Anaerobic treatments

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Besides being slower, anaerobic treatment is more difficult to manage and can generate by-products that are more mobile or toxic than the original compound, for example, the daughter products of TCE, ie, dichloroethenes and vinyl chloride. It requires a longer acclimation period which means slower startup times in the field. The microbial processes are less well understood, and hence, ate less controlled than for aerobic systems. 

Aerobic treatment is generally appHed to lower strength wastewaters, whereas anaerobic treatment is employed as a pretreatment for high strength wastewaters. The choice of process depends both on the concentration of organics and the volume of wastewater to be treated. 

Anaerobic treatment is usually employed for high strength wastewaters. In anaerobic treatment, complex organics are broken down through a sequence of reactions to end products of methane gas, CH, and carbon dioxide, CO2 ... 

With the exception of the ADI process, anaerobic processes usually operate at a temperature of 35°C. In order to maintain this temperature, the methane gas generated ia the process is used to heat the reactor. Anaerobic processes are shown ia Figure 18. Anaerobic treatment performance data are shown ia Table 14. 

The anaerobic filter, UASB, and fluidized bed reac tors have all been used for anaerobic treatment of industrial wastes, as each is especially suited for use in anaerobic treatment. Table 25-44 presents results from these applications. 

Anaerobic Treatment of Sulfate-Rich Wastwaters (J.-P. Steyer, N. Bemet, P. N. 

Anaerobic treatment results in a drastic alteration in the pattern of protein synthesis in maize seedlings (Sachs, Freeling Okimoto, 1980). Pre-existing (aerobic) protein synthesis is repressed while selective synthesis of new polypeptides is initiated (Sachs et al., 1980). This is most likely a plant s natural response to flooding. 

The induction of anaerobic treatment synthesis occurs in two phases. During the first few hours of anaerobic treatment there is a transition period during which there is a rapid increase in the synthesis of a class of polypeptides with an approximate molecular weight of 33 kDa (Fig. 3). These have, been referred to as the transition polypeptides (TPs) as they represent most of the protein synthesis occurring in early anaerobiosis. 

The rapid repression of pre-existing protein synthesis caused by anaerobic treatment is correlated with a near complete dissociation of polysomes in primary roots of soybeans (Lin Key, 1967) and maize (E.S. Dennis and A.J. Pryor, personal communication). This does not result from degradation of aerobic mRNAs, because the mRNAs encoding the pre-existing proteins remain translatable in an in vitro system at least five hours after anaerobic treatment is initiated (Sachs et al., 1980). This is in agreement... 

This process is an extension of the anaerobic treatment of waste diseussed in Chapter 2, and is also similar to the natural process operating in landfill sites, which evolves methane. By treatment of biomass with bacteria in the absence of air a gas rich in methane can be produced a typical digester may produce over 300 m of gas containing over 50% methane per tonne of dry biomass. The economics of biogas generation for use as a fuel are currently unfavourable. The plants that do exist have been built because of the need to treat waste such as sewage sludge. 

General procednres inclnding the provision of oxygen and comments on anaerobic treatment (Bowlen and Kosson 1995)... 

Corbo, P. and Ahlert, R.C., Anaerobic treatment of concentrated industrial wastewater, Environ. Prog., 4, 22-26, 1986. 

Hybrid (aerobic-anaerobic). The hybrid bioreactor landfill accelerates waste degradation by employing a sequential aerobic-anaerobic treatment to rapidly degrade organics in the upper sections of the landfill and collect gas from lower sections. Operation as a hybrid results in an earlier onset of methanogenesis compared to aerobic landfills. 

Miller, K.M., Suidan, M.T., Sorial, G.A., Khodadoust, A.P., Acheson, C.M., and Brenner, R.C., Anaerobic treatment of soil wash fluids from a wood preserving site, Water Sci. Technol., 38, 63-72, 1998. 

Bacteria can grow in two main environments, aerobic and anaerobic. In aerobic treatment, aerobic and facultative bacteria use molecular oxygen as their terminal electron acceptor. The treatment occurs in the presence of a molecular oxygen supply. In anaerobic treatment, anaerobic and... 

The wastewaters generated by the adhesive industries contain high concentrations of both carbon and nitrogen compounds. The process chosen to treat these wastewaters will depend on their COD/N ratio. When the COD/N ratio is high, an anaerobic treatment is the best option as it will save costs... 

The toxicity of formaldehyde during anaerobic treatment has been reported by several authors. 1 2 3 4 5 -8 Its toxicity depends of several different parameters ... 

Different kinds of bioreactors and configurations have been used to treat wastewater containing formaldehyde and urea, and three different kinds of treatments can be applied anaerobic treatment, aerobic treatment, and combined nitrification and denitrification treatments. 

Anaerobic treatment is recommended for highly concentrated COD wastewater, as the amount of methane generated can compensate for the energy cost in maintaining the temperature of the reactor. 

Vidal, G., Jiang, Z.P., Omil, F., Thalasso, F., Mendez, R., and Lema, J.M., Continuous anaerobic treatment of waste-waters containing formaldehyde and urea, Biores. Technol., 70, 283-291, 1999. 

Zoutberg, G.R. and Frankin, R., Anaerobic treatment of chemical and brewery waste water with a new type of anaerobic reactor the Biobed EGSB reactor, Water Sci. Technol., 34, 375-381, 1996. 

Bekker de, P., Jans, T., and Piscaer, P., Anaerobic treatment of formaldehyde containing waste water, in Proc. European Symposium AW, van den Brink, W.J., Ed., November 23-25, 1983, Noordwijkerhout, TNO Corporate Communication Department, The Hague, The Netherlands, pp. 449-463, 1983. 

Neutralizing of weak liquor before evaporation followed by reuse of most condensate in the process or anaerobic treatment... 

In this section, we will discuss selected anaerobic treatment systems that are in use for food industry wastewater treatment. 

The design and performance of the anaerobic treatment processes that we have discussed are shown in Table 30.3. According to the table, the AFBR outperforms the UASB and the AF. An AFBR can achieve higher removal efficiency within a shorter HRT. The volumetric loading rate of the AFBR is comparatively higher than that of the UASB and AF. However, the choice of appropriate technology should consider factors such as the footprint, operational and maintenance cost, and the level of treatment required. 

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