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It is very important to maintain active and mixed microorganisms in a biological wastewater treatment system because it influences the successful working of the biological treatment process (Dara, 1993). In rotating biological filter and trickling filter, microbes are found attached to certain types of medium that support their growth, and in activated sludge process and anaerobic digestion, they are found as suspended growth (Cohen, 2000). Microbes utilize the organic waste matter as then- food resource, which helps them in the synthesis of new' cell material, and the degradation of certain organic matter to more simpler compounds provides energy for synthesis and functioning of cell maintenance (Waites et al., 2001). Biological growth includes both the processes of biodegradation and cell synthesis. Biological growth is influenced by environmental factors like the presence of toxic agents, pH, temperature, and mixing intensity (Grady et ah, 2011). The deficiency of these factors will affect the biological growth, which leads to the inefficiency of the process. In order to maximize the process efficiency, all the operational conditions should be maintained constant (Grady et ah, 2011). Wastewater treatment using microorganisms are influenced by factors like pH and alkalinity, temperature, nutrient availability and oxygen demand (Gerardi, 2006; Fulekar, 2010) 7 7.7.7 pH AND ALKALINITY

Microbes used for wastewater treatment require optimum pH for proper growth, and most of them prefer pH value of 6 to 9 (Fulekar, 2010). If the pH value becomes less than 6 then it will affect the enzymatic activity (reduction), hydrogen sulfide production (increase), formation of floe and uncontrollable growth of certain other microorganisms. When pH value exceeds 9, it affects enzyme activity, ammonia production, nitrification process, and formation of floe. The pH regulates the degree of substrate ionization, waste, and nutrients. Substrate utilization and waste production by microbes cause a change in the pH of the biological treatment plant, which in him affects the ability of microbes to treat wastewater (Gerardi, 2006). Alkalinity acts as a buffer to maintain the pH at a normal level. Urea, protein, and carbonates of calcium and sodium are the source of alkalinity. When acids are produced as a result of metabolism by the microbes, alkalinity prevents the sudden change in pH (Fulekar, 2010).


Enzymatic activity, substrate, and nutrient diffusion into cells of microbes are related to temperature change. These processes increase with an increase in temperature. If the temperature is very high, it will result in the denaturation of an enzyme that is related to the catalysis of biochemical reactions (Gerardi, 2006). Psychrophilic microbes prefer less tempera- hire (15-20°C) for their growth compared to thermophilic and mesophilic microbes (Russell and Fukunaga, 1990; D’Amico et al., 2006; Gerardi, 2006; Fulekar, 2010), thermophilic bacteria prefer high-temperature range between 45-65°C (Russell and Fukunaga, 1990; Gerardi, 2006) and mesophilic prefer a temperature range of 25-45°C (Bergey, 2014). If the temperature goes beyond 45°C, it will cause the death of mesophilic microbes, which results in the growth of thermophilic microbes.


Macronutrients such as magnesium, calcium, potassium, sulfur, phosphorus, nitrogen, and micronutrients such as cobalt, chromium, zinc, manganese, copper, iron, and boron are essential for the growth of microbes because they promote the growth and helps in enzyme synthesis which is responsible for biochemical reactions. Phosphorus and nitrogen play an important role in the synthesis of cell mass (Fulekar, 2010). Nitrogen helps to breakdown the carbonaceous substrates (Bergey, 2014). Another important nutrient is carbon, which is an important component of carbohydrates, proteins, and lipids that promotes cell growth of the microbes (Mara and Horan, 2003).


Oxygen is an important requirement for microbes because aerobic microbes decompose waste material using oxygen. Biological oxygen demand (BOD), COD, and DO are important parameters that determine the strength of pollutants present in wastewater (Dara, 1993; Fulekar, 2010; Bergey, 2014). BOD refers to the amount of oxygen required by the microbes to biochemically degrade and transform the organic content of the wastewater aerobically (Dara, 1993). American Society of Testing and Materials (ASTM) defines COD as the amount of oxygen (expressed in mg/1) consumed under specified conditions in the oxidation of organic and oxidizable inorganic matter, collected for the influence chlorides (Dara, 1993). The level of DO is important to understand the efficiency of a biological wastewater plant, and a low level of DO content will lead to anaerobic conditions, thus resulting in an inefficient biological treatment plant (Bergey, 2014). Microbes require DO in the range of 1 to 3 mg/1 for decomposing the waste. When the pollutant content is high, a huge amount of microbes will be required to decompose the waste, which requires a large amount of oxygen content, thus resulting in high demand for oxygen (Fulekar, 2010).


Despite the high relative proportion of the population served by waste- water treatment facilities, discharge of municipal and industrial effluents continues to have significant adverse impacts on receiving water bodies. The environmental consequences of wastewater discharge into the environment are, however, difficult to generalize largely due to regional variations in the level of wastewater treatment and the nature of receiving water bodies. The significance of wastewater treatment is to avoid the spread of diseases by protecting water resources against pollutants. Treatment of wastewater is one of the strategies for the management of water quality and its sustainable utilization. Due to some limitations on the use of chemical treatment in wastewater treatment, biological treatment is now employed to avoid the unnatural conditions in water resources. The incidence of nitrogen and phosphorus compounds in wastewater treatment and their effective removal from the wastewater has been extensively discussed. Most of the nutrient removal studies happen in the presence of bacteria and protozoa, and their roles in the removal of nutrients have been well documented. Fungi have also reported to increase the settleability, degradability of wastewater sludge, and contribute to the sludge management strategy. Our understanding of microbial community structure in waste- water treatment systems continues to advance rapidly owing to ongoing development and application of molecular methods. Nowadays, for most of the major processes in wastewater treatment systems, the application of culture independent eukaryotes and prokaryotic microorganisms has been analyzed, which provides a great opportunity for the exploration of novel microorganisms in the studies of wastewater treatment. The significant investigations have shown that the functional diversity of important prokaryotic groups in wastewater treatment systems can be influenced by the plant design and also by the changes in the process stability. Hence, it is necessary to look towards dynamic, safe, and sustainable wastewater treatment plans and policies confining low-cost decentralized microbial mediated wastewater treatment technologies.


  • • effective microorganisms
  • • indigenous microorganisms
  • • oxygen demand
  • • sustainability
  • • urbanization
  • • wastewater treatment
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