the anaerobic, anoxic and aerobic zones were 1.4, 0.9, 1.0, 0.9 hours, respectively. The syntetic domestic wastewater was used as the feed to the pilot plant system. Glucose, urea and K2H2PO4 were used to prepare the wastewater. The wastewater was a typical medium strength domestic wastewater. COD concentration was 500 mg/lt, nitrogen concentration was 50n mg/lt, phosphorus concentration was 10 mg/lt. The average TKN/COD ratio was 0.1 and the average. P/COD 0.03. Maintaining anaerobic conditions in the anaerobic zone of excess biological phosphorus removal systems has been stressed by many investigators as an important factor for the success of this systems, efforts were directed towards reducing the dissolved oxygen concentration in the wastewater before treatment. Nitrogen gas was used to strip out dissolved oxygen and reduce it to the required level. The nitrogen gas bubbled through the wastewater for about one hours, until the dissolved oxygen level was less than 0.20 mg/1. The pilot plant system was operated as UCT process. In order to improve the phosphorus removal, acetic acid and glucose was added to the anaerobic reactor. It is then, that performance of the system was observed.