Date of Award

Spring 1986

Project Type

Dissertation

Program or Major

Engineering

Degree Name

Doctor of Philosophy

Abstract

Aquatic treatment systems are a low cost, low energy alternative to conventional treatment systems; they can provide secondary and advanced secondary wastewater treatment capabilities for small communities. Their potential application in temperate climates has been ignored. The research presented here was conducted to examine their applicability for use in temperate regions. A pilot-scale aquatic macrophyte-based aquatic treatment system was designed to treat primary effluent. Four aquatic macrophytes (Elodea nuttallii, Lemna minor, Myriophyllum heterophyllum, Ceratophyllum demersum) were evaluated as candidates. The hydraulic, organic, and nutrient loadings to the reactors were similar to design values for water hyacinth (Eichornia crassipes) systems. Nitrification occurred on a year round basis. Elodea nuttallii was the best candidate. The plant was productive year round (0.5-4.5 g dry wt(.)m('-2)(.)d('-1)) and resistant to fouling by filamentous green algae. Percent removals and removal rates of wastewater constituents in Elodea reactors indicated that these systems can provide advanced secondary treatment capabilities. Removal rates were usually correlated to plant biomass and productivity. When productivities were high, plant uptake accounted for 28-56% of the nitrogen and 61-99% of the phosphorus removal. Detrital sedimentation accounted for a significant proportion of nitrogen and phosphorus removal when the plants were less productive. Denitrification was always an important nitrogen removal mechanism. The total nitrogen (TN) and total phosphorus (TP) content of the macrophytes was high (E. nutallii; 52.6 mg TN(.)g dry wt('-1); 17.7 mg TP(.)g dry wt('-1)), and were not rate-limiting to productivity. Ammonia- and nitrite-oxidizing bacteria were also present in high concentrations in the reactors, particularly in association with macrophyte and sediment samples (NH(,4)('+)-oxidizers, 10('8)(.)g dry wt('-1); NO(,2)('-)-oxidizers, 10('7)(.)g dry wt('-1)). E. nuttallii was shown to be photosynthetically robust; its CO(,2) compensation point ((GAMMA) = 44.4 (mu)l(.)L('-1)), oxygen evolution kinetics (K(,m) (CO(,2)) = 96 (mu)M; V(,max) = 160 (mu)mol(.)mg Chl('-1)(.)h('-1)), and RUBISCO/PEPcase ratio (6.6) indicate that it was adapted to low carbon conditions in the reactor. Isotope disequilibria experiments and metabolic inhibitors were used to show the presence of an active transport HCO(,3)('-)-H('+) symport which provided high internal CO(,2) concentrations; making Elodea particularly well suited for use in aquatic treatment systems where inorganic carbon may, at times, be limiting.

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