Hydrogen sulfide (H2S) production is a major issue in the paper industry where wastewater volume is substantial and processes primarily organic. This is the same in municipal wastewater treatment plants where H2S has historically been a difficult issue that's closely regulated for environmental and safety reasons.
Caldwell's Paper Mill lies in an environmentally sensitive area along the River Forth on Inverkeithing Bay, Fife, Scotland, which is widely used by commercial shipping and leisure sailing/fishing vessels. Water use flow rates for the mill are about 1.8 to 2 mgd. Solids content is substantial at the beginning of the process, ranging from 1,500 to 12,000 ppm on average. Settling tanks and a conventional belt pressroom provide reasonable solids separation prior to treated effluent entering the river estuary.
Historical H2S fugitive emissions of 5 ppm were already being treated effectively with an air wall H2S elimination system (see Airborne H2S below) from NanoVapor Systems UK Ltd., which blows a biocatalytic odor-suppressing compound into the treatment area. This serviced two large settling tanks (primary aeration and secondary clarifier). The new H2S treatment system effectively eliminated fugitive mill emissions, satisfying both local and national regulatory bodies as well as residents of the neighboring town of Inverkeithing.
The issue of absorbed H2S in mill effluent and biofilms also was a major issue and represented an ideal opportunity to introduce an advance in probiotic bacteria control using a sulphur-reducing bacteria (SRB) enzyme site blocker, or Nano Sulphur Inhibitor (Nano SI), developed by NanoVapor Systems for aqueous phase applications in the management of organic based waste streams. The new technology's principle and economic rationale is based on inhibiting H2S creation rather than treating H2S in an aqueous or gas phase as effluent or downstream emissions
Despite using heavy and multiple applications of traditional biocidal chemicals -- e.g., sodium hypo chloride -- the mill was unable to dislodge or destroy the biofilms present in the effluent system by eliminating SRBs. In the end, further application of biocides was shown to be pointless as the biofilm re-established itself within a few days and the usual 5-ppm H2S level returned virtually immediately. This effect was clearly shown in the application data (see Figure 1) when mill production was stopped due to heavy solids loading. Within hours, the aqueous phase H2S level returned to 5 ppm.
When the plant restarted and Nano SI dosing commenced, the H2S levels dropped immediately to 0.010 ppm. Dose rates were adjusted within a narrow band of 1-3 gpd at the end of the first week to determine the exact rate for assured regulatory compliance and cost benefit analysis. This was determined to be 0.5 ppm, similar to most U.S. paper mills. The effective dose rate is based on sub-compliance levels to reconcile production flow spikes. The range of flow varied roughly between 250 and 325 m3/hr and recorded data for this facility indicated an effective dose rate of 25-30 gpd at +/- 300m3/hr or 1.8-2 million gpd.
Among its advantages, this probiotic bacteria control approach offers:
* A low dose rate that allows for 55-gallon drums or 1,000-liter containers with a simple dosing pump accurate to +/- 0.5 gpd.
* A safe, non-caustic solution that won't harm personnel, wildlife or the environment.
* Lower treatment costs while satisfying regulators and increasing production capability.
* Lower corrosion in effluent piping and storage tanks or any other facility affected by aqueous or airborne H2S -- saving on maintenance or facility upkeep costs as well.
Additional subjective results include improved neighbor relations and an ongoing improvement in regulatory relationships that "bad smells" can erode. Industries benefiting from this probiotic technology include: paper, municipal wastewater treatment, petrochemical, food processing, livestock or animal confinement, mining, and all water based organic process manufacturing.
It should be understood that Nano SI is not a biocide. It won't kill bacteria, including SRBs, in the treated waste stream. This probiotic technology works by blocking the enzyme-producing site of the bacteria, inhibiting its ability to create sulfites. This forces the SRBs to alter their metabolism and obtain energy from other nutrients, such as acetate thereby forming methane instead of H2S. It will also aid the performance of the existing biomass reduction processes by lessening the workload demanded of them.
NanoVapor Systems LLC, the biochemical technology division of The Moorhead Group, is based in Aptos, CA, with subsidiaries in Berwickshire, Scotland, and Seoul, South Korea. For more information, contact 831-685-1148 or www.nanovapor.com
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Airborne H2S eliminated at sewage treatment works
In addition to hydrogen sulfide (H2S) issues in wastewater effluent systems, biotechnology has overcome the social and workplace problems associated with fugitive emissions in open-air situations (outside sludge stores) and enclosed areas (sludge press rooms). A good example can be seen at a sewage treatment works in Perth, Scotland.
Perth is a medium-sized city of about 200,000 people. The sewage treatment works is on the south bank of the River Tay east of the city, and is managed by the Scottish Water Authority. The site is fairly conventional comprising a raw sewage "screw fed" inflow system, settlement and clarifier tanks, and a building housing sewage pasteurization equipment. From this building, processed sewage "sludge cake" is transported by conveyor to an outside storage area. It will be used later for land reclamation projects.
This storage area was a source of strong odors generating many complaints from local residents. Called in to discuss its solution to this issue, NanoVapor Systems proposed an odor-eliminating barrier utilizing an air wall/curtain machine that's projected by ducting positioned on top of a wall surrounding the storage area and employs a biocatalytic compound, NanoZyme, to treat the air.
At the same time, the serious issue of H2S fumes within the sludge process building was resolved by extending ducting into the building from the main odor-reduction system, which blows the odor-suppressing compound into that area as well. H2S fumes were eliminated from a high of 40+ ppm to non-detectable levels.
An additional project was the supply of two 3-hp machines required to eliminate atmospheric H2S fumes/odors emanating from vents in the sewage screw inlet system. Another installation benefit here was reduced H2S corrosion levels within the screw system.
Process operators can now freely and safely work in the treated atmosphere.
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