Biological Filtration Hugh S. Hammer, PhD GSCC David Cline, ACES Ron Malone, PhD LSU

Biological Filtration NH3 Ammonia NO2 Nitirite NO3 Nitrate

Ammonia Sources Decomposition of uneaten feed Decomposition of fecal materials Decomposition of dead materials By product of protein (feed) metabolism

Ammonia Exists in 2 Forms NH3 NH4+ Total Ammonia Nitrogen (TAN) Toxic More at High Temp More at High pH Less Toxic More at Low Temp More at Low pH

NH3 <-> NH4+ Equilibrium

NH3/NH4+ NO2- Bacteria of Reaction #1 Grow Quickly Nitrosomonas sp. Nitrosospira sp. Nitrosolobus sp. Nitrosovibrio sp. Nitrosococcus sp. Grow Quickly Oxidation NH3/NH4+ NO2-

Chemistry of Reaction #1 Requires Oxygen Results in decreasing (more acidic) pH Requires 7 grams of alkalinity (CO3-2) for each gram of ammonia (NH3) converted to nitrate (NO3)

pH = -log hydrogen ion concentration

pH - What Should It Be

Alkalinity (Carbonate CO3-) Stabilizes pH around pH 7-8 Resists changes in pH (acts as a buffer) Required by nitrifying bacteria as a carbon source for survival

Biological Filtration Reaction #2 NH3 Ammonia NO2 Nitrite NO3 Nitrate

Nitrite Conversion to Nitrate Requires oxygen Does not change pH Requires alkalinity

NO2- NO3 Bacteria of Reaction #2 Grow Slowly Oxidation Nitrobacter sp. Nitrospira sp. Nitrospina sp. Nitrococcus sp. Grow Slowly Oxidation NO2- NO3

B1 B2 NH3 NO2 NO3 What About Nitrate? Non toxic in most fish up to 300 ppm Easily solved via water change Also managed through addition of plants Can be toxic for many invertebrates (i.e. shrimps) B1 B2 NH3 Ammonia NO2 Nitrite NO3 Nitrate

Biofiltration The classification of heterotrophic bacteria encompasses a great number of genera/species which share the common characteristics of extracting their nourishment from the breakdown (decay) of organic matter. Biochemical oxygen demand (BOD) is largely an indirect measure of the biodegradable organic material in water. Heterotrophic bacteria reduce BOD levels, consuming oxygen in the process. About 60 percent of the organic matter consumed is converted to bacterial biomass; whereas, the balance (40 percent) is converted to carbon dioxide, water, or ammonia. Heterotrophic bacteria grow very fast, capable of doubling their population every ten to fifteen minutes. If the BOD in the water being treated is very high (> 20 mg -O2/l), the heterotrophs will quickly dominate the bead bed, overgrowing the slower growing nitrifying bacteria and consuming tremendous amounts of oxygen. The second, yet more important, classification of bacteria is the nitrifying bacteria. These bacteria are specialists, extracting energy for growth from the chemical conversion of ammonia to nitrite and from nitrite to nitrate (Figure 3.6). Nitrate is a stable end product which, although a valuable nutrient for plants, displays little of the toxic impacts of ammonia and nitrite. Composed principally of two genera (Nitrosomonas and Nitrobacter), nitrifying bacteria are very slow growing and sensitive to a wide variety of water quality factors. It is not surprising that most bead filters used for biofiltration are managed to optimize conditions for nitrification.

Optimal Nitrification Conditions pH 7.5 High Dissolved Oxygen Alkalinity CO3- (Carbon Source) Surface Area (Media) Food (ammonia and nitrite) Low Light (Light inhibits growth) Ammonia oxidizing bacteria grow fast Nitrite oxidizing bacteria grow slowly

How Can You Tell If Your Filter Is Working ?

Filter Media

Bead Filters and Drop Filters Probably the industry standard Both mechanical and biological filtration A type of fluidized bed filter Space saving (consolidated approach) Can be expensive Drop filters are great for saving water, they concentrate solids Drop filters don’t clog easily

Biofiltration

Propeller-washed Floating Bead Filters

Floating Bead Bioclarifiers Filter Mode Drop Filters : Low Water Loss Floating Bead Bioclarifiers Air Bleed Builds Charge Settled Backwash Waters returned to system

Drop Filters : Low Water Loss Floating Bead Bioclarifiers Backwash mode Drop Filters : Low Water Loss Floating Bead Bioclarifiers Released Air Washes Beads Internal Sludge Capture

Circulation Aeration Degassing Solids Capture Biofiltration Inlet Airlift

Fluidized Bed Filters Can use any type of media (sand and beads are most common) Uses a mixing media/water matrix Great biological filtration Bead filters are a type of fluidized filter that also accomplish solids capture. Also called submerged filters when large void volume media is used.

Foam Block Media Fluidized Beds Active Media

Fluidized Sand Bed Filters THESE ARE NOT RAPID SAND FILTERS Advantages: Tremendous surface area (the most) Nitrite eating bacteria grow great Best biological filters Huge biological loads Aquarium industry gold standard Disadvantages: Heavy, may require multiple pumps during power outages Bacteria die quickly from O2 deprivation during power outages MUST have all of the solids out of the water (solids can cause serious problems with channeling)

Trickle Filters, Packed Towers, Bio-wheels, RBCs Media is not continually submerged but moist Efficiency depends on water distribution Inexpensive to build Good biological filtration Not good for solids removal (hard to clean) Great for aerating water and stripping carbon dioxide Will change the temperature of water (cools it off, sometimes good and sometimes not) Some RBCs are very expensive but are great biofilters

Packed Tower Adds Oxygen Removes Carbon Dioxide Biological Filtration Easy to construct

Trickle Filter Bioballs

RBC Rotating Bio Contactor

Wet Dry Filters Screen + Trickle Filter + Fluidized Bed Filter = Wet Dry Filter Consolidated approach Good for small loads (aquariums) Advantages and Disadvantages of all the components