Menahem Rebhun

Formation and distribution of haloacetic acids, THM and TOX in chlorination of bromide-Rich Lake water

Abstract Lake Kinneret (Lake Galilee) water has a high bromide content that affects the chlorination process. Disinfection by products (DBP) of highly chlorinated lake water were studied. By combination of GC-MS and HPLC, six haloacetic acids, in which four of them containing bromine, were identified. Tribromo, dibromochloro, and bromochloro acetic acids were found for the first time in high concentrations in chlorinated surface water. Total haloorganic (TOX) formation per unit carbon was low compared with other water sources. THM and dihaloacetic acids formation per unit carbon were in the common, reported ranges, trihaloacetic acids and unidentified TOX had low yields of formation. The TOX was characterized by a high fraction, over 50%, of THM. The identified THMs and haloacetic acids accounted for about 75% of TOX. Brominated species constituted over 85% of the THMs and haloacetic acids. Tribromoacetic acid was found to undergo decomposition to form bromoform. This distribution of the TOX was the result of the following factors: (1) efficiency of bromination process compared with chlorination, (2) high content of aliphatic precursors and (3) decomposition of tribromoacetic acid to bromoform.

Binding of organic solutes to dissolved humic substances and its effects on adsorption and transport in the aquatic environment

Abstract Humic substances constitute a major fraction of dissolved organic matter in natural water and effluents. Their effect on the adsorption of organic contaminants to aquifer material was elucidated, and a model was proposed for the adsorption of organic solutes to aquifer solids in the presence of dissolved humic substances. The model is based on the assumption that organic solute binds to dissolved humic substances in a reversible manner to form a solute-humate complex. Following binding, both free and bound fractions of the organic solute are independently adsorbed onto the solid phase. In order to evaluate the validity of the model, the following parameters were determined: (1) the adsorption coefficient of the organic solute to clay; (2) the binding constant of the solute-humate complex; and (3) the adsorption of humic acid (HA) to clay, assuming that the solute-humate complex is adsorbed similarly to humic acid itself. Using these parameters in the model enabled the effect of dissolved humic substances on adsorption to be evaluated. Experimental results obtained for the adsorption of fluoranthene (a model compound of the PAH group) to clay in the presence of dissolved HA were compared with calculated values derived from the model described above. The sensitivity of the model to various parameters was evaluated and a prediction was made with respect to the effect of dissolved humic substances on the adsorption of a variety of organic solutes. It appears that dissolved humic substances solubilize organic solutes which have higher adsorption coefficients to clay than humic substances, but increase the adsorption of solutes having lower adsorption coefficients relative to humic substances.

Denitrification at various carbon to nitrogen ratios

Abstract The aim of this research was to examine whether the residual dissolved organic matter, remaining in chemically treated raw sewage would be able to satisfy the carbon demand in a denitrification process. In the first stage of research we investigated the effect of type and amount of organic substrate on denitrification efficiency. The critical weight ratios of methanol and sodium acetate to total concentration of nitrite and nitrate which enable the occurrence of complete denitrification were studied. It was found that when the concentration of the organic matter was expressed as BOD, a critical ratio of (mg BOD/mgΣNO x -N) = 2.3 ensured 100% denitrification. Lower ratios decreased denitrification efficiencies proportionally. The same critical ratio was found when the chemically treated raw sewage was used as an available organic carbon source. Denitrification-nitrification process was also investigated by recirculating the nitrified effluent into the denitrification reactor, to which effluents from chemical treatment of raw sewage were fed to satisfy the carbon demand. The same critical ratio of BOD/ΣNO x -N) = 2.3 was found. By increasing the recycling, nitrate concentration in effluent was decreased.

Strength of ferric hydroxide flocs

Abstract Strength and break-up of flocs produced in flocculation of water and effluent with ferric chloride were studied. Floc size was determined by a photographing technique and area and perimeter measurements by a Quantimet apparatus. The experimental results obeyed the expression dmax = GC−2γ with γ = 0.3 for effluent and γ = 0.5 for water indicating both viscous and inertial effects in break-up. Floc strength parameter C increased with polymeric coagulant aid addition, higher C values were obtained in water than in effluent. Floc break-up seems to take place by erosion of particles and flocs once disrupted do not grow again.

Organic groups and molecular weight distribution in tertiary effluents and renovated waters

Abstract Group composition and MW distribution of soluble organics in effluents from successive biological and chemical treatment stages were investigated. In secondary effluents, most of the organics fell within the high MW range. Lime treatment caused marked reduction of the latter group, combined with removal of proteins, humics, and carbohydrates. (The overall removal amounted to approx. 65–75%). Simultaneously, there was an increase in the lowest MW range group—strongly hydrophilic, unidentifiable compounds outside the classification scheme used.

Sorption of organics on clay and synthetic humic-clay complexes simulating aquifer processes

Abstract Sorption/partition of several organic solute (contaminants) of a wide range of hydrophobicities was studied on clay and on clay-humic complexes representing aquifer-soil systems. The role of the mineral and of the organic (humic) fractions was elucidated and a model considering both fractions in the sorption process was proposed. The adsorption constants on humic (organic fraction), K∝, were 8–20 times higher than on “pure” clay, Km. But with soils with low to medium organic fractions ( ƒ ∝ ) the contribution of the clay mineral to adsorption was quite significant, in spite of the fact that half of the sorption sites on the mineral surface were blocked by the humic. In the range of very low organic content in aquifer soil a non-linear pattern going through a minimum is observed between the overall partition coefficient and soil-organic fraction, transforming to the familiar linear relationship at higher ƒ ∝ s . Both the K∝ and Km followed the linear-free energy relationship to the octanol-water partition coefficient Kow.

Effect of magnesium and calcium precipitation on coagulation-flocculation with lime

Abstract Coagulation-flocculation studies were carried out to identify and quantify the organic matter (TOC) fraction removed by Mg (OH)2 precipitation and the fraction removed due to CaCO3 precipitation in lime treatment of wastewater. Most experiments were carried out with domestic sewage and some with a tannic acid solution simulating coagulable organics in wastewater. The experiments showed a clear relation between the amount of TOC removed and the amount of Mg (OH)2 formed. This relation between TOC removal and Mg(OH)2 precipitation can be expressed in terms of an adsorption isotherm. The coagulation-flocculation tests of sewage with lime as a coagulant indicated that about 26% of the removable TOC in sewage is eliminated by Mg(OH)2.

Organic pollutants adsorption from multicomponent systems modeled by freundlich type isotherm

Abstract A novel Freundlich-type multicomponent adsorption isotherm is employed successfully to describe the adsorption of parabromophenol, phenol and benzensulfonate on activated carbon from the respective bicomponent and three-component aqueous solutions. The superiority of the proposed isotherm over the commonly employed multisection Langmuir isotherm is discussed.

Substrate inhibition and multiple states in a continuous nitrification process

Abstract Multiple steady states were observed in a continuous nitrification process in a laboratory activated sludge reactor operating at 18°C and subject to high ammonium concentration in feed (up to 300 mg/l as N): under the same operating conditions a state of either complete oxidation to nitrate or of partial oxidation to nitrite may be attained, depending on the initial conditions. A model incorporating Monod and Andrews kinetics for growth of the two species was developed and employed for parameter estimation. A steady-state solution, expressed in terms of the measured variables—total biomass concentration in the reactor and in the effluent—was derived and its parameters were estimated. The model was then analyzed to show domains of steady state multiplicity under two control strategies in which either the sludge age or the total biomass concentration is kept constant.

Volatile organic acids in raw wastewater and in physico-chemical treatment

Abstract The purpose of the present study was to identify soluble organics, which comprise the high BOD remaining in the effluent from direct physico-chemical treatment of strong raw sewage. Salts of volatile organic acids were found to be the main constituents of the organic fraction remaining after chemical treatment and activated carbon adsorption. The fate of the volatile acids such as acetic, propionic, butyric, valeric, isovaleric and hexanoic acids was followed in each stage of the physicochemical treatment.