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BIOTOWER SIZING GUIDELINES

While both aerobic and anaerobic biotowers have seen their market share increase so to speak, easily or readily transferable design/bioengineering formulas have yet to arrive if at all.  Let's discuss each type separately.

In the case of aerobic biotowers limitations arise because much of the available material/equations/models say derives from either

 - low strength, municipal type contexts

- installations or designs using just one type of media, say either cross-flute OR vertical-flute media, and/or

- general problem/solution formulations focusing or addressing soluble or dissolved biological oxygen demand, sBOD for short.

We're left sort of unaided when it comes to address high strength, mixed media, lump BOD/COD all at the same time scenarios.

For municipal wastewater, many reputable media vendors provide some sort of computerized/courtesy design/ballpark sizing based on modified Velz formula variants.  It is also very common that they specify minimum and maximum wetting rates, basically hydraulic loading ranges 0.25 - 0.75 gpm/sq.ft. being possible figures, as well as maximum organic load per cubic feet, say 50 lbBOD/day per 1,000 cu.ft.  Taking this into account and sticking to predominantly/solely municipal wastewater aerobic biotowers find their way in  many engineering reports.  Even then, things can get tricky.

One can seldom can apply equations developed for municipal wastewaters (ie the Velz equation for TFs) to industrial wastewaters. The reason is that the sizing and performance equations for municipal systems almost always are related to hydraulic factors, ie HRT, wetting rates, etc, while industrial systems are almost always load controlled (ie SRT, organic loading rate, etc.). The problem with biotowers is that when even treating municipal wastewaters, say at 1 kg/m3/day, the BOD is spread out from around 400 mg/L at the top to 25+/- at the bottom of the tower. With industrial wastewaters for the same loading rate, the BOD at the top of the reactor is substantially higher even with direct recycle, so that oxygen transfer limits are reached rapidly in the top few feet or meters of depth.  Under these conditions, excessive growth occurs with associated plugging and odor production, usually occur.

DISTRIBUTION AND PUMP SIZING

Since the TF is open at the top, any recirculation pump will have to overcome the entire elevation head plus friction headloss for the influent and the recycle streams. So the elevation head is the height from the bottom of the sump for the recycle pump to the top of the highest point in the TF distributor.

ROUGHING FILTERS

Roughing filters are trickling filters employing relatively coarse media and operated at high rates to perform aerobic biological preliminary treatment, e.g. target soluble BOD 50-80 % removals.

It is very difficult to treat high strength industrial wastes with a TF of this type because of the high COD/BOD at the distributor. Usually excessive growth occurs at the surface with fairly rapid plugging.  Also, when the recycle ratio exceeds 3:1, the cost of pump power tends to negate the inherent advantages of a trickling filter.  Work out pump rough HPs and compare with aeration HPs were an aerobic approach considered.

www.AerationFundamentals.com - www.ExtendedAeration.com - www.OxidationDitches.com - www.TricklingFilters.com

www.Biotowers.com - www.MembraneBioreactors.com - www.AnaerobicReactors.com - www.AnaerobicFilters.com 

www.UASBs.com - www.EGSBs.com - www.CoolingTowerFundamentals.com - www.EvaporativeCondensers.com

www.DewateringFundamentals.com - www.BioremediationFundamentals.com - www.IncinerationFundamentals.com