GRANT NUMBER:  NA66FD0017          NMFS NUMBER:  95-NER-087

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

AUTHOR: Don Karp

PUBLISH DATE:  November 30, 1999

AVAILABLE FROM:  National Marine Fisheries Service, Northeast Region, One Blackburn Drive, Gloucester, MA 01930.  TELEPHONE:  (508) 281-9267

ABSTRACT

A pilot lab study tested the ability of a constructed wetland (CWL) to remove phosphate and other aquacultural wastes. Bioshelter's (BSI's) CWL had primary treatment drying beds (PTDBs) with sand planted in phragmites. Secondary treatment trenches (STTs) composed of peat and rockwool were planted in reed canary grass. The STT media functioned 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 PTDB effluent were run through the reactor, most of the phosphate continued to be removed without cessation. BSI plans to take advantage of this chemistry in subsequent design modifications, to remove most of the phosphate upstream from the STTs. During a year of bimonthly monitoring, the average phosphate leaving the greenhouse was 30mg/L. To reach the goal proposed for phosphate discharge (0.03 mg/L), 99.9 percent would need to be removed by the CWL. Refinements made in 1998, including an aeration step, resulted in a 50 percent removal. Laboratory studies showed that reduction to 2.7 mg/L is possible in water just as it leaves the greenhouse. By combining aeration with ferric chloride, a total removal efficiency of 91 percent was achieved. To reach the goal set forth in the proposal, another 9 percent needs to be removed. This next step of removal, going from 2.7 mg/L to 0.03 mg/L (or 98.9 percent), will be very difficult, although BSI has obtained several insights that may contribute to the eventual successful realization of this goal.