Employing a type of filter unit not previously used in southwest Florida and juggling the environmental concerns of three permitting agencies are just a couple of the challenges HDR is helping North Fort Myers Utility, Inc. (NFMU) solve during the expansion of its Del Prado wastewater treatment plant.
NFMU officials were seeking a way to expand capacity of its wastewater facility, which is located in a compact, non-expandable site. Using disc fabric filters for processing effluent water – which has proven to be effective in other parts of the country – will help the Del Prado plant overcome its site limitations and still meet aggressive goals.
The disc filters use about one-sixth of the footprint that effluent filters would normally require for a project of this size. There isn't room to expand the site because the plant property is surrounded by a major road on one side and a county-owned preserve on the other three.
Even with those restrictions, the Del Prado treatment plant expansion is scheduled to more than double its capacity – from 3.5 million gallons per day to 7.5 mgd. This expansion is necessary to meet the growing needs of the area and of customers who were asking for more water to use on golf courses and large-use landscaped areas. With the South Florida Water Management District (SFWMD) implementing additional water use restrictions, the demand for reclaimed water continues to increase.
The plant is expected to provide high quality reclaimed water to dispose of the effluent to these public access irrigation sites instead of the current method of using deep injection wells. To limit nitrate levels in the effluent during HDR’s preliminary design, BioWin® biological process computer modeling was used to size the biological nutrient removal (BNR) process basins for the proposed expansion.
This modeling resulted in including two new 2.5 mgd average daily flow Eimco Water Technologies DenitIR® process basins for partial nitrogen BNR with mechanically mixed anoxic basins and Carrousel® aeration basins in the plant expansion proposal.
BNR is a fast-growing method of removing biological pollutants, primarily nitrogen and phosphorus, from wastewater. Implementing this type of nutrient removal process in this design means future upgrades to the plant won’t be necessary to continue providing low effluent nitrate levels.
NFMU officials hope to begin conventional bidding of the project in the first quarter of 2008 and that HDR will provide the post-design construction services for the project.