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
ABSTRACT
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.
