Treatment of organic pollution in industrial saline wastewater: a literature review

Carbon/nitrogen ratio as a control element in aquaculture systems

Over 160 publications related to fermentative hydrogen production from wastewater and solid wastes by mixed cultures are compiled and analyzed. Of the 98 reported cases, 57 used single substrates (mainly carbohydrates), 8 used actual wastewater, and 33 used solid wastes for hydrogen conversion. The key information is compiled in four tables: (1) pretreatment conditions for screening hydrogen-producing bacteria from anaerobic sludge or soil, and the process and performance parameters for (2) single substrates in synthetic wastewaters, (3) actual wastewaters, and (4) solid wastes. Process parameters discussed include pH, temperature, hydraulic retention time, seed sludge, nutrients, inhibitors, reactor design, and the means used for lowering hydrogen partial pressure. Performance parameters discussed include hydrogen yield, maximum volumetric production rate, maximum specific production rate, and conversion efficiency. The outlook for this new technology is discussed at the end.

Fermentative Hydrogen Production From Wastewater and Solid Wastes by Mixed Cultures

This paper presents a literature review of anaerobic digestion of munidpal wastewater sludges. The paper focuses on the fundamentals of anaerobic digestion, setting forth a checklist for review of key process factors including: retention time, mixing, pH, temperature, nutrients, toxic materials, and feed characteristics. Major areas discussed are the microbiology and biochemistry of digestion, kinetics of digestion, environmental factors of concern, process performance indices, product stability, and laboratory and pilot studies on digestion. Although the text is aimed at digestion of municipal sludges, the fundamentals are sufficiently general to permit extrapolation to decomposition of other organics.

Fundamentals of Anaerobic Digestion of Wastewater Sludges

Growth kinetics, i.e., the relationship between specific growth rate and the concentration of a substrate, is one of the basic tools in microbiology. However, despite more than half a century of research, many fundamental questions about the validity and application of growth kinetics as observed in the laboratory to environmental growth conditions are still unanswered. For pure cultures growing with single substrates, enormous inconsistencies exist in the growth kinetic data reported. The low quality of experimental data has so far hampered the comparison and validation of the different growth models proposed, and only recently have data collected from nutrient-controlled chemostat cultures allowed us to compare different kinetic models on a statistical basis. The problems are mainly due to (i) the analytical difficulty in measuring substrates at growth-controlling concentrations and (ii) the fact that during a kinetic experiment, particularly in batch systems, microorganisms alter their kinetic properties because of adaptation to the changing environment. For example, for Escherichia coli growing with glucose, a physiological long-term adaptation results in a change in KS for glucose from some 5 mg liter−1 to ca. 30 μg liter−1. The data suggest that a dilemma exists, namely, that either “intrinsic” KS (under substrate-controlled conditions in chemostat culture) or μmax (under substrate-excess conditions in batch culture) can be measured but both cannot be determined at the same time. The above-described conventional growth kinetics derived from single-substrate-controlled laboratory experiments have invariably been used for describing both growth and substrate utilization in ecosystems. However, in nature, microbial cells are exposed to a wide spectrum of potential substrates, many of which they utilize simultaneously (in particular carbon sources). The kinetic data available to date for growth of pure cultures in carbon-controlled continuous culture with defined mixtures of two or more carbon sources (including pollutants) clearly demonstrate that simultaneous utilization results in lowered residual steady-state concentrations of all substrates. This should result in a competitive advantage of a cell capable of mixed-substrate growth because it can grow much faster at low substrate concentrations than one would expect from single-substrate kinetics. Additionally, the relevance of the kinetic principles obtained from defined culture systems with single, mixed, or multicomponent substrates to the kinetics of pollutant degradation as it occurs in the presence of alternative carbon sources in complex environmental systems is discussed. The presented overview indicates that many of the environmentally relevant apects in growth kinetics are still waiting to be discovered, established, and exploited.

Growth Kinetics of Suspended Microbial Cells: From Single-Substrate-Controlled Growth to Mixed-Substrate Kinetics

Microbiology for environmental scientists and engineers , Microbiology for environmental scientists and engineers , کتابخانه دیجیتال جندی شاپور اهواز

Microbiology for environmental scientists and engineers

The effect of NaCl on the yield of biological solids and on the ability of continuously cultured heterogeneous microbial populations to remove substrate was assessed by changing the salt concentration in the inflowing synthetic waste. During the period of increasing the salt concentration to 30,000 mg/l the system could not maintain a high substrate removal efficiency. However, after an acclimation period the system regained its former efficiency. Upon diluting the salt out of the system, a significant rise in cell yield was noted as the salt level passed through the range 8,000–10,000 mg/l. It was found that steady operation at a salt level of 8,000 mg/l sustained the cell yield at a high level.

Response of biological waste treatment systems to changes in salt concentrations

A simulated stream channel was used in laboratory investigations to determine a rational expression relating stream variables and fluid properties which define the reaeration rate constant, k2. Direct measurement of the reaeration coefficient at controlled depths and stream velocities enabled the development of a dimensionally homogeneous expression for k2. The developed expression accounts for variations in k2 due to changes in temperature as well as changes in fluid flow conditions. For the rectangular cross section employed in these studies, the reaeration rate constant, k2, was found to be directly proportional to average stream Telocity, and inversely proportional to the average stream depth raised to the 3/2 power. The constant of proportionality was found to be 3.053. When the same analytical approach was applied to the best available natural stream data, the proportionality constant obtained was 3.739. Both analyses yielded highly acceptable correlation coefficients. It is believed that the difference in the values of the proportionality constant is due primarily to differences in channel geometry, i.e., smooth rectangular laboratory channel versus irregular-shaped natural river channels.

Atmospheric Oxygenation in a Simulated Stream

The kinetic behavior of heterogeneous microbial populations was studied in a continuous flow completely mixed reactor operated at various dilution rates. Glucose was used as the growth-limiting nutrient. The physiological growth parameters for cells harvested from continuous flow reactors were determined using batch experiments. It, was found that the growth parameters, maximum growth rate (μm), saturation constant (ks), and cell yield (Y) vary for each dilution rate, and cannot be considered as precise constants in depicting the kinetic behavior of heterogeneous populations. In addition, it was found that the yield coefficients obtained from batch experiments were always lower than those obtained from continuous flow experiments. Levels of substrate and biological solids calculated for different dilution rates using growth constants from batch experiments did not agree with the experimental values observed in steady-state experiments. However, when the yield values from, the continuous flow experiments were used in conjunction with batch values for μm and ks the theoretical and experimental dilute-out curves agreed fairly closely (within the range needed for engineering prediction) until the culture began to wash out of the unit. In general, the data substantiated the use of the single phase relationship between growth rate and substrate concentration described by the Monod equation, μ = μmS/(ks + s).

Kinetic behavior of heterogeneous populations in completely mixed reactors

The general applicability of the Monod relationship between the logarithmic growth rate constant and substrate concentration was studied for heterogeneous populations metabolizing a variety of substrates including concentrated municipal sewage. It was found that growth could be described by the Monod equation, μ = μm/ks + s. The kinetic “constants” for heterogeneous populations growing on concentrated sewage were comparable to those found with glucose as substrate.

A. F. Gaudy

Papers

Microbiology for environmental scientists and engineers

Response of biological waste treatment systems to changes in salt concentrations

Atmospheric Oxygenation in a Simulated Stream

Kinetic behavior of heterogeneous populations in completely mixed reactors

Kinetic constants for aerobic growth of microbial populations selected with various single compounds and with municipal wastes as substrates.