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Technology mounds between the hoses or below the vertical lift aerator. In these cases, water mixing is minimal at best. These mounds, or rows, of sludge in waste lagoons short- en the life of the lagoon and provide major problems for the owner. The first problems that appear are odors, extremely high algal blooms, and the inability of the water in the lagoon to hold dissolved oxygen through the night. Eventually, the degradation of effluent water quality results in problems with lagoon owners' state and local environmental quality authorities. When a sludge mound is analyzed, it is common for the mound to include from 30% to 60% undigested organic sol- ids. These are solids that could not be digested by the natu- ral bacteria in the lagoons, primarily, because of the excess of noxic gases from biological waste trapped in the sludge mounds. Visual proof of the existence of this trapped gas is the large methane bubbles that break the surface of a waste lagoon throughout the year. Solar Powered Mixing A recent technology introduced to the lagoon industry to aid water mixing is the solar-powered surface skimmer. While these products have the advantage of not requiring electric- ity, their effectiveness as true lagoon mixers is limited. In fact, they do cause a small amount of surface mixing, but the mix- ing influence is not much greater than a constant fair wind over the surface of the lagoon. There is never enough move- ment to affect the sludge mounds that have naturally built up on the lagoon bottom; so, eventually, the effluent water quality of lagoons using this technology will exhibit the same negative results as if they were never used. This minimal mixing influence does help in keeping algae mixed — to a point — as long as there are large numbers of the mixers in a relatively small area. But initial cost and maintenance upkeep have often been recognized as a poor cost-to-advantage ratio. The Water-Moving Aerator Just over three years ago, a new technology was introduced to the waste lagoon industry for the rehabilitation of old waste lagoons, some of which cannot meet effluent permit requirements due to the amount of sludge in the lagoon. This patented technology is unique because it recognizes that sludge mounds exist and understands how they negatively affect water quality. The Model WQA Water Moving Aerator performs two key requirements necessary for the complete success of any waste lagoon: • The continuous pressure of mov- ing water that slowly falls to the lagoon bottom to quietly move sludge for full biological digestion of organic wastes, and • Adding dissolved oxygen required to keep the lagoon's natu- ral biology capable of digesting the organic sludge. This unique aerator design uses only two horsepower of energy to move from two to five acres of water continuously — not on the surface — but on the bottom, where the weight of the water is used to shear the mounds of sludge and break them up. Within several days, the sludge becomes a low level, fluid mass. This movement allows for natural bacteria in the lagoon sediments to digest the organic sludge. The slow but con- tinuous movement of the sludge also frees trapped ammonia and nitrogen gases to oxidize in the water column. Also, due to the downward move- ment of the water within the water column, a slight vacuum pulls algae 42 Water Online The Magazine, Wastewater Edition ■ wateronline.com