Dennis B. George

GROWTH OF SOFTSTEM BULRUSH (SCIRPUS VALIDUS) IN MICROCOSMS WITH DIFFERENT HYDROLOGIC REGIMES AND MEDIA DEPTHS

Factors affecting growth of softstem bulrush (Scirpus validus), an obligate wetland plant frequently used in subsurface-flow constructed wetlands in North America, were studied in a controlled environmental chamber. Effects of media depth (30-and 46-cm), hydraulic retention time (HRT) (2- and 6-day), and water-level drawdown (drawdown vs. no drawdown) on plant growth in 24 microcosms were investigated. Weekly root and stem growth was measured and stem health assessed to determine effects of treatments on plant vigor. Water-level drawdown was detrimental to plant growth, increasing the percentage of dead stems. Stem production was higher in microcosms with a 46-cm media depth than those with a 30-cm depth and also higher in microcosms that were permanently flooded than in those with fluctuating water levels. Root production was greater in microcosms with a 30-cm media depth than in those with a 46-cm depth, and root production was also greater in microcosms that were constantly flooded than in those drawn down. Scirpus validus is a robust plant that grows well in gravel media microcosms; however, problems are experienced when rhizomes and roots dry out during water drainage.

Monitoring advanced oxidation of Suwannee River fulvic acid

Environmental context.Potentially toxic disinfection by-products form when water containing humic and fulvic acids is chlorinated to destroy pathogenic microorganisms. A pulsed electrical discharge was examined for its ability to destroy an aquatic fulvic acid by oxidation. Spectroscopically, changes in the organic structures were observed, but carbon content and disinfection by-products were not reduced. Abstract.A pilot-scale pulsed electrical discharge (PED) system was used to treat Suwannee River fulvic acid (SRFA) as a representative precursor material for the formation of disinfection by-products (DBPs), specifically trihalomethane compounds. Ultraviolet-visible and fluorescence spectroscopy, dissolved organic carbon (DOC), and the trihalomethane formation potential (THMFP) were used as analytical parameters to monitor the effects of treatment on the substrate. The potential for SRFA degradation (5 mg L–1 DOC) was examined over 60 min at each of four operational configurations, varying pulse energy and frequency (0.15 J and 60 Hz, 0.15 J and 120 Hz, 0.4 J and 60 Hz, and 0.4 J and 120 Hz) in a factorial design. Statistically significant changes occurred for UV254, EX254EM460, and EX328EM460 under selected conditions; however, concomitant changes in DOC and THMFP were not observed. The composition of SRFA changed, but organic carbon was not mineralised to carbon dioxide. In addition to showing degradation by PED, the significance of the preliminary findings of this research was to demonstrate that spectroscopic monitoring of precursor degradation alone can be misleading, and that whereas ultraviolet-visible and fluorescence spectroscopy indicated degradation of precursor compounds, DOC and THMFP measurements were unchanged and did not support the occurrence of mineralisation in this system.

Prediction of Microcystis Blooms Based on TN:TP Ratio and Lake Origin

We evaluated the relationship between TN:TP ratio and Microcystis growth via a database that includes worldwide lakes based on four types of lake origin (dammed, tectonic, coastal, and volcanic lakes). We used microcosm and mesocosm for the nutrient elution tests with lake water and four kinds of sediment (nontreated, MgO sprinkling treated, dissolved air flotation [DAF] treated, and combined treated sediment) in order to control TN:TP ratio and to suppress Microcystis growth. Microcystis growth was related to TN:TP ratio, with the maximum value at an optimum TN:TP ratio and the minimum values when the TN:TP ratios reached to 0 or ∞. The kurtosis of the distribution curve varied with the type of lake origin; the lowest kurtosis was found in dammed lakes, while the highest was found in volcanic lakes. The lake trophic state could affect the change in the kurtosis, providing much lower kurtosis at eutrophic lakes (dammed lakes) than that at oligotrophic lakes (volcanic lakes). The relationship between TN:TP ratio and Microcystis growth could be explained by the nutrient elution tests under controlled TN:TP ratios through the various sediment treatments. A significant suppression of Microcystis growth of 70% could be achieved when the TN:TP ratios exceeded 21. Lake origin could be regarded as an index including morphological and geographical factors, and controlling the trophic state in lakes. The origin rather than trophic state for lakes could be considered as an important factor of TN:TP influences on Microcystis growth.

Synergistic effects of potassium permanganate and PAC in direct filtration systems for THM precursor removal

Abstract Some traditional methods for reducing trihalomethane concentrations in finished water may be less effective or inappropriate for direct filtration water treatment systems. Reduced prefiltration hydraulic detention times and mass solid loading considerations affect the use of potassium permanganate (KMnO4) and powdered activated carbon (PAC) in direct filtration systems. KMnO4 and PAC were investigated both individually and in combination to determine the effectiveness in reducing maximum total trihalomethane potential (MTP). The effectiveness of the chemicals was evaluated by using jar tests and/or a 23,850 l d−1 direct filtration pilot plant. The results indicated that permanganate oxidation of THM precursors to reduce MTP was ineffective at low concentrations (

The effects of selected iron compounds on the sensitized photooxidation of bromacil

Abstract Sensitized photooxidation processes using methylene blue, riboflavin, and rose bengal degraded bromacil from 70 to 100 percent on silica at pH of 9 or greater in a thirty-six hour irradiation period. The process, however, is inhibited by ferric oxide (Fe 2 O 3 ), ferrous-ferric oxide (Fe 3 O 4 ), and ferric hydroxide (FeO(OH)), the most common forms of iron compounds found in soils. Rose bengal enhanced photolysis showed the least effect of the iron with 71–83 percent degradation of the herbicide in a 36 hour irradiation period at pH greater than 9.

Removal of Nitrogen, Phosphorus and Prodiamine from a Container Nursery by a Subsurface Flow Constructed Wetland

Plant nurseries apply large amounts of agricultural chemicals that may run off causing problems to surface water. Constructed wetlands have been used to treat agricultural chemical runoff. A 128 m2 gravel subsurface flow constructed wetland was designed and installed at Pirtle’s Nursery in Smithville, TN. The wetland was 46 cm deep and contained an estimated 16.5 m3 of water. Softstem bulrush (Scirpus validus), cattails (Typha latifolia L.) and juncus (Juncus spp.) were planted in the wetland. A standpipe controlled water level in the wetland, and a bypass pipe averted heavy flow. Total nitrogen (N), phosphorus (P) and the pesticide prodiamine were measured from the influent and effluent water during daily irrigation events. A valve controlled flow into the wetlands to produce computed nominal hydraulic retention times of 0.7, 1.2 and 1.9 d. A Stevens Chart Recorder measured the influent water level to develop a flow versus water stage correlation at specific valve settings. Mean N removal was 70 to 72% of total influent N. Mean P removal varied from -2 to 10% of total influent P. Mean prodiamine removal ranged from 49 to 65% of total influent prodiamine. The wetland required little maintenance other than occasional sediment removal after heavy rain and occasional sediment flushing of the inflow pipe to maintain flow.

Using microcosms to assess aeration, cement, and clay mitigation of iron contaminated lake sediments

Abstract A sediment‐water phase laboratory microcosm experiment was designed to assess iron dynamics for Fall Creek Lake located in the Cumberland Plateau Region of Tennessee, the United States. Aeration, clay, and cement treatments were compared with control. Representing the lake hypolimnion, microcosms were maintained under dark conditions at 9 ± 1 °C for six months. For the initial six weeks, the dissolved oxygen (DO) concentration in clay, cement and control microcosms was 5–6 mg/L The DO in the aerated microcosms was 10–11 mg/L. After six weeks, the DO concentration was reduced by nitrogen purging to 0–2 mg/L in all microcosms except the aerated one. All treatment microcosms demonstrated significantly lower water column iron concentrations. The rate and extent of iron release from lake sediments to water was influenced by mechanisms involving oxidation and sorption processes. Of the treatments, aeration and clay appeared to be effective in capturing iron released from sediments. Cement treatment cau...