6. With knowledge of the main structural features of a bacterial cell, which of
ID: 1885387 • Letter: 6
Question
6. With knowledge of the main structural features of a bacterial cell, which of these do you think might cause the most trouble in water treatment processes such as filtration or ion exchange, where the maintenance of a clean, unfouled surface is critical? Explain.
6. With knowledge of the main structural features of a bacterial cell, which of these do you think might cause the most trouble in water treatment processes such as filtration or ion exchange, where the maintenance of a clean, unfouled surface is critical? Explain.
Explanation / Answer
ANSWER
Biological process
Biological wastewater treatment is mainly carried out by prokaryotes, even if fungi, protozoa, algae and rotifers may also be represented ]. The microorganisms remove carbon and nutrient from sewage by employing various metabolic and respiratory processes. The most frequently found prokaryotes in biological wastewater treatment systems belong to the classes Alpha-, Beta- and Gammaproteobacteria, Bacteroidetes and Actinobacteria Municipal wastewater is composed of organic material, i.e. proteins, carbohydrates, fats and oils; nutrients, mainly nitrogen and phosphorus; as well as trace amounts of recalcitrant organic compounds and metals Biodegradable organic material is biochemically oxidized by heterotrophic bacteria under aerobic conditions resulting in production of carbon dioxide, water, ammonia and new biomass. Under anaerobic conditions methanogenic archaea, partially oxidizes organic material to yield carbon dioxide, methane and new biomass []. Biological nitrogen removal is achieved by a combination of nitrification, the oxidation of ammonia to nitrate, and denitrification, the reduction of nitrate to nitrogen gas. Nitrifying bacteria are chemolithotrophs, using the inorganic nitrogen compounds as electron donors. Ammonia oxidizing bacteria (AOB), like e.g. Nitrosomonas, Nitrosospira and Nitrosococcus, convert ammonia to nitrite according to equation (1). Nitrite oxidizing bacteria (NOB), like e.g. Nitrobacter, Nitrospira, Nitrococcus and Nitrospina subsequently convert nitrite to nitrate consistentwith the stoichiometric formula described by equation (2)
15 CO2 + 13 NH4+ 10 NO2-+ 3 C5H7NO2 23 H+ + 4 H2O........ (1)
5 CO2 + NH4+ + 10 NO2- + 2 H2O 10 NO3- + C5H7NO2 + H+........ (2)
The denitrification process reduces the nitrates to nitrogen gas, thus removing nitrogen from the water phase. In the absence of molecular oxygen denitrifying organisms can respire nitrate or nitrite through a chain of enzymatic reactions coupled to the bacterial inner membrane . Synthesis of the enzymes involved in denitrification is induced under anoxic conditions. In the presence of molecular oxygen the aerobic electron transport system is employed since the redox potential of oxygen is higher than for nitrate . The stoichiometric formula for the overall process, here with acetate as electron donor, is presented below.
5CH3COOH + 8NO3- 8HCO3- + 2CO2 + 6H2O + 4N2..........(3)
Problems in filteration process
Abrupt changes in water quality indicators such as turbidity, pH, alkalinity, threshold odour number (TON), temperature, chlorine demand (source water), chlorimi residual (in-process), or colour are signals that the performance of the filtration process, as well as pre-treatment processes (coagulation, flocculation, and clarification/flotation)
Other indicators of abnormal conditions are as follows:
• mud balls in filter media;
• media cracking or shrinkage;
• media boils during backwash;
• excessive media loss or visible disturbance;
• short filter runs;
• filters that will not come clean during backwash;
• algae on walls and media; and
• congealing of sand grains
The degradation of the filter media over time can be determined by calculating the 'resistance to filtration' and the 'efficiency of filtration'. If the nature of the filter media does not account for the head loss, the filter underdrain system and the head loss measurement equipment should be checked for malfunctioning. High head losses can be caused by reduction in the size and number of underdrain openings. The underdrain openings can be reduced in size or clogged by media, corrosion or chemical deposits. Pipework should also be checked for blockages; deposits, for example, have been associated with the use of magnetic flowmeters and soda ash.
Problems in ion exchange process
1) Resin fouling- resins work by holding electrically-charged ions in place so that they may be swapped with contaminant ions in the feed solution. Some contaminants, however, can bind to the resin, preventing further ion exchange reactions from taking place. Unless this is remediated, the fouled resin will compromise effluent quality, and ionic functional groups cannot be easily restored through a normal regeneration cycle. Contaminants that frequently contribute to resin fouling include:
• Aluminium
• Hardness precipitates
• Iron
• Manganese
• Microbiological
• Oil
• Organics
• Silica
• Sulphate
2) Resin oxidation - resins are comprised of cross-linked polymers that are able to stand up to a variety of substances. Still, they are vulnerable to oxidizing agents, such as nitrates, peroxides, halogen compounds, chlorine, and hypochlorite compounds, among others. When present in a feed stream, oxidants degrade IX resin polymers, causing them to deform and compact over time. This compaction obstructs the flow of liquids through the resin bed, which can compromise the overall effectiveness of the IX unit, and lead to inconsistent effluent quality due to channelling in the resin bed.
3) Thermal Resin Degradation - Extremely high or low temperatures can permanently compromise the effectiveness of IX resins. Over time, thermal degradation alters the resin’s molecular structure such that it is no longer able to bind with the functional groups of ions that are key to the IX reaction, resulting in compromised operational performance and shorter product life.
4) Resin loss or migration
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