Using biofilters to control wastewater odours
Over the past 15 years, biofiltration methods that improve odour quality of wastewater treatments have made significant strides. Original designs were open bed systems, which had a limited lifespan. They also came with high operational costs due to the regular replacement of media.
Operating efficiencies were affected by poor water distribution and humidity control. Blockages in the system would cause preferential airflow paths, reducing the residence time of air in the system.
This resulted in odour excursions and community complaints.
Nevertheless, advanced biofiltration technology saw the rise of OdourPro's FiltaOdor system - making biofiltration a viable and cost-effective solution for odour management.
What is biofiltration?
A biofilter removes volatile organic compounds (VOCs) and pollutants from an air stream by converting them into water, carbon dioxide, and salts. This removal is accomplished by the activity of micro-organisms such as bacteria.
The removal of compounds from the air happens in two stages:
- A biomass transfer takes offending compounds from the air stream to the bacteria.
- Biological degradation allows bacteria to convert these compounds.
Air streams containing odours are complex, often having more than one odour compound present. Therefore an effective biofilter contains more than one type of bacteria in order to target these different compounds.
The design may require certain compounds to be targeted first as the air passes through the biofilter so that those compounds don’t negatively impact the performance of bacteria further down the system.
What are the components of a biofilter?
The inlet air stream is introduced to a biofilter by a diffuser, working to distribute the air flow evenly at the base of the filter unit.
Some diffusers have a simple configuration of pipes with holes at regular intervals. However, any media collapse or contact with the diffuser can block some of the distribution holes thereby affecting the evenness of air flow. FiltaOdor has a plenum for air distribution, which eliminates this potential inefficiency.
Media beds create the environment for micro-organisms to live and feed on the compounds in the air stream. Original designs used soil beds or bark and wood-chip, leaving the bed itself subject to biodegradation. FiltaOdor uses an organic fibre and mineral bed, which is much more stable and maintains its integrity for over 10 years.
Moisture control is a critical component of a biofilter and has a significant impact on the effectiveness of the system. The micro-organisms live in a thin water layer on the media bed. Too much water makes the water layer too thick and the barrier for micro-organisms to absorb odour compounds becomes higher.
Too little water can cause micro-organisms to die. Water is controlled by humidifiers in the air stream as well as water spray systems in the filter itself.
Temperature control is also important for biofilters. Lower temperatures tend to slow down microbiological action, while higher temperatures tend to accelerate the activity of micro-organisms. Of course, extremes on either side of the temperature scale are harmful to micro-organism life.
A fan ensures a consistent airflow through the filter, while ducting leading to a vent releases the cleaned air into the atmosphere.
What is a hybrid system?
A hybrid system uses a two-stage process to achieve maximum reduction in odour from wastewater systems. The first stage is a biofilter as described above. The second stage is an active carbon filter, which acts as a polisher to remove trace odour compounds and capture minor excursions from the biofilter due to process upsets.
A highly effective hybrid solution was installed at the Erina Siphon Sewer Pump Station for Gosford City Council. OdourPro implemented a custom designed and inconspicuous FiltaOdor™ Hybrid Extension 3000Lps unit, which reduced odours by 99.9% and removed 99.9% of H2S in the air stream.
The advantages of FiltaOdor for wastewater odour treatment
A key advantage of the FiltaOdor system over other biofilters is the low airflow resistance of the media beds. This enables FiltaOdor to have deeper beds and a smaller footprint, making it a more aesthetic solution.
This was a critical factor in the Gosford City Council project where all stakeholders were satisfied with the final design and performance. The custom solution developed here was limited in size, to the equivalent of two shipping containers.
FiltaOdor uses a joint humidifier and irrigation control system to manage the moisture levels. A specially designed “wobbler” sprayer creates an even distribution of water across the media. Excess moisture is captured for recirculation.
Contact OdourPro for more information about biofilters
OdourPro has more than 25 years of odour management experience in wastewater systems. Our FiltaOdor technology is state of the art and delivers outstanding odour reduction and H2S removal. Our experts provide custom solutions and consulting expertise to help you identify your odour sources and provide effective solutions.
OdourPro on 21 November 2016
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