Wastewater Treatment

Microorganisms are essential for human life. Microorganisms decompose the carbon compounds in dead animals and plants and convert them into carbon dioxide. Intestinal bacteria assist in food digestion. Some vitamins are produced by bacteria that live in the intestines. Sewage and industrial wastewater are treated by activated sludge composed of microbial communities. All of these are due to the ability of microbes to produce many enzymes that can degrade chemicals. How do teachers make students understand that microorganisms are always associated with humans, and that microorganisms have the ability to degrade chemicals? The presence of microorganisms on humans can be shown by incubating agar plates after they are touched by the hands of students. The ability of microorganisms to degrade chemicals can be shown by an analytical measurement of the degradation of chemicals. When the chemicals are dyes (colorants) in water, microbial activity on degradation of dyes can be demonstrated by observing a decreasing degree of color as a result of the enzymatic activity (e.g., azoreductase). Dyes are widely used in the textile, food, and cosmetic industries. They are generally resistant to conventional biological wastewater treatment systems such as the activated sludge process (4). The discharge of wastewater containing dye pollutes surface water. The ability of microorganisms to decolorize and degrade dyes has been widely investigated to use for bioremediation purposes (5). The goal of this tip is to understand the presence of bacteria on human skin and the ability of bacteria to degrade colorant chemicals (decolorization). In this tip, students first cultivate and isolate bacteria on their hands, and then examine potential decolorization activity of each bacterium by observing the degree of color of the liquid in tubes in which bacteria isolated from students’ hands were inoculated. Decolorization activity of bacterial isolates from human skin has been reported recently (6). To date this author has frequently obtained colorant-degrading bacterial isolates from human hands as a result of work on a scientific education project. This tip does not require analytical measurements. Students can examine a number of bacterial isolates simultaneously. Therefore, it is appropriate for high school and introductory level college courses.

Nitrogen is an essential element for life, a major component of proteins and nucleic acids. Cultivated ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) provided the basis for investigations into the physiology and biochemistry of nitrification for decades and supported the ecological inferences obtained from field studies. Most of this work was done on AOB, and even now, the NOB are much less studied in the environment. The discovery of novel organisms and novel pathways are the most important findings to be documented in the field of nitrification since the publication of the last monograph in 1986. But just as important, and absolutely critical to these discoveries, are the changes in the study and methodology of nitrification. Both independently and in parallel with these advances in the molecular biology of nitrification, major advances in understanding their biochemistry and regulation have also occurred in the last 25 years. Major insights about ammonia-oxidizing archaea (AOA) genomics and metabolic capabilities are discussed. Microbial ecology has been transformed into molecular ecology, so great has been the impact of molecular biological methods in the study of microbes in natural and managed systems. Ribosomal RNA and functional gene sequence data are now the standard for investigation of microbial diversity, distribution, and activity in the environment. These methods have made it possible to investigate environmental control of nitrification, regulation in response to changing conditions, the discovery of great uncultured diversity, and an understanding of succession and biogeography among functionally similar types.

Microbial nitrification is a necessary step in removing nitrogen from wastewaters via biological denitrification and is becoming more important due to strict regulations on nitrogen discharge. However, microbial nitrification is recognized as being difficult to maintain in practical wastewater treatment plants (WWTPs) owing to the lower kinetics, yields, and sensitivity of nitrifying bacteria to physical, chemical, and environmental disturbances as mentioned, even though nitrification has been studied more than any other specific biochemical reactions occurring in wastewater treatment to date. Influent NO2 -, chromium, and nickel influenced the AOB community structure, while correlations between other metals analyzed in this study and the AOB community structure were insignificant. As an oxidation process, nitrification significantly consumes oxygen, and dissolved oxygen (DO) concentration is a key factor for maintaining nitrification stably as well as pH. In an activated sludge process, 3% salt inhibited both the maximum utilization rate and the saturation constant, suggesting uncompetitive inhibition. Nitrification in wastewater treatment systems has been studied extensively. Despite their importance, knowledge about the identity and ecology of nitrifying bacteria carrying out nitrification in WWTPs has been scarce. Thus, biological nitrogen removal processes have been regarded as “a black box” in practice because the lack of fundamental microbiological understanding hampers knowledge-driven process design and operation.

The major applications of continuous culture are, however, still found in fundamental studies and process optimization at laboratory scale. This chapter provides a brief introduction to the general concept and theory of different types of continuous culture. The design and operation of equipment and experiments are discussed from an application point of view. Depending on the control parameter and the operation mode, continuous culture can be classified into four general types. The general concept and theory of four types of continuous culture are described in a detailed manner. A chemostat is usually started as a batch culture. The specific growth rate of a chemostat culture can be determined from a material balance for biomass: net increase in biomass = biomass in incoming medium + growth - output - death. Generally speaking, auxostats have the following advantages over conventional chemostats. First, auxostats permit stable operation in the “high-gain” areas near the maximum growth rate. Second, they reach steady state more rapidly at high dilution rates than the open-loop chemostat. Third, population selection pressures in an auxostat lead to cultures that grow rapidly. Finally, it is possible to design a dual set point auxostat that controls two growth parameters simultaneously. Nutrient reservoirs for continuous culture should have ports for feeding, addition and/or mixing of heat-labile nutrients and substrate, venting, and sparging of the medium. In particular, recent developments in implementing continuous culture in microfluidics or microdevices are worth mentioning and are briefly summarized in this chapter.

One of the most important aspects of water microbiology, from a human perspective, is the fact that we acquire numerous diseases from microorganisms found in water. The reservoirs for pathogenic microorganisms found in environmental waters can be humans, animals, or the environment itself, as summarized in this chapter. However, it commonly is presumed that many of those microorganisms that infect humans and are found in our aquatic resources originate from human sources. This anthropogenic contamination can occur during either defecation in water or recreational activities conducted in water. In addition, domestic wastewater is of particular importance as a contributor of the pathogenic contaminants found in aquatic environments; the attendant public health concerns have resulted in the development of methods for studying and reducing the levels of pathogens in wastewater. The treatment of wastewater also is intended to reduce the contamination of crops that may occur when wastewater is eventually discharged onto land surfaces. The goal of this chapter to represent and summarize the current knowledge on public health aspects of water microbiology.

Reservoir souring is experienced in most fields flooded with water containing sulfate. The principle in nitrate treatment is to promote an acceptable microbial population of nitrate-reducing bacteria (NRB) at the expense of the unwanted sulfate-reducing bacteria (SRB) population. Water injection into oil reservoirs would be expected to radically change the conditions for the microbes in that environment. The environment close to the injection well will therefore be different from the environment deeper in the reservoir. SRB growing on hexadecane in pure cultures can produce close to 680 mg of hydrogen sulfide (H2S)/liter before sulfide becomes inhibitory. The main modification from the published version is the incorporation of the observed relatively low potential for H2S generation. The biofilm model is supported by field observations. In a recent study, treatment with 0.5 mM nitrate resulted in complete inhibition of SRB activity. The existing biocide injection pumps can normally handle the required nitrate volumes, but on most platforms additional storage capacity must be made available. This can be achieved by installing a new tank or by dedicating an old completion tank, for example, to the nitrate brine. The chemical storage area is now free from the irritating and potentially carcinogenic fumes of conventional biocides.

Biotreatment covers a broad field and it likely has different definitions in the view of different individuals. This chapter covers some aspects of biotreatment, and then briefly discusses different biotreatment topics. There are many different technologies used in biotreatment from classical to procedures that are still under development. The chapter focuses on the approaches from the biotreatment industry and some of the limitations of biotreatment. The biotreatments presume the employment of microorganisms. Several novel microorganisms have been discovered in the biotreatment industry, and many of them are as yet not in pure culture. A plethora of studies have explored the microbial community structures of different biotreatment systems where novel biodiversity is a common theme. Different biotreatment processes collectively accommodate an extremely wide spectrum of the diversity of microorganisms. The chapter concludes with a detailed case study of enhanced biological phosphorus removal (EBPR). The EBPR is a widely applied process to facilitate the removal of phosphorus from wastewater via microbial activity.