NUI Galway – UL Alliance First Annual ENGINEERING AND - ARAN ...

Optimisation of a Novel Biofilm Technology for the Removal of Nuisance Odours and Greenhouse
Gases
C. Kennelly 1 , S. Gerrity 2 , G. Collins 2 , E. Clifford 1 ,
1. Civil Engineering, National University of Ireland, Galway
2. Department of Microbiology, National University of Ireland, Galway
Email: c.kennelly1@nuigalway.ie
Abstract
In this study, a horizontal flow biofilm reactor (HFBR) has
been designed and is being investigated for its efficacy
biologically treating nuisance gases associated with
emissions from wastewater treatment plants, namely
methane (CH4), hydrogen sulphide (H2S) and ammonia
(NH3). Recent results have shown CH4 removal efficiencies
(RE) averaging 50 – 65% with maximum RE of up to 80%
observed. Experiments investigating removals of H2S and
NH3 are underway with initial results focusing on biofilm
growth and acclimation.
1. Introduction
Recent studies have identified numerous health and
environmental problems that arise from emissions of
greenhouse, toxic and odorous gases generated in
wastewater treatment plants (WWTPs). New cost-effective,
sustainable solutions are required to emissions such as
CH4), hydrogen sulphide (H2S) and ammonia (NH3)
[1], [2]
In this study, laboratory scale horizontal flow biofilm
reactors (HFBRs), a novel NUI Galway developed
technology, have been constructed to examine the removal
of CH4, H2S and NH3 from waste gases
2. Materials and Methods
The HFBR technology comprises a stack of horizontal
plastic dimpled sheets across which the gas to be treated
flows sequentially over. The HFBR units (Figure 1) are
housed in an external temperature controlled laboratory.
The temperature is controlled at 10 o C, typical of on-site
operating conditions.
Figure 1 – HFBR units
Air and gas are mixed to simulate typical WWTP off gas
concentrations. To provide sufficient substrate and moisture
to the biofilm a synthetic wastewater (SWW) is also
supplied to each HFBR unit.
Nine laboratory scale HFBR units have been
commissioned, 3 each to examine CH4, H2S & NH3
removal. Each reactor was inoculated with microorganisms
to expedite acclimation and optimise oxidation. Three of
the HFBRs were seeded with a methanotrophic rich
biomass. The remaining 6 units were seeded with activated
sludge, which contained bacteria capable of oxidising H2S
and NH3. CH4 gas concentrations are analysed using Gas
Chromatography. H2S and NH3 are monitored using
handheld sensors. Samples of the biofilm are also analysed
104
and microbial profiling of the system is being carried out
using techniques such as Terminal Restriction Fragment
Length Polymorphism (TRFLP) and Polymerase Chain
Reaction (PCR).
Wastewater analysis is carried out using standard methods
(APHA, 2005). This allows for precise mass balance
analysis to be carried out.
3. Results
These reactors have a working volume of 20 litres (L) and a
top plan surface area (TPSA) of 0.04 m 2 . For the CH4
reactors an air and CH4 (1 % v/v) mixture is introduced at
the top of each reactor. The empty bed residence time
(EBRT) within these reactors is 50 minutes. Gas flows
downwards concurrently with the applied SWW (8 L
SWW/HFBR/day). The total gas flow rate to the CH4
reactors is 1.2 m 3 /m 3 reactor volume/hr and the CH4
loading rate is 8.5 – 9.0 g CH4/m 3 reactor volume/hr.
Recent results show average CH4 removals of 60 – 65%
with maximum removals of 85% observed (Fig 2). The
composition of the influent SWW has a significant effect
on CH4 removal rates. Various SWW combinations are
being trialled.
RE %
80
70
60
50
40
30
20
10
Average Removal
Average Influent
Average Effluent
CH4 Removal
0
0
140 150 160 Day 170 180 190 200
Figure 2 – CH4 Removal
The total gas flow rate to the H2S and NH3 reactors is 60
m 3 /m 3 /hr (30 m 3 /m 2 TPSA/hr).The EBRT is 60 seconds. In
each case the influent gas concentration is 100 ppm. The
H2S and NH3 trials have just commenced and results are
pending.
4. Conclusion
The results to date indicate that the HFBR has excellent
potential to biologically treat greenhouse and noxious gases
in an effective manner, reducing the carbon footprint of
waste treatment facilities and making their presence more
acceptable to the public. The system is extremely costeffective
requiring no mechanical moving parts and
operated solely using pumps controlled by timers or simple
control panels.
5. References
[1] Haubrichs R., Widmann R. (2006) – Evaluation of Aerated Biofilter
Systems for Microbial Methane Oxidation of Poor Landfill Gas – Waste
Management 26, 408-416.
[2] Shareefdeen Z, Singh A (2005) - Biotechnology for Odor and Air
Pollution Control – Springer-Varleg Berlin Heidelberg
2.5
2
1.5
1
0.5
CH4 Concentration %