Introduction 411 Trends

Changes in the basic approach to the design of pond systems in the past 20 years have been limited primarily to the introduction of floating plastic partitions to improve the hydraulic characteristics of the pond system, modifications to basic designs, and the development of a wider selection of more efficient aeration equipment. Several modifications of complete mix and partial mix combinations have been developed and evaluated, but the basic design concepts are unchanged. Examples of these modifications are the BIOLAC® processes, the Rich aerated lagoon design procedures, and the LemTec® biological treatment process. These among other modifications are described in this chapter.

The importance of hydraulic characteristics was emphasized in the 1983 EPA lagoon design manual (USEPA, 1983) and has been restated numerous times in many publications; however, based on the number of pond systems constructed over the past 20 years with poor hydraulic characteristics, one would assume that many designers have not read the literature or have ignored what they read. More recent designs have improved hydraulic designs considerably, and it is hoped that this trend will continue.

The trend toward omitting redundancy in the design of lagoon systems has been alarming. It appears that little thought is given to the need for maintenance in the future. Operating costs associated with aerated lagoon systems frequently have been ignored or overlooked in comparing options available to a community. The initial cost of systems without redundancy obviously is lower than that obtained with systems that include flexibility in operation, but the cost to the environment and the owner will be far greater when maintenance is required.

Several design procedures have been proposed and implemented since the 1983 design manual was written. Several have been applied, some with great success and others with moderate success. Some of these modifications have been developed and operated successfully in warm climates, and the application of these systems has expanded to cold climates. The degree of success with these systems has varied, and much of the lack of success can be attributed to a lack of valid design information and considerable experimentation on the part of designers. An extensive description of these systems along with a comparison with more conventional design methods are sorely needed. The major procedures, processes, and design methods, old and new, are listed below and described in the following sections:

• Facultative ponds

• Partial-mix ponds

• Complete-mix ponds

• Anaerobic ponds

• Controlled discharge pond

• Complete retention pond

• Hydrograph controlled release

• High-performance aerated pond systems (Rich design)

• Proprietary systems

• Advanced Integrated Wastewater Pond Systems® (AIWPS®) (Oswald Design)

• BIOLAC® process (activated sludge in earthen ponds)

• Lemna systems

• LAS International, Ltd.

• Nitrogen removal in pond systems (including proprietary systems)

• Modified high-performance aerated pond systems for nitrification and denitrification

• Nitrogen removal in ponds coupled with wetlands and gravel bed nitrification filters

• Control of algae and design of settling basins

• Hydraulic control of ponds

• Phosphorus removal

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