Review – Surface Area – high numbers alone do not make better quality water

July 19, 2013 Phil Overton

Review by Gareth Barber

Surface area- high numbers alone do not make better quality water

In my 10+ years In the aquatics industry designing and building things from single tank display systems to filtration systems for stores, hatcheries, breeding facilities, retail establishments, aquaculture systems, live seafood holding systems and oceanariums, I have seen literally hundreds of different sorts of medias applied in dozens of different ways.

The main thing with any media when it comes to efficiency and quality is surface area, and this doesn’t just mean the number on the box.  A term you won’t hear or see very often in “USABLE” surface area. And this is the most important factor when choosing and applying any media for biological filtration.  Weather you are using a fluidized bed filter, trickle filter, or submersed static filter, it is the amount of surface area that is able to be utilized on a consistent basis in a mature bio filter that is the number one concern.

Below is a comparison of the most popular and highest surface area medias on the market compared to CerMedia’s MarinePure, when I first compared these I wanted to put MarinePure to the test against the best and most widely used medias.  All numbers have been converted and expressed as square meters of surface area per liter of media

Bioballs – the highest surface area rating of bioballs available is 500m2 per cubic meter. This is equal to 0.5m2 per liter.
Sintered glass – Matrix (700m2 per litre) Siporax (270m2 per liter, represents the noodle category and would be the most efficient noodle on the market), Eheim Substrate Pro (450m2 per liter)

Out of all these medias, Matrix is the highest. And so this was used as the comparison.

MarinePure 1.5″ sphere (suitable for both nitrification and de-nitrification) 435m2 per litre

Surface area as a function of usable surface area

I outlined above that “usable” surface area in a “mature” biofilter is what is most important. In a matured biofilter system, biofilms in and on the media surface become thicker, mulm builds up between filter cleans on the outside of the media and in the media structure and as the media matures, more complex and diverse colonies of all manor of bacteria and microorganisms build up in the system and especially on the biological media surface’s.

Two very important things are needed for a biological filter to function for nitrification (removal of ammonia and nitrite)

  1. Oxygen
  2. water flow (for de-nitrification, in most cases oxygen is not needed and denitrifying bacteria will not usually grow in oxygen rich environments, but the de-nitrifying bacteria still need water flow to bring them the nitrate to feed on)

As these mulm and bacteria deposits build up, they clog the pores of the biological media, suffocating bacteria and reducing the usable surface area.  When this happens, a great deal of the surface area advertised (depending on how clean the water is prior to entering the biological media, and how frequently the filter is cleaned and the biological media flushed) is lost to, well, lets not sugar coat it, crud building up on, and in the media.

Essentially, in a mature biofilter, only the surface area on the outside of the media is really usable in most circumstances, unless the media has some way to stay clean, flush mulm and flush old inefficient layers of biofilm.

  • Bioballs, will very rarely clog, but only has aerobic biofilms colonizing its surface area as it has no internal pore structure to utilize for de-nitrification.
  • Sintered glass medias will not appear to clog (apart from visible mulm deposits) but as biofilms build up, the internal pore structure not only gets blocked, but as internal flow is reduced, any bacteria that may be residing in the internal structure of the media cannot get oxygen or water flow to bring the waste to it that it is designed to digest.
  • Marine pure also, like bioballs, very rarely clogs, because the holes in the pore structure are much larger (visible to the naked eye) the water can freely flow through the media, any waste that does pass into the media will usually pass straight through or be very easily flushed when the media is maintained as part of regular filter maintenance.

Just by simply looking at a piece of sintered glass type media, you can see that after 6 months of use, assuming 10% of the media surface area would still be usable (probably a realistic number to be using) at maximum, if we use Matrix as an example, that would be 70m2 per liter of usable surface area. and given that this is surface area on the outside of the media, very little of this would be allowing de-nitrification to occur.

Advantages of MarinePure over other medias
Anyone who has used a multitude of different filter medias in a wide range of application will know that bioballs will do the job of nitrification just fine, and these have ONLY 0.5m2 per litre of media at MAX!!!!!! so why use a higher surface area media?

Well for starters, a higher surface area media will assimilate more ammonia and nitrite per pass, meaning that overall water quality will be improved, and be achieved at a faster rate.

Secondly, depending on the design of the media, other heterotrophic bacteria, especially de-nitrifying bacteria, may be able to colonize the inner structure of the media to achieve de-nitrification, improving water quality.

Thirdly, and this will also depend on the design of the media, waste will be less likely to build up in a well designed media, reducing dead spots and mulm deposits, allowing better breakdown of waste and more efficient removal by other forms of filtration.

In short, as a general media, the functionality of the 1.5” MarinePure sphere functions as follows:

  • the outer 5-10mm, being exposed to highly oxygenated water, achieves the bulk of the nitrification (removal of ammonia and nitrite)
  • the remainder of the media is then free to be colonized by other bacteria, heterotrophic bacteria, most likely in the form of de-nitrifying bacteria. The water now passing through the inner structure of the sphere, laden with nitrate and relatively free of oxygen (as it has been used up by the nitrifier’s in the outer portions of the sphere) is then processed by the de-nitrifying bacteria.
  • because of the porous, open cell structure of MarinePure, not only is any mulm eventually pushed through the media reducing and effectively eliminating clogging, but old biofilms (that are thicker and less efficient at nutrient reduction) are flushed out of the media, resulting in a cleaner environment and more efficient nutrient removal.
  • because of the massive internal structure of the MarinePure media, the application of probiotic, waste assimilating bacteria is more effective, especially in bare bottom retail environments and breeding systems, as the bacteria can colonize the media as well as the system, without being aggressively flushed off like in a trickle filter using bioballs.
  • it holds water in in its internal structure when out of the water. for instance, if used in a trickle filter application, if flow was to stop, the media stays wet for a long time, keeping the bacteria alive.

I have actually done an experiment with a MarinePure ball I left sitting in the bottom of a sump, untouched for 6 months, i got it out, waited until it had stopped dripping water and blew the water out of it into a measuring cup. i got 15mls of water out of one MarinePure ball that was just sitting, locked up in the ball when exposed to the air, showing just how well this material holds water.

Interestingly enough, after 6 months of sitting in the bottom of a dirty sump, when I blew that water out of it, there wasn’t any waste in it, it was clear water.

In new blocks, if you put on end in water, you can physically see the water travel up the block, above the surface of the water, the surface tension of the inner pore structure actually pulls water into in.

Note: in medias with very fine inner pore structure that clog, this cannot occur, as it is blocked and does not allow the efficient flow of water carrying nitrate to find oxygen free zones that may contain de-nitrifying bacteria

To be conservative, if you were to say in a mature biofilter, the efficiency of marine pure was reduced by 50%, then the USABLE surface area would still be 217m2 per liter, just over 3 times that of even the most efficient and highest advertised sintered glass type media in a mature system (as i stated above).

In all honesty, seeing MarinePure operate for over 2 years in multiple different applications, i can say that close enough to 100% of the surface area is usable. As I said above, 50% reduction in efficiency, is being conservative, incredibly conservative, I would say realistically 10% reduction in efficiency at most.  Out of all of the media I have ever applied and used in all the filtration systems I have ever designed, MarinePure is by far the most versatile and high powered media I have used for trickle and submerged filter applications, to achieve both nitrification and de-nitrification.

Even if applying high power nitrifying filters like MBBR filters (moving bed bio-reactors, that are designed to house and promote a large variety of bacterial populations) i would still apply, in some way or another, a volume of MarinePure, simply for its de-nitrification capabilities.  The effectiveness and versatility of MarinePure as a submerged and trickle filter based media is, in my experience, unmatched so far in the Aquatic Industry. As a media for use in most application for simultaneous nitrification and de-nitrification, there really is no better media out there.

Its incredibly high USABLE surface area is reason enough alone to use it, coupled with the ability is has to stay relatively waste free, makes this media a long term investment that will provide years of reliable service.

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