Arıtma çamuru yoğunlaştırıcılarının boyutlandırılması üzerine bir araştırma

Abstract

- I- ÖZET Bu çalışmada, su ve kullanılmış su arıtma tesisler ip.- de meydana gelen çamurların yoğunlaştırılması için yapılan yoğunlaştırıcı alanının belirlenmesinde -gerekli parametrelerin hesap, yolu- ile elde edilmesi : için, yolları araştırılmıştır, Birinci bölümde, incelenecek problem açıklanarak amaç ve kapsam belirtilmiştir. -İkinci bölümde, yoğunlaşma olayı ile ilgili olarak bugüne kadar yapılan çalışmalar değerlendirilmiş ve arakesiti! çökelme hızına ait ampirik bağıntılar ile sürekli yoğunlaştırma için teorik ve deneysel çalışmaların kısa bir özeti verilmiştir. ' Üçüncü bölümde, yoğunlaştırmada arakesitli çökelme hızı için bir model belirlenmiş, kritik katı madde akısı (qc) ve kritik konsantrasyon (Cc) ile yoğunlaşmış çamura ait (Cu) katı madde konsantrasyonu değerlerinin, alt akım hizı (U) ya bağlı olarak heşaplanabilmesi için teorik metodlar geliştirilmiştir. Dördüncü bölümde, deneysel çalışmalarla arakesitli çökelmeye etki eden faktörler incelenmiş ve silindir çökelme deneyi sonuçları kullanılarak, üçüncü bölümde belirlenen arakesitli çökelme modeline ait k1 ve k2 katsayıları regrasyon analizi sonucu tesbit edilmiş ye seçilen çamurun çökelme özelliğini belirleyen bir bağıntı geliştirilmiştir. Ayrıca yoğunlaştırıcı alanının hesaplanabilmesi için gerekli kritik katı madde akısı bağıntısı (q ) ve kritik konsantrasyon CCC) ile sürekli yoğunlaştırıcı alt akımına ait katı madde konsantrasyonu Cu değerlerinin, alt akım hızı (U) ya bağlı olarak, hesaplanabilmesi için, elde edilen arakesitli çökelme bağıntısı kullanılarak. ve üçüncü bölümde geliştirilen teorik metodlar yardımı ile matematik bağıntılar elde edilmiştir.- II - Sürekli yoğunlaştırma deneyleri ile kararlı akım şartları gözlenmiş ve çamurun yoğunlaşma verimi araştırılmış, deney sonuçları kullanılarak yoğunlaştırma verimi ile ilgili bir bağıntı elde edilmiştir. Beşinci bölümde İse bu çalışmada elde edilen sonuçlar özet halinde verilmiştir.

- III - SUMMARY In this study, new computational methods have been explored to assess necessary parameters defining thicknening areas required for dewatering sludges from water and waste water treatment plants. /. ',.. In the first section, the importance of the problem to be investigated has. been outlined and scope, with structu ral content, of the study has been summarized, s The second section has been mainly devoted to the critical evaluation of related,work up to date. First, deter mination of settling velocities for concentrated sludge, by batch settling column tests, have been reviewed with further emphasis on the. design methodologies of continuous thicke ners using the same experimental testing. Empirical relations defining blanket clarification have been listed. A short outline of theoretical and experimental efforts on continuous thickening has been given. ' ; - In the third section, an attempt has been made to deve lop a new method to yield critical solids flux, critical solid concentration and underflow solids 'concentration in continuous thickeners, in the light of pertinent error limits., approaches in previous studies, this has led to the following expression v =s C-k2 describing «blanket clarification and compaction region* The coefficients kx and k2 in this expression change. in accordance-IV - with the sludge properties. This models also. confirms the general statement of `settling velocity is a function of solids concentration` first proposed by Kjmch. The discriminant of the second order equation deve loped by means of the sludge settling velocity and by the, solids flux as a function of the underflow f xom a continuous thickener may be equated to zero to yield the horizontal tangent passing by the minimum- point of the solids flux ' curve. The same equation also gives critical solids flux. `qc`as a function of the underflow velocity `Ulr from a continuous thickener* > Using the same model again, the following expression may be obtained by taking the derivation of the solids flux with respect to concentration. ' d(v+v_+U)C = 0 dC This expression determines the critical solids flux `Cc` as. a function of the underflow velocity `tJ`. Further more, a theoretical model has been developed to1 obtain the concentration Cu of the thickened sludge., In the fourth section, the effect of pH, sludge deten tion time and sludge height in the settling column on the settling velocity have been investigated by using syntheti^- caliy prepared calcium hydroxide sludge. For this purpose experiments have been carried out for 7 different concentra tion and 7 different heights. Figures exhibiting interface- height-time^ settling velocity-concentration, and solids;, flux-concentration relationships have been prepared on the basis of experimental results* > :~ These results have indicated that sludge detention time and pH variation have rio appreciable effect on the sludge settling velocity. But the sludge height in the settling column has been observed to exert some influence Lk_<~_ ' ^J,^-_-L-^- V - on the settling phenomenon. This influence has been inter preted in the following expression which includes sludge height as effecting the settling velocity. 0.06 v ? C-3.18+0.7 H Values of coefficients kx and k£ have been obtained from experimental results by regression analysis. It should be noted that, kx in this expression remains constant but k2 = 3.18 + 0.7 H becomes a variable as a function of sludge height in the settling column. For a height of 2.0 m, which iş the upper limit in the experiments and at the same time more generally applied dimension in real thickeners, the above expression becomes. 0.06 v - C-1.78 The critical solids flux hâs been evaluated as, qc= 1.78 Ü +0.06 +/0.427 U` by incorporating the above settling velocity into q = (v+ vr+ U)C and equating its discriminant to zero. In continuous thickening, qu = qc may be written at the point where the lines representing, solids flux from the underflow of a continuous. thickener qu = U>CU and the horizontal tangent passing by the minimum of the solids flux curve. This equality combined with the experimental- VI - results, yields the following expression for Cu 0.06 Cu = 1.78 + `^ + /0T427/U The solids concentration in the thickened sludge may be computed using the above expression. On the other hand, the critical concentration becomes, Cc-= 1.78 + /0.107/U' by differentiating total solids flux with respect to con centration. Normally graphical methods are used to determine the parameters necessary for the design of thickeners. In this study mathematical methods have been suggested instead of graphical ones for the same purpose. Results from the developed mathematical expressions have been compared with, known values from graphical computations from, the literature and have been observed to correspond within the %10 con fidence limit. In the same section, the effect of concentration on the thickening yelocity has been investigated in con tinuous thickening experiments conducted for 6 different inlet concentrations. In these experiments the main purpose, hats been to obtain blanket formation at steady flow condi tions. In all experiments, blanket has been formed above the inlet structure. Concentration values for the upper and underflow have been obtained for different levels of sludge blanket. A relationship has been derived for thickening efficiency from experimental results. Theoretical and experimentally- VII - observed values for the underflow concentration values did not agree mainly because of the large difference of thicke ning areas between laboratory scale and real units. The- last section summarizes the principal findings of this study.