An ageing basin liner risking untreated water leakage into the ground? Worries about environmental contamination breaches or a cease-and-desist notice?
All rather dramatic-sounding, yet numerous small treatment plants (<500 000 gallons per day) operate with just one aeration pond, one clarifier and a wearing liner nearing the end of its design life. Many of these systems lack any form of redundancy or back-up.
One might suggest constructing a new pond to remedy this, but not only is that likely uneconomical, but space on site is often insufficient. So, with only one aeration basin in place, how can it be taken offline for cleaning, maintenance and relining?
In a recent project, WSI International, a Denver-based equipment manufacturer and engineering firm, demonstrated a cost-effective way to embed treatment redundancy for safely renovating a 300 000 GPD extended aeration activated-sludge facility’s ageing infrastructure.
The facility’s Utility Manager took a proactive stance and enlisted WSI to design and build a system that would allow the activated-sludge lagoon to be taken offline.
From conceptual design through to project delivery, WSI faced the task of ensuring that the WWTP (built in 1995) on Hawaii’s Big Island would, for the first time, be able to take its aerated lagoon offline for cleaning and relining without halting overall treatment operations.
Moreover, the plant required added redundancy for both aeration and clarification, without expanding its site footprint. The liner on the existing aeration lagoon (443 000 gallons) was deteriorating at the edges due to weathering, and grit accumulation threatened treatment capacity.
Removing the lagoon to inspect the liner, carry out repairs or relining and clean it would be feasible if the wastewater could be diverted to a temporary basin—but redundancy for the aeration basin and secondary clarifier was lacking.
Aeration-basin redundancy wasn’t deemed critical, but a clarifier failure, perhaps due to a broken rake or main shaft, could pose a major operational challenge and risk effluent exceedance.
WSI identified a clever solution: repurpose the existing secondary clarifier as an aeration tank for the activated-sludge system, as Ben Garcia, WSI’s Vice-President of Engineering, explains:
“As we set out to design a compact, integrated system, we needed to develop a DAF unit capable of managing Mixed Liquor Suspended Solids (MLSS) from the existing activated sludge treatment process within a much smaller footprint—while still providing the same level of clarification as the significantly larger existing clarifier. Additionally, the DAF system, being located downgrade, required an effluent pump system to send clarified water uphill to the existing chlorine contact tank as well as a sludge transfer system for the RAS and WAS operations of the activated sludge treatment process.”
WSI’s integrated DAF system needed to function as a clarifier for the existing system while transitioning seamlessly between temporary conversion, operation and reverting to the original WWTP setup.
As the aeration lagoon was being refurbished, WSI’s DAF unit replaced the secondary clarifier, returning RAS (Return Activated Sludge) to the aeration basin and diverting WAS (Waste Activated Sludge) to solids processing to balance the biological mass.
The site’s steep terrain, originally used for a gravity-flow system, posed an added challenge. WSI made use of a small (38′ × 14′) flat area next to the control building for the integrated DAF unit.
‘Landia allowed us the flexibility to install the air induction nozzles outside of the clarifier.’
Ben Garcia added:
“Since this was a temporary project, we set up a system of interconnecting hoses from the site’s existing equipment to connection points on the integrated DAF system for influent, effluent and sludge disposal. Once the DAF was operational, the site took down the clarifier to prepare its conversion as the WWTP’s temporary home for the biological treatment process.”
Given the existing clarifier’s scum rake, sludge scraper and sloped base, introducing a conventional blower and aeration grid, even temporarily, was not feasible.
Ben Garcia explained:
“We looked long and hard at various air-eductor/mixing pump options, even though some meet the criteria of supplying 40 lbs O₂/hr, they had larger air induction nozzles that required installation inside the clarifier, which, as with an aeration grid, would have been incredibly difficult to install. The AirJet diffuser from Landia allowed us the flexibility to install the air induction nozzles outside of the clarifier.”
The Landia AirJet, designed as a venturi system, draws atmospheric air into a recirculating flow from the clarifier, aerates it and returns it, providing mixing and aeration to operate as an activated-sludge basin. The aeration nozzles also ensure sufficient mixing energy is delivered to prevent solids from settling.
Ben Garcia continued:
“The Landia AirJet could be introduced far more conveniently just by adding penetrations through the clarifier wall. Landia worked with WSI to configure the angles of aerator injection nozzles that best suited the project. The aspirator and venturi section are positioned outside of the walls so as to not interfere with the scum-rake assembly at the water surface or sludge-rake assembly at the base of the clarifier.”
‘Creates exactly the right amount of mixing needed.’
The nozzles simply protrude through the clarifier wall by a few inches, while the main component, the Landia Chopper Pump, remains outside, easing maintenance. The Landia AirJet proved ideal for this clarifier-to-aeration basin conversion.
It not only provides air for the biological process but also offers the right mixing energy to suspend solids effectively. The direct OEM and engineering collaboration from Landia ensured the best outcome.
“The Landia AirJet worked exactly as designed, providing the oxygen needed for biological nutrient removal that was required. It runs very smoothly. We and our customers are very happy.”
Landia Ltd
- 0194 8661 200
- info@landia.co.uk
- http://www.landia.co.uk
- Waymills Industrial Estate, Whitchurch, Shropshire, SY13 1TT GB
About us
Landia's headquarters are located in Lem, which is how it has been since 1933. Today, Landia has subsidiaries in England, Germany, Norway and the US, and a sales office in China. In addition, Landia products are sold in 45 countries worldwide. Landia supplies pumping and mixing solutions to many different industries, with the most important ones being agriculture, wastewater, biogas plants and the fish industry. In general, you will find Landia's products wherever there is a difficult medium to be pumped or mixed. Landia survives by selling quality solutions in close partnership with the customers.
Landia is not a supermarket where customers select products from the shelves. Our technical sales people are always in close discussions with customers, which ensures solutions that work. For Landia, quality in every phase a matter of course, and we have been ISO9001 certified since 1994. Quality also means that many of Landia's products have been in operation for 20-25 years even though the operating conditions may be extreme. In that way, Landia's customers achieve the lowest lifespan costs, while resource consumption is minimised, which further results in a positive impact on the environment.
Where we supply to
Europe, Africa, Asia, Australia, South America, North America
Industries we supply to
Chemicals
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Landia GasMix operating in tank
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LANDIA's EradiGator - Heavy Duty Chopper Pump Mixes & Chops To Clean Your Wet Well
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POPL Tarm WWTP
