WASTE MANAGEMENT AND THE ENVIRONMENT KALMAR, SWEDEN, November 5-7, 1997
6
BIOLOGICAL (TROPHIC)
APPROACH TO WASTEWATER
TREATM ENT TECHNOLOGY
Yury Reshetilov Sergei VolodinPrivate ecological enterprise "Resetilovs un Coe" Latvia
In this research I try to detennine main principles of biocenosis variation for ad vanced municipal wastewater treatment. Pure hydrobiological approach has been used.
Besides excessive sludge utilisation - is one of difficult problems in aerobic wastewater treatment. Discussed complicated trophic structure (or several trophic levels) of biocenosis allow to assimilate biomass of bacteria with high rate. Rich and variable biocenosis with complicated trophic structure - is the key to ad vanced wastewater treatment and perfect excessive sludge utilisation.
Trophic relations are main part of ecosystem (biocenosis) relations. We must well know trophic relations for wastewater treatment process understanding. There fore, the hydrobionts trophic relations determine a quantity and a quality of acti vated sludge.
Main nutrition types and trophic relations of activated sludge are shown in Fig ure I .
Yury Reshetilov, Sergei Volodin, Latvia 5 1 https://doi.org/10.15626/Eco-Tech.1997.006
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WASTE MANAGEMENT AND THE ENVIRONMENT KALMAR. SWEDEN, November 5-7, 1997
In the first treatment stage ( or first trophic level) the treatment begin bacteria, some of Flagellate and Infusoria with saprozoic nutrition type (it'as nutritions through cell membrane). Mostly pollution removed by bacteria due to they large cells surface, high enzymatic activity and reproduction rate.
Second and third trophic levels characterised by holozoic nutrition type (organism utilise solids - another organisms or large organic particles [patikls]). Quantity of organisms with such nutrition type is limited nor dissolved organic but solids presence. These microorganisms are divided to bacteria-eating and predator. Mostly important bacteria-eating group - "sedimentation-makers" (genera [dzenere) Paramecium, Colpidium, Glaucoma, Tetrachymena, Stentor and others ciliates), which extract special biological lime for large particles of food production. One part of these particles is consumed by ciliates but another increases sedimentation of bacterial mass in clarifier and help treated water clari fication.
Highest trophic level - predators and some of bacteria-eating microorganisms. Such nutrition type is usual for predator Rotifera, Nematoda, Oligochaeta, other protozoans and metazoans. These organisms can eat practically all organisms from lower trophical levels
The quantity and biomass of activated sludge organisms, as it usually appear in food pyramids, from level to level decreases several times (up to 10 times). Also there are shown in this figure relationships of trophic structure and enter prise technologies development.
As you can see in the scheme even enterprise' s simplest technology (9 type) utilises all trophic levels, but more advanced technologies provide a conditions for development in large quantities worms, rotifers, ciliates and other predators for bacterial biomass removal in last stage of treatment process.
And some words about Trophic theory and technology.
As has been shown earlier by different researchers - the bacterial mass varies during treatment in high degree. From our point of view, researchers didn't ex plain real reason of such variation. They not mention protozoan and metazoan influence.
Common aerotank designed for full oxidation have low excessive sludge pro duction but it characterised by first trophic level and beginning of second level presence due to strong sludge circulation, loading variation and poor oxygen supply (Fig. 2).
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WASTE MANAGEMENT AND THE ENVIRONMENT KALMAR, SWEDEN , November 5-7, 1997
JOO BODtotal - total Biological
Oxygen Demand
q - suspended sludge dose
L - aerotank lenght q ( gll)
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BODtotal "::::Oo Q � C <::,-, Q:) 0 0Fig. 2: BOD removal -suspended sludge dose relationship in traditional aerotank
As you can see - traditional aerotank is characterised by permanent suspended sludge dose during BOD decreasing along it's length.
Ideal aerotank with beautiful trophic structure is aerotank with fixed-film media without suspended sludge and recirculation (Fig. 3).
Fig. 3: BOD removal -protozoan and bacterium doses realtionship in aerotank with fixed film media
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qu -protozoa mass in fixed sludge q11 -bacteria mass in fixed sludge L - aerotank length
Yury Reshetilov, Sergei Volodin, Latvia
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WASTE MANAGEMENT AND TI-iE ENVIRONMENT KALMAR, SWEDEN, November 5-7, 1997
It is shown that protozoan dose increase but bacteria dose decrease along aero tank length. The protozoan beautifully remove biomass of bacteria on fixed me
dia.
But such technology has main fault - during treatment not removed nutrients ni trogen and phosphorus). This problem can be decided by using of suspended and immobilised (or fixed) sludge simultaneously. Such principle used in all our enterprise technologies (we have about ten Latvian Republic patents). A data of other researchers and our long-term smdy show, that biofilm contains 2-3 times more protozoan and metazoan than suspended sludge. Fixed sludge has very complicated trophic strucmre. Relations among doses of bacteria in suspended sludge and fixed sludge and protozoan in fixed sludge are shown on Fig. 4.
q11
r--q -suspended sludge dose
q11 -protozoa mass in fixed sludge q,, -bacteria mass in fixed sludge L -aerotank length
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Fig. 4: BOD removal -doses of bacterium in suspended/fixed sludge and proto
zoan relationship in "Resetilovs un Coe" reservoirs
Bacterium mass decrease in fixed and suspended sludge but protozoan mass in fixed sludge increase. There are closest relationships among BOD removal and biomass changes in such case (Fig. 5).
---WASTE MANAGEMENT AND THE ENVIRONMENT KALMAR, SWEDEN, November 5-7, 1997
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BODtotal -total Biological Oxygen Demandq+q11 - cumulative curve of bacterium mass in suspended and fixed sludgt
L -a,rotank length
,;:,,, BODtotal
0 0 L
Fig.5: Relationship BODremoval and biomass change
This circumstance is perfect for wastewater treatment. It is known that excessive sludge utilisation talces up to 50% wastewater treatment plant price. Our tech nologies allow remove bacterium mass (excessive sludge). Biological sludge as similation decides problem with sludge utilisation.
FINALLY CONCLUSIONS
1. First of all, the technologies with complicated trophical structure allow to op timise biological sludge utilisation.
2. Secondly, the biological sludge utilisation: • minimise capital cost and energy consumption;
• allow to simplify WWTP maintenance.
Yury Reshetilov, Sergei Volodin, LaMa
