anoxic filtration

8/8/2019 Anoxic Filtration

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2010 R E A D M E F I R S T BY: SYD MITCHELL

In this section of the book I

decided in the best interest of the

hobbyist, that reading what Syd

Mitchell has to say from the UK

about the Anoxic FiltrationSystem would be more

appropriate than myself.

Syd is a professional writer for

hobbyist magazines in the UK;

like Koi and Koi/Carp magazines.

He has been writing about the

Anoxic Filtration System for

sometime now and uses words and

examples that most hobbyistunderstand better than my

scientific vernacular. For example:

He will use the word bug, instead

of Microaerophile bacteria or

Aerotoerant bacterium to refer to

the types of bacteria use in this

system. A little easier to

understand if youre a newbie to

the hobby or one thats not too

familiar with microbiology.

So please take the timeout to

read what is being said in the UK;

it may help you get a better grasp

on the filtrations schematics-Ed.

Read me first!

ESCARBOUCLE WATER LILY PSTLINGBERGWATERLILY FROEBELI WATER LILY

ANOXIC FILTRATION SYSTEM
http://www.mankysanke.co.uk/html/anoxic_filtration.htmlhttp://www.mankysanke.co.uk/html/anoxic_filtration.htmlhttp://www.mankysanke.co.uk/html/anoxic_filtration.html


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Anoxic Filtration is it a bogfilter?Part 1

Take a planting basket, fill it withcat litter, then scoop out adepression from the centre andfill that depression with anaquarium plant fertiliser calledLaterite. Put a plant into thebasket if you wish, but it is notnecessary.

I f i t i s t h a t s i m p le a n di n e x p e n s i v e t o m a k e abiocenosis basket, why are moreKoi keepers not using the anoxicfiltration system? Possibly theanswer lies in the fact that it israre to find a Koi keeper whoactually understands what anoxicfiltration actually is, what it doesand how it works. The reason forthis lack of understanding shouldim m e d ia te l y b e o b v io u s .Already, I have used three wordsthat many Koi keepers will findnew and mysterious. What isLaterite? What is a biocenosis

basket? And isnt anoxic,something to do with anaerobicsludge where harmful bacteriacan live?

If it were possible to describe theanoxic system without usingsuch words I would do so, but,whilst it is easy to build thesystem, the way it works isextremely complicated. So let usbegin by expla in ing whatLaterite, biocenosis and anoxic

mean.

Laterite: - This is easy enough tounderstand. It is simply a claybased material that is rich in iron.It is used in tropical fish tanks asa plant fertiliser and can bebrou ght from trop ical f ishdealers.

Biocenosis: - This is a scientificterm for a place where differentbiological processes take place,each process being of mutual

benefit to the other processes.

Anoxic: -Anoxic does not meanthe same as anaerobic. In ananaerobic region there is acomplete absence of oxygen. Inan anoxic situation, there isoxygen present but it is at a verylow level. In a biocenosis basketthere is always a low level ofoxygen. Levels are typicallybetween 0.5 ppm (mg/L) and 2ppm. This is the key factor thatwill influence a situation whereanoxic filtration can occur. Thepresence of an extremely lowlevel of oxygen is crucial to thesystem as will be described later.In passing, it might be worthwhileto contrast the oxygen level in abiocenosis basket with theoxygen level in the pond itself.T h e a b s o l u t e m i n i m u macceptable oxygen level in a Koipond is 6 ppm, although 7 ppm is

more often recommended as asafer minimum to adopt and, inpract ice , i t shou ld be a tsaturation level (as high as isp o s s i b l e a t a n y g i v e ntemperature).

Wi t h the f i rs t few te rmsexplained, it should now bepossible to move on to a betterunderstanding of how the anoxicfilter system is quite unlike anyfilter system that is commonly in

use by pond keepers. There willbe more complicated terms asthe description unfolds, but eachwill be explained as we explorethe system. To contrast anoxicf i l trat ion with conventionalfiltration, it is first necessary tounderstand how biological filtersactually work

Conve nt iona l b io log ic a lfiltrationFish continuously excreteammonia which is toxic to fish,

and so it has to be removed from

the pond water before it can

cause them harm. We all know

this. Any well designedconventional biological filter

system will be effective at taking

this ammonia and converting it,

first into nitrite, and then into

nitrate by a process called thenitrogen cycle. This is also well

known. Having achieved the

conversion of ammonia into

nitrate, the task of a conventional

biological filter is complete. Nofurther biological action to

remove the nitrate takes place

and so the level of nitrate in the

water slowly rises. This is the

first disadvantage ofconventional bio-filter systems.

Nitrate is nowhere near as toxic

to Koi as either ammonia ornitrite but that doesnt mean thatthey are not affected by it. Hardscientific research on this subjectis difficult to come by, but, thereis plenty of anecdotal evidence toshow that Koi kept in low nitrateponds, show better growth andcolour development than thosekept in a pond where the nitratelevel has been allowed to rise.Easier to prove, is the effect thatnitrate has on algae of all types.

Nitrate is a plant fertiliser. A risinglevel will encourage blanketweed and the kind of algae thatturns water green. Waterchanges will help but, even aftera 10% water change, the nitratelevel will still be 90% of theoriginal value, and, as moreammonia is converted, the nitratelevel will soon begin rising again.

Anoxic Filtration System by: Syd Mitchell


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label could be applied to a conventional system

that has not been kept sufficiently clean!

The anoxic filtration system

Figure 1 shows a typical anoxic filtration pondwithout the plants. It is simply a shallow pond,around 24 inches deep, with water being pumpedinto one end and overflowing by gravity back intothe main pond at the other. This one contains 22biocenosis baskets. The small pebbles on top ofthe baskets prevent water flowing past them fromdisturbing the cat litter inside and causing it tofloat away. Figure 2 shows how the entire anoxicfiltration system can be hidden in plain sight.The anoxic pond looks like a water garden, not afilter, and yet everything except the pump in themain pond can be clearly seen. For those who donot like pump fed systems, the anoxic pond can begravity-fed from a bottom drain. Build the anoxicpond at the same level as a conventional gravityfed system and use a submersible pump orexternal dry mounted pump to pump water fromthe anoxic pond back into the main pond. Theonly limit to how this system can be built oradapted is your ingenuity!

There are few hard and fast rules as to how tomake biocenosis baskets. It is important that theplanting baskets used should have open lattice

type sides to allow ammonia to be drawn inthrough them, but apart from that, any basketaround 30 cm x 30 cm x 20 cm deep will do. Thecat litter should be a granular, unscented, Non-clumping type that should retain its granularstructure when wet. Laterite can be obtained fromtropical fish outlets or purchased on-line in 1.6 kgpackets for less than (GB) 25. Biocenosisbaskets need very little maintenance because thelife of the cat litter is indefinite and the Laterite iso n l y ve ry s lo w ly d e p le te d b y p la n t s .Photosynthesis is the process that plants use tomake energy from sunlight and a green pigment

called chlorophyll is essential for this process.Plants need iron to make chlorophyll, so if there isa plant in the biocenosis basket, the iron in theLaterite will become exhausted after about five toten years and you will have to add some moreLaterite or remake the basket.

Part 2 will describe how to build the anoxicfiltration system, and how ammonia can be drawninto a basket and destroyed without leaving nitrateto build up in the pond.

Figure 1:

Figure 2:

Anoxic filtration system by: Syd Mitchell

[Oil Dri can be used as a substitute if cat litter isnot available. Please check with manufacture fordetails on such. Also; always check all cat litter orOil Dri before using to validate whether or not it issafe for aquatic animals - Ed.]


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Anoxic Filtration part 2

Nitrifying bugs are everywhere

Nitrifying bugs, (nitrogen cyclebugs), are abundant in nature.They do not just grow and thrivein a biological filter. In fact, theywill grow everywhere in a pondenvironment. In a natural pond,lake or river, they grow on everyavailable surface. This includesthe pond bottom, rocks andplants. In an ornamental pondthey will also grow on allavailable surfaces, not just withinthe filter. The purpose of abiological filter is to make abacteria friendly environmentthat will concentrate the bulk ofthe population in one easy tomanage area where the mainnitrogen cycle will occur. Butthat does not mean that this isthe only place where ammonia isbeing nitrif ied (turned intonitrate). Ammonia is also beingnitrified throughout the wholepond. All that is necessary for

this to occur is a wet surface anda supply of ammonia, oxygenand carbonate. Taking all thebiological media out of thefiltration system, therefore, willnot stop the production of nitratealtogether, it will still be producedelsewhere. It may not beimmediately obvious but thereare also ample opportunities forthe nitrogen cycle to take placeactually within the biocenosisbaskets themselves.The baskets

are underwater and so, statingthe obvious, all surfaces of theclay particles are wet. The waterthat is just inside the basketswill also be rich in oxygen andcarbonate, so we have an idealplace for nitrifying bugs to set uphome and to convert ammonia tonitrate. If nitrate is actuallyproduced within a basket that isdesigned to eliminate nitrate,

does this mean that thesebaskets are a failure? Not in theleast, as will be described later.

There are two equations that Ilight-heartedly refer to as; whatnitrosomonas and nitrobacter eatfor lunch. They are included forthose that may be interested. Itis not necessary for thepurposes of this article to try tounderstand them, but they arehow a biochemist would makesense of the nitrogen cycle. Thedescr ip t ion fo l low ing theequations that explains whatthey mean has been simplifiedas far as is possible with all thenasty chemistry taken out. Youmay need to read it a couple oftimes to understand it, or if youprefer, you may safely skip theequations and the paragraphthat follows them.

What Nitrosomonas eat forlunch:-55NH4++76O2+109HCO 3-=C5 H7 O 2 N + 5 4 N O2 - + 5 7 H2 O+

104H2CO3

What Nitrobacter eat for lunch:4 0 0 N O 2 - + N H 4 ++ 4 H 2 C O 3 + H C O 3 -+195O2=C5H7O2N+3H2O+400NO3-

What the equations tell usYou can either count atoms andmolecules, or you can take myword for it, that these equationscould very, roughly be described

as saying:-One molecule ofammonia + four molecules ofoxygen + seven molecules ofc a r b o n a t e b e c o m e s o n emolecule of nitrate + a bit of bugtissue (that is what C5H7O2Nmeans in these equations, amolecule of bug). In otherwords, the bacteria can bethought of as eating ammonia,oxygen and carbonate and

g e t t i n g s l i g h t l y b i g g e r .(Eventually when they haveconsumed enough, each bug willdivide into two separate bugs,

but that is beyond the scope ofthis article). If we ignore thecarbonate and also ignore thefact that the bugs are gettingfatter in this process and we justconcern ourselves with whathappens to the ammonia, it getseven simpler. One ammonia +four oxygen eventually equalsone nitrate. Let us now apply thisto what is going on inside abiocenosis basket, and follow theammonia molecules as they aredrawn by the Laterite into thebaskets to their doom.

Figure 1. For clarity, zones A andB have not been drawn to scale.In practice these two zones areonly a few millimetres thickbefore all the oxygen has beenexhausted.

Zone ANegative charges in the Laterite

start to attract ammoniamolecules towards the centre of

the basket. As these molecules

pass through zone A, nitrifying

bacteria, (nitrogen cycle bugs),will grab one ammonia molecule

and four oxygen molecules; they

will then excrete one nitrate

molecule.


Figure 1: Cutaway of biocenosis basket


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The ammonia level in zone Awill have dropped a little, thenitrate level will have risen byroughly the same amount but the

oxygen will have droppedconsiderably, (four times asmuch). Although there is now farless oxygen, there will still beenough of it for the nitrogencycle to continue. We willcontinue to journey with theAmmonia molecules into zone B.

Zone BAs more and more ammonia isconver ted to n i t ra te , theammonia level drops even moreand the nitrate level rises. Somuch oxygen has been used inthe process that this area can nolonger be called truly aerobic,(oxygen rich), but there is still alittle oxygen left to sustain somenitrifying bacteria so we willfollow the remaining ammonia asit journeys into zone C.

Zone CThe biochemistry in this zone is

the stuff of nightmares andalmost defies simplification, but Iwill try. The ammonia is stillbeing pulled remorselesslytoward the Laterite but almost alloxygen in the water has alreadybeen used. The nitrogen cycle,a s w e k n o w i t , c e a s e s .Nitrification cannot occur ifdissolved oxygen levels arebelow 2 ppm, and it will be lowerthan that in zone C. In this zone,f a c u l t a t i v e a n a e r o b i c

heterotrophic bacteria live. Thefirst thing to understand aboutthis zone is; what on Earth is af a c u l t a t i v e a n a e r o b i cheterotrophic bug anyway?Roughly speaking, facultativeanaerobic, means that it has thefacil i ty (or abil i ty) to l iveanaerobically, (where there isvery little oxygen), provided itcan steal some. Heterotrophic

bacteria is simply a descriptionof their eating habits; they liketo eat organic molecules. So afacultative anaerobic heterotroph

is simply a bug that can livewhere there is very little oxygenand likes to eat organicmolecules. That wasnt so hardwas it?

Where it can steal its supply ofoxygen from is not hard tounderstand either. Rememberthe nitrate that was produced bythe nitrogen cycle bugs? Thechemical symbol for nitrate isNO3, (one atom of nitrogen,

joined to three atoms of oxygen).For a facultative anaerobicheterotroph, this is a feast. It caneasily take the three oxygenatoms and leave the nitrogen.Although it is convenient to referto bugs eating ammonia ornitrate and needing oxygen, inpractise, they do not have littlem o u th s , n o r i n d e e d , d othey have lungs. Ammonia,nitrate and oxygen are simply

absorbed directly through theircell walls, just as if we were ableto eat by placing food onto ours t o m a ch s o r b re a th e b yabsorbing oxygen through ourchests. When oxygen is takenfrom nitrate in this way, theatoms of oxygen enter the bugand the nitrogen is left behind.This nitrogen is still dissolved inthe pond water but it will bepleased to leave the waterbehind and go back into the

a t m o s p h e r e a t t h e f i r s topportunity. In this way, althoughthere are nitrogen cycle bugsliving in the biocenosis basketsand they will be busy puttingnitrate into the water, other bugsin that same basket are just asbusy disposing of it. The overalleffect of a basket is to totallyremove ammonia with no by-

product chemicals remaining inthe water.

Theres more

If that was all a biocenosisbasket achieved, it would bepretty marvellous, but there iseven more science going on.We havent even considered thefull extent of what the Laterite isdoing yet, other than to say thatelectrical charges attractammonia molecules toward thecentre of the basket. How doesit do this, and what happens tothe ammonia when it gets there?Molecules are not little magnets,but for a basic understanding ofhow molecules work, it isconvenient to imagine that theybehave just like little magnets.When we played with magnetsas children, we discovered thattwo similar magnetic poles repeleach other but opposite polesattract and will stick together.Molecules behave just like that,but the forces are electricalcharges, s imi lar to stat ic

electricity, not magnetism.

The charge on an ammoniamolecule (NH4+) is positive, andthe charges on the Laterite arenegative. Opposite chargesat t ract , and so ammoniamolecules will be pulled insidethrough zones A, B and C asdescribed above. So, theLaterite has been responsible forattracting ammonia from thepond water flowing past the

basket, right into its centre.Although some of the ammoniawill have been totally disposed ofalong the way, much will stillremain, and once it is there, itcannot escape. The wayAmmonia is taken up by plantsroots is a complex relationshipinvolving yet more molecularcharges and it is not necessaryto understand this mechanism in



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order to understand how biocenosis baskets work. It is sufficient to say that the Laterite attractsammonia right up to the plant roots and holds it there. When the plant is good and ready, (dependanton more biochemistry), its roots will simply absorb the ammonia and the plant will produce luxuriantgrowth. Yet more ammonia has been permanently removed from the pond ecology.

What happens in unplanted baskets? More bugs, Im afraid. For those biocenosis baskets that do notcontain plants, the facultative anaerobic bacteria that inhabit zone C will perform a second clever trick.Earlier, we discovered that these bacteria preferred to take oxygen directly from the pond water, butwhen there was little or no oxygen available, as in zone C, their first trick was to obtain some by takingthe atoms of oxygen from any nitrate that had been produced by the nitrifying bacteria, (nitrosomonasand nitrobacter). What happens when they have used up all that nitrate? They simply switch to directlymetabolizing ammonia to provide their energy needs! The expression clever as a sack of monkeysshould be changed to clever as a basket of bugs. Whether or not the biocenosis baskets containplants, the ammonia that is drawn into a basket has no escape. If plants dont get it, the bugs will.

Not every pond keeper wants to have a pond full of aquatic plants behind their Koi pond, or they maynot have the space to do so. The fact that the biocenosis baskets do not have to contain plants to mopup ammonia because a colony of bugs will soon develop and will take the opportunity of a freeammonia lunch, enables anoxic filtration to be sited indoors or disguised under decking.

Building the systemFortunately, building an anoxic pond is far easier than understanding how it works. In Kevin Novaksoriginal pump-fed design, (figure 2), water is pumped from the main pond into the anoxic pond. In orderto prevent the flow of water from disturbing the baskets, it enters through a simple diffuser. Figure 4shows Kevins suggested diffuser but any other design could be used if preferred. The water thenreturns back to the main pond by gravity. The anoxic pond should be about 24 inches (600 mm) deepand it can be any convenient shape that is large enough to allow approximately one basket per adultfish.

It is possible to modify the design to a gravity fed system for those who do not like pump fed systems orwho want to modify an existing gravity fed system (see figure 3). As in the pump fed system, the watershould be diffused as it enters the anoxic pond. One way to achieve this would be to extend the 4bottom drain pipe above water level and to drill around 100 x (6 mm) holes in it.


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Are there any drawbacks?There are no drawbacks but one point is worth careful consideration. Settlement will occur in theanoxic pond and it will eventually need to be emptied or flushed to waste just as any other settlementchamber. In order to keep the drawings as simple as possible, I have left out details of pre-filtration anda drain to make emptying easier. A sieve is a suitable pre-filter for the gravity system and a simple wayto close off the main pond when a gravity fed anoxic pond is being emptied would be to make theperforated section of pipe removable and have a suitable length of un-perforated 4 pipe that canreplace it whilst emptying.

And the advantages?Apart from the reduction in nitrate levels, and the fact that the system can be built so inexpensively, it isubiquitous. It will fit anywhere because it can be built to fit whatever space is available; the onlyconstraint is that there should be about one basket per full size fish. But even in this, there is flexibility.If ever you need more baskets and space is limited, simply stack an extra layer of baskets on top of thebottom layer, taking care that they are spaced so that the bottom of one basket doesnt rest directly onthe surface of the one below so that water can still flow past all surfaces of all baskets.

The futureThe anoxic system has been developed in America over the past 20 years. It has gained considerable

respect over there, from those who have tried it and found that it provides nitrate reduction even belowthat of the incoming tap-water, leading to crystal clear pond water. In this country it is becoming a muchtalked-about subject and I believe that none who have tried it so far are disappointed. Keep yourmagazine subscription up to date, there will be more written about anoxic filtration in the near future.

AcknowledgementThe anoxic filtration system was design by Dr Kevin Novak Ph.D. Full details have been published inhis CD book which can be obtained directly from him or read on-line at www.mankysanke.co.uk (clickanoxic filtration).


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Figure 4. A simple diffuser to prevent water currents in the anoxic pond disturbing the baskets.


The photo on right shows what a

water outlet diffusion system may

look like when done. Remember this

is only oneway to diffuse inlet waterto the filter. Im sure there are many

more ways that can be implemented

to come to the same means.This is

nothing more than PVC painted black

to camouflage it from onlookers.

anoxic filtration

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