LAGOON MANAGEMENT USING BODOX® - the GREEN Solution
ESC Technical Note 2
ESC Technical Note 1 discusses the operation of a lagoon wastewater treatment system. In this technical note, we will explain one method of making a lagoon system work.
We, at ESC, along with our associates including engineers, operators, biochemists, and biologists, have developed a RECIPE FOR SUCCESS with respect to treating wastewater in a lagoon. It is called BODOX® - the GREEN SOLUTION. The reason for the name is that BODOX® uses all natural substances and recyclable materials. It includes four major elements:
. Algae and ammonia control
. Sludge reduction
Aeration alone will not normally produce effluent quality needed for most permits. Aeration makes treatment more efficient; thus, less land is needed. Aerators must also be good mixers. The suspension of solids is important in reducing the oxygen demand and limiting the growth of algae. It has been reported that at about 30 HP/MG of volume, little or no algae will grow. At this mixing intensity, the algae have little or no exposure to sunlight that is required for their growth and reproduction. A five-acre pond five feet deep would require 240 HP to minimize or eliminate the growth of algae. This amounts to approximately $360 per day or over $130,000 per year. This method of algae control is prohibitively expensive.
However, an aeration/mixing intensity of about 5 HP/MG is important because it: (1) prevents thermal stratification reducing the growth of algae; (2) helps stabilize pH by removing most of the carbon dioxide; and (3) minimizes feedback of BOD5 and nutrients from bottom sediments.
Typical design of lagoons will include an aerated first cell followed by an un-aerated second and perhaps third cell. It is vitally important for aeration and mixing to occur in all cells including settling and polishing cells so that the lagoon system has a better chance of meeting effluent limits.
Since aeration may be 50-90% of total energy cost in a municipal facility, it makes good sense and "cents" to get the most energy-efficient aeration system available for a particular lagoon operation. Fine bubble diffused air systems on or just above the lagoon bottom usually will be among the most energy-efficient and also will provide the best mixing.
In evaluating aeration systems, ask the manufacturer or vendor to help calculate the cost of a pound of oxygen transferred to the wastewater. This number will give a clue as to the long term operational cost of the aeration system. The daily cost to run a one horsepower electric motor at 8.5˘ per kilowatt hour will be approximately $1.50.
ALGAE AND AMMONIA CONTROL
We could write a book about the various means available for controlling algae all of which have limitations. Even though algae are an essential part of pond biology, they tend to be an overall liability in lagoon wastewater treatment. Consideration should, therefore, be given by the operator to control algae growth.
The recipe for successful control of algae involves the control of nutrients in the water column and in the sludge. This can be done by using all natural substances that bind the nitrogen and allow the bacteria time to consume it. In the meantime, algae which must have nitrogen to grow are deprived of an essential nutrient and no longer grow or reproduce. The dead algae are then consumed by other natural organisms some of which must be added.
The theory is not to eliminate algae because they are important part of lagoon biology and a cheap source of oxygen. Algae are controlled to the extent that blooms do not occur. Therefore, an understanding of the natural substances to be used for nutrient control is essential. Also, it is very important to have a good knowledge of pond biology and dosing requirements.
Sludge reduction is accomplished by the addition of natural micro-organisms that attack the organic material in the water column and in the bottom sediments. This is another reason why mixing is important especially in a lagoon that has been in service for a long period or one that for some unexplained reason tends to accumulate considerable sludge. These added organisms will first attack the food in the bottom sediment because it is readily available.
In the process of consuming organic substances in the bottom sediment, the sludge will be reduced significantly in a few months. A recent pilot program in Maine showed that the depth of bottom sludge was reduced by 34% from October to February - the coldest part of winter.
This process of sludge reduction is called bio-dredging. It is much more efficient, much less disruptive, and much less costly than mechanical dredging. Additionally, hauling and disposal costs are eliminated.
Some of the benefits to be derived from implementing BODOX® in a wastewater treatment facility include:
. Reduction in sludge accumulation
. Lower operating cost
. Improved air usage
. Improved settling
. Improved handling of shock and slug loads
. Improved ammonia reduction
. Elimination of algal blooms
A lagoon by any name is a treatment-effective and cost-effective manner for treating municipal and industrial wastes. The disadvantages can be overcome with new information on controlling algae and ammonia and reducing sludge. Therefore, it is my choice for wastewater treatment. If a municipality or industry has a wastewater treatment lagoon, it should be managed in such a way that it will continue to serve the owner well and be a very good asset.
This document is the property of Environmental Services Company, LLC. It is not to be duplicated in any form without the express written consent of the owner. It may not be used for any purpose other than its intended purpose.