Renovation of Phosphorus and Other....
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GRANT NUMBER:  NA66FD0017           NMFS NUMBER:  95-NER-087

REPORT TITLE:  Renovation of Phosphorus and Other Aquacultural Wastes using Constructed Wetlands with Peat and Rockwool

AUTHOR:  Karp, Don

PUBLISH DATE:  January 21, 2000

AVAILABLE FROM:  National Marine Fisheries Service, Northeast Region, One Blackburn Drive, Gloucester, MA 01930.  TELEPHONE:  (978) 281-9267


A pilot study in the lab tested the ability of a constructed wetland (CWL) to remove phosphate and other aquacultural wastes.  Bioshelter’s (BSI’s) CWL has primary treatment drying beds (PTDB’s) with sand planted in phragmites.   Secondary treatment trenches (STT’s) composed of peat and rockwool are planted in reed canarygrass.  The STT media functions as an unsaturated, subsurface flow environment with a high surface area enhancing bacterial activity and enabling the CWL to handle waste in a small area. Originally, the project proposed addition of dopants to STT media to bind phosphate. Lab studies using a packed column reactor loaded with PTDB effluent produced some unexpected results. When large volumes of PTBD effluent were run through the reactor, most of the phosphate continued to be removed without cessation.   BSI postulated that phosphate in watsewater leaving the PTBD binds iron rendering it unavailable to the phosphate assay before passing through the reactor. BSI plans to take advantage of this chemistry in subsequent design modifications and remove most of the phosphate upstream from the STT’s.

During a year of bimonthly monitoring the average phosphate leaving the greenhouse was 30 mg/L. To reach the goal proposed for phosphate discharge of 0.03g/L,99.9% would need to be removed by the CWL. Refinements made in 1998, including an aeration step, resulted in a 50% removal. Laboratory studies showed reduction to 2.7 mg/L is possible water just as it leaves the greenhouse. By combining aeration with ferric chloride addition a total removal efficiency of 91% was achieved. To reach the goal set forth in the proposal another 9% needs to be removed. This next step of removal, going from 2.7 mg/L to 0.03 mg/L or 98.9%, will be very difficult.  BSI has several insights to continue this pursuit.  Conventional sewage treatment systems require seven times the capital outlay to set up, and cost over 200 times as much to maintain, based on this research and previous work. The CWL is inexpensive, efficient and simple to maintain, encouraging its adoption.

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