What Are Facultative Biological WWTPs Capable Of?
Gurney Environmental's advanced biological systems are well-proven and easily capable of very consistent performance with high processing rates, advanced treatment levels, no perceptible odours, no sludge accumulations and excellent accommodation of peak and shock flows. They can, in some cases, even be practical for very large population applications as well.
What has been the cause of misconceptions and myths about "lagoon-based" biological systems? Essentially, incorrect myths, wrong assumptions and poor design. Often lagoon systems are actually designed assuming that erratic, poor performance is "normal" operation.
The "Cardinal Sins" of Lagoon Design
In correct "advanced" facultative biological lagoon design, there are several key design factors that will affect various aspects of performance. Using Gurney Environmental's advanced design criteria – based on years of correcting and resolving problems with existing wwtp's – ensures superior performance.
Wastewater Design Considerations
Cell Geometry and Flow +
An extraordinarily critical factor in the performance of lagoons is correct physical design. Based on experience with hundreds of lagoon-based municipal and industrial wwtp's, experience proved that better physical design results in superior, more reliable, robust and predictable performance of Gurney Environmental designed wwtp's.
Detention Time +
The amount of time wastewater spends in each stage of treatment is highly critical and is temperature dependent. Modern lagoon-based systems are typically comprised of two or three stages of treatment — primary, secondary and possibly a tertiary or polishing stage. Each stage is designed for an approximately 80–85% reduction at summer water temperatures (20° C) taking a predictable amount of time at any given water temperature for the biology to establish and perform its reductions. Colder water temperatures are offset by longer detention times. However, note that historically systems successfully operate in 1- 2° C water temperatures. The warmer the average yearly water temperature, the faster the biological/biochemical removal rate.
Surface Organic Loading Rate +
Nature can only provide a certain amount of natural aeration/oxygen production through photosynthesis and atmospheric absorption for a given climate. In colder climates, correct non-aerated/"accelerated" primary cell loadings typically run 20–25 kg/ha/day, while warmer climates can be loaded at up to 50–75 kg/ha/day.
The Effects of Loading Rates That Are Too High
Loadings in excess of these rates in non-accelerated systems will cause the biology to become dormant (anoxic) and sluggish resulting in odours, sludge accumulations and lower processing rates. Therefore, very specialised supplemental aeration and process "optimisation" equipment must be added to systems with higher loadings. Correct loading rates and detention times have been proven to provide strong, reliable and consistent performance in full-sized, commercially successful facilities — not just in "test" or experimental systems.
Ignoring these basic design rules simply means that lagoon-based systems will not perform as well as correctly designed, optimised lagoons can and do.
"Real-World" Cell Loading +
Correct cell loading is critical in order to maintain truly aerobic cells. Unfortunately, many lagoons are designed so that a bulk of the organic loading is concentrated within the influent zone and the waste then short circuits directly to the effluent structure reducing actual true detention time. Massive overloading occurs in that influent-to-effluent stream whilst huge areas of the cells are dramatically under-loaded and poorly utilised.
The simple addition of the Gurney Environmental SERIES 3 windpowered aeration/optimisation units within the influent zone and throughout the cell does several critical things:
Disperses the loading out from the influent zone, thereby uniformly loading the entire cell area;
Increases true detention time by eliminating short circuiting, thus increasing removal rates;
Improves the DO of the entire water column without disturbing the critical layering of the cell.