Evsel atıksularda biyolojik arıtma sonrasında kimyasal fosfor giderimi
Chemical phosphorus removal in domestic wastewaters after biological treatment
- Tez No: 46263
- Danışmanlar: DOÇ.DR. FATOŞ GERMİRLİ
- Tez Türü: Yüksek Lisans
- Konular: Çevre Mühendisliği, Environmental Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1995
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 52
Özet
ÖZET Bu çalışmada, alıcı ortamlar için oldukça önemli olan fosfor parametresinin; evsel atıksulardan karbon giderimini sağlayan biyolojik arıtma sonrasında kimyasal olarak arıtılmasını içeren bir deneysel araştırma yapılmıştır. Birinci bölümde, yapılan çalışmanın önemi vurgulanarak, amaç ve kapsamı açıklanmıştır. İkinci bölümde ise, evsel atıksuların genel özellikleri ve arıtılması ile ilgili bilgilere yer verilmiştir. İstanbul için Tuzla ve Büyükçekmece de yapılması planlanan tesisle ilgili bilgiler de bu bölümde verilmiştir. Bu tesiste biyolojik arıtma olarak aktif çamur tesisi tasarlandığı için diğer biyolojik arıtma yöntemlerinden sadece aktif çamur prosesi üzerinde durulmuştur. Üçüncü bölümde, fosforla ilgili bilgiler verilerek, fosfor arıtma yöntemleri açıklanmıştır. Biyolojik fosfor giderme yöntemi genel olarak incelenmiştir. Kimyasal fosfor giderme yönteminde, kireç kullanımı, demir ve alüminyum kullanımı halanda açıklamalara yer verilmiştir. Dördüncü bölümde, Kadıköy Evsel Atıksu Pompa İstasyonu'ndan elde edilen atıksular ile yapılan deneysel çalışmanın yaklaşımı, düzeneği ve elde edilen deneysel sonuçlar verilmiştir. Beşinci bölümde ise deney sonuçlarının bir değerlendirmesi yapılmıştır. Bu değerlendirme sonucu, kimyasal madde ilavesiyle fosfor gideriminde, çok yüksek giderme verimlerine ulaşıldığı görülmüştür.
Özet (Çeviri)
SUMMARY CHEMICAL PHOSPHORUS REMOVAL IN DOMESTIC WASTEWATERS AFTER BIOLOGICAL TREATMENT Phosphorus can be found different forms in wastewaters. Chemical classification of phosphorus covers, condansed phosphate ortophosphate, and organic phosphorus. Two organic matter removing treatment plants are planned to be constructed in Tuzla and Büyükçekmece for treating the domestic wastewaters of Istanbul city. These plants are designed to contain primary and biological treatment processes. Since the phosphorus loads of the wastewaters have a significance in terms of the quality of receiving waters that are going to be faced with the wastewaters, it is necessary to decrease the phosphorus content of the wastewaters prior to discharge into the receiving media. In this study the chemical phosphorus removal after biological treatment is investigated by the use of an experimental work. The stages of treatment can be classified into primary treatment, secondary treatment and advanced treatment. Primary treatment involves physical treatment methods while secondary treatment deals with the removal of organic matter by the aid of biological and chemical processes. The advanced treatment may be used after the secondary treatment and the aim of it is to reduce the nutrients. Activated sludge systems, as out of the most spread biological treatment processes, depends on the principle of the degradation of organic matter content of wastewater under aerobic conditions by biochemical processes. Substrate and biomass are the two basic parameters of the activated sludge. While organic matter is removed within the system, microbiological growth takes place. Growth rate is expressed as r_ - v.X Completely mixed continuous activated sludge systems can be operated with recycle or without recycle. At steady state from the mass balance equations it is possible to formulate the substrate and microorganism concentrations as follows Va(S0-S) Ke(l*Qkd) Q(Yk-ka)-l IXSludge age (0 ) and F/M ratio are important operating parameters of activated sludge system. ec F/M Efficiency can be expressed as E E - V.X Q.X S0 s0-s S0 Phosphorus removal from wastewater can be achieved either through chemical removal, advanced biological treatment or combination of both. The chemical removal of phosphorus involves the addition of calcium, iron and aluminium salts to achieve phosphorus precipitation by various mechanisms which are discussed. In addition; the effects of operation conditions, especially wastewater characteristics; sludge production in terms of quality and quantity; optimisation of chemical use; points of chemical addition combined with biological treatment; alternative chemical/physical treatments and examples of full-scale applications are also reviewed. Biological phosphorus removal is dependent upon the uptake of phosphorus in exces of normal bacterial metabolic requirements and is proposed as an alternative to chemical treatment. Presently, since there is not even a complete biological carbon removal treatment plant in Turkey, the application of phosphorus removal must be handled very carefully. In chemical phosphorus removal, according to the place of the chemical matter addition in the biological treatment a classification can be done as pre-precipitation, simultaneous precipitation, and post-precipitation. In the context of this study some treatment plants using chemical phosphorus removal located in US are evaluated and domestic wastewater sample obtained from Istanbul, after passing through biological treatment subjected to chemical phosporus removal. The most commonly used phosphate precipitant - chemical matter have been lime and the salts of aluminium and iron. In this study used lime and FeSCK. Phosphorus removal with the addition of lime lies in the fact that Ca and OH“ ions are given to the media and as a result hidroxyapatite, and other calcium phosphates will precipitate. The pH must be adjusted to 10.5 or over in order to reach a low phosphate residue. However under high pH values the bicarbonate alkalinity of the wastewater will react with the lime to give CaCOg precipitate. The bicarbonate alkalinity of the wastewater will react with the lime as follows.Ca(OH)2 + HCO, - CaC03(s) + H20 Therefore, lime dosage must be determined by the total alkalinity of the wastewater concerned. Pre and post precipitation processes can be applied when lime is used as a chemical matter. pH must be adjusted prior to biological treatment when pre precipitation processes are going to be applied. While with post precipitation, pH must be also arranged to have a pH of 6-9 at the effluent. Fe and Al salts can also be used as chemical matter. The results will be the formation of ferrous phosphate and aluminium phosphate both having very low solubilities. These will precipitate and the phosphate is removed. In order to get low ortophosphate residue, high Fe dosages are required. Two predominant regions can be identified: ”stochiometric“ region at relatively high effluent phosphorus concentrations and an ”equilibrium" region at low effluent phosphorus concentrations, with a slight transition between the two regions. For the addition of either of the metal ions Al(III) or Fe(III), the two possible precipitates are a ferric or aluminium phosphate and a ferric or aluminium hydroxide. For a given metal, the formation of these precipitates is dictated by the equilibrium constants governing their solubilitres and by the initial pH, alkalinity, and soluble ortophosphate concentration of the sewage. The most important equation is the one that describes the formation of the metal phosphate precipitate. The actual composition of these precipitates is not known, but most experimental work suggests that it deviates from the simple forms FePO^s) and AlPO^s). An empirical formula for the precipitate of the type Me (HLPO^XOH)^ i is accepted. The precipitation can be described as: MejizP0A(0H)3r_i(s) - z Me3* + Hz POl + (3r-i)Oir This formula does not incorporate cations other than Fe or Al (such as Ca or Fe ) although they may play some role in the precipitation process. According to Jenkins and Hermanowicz is experimental work values of r were 0.8 for Al(m) and between 1 and 2 for Fe(JJI). Precipitation of a metal hydroxide, MeOOH(s), is also included in the model: Me3+ + 2 HzO - am-MeOOH(s) + 3H+ 1+ together with hydrolysis of the metal ion (Me ) and formation of its hydroxy complexes: XIMe3* + H20 - MeOH2* + H* Me2* + 2Kp - Me(OH} 2 + 2ff+ Me3* + 3Jf20 - Me{om% (ag) + 3fT Afe3+ + 4^0 ?= Afe(0fl)i + 4#+ Additional equations constituting the model represent discossiation of phosphoric acid: £f3po4 = h* + h2po; R^POl - H* + HPOt HPOt = H * + P0|~ 2- and the formation of soluble complex of the metal ions with HPCh and H^POa Me3* + HPOt - MeHPOl Me** + H2P0Î - MeH^POl* In the second chapter, typical data on the individual pollutants found in domestic wastewater are reported and depending on the concentrations of these pollutants, wastewater is classified as strong, medium or weak. The characterization of the raw wastewater is made on 6 samples taken from the Kadıköy Pump Station. It can be seen from the characterization made on these 6 samples that concentrations of the parameters vary. The experimental approaches of the study are described. The equipment required to define the suitable operating conditions for coagulation and jar tests are explained. For the biological reactor values were volume 4 1, F/M ratio:0.4 and 6 sludge age 3 day. In the jar test experiments, chemical matter solutions were added to the six beakers and mixed rapidly at 100 rpm for one minute. Then it was flocculated at 20-25 rpm for 20 minutes and after flocculation, paddles were removed and it was allowed to settle for 1.5 hours. Experimental results are given in the fourth chapter, and evaluated in the fifth chapter. In experiments, in which two chemical matter were used both the favourable dosage of chemicals and favourable pH were investigate. Firstly, lime was used as chemical matter. To determine the suitable pH for lime, 200 mg/1 lime were added into the biological reactor effluent and pH was adjusted to 7,8,9,10,11,12. Only TP were measured in the supernatant. Effluent concentrations and removal efficiencies in relation to pH were illustrated and suitable pH was found as 10 for lime. xnDifferent lime concentrations were examined in the pH 10 value to determine favourable lime dosage. Effluent concentrations of TP and removal efficiencies of TP are illustrated in relation to the lime dosage for pH 10 value. As a result of these experiments it was observed that the favourable lime dosage range varies between 250- 300 mg/1. In the second experiment, FeSO, was used as chemical matter as 150 mg/1 FeSO, was added into the biological effluent to be treated in the jar test beakers and pH was adjusted, from pH 6 to pH 11. After the jar test experiment, TP parameter measured in the supernatant and the effluent concentration and removal efficiencies were plotted in the relation to pH, plotted graph show that the favourable pH can be accepted as 11. After determining favourable pH for FeSO^, the effect of dosage on FeS04 usage was examined. pH adjusted to 11 and TP measured in the supernatant. Suitable dosage was obtain as 100 mg/1. As a result of evaluation of the experimental data, it is understood that the this type treatment is sufficient phosphorus removal. xin
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