MOVING BED BIOFILM REACTOR: A NOVEL METHODOLOGICAL APPROACH FOR BIOMASS
AND POPULATION DYNAMIC ASSESSMENT FROM SEVERAL PILOT AND FULL SCALE REACTORS
Pasinetti E.* - Emondi V.*
This proposed novel method is intended to evaluate the biomass concentration as well as the biofilm development and the population dynamics in MBBR systems. The results come from 29 tests conducted over the last 4.5 years using pilot and full scale plants
for a total of 600 studied samples. Attached biomass values, ranges from 5-7 gTS/m2 for nitrification to values >20 gTS/m2 for carbon removal under high applied loads. It seems to be possible to correlate the presence and relative abundance of the functional
categories populating the biofilm (protozoa, metazoa, fungi, zooglea, filamentous and dispersed bacteria) to the type of wastewater, the surface applied load and the plant performance. Stalked ciliates protozoa colonized most of the biofilm at 70% rate; their
population dynamics may signify changes in process quality: for example, Stentor sp. is an indicator of ammonia concentration < 5 mg/l in tertiary nitrification effluent. Among the metazoa, the nematodes, due to their grazing, constitute a warning signal for
plant performance when biomass concentration falls below 4gTS/m2.
Biological component analysis
A sub-sample of at least 5 carriers is used to determine the qualitative and semi-quantitative content of the biological component. This is to be carried out by means of double sampling. Portions of biofilm are scratched from the carriers by means of pincers,
positioned on a slide, amalgamated with a drop of distilled water and covered with a 20x20 mm cover slip. Microfauna observations are carried out by means of a microscope Zeiss mod. Axioskop 2 plus in bright field and phase contrast (100x, 200x, 400x).
For each sample, the presence/absence of the following categories is recorded:
• Protozoa [stalked ciliates (Opercularia sp./ Vorticella sp./ Epistylis sp./ Carchesium sp./ Stentor sp.),
crawling ciliates, free-swimming ciliates; testate amoebae, naked amoebae]
• Metazoa (nematodes, rotifers)
• Filamentous microorganisms
• Zooglea like microorganisms
• Dispersed bacteria
• Fungi
The occurrence of protozoa and metazoa is marked by a numerical value which represents density and relative abundance of the
group concerned with respect to the population present on the prepared slide, according to the criteria specified in Table 2.
Table 1: Working conditions of the MBBR plants
for different types of wastewater and processes
Table 2: Micro and macrofauna presence index (PI)
Presence index Meaning
0.25
0.5
1
1.5
3
3.5
Super rare: the organism is noticed in one or two units on the entire slide
Rare: the organism is noticed in some units (<5) on the entire slide
Secondary: the organism is noticed with log ≤ 1; for stalked ciliates in colonies, the latter are considered
Super secondary: the organism is noticed with log ≤ 1.4; for stalked ciliates in colonies, the latter are considered
Dominant: the organism is noticed with log ≤ 2; for stalked ciliates in colonies, the latter are considered
Super dominant: the organism is noticed with log > 2; for stalked ciliates in colonies, the latter are considered
The index choice to be attributed to taxa depends on the density of the organisms on the slide and the joint presence of
several categories of organisms. Calculation of % relative abundance (RA) is carried out by taking into account the total
number of taxa found in the sample (excluding those with a “super rare” presence index) in the following way:
Industrial wastewater – carbon removal
Roughing
Very high rate
High rate
Normal rate
Low rate
Loading rate
gCOD/m2*d
>200
100-200
50-100
20-50
<20
% removal
During 29 pilot and plant tests with the
Kaldnes Moving Bed(TM) process, many
information were collected on biomass
concentration and on biological composition of
the biofilms. The experimental results, coming
from nearly 600 studied samples, were related
to the kind of process, the working conditions
and the influent quality (Tab 3).
This novel approach confirms that the
proposed methodology is a good practice tool
in order to describe the biological process and
to check during time the plant performances as
well as the effluent quality. It is therefore an
helpful mean for a good management of a
biological wastewater treatment plant.
20-30%
40-50%
60-70%
70-80%
≥ 80%
Denitrification
Post denitrification
Loading rate
gNO3 -N/m2*d
1.5-6
% removal
80-90%
Tertiary nitrification
High rate
Normal rate
Low rate
Loading rate
gNH4 -N/m2*d
5-13
1.5-5
<1.5
% removal
≤ 70%
70-80%
70-90%
Municipal wastewater - carbon removal
Normal rate
Low rate
Loading rate
gCOD/m2*d
20-50
<20
Dispersed grown - 9 X
% removal
75%
90%
Nematoda - 360 X
Table 3: QUALITY
Stentor sp. - 180 X
Working conditions
Process Quality
Dispersed bacteria
Start up
High-very high load
% removal: increasing
% removal: steady
(Table 1)
% removal: unsteady
% removal: steady
if dissolved oxygen
not limiting
Not relevant
% removal: steady
(Table 1)
Increase % removal
with toxic compounds presence
Not relevant
% removal: steady
(Table 1)
% removal: steady
(Table 1)
% removal: steady
(Table 1)
% removal: steady
(Table 1)
Fungi colonization - 7 X
Fungi
Yeast
Zooglea like organisms
Microfauna absent
(0 taxa)
Microfauna
(taxa 1-4)
Micro and macrofauna
(taxa from 5 to 10)
Stalked ciliates protozoa (D)
(Vorticella sp. and
Opercularia sp.)
Stalked ciliates protozoa (D)
(4-5 taxa)
Anomalous stalked ciliates protozoa
(stalks only, telotrochs, deformed cellular bodies,
broken up myonemes of Carchesium sp. and
Vorticella sp.)
Epistylis sp. (at least S)
Grass like biofilm - 11 X
Stentor sp. (at least S)
Testate amoebae (at least S)
(Arcella sp.)
Naked amoebae
Rotifers
(bdelloid)
Nematodes (at least SS)
(Rhabditida)
Difference nitrification colonization:
1 month (white) - 3 months (light brown) - 6 X
PROCESS BASED ON ORGANISMS OCCURRENCE
Functional category
Filamentous microorganisms
(S. natans and Thiotrix II)
Fluffy colonization - 7 X
Rotifer in nest with egg - 180 X
Transition
Carbon removal with TS > 8 g/m2
Denitrification
C/N > 25
Food industry wastewater
Typical of attached biomass in all types of treatment
except for high load carbon removal
Carbon removal in industrial
wastewater and denitrification with alcoholic carbon source
Carbon removal in industrial
wastewater
Carbon removal in municipal plants
Nitrification III
Post denitrification
Start up
Carbon removal in industrial
wastewater
Carbon removal in municipal plants
Tertiary nitrification
Acute inhibition phenomena
Carbon removal in municipal plants
Nitrification III at medium-high load
Nitrification III at low load
Nitrification III at low load
Low carbon applied load
Carbon removal without biodegradable substances
Nitrification III with CODin = CODout
Carbon removal in municipal plants
Tertiary nitrification
Carbon removal in municipal plants
Nitrification III
Seasonal presence and persistence in relation to the
biomass concentration and applied load
Carrier stalked ciliates colonization - 15 X
Stalked ciliates - 30 X
% removal: increasing
% removal: steady
(Table 1)
% removal: steady
(Table 1)
% removal: unsteady
% removal: steady
(Table 1)
NH4 - Nout < 5 mg/l
% removal: steady
(Table 1)
BOD5 out < 5 mg/l
% removal: unsteady
% removal: steady
(Table 1)
% removal: steady
(Table 1)
Interference with % removal if TS < 4 g/m2
Total stalked ciliates colonization - 6 X
D, S, SS = dominant, secondary, super secondary according to Table 2
Sigmoidal biofilm - 9 X
Tertiary nitrification biofilm - 9 X
Cyanide inhibition effect on stalked ciliates - 15 X
Opercularia sp. - 180 X
Testate amoebae - 180 X
Epistylis sp. and Suctoria - 360 X
Stentor sp. colonization - 6 X
*SIAD - Laboratory of Environmental Biology and Chemistry - ITALY - www.siad.com - [email protected]