MODIFIED AERATED LAGOON WITH TERTIARY WETLAND TREATMENT
Abstract:In 1990, Tangipahoa Parish Sewerage District No. 1 was required to provide sewer service to an area Southeast of the City of Hammond, but lying out of the city limits, which consisted of a densely populated area of subdivisions and apartment complexes with individual or no waste treatment. None of the existing subdivision treatment plants could be expanded to service the entire eighteen (18) square mile area nor would the City of Hammond provide sewer service to the area. Several older developments had collection lines but no treatment, resulting in the discharge of large quantities of untreated waste. Further, the area was too affluent to qualify for a grant for the entire area. In addition to a sewer collection system, the area would require a sewerage treatment facility capable of treating a minimum of 200,000 gpd and a maximum of 500,000 gpd. No existing treatment process would provide the level of treatment required for the funds that were available for the project. Because of the fixed cost of the collection system only two hundred fifty thousand dollars (250,000.00) was available to acquire the site and build the waste treatment facility. Further, the facility had to have low operating cost due to the fact that the District did not have a tax base and had to operate solely on sewer service charges.
Tangipahoa Parish Sewer District No. 1, whose jurisdiction the area fell under, sought and received a low interest loan from FmHA. However, the maximum amount that could be borrowed was eight hundred thousand dollars (800,000.00). Because of the fixed cost of the collection system, only two hundred fifty thousand dollars (250,000.00) was available to acquire the site and build the waste treatment facility.
Therefore, in 1991, a new type of facility was designed and constructed specifically for this application in order to reduce construction and operation cost and improve reliability. The facility was based on empirical design parameters amassed by the District since its inception. This facility was so successful that a second facility was constructed in the Velma Community in 1995 using LCDBG funds. Both facilities have been extensively tested to empirically determine their operating parameters and to verify the design used. The effluent test results for the Southeast Hammond Facility for the last five years have been summarized in Table 1.
A facility capable of treating the specified waste load to tertiary limits was constructed for one hundred eighty three thousand dollars (183,000.00) on a five-acre (5) tract which was purchased for twenty thousand (20,000.00). The facility consists of an Aerated Lagoon followed by a High Rate Clarifier, which re-circulates the M.L.V.S.S. This is followed by a diffused air basin which discharges over a rock filter wall to an anoxic basin. The discharge from the anoxic basin is passively re-aerated prior to entering a manmade wetland which polishes and disinfects the waste stream. The effluent then enters a final basin after passing over a rock filter wall. In this basin chlorinated water is added, if necessary. The facility treated its initial waste load of 200,000 gpd and met its discharge limits without chlorination, and with only one of its three high rate clarifiers in operation, see attached results. The facility currently treats 440,000 gpd and the effluent BOD5 is normally less than 10.0 ppm and frequently less than 3.0 ppm. The facility currently costs one thousand six hundred sixty one dollars and sixty-seven cents (1,661.67) per month to operate. This cost, which is from the Districts most recent audit, includes power, labor, chemicals, and maintenance cost. Because of the success of this design the District is currently constructing two (2) additional regional facilities using R.U.S. funds which will replace six (6) conventional facilities and operate for one half (½) the current cost.
The facility constructed by the District provides a low cost innovative alternate to currently accepted methods of waste treatment. The cost of construction is fifty (50) cents per gallon and the cost of operation is less than one half (½) cents per gallon per month. Therefore, this innovative method of waste treatment, which is a site specific design, can be an economic waste treatment alternative for smaller communities, especially those with limited resources for labor and operation who are forced to hire unskilled personnel.
Document Type: Research Article
Publication date: January 1, 2003
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