Cover and shade (no chemical, maintenance free)
Cover of any type, solid or modular, that will prevent light from entering the water column of a lagoon will prevent the growth of algae. Commercially available floating polyester fabrics have been used to shade aerated lagoons. However, solid covers tend to have several drawbacks and will not last as long as modular covers.
Modular covers are the only permanent, electricity free, maintenance free, chemical free, method available to stop algae growth and maintain lagoon mostly algae free. When correctly sized, a modular floating cover will prevent algae from growing by simply blocking sunlight and therefore photosynthesis. It will also reduce evaporation and reduce the water temperature. Compared to other methods, it is more capital intensive but always cheaper in the long run. Studies shows that a modular floating cover is, over a period of 10 years or more, significantly cheaper than other option methods of algae control as it only represents a one time expense. Cover such as the Hexoshield cover from AWTT has proven to be one of the most efficient modular covers for algae and evaporation reduction by providing constant coverage even in high winds.
Wetland floating covers can also be used. Just like regular floating covers, they also provide areas for beneficial bacteria to grow.
If you cannot afford a complete cover, you may want to temporary control the algae until colder temperatures slow down growth. Information is available algae control method here.
During the late 1960’s and early 1970’s, much research was conducted on the removal of algae in the effluents of lagoon. At least three review papers describes the scope of such research (Kothandaraman and Evans 1972; Middlebrooks et al. 1974; Parker 1975). A wide range of wastewater treatment processes were investigated in the hope that effluent treatment would be economically feasible. With a single exception, it appears that none of the processes are at the present considered to be feasible, especially for the treatment of aerated lagoon effluents. The exception is intermittent sand filtration, which is used primarily to achieve nitrification, the removal of algae being an added benefit. The performance of intermittent sand filtration in the treatment of aerated lagoon effluents varies depending on operation and type. Rapid sand filtration has two disadvantages. The removal of some algal species is marginal, and there is always the problem of what to do with the back-wash water. If the back-wash is simply recycled to the lagoon, algae accumulates in the lagoon, causing more frequent back wash. Modular covers still represent the most viable option to eliminate algae in a lagoon.
UV Clarifiers & Sterilizers
For small pond, A UV clarifier is a safe, effective, and proven way to reducing water borne or free-floating algae. A properly performing UV clarifier can achieve a 99% reduction in waterborne algae. In addition, the cleansing effect of UV clarification may eliminate many harmful biological organisms.
UV clarification by itself will not adversely affect your pond’s inhabitants, requires little maintenance, and is available in various wattages, so it is easy to match to any pond size. Adequate biological and mechanical filtration must be used when operating a UV clarifier, as the added waste from the dying algae must be removed regularly to prevent polluting water conditions. It is important to clean all mechanical and chemical filters regularly, and even more frequently when using additives to control algae.
It is important to recognize that UV clarification could also kill any beneficial bacteria free-floating in the pond. While this is not a problem in an established system, it may be necessary to delay use of the unit to allow for re-growth of bacteria after your filter has recovered from the winter. Use of bacterial additives is not recommended in ponds while running a UV clarifier because the added bacteria will likely be efficiently eradicated.