Nava Narkis

CHARACTERISTICS OF ORGANICS REMOVAL BY PACT SIMULTANEOUS ADSORPTION AND BIODEGRADATION

Abstract The use of powdered activated carbon treatment (PACT), based on simultaneous adsorption and biodegradation, is effective for treating organic toxic pollutants, present in industrial wastewaters. Removal of phenol and aniline from aqueous solutions by biological treatment alone, by adsorption on powdered activated carbon (PAC) alone and by simultaneous adsorption and biodegradation were compared. In the adsorption experiments, Langmuir adsorption isotherms were obtained, from which Qo, the limiting adsorption capacities, and b, the constant related to the energy of adsorption, were determined. Qo values of phenol and aniline were found to be similar, while the energy-related constant for aniline was five times higher than for phenol. Addition of mineral nutrients, needed for the biological treatment, and inactivated microbial cells increased the limiting adsorption capacities and significantly decreased the energy related constants. In biological treatment alone, kinetic studies showed that aniline was more resistant to biodegradation than phenol. In the simultaneous adsorption and biodegradation process, the PAC presence differently affected the biooxidation of phenol and aniline. While the PAC enhanced the microbial respiration in the phenol bioreactor, it significantly reduced the microbial respiration in the aniline bioreactor. Different organic removal mechanisms are suggested in PACT for phenol and aniline, due to their different energy of adsorption. The respirometric studies are recommended as an adequate tool for prediction of toxic organics removal capabilities from industrial wastewaters by PACT.

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.

Adsorption of non-ionic surfactants on activated carbon and mineral clay

Abstract A series of non-ionic surfactants of nonyl-phenol ethoxylates, with n = 4−23;0 ethylene oxide groups and dinonyl-phenol ethoxylate were studied in dilute aqueous solution. Their removal efficiencies and mechanisms by adsorption on powdered and granular activated carbon and on Na-montmorillonite clay were investigated. The powdered activated carbon proved to be the most efficient with 94–100% non-ionic surfactants removal by addition of 40–80 mg activated carbon. Various models of adsorption isotherms such as Langmuir, BET and S-type were used to determine Q 4 , the limiting adsorption capacity. The relationships between Q o and parameters affecting the adsorption of non-ionic surfactants such as n , HLB and CMC were determined. The cross-sectional area σ 0 occupied by surfactant molecules on the adsorbent was calculated. Adsorption has been proven to be a potential advanced physicochemical treatment method for the effective removal of non-ionic surfactants present in effluents intended for reuse.

Ozone-induced biodegradability of a non-ionic surfactant

Abstract An adaptation of the OECD biodegradability screening test was used to evaluate the ozone-induced biodegradability of a non-ionic surfactant, branched chain nonyl phenol ethoxylate. The higher the ozone dose the better the removal of non-ionic surfactants. Overall removal of 70% of COD and 62.5% of the TOC were achieved by biodegradation after ozonation, in comparison with 8–25% removal of COD and 23% of TOC during biodegradability test of the non-ozonized non-ionic surfactant. The improvement in biodegradability caused by ozonation can be explained as due to removing inhibitory effects by changes in the molecular structure, which further enhanced biodegradability.

Evaluation of ozone induced biodegradability of wastewater treatment plant effluent

Abstract A long terre BOD test was used for quantitative determination of biodegradability induced by ozone on refractory organic matter remaining in solution after conventional biological and lime treatment. The improvement in biodegradability cansed by ozonation can be assumed as removing inhibitory effects due to changes in molecular structure. In all biodegradability tests of ozonated efltuents acclimation was required. When a seed material consisting of micro-organisms already acclimated is used, the iag period disappears.

Removal of chlorine dioxide disinfection by-products by ferrous salts

Chlorine dioxide when used as an effective disinfectant forms undesirable disinfection by-products, i.e. chlorite and chlorate ions. The aim of this research was to study the removal of these ions by ferrous ions in the presence or absence of oxygen. The efficiency of Fe+2 for ClO2- and ClO3- removal was followed by a determination of their initial and final concentrations, pH and delta Fe+2 consumed/delta ClO2- removed ratios. The optimal weight ratio of delta Fe+2 consumed/delta ClO2- removed for complete ClO2 removal was found to be close to the theoretical calculated value of 3.31. It was proved that ferrous salts can reduce chlorite ions to harmless Cl- ions. This method can be recommended as a part of ClO2 disinfection to ensure safe drinking water, with no harm to water consumers and to the environment.

Effect of suspended solids on wastewater disinfection efficiency by chlorine dioxide

Abstract Effluents enriched with high suspended solids concentration were tested for disinfection with chlorine dioxide. Following disinfection with various chlorine dioxide concentrations from 0 mg/l to 52.78 mg/l and contact times from 2 up to 24 h, half of the experimental samples were crushed (by Ultra-Turax) and tested for survival of indicator microorganisms. The crushing process revealed that a certain fraction of indicator microorganisms were left intact as a result of chlorine dioxide disinfection. This fraction was found to be able to regrow as was shown for all bacterial indicators, such as coliforms, fecal coliforms, enterococci and heterotrophic count, despite high disinfectant concentrations. The study results indicate that some microorganisms fraction entrapped into suspended flocs can survive disinfection with chlorine dioxide, depending also on indicator type, therefore their prior removal by coagulation, sedimentation and filtration is a major prerequisite for successful disinfection.

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.

Direct analytical procedure for determination of volatile organic acids in raw municipal wastewater

Abstract A direct analytical method for identification and determination of the individual volatile acids in raw sewage was developed. The proposed procedure is rapid, omitting tedious sample pretreatment and thus avoiding possible losses involved in steam distillation, evaporation or extraction. It consists of direct injection of raw sewage into a gas chromatograph, including Carbowax 20 M on acid washed Chromosorb W column and a flame ionization detector. Sample preparation is confined to addition of solid metaphosphoric acid to the raw sewage, and removal of precipitated proteins and suspended solids by centrifugation. The direct injection method proved to be practicable, accurate and rapid. Volatile acids content in raw municipal sewage in Haifa, Israel, was found to be in the range of 150–160 mg l −1 , of which 120–125 mg l −1 was acetic acid, 30–33 mg l −1 propionic acid, 6–8 mg l −1 butyric acid, 2 mg l −1 isovaleric acid, and 0.5–1 mg l −1 valeric acid.