This document describes DMT Environmental Technology's development of a new 3-stage biological odor control system called Odourex that is more effective than conventional single-stage biofilters. The system uses DMT-HS media that has proven to eliminate hydrogen sulfide 3-5 times better than lava rock or plastic media due to its highly structured surface area. Testing showed the DMT-HS filter achieved elimination capacities over 100g H2S/m3*hr with over 95% removal efficiency, outperforming other media. The multi-stage Odourex system treats different odors like H2S and mercaptans under their optimal pH conditions using 20% less space than conventional filters.

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Multiple Stage DMT Odourex®
The next generation Biological Odour Control systems
R. Lems M. Sc.1
, E.H.M. Dirkse B(a) Sc.2
, J. Edens B.(a) Sc.3
,
1
R &D manager DMT, 2
director DMT, 3
Process engineer DMT, RLems@dmt-et.nl;
DMT, Yndustrywei 3, 8501SN, Joure, Netherlands, tel: +31 (0) 513 636 789, fax:+31 (0)513-636841.
Abstract
DMT Environmental Technology B.V. has developed in the period medio 2006 until medio 2008
an improved technique to remove H2S, mercaptanes and other VOC’s in a biological way. The
Odourex®
system is a 3-stage bio-trickling filter with an acid and a neutral stage followed by a
polishing step. During a demonstration project the DMT Odourex®
systems has show to perform
3 to 5 times better than the conventional filters (lava-rock/ pall rings). The elimination capacity
for H2S has proven to be at least 100 gH2S/m3
*h at optimum conditions. The filter proofed to be
self-cleaning with minimum air pressure drop during the year of testing. The footprint of the
Odourex®
system is only 20% compared to a conventional lava rock filter.
Key words
Bio-trickling filter, bio filter, DMT-HS, H2S, mercaptanes, Multi- stage, odour control
Introduction
Odour is usually caused by the presence of a great variety of components like: hydrogen sulphide,
mercaptanes, ammonia and different kinds of VOC’s. An odour control system therefore will
have to treat not only hydrogen sulphide, but also other pollutants to reduce the total mal odour.
In biological processes every micro-organism prefers it’s own process conditions; especially pH,
temperature and substrate are playing important roles. So placement of only one biological filter
often appears not to be sufficient. For that reason a combination of processes/ filter steps is
necessary.

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Theoretical back ground
Development of packing/ filter media for biological filters
The first bio-filters were large beds containing soil and/ or compost and could only remove small
concentrations of a large variety of (organic) compounds. Different filter materials have been
developed to improve these bio-filters. Pure material or mixtures of compost, manure, bark,
wood and coconut fibres have been used to increase the capacity of the bio-filters and decrease
the footprint.1
A second step in the development of biological treatment, which was more
focussed on H2S rich air streams, was the introduction of lava rock bio-trickling filters (BTFs).
The high specific surface of the lava rock increased the population density of the (H2S degrading)
bacteria reducing the total required filter volume. Due to the water circulation it was more easy to
control process parameters like humidity, temperature and pH, which made it possible to operate
near optimum conditions.2
At the same time higher filters were possible due to the decrease in
pressure drop which reduced the footprint significant. This resulted in higher removal
efficiencies and EC’s up to 20-60 gH2S/m3
*hr3,4
at an air load of 300-350 m3
/m2
. Also the first
multi stage biological treatment systems were introduced, which consist of two lava rock in
series, if necessary followed by a conventional bio-filter. In this way different environmental
systems (e.g. pH) can be created to degrade different pollutants by specialized bacteria. However
the lava rock is difficult to handle, has a large weight and is susceptible to clogging especially at
high H2S concentrations and can therefore only be used for small to medium air flows with
maximum H2S concentrations of 100-500ppm.
Highly structured media
The last years plastic and foam packing materials for bio trickling filters have been developed to
increase the biofilm surface and at the same time minimize resistance and weight.5
This resulted
in either high EC’s but increased the chance of clogging (foam), or reduced the chance of
clogging but did not increase the EC significant (Pall Rings). The plastic filter materials do result
in an excellent process control (pH, T, pressure loss etc.) due to higher water circulation
capacities. DMT is now introducing a new plastic packing material for BTF’s; the DMT-HS filter
media. Due to its highly structured, open media, clogging problems and declining removal
efficiencies are being solved. The specific round spikes stimulate the growth of the micro
organisms which increases the total bio film surface (increase in spike diameter) to
approximately 1000 m2
/m3
. When the bio film becomes to thick/ heavy it falls of the vertical
positioned pins due to the shear of the water circulation. This makes the media self cleaning.

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Practical data
A demonstration project was started in March 2007 at the WWTP of Eerbeek (the Netherlands)
to test and compare the DMT-HS packing material in a practical situation6
. Three types of media
in BTF’s filters were tested: Lavarock, Pall Rings and DMT-HS (See figure 1). The main
objectives of this field research was to compare removal efficiencies, elimination capacities and
fouling rates. The second objective was to find the optimal process parameters for different
components.
Obtained measurements
In the next graph (graph 1, top) the H2S load is
displayed against the elimination capacities. The
diagonal line presents a 100% removal efficiency. The
graph demonstrates a EC for the DMT-HS of
>100g/m3
/hr with still no reasonable decline in removal
efficiency (>95%). For the pall rings the EC is
maximum near 50g/m3
/hr with decreasing removal
efficiencies. The lava rock has a maximum EC of about
15-18 g/m3
/hr. At >95% removal the maximum is 22
g/m3
/hr for Pall and 9 g/m3
/hr for lava rock.
Measurements concerning temperature showed that
below 15ºC, removal efficiency dropped quickly to an
average 20-30% at 8ºC (all systems, see graph 1,
middle). The pH had a negligible effect on the systems
between 0.5-3 (all systems, see graph 1, bottom).
Nutrient addition was very important for all systems but
had the most effect on the plastic filter materials.
Figure 1: Left; PFD, middle; filter materials, right; photo of the demonstration plant.
Graph 1; Top; EC different filter
media, middle; relation temperature
and EC; bottom; relation pH and EC.
pH and EC
0,0
0,5
1,0
1,5
2,0
2,5
3,0
3,5
14-06-0710-07-07 3-08-07 25-09-0717-12-0713-02-0816-04-08 8-05-08 20-05-0812-06-0825-07-08
Date
pHpercolatewater
0
13
25
38
50
63
75
88
100
113
EC(gH2S/m3/h)
pH HD Q-pac
EC HD Q-pac
DMT-HS

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A mixture of ammonium and phosphate salts performed as good as effluent and even as good as
a special nutrient mixtures with trace elements. A ratio of 100:30:1 (DMT-HS system, S:N:P)
was found optimal. GCMS analysis showed that 50 % of total VOC and 90 % of the alcohols
were removed with DMT-HS.
During testing, measurements concerning
pressure loss showed that DMT-HS caused a
pressure drop between 20 and 50 Pascal
(versus 350-450Pa for Lava Rock) without
clogging even at over-loading and dehydration
conditions. After artificial clogging, the system
was self cleaned within 1 day. The lava rocks
clogged frequently (two monthly). See table
1 for an overview of all test results.
DMT Odourex®
The results from the demonstration plant in Eerbeek were
combined with field data of multiple BTF’s for treatment of
various pollutants which have been extrapolated to create a
multi-stage system for complete odour removal (see figure 3).
This single tower, three stage purification plant uses the DMT-
HS in two stages and a foam filter as a polishing step as a third
stage. All odour components can be degraded in a biological way
at their own optimal conditions like T and pH. H2S, NH3 and
alcohols are removed in the first stage at a acidic pH (0.5-1.5).
Mercaptanes and other VOC’s will be degraded at the second stage at a pH of 6-9. The last step
is a polishing stage with foam, creating a very dense population of bacteria which are directly fed
with fresh, nutrient rich water to accomplish maximum removal efficiency on all left trace
components.
Parameter DMT-HS 2”Pall Lava
EC (g H2S/m3/h) 35 - 100 5 – 50 5 – 20
EBCT (s) 10 - 20 10 - 30 30 - 70
P. drop (Pa/m) 10 -20 20 - 100 150 - 200
H2S % 80 -100 50 - 80 70 - 100
Mercaptanes % >70 30 - 50 40 – 50
VOC % 50-90
Table 1: Overview test results.
Figure 3: Odourex®
system

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Compared with 2 lava rock
filters in serie, followed by
activated carbon as polishing
step this results in a 4 times
smaller volume and even 5
times smaller footprint (see
table 2 and figure 2).
Still the pressure drop is less, the load can be higher and it is self cleaning. With these parameters
the biological odour removal is even better for the Odourex® system (99.8%) than for the lava
rock system (98.3%).
Conclusion
The development of bio filters for odour abatement has been driven by problems with clogging,
footprint and removal efficiencies. This has resulted in the multi stage DMT Odourex® which
treats different odour components like H2S, mercaptanes and VOC’s in different stages at
optimal process parameters. The elimination capacity of the DMT-HS packing material is more
than 3 to 5 times higher than lava rock and 2” pall-rings. This results in removal efficiencies on
odour of >99% on a very small footprint with a self cleaning clogging free packing material.
References
1
G.R. Moosavi et al, Biotechnology advances in treatment of air streams containing H2S, Journal of Biological
Sciences, 5 (2):170-175 (2005)
2
Smet, E. (1996) Biofiltration of Volatile Organic Sulfur Compounds. Gent University, Gent.
3
Evaluation of Biological air treatment systems at WWTPs (Dutch), 2003
4
Various internal inspection reports
5
Deshusses, M.A., H.H.J. Cox. (2000) Biotrickling filters for air pollution control, In: G. Bitton (Editor-in- chief),
The Encyclopedia for environmental microbiology, New York.
6
Dirkse, E.H.M. (2007) Odour control on Waste Water Treatment Plants and Pumping Stations using DMT
Biotrickling Filtration, DMT environmental Technology. 12th European Biosolids Conference, Manchester.
Table 2 and figure 2: Overview of an odor control system design for
a DMT-HS and a lava rock for system for 4400m
3
/hr and 50-75ppm
H2S, 5-7.5ppm Mercaptanes and 10-30ppm VOC.
Two stage lava filter with AC as polishingOdourex
Odourex®
Lava
A (m2
) 5.7 28.2
Vt (m3
) 20 80
Dp (Pa) 200Pa 2100
RE (5) 99.8 98.3