Oliver J. Hao

Decolorization of Wastewater

The public demand for color-free waste discharge to receiving waters and tougher color standards have made decolorization of a variety of industrial wastes a top priority. Unfortunately, with the complicated color-causing compounds, the decolorization of these wastes is a difficult and challenging task. This article first describes the background information of dye molecules and dye waste characteristics. The methods for color measurements and standards are then discussed. Different techniques including almost all the known physical, chemical and biological techniques are described for decolorization. Each process alone may not be able to meet the requirements. A combination of these processes, for example, chemical-biological, biological-chemical, chemical-physical, chemical-chemical, etc. is often used. The formation of intermediates during the decolorization process is emphasized. These byproducts may be more toxic than the parent compounds. Thus, the extent of the mineralization in waste decolorization should be evaluated.

Sulfate‐reducing bacteria

Abstract The corrosion of sewers and the control of odor are the major operational and maintenance problems in wastewater collection systems. The generation of hydrogen sulfide and subsequent sulfuric acid results from microbially mediated reactions, by sulfate‐reducing bacteria (SBR) and sulfide‐oxidizing bacteria. This review covers pertinent information about sulfate reduction‐induced problems in general and SBR in particular. Metabolism with respect to carbon, energy, and sulfur sources, ecology, growth factors (dissolved oxygen, temperature, pH, and sulfide), and the competitive effects of methane‐producing bacteria on SBR are discussed. Because metals react with sulfide to form metal sulfide precipitates with extremely low solubilities, metal interactions in sulfate reduction environments are discussed.

Microbial Chromium (VI) Reduction

This review was conducted to describe the microbial reduction of hexavalent chromium [Cr(VI)] in general and a potential for biological treatment of Cr(VI)-containing wastes in particular. Cr(VI) is the highest oxidation state of the metal chromium, which is widely used in various industries. Chromate (CrO4 −2) is the prevalent species of Cr(VI) in natural aqueous environments and is the major pollutant from Cr-related industries. Cr(VI) exhibits inhibitory effects on biological wastewater treatment processes. Several microorganisms, however, have been found to be able to resist and/or reduce Cr(VI) within a wide range of Cr(VI) concentrations. The microbial Cr(VI) reduction activities are either plas-mid-or membrane-associated phenomena. Factors affecting microbial Cr(VI) reduction, including biomass concentration, initial Cr(VI) level, carbon source, pH and temperature, oxidation-reduction potential, oxyanions and metal cations, are discussed. The kinetic models for Cr(VI) reduction are described. Biolo...

Kinetics of phenol and chlorophenol utilization by Acinetobacter species

Although microbial transformations via cometabolism have been widely observed, the few available kinetic models of cometabolism have not adequately addressed the case of inhibition from both the growth and nongrowth substrates. The present study investigated the degradation kinetics of self-inhibitory growth (phenol) and nongrowth (4-chlorophenol, 4-CP) substrates, present individually and in combination. Specifically, batch experiments were performed using an Acinetobacter isolate growing on phenol alone and with 4-CP present. In addition, batch experiments were also performed to evaluate the transformation of 4-CP by resting, phenol-induced Acinetobacter cultures. The Haldane kinetic model adequately predicted the biodegradation of phenol alone, although a slight discrepancy was noted in cases of higher initial phenol concentrations. Similarly, a Haldane model for substrate utilization was also able to describe the trends in 4-CP transformation by the resting cell cultures. The 4-CP transformation by the Acinetobacter species growing on phenol was modeled using a competitive kinetic model of cometabolism, which included growth and nongrowth substrate inhibition and cross-inhibition terms. Excellent agreement was obtained between the model predictions using experimentally estimated parameter values and the experimental data for the synchronous disappearance of phenol and 4-CP.

Sequencing batch reactor system for nutrient removal : ORP and pH profiles

The sequencing batch reactor (SBR) process is known for its flexibility to meet a wide range of treatment needs, including nutrient removal. However, information related to the operational stability of SBR nutrient removal systems and control parameters to adjust the cyclic duration is sparse. Consequently, this study was undertaken to identify process parameters (pH and oxidation reduction potential) that could be useful for monitoring and real-time control purposes. In general, the system achieved removal efficiencies of 91, 98 and 98%, respectively, for Chemical Oxygen Demand, total nitrogen and phosphate at the solids retention time of 10 days, with a cyclic duration of 6 h. Shock loadings of nitrogen (20 mg dm -3 of NH 4 + -N, four cycles) exhibited little impact on effluent quality, except for a higher nitrate content. Activated sludge settled well throughout the entire study period. Several significant points associated with different reactions within SBR cycle, e.g. end of nitrification, end of phosphate release and completion of phosphate uptake, were identified in pH profiles. Slope changes in pH profiles (dpH/dt, or d 2 pH/dt 2 ) were found to better represent the corresponding biological reactions. The application of these significant points in pH profiles as real time control parameters appears promising.

Effect of functional groups of humic substances on uf performance

The role of different functional groups present in humic substances on the membrane flux is unclear. This study is undertaken to (1) separate the carboxyl and phenolic groups from a humic solution, and (2) evaluate the effect of each fractionated humic substances on the ultrafiltration (UF) performance. A weak-base amine resin was used for the adsorption (pH 7) and the subsequent desorption (pH 13) of the phenolic groups from a commercial humic solution. These fractions were evaluated qualitatively (via Fourier transform infrared spectroscopy) and quantitatively (titration); they were further subjected to the analyses of the trihalomethane formation potential (THMFP) and ultrafiltration performance. Although, a complete separation of the phenolic and carboxyl groups is not possible, the results nevertheless provide useful information about their effects on UF performance. The fraction with a higher content of the phenolic OH group exhibits the highest THMFP (190 microg/mg C), whereas the fraction with a higher content of the carboxyl groups exhibits more flux decline. The UF system evaluated is unable to remove a significant portion of THM precursors, resulting in high THMs in permeate. The use of powdered activated carbon for the pretreatment of these fractions fails to improve membrane fouling. The pore size of UF membrane does not appear to affect the membrane flux, and the switch from the hydrophobic to hydrophilic membrane only slight improves the permeate flux.

Effects of metal additions on sulfate reduction activity in wastewaters

Abstract Sulfate reducing bacteria (SRB) convert sulfate to sulfide resulting in the odor and corrosion prohlems in sewers. Evaluation of metal toxicity on SRB was conducted in three phase: screening tests in test tubes, batch tests of wastewater with enriched SRB culture, and serum bottle tests with raw wastewater. The inhibitory metal concentrations towards SRB in test tubes were relatively high, and the inhibitory order was: Cu > Cd > Ni > Zn > Cr > Pb. The addition of metal mixture exhibited a synergistic toxic effect. In the batch tests, the dissolved metal concentrations were found to be much lower than those added; thus, the dissolved metal concentrations per se might not be responsible for inhibiting sulfate reduction. Inhibition of sulfate reduction was observed at relatively high metal dosages: 20 mg/L Cd, 20 mg/L Cu, 25 mg/L Zn. 20 mg/L Ni, 60 mg/L Cr(III), 75 mg/L Pb, and 10 mg/L metal mixture. Similar pattern was also observed in the serum bottle tests.

Wet oxidation of TNT red water and bacterial toxicity of treated waste

Abstract This laboratory study determined the composition of the off-gas after wet oxidation (WO) of trinitrotoluene (TNT) red water, and monitored bacterial toxicity of treated waste. The amount of sulfate concentration in the treated sample is much higher than the sum of the measured inorganic sulfate and the organic sulfur associated with the dinitrotoluene sulfonates initially present in the raw red water. This indicates the presence of other unidentified S-containing organic compounds in red water. The nitrogen analyses indicate a significant NH 4 + concentration (32 mg N/l) in treated waste and a high N 2 concentration (14.6%; net increase of 4.6%) in the off-gas. The toxicity results indicate that the WO-treated red water exerts toxic effects on Acinetobacter and Nitrosomonas growth, but has less impact on activated sludge. Furthermore, treated samples at 340°C appear to exhibit a more inhibitory effect on both Acinetobacter and Nitrosomonas than those treated at 260°C.

Control of an alternating aerobic–anoxic activated sludge system — Part 1: development of a linearization-based modeling approach

Abstract A two-phase model (linear in each phase) is developed for an alternating aerobic–anoxic completely mixed activated sludge process for the removal of carbonaceous substrates, nitrification, and denitrification. The linearized model is adapted from the activated sludge model No. 1 (ASM1) originally developed by the International Association on Water Pollution Research and Control. The modified dynamic model captures the essential process features of ASM1 while dramatically reducing demand on computational resources. Simulations may be conducted in such short times that the simplified model is suitable for inclusion in on-line optimization-based process control schemes. Calibrated model parameters are within the ranges specified in ASM1. Comparison of model predictions with experimental measurements from two different sets of bench-scale alternating aerobic–anoxic reactors indicates reasonable prediction accuracy of the model; further compensation for inaccuracy is achievable by introducing a feedback loop.

Biological Removal of Aqueous Hexavalent Chromium

The conventional chemical reduction of Cr(VI) to Cr(III) and subsequent Cr(OH) 3 precipitation are expensive due to the use of large amounts of chemicals and the generation of chemical sludges. An attempt was carried out for microbial Cr(VI) removal in an anaerobic chemostat fed with an acetate-containing synthetic medium. With 26 mg Cr(VI) dm -3 in the influent, almost complete removal of Cr(VI) was achieved at dilution rates of 0.15 and 0.32 day -1 at 20°C and at 35°C, respectively. The optimum Cr(VI) mass loading and the specific Cr(VI) applied rates were found to be 5 mg Cr(VI) dm -3 day -1 and 0.02 mg Cr(VI) mg -1 VSS day -1 respectively. Either the influent Cr(VI) concentration or the dilution rate could be adjusted to maintain an efficient removal of Cr(VI) in a continuous operation. Since the Cr(VI)-reducing activity is associated with the biomass concentration in the system, recycling the effluent solids is essential for practical application. In a batch reactor with the biomass collected from the chemostat, NaAc degradation appeared to be proportional to Cr(VI) reduction with the ratio of 9 mg C mg -1 Cr(VI) at 35°C. As reactions proceeded, the oxidation reduction potential correspondingly decreased and both pH and alkalinity increased.