Robert C. Hoehn

Complementary uses of chlorine dioxide and ozone for drinking water treatment

Abstract Application of both chlorine dioxide (ClO2) and ozone (O3) at a single drinking water treatment plant is rare in the United States but not in other countries. European utilities that use both oxidants commonly add ozone at one or more points prior to filtration and then apply ClO2 after filtration. In this mode, the oxidant demand is considerably reduced prior to ClO2 addition, thus reducing the ClO2 requirement for maintaining a concentration of 0.1 mg/L to 0.2 mg/L in the distribution system. The combined use of ClO2 and O3 has merit in many situations, but the way in which the oxidants are sequenced (e.g. pre‐ozonation followed by ClO2 treatment or vice versa) is critical in terms of finished water quality. The objectives of this paper are: (1) to review the most common water‐treatment goals associated with ClO2 and O3, and (2) to discuss the potential consequences and benefits of applying both oxidants at various points in the treatment train.

THE IMPACT OF ATMOSPHERIC CONTAMINANTS ON STORM WATER QUALITY IN AN URBAN AREA

Summary Composite precipitation samples were collected by recording raingages at nine stations in the Virginia portion of the greater Washington, D.C. metropolitan area. The samples were analyzed for COD, TOC, all nitrogen and phosphorus forms, and seven heavy metals; iron, zinc, lead, copper, cadmium, chromium and manganese. The results showed that wash out of the atmospheric contaminants occurred during the early stages of precipitation events, and that these contaminants are present in sufficient quantity to have a significant impact on surface water quality. Samples tended to contain similar amounts of pollutants after the same rainfall event regardless of land use location and distance from the center city up to 33 miles. Ranking techniques indicated, however, that precipitation in agricultural and land disturbance areas tends to contain more nutrients. Principal factors affecting the total quantity of pollutants in rainfall are atmospheric conditions (stagnant or turbulent) and antecedent conditions (time since previous precipitation event).

Revaluation of ortho-phosphorus and inorganic nitrogen levels in an antarctic meromictic lake

Recent studies of Lake Bonney, a meromictic Antarctic lake, utilized techniques modified for hypersaline waters and produced results significantly different from those of previous investigators. Notably higher values are reported for ammonia and nitrate, while phosphorus levels tend to be in distinct disagreement with those obtained by other workers except for limited data reported by one author using a technique similar to that used in the current studies. The method of standard additions was employed as a partial solution to salinity interferences.

Trace element distributions in an antarctic meromictic lake

Summary1.The relative abundance in Lake Bonney of the trace elements studied was B≫M>Fe>Cu>Ni>Mo>Co, with more than 90 per cent of each element in the monimolimnion.2.The monimolimnion contains concentrations of B which are probably toxic to phytoplankton, and Cu concentrations which are at least potetially toxic to these organisms.3.Concentrations of B, Cu, and Mn in the mixolimnion occassionally reach potentially toxic concentrations, but there exist mitigating influences such as high calcium levels.4.The relative amounts of trace elements contributed by the Sollas-Lacroix meltstream to the lake were Mn>Fe>Cu>Ni≃Co>B. Except for Co and Mo, the Sollas-Lacroix meltstream did not appear to contribute trace elements in quantities which would explain the weekly changes found in the mixolimnion.

THE STIMULATION OF AUTOTROPHIC PRODUCTION BY URBAN STORMWATER-BORNE NUTRIENTS

SUMMARY Composite samples of stormwater runoff were collected from thirteen urban catchments representing six homogeneous land uses in the Virginia suburbs of Washington, D. C., USA. Phosphorus and nitrogen concentrations and availability in the stormwater samples were found to be sufficient to support moderate to high levels of production of the test alga, S. capricornutum . Lead and zinc concentrations in stormwater from certain urban land uses were found to be inhibitory to algal production. The annual average biomass to be supported by urban stormwater was found to bear a generally positive relationship to density of development.

THE SIGNIFICANCE OF PLANT NUTRIENT YIELDS IN RUNOFF FROM A MIXED LAND USE WATERSHED

Plant nutrient production was monitored during dry weather and storm flow conditions in seven sub-basins of the Occoquan Watershed. The areas monitored included land uses devoted to silviculture, agriculture, and suburban-urban development. Point source discharges were found to account for less than fifteen percent of total nutrient load during the period of minimum storm runoff. Drainage from urban land was found to export much more nitrogen and phosphorus than an equivalent amount of rural land. Log-linear relationships were observed to exist between plant nutrient loading(kg/ha) and runoff quantity (cm over the basin area) Log-linear regression models showed the effect of an impoundment at an intermediate point in the basin in reducing pollutant transport.

The Importance of Hydrologic Factors on the Relative Eutrophic Impacts of Point and Non-Point Pollution in a Reservoir

The Occoquan Reservoir, located downstream of a rapidly urbanizing Northern Virginia (USA) area, is a highly eutrophic water supply, which exhibits all the symptoms of excessive enrichment. Data collected during an intensive monitoring program since 1972 have vividly demonstrated the relative impacts of stormwater runoff and point-source sewage dis-charges on water quality.

Reactor technique for prediction of dissolved oxygen profiles in streams

A laboratory experiment that can provide significant design information to an environmental scientist or engineer can be performed rapidly and inexpensively with an open stirred-reactor that simulates a receiving stream. The experiment requires only a laboratory beaker, stirring apparatus, dissolved oxygen meter, wastewater sample and receiving stream sample. Wastewater and receiving stream water are mixed in the laboratory beaker and are stirred at different speeds to obtain different reaeration rates. A probe is used to monitor dissolved oxygen concentrations of the mixture. A series of experiments were performed at different waste loadings and different reaeration rates. Sample results are shown which indicate the depletion of dissolved oxygen due both to carbonaceous and nitrogeneous oxygen demands. This technique can be used to predict response of a receiving stream to a waste discharge without use of a mathematical model. Results are shown which illustrate the difference between experimental results and theoretical predictions.

Evaluation of select techniques to model nonpoint source flows and specific pollutants from small watersheds

Abstract An existing hydrologic model has been altered to allow simulations and predictions of suspended sediment and bound ion loadings. Application to synthetic and actual data bases illustrates the models usefulness.