In this section:
Lagoon Aeration
The Problem
Typical license requirements for lagoon effluent CBOD5 (Carbonaceous Biochemical Oxygen Demand) concentrations range from 10 to 25 mg/l. Existing pond based wastewater treatment systems often exceed allowable concentrations when there is:
- No supplementary aeration (shallow wastewater stabilization ponds)
- Failing or inadequate aeration systems (existing aerated lagoons)
- Inadequate hydraulic retention time (HRT), or organic overloading in existing ponds as a result of loads or flows exceeding the original design, or because of excessive sludge accumulation.
The Nelson Environmental Solution
In an OPTAER® lagoon based wastewater treatment system, CBOD5 is reduced to carbon dioxide, water, and inert ash by natural bacteria. The bacteria receive their oxygen supply from air provided through fine bubble or coarse bubble aeration diffusers. These aeration technologies are a proven means of effectively providing optimum CBOD5 reduction in newly constructed and retrofitted existing lagoon systems.
Failing existing aeration systems can be upgraded without dewatering lagoons or interrupting service. With various aeration technologies and patented float-sink and floating air header options, upgrades of complex lagoon configurations are feasible.
OPTAER® Aeration Diffusers: OPTAER® fine bubble aeration diffusers (HA-16, HA-24 and TA22) are specifically designed for lagoon aeration. The HA series diffuser is constructed with an HDPE air distribution body with individual tubular micro-porous membrane fingers extending outwards in a horizontal plane. This unique design prevents bubbles from coalescing, and results in an exceptional oxygen transfer rate with minimal head loss. Each diffuser can efficiently handle airflows ranging from 6 – 25 scfm, allowing for operational flexibility in the aerated lagoon.
Clean water oxygen transfer testing shows negligible changes in both the operating pressure and oxygen transfer ability of the OPTAER fine bubble diffusers even after five years of operation in wastewater. Depending on the design application, the diffusers have a design lifecycle of 10-15 years.
OPTAER HC-16 Coarse bubble aeration diffusers are constructed of HDPE, which provides excellent chemical and corrosion resistance. The HC-16 diffusers are an excellent option for systems where reduced backpressure is required, or in extreme cases where water quality is not compatible with fine bubble diffusers. The HC-16 diffusers are interchangeable with HA-16, HA-24 and TA22 diffusers on any of Nelson Environmental's aeration header systems.
OPTAER® Aeration Header and Lateral Systems
Floating Laterals: For most applications, floating HDPE laterals are ideal for supplying air to the aeration diffusers. A cost effective and reliable air supply system, floating laterals offer important advantages.
- Reduced slope maintenance compared to out of water header systems (i.e. grass cutting)
- Ideal for ponds/lagoons with fluctuations in water depth
- All installation and maintenance can be performed from a boat without dewatering
- Can be adapted to any pond shape or size
- Ensures that all diffusers are level and balanced
Laterals are secured against wind and wave action with a stainless steel cable system. The cables are fastened to anchors at the tops of the berm. Nelson Environmental's automatic lateral self-tensioning system allows for expansion and contraction of laterals and water level fluctuations.
Float-Sink (Patented): Float-Sink aeration laterals are ideal for intensively aerated complete mix lagoons where diffuser retrieval capability is required without dewatering.
- System can be raised or lowered by simply manipulating ballast control valves
- Diffuser and header maintenance can be performed from water surface
- System can be installed without basin dewatering
- No concrete weights or other components are left on the pond bottom to interfere with sludge removal when the system is raised
All header and lateral piping is constructed with UV resistant High Density Polyethylene (HDPE) pipe. All header joints and saddles are thermally fused connections, providing long-term reliability.
Both floating laterals and float-sink laterals connect to shallow buried HDPE main air supply headers. Headers are typically buried above the water line in the berm between ponds, or in the lagoon liner anchor trench. HDPE Headers do not corrode, and are not susceptible to cold temperature damage, providing excellent long-term reliability. Laterals are individually valved and typically enter the pond above the liner, eliminating most liner penetrations.
Performance
Typical CBOD5 removal efficiencies in an OPTAER municipal wastewater lagoon are 90 to 95 percent with effluent concentrations of 10 to 25 mg/l.
