FABE 652
Ecosystems for waste treatment

Lecture #7 -  4/22/03
Macrophytes in Ecological Treatment Systems

Begin class with discussion about how to better design the SAS to utilize more of the incoming ‘waste’ as a ‘resource.’

Peterson, S.B. and Teal, J.M. The role of plants in ecologically engineered wastewater treatment systems. Ecological Engineering. 1996. 6: 137-148. Harwich MA-SAS

DeBusk, T.A., Peterson, J.E., Reddy, K.R. 1995. Use of aquatic plants and terrestrial plants for removing phosphorus from dairy wastewaters. Ecological Engineering. 1995. 5: 371-390.

-Compare Harwich and Marion SAS systems. Lack of conditioning tank in Harwich is only difference. Both systems have similar performance—most nutrients, solids removed in sludge from primary clarifier. Had to add carbon (acetate) to stimulate denitrification rates-similar to Burlington study. Costs were found to be lower than conventional options.

Now focus on vegetation.

-This study tracks the contribution of the macrophytes to water quality improvements in an Ecological Treatment System (SAS).

IV. Role of Plants (overhead)

Purpose - provide high surface area for fixed film attachment (p.141), natural odor control, maintain volatile organic compounds (VOC) in the water column—combine suspended and attached growth processes, biodiversity of microbes increased?

What are the main plant species? How do they compare with our system? (water hyacinth, Salix nigra-black willow, red maple-acer rubrum, and others). While there is some variation a common mixture of species is beginning to emerge for these systems.

Assimilation - 4.4%N & 2.5% P overall (Tab.2 ’96), 1.2%N & 0.3%P marsh, relative to other systems % are low-but loading rate high-more mass of N than other systems

Disagree with assertions (p.143, 144) that vegetation uptake and harvest is principle instrument for nutrient removal. But looking at Table 4 assimilation is more important in strictly wetlands than in ETS.

Compare loading rates across systems—for ETS the loading rates are much higher than trad. Wetlands.

Harvesting - 15 kg/m2/yr. Productivity of plants similar to systems with lower loading rates.

Loading (Tab.4 ’96) - much higher than trad. Wetland systems (N 238 mg/L vs. <5mg//L, P 48mg/L vs. <5mg/L,

HRT- similar to constructed wetland systems for whole aquatic portion

Plant concentrations - High levels of N (>3%) and P (.3-.6%), Redfield 106/16/1

Metals (Tab.5&6 ’96) - High metals in septage, low percentage removal in plants, preferential uptake by species

Debusk et al.
Water hyacinth is productive—assimilates relatively large amount of N and P (Table 3), has thick root structure with high surface area.

Figures 1 and 2 clearly show effect of temperature and sunlight.

Table 4 denotes difference between observed removal and calculated removal—how can this be explained. Does this have any implication for processes in the root communities?

Figure 3 compare shoot/root ratios. While there is variation often 1:1 is a good assumption. Lack of research about roots.