Why it’s so important to remove the SSD

 TSS (Total Suspended Solids) removal is probably considered as the first important treatment to be done in a system. Turbidity is the most visible criteria on water parameter and particles are the primary responsible for it. Consequently, the simplest system will consist on particles removal at the first place.

在循环水系统中，总悬浮颗粒物（TSS）的去除往往被当做水处理单元的第一个重要环节。浊度是最容易直接观察出来的水质参数，而颗粒物也是引起浊度变化的最主要原因。所以，即使最简单的系统也会把颗粒物的去除放在首位。

How to quantify TSS? from this result depends a lot the criteria to build the particles removal system.

颗粒物的含量是设计循环水系统规格的重要参数，那么如何定量颗粒物呢？

Let’s consider a bit of physiology of fish.

我们从鱼的生理机能来分析一下。

BonAqua:

The range of uneaten feed could reach 2 to 5% easily

没有被吃掉的饲料占比可以很容易到达2%到5%

Where do solid particles come from?

固体颗粒物从哪里来?

 As shown from the graph, they come mainly from 2 sources:

通过上面图例的分析，我们可以知道，颗粒物主要来自两方面：

○Uneaten feed 没有被吃掉的饲料

○ Unassimilated nutrition 没有消化的饲料（排泄物）

Uneaten feed is generally totally link to the feed management. As price of feed is increasing and price of fish tends to decrease, farmer show more and more concern about feed management. It is rather difficult to know what could be the level of feed waste but in all cases, it is not negligible and will negatively impact the FCR. In RAS system where usually, the water is clear and the management stricter it might be that uneaten feed has the least impact of all systems of production.

没有被吃掉的饲料通常与投喂管理相关联。由于目前饲料的价格持续上涨，同时鱼价下跌。养殖户越来越关注如何制定比较合理的投喂方案。想比较准确的知道浪费的饲料量是有些困难的，但是这会影响饲料转化率的计算，不容忽视。因此循环水系统在这方面有很大优势，清澈的水体加上严格的管理可以使过量投喂的饲料对系统和生产的影响降到最低.

However uneaten might have another reason: the “bad taste” of it that make the fish reluctant to eat it. Feed composition is usually tested in trials in research centre to reach the best quality possible but not all companies have such a program. Then It might not be too surprising that fish may not like all feed.

除此之外，饲料没有被完全吃掉可能还有另一种原因：就是饲料的口感不好，鱼不喜欢吃。一般饲料厂都会在测试中心对饲料的成分进行测试和试验以保证饲料的品质，但是并不是所有的饲料供应商都具备这样的测试流程。所以出现不合鱼胃口的饲料也并不稀奇。

Undigested feed is linked to the quality of the raw material and all ingredient included in feed. Usually, it is common to talk about protein digestibility or fat digestibility as they determine fish growth and contribute to most of the price of the feed. but also, all other ingredients contribute to produce solid waste.

没有被消化的饲料取决于饲料的组成成分和质量。我们经常会讨论饲料中可吸收蛋白和可吸收脂肪的含量，因为这些是保证鱼类生长的决定因素，同时也是饲料的主要成本。但是，饲料中其他的组成部分也会产生固体废物。

BonAqua

Digestibility is in a range of 90 +/- 5%

饲料的消化率通常在90%±5%左右。

In the worst case the solid waste could reach 20%!

但是在一些比较糟糕的情况下，固体废物可以达到20%

Why TSS removal is important?

为什么去除固体颗粒物如此重要？

In a system of 500m3 with a density of 40kg/m3, the standing biomass is 20 tons of fish. The feeding rate could be between 0.6 to 2% according the size and species. If we just take 1 % as an example the feeding load could be 200kg/day. the amount of TSS produced could reach 40kg in the worst case meaning 80g of TSS /m3! Or 80mg/l ! which is incredibly high for a RAS system.

在一个500立方，养殖密度为每立方40公斤的系统中，标准的总生物量为20吨鱼。饵料比根据鱼的尺寸和种类，在0.6%到2%之间。我们如果取1%作为参考值，那么每天的饲料投喂量为200公斤。那么在最坏的情况下，总悬浮颗粒物可以达到40公斤，也就是说每立方80g！80mg/l的总悬浮颗粒物对于循环水系统来说，是相当高了。

In RAS, the level of TSS is usually between 10 and 30mg/l of TSS. By comparison, the worst level of TSS might be found in biofloc system where it is recommended not to overpass 500mg/l and where the turbidity may not allow to see more than few centimetres into the water column.

在循环水系统中，总悬浮颗粒物一般在10到30mg/l之间。与之相比较，生物絮团系统中的悬浮颗粒物总量通常不会超过500mg/l，在这种浊度下，水体的可见度可能不会超过几厘米。

This is the production of one day evenly spread over the day. if nothing is done to remove TSS, it may take only few days to reach a level of TSS unbearable for aquatic life. Turbidity linked to particles would mainly affect fish health by clogging and damaging gills and creating a stressful situation, being a major “un-seen” issue in fish farming

上面的计算仅仅是参考了一天的投喂量。如果没有任何处理悬浮颗粒物的措施，悬浮物总量可能会在几天内就达到鱼类没有变法承受的程度。引起浊度升高的颗粒物会阻塞甚至损坏鱼的鳃部，同时也会引发胁迫状态，增大安全隐患，是渔场最主要的“隐性”风险。

This is the main reason why TSS should be removed in an efficient and constant way. There are also two indirect reasons why TSS must be removed:

这是固体颗粒物需要有效并持续去除的最主要原因。但是还有两个间接原因，使颗粒物必须要去除掉：

Heterotrophic bacteria activity Vs nitrifying bacteria activity in the MBBR

生物床中异养菌与硝化细菌的竞争关系。

There is a clear correlation between particles surface area and bacterial activity

颗粒物表面积与细菌生长的正相关性。

Biofiltration is a bacterial process. Two main families of bacteria are involved in this process. But as other living organisms, bacteria compete for space and food. Due to their relative slow growth nitrifying bacteria take several days if not weeks to be able to develop and settle down in MBBR, whereas heterotrophic bacteria, which feed directly on organic matter (waste and particles) has a rapid growth and can settle down in a given space in few hours only !!! if there would not be an efficient particles filtration, MBBR would be overload by organic matter resulting in rapid thick biofilm growth that would negatively interfere with nitrifying bacteria settlement.  A malfunctioning MBBR would result in fluctuation and peaks of ammonia which is toxic for fish.

生物处理是一个细菌的生化处理过程。在这个过程中，有两大细菌族群参与其中。和其他生物一样，细菌会抢占生长空间和食物。硝化细菌的生长速度较慢，通常需要数天甚至数周的发育时间才能在生物床中开始附着，但是相对而言，异养菌的生长速度就要快的多。它可以直接吸收分解有机物（残饵和粪便），只需要几个小时就可以在特定的空间内附着。如果颗粒物的去除不够充分的话，生物床将充满有机物，这会在短时间内导致异养菌的生物膜形成，从而影响硝化细菌的附着和生长。一个培养失败的生物床可能导致氨氮的超标，以至于毒死鱼类。

The second reason is also link to disease through the bacteria load of one system. In RAS management, the tendency is to keep water as clear as possible and disinfect this water through a disinfection unit (most likely UV based device) keeping bacterial load quite low as it seems that low bacterial load means low risk of disease breakdown.

第二个原因也是涉及系统内细菌总数和疾病的关系。在循环水系统管理中，由于细菌总数过高会引发疾病爆发的风险，所以大部分工作是要保证水体尽可能的清洁，同时通过一些杀菌设备（比如紫外等相关技术）确保细菌总数在较低的范围内。

Suspended solids in water provide surface area that can be colonised by bacteria. The more particles the more surface area. By constantly producing particles, there is new space available for new bacteria to develop. Bacterial activity usually reflects intensity of RAS which is commonly measured by feed load kg feed / m3 of new makeup water. in other words, if you decrease exchange water, you increase intensification. Doing so bacterial activity in RAS will strongly increase providing a higher risk for “bad” bacteria to reach a critical level. Therefore, particles removal need to be more efficient in intensive RAS. This a far complex issue that cannot be described in few sentences. So far too little is known about interaction bacterial activity but new research shows clearly how strongly influenced are bacterial populations activity by equipment and management.

但是，水中的悬浮颗粒物为细菌提供了繁殖的表面面积。颗粒物越多，表面面积越大。随着颗粒物的持续产生，细菌可发展的空间也就越来越多。通常细菌的活动反应了循环水系统的集约程度，这个集约程度是指饲料投喂量和新水补充量的比率。换句话说，如果你减小换水量，就是增加了集约化。这样一来，循环水系统中的细菌会大规模生长，从而使“有害”细菌达到一个非常危险的量级。因此，集约化循环水系统中颗粒物的去除就必须特别有效。但是这个过程相当复杂，不是一两句话可以讲清楚的。其实目前所能了解的关于细菌间的相互作用的信息少之又少，不过最新的研究清楚的表明设备及管理对细菌数量的影响非常之大。

In most visited farms, RAS system are quite low technology or inappropriate technology resulting in an inefficient particles filtration. In those farms, the key management to overcome all encountered issues is to exchange water.  therefore, most of RAS in china are in a range of low to medium intensification. The range of exchange water might be between 3-5m3 water/kg feed up to 10 m3 of water/kg feed meaning several total daily exchanges of water in some case. We can therefore, wander if the term of RAS is appropriate.

在中国参观的大多数渔场中，循环水系统的技术水平较低，或者使用的处理方式不合理，这导致了颗粒物去除的不够充分。在这些渔场中，解决问题最主要的方式是通过换水。因此大部分中国的循环水系统是低集约或者中集约化的。一般换水量可以达到一公斤饲料换3-5立方水，最高甚至到10立方，这意味着系统的每天需要换好几次水，我们有理由质疑，这样的系统是否可以被称之为循环水了。

What is an efficient way 

of removing particles?

最有效的去除颗粒物的方式是什么?

Without entering technical details about equipment and devices, it is however important to understand the challenges in removing them.

在我们涉及具体的设备和装置之前，非常重要的一点是了解去除颗粒物是怎样一个挑战.

BonAqua:

95%of the counted particles in RAS are under 20ɥm!!!

循环水系统中超过95%的颗粒物是低于20微米的！！！

Meaning that most of the available commercial equipment may not be that efficient. As mentioned before, if the exchange water is important, then the system will reach an equilibrium. However big particles account for a much higher volume of organic matter and then it is still important to deal with them too. Other equipment may have a significant effect on smaller particles such as Protein skimmer in sea water but not very efficient in fresh water. in RAS at the end the value of particles will reach a stable level that will reflect the degree of technology of the system. The fact that most particles are very small and remain in system will affect bacterial activity as, at equal volume, smaller particles provide much more surface area than big particles contributing to high bacterial activity in the system. It is therefore important to consider water quality related to TSS when choosing to use RAS at a high level of intensification.

这说明市面上销售的绝大部分过滤设备在这种颗粒物面前并不是特别有效。我们之前提到过，通过换水可以使系统达到一个平衡，因为组成大颗粒物的大量有机物需要好好处理。有一些设备，比如蛋白分离器，在海水系统中处理小颗粒物会行之有效，但是在淡水系统中却不是很好用。所以在循环水系统中，最终系统的颗粒物含量往往可以体现了系统设计的技术水平。事实上，小颗粒物相对于大颗粒物来说，为细菌的滋生提供了更多的表面积。所以如果想使用高集约化的循环水系统，考虑悬浮颗粒物的去除就变得非常重要。

• [cf7ic]