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[폐수처리]전하적정을 이용한 응집제의 선정 및 투입량 측정
작성자 : 삼보과학   작성일 : 2011-04-06   조회수 : 4821
파일첨부 :
아래 자료는 Muetek사의 Mrs. Lydia Bley가 발표한 논문의 일부를 발췌한 것이다.
매립비용이 증가하고 방출되는 물의 품질에 대한 요구가 훨씬 엄격해짐에 따라 슬러지 탈수장의 운영자들은 고액분리기술의 효율을 향상시키기 위해 노력하고 있다. 기계적인 탈수공정을 적용하고 있다면, 응집제로 화학적 조절을 함으로써 슬러지 입자의 불안정화를 도와서 응집메카니즘을 아주 많이 향상시킬 수 있다. 응집공정을 최적화시킬 때 가장 중요한 것은 최적의 응집제 유형과 주입량을 결정하는 것이다. 일상적으로는 응집제는 보통 과투여된다. 그래서 재안정화 현상이 일어나 총경비는 추가되는 반면 슬러지의 질은 나빠진다.

적절한 고형분을 함유하는 최적으로 안정화된 슬러지를 얻기 위한 노력의 결과로, 이제 슬러지 처리장의 운영자는 응집제의 실제 전하와 슬러지의 표면전하를 측정할 수 있게 되었다. 여과율과 침전율 측정외에도, 전하 측정법은 특정 응집제의 특이적인 효과를 평가하는 데 유용한 수단이다. 이와 관련하여 보다 자세한 내용을 필요로 하시는 분은 아래 논문을 전화나 이메일로 당사에 신청하여 주시기 바랍니다.
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Charge Titration for Selection and Dosage of Flocculants
                                             By Lydia Bley, Muetek GmbH, Germany

<목차>
1. Background of Surface Charge Measurements
  Effects of surface charge on the stock system
  Neutralization of surface charges
  Surface charge reversal
2. Fundamentls of Charge Measurements
  Electrokinetic phenomena
  Charge titration using the streaming current
3. Characterization of Flocculants
4. Characterization of Sludges
5. Selection of Flocculant and Predetermination of Flocculant Requirement
6. Process Control and On-site Optimization of Flocculation
7. Conclusions and Outlook

In view of increasing land filling costs and ever tougher demands on the quality of effluents to be discharged, the operators of sludge dewatering plants find themselves compelled to enhance the efficiency of solid-liquid separation techniques. If mechanical dewatering processes are applied, chemical conditioning with flocculants will assist a destabilization of the sludge particles, which greatly improves the flocculation mechanisms. When it comes to optimizing the flocculation process it is of prime importance to select just the right flocculant type and dosage. In everyday practice, flocculants are usually overdosed, which results in added overhead costs whilst sludge qualities deteriorate owing to restabilization henomena.

Striving to obtain an optimally stabilized sludge of an appropriate solids content, operators of sludge treatment plants are now able to determine the surface charge level of a sludge as well as the active charge of a flocculant. Besides the measured filtration and sedimentation rates, this determination is a useful tool for assessing a particular flocculant and its specific effects.

1. Background of Surface Charge Measurements
In terms of their material components, treated sludges consist of organic and inorganic solutes and undissolved matter. Inorganic solutes in the form of metal ions etc. do not directly affect the colloid chemical balance and are therefore not included in charge measurements. Ions merely influence the development of the surface charges of colloids in that they may either have a stabilizing or a destabilizing effect. In their majority, natural solid particles (clay minerals or sand) and colloids (polysccharides, proteins, humic acids) dissolved in water exhibit negative surface charges at the phase interfaces. Accordingly, they are most effectively flocculated and destabilized by additions of cationic flocculants or metal cations.

Charges generally are set up by different mechani느. Most frequently, charges are caused by specific adsorption of ions at a surface or by ionization of functional groups. As a rule, dissociation products from an aqueous medium -which normally take the form of OH- or H+ ions - are adsorbed on the phase interface of a solid particle. The aqueous medium largely influences the adsorbent type, like surface charges of the particles cause their electric repulsion, which stabilizes the entire suspension.

Alternatively, charges may develop through ionization of functional groups on the phase interface. If acid-alkali reactions take place, the surface groups are either protonated or deprotonated, and the associated charges are produced accordingly. As the pH is shifted from the acid to the alkaline range, a colloid system tends to become more anionic in nature, since the carboxyl groups, e.g., are deprotonated in the process.

It may also happen that suspensions undergo a charge reversal from positive to negative. The point of zero charge, which is also called isoelectric point, is the pH level at which the charge is zero. This analytical parameter is typically used in colloid chemistry. On the other hand, quaternary ammonium compounds, such as ply-DADMAC, do not change their ctionic activity in spite of pH shifts.

- 중략 -

7. Conclusions and Outlook
Flocculant overdosage may become extremely critical in that they increase the COD load of the recycled water to an unnecessarily high level. Quite apart from the added flocculant costs involved, many suspensions undergo restabilization phenomena that are irreversible. During each phase separation process, the process performance - e.g. filtration results - are improved until the point of neutral charge is reached. In the case of excessive flocculant additions, the point of neutral charge has very likely been exceeded so that flocculation results deteriorate. This effect is likewise oberved with anionic and cationic flocculants.

Determining the charge quantity of a medium, the PCD02 Particle Charge Detector is a useful tool in effluent diagnosics. Four potential applications are illustrated in Fig 18(원본참조). The findings obtained help to identify the optimum flocculant types and dosages to meet specific user needs.

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이전글 [폐수처리] 슬러지 탈수 기술에 전하측정법의 적용
다음글 [기공측정] 다층구조 세라믹물질의 기공구조 측정
       

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