过滤的原理及其必要性

j教你玩转过滤器（伊罕原文翻译）过滤的原理及其必要性

      译：Portial_Liu 校：reddish

      水族箱内有机物质的积累导致水质逐渐污染，这些有机物主要来来自于饲料残渣的腐烂和动植物的代谢物。随着时间推移这些垃圾的积累会妨

碍水族箱内生态系统发展，危及鱼类和植物的生长，过多的垃圾会致使它们中毒。“水的自净化”是现代普遍高密度饲养的水族箱无法企及的奢望。

过滤，则试图缓解这个问题。除了重要的生化降解外，过滤还必须有效的除去水草残叶、悬浮微粒和细小物质以获得清亮的水质。

      第一部分：过滤咋弄才好啊

      仅仅通过微细孔隙过滤（比如渗透过滤）这种物理的方式想要集中所有的污物是不大可能的。只有较大的悬浮物质如水草残叶或饲料残渣能通

过这种方式滤掉。如果要通过孔隙过滤去除水中的悬浮物质，那么过滤的孔径不能超过0.0005mm，而在这个孔径下，由于过滤阻力的存在孔隙几乎立

即就会被堵塞。要去除所有的悬浮物，孔隙大小的选择应该满足能够截留所有大小超过光波波长的微粒。这解释了为什么再厚的纤维滤材也无法消除

浑浊。

      那么水族箱的过滤器如何才能净化水质呢？孔径达到几毫米的滤材又如何能截留微小颗粒呢？物理过滤肯定无法做到！它是通过一种称之为电

－化学的机制实现的。在滤材表面的蛋白质微粒（大小0.001－0.00001mm）会改变电化学特性，从而丧失其溶解性而附着在滤材的表面。随着蛋白质

颗粒的积累，就在滤材表面形成了一层蛋白质膜。

      这层蛋白质膜具有很高的吸附能力，能吸附细小颗粒。这就解释了为什么刚刚投入使用的或者刚刚清洗过的过滤器的过滤效果会不理想，因为

滤材上没有足够的蛋白质附着，所以吸附能力在一段日子内暂无法有效形成。若试图以频繁清洗过滤器来对付浑浊往往适得其反，因为滤材上的黏性

蛋白膜被破坏了。频繁更换滤材同理也会引起浑浊。滤材的表面积越大，对微细颗粒的吸附能力越强。然而，过于粗糙的滤材结构是无法形成理想的

吸附层的。因此陶瓷环并不是非常理想的滤材，使用Eheim的Ehfisubstrat（滤材）则能够获得非常好的效果。

      第二部分：传说中的生化过程

      接下来，细菌就开始降解工作了。细菌以部分降解的蛋白质（氨基酸）作为食物，发挥降解作用，氧化过程中所产生的低能量代谢产物又可以

滋养其他细菌。水族箱的水中有机污物的主要成分就是不同种类的蛋白质降解物，这些有机物（矿物化）化合形成无机化合物。因此水中无机物逐步

累积（例如硝酸盐和磷酸盐），这类物质比起他们在生化过滤前形成的氨、亚硝酸盐来说在生理学上危害非常小，鱼类能忍受高浓度的这类物质。

      简单说来，上述的矿物化过程如下：蛋白质被分解成多肽，然后再分解成氨基酸，进一步分解成铵/氨（与pH值有关）和二氧化碳，铵或氨再

通过细菌的氧化，先变成亚硝酸盐，最终变成硝酸盐。这是一个非常难以置信的过程，不幸的是它有一个最大的缺点：细菌数量不够时便无法有效工

作。新缸建缸时，细菌随着器材和设备等一同被引入缸中，早期阶段菌群规模不够，于是它们便无法充分地完成上述过程。当环境条件适宜时，细菌

繁殖是非常迅速的，约每20－30分钟分裂增殖一次。然而，即使这样仍然需要最少3－4周的时间过滤器才能达到完全降解物质的阶段。在这段等待时

期内，水族箱是不能够饲养鱼类的，为什么？如前所述，氨基酸的分解需要两个阶段，铵/氨到亚硝酸盐再到硝酸盐，这个过程中两种起决定性作用

的细菌分别是亚硝化单胞菌和硝化菌。蛋白质降解初期，大量的铵/氨放出，亚硝化单胞菌逐渐开始将之转化为亚硝酸盐。大约需要20天亚硝化单胞

菌才能繁殖到实现及时有效的转化氨/铵为亚硝酸盐的阶段。而在这段时间里，由于没有足够的亚硝酸盐作为食物，硝化菌无法大量繁殖，只有当亚

硝基单胞菌能提供足够的亚硝酸盐后，硝化菌才能开始将亚硝酸盐转化成硝酸盐的过程。这个过程也需要大约20天。所以，菌群的繁殖速度决定了过

滤器的磨合周期大约在3－4周。使用以前用过的旧滤材能够缩短这个周期。然而，这只是蛋白质降解产物的一小部分，从化学的观点来说，蛋白质含

碳、氢、氮、硫、磷元素，降解的过程中这些成分转化成二氧化碳、水、硝酸盐、磷酸盐和硫酸盐。尽管鱼儿能够忍受水中高浓度的硝酸盐、磷酸盐

和硫酸盐，为了避免这些水族箱中这些最终产物的不断积累而过量，定期换水仍然是绝对必要的。

      第三部分：过滤器里的垃圾是啥？

      在所有的水族箱过滤器里都能找到褐色的淤泥，而这种淤泥状污物又是什么呢？是食物残渣？粪便残留物？蛋白质沉淀？或者是他们的混合物

？都不是，它是铁和锰！铁和锰是植物所需的重要养分，在水族箱中却很缺乏，所以必须一直循环利用。在添加铁肥料后的两三天里，尽管有再循环

利用的过程，水族箱中的铁含量还是会表现出一定量的减少，对于锰的含量也有类似的现象。那么这些铁和锰元素到哪里去了呢？答案就是过滤器里

淤积的褐色泥状物质了。为了证明这一点，将淤泥物质溶解在化学药剂中，并从中检验到了大量的铁锰元素。尽管现在已经采用鳌合（对铁锰添加一

个保护层）的铁锰肥料以避免氧化，然而铁合锰仍然会沉积在过滤器中，因为细菌非常迅速地破坏掉鳌合形成的保护层，铁锰又被氧化并以褐色淤泥

形式析出。

      附上原文吧，有兴趣的可以看看。有意见的可以提。

      Why is filtration necessary?

      Aquarium water ages because organic matter originating from decomposing

      food residues and metabolic products of creatures and plants accumulates.

      In the course of time the accumulation of this waste impedes the

      biological development of the aquarium, plant and fish growth deteriorate.

      If too much waste accumulates this may lead to toxic effects.

      "Self-purification of the water" is an expectation that modern aquariums

      with their dense population and the resulting feeding requirements

      definitely cannot fulfil. Filtration tries to delay this process. In

      addition to this important bio-chemical task the filter must also provide

      optically clear water by removing leaf fragments, floating particles and

      minute substances.

      An attempt at collecting all pollutants by purely mechanical means with a

      very fine-pored filter (somewhat like a percolator filter) has very

      limited prospects of success.

      Only relatively large floating particles such as leaf fragments or food

      flakes can be removed. If the water were to be cleared of floating

      particles by such a method, the pores of the filter would have to be no

      larger than a maximum of 0.0005 mm. Due to the filtration resistance such

      a filter would become clogged almost at once.

      For the retention of all floating particles the choice of pore size would

      have to allow the trapping of all particles larger than the wave-length of

      light. This explains why even extremely thick wadding filters cannot

      remove turbidity.

      So how can aquarium filters purify the water and retain minute particles

      although the pore width of the filter material is several millimetres? It

      definitely cannot by a mechanical, but by an electro-chemical function. On

      the surface of the filter medium protein particles (size 0.001 - 0.00001

      mm) change their electro-chemical properties. They lose their solubility

      and settle on the surface of the filter medium. Further protein particles

      follow, covering the filter medium with a protein layer.

      This protein coating is highly adhesive and retains even fine particles.

      This explains why the filtration performance of new or freshly cleaned

      filters is not satisfactory. The adhesion does not become effective until

      after a few days, when sufficient protein has settled. If attempts at

      combating turbidity by cleaning the filter are made too soon the adhesive

      coating is destroyed and the aquarium remains turbid. Frequent exchange of

      the filter media also results in turbidity. The larger the surface of the

      filter medium, the better the adhesion for fine particles. However, too

      coarse a structure of the filter medium impedes the desired adhesion,

      therefore clay pipes are not very suitable. Very good results are achieved

      with Ehfisubstrat. Then bacteria begin their work of degradation. Bacteria

      feed on the partially degraded proteins (amino acids), and after oxidation

      they release lower-energy metabolic products, which, in turn, serve as

      food for other bacteria.

      The main components of organic pollution in the aquarium water are various

      kinds of protein degradation products. This organic matter is mineralised

      into an-organic compounds. As a result, there is enrichment with

      an-organic matter (example: nitrate, phosphate), which is physiologically

      far less harmful than their previous stages (ammonia, nitrite). Fish can

      tolerate it in much higher concentration.

      A simplified description of this "mineralisation" is as follows: Protein

      is broken up into polypeptides, then further into amino acids. These are

      further separated into ammonium/ammonia (depending on pH value) and carbon

      dioxide. This is followed by bacterial oxidation by means of bacteria, via

      nitrite to the final product nitrate. This is an incredible process:

      unfortunately it has a great disadvantage: it cannot work properly without

      a sufficient amount of bacteria.

      When a new aquarium is set up, bacteria are introduced together with the

      material, equipment etc. Unfortunately they cannot fully perform the

      process described above because in the early stages their number is too

      low. In favourable environmental conditions bacteria propagate very

      quickly. Propagation by division may happen every 20 - 30 minutes.

      However, it will take at least 3 - 4 weeks until a filter can degrade all

      occurring substances, and the aquarium should not be stocked with fish

      before the end of this waiting period. What is the reason? As described

      above, amino acids are broken up in two stages, via ammonium / ammonia to

      nitrite and then to nitrate. Two decisive groups of bacteria, nitrosomonas

      and nitrobacters contribute to this process. When the protein degradation

      begins, large amounts of ammonium / ammonia are released which the

      bacteria group of nitrosomonas gradually convert intro nitrite. It takes

      about 20 days for the nitrosomonas to propagate sufficiently to convert

      ammonium/ammonia immediately. At this point the bacteria group of

      nitrobacters have no incentive for propagation because there is no nitrite

      for nutrition yet. Only when supplied with nitrite by the nitrosomona

      bacteria do the nitrobacters begin to propagate and to convert nitrite

      into nitrate. This process takes about 20 days. Therefore, the propagation

      speed of the bacteria groups of nitrosomonas and nitrobacters determine

      the "running-in time" of a filter of approx. 3 - 4 weeks. Introducing

      previously used filter medium can speed up this process. However, this is

      only a small, if important, sector in breaking up protein products. From a

      chemical point of view protein consists of carbon, hydrogen, nitrogen,

      sulphur and phosphorus. During degradation these individual components

      produce carbon dioxide, water, nitrate, sulphate and phosphate.

      To avoid a permanent increase of these final substances in the aquarium,

      the regular exchange of (parts of) the water is absolutely necessary.

      What does the dirt in the filter consist of? In all aquarium filters you

      find brown sludge. Is this a combination of food particles, residual

      faeces, or deposited protein? - No. Iron and manganese, two important

      plant nutrients, are scarce commodities in the aquarium; they have to be

      re-fertilised all the time. When the iron value is determined 2 - 3 days

      after the addition of fertiliser, this will show a decrease despite

      re-fertilisation, and the same applies to manganese. Where have the iron

      and the manganese gone? The answer lies in the brown sludge in the filter.

      For measuring purposes, the sludge must first be dissolved chemically, in

      the proof iron and manganese will be found again in profusion.

      Although chelate (a protective coating for iron and manganese) is nowadays

      added to the fertilizing substances in order to avoid oxidation, iron and

      manganese are deposited in the filter. The bacteria destroy this chelate

      coating comparatively fast, iron and manganese can again react with oxygen

      and are deposited as a brown "sludge".